OCCURRENCE OF STUNF CALLUSING IN SECOND-GROWTH
DOUGLAS-FIR (PSEUDOTSUGA ]YENZIESII
(MIRB.) FRANCO)
by
ROBERT PAUL SCHULTZ
A THESIS
submitted to
OREGON STATE UNIVERSITY
in partial fulfillment of
the requirements for the
degree of
MASTER OF SCIENCE
June 1963
APPROVED:
Signature redacted for
privacy.
i
1
I
-
-
Professor and Head, Forest Management Department
In Charge of Major
Signature redacted for privacy.
ChairmaL of School Graduate Committee
Signature redacted for privacy.
Dean of Graduate School
Date thesis is presented
Typed by Nancy Kerley
AC }O'TOWLEDGNT
The author wishes to express his appreciation
to the many people who aided very substantially the
progress of this study.
First a special word of
appreciation is due to Mre A. B. Berg for providing
much valuable data and for his constant and enthusiastic
help throughout the course of this investigation.
Othermembers of the Oregon State University faculty
who were of great help were Dr
J0 R. Dilworth,
Dr. W. K, Ferrell, Dr. D, J. Jensen, and
Mr. J. F. Bell.
The writer is indebted to each of
these men for their interest and helpful suggestions.
Sincere appreciation is also extended to the Oregon
State University Forest Research Laboratory for
providing the pictures represented in Figures 1, 17,
and l.
The writer is especially indebted to the
South Santiam Education and Research Committee for making
funds available for the completion of this work.
TABLE OF CONTENTS
Page
INTRODUCTION
.
.
.
REVIEWOF LITERATURE.
STUDYAREA .
.
,
o
.
.
,
a
METHODSANDPROCEDURES.
.
.
a
,
o
a
a
.
.
.
1
.
3
a
19
22
.
Examination of Stumps and Trees
Measuring Increased Growth
.
Determining the Ability of Rootgrafts to
Transmit Solutions
.
.
.
.
.
.
RESULTS AND DISCUSSION
.
.
.
,
.
,
.
24
.
.
27
.
.
.
.
General Observations
Total Percent of Stump Callusing
.
.
.
Relation Between Stump Callusing and the
Month of Cutting
Relation Between Stump Callusing and the
Length of Time Following Cutting
Relation Between Stump Callusing and the
Crown Class of the Severed Tree
Relation Between Stump Callusing and the
DBH Class of the Severed Tree
.
.
Relation Between Stump Callusing and the
Crown Class of the Nearest Living Tree
Relation Between Stump Callusing and the
Number of Trees Per Acre
.
.
Relation Between Stump Callusing and .he
Basal Area Per Acre
,
.
Relation Between Stump Callusing and Type
.
.
.
and Density of Thinning
.
Relation Between Stump Callusing and the
Soil Series
Relation Between Stump Callusing and the
.
.
.
.
.
Percent of Slope
.
Relation Between Stump Callusing and the
Subsequent Growth of Grafted Trees
.
.
.
Movement of Materials in Solution through
.
.
.
.
D,
.
,
.
.
.
.
.
.
,
,
.
.
.
.
.
.
.
,
.
.
.
.
.
.
Rootgrafts .
0.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Movement of Poria weirii through Root.
.
.
.
.
.
.
.
grafts .
.
.
.
.
.
.
.
.
.
.
.
22
23
.
.
27
33
36
3
4l
43
45
49
53
55
61
63
69
Page
SUIVIMARY AND CONCLUSIONS
BIBLIOGRAPHY
.
.
.
.
.
.
.
.
.
.
.
.
.
LIST OF FIGURES
Figure
1
2
Page
Map of the black rock forest research
area showing the management thinning
plots
.
.
.
.
.
The application of acid fuchsin to a
.
.
root-graft
.
.
.
.
.
,
.
.
20
25
.
A Douglas-fir stump with a callus on one
side
4
.
.
.
a
.
Old-growth stump callus with a bowl
.
shaped center
.
.
.
.
.
.
.
.
.
29
.
31
5
A callused stump after mechanical damage
32
6
A callused stump root-grafted to a live
tree
34
7
Relation between the percent of stump
callusing and the year of cutting
.
.
Relation between the percent of stump
callusing and the diameter class of the
severed tree
.,, . ,
.
9
A regression relationship between the
percent of stump callusing and the number
of trees per acre
.
.
51
A regression relationship between the
percent of stump callusing and the basal
area per acre
.
.
,
.
54
.
10
13
.
.
.
.
Four root-grafts which were treated with
.
.
.
.
.
.
acid fuchsin
.
.
.
.
12
.
.
.
.
11
44
.
.
39
.
,
.
A root-graft between a tree,, blown over
following Poria weirii infection, and a
"living stump." A callus can be seen on
the "living stump."
A section of a root-graft (Figure 12)
showing included bark and acid fuchsin
transmis$ion between roots . . . . ..
.
71
72
.
74
Figure
14
Page
An active root-graft showing mechanical
root damage, and the application of acid
fu c h Sin
15
.
.
.
.
.
.
.
.
.
.
.
.
.
76
The cross-sectionof a root-graft showing
the fusion area, oval shaped roots due to
grafting pressure, and erratic growth rings
.
.
following grafting
.
7
.
16
.
.
.
.
.
.
.
.
A root-grafted area under 70X magnification.
The central area showing a cross-sectional
trend is the fusion area. The upper and
lower cells are xylem from the roots of
two different trees oriented in different
directions
.
.
.
.
.
.
,
.
.
.
.
.
.
.
17
Root wash area showing a grid system used
for mapping. Poria weirii rot can be
seen in each of the stumps
l
Root wash area (Figure 17) following
mapping.
The dark areas are infected
,
,
.
with Poria weirii,
.
.
.
.
.
.
.
LIST OF TABLES
Page
Table
1
2
The number of stumps from which the bark
was removed and the number of hidden
$
.
.
.
.
calluses found ,
,
..
.
37
.
.
test of independence relating the
amount of callusing to the month of
cutting
.
4
35
Relation between stump callusing and the
monthofcutting.
3
.
.
.
.
.
.
.
.
.
Relation between stump callus ing and the
yearof cutting
.
.
.
.
.
39
.
.
test of independence relating stump
callusing to the year of cutting . , .
.
40
Relation between stump callusing and the
crown class of the severed tree
41
.
.
2
6
7(2
7
test of independence relating the
amount of stump callusing to the crown
class of the severed tree
.
.
42
Relation between stump callusing and the
diameter class of the severed tree . . .
.
43
.
9
10
.
12
46
2
test of independence relating the
amount of stump callus ing to the crown
class of the nearest tree
,
.
Relation between stump callusing, the
crown class of the severed tree, and the
crown class of the nearest living tree .
.
46
.
Regression analysis relating the amount
of stump callusing to the crown class of
thenearesttree.
13
.
Relation between stump callusing and the
crown class of the nearest living tree
.
11
.
.
.
.
.
.
.
.
.
.
.
50
Regression analysis relating the amount
of stump callusing to the basal area per
acre- .
.
.
.
. . . . . .
. . .
55
Table
14
Page
Relation between stump callusing and the
type of thinning.
.
.
.
15
.56
Relation between stump callusing and the
soil series
.
,
59
test of independence relating the
amount o± stump callusing to the soil
series
.
.
o
59
.
16
.
17
.
a
a
Relation between stump callusing and the
soil series with similar slopes
.
.
.
60
test of independence relating the
amount of stump callusing to the soil
series with similar slopes .
.
.
60
Relation between stump callusing and the
percent of slope on Hembre soil
.
61
.
.
19
22
.
.
.
I'- test of independence relating the
amount of stump callusing to the percent
of slope
21
.
.
.
20
e
62
.
The effect of stump callusing on the
subsequent growth of root-grafted trees
.
64
Root-grafts which were treated with an
aqueous solution of acid fuchsin
.
70
e
.
OCCURRENCE OF STUI' CALLUSING IN SECOND-GROWTH
DOUGLAS -FIR (PSEUDOTSUGA MENZIES II
(MIRB,) FRANCO)
INTRODUCTION
Descriptive references have been made concerning
natural root-grafting since before the birth of
Christ (15).
However, until recently such grafts were
considered principally as botanical curiosities to
which the occasional continued growth and healing over
of stumps could be attributed.
During the latter half of the nineteenth century,
it became necessary for European foresters to employ
intensive management practices.
The use of continuous
thinnings brought to the attention of foresters greater
amounts of visible stump callusing (42, p. 4).
Some
interested scientists began to probe into this
phenomenon in an attempt to discover the biological
factors or relationships that might be involved.
These preliminary studies raised a good deal of
controversy.
Most of the early researchers believed
that "living stumps" were the visual effects of rootgrafting.
Others hypothesized that the overgrowths
were due to accumulated food reserves in the stump an
roots.
It was also believed by some that once the
callusing-over had taken place, the stump could continue
2
to carry on photosynthesis and subsequent food production
through chlorophyll located within the cortex of the
callus (13).
The results of these early superficial studies
proved very little.
However, they did bring to light
the possibility that trees do not always grow as single
individuals in direct competition with one another.
There may exist a direct interrelationship of many
trees that could react in various ways upon the stand
as a whole.
As more and more knowledge accumulated and
scientific techniques were improved, it became evident
that group interrelationships of trees combined with the
interference of man in nature was resulting in many
changes within the forest.
Not only was there the
possibility of increased stability and nutrient
passage from one tree to another, but it became evident
that numerOus diseases were also finding their way from
tree to tree via these same channels.
The present state of our intensive forest practices
demands that as much as possible be learned about the
positive and negative effects of this phenomenon so that
future steps can be taken to achieve the best possible
results from root-grafting, one of nature's most
interesting, phenoniena.
3
REVIEW OF LITERATURE
Living stumps of Douglas-fir (Pseudotsuga menziesii
(Mirb.) Franco) were probably first described in
Lamb (21) under the title of "root suckers."
l99
by
A
subsequent study in 1913 (2) reported that Sequoia
gigantea (Lindl.) Decne, Pinus heterophylla,. Mill.,
and Pinus palustris,. Mill., along with Douglas-fir,
were "parasitic" and would form root-grafts with
neighboring trees.
This article also stated that the
irregularity with which the wood is often deposited on
the stump clearly indicates that the roots of only one
side of the stump has joined those of the living trees.
The first comprehensive study on root-grafting in
the United States was carried out by Newins (29) in
1916.
He cited a number of instances in which he
proved by actual excavation that "living stumps"
which were apparently isolated were, as a matter of fact,
connected by natural root-grafts with standing trees.
He also reported that natural root-grafting could be
found in many localities in the Douglas-fir forests of
the Pacific Northwest.
Other findings by Professor Newins can be summed
up as follows:
Among the conifers the phenomenon of
the "growing stump" appears to be most common in Douglasfir.
In some areas,,whole stands of trees appeared to
4
be firmly united below the ground through root-grafts.
These natural root-grafts, being a union of two or more
roots, were noted to occur between the roots of one
tree, or of two or more trees of a "similar species."
Interspecific natural root-grafting is resisted.
Because natural root-grafts are completed only between
living trees of a "similar species," more grafts are
likely to be found in pure stands.
Professor Newins
also stated that the large, superficial, 'and wide
spreading roots of younger trees appear to graft most
often.
It was suggested by Newins that root-grafts
originate through pressure exerted by opposing roots of
a "similar species."
This pressure, caused by the
growing roots, forces away the cortex at the points of
contact, thus exposing the cambial layers which
subsequently unite; as long as an "affinity" exists
between the roots.
These grafted roots can transmit
diseases or the effects of diseases, but can also be
beneficial in that one partner can help to heal an
injured portion of another.
Newins reported that the
result of this "conjunctive symbiosis" can be a living
stump if one of the trees is cut or broken off.
Living
stumps were found as far as 20 feet from the nearest
living trees.
The exposed surface of a root-grafted
5
stump appears to heal in the same manner as any other
wound on a tree.
The wound is impregnated with resin
as a protection from decay micro-organisms.
Once the
longitudinal ducts are closed by resin, the loss of
food substances and water is halted and a healing
tissue, "callus" is produced by the cambial cells.
Professor Newins also stated that the greater
amount of callus formation is on the portion of the
stump nearest the grafted root.
He subsequently
reported that a stump will not actually begir to grow
in diameter until it is completely healed over or
"capped."
Douglas-fir and Grand fir (Abies grandis,
(Doug.) Lindl.) were noted to heal over rapidly,
however, callusing occurred less frequently in the
latter.
Ponderosa pine (Pinus ponderosa,. Laws.)
appeared to heal over very slowly.
In 1920 (34)
and
1921 (35),
Pemberton confirmed
Newins theory that stump callusing was directly
attributed to root-grafting, when heexcavated a small
area and found that seven stumps were linked with one
another and with one large tree.
When this tree was
felled the stumps died.
A subsequent study of ten trees by McMinn in 1954
(27) showed only one root-graft between trees in Douglasfir, however, grafts between roots of the same tree were
6
very common.
The author noted a tendency for grafts to
occur where roots were deflected toward one another due
to obstructions such as rocks, hardpans, or by the lack
of rooting space.
Thus he concluded that "on good
sites where root depth is restricted by a high. water
table, grafting will probably be more common than on
poorer sites where roots are smaller or on areas where
structural roots are well placed."
In 1927, the Finnish forester Laitakari (22)
made the first definite confirmation of rootgrafting in pine.
Eight grafts were found on 31
excavated sample plots, however, no stump calluses were
found.
He believed that root-grafting commonly occurs
in pine stands but not as frequently as in spruce
stands.
This study revealed that stump callusing will
not necessarily occur in all species as a result of
root-grafting.
Laitakari (23) also found numerous
root-grafts in Betula verrucosa, L. and Betula odorata,. L.
He noted that trees of different sizes (36.
cm. and
5 cm. dbh and 10.3 cm. and 1 cm. dbh) as well as
different sized roots form grafts, and that these
grafts are important for wind resistance and possibly for
water and nutrient transfer between trees.
A study was undertaken, by Page (33) in 1927, in
eastern white pine (Pinus strobus, L.) and eastern
hemlock (Tsuga canadensis, (L.) Carr.).
He found that
two years after cutting in two separate areas, approximately 35 percent of the stumps had calluses, however,
in large openings the percent of living stumps was much
reduced.
Subsequent examinations in later years showed
a continued decrease in the percent of living stumps.
The youngest pair of grafted roots found were 10 and 13
years old.
The author suggested, in agreement with
Newins (29), that root-grafting probably does not take
place until roots are large enough to exert considerable
pressure when they grow in contact.
Page also believed
that an increased rate of growth may occur in certain
stands as a result of the increased absorptive system
available through root-grafts.
LaRue (24) found that eastern white pine trees
grafted in stiff clay where they could not sway
sufficiently to wear away bark by friction.
It had
previously been hypothesized that wind action was a
possible cause of grafting.
Subsequent studies in eastern white pine, by
Graham (15 and 16) and Bormann and Graham (9 and 10),
confirmed the previous investigations made in this
species.
1)hite pine roots will grow and graft under a
wide range of subsoil drainage conditions.
Grafting
occurs between the ages of 15 and 71 years which results
in mature stands composed of many grafted unions of two
or more trees, with an occasional interspersed ungrafted
The authors believed that the degree of
individual.
grafting in any stand is probably related to age,
density, and purity of the stands
They also confirmed
that materials in solution can move, through rootgrafts, from tree to tree and from callused and/or
freshly cut stumps to trees.
Some grafts, however, may
not function at all in translocation as was shown by
the failure of dye to move through certain grafts.
In 1940, Adams (1) carried out a study on rootgrafting in Monterey pine (Pinus radiata, D. Don)
in Australia.
He reported that root fusion of neighboring
trees in plantations are common, particularly between
trees bounding open spaces.
All grafts were observed
in the layer of soil between six inches and two feet
six inches from the surface.
These fusions were all
within ten feet of the host tree and very few were within
two feet.
It was noted that grafts involving three
roots were not uncommon.
Adams also reported that
early thinnings are slow to respond while late heavy
thinnings produce immediate and substantial growth
increases.
He suggested that this is possibly due to
the increased number of root-grafts among the older
9
stands, which would thereby give the remaining trees
an increased root surface.
Armson and Driessche (3) found a definite increase
in root-grafting ofred pine (Pinusresinosa, Ait.) where
stands had been periodically thinned, however, no
root-grafts were found in trees less than 15 years
old.
They suggested that foresters may increase the
frequency of grafting through thinnings.
They also
stated, as has previously been mentioned by Newins
(29) and Page (33), that pressure is the major factor
favoring the formation of root-grafts and therefore
it is possible that thinnings may result in increased
diameter growth of the roots, which could subsequently
cause the increased amount of root-grafting.
Observations in northern Wisconsin during the
summer of 19.59 (19) showed that natural root-grafting
is very common in species indigenous to that area.
Root
fusions were found to occur in both saplings and older
trees but were more common in the older trees.
Cross
sections of the grafted roots showed a common cambium
and actual unions of vascular elements.
Roots as small
as l/-inch in diameter were found to graft and the
small roots usually grafted to roots of considerably
greater diameter.
These same conditions had previously
been found to exist by Kuntz and Riker (20) and
10
It was again suggested that the main
Laitakari (23).
requirements for intraspecific root-grafting is growth
pressure.
The authors found that feeder roots do not
graft readily and that the angle of approach does not
seem very important, as roots were found to graft at
all angles.
Instances where abrasions and callus
development were observed at points of root contacts
suggested that these points of contact would eventually
graft as a result of the growth pressure.
Kozlowski
and Cooley also reported, in agreement with McMinn (27),
that root grafting is common over or adjacent to sharp
edged stones.
Apparently this is due to diameter growth
pressure of a root on another root which is lodged
against a stone.
They clearly stated however, that
stones need not be present for grafts to occur.
Some
species also showed a greater tendency to root-graft than
others.
Through the use of radio-isotopes, Kuntz and Riker
(20) carried out a study in 1955 to determine the role
of grafting in the translocation of water, nutrients,
and disease inducing organisms.
They investigated
hundreds of trees of 14 different species with the
following results:
1.
Root-grafting was common among northern pin oaks
(Quercus ellipsoidalis, E. J. Hill), but was infrequent
11
among bur oaks (Quercus macrocarpaMichx.) and white
oaks (Quercus alba,. L.).
Only one interspecific graft was found; namely, a
northern pin oak and a bur oak.
Roots of all sizes, l/-inch or larger, were found
grafted together.
Trees in dense stands were united much more frequently
than were those in open stands.
Thus, trees of a forest
stand might be considered as a united community rather
than independent individuals.
When dominant and suppressed trees were connected
by root-grafts, isotopes and moisture moved both ways
but usually from the dominant to the suppressed trees.
Through investigations in natural pine stands in
southern Finland in
1953, Yli-Vakkuri (43)
demonstrated
experimentally that nutrients and water may be trans-
located from one tree to another via root-grafts.
Other
results obtained were that, in general, the frequency
of root-grafts increased with increasing diameter
classes in mature natural stands, and that 21 to 2a
percent of the trees had root-grafts with other trees.
In very young stands little root-grafting occurred.
Grafting was found to take place mainly among trees
30-60 years old and among thin roots of approximately
one to two centimeters in diameter.
Most frequent
12
grafting was noted in the more vigorous, dominant, and!
or trees in close proximity.
Most of the trees
investigated had root-grafts with one or two living
trees or stumps.
These in turn often were connected
with other trees or stumps, thereby producing a network
of ten or more interconnected trees and stumps.
The
majority of the grafts noted were between superficial
roots.
The author also stated that stumps of felled
trees which are root-grafted to healthy living trees
will remain sound for many years due to the heavy
secretion of resin.
Following the same general research pattern as
Yli-Vakkuri, several Russian foresters reported that
root-grafting increases growth and survival of
individual trees, but suggested that it also increases
the amount of disease infiltration.
In 1952, Nikitin
(30) cited several examples in which trees grown in
dense grpups, with natural root-grafting, appeared to
have increased vitality (as judged by survival) and
growth compared to isolated individuals.
During the same
year Junovidov (la) reported that in Russia when natural
stands of Pinus palustris and Larix sibirica,. Ledeb.
were cut the remaining trees benefited by increased
growth.
Two years later Ljubic (26) concluded a study
on the interrelationships of the root systems of
13
Quercus robur, Linn. sown on irrigated plantations.
He noted that during the fourth and fifth years numerous
root-grafts occurred between seedlings, and as the
weaker trees died their roots were taken over by the
survivors.
Safar (3) reported that the proportion of
living stumps is a function. of the distance from the
nearest living tree and that more living stumps are
found on soil overlying limestone than on soil overlying
siliceous bedrock.
Bezkaravainyi (4) studied the responses of Acer
negundo,. L., and Pinus sylvestris, L. to root-grafting.
He reported that if members of a root-grafted pair were
of equal dominance both trees would grow faster than
ungrafted trees, while a more dominant tree would
suppress a lesser dominant tree of a pair.
These
conclusions appear to disagree with the previously
mentioned findings of Kuntz and Riker (20).
Beskaravainyi (5) also found that continued growth of a
stump may reduce the amount of nutrients available to
a root-grafted tree.
A very interesting study was
carried out by the same author (6) in l95,. showing
that root-grafted pines had aconsiderably higher
transpiration rate than isolated trees.
Rahteenko (36) applied radioactive P to leaves of
two to fifteen year old trees of Quercus, Acer, Tilia,
14
Picea, Larix, Betula, Fraxinus, and Pinus.
Movement of
this element, to trees of the same and of other species
and genera, was noted up to two meters from inoculated
trees.
Movement occurred through natural root-grafts
and also through root contacts.
Possibly other
transfers may have been carried out via soil solutions
between roots in proximity.
Two Russian authors (4 and 30) reported morphological
changes in trees which had grafted interspecifically,
These included changes in stem and crown form, needle
length and the number of resin ducts.
They hypothesized
that this hybridization operates by means of substances
in the sap of the trees.
This theory of "natural
vegetative hybridization" was originally brought to
light by Michurin and was subsequently incorporated by
Lysenko as one of the aspects of his doctrine on
heredity.
obtained i
Thus far these results have only been
the USSRO
Many. investigators have studied the possibility
of diseases being spread through root-grafts.
Poria
weirii, Murr., a laminated root rot, is known to spread
from tree to tree through root-grafts attacking both
vigorous and depressed trees (7 and 40).
Investigations
have been carried out (II,. 14, 17, and 44) which
definitely show that one of the methods of oak wilt
15
(Ceratocystis fagacearum (Bretz) Hunt) transfer is from
"foci" to surrounding trees via root-grafts.
It has
also been demonstrated that Dutch elm disease
(Ceratocystis ulmi (Buism.) C. Moreau) is transferred
through natural root-grafts (39).
Fomes annosus (Fr.) Cke.
Recent research on
(41, p. 45) has revealed that
this pathogen can be spread through the root contact
of diseased and healthy trees.
The destructive capacity
of these pathogens demonstrates that root-grafting is
not necessarily a desirable occurrence.
In the past few years the occurrence of "back-flash"
in many stands has brought added attention to the
importance of root-grafting.
"Back-flash" is the
transfer of a toxic chemical from a poisoned tree to an
adjacent healthy tree via root-grafts.
The resulting
damage may be serious, killing large numbersof desirable
trees or it may be inconspicuous and negligible.
It
was reported (10) that 43 percent of the untreated
trees, in a 30-year old white pine plantation, were
killed as a result of "back-flash" following a thinning
with ammonium sulfamate.
Molotkov (2) noted that
poison solutions injected into the root collars of Faus
sylvatica, L. and Populus trernula, Linn. killed trees
of the same species at distances up to seven meters.
Cook and Welch (12) also observed this phenomenon in
Pinus resinosa stands.
16
Summary
In the light of past investigations it appears that
wherever a forest tree species occurs in groups,
whether extensive pure stands or in small clumps,
natural root-grafts are probably present,
To date,
root-grafts have been observed in nearly 70 tree species
of the temperate zones and LaRue (25) states that a
greater number of tropical species appear to root-graft.
The forest therefore is not composed entirely of
individuals occupying the same general area and
depending upon the same physical factors, but contains
numerous grafted tree unions capable of direct
physiological interaction.
The presence of root-grafting has been determined
through the transfer of dyes, poisons, radio active
isotopes, and by actual excavation, sectioning, and
microscopic study of the interconnected vascular
systems.
The use of radio active isotopes has greatly
facilitated the study of root-grafting.
Even at low
concentrations, their presence can be detected immediately
and for long periods of time.
As a result,, the movement
of these isotopes can be mapped and only a minimum of
excavation need be carried out to expose the desired
root fusions.
17
Root-grafts appear to be capable of acting as
transmission paths for water and nutrients.
The extent
of this physiological activity seems to vary among
species and is not yet fully understood.
The possibility
that grafted trees may have an increased growth, over
and above their ungrafted neighbors, has been
suggested; however, no actual experimental evidence
to this effect has been obtained thus far.
The occurrence of "back-flash" and the incidence
of transmission of several destructive pathogens suggests
strongly that continued research on this subject will
bring to light many more indications of undesirable
transmissions via root-grafting.
The possibility that
thinning increases root-grafting may also compound this
problem.
Root-grafting occurs at all ages from seedlings to
maturity, but appears to be most frequent in 15 to 60year old stands.
Grafts occur most often on the larger
lateral roots but have been noted in roots as small as
one cm. in diameter.
Most grafts occur between two and
ten feet from the host tree with a maximum noted distance
of 50 feet (34).
It is possible that up to 50 percent
of any one stand may be interconnected with one or more
partners, depending upon age, density and purity of the
stand.
In the United States, Douglas-fir and eastern
white pine appear to have the greatest ability to form
root-grafts.
This conclusion may be misleadingbecause
the most work has been done in the root-grafting of
these species.
At present, due to a lack of research,
it is not known how many of our indigenous species will
root-graft.
Interspecific grafting seems to be very rare in
nature.
With a very few exceptions, the only grafts
between species which have been found in nature were
noted among trees which readily hybridize.
Inter-
specific root-grafting appears to be the result of
growth pressure of contiguous roots which have an
"affinity," however, other suggestions have been
offered as to the actual reasons for this phenomenon.
The phenomenon of the "living stump" has quite
definitely been connected with root-grafting.
"Healing
over" of a stump is the external effect of continuity
between two or more trees.
It results from cambial
activity in the stump of the severed tree assisted by
its grafted counterpart(s).
19
STUDY AREA
All field data for this study were obtained from
the Black Rock forest management research area,
Township
South, Range 7 West, Willamette Meridian,
Polk county, Oregon (Figure 1).
This area consists of 500 acres of 45-50 year old.
second-growth Douglas-fir.
The site quality of the
stand is mainly Site III.
The aspect of the area is
predominantly southern and the elevation extends from
700 to 2000 feet.
The soil is composed of the Blachly,
Hembre, and Melbourne series, of medium texture (with
some stony areas), and a soil depth of approximately
two to six feet.
The slope ranges from 7 to 45 percent
with an average of about 15 percent.
The drainage is
excellent with several small streams running through
the area.
In 1952, the State of Oregon allocated this area
to the present Oregon State University Forest Research
Laboratory for research in forest management and forest
products.
Since 1952, a total of 46 management research
plots have been established throughout the area and
thinned to different specifications.
These plots range
in size from one-fourth acre to one acre, with, 34 of the
plots being of the latter size.
Thinnings have been
carried out in at least one of these plots during every
20
SILVICULTURAL STUDIES
BLACK ROCK
FOREST MANAGEMENT RESEARCH AREA
TOWNSHIP & SOUTH RANGE 7 WEST WM.
POLK COUNTY
Scale: l6inches
mile
ContoM interval 100 feet
Primary Road
Secondary Road
o -
H
TREATMENT,
etocK UNOERDLANTING
£NVIROINT STUDY
PLOT
0 - Opie
F- Finn
C - Rep.edeetloe. CrieS
II - LuSt thiele
2 - Control
ID - Hieey tMeeleq
Figure 1.
Map of the Black Rock Forest Research
Area Showing the Management Thinning
Plots
21
month of every year since 1954, with some cutting also
taking place in 1953.
Several plots have had three
thinnings, some two, and others have been thinned only
once.
Different types and densities of thinnings have
also been carried out.
Cutting was confined, for the most part, to
merchantable stems seven inches dbh and over, however,
many stems of from four to six inches dbh were felled
and left.
A few stems as small as two inches dbh were
also cut while "brushing out" around larger trees.
As
a result stumps of widely varying sizes were available
for study.
A map was made for each plot on the forest,
showing the exact location of every living tree.
The
diameter (to 1/10-inch) and the crown class of every
tree were recorded when each plot was established.
Remeasurements were made after each growing season.
The
basal area, Scribner volume, and number of trees per
acre were determined after each thinning and/or growing
season.
Records were also kept on the dbh, crown class,
and date of thinning for each tree removed.
22
METHODS AND PROCEDURES
A total of 26 plots (control plots and plots thinned
after January 1961 were omitted) covering 24.25 acres
were inspected for stump callusing during December, 1961
and January,. 1962.
A.
Examination of Stumps and Trees
The stump of every tree cut during a regular
thinning operation (excluding salvage cuts) was examined
for callus tissue.
Those stumps which had no visible
evidence of callusing but which had visible resin
stains, or in any other way left doubt as to their
status, were girdled at the root collar in an effort to
record all callused stumps.
Even though the callus was
not actually visible to a casual glance, often a slight
separation of the phloem from the xylem on an otherwise
sound stump gave evidence of a callus a few inches below
the stump surface.
By inserting an axe blade into the
crevice and prying the bark away the callus could be seen.
All of the entirely hidden calluses were recorded to
determine the percent of hidden calluses.
Each callus
was chipped to make sure it was still living.
Due to
the effective masking of callus development by resin
flow on newly cut stumps, trees cut after January, 1961
were not included in this study.
23
Other data recorded in the field included the
crown class of the tree nearest to each stump, and the
distance (in feet) from this tree center to the center
of the stump.
In a few instances where it could be
determined that the actual union was with a tree other
than the nearest tree, this actual distance was recorded.
Various general characteristics such as the effect of
mechanical damage on callusing, the irregular growth of
calluses around the stumps, and the rapidity of stump
rotting for both the callused and uncallused stumps
were also recorded.
B.
Measuring increased growth
From the 26 inspected field plots a group of 2
trees were measured to determine the relative effect of
root-grafting on subsequent growth of the grafted trees.
Callused stumps which showed definite signs of being
grafted to neighboring trees were compared with
It
similarly situated stumps which were uncallused.
was attempted to make these paired observations as
similar as possible.
The stumps were of approximately
the same size and the distance from each stump to its
living counterpart was approximately the same.
The
crown and diameter classes of the living trees of each
pair and the severed trees of each pair were as nearly
the same as possible, and the trees were cut at the same
24
The soil series and texture, slope and elevation
time.
were the same for each of the sample pairs.
The fourteen
pairs were obtained from six widely scattered plots
ranging in elevation from 1000 to 1500 feet.
They
were also representative of the different soils and
slopes.
Each of the living trees had been measured prior
to the cutting of its related stump and were again
measured by the author in January, 1962.
Both of the
measurements were taken at a dbh paint mark with a
diameter tape.
C.
Measurements were taken to 1/10_inch.
Determining the Ability of Root-grafts to Transmit
Solutions
In an effort to determine whether or not materials
can pass in solution through Douglas-fir root-grafts,
one root of each of five apparent root-grafts was
treated with a .4 percent aqueous solution of acid
fuchsin for a period of fifty days during April and
May, 1962 (Figure 2).
All of the grafts were over ten
years old and the roots ranged in size from L5 to 6
inches in diameters
All of the grafts were within one
foot of the ground surface while the trees and their
grafted stumps ranged from a minimum of four feet to
a maximum of seven feet apart.
All five of the stumps
:
.1
i
2.
2.
E
pli.
t-grL
to a
26
showed well-formed calluses which were heaviest on
the side facing the graft and living tree.
From one to three holes (3/4-inch in diameter and
from one to two inches deep), depending upon the root
size, were drilled into one root of each p.air near the
root-graft.
Holes were drilled in the stump root of
one graft and in the tree root of the other four grafts.
An attempt was made to place the holes in the lower root
of eachpair so the dye need not travel around the
root to be translocated.
Each hole was kept continuously
filled with this red dye solution by means of a short
length of rubber hose and a thistle tube (Figure 2).
The grafts were removed from the ground on May 29,
1962 and they were subsequently sectioned to determine
the extent of dye penetration into the second root of
each graft.
Cross-sections were made for visual
observation of the grafted roots.
Slides were also
made on a microtome for microscopic study of the interconnecting cambiuxn systems, tracheids, and other tissues
at the point of contact.
27
RESULTS AND DISCUSSION
From all available literature it appears certain
that stump callusing is a direct result of root-grafting
between two or more trees of the same species.
Therefore, in the preparation of this study, a direct
reference between root-grafting and stump callusing
is assumed.
A.
General Observations
Most Douglas-fir stumps on this area show a heavy
resin flow soon after felling.
This situation often
remains for up to one year even though there is no
subsequent callus development.
Bormann () also
observed this characteristic in eastern white pine.
It is quite possible that this is the result of food
materials stored in the roots.
After a period of one
year nearly all the stumps which are root-grafted show
a definite brownish callus protruding from between
the xylem and the phloem.
Callus tissue was observed,
however, on several stumps which had been cut only
three and four months earlier.
If no callus tissue
develops, resin usually ceases to flow by the end of
one year and the stump subsequently begins to decay and
lose its bark.
Stumps with calluses usually remain
sound for many years even though it takes several decades
28
for them to completely callus over.
The bark of these
stumps remains as firm as the bark on a live tree
whenever callus tissue is located under it.
Very few stumps show a unifoiiii callus dustribution
around their perimeters.
In many cases a definite one-
sided effect was noticed as had been previously
observed (2 and 29).
Often, the callusing will be very
heavy on the side where a large root leads directly to
a nearby tree, while on the other side of the stump no
visible callus is present (Figure 3).
When the
bark
is removed from these stumps however, live tissue can
usually be found around the entire stump.
Callused stumps were observed up to 29 feet from
the nearest living tree.
In most cases where large
distances separated a callused stump and the nearest
tree, both the tree and the stump were over 15 inches
in diameter.
The actual capping over of stumps is a very slow
process once the first layer of callus tissue has been
formed.
Calluses up to eight years old covered only
about one inch of the sapwood around the stump and were
rarely elevated more than one inch above the surface
of the stump.
Whenever a callus was observed it was
noted that all superficial roots of that stump were
active.
In many cases a callus will never completely
29
r(j
.
DOI-iL ;t!iip
b ide
Wi
a
11
r
One
30
cover the surface of a stump (Figure 4).
The very
center of the stump will be left with a bowl shaped
opening, which is probably the result of the continued
presence of water.
From this vulnerable point, the
entire center of the stump will eventually rot and
leave a hollow shell which continues to grow in
diameter at an irregular rate.
Callus tissue will not form on that part of a
stump where the bark has been removed through logging
damage or other mechanical action.
A callus will,
however, form under any bark which remains on the stump,
if the stump is root-grafted to another tree.
A close
inspection of Figure 5 will show a callus at the root
collar even though the bark has been removed above.
It was observed that when all of the bark was removed
from a stump or the stump was cut off at the ground
line, a callus formed around the root collar and all
of the roots remained active.
It is therefore concluded
that the entire root system of a callused stump remains
active regardless of whether or not the callus is
visible on all sides of the stump.
Trees as small as six inches in diameter were
noted grafted to stumps over 20 inches dbh.
The
opposite extreme was also found along with all variations
in between.
This suggests, as has previously been
i;
I
ig rc
L.
()±d-g awth
Cen.t1r
ip Gail s wilL e iilwl Shaped
-a,-
Id
(ai1:SAd S
]rflp
r ijchaiiica1 i)ariIae
33
reported (20, 23, and 31+) that roots of all different
sizes as well as trees of all different sizes form
grafts and a very small tree can support the "callusing
over" on a much larger stump.
It was observed on one occasion where the stump of
an eight-inch second-growth Douglas-fir appeared to be
grafted to a 30-inch residual old-growth Douglas-fir.
These two trees were approximately five feet apart.
The nearest other tree was over 20 feet from and
approximately the same size as the callused stump.
No
mention has previously been made as to whether or not
old-growth and second-growth trees have been observed
grafted.
As was previously mentioned, grafts of larger
trees were noted up to 29 feet in this area.
Therefore,
it is possible that this stump is grafted to one or
more of the more distant second-growth trees.
Although
this phenomenon of root-graftiig between two different
generations has never been repQrted and is undoubtedly
rare, the author believes that it can and does occur
in nature.
B.
Total Percent of Stump Callusing
A total of 2014 stumps were inspected on 26 plots
scattered throughout the Black Rock research area.
this total, 24.7 percent (49
living calluses (Figure 6).
Of
stumps) were observed with
It was necessary to remove
3L
r.
ligure 6.
A Cai1ed
t
rnp
:'-gr8fd tD a Liv
Tree
35
the bark of 203 of the 2014 stumps at the root collar
(Table 1).
These stumps had no visible calluses but
left doubt as to their status due to a persistent resin
Of these girdled
flow or slightly protruded bark.
stumps,
4.9
percent were noted to have hidden calluses.
Approximately one-half of the stumps girdled had been
cut only two to three years previously.
These stumps
usually had very little decay and tight bark.
If any
resin was visible on a stump, it was usually necessary
to remove the bark to be certain no callus existed.
The remaining girdled stumps consisted of doubtful
cases which had been cut during the years 1953 to
l95.
Table I
THE NUMBER OF STUMBS FROM WHICH THE BARK WAS
REMOVED AND THE NUMBER OF HIDDEN CALLUSES FOUND
Year
Cttt
1953
1954
1955
1956
1957
l95
1959
1960
1961
Total
Stumps
Girdled
30
14
15
29
11
47
44
Percent
of Hidden
Calluses
Calluses
Found
03.3
12.5
21.4
00.0
06.9
00.0
04.3
02.3
00.0
1
1
3
0
2
0
2
5
1
0
203
10
Avg.
04.9
36
Stumps cut after January, 1961 were not included in
the study because, for the most part, they had not had
sufficient time to develop a definite callus.
It was
therefore quite difficult to tell the difference
between grafted and ungrafted stumps cut subsequent
to this time.
With only ten hidden calluses found from a total
of 2014 stumps it is concluded that over 99 percent of
the stump calluses on this area are visible with the
naked eye.
While it is possible that small root-grafts
can form and result in no subsequent callus formation
on the stump, it is deemed highly improbable that any
root-grafts which persist as avenues of water and
possibly nutrient transfer would show no effects above
the ground level.
C.
Relation Between Stump Callusing and the Month of
Cut t ing
The thinnings on each plot were tabulated by the
month of felling (Table 2).
The most productive months
had representative cuttings from several different
years and plots, however, the months of March, September,
and. December were represented by only small samples cut
from single plots.
With such small sample sizes, the
results obtained from these months should be viewed with
reservation.
37
Table 2
RELATION BETWEEN STUNP CALLTJSING MD THE
MONTH OF CUTTING
Month of
Felling
No. of
Stumps
Jan.
Feb.
Mar.
Apr.
No. of
Stump
Calluses
14
2O
157
336
316
256
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
21.9
2a.6
27.4
27.4
l,O
32.
l
50
107
314
30
Total
2a.l
25
30
4
39
43
92
57
4
137
May
Percent
Callusing
36.0
27.1
22.3
23.4
29
70
7
2014
49
Avg.
24.7
A statistical analysis showed that there is a
linear trend between the amount of stump callusing and
the month of cutting (Table
3).
The deviation from
linear regression is large enough to reject the linear
regression hypothesis at the five percent significance
level but not large enough to reject it at the one
percent level.
This seems to suggest that there is a
more than linear relationship between these two
variables.
However, due to the erratic sample sizes it
is felt that no firm analysis can be carried out to single
out periods which may have higher percentages of callusing,
3
Table 3
TEST. OF INDEPENDENCE RELATING THE AMOUNT OF
CALLUSING TO THE MONTH OF CUTTING
Source of Variation
among sample
regression
dev. from linear
regression
SS
DF
5.297
11
29.41
1.541
1
.56
3.4
24.72
6.63
3.756
10
2O.7
l.3l
23.21
l9.6
Y ( 1-!)
D.
Relation Between Stump Callusing and the Length of
Time Following Cutting
It was previously found (33) that the percent of
stump callusing decreases with increasing age of the
stumps.
It would also be expected that the greatest
natural decrease would occur after the first year due to
false callusing caused by stored reserve materials.
A somewhat similar situation was found on this study
area (Figure 7 and Table 4).
A significant difference
in the percent of callusing was found to exist among the
eight different stump ages (1961 was omitted due to an
extremely small sample size).
Table 5 also shows that the
period 1957-1960 has a significantly higher amount of
stump callusing than the period 1953-1956.
39
30
H
Cl)
o20
F-i
0
1953
Figure 7.
514.
55
56
57
5
YEAR OF CUTTING
59
60
Relation Between the Percent of Stump Callusing
and the Year of Cutting
Table 4
RELATION BETWEEN STUMP CALLUSING AND THE
YEAR OF CUTTING
Year
Cut
No. of
Stumps
No. of
Calluses
1g4
157
143
373
216
131
37
35
20
77
64
1959
1960
1961
.471
143
79
Total
2014
1953
1954
1955
1956
1957
l95
297
42
Percent
Callusing
20.1
22.3
14.0
20.6
29.6
26.0
30.4
26.6
21.4
34
9
49
Avg.
24.7
40
Table 5
2
-
''
TEST OF INDEPENDENCE RELATING STUMP
CALLUSING TO THE YEAR OF CUTTING
Source of Variation
SS
among sample
1953-56 vs 1957-60
11.3212
4.9400
DF x2
7
1
x2
27.44 14.07
62.9
3.4
6.63
The main reason for tl. is significant difference
probably was the occurrence of succeeding thinnings on
these areas.
Many of the plots studied were thinned
several times at two or three year intervals.
It was
found on many occasions that when a tree near a
callused stump was cut the latter died soon after.
It
was also noted in several instances that when the tree
nearest a callused stump was cut it developed a callus
and the older callused stump continued to live.
From
this it is concluded that if the root-grafting connects
three or more trees, one tree can be cut every few
years or several at one time without affecting the
stump calluses, as long as one of the grafted group
remains alive.
If root-grafting connects only two
trees and one is cut, any resulting callus will live
only as long as the second tree remains alive.
41
E.
RelationBetween Stump Callusin
and the Crown Class
of the Severed Tree
The amount of stump callusing appears to be directly
related to the crown class of the severed tree (Table
6).
The X2 test of independence shows that there is a
significant difference in stump callusing among the
different crown classes, between the two upper and the
two lower classes, as well as within the two upper and
the two lower classes (Table 7).
There appears to be
very little physical difference in the percentages of
callusing between the dominant and codominant classes.
However, it should be kept in mind that percentages
are not directly comparable unless the sample sizes are
equal.
Also, the amount of callusing was analyzed
rather than the percent.
Table 6
RELATION BETWEEN STUIVIP CALLIJSING AND THE
CRO1/N CLASS OF THE SEVERED TREE
Crown Class
of the
Severed Tree
dominant
codominant
intermediate
overtopped
Total
No. of
Stumps
No. of
Stump
Calluses
Percent
Callusing
233
49
30.4
29.9
22.6
931
71
149
210
352
6
2014
49
19.3
Avg.
24.7
42
Table 7
TEST OF INDEPENDENCE RELATING ThE AMOUNT OF
STUIVIP CALLUSING TO THE CRGWN CLASS OF THE SEVERED TREE
Source of Variation
among sample
DF x2
33
l9.
3.579
3
1.670
1
.323
1
dom. & codorn. vs.
mt. & sup.
dom. vs. codom.
irit.vs. sup.
7(i-)
15.716
1
.lo
9.2
x2.05 x2.01
7.l
11.34
3.4
46,24 3.4
?.3l 3.4
6.63
6.63
6,63
The intermediate and overtopped classes were
similar to each other but showed much lower grafting
than the two larger classes.
This is probably due to
the larger and wider spreading root systems of the
dominant and codominant trees.
The result is that most
grafts will occur between the more vigorous dominant
and codominant trees.
This effect is shown quite
clearly when one observes the large number of lower
crown class trees which appear to remain separate
from the surrounding trees.
They are isolated,
suppressed, and eventually succumb to competition from
the sea of roots which engulf them yet do not appear
to graft with them.
43
F.
Relation Between Stump Callusing and the DBH Class
of the Severed Tree
The diameter classes of the severed trees, which
are closely correlated with the crown classes, also
show a steady increase in the percent of callusing
(except for the class 16 inches and over) with an
and Figure
increase in tree diameter (Table
).
These trees are all approximately the same age, therefore, the root size and root area appear to be the
main factors for this increase in stump callusing.
Table
RELATION BETWEEN STUMP CALLUS ING AND THE DIAMETER
CLASS OF THE SEVERED TREE
Diameter
Class
(inches)
2
4
6
10
12
14
16+
Total
No. oT
Stumps
Np. of
Stump
Calluses
23
39
174
101
231
103
75
2014
15.4
16.7
2
13
13
366
699
Percent
Callusing
21.6
24.9
26.0
79
2.l
35.0
6
36
24.0
1
49
Avg.
24.7
44
30
z
Cf)
20
C
l0
C-)
p-4
12
6
10
16-23
2
14
4
DIAMETER CLASS OF THE SEVERED TREE (INCHES)
Figure
.
Relation Between the Percent of Stump
Callusing and the Diameter Class of the
Severed Tree.
The lowest diameter class shown (two inches) was
represented by only 13 stumps, however, it appears to
correlate well with the succeeding classes and is
possibly indicative of this size class.
The root
system of such small trees will undoubtedly be small and
weak, and would not be expected to graft readily with
larger and more vigorous individuals.
On the other
hand, the small suppressed trees which live for
40-50
years and are no bigger than two to four inches probably
45
have some external means of support to keep them
alive.
The four to fourteen-inch diameter classes are
represented by from 100 to 700 stumps each.
They show
a steady increase in callusing to a peak of 35.0
percent at fourteen inches.
The larger stumps
consisted of 75 stems ranging in diameter from 16 to 23
These classes were combined because a
inches.
representative sample was not available for any one
class.
It would be expected that these larger trees
would root-graft as often or more often than the
smaller diameter trees.
The inconsistency of the
larest DBH class is unexplained.
G.
Relation Between Stump Cailusing and the Crown Class
of the Nearest Living Tree
It is realized that a callused stump will not be
grafted in all cases to the nearest living tree.
It is,
however, felt that in the majority of cases this
situation will previal due to the greater probability
of root contact.
In certain instances where it could be
determined that the actual root-graft was with a tree
other than the nearest tree, the crown class of the
more distant tree was recorded and used for this
analysis.
46
In contrast to the previously mentioned relation-
ship between the amount of callusing and the crown class
of the severed tree, the amount of stump callusing
showed no definite correlation with the crown class of
However,
the nearest living tree (Tables 9 and 10).
where the upper crown
the trend, as shown in Table 6
classes appear to graft more often, still seems to hold
true.
Table 9
RELATION BETWEEN STUMP CALLUSING AND THE
CROWN
CLASS OF THE NEAREST LIVING TREE
Crown Class
of the Nearest Tree
dominant
codominant
intermediate
overtopped
Total
No. of
Stump
Calluses
No. of
Stumps
42
25
737
204
196
66
150
32
49
2014
Percent
Callusing
24.2
26.6
23.2
21.3
Avg.
24.7
Table 10
TEST OF INDEPENDENCE RELATING THE AIVIOUNT OF
STUMP CALLTJSING TO THE CROWN CLASS OF THE NEAREST TREE
Source of Variation
among sample
SS
.521
DF
3
X
2
2.9
2
2
.05
7.l
.01
11.34
47
A tabulation of data by both the crown class of
the severed tree and the crown class of its nearest
tree (Table 11) also showed no conclusive evidence that
a particular combination of trees (within each of the
crown classes of the severed trees) root-graft to a
greater degree (i.e. dominant with dominant, dominant
with codominant, etc.).
However, in three out of the
four cases the codominant crown class of the nearest
tree had the highest percent of callusing.
The effect
of this has already been seen in Table 9.
One possible reason for the difference in the amount
of stump callusing between the crown classes of the
severed trees and the nearest trees is that the crown
regime has been changed by the thinnings.
The removal
of crown trees through thinning will usually result in a
change in the classification of many of the remaining
trees.
The crown classes of the severed trees were
obtained prior to each thinning while the crown classes
of the nearest trees were all obtained at one time
following all the thinnings.
The effect of this may have
been sufficient to result in the difference obtained
between Tables 6 and 9, especially for the dominant and
codominant crown classes.
It is also possible that the
number of root-grafts related to the intermediate and
overtopped crown classes are overestimated somewhat by
Table 11
RELATION BETWEEN STUMP CALLUSING, THE CROWN CLASS OF THE
SEVERED TREE, AND THE CROWN CLASS OF
THE NEAREST LIVING TREE
Crown Class
of
the Severed Tree
Crown Class
of the Nearest Live Tree
dominant
dominant
dominant
dominant
dominant
intermediate
overtopped
co dominant
o odominant
o odominant
dominant
codominant
intermediate
intermediate
intermediate
interme diate
overtopped
overtopped
overtopped
overtopped
Total
No. of
Stumps
No. of
Stumps
Callused
96
25
o odominant
33
27
16
5
63
61
62
17
39
9
204.
Percent
Callusing
26.0
35.2
29.6
31.2
29.9
32.3
27.0
23.1
codominant
intermediate
overtopped
192
dominant
357
339
156
24.
7
17
2l.
3
20.5
co dominant
intermediate
overtopped
dominant
o odominant
intermediate
overtopped
l5
111
41
16
2014
23.2
25.4
19
15.4.
17.1
10
24.. 4
1
6.3
49
Avg. 24.7
LF9
arbitrarily picking the nearest living tree.
If this
is true, the actual percent of callusing by crown
class would be much the same as the percent of
callusing as related to the crown class of the severed
trees (Table 6).
From all indications this trend
would be the most logical explanation.
H.
Relation Between Stump Callusing and the Number of
Trees Per Acre
Data were obtained from widely divergent plots in
an attempt to show a direct correlation between the
number of trees per acre and the amount of stump
callusing.
The number of trees per acre following
thinnings ranged from a minimum of
of 704.
.55
to a maximum
A statistical analysis using the F test showed
a linear relation between the amount of stump callusing
and the number of trees per acre (Table 12).
From these
data a regression line was drawn, as shown in Figure 9,
from
.5 percent callusing at 50 trees per acre to
46.0 percent callusing at 700 trees per acre.
50
Table 12
REGRESSION ANALYSIS RELATING TI-FE AMOUNT OF STUMP
CALLUS ING TO THE NUMPER OF TREES PER ACRE
Source of Variation
treatment
regression
dev. from linear
regression
error
total
33
DF
2022.62
l39.54
l3.O
3446.3
5469.00
1VIS
F
404.52
5
1
l39.54
4
35
45.77
9,47
40
F05 F01
4.13
.46
7.43
2.64 3.92
It must be kept in mind that these figures are
probably only accurate for Douglas-fir of approximately
50 years of age on site III.
It has been shown in
past studies of other species that most root-grafting
is completed by age
60-70 (9 and
43), therefore it is
quite possible that more grafting will occur in this
species between the ages
50-70.
As would be expected the plots with the smallest
number of trees per acre also had the fewest calluses
and the smallest percent of callusing.
On the
acre which had been reduced to 55 stems, a total of 171
trees had been cut, of which only nine stumps
percent) revealed callus tissue.
(5.3
The average distance
from each of the 171 stumps to the nearest tree was
13 feet,. while the average distance of the callused
stumps from their nearest tree was eight feet.
These
50
S
3o
C!)
0
114
z
20
10
100
200
300
400
500
600
NU1VER OF TREES PER ACRE
Figure
9.
Regression Relationship Between the Percent of Stump
Callusing and the Number of Trees Per Acre.
700
52
figures are opposed to the same averages of six and
four feet respectively for the entire Black Rock area.
This is another indication of the fact that the fewer
the stems remaining on an area, the fewer the actual
number of calluses due to the greater average distance
between stumps and the nearest living trees.
It was on this area where a distance of 29 feet
was noted between one callused stump and its nearest
living tree.
Numerous other distances of 20 feet or
over were also observed.
This again suggests the
probability of multiple grafting.
If a tree can root-
graft at a great distance from itself,it probably will
be able to form several grafts with surrounding trees.
To the opposite extreme, the acre which had 704
trees left following cutting had 3.7 percent callusing.
A total of 31 trees had been removed during January,
of which 12 stumps had subsequently callused.
The light
cutting on this area resulted in a distance of only
approximately three feet between the stumps and the
nearest living trees, for both uncallused and callused
stumps.
The effect was that even though most of the
trees cut were of the intermediate crown class, the
percent of callusing was much greater than would
normally be expected even for vigorous dominant trees.
This again confirms the theory that the greater the
53
concentration of trees and roots, the higher the
probability of the occurrence of root-grafting.
Between the two extremes of 55 and 704 trees per
acre, the percents of callusing for the other 24 plots
were scattered in a rough regression order due to a
multiplicity of causes.
An attempt will be made to
clarify some of these variables in the succeeding
sections of this study.
1.
Relation Between Stump Callusing and the Basalt
Area Per Acre
The percent of stump callusing shows a similar
relation to basal area per acre as it does to the
number of trees per acre.
Statistical analysis reveals
a direct linear regression relationship (Table 13)
between the basal area per acre and the percent of
stump callusing.
Figure 10 shows that the percent of
callusing ascends from zero percent at 70 square feet
of basal area to 36 percent at 210 square feet.
These results suggest that the basal area per
acre and the total number of trees per acre will give
similar estimates of the percent of root-grafting in
even aged stands.
This is to be expected due to the
close relationship of the two measures for the same site
and age.
50
40
H
U)
30
H
Cl)
020
H
z
cI
0
1J
10
BASAL AREA PER ACRE (SQ. FT.)
Figure 10.
Regression Relationship Between the Percent of Stump Callusing and
the Basal Area Per Acre.
55
Table 13
REGRESSION ANALYSIS RELATING THE ANOUNT OF STUMP
CALLUSING TO THE BASAL AREA PER ACRE
SS
DF
2476.61
5
Source of Variation
treatment
regression
dev. from linear
regression
error
total
J.
113e63
662.9
266.11
5342.72
1
4
33
.05
495.32
ll363
F01
4.15 7.49
1.91 2.66 3.96
2O.
165.74
3
Relaton Between Stump Callusing and Type and
Density of Thinning
Three specific types of thinnings were carried
out on this area (crown, low, and field choice).
Field
choice thinning consists of removing those trees
which the marker believes should come out to better the
stand, with no special emphasis being put on any one
of the crown classes.
of thinning,
Within these different types
appears to be a definite trend
which is closely related to the crown classes of the
severed trees, basal area per acre, and number of trees
per acre (Table
14).
All of the plots were similar
in slope, elevation, soils, and drainage.
In the crown
thinning, over 70 percent of the trees cut were of the
dominant and codominant classes; one-half of which
subsequently showed callus formations.
The trees cut
Table 14
RELATION BETTEEN STUI
Type of
Thinning
No. of
Stumps
CALLUSING AND THE TYPE OF THINNING
No, of
Calluses
Percent
Callusing
B.A. Per
Acre
(sq. ft.)
No. of
Trees
Per Acre
21
65
47.
lO.4
low-light
low-heavy
120 crop trees
100 crop trees
44
304
77
21.4
22
2.6
163.6
197.2
319
311
274
2l
134
44
20.2
12.7
123,0
135,3
172
133
Total
777
169
fied choice
17
Avg. 21.
57
were vigorously growing individuals which had large and
widespreading root systems.
As was shown in part E,
the upper crown classes will show a significantly
greater amount of root-grafting due to their greater
vigor and size.
The field choice thinnings had a somewhat lower
percent of callusing than might be expected for thinnings
which showed 60 percent dominants and codominants among
the trees removed.
Part of this effect may be the
result of the substantial number of small trees on
these plots, as shown by the relatively low basal area.
In the low-light thinnings, only eight percent of
the trees removed were of the two upper crown classes.
The result was that a much smaller percent of callusing
was found even though the basal area following thinning
was the highest of the group and the number of trees
per acre also quite substantial.
The two instances of
low-heavy thinning resulted in only 30 percent (120
crop trees), and 37 percent (100 crop trees) of the
dominant and codominant trees being cut.
This combined
with the greatly reduced basal area and number of trees
per acre resulted in low percentages of stump callusing.
Several different densities of thinning (based on
basal area per acre) are being carried out on this
area at the present time.
Due to the necessity of a
slow reduction in basal area to avoid excessive opening
of the crown and the resulting exposure and windthrow,
most of these plots have not as yet been reduced to
their desired densities.
However, the available
information on these plots substantiates the previous
results that as the basal area and number of trees
per acre are reduced, the subsequent amount of stump
callusing is also reduced.
No one factor can determine the percent of rootgrafting, however, the three most important factors
which appear to regulate this phenomenon are the basal
area per acre, number of trees per acre, and the crown
class and vigor of the trees.
The type of thinning
will invariably determine the crown classes which will
be cut while the density will determine the basal area
and number of trees left.
K.
Relation Between Stump Callusing and the Soil Series
There are three soil series (Blachly, Hembre, and
Melbourne) located within the Black Rock forest
management area.
Of the 26 plots studied, 20 were of
the Hembre series, four Melbourne, and two Blachly
(Table 15).
TheX2 test of independence revealed a
significant difference in the percent of stump callusing
for the different soil types (Table 16).
It is,
however, believed that this conclusion is misleading
59
because the vast majority of the plots were located on
Hembre soil which covered a wide range of slopes.
In.
contrast, the Melbourne and Blachly soils were quite
homogeneous throughout.
Table 15
RELATION BETWEEN STUMP CALLUSING AND THE SOIL SERIES
No. of
Stump
Calluses
No. of
Stumps
Soil Series
Blachly
Melbourne
Hembre
323
290
1401
64
375
Total
2014
49
Percent
Callusing
l.3
59
22.0
26.g
Avg.
24.7
Table 16
TEST OF INDEPENDENCE RELATING THE AIVIOUNT
OF CALLUSING TO THE SOIL SERIES
Source of Variation
among sample
SS
2.14
DF
2
X2
11.7
2
.05
5.99
X
2
.01
9.21
The slope of the plots on Blachly and Melbourne
soils never exceeded 15 percent while the plots on Hembre
soil ranged from 10 to 45 percent and also encompassed
some rocky areas.
Table 17 contains all of the Blachly
60
and Melbourne plots plus the Hembre plots which were
located on slopes of 15 percent or less.
TheX2 test
of independence for these data resulted in a nonsignificant difference in the amounts of callusirig for
It is therefore
the different soils (Table l).
concluded that there is no essential difference in the
amount of root-grafting for these three soil series.
Table 17
RELATI0N BETWEEN STUMP CALLUSING AND THE
SOIL SERIES WITH SIMILAR SLOPES
Soil Series
Blachly
Melbourne
323
290
590
59
64
11
1203
241
Heinbre
Total
No. of
Stump
Calluses
No. of
Stumps
Percent
Callusing
l.3
22.0
20.0
Avg.
20.0
Table 1
TEST OF INDEPENDENCE RELATING THE AMOUNT OF
CALLTJSING TO THE SOIL SERIES WITH SIMILAR SLOPES
Source of Variation
SS
among sample
.22
Y(l-Y)
.16
DF
x2
2
l.3
x2
5.99
X2.ol
9.21
61
Relation Between Stump Callusing and the Percent of
L.
Slope
The 20 plots located on the Hembre soil were divided
according to the percent of slope on each plot (Table 19).
TheX2 test of independence showed a significant
difference in callusing between the different percents
of slope (Table 20),
The data show
that the plots
with the smLlest percent of slope have the least
amount of stump callusing.
It is believed that this
effect is mainly the result of the greater soil depth
on these plots.
The deep loamy soil combined with
very little slope and/or rocks undoubtedly allows the
roots complete freedom to spread out and penetrate
deeply.
grafting
Consequently the chance of roots meeting and
is greatly reduced.
Table 19
RELATION BETWEEN STU
CALLUSING AND THE PERCENT
OF SLOPE ON HERE SOIL
No. of
Plots
4
5
3
Total
Percent
Slope
Soil Depth
(inches)
10-15
60+
25
37-60
21-36
37-60
30-35
40-45
No. of
Stumps
590
l7
377
256
1401
No. of
Stump
Calluses
11
60
124
73
Percent
Callusing
20.0
3307
32.9
2.5
375 Avg. 26.
62
Table 20
2 TEST OF INDEPENDENCE RELATING THE AMOUNT OF
CALLUSING TO THE PERCENT OF SLOPE
Source of Variation
among sample
SS
5.05
DF
3
2
x2
25.77
2,05
7.l
l3.2
.20
Y(l)
The plots on a 25 percent slope showed moderately
deep soil, however, the amount of callusing was greater
than that shown by plots with much steeper slopes and
less soil depth.
These four plots were the only ones
(with one exception) located on rocky soil.
It has
previously been reported (19 and 27) that root-grafting
is common around stones due to deflections and growth
pressure caused by roots being lodged against stones.
From all
indications it appears that an increase in rocks
in the soil will effect a greater number of root-graftR,
regardless of the soil depth and/or percent of sloper
The plots located on
least soil depth.
30-35 percent slope had the
Although the areas were not rocky,
the reduced soil depth apparently resulted in a lesser
amount of space for roots to spread out.
The resulting
percent of callus ing was quite high as would be
indicative of a shallow soil and high percent of slope.
The plots located on the greatest slopes (LO-45
percent)
had a moderately great soil depth.
The steep
slope would appear to result in a greater root
concentrati..on but the moderate soil depth may have off-
set this effect which would account for the somewhat
lower percent of callusing.
From all available evidence it is concluded that
the percent of slope, depth of soil, and the rockiness
of the soil have definite effects upon the amount of
root-grafting which may occur in an area.
The greater
the slope and/or concentration of stones, the higher
the percent of root-grafting.
M.
Relation Between Stump Callusing and the Subsequent
Growth of Grafted Trees
A total of 2
trees were measured and paired
(Table 21) to determine the relative effect of rootgrafting between callused stumps and living trees
(see field procedure).
No significant difference in
growth could be found by using the T-test for paired
observations.
Trees root grafted to stumps appeared
to have no growth advantage over similar trees not
grafted to stumps.
Four similar paired observations, which had been
cut in 195, showed a greater dbh growth for the trees
near uncallused stumps in three cases and the same
Table 21
THE EFFECT OF STUMP CALLUS ING ON THE SUBSEQUENT GROWTH OF ROOT-GRAFTED TREES
SEVERED TREE
LIVING TREE
of
Stump and
DBH at
Time of
Thinnin
Cut
Tree (ft.)
(inches
Distance
Pair
No.
1
2
3
4
S
6
7
DBH
7.7
7.5
7.E
5.5
10.
9.7
9.7
7.4
7.
7.4
6.5
10.1
9.
6.0
9.0
9
10
11
16.3
l.5
11.1
9.
l2.
13.4
Stump
Callus
Present
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Date
11/53
11/53
Be twe en
1
1
2
4/55
3
3
3
4/55
4
4/55
4/55
6/56
9/56
6/57
7/57
9/57
3
2
4
2
2
4
2
2
2
9.7
9.6
7.0
7.1
9.9
10.6
9.4
.7
13.7
14.4
12.6
14.0
9.9
10.1
Present
(in.)
DBH
1.1
7.4
11.3
12.4
11.1
9.6
0.3
15.2
16.2
14.5
15.4
13.5
D
I
I
D
CD
CD
GD
CD
CD
CD
CD
D
D
D
D
D
D
D
I
I
D
1. 0
D
D
D
D
D
D
2.1
14.1
1.
D
CD
D
D
D
15.2
12.3
CD
CD
1.7
1.3
1.2
14.0
5
1.4
1.7
.9
1.5
1.9
1.4
CD
CD
D
1.1
1
15.9
2.5
1,6
1.4
Present
Crown
Class
11.2
11.1
19.1
2
2
1.3
Crown
Class at
Time of
Thinning
CD
CD
CD
CD
17.4
1 .2
(inches)
9.7
10.1
12.2
11.2
4
2
Increased
Growth
19. 5
14.5
Continued on Page 65
1.2
1.0
D
CD
CD
Table 21 (continued)
SEVERED TREE
LIVING TREE
Distance
Pair
No.
DBH
10.4
9.9
9.3
9.2
11.7
10.5
Stump
Callus
Present
Date
of
Cut
Yes
No
Yes
No
Yes
No
9/57
4
9/57
3
9/57
2
B etwe en
Stump and
Tree (ft)
2
6
5
DBH at
Time of
Present
Th inn in
DBH
(inches
(in.)
6.7
6.g
12.6
12.3
11.4
10.2
6.
7.0
13.1
13.0
12.2
10.6
Increased
Growth
Crown
Class at
Time of
(inches)
Th inn in
Present
Crown
Class
0
0
I
I
0.7
0.
I
CD
CD
0,4
CD
CD
CD
CD
CD
0.1
0.2
0,5
66
growth for the fourth pair.
This growth reversal was
probably due to the fact that the area was cut exceedingly
heavily.
Under such conditions a grafted stump may have
a relatively deleterious effect on immediate response
due to the sudden lack of competition among the trees,
the increased efforts of the tree, grafted to a new
stump, to stop water and nutrient loss, and & subsequent
attempt to heal the wound.
It has been suggested by some earlier writers
(1 and 33) that one of the possible reasons for a
substantial increase in the growth of certain stands
following thinnings may be due to increased absorptive
systems and stored food made available by the roots of
severed trees.
From the available data several poss-
ibilities exist to explain the pattern of response
obtained in this study:
1.
A significant amount of
nutrients are not passed from stumps grafted to healthy
neighboring trees.
2.
A period of from four to eight
years is not long enough for a significant growth
difference to be realized.
3.
The usual response to
release may overlap and mask any response resulting from
additional nutrients and water passing through rootgrafts.
L1.
Callused stumps may be grafted to several
nearby trees which would distribute any nutrient
passage and possibly preclude a measurable advantage for
67
any one tree.
5.
Inherent differences among the
individual trees may mask any significant results.
6.
Any combination of the above.
The growth differences among these paired
observations suggests that certain interactions among
the trees themselves have a definite effect upon the
utilization of increased growing space, root systems,
nutrients, and water.
It is well known that trees do
not always respond immediately to thinning.
It is
often necessary for a tree to increase its crown size
and adjust to its changed environment before it can
fully utilize its site.
It is therefore quite possible
that the short period of four to eight years is not
long enough for root grafted trees to show a significant
growth increase over neighboring trees which may be
grafted to each other, but have no greatly increased
root system due to the complete loss of a grafted
partner through cutting or breakage.
These paired observations were obtained from
different intensities of thinnings, but showed no
definite correlation of growth increase with the length
of time following thinning.
Some sample pairs cut in
1957 showed as great an increase in growth as others cut
in 1953.
The inherent differences in the trees along
with a higher reduction in basal areaon some plots
probably accounts for this seeming paradox.
The different crown classes do not appear to have
any difference in subsequent response to growth
following the cutting of their grafted counterparts.
Table 21 shows that regardless of the present or past
crown classes of the pairs, the resulting increase in
growth varies little.
It has been shown (29 and 34) that often times
several trees are root-grafted together.
If this
situation is prevalent and only one or two of the group
are cut, the additional support provided the remaining
stems may be negligible.
The necessity of immediate
callus tissue formation on a severed tree may
sufficiently reduce the vigor of a graIted tree so that
it cannot take complete advantage of increased light
and reduced competition.
If this situation held for
a few years, neighboring trees might have enough of
an advantage to allow them to compete favorably with
trees grafted to callused stumps.
It was observed on many occasions that certain
small overtopped trees continued to survive when the
surrounding trees of similar stature succumbed within
a few years.
Douglas-fir is not of sufficient tolerance
to withstand suppression for many years without external
69
support, therefore, the author believes that such
situations are the result of root-grafting of these
suppressed individuals with one or more of the
surrounding trees which are in the crown canopy.
This
suggests that sufficient nutrients and water, to sustain
life, must pass fromthe dominant tree(s) to these
overtopped stems.
The amount of this passage is
undoubtedly small or else the overtopped trees would
show sufficient growth increases over a period of
years to put them in the crown canopy.
N.
Movement of Materials in Solution through Root-Grafts
Five apparent root-grafts were treated with an
aqueous solution of acid fuchsin for 50 days, as
described in the field procedure.
During the first
few days a great deal of the solution was absorbed by
each of the roots,
After this initial consumption the
intake was slowly reduced (due mainlyto pitch plugging
the conducting tissues) to the point of little or no
absorption by the end of 30 days.
The roots (Figure 11)
were subsequently sectioned in the laboratory with the
result that two of the grafts showed a definite passage
of the bright red dye between the two roots of
different trees (Table 22).
In both cases the dye had
been applied to the root of the living tree rather than
the stump root.
70
Table 22
ROOT-GRAFTS WHICH NERE TREATED WITH AN AQUEOUS
SOLUTION OF ACID FUCHSIN
Root-Graft
No.
Tree
Root
(in.)
1
2.5
2
5
3
4
4
4
5
6
Stump
Root
(in.)
6
3
3
4
1.5
Root of
Dye
Application
Translocation
of Dye Between
Roots
tree
tree
tree
stump
tree
yes
yes
no
no
no
In the first graft the dye was applied to a 2.5
inchroot of a tree which had fallen over following a
high wind during March 1962 (Figure 12).
All of the
roots exposed by the upending of the tree were
infected with Poria weirii to the point where the
root tissue would crumble if any pressure was appli.ed
to it.
The root which was subjected to dye showed
signs of Poria weirii but continued to have a strong
sap flow even though the tree waslyingon the ground.
The stump did not appear to be infected by the pathogen
as yet.
As can be seen in Figure 12, the root from thetree
injected withacid fuchsin was solidly connected to a
six-inch root immediately below the root collar of the
stump.
Close examination of this stump will show a
definite, though small, callus formation around its
7'
ure 11.
Four
cid
graffE
chsin
ic
Jre Tretod with
72
3
12.
.D110
.V1Ig
'ria welrll
li1
3lJf1, Over
cti3n
Ca11is Cart oe
tg
-,
mp.
&nd a
73
perimeter.
This tree was cut in August 1957, with the
result that four years was required to form this small
callus.
This slow callus formation mayhave been the
result of the weakened condition of the root-grafted
tree.
When this union was sectioned for study in the
laboratory, the dye could be seen in all parts of the
graft.
A close examination of the graft in the lower
left hand corner of Figure 11 will show areas in the
root of the stump where the dye had penetrated.
A
cross-section of the two connecting roots (Figure 13)
revealed that acid fuchsin had passed along nine growth
rings of the tree root into the same annual rings of
the stump root.
A curved area of included bark,
about *-inch by 2-inches on the underside of the tree
root at its intersection with the stump root, is also
clearly visible.
A short distance below the root-
graft, the stump root separated into two main arteries.
Dye stains were still very heavy in both of these roots
where they disappeared below the shallow excavated
area.
A small area in the side of the grafted stump
also showed the passage of dye toward the stump surface.
The dye hadpenetrated the new callus to apoint about
eight inches from the top of the stump.
If more time had
7L.
.ire 13. b'Dwau:'''
ci
a
Iran5 mi3inn I
:
t-grai (ir 12)
ded ak end Acid jchc1i
1nLu...
75
been allowed, the dye would undoubtedly have reached
the stump surface.
The tree root consisted of approximately 30 growth
rings.
Heavy Uye was noted throughout all of the
annual rings except the heartwood center.
This same
root was only about i-inch in diameter at the point
where it exited on the far side of the stump root.
It
also was completely stained with dye.
The second root-graft (Table 22) which showed
evidence of dye interchange is shown in Figure 14.
Again the dye was visible in all segments of the
grafted roots.
Most of the dye going into the stump
root made a 160 degree turn at the junction of the two
roots, through 12 annual rings, and followed the
stump root which lead away from the stump.
This indicated
that the live tree had taken over this stump root.
The
majority of materials were passing directly from the
stump root to the live tree, thereby bypassing the
stump itself.
Avery slight trace of dye was noted
going towards the root which again substantiates
.
direct relationship between the tree and its rootgrafted stump.
A great deal of the dye was also noted
passing throughout the tree root on both sides of the
graft.
76
Iigure 12+.
n
cti\r i. t-graft Shwing lIE chanic81
and the 'pplication of
toot DarrlBge
cid 'ochsin.
77
The other three root-grafts were also sectioned
but showed no dye translocation between roots.
In each
case, however, several annual rings were noted
encompassing both roots (Figure 15), which shows
definitely that the two systems are connected.
It was noted in all five grafts that the dye
passed freely along the annual rings to which it was
applied, but traveled around the root within a growth
ring very slowly.
The 50 days of application were not
long enough to allow maximum movement around the rings
from one small point of concentration.
The result was
that in grafts number 3 and 4 (Table 22) the dye was
not able to work its way around the annual rings, and
thereby go into the second root which was grafted on the
lower side.
Graft number five (Table 22) showed a
direct connection between the roots which looked similar
to the connection between the bole of a tree and one of
its limbs.
The core of a small (1.5-inch) root could
be directly traced to one of the annual rings of the
larger root.
Several outer rings of the large root
circled around the smaller root (as shown by dye movement)
but appeared to have no direct connection with the
smaller root.
The hole drilled for the dye was not
deep enough to reach the rings which were directly
7
1gre 1.
The Oross-secio
the
cf a
t-graft Showing
r:a. Oa1 Sepd Roote due
Gra±t.i'-g Rressur, and rratir GrowGh
Jiogo olicwiiig Gratin.g
79
connected with the smaller stump root, consequently no
dye was transmitted between the two roots.
It was observed that the dye passed between annual
rings only at the points of application.
This was
probably due tothe very heavy concentration of dye at
these points.
Throughout the rest of the exposedareas,
the dye was not noted passing between annual rings.
As
would be expected, most of the dye spread via the sprLn
wood due to the lesser density and greater concentration
of materials in solution.
This reduced dye transmission between annual rings
may be due to a lack of pits in root tissue.
If this
is so, roots would be somewhat limited in their
transmission of materials.
The result would be that
materials passed through annual rings formed prior to
root grafting could not benefit a root-grafted partner.
This probably would have a minimum effect however,
because the central rings form a heartwood as the root
gets older and the outer rings ultimately carry on
most of the activity.
A great deal of included bark and pitch pockets
were noted in all of the grafts (Figure 13).
This
material, along with some dead cambium tissue, is
undoubtedly trapped inside the graft when new cambium
is formed as a result of pressure exerted by the growing
roots.
The pressure of the roots on each other prior
to and during the fusion is great enough to cause the
roots to take on an oval shape at the points of contact
(Figure 15).
A new cambium then joins the two root
cambiums, which subsequently results in several eccentric
growth rings which encircle both roots.
Microscopic sections of the fusion areas were
taken from three of the root-grafts.
In every case
there was a common cambium and actual union of
vascular elements.
The fusion area invariably could
be easily viewed because of its different structure.
The tracheids were short, often occluded with resin
droplets, and were oriented in every possible direction.
Figure 16 shows a grafted area under high magnification.
The central area which appears to be a cross section is
the actual fusion area.
The upper and lower cells are
from the two fused roots and as can be seen the celj.s
need not be oriented in any particular directions for
grafting to take place.
Figure 16.
Rootgrafted Area under 70X agnification..
tra1 Frea Showing a Cross-sectional
Trend is tIne
usion Area.
The upper and
Lower CelLs are X 1
from th Roots of Two
Different Trees Oriented in Different
Directions
The C
0.
Movement of Poria weirii through Root-grafts
Poria weirii has been found, scattered in small
pockets, throughout this study area.
In one place where
this disease was most serious, nearly all of the trees
on i-acre succumbed during the past few years; allowing
hardwoods and brush to take over.
Numerous other
small areas have trees which blow down each year with the
result that this disease is becoming a serious challenge
to the management of even-aged Douglas-fir stands.
It is quite evident that aace Poria weirii is
established in the roots of one tree, it spreads to
neighboring trees via root-grafts, root contacts, and
possibly even through the soil itself under ideal
conditions
Three small plots which were infected with
this pathogen were root washed during l95
Figures 17 and l
(32, p. 15).
show one of these root wash areas.
It is very difficult to observe many places where the
disease could pass from one tree to another because
washing or digging destroys most of the small grafts
and/or root contacts.
Root washing and/or digging will
therefore uncover only the larger grafts and contact
areas.
Regardless of this drawback, a definite pattern
of spreading in many directions from the focal point
can be observed.
LI
-4
igure 17.
Root
05h
Lippi.
of the S
ea Showmg
B
ps
sd fr
Grid $yst
Foria wirij Rot CBn be S
i
ir
)FlA WEIRII ROOT WASH IAREA NO
BLACK ROCK
AUGUST- SEPJEMEER 1958
/
.5m.f1
..
,ff
A
\VL)
yo
1
7
Figure 1.
Ro3t Wash Area (Figure 17) Following f-lapping.
Infected with Poria weirii.
The Darl
eas Are
The focal point of the infection is probably the
remains of an old growth stump.
The disease spreads in
several directions infecting some trees and not others.
In one instance it was noted where a root of one nearby
healthy tree was infected but the tree subsequently
developed a callus which halted the disease before it
reached the trunk.
It therefore appears that some
trees can develop a resistance to or have an inherent
resistance to this pathogen.
It is important to note that many of the small
trees within these plots had no infection although
they were literally surrounded by the disease.
As has
been previously mentioned and is further confirmed here,
the less vigorous trees tend to have fewer root-grafts
with the result that Poria weirii will find fewer
avenues to spread to these suppressed trees.
Through this root washing, it was determined that
in second-growth Douglas-fir, at least 75 percent of
the main roots must be infected with advanced decay
before a tree will succumb.
However, windthrow
causes the death of trees in many instances before root
rot has developed to this advanced stage.
SU]YU4ARY AND CONCLUSIONS
A total of 24.25 acres of 45-50 year old Site III
Douglas-fir, scattered throughout a thinned 500 acre
tract, were inspected for stump callusing.
Of the
2014 stumps observed 24,7 percent (49) had callus
formations.
Removing the bark of 203 doubtful stumps
revealed only ten hidden calluses.
Statistical analysis
showed that the amount of stump callusing decreases
with time due to "false callusing" (food reserves
stored in ungrafted stumps) and subsequent thinnings
which remove trees root-grafted to callused stumps.
The data revealed that stump callusing of felled
trees increases from a minimum of 15,4 percent for the
two-inch diameter class to a maximum of 35.0 percent
for the 14-inch diameter class.
A significant difference
was also observed between the crown classes of the
felled trees.
The percent of callusing increased frQm
:19.3 for overtopped stems to 30.4 for dominant stems.
Correlations were found to exist between the amount
of stump callusing and the basal area per acre, number
of trees per acre, and the type of thinning.
Regression
analysis showed that callusing increased. from zero
percentat 70 square feet of basal areaper acre to
3.7percent at 220 square feet per acre.
Further
analysis relating stump callusing to the number of trees
per acre resulted in a minimum of
E.4
percent callusing
at 50 trees per acre and a maximum of 46.0 percent
callusing at 700 trees per acre.
from
12.7
to 47.
Callusing increased
percent for a low thinning of 100 crop trees
percent for a light crown thinning.
It was
also noted that an increase in slope and/or rockiness
of soil resulted in a statistically significant increase
in stump callusing.
No significant difference in callusing could be
attributed to the different crown classes of the nearest
living trees or to the three soil series studied
(Blachly, Hembre, and Melbourne).
Due to erratic
sample sizes, no firm conclusions could be drawn
relating the month of cutting and the amount of stump
callusing.
Other findings showed that materials in solution
will pass through graftedroots of Douglas-fir.
Of
five root-grafts studied, two revealed a definite transfer
of dye between grafted roots demonstrating conclusively
that materials in solution and water do pass between
trees of this species.
As a result of sectioning and
microscopic study, all five grafts revealed interconnected cambial systems and vascular elements.
Through apaired T test, using 14 samplepirs,
it was found that no significant growth increase could
be attributed to root-grafting between a tree and a
callused stump during the period of four to eight
years following thinning.
From the results of this study it appears that
root-grafting can effect some water and nutrient
transfer.
However, no evidence could be found to
substantiate the hypothesis that trees root-grafted
to callused stumps have a growth advantage over trees
not grafted to callused stumps.
Numberous factors
are involved which may have overlapped and masked any
possible significant growth increase.
BIBLIOGRApHY
Adams, A0 J. S.
Observations on root fusions in
Monterey pine. Australian Forestry
5:7g-0.
1940.
Anonymous.
Scientific American0
5(5):l12.
1913.
Armson, K. A. and R. Van Den Driessche. Natural
root grafts in red pine (Pinus resinosa Ait.).
Forestry Chronicle 35:232-241. 1959.
Beskaravainyi, M. M. Root-grafting in some woody
speci-es in the Kamyshin district. Agrobiologiya.
1955. (Abstracted in Forestry
Abstracts 17:no. 2561. 1956)
3:7-9.
.
The development of root-grafted
tree groups in pine stands of the Kainyshin
field station. Agrobiologiya 1:143-146.
1956.
(Abstracted in Forestry Abstracts l: no. 3791.
1957)
.
The transpiration of root-grafted
Pinus sylvestris. Fiziologiya Rastenij, 5:366368. 1958. (Abstracted in Forestry Abstracts
20: no0 1432.
1959)
Bier, J. E. and D. C. Buckland. Relation of
research in forest pathology to the management of second-growth trees.
1.
Poria weirli
root rot, an important disease affecting
immature stands of Douglas-fir. British
Columbia Lumberman 31:49-51, 64, 66.
1947.
.
Bormann, F. H.
Intraspecific root-grafting and the
survival of eastern white pine stumps.
Forest Science 7;247-256. 1961.
Bormann, F0 I-I. and B. F. Graham, Jr.
The occurrence'
of natural root-grafting in eastern white
pine, Pinus strobus L., and its ecological
implications. Ecology 40:677-691.
Oct.
1959.
10.
.
Translocation of silvicides
Journal of Forestry 5:
thro-ugh root-grafts.
402-403.
1960.
90
Boyce, J. S. Jr.
Oak wilt spread and damage in the
southern Applachians.
Journal of Forestry
55:499-505. 1957.
Cook, D. B. and D. S. Welch,
Backflash damage to
residual stands incident to chemi-peeling.
Journal of Forestry 55:265-267. 1957.
Dallimore, D0 Iatural grafting of branches and
roots.
Kew Bulletin nos,9 & 10:305. 1917.
Drake, C, ft., J. E. Kuntz and A. J. Riker.
Chemical control of the oak wilt. Superior,
1957.
2 p. (Wisconsin College of Agriculture.
Forest Research Note no, 35)
Graham, B. J. Jr. Root grafts in eastern white
pine, Pinus strobus L.: their occurrence
and ecological implications.
Ph.D.
dissertation. Durham, N. C., Duke University,
101 p.
1959.
(Abstracted from Dissertation
Abstracts 20:466.
1959)
.
Transfer of dye through natural
root grafts of Pinus strobus. Ecology41:
57-64.
1960.
Henry, B. W. et el. Oak wilt: Its significance,
symptoms and cause. Phytopathology34:636_
647.
1944.
Junovidov, A. P.
Intraspecific relationships in
the forest.
Lesnoe Hozjajstvo 5:11-13. 1952.
(Abstracted in Forestry Abstracts 16 no. 3887.
1955)
Kozlowski, T. T. and J0 H.Cooley. Natural root
grafting in northern Wisconsin. Journal of
Forestry 59:105-107. 1961.
Kuntz, J. E. and A. J. Riker. The use of radioactive isotopes to ascertain the role of root
grafting in the translocation of water,
nutrients, and disease-inducing organisms.
Proceedings of the International Conference
on the Peaceful Uses of Atomic Energy. Geneva,
Switzerland, 1955. Vol.12. p. 144-148.
Lamb, F. H. Root suckers in Douglas-fir.
Gazette 28:69. 1899.
Botarnical
91
22.
23.
Laitakari, E,
The root system of pine.
forestalia fennica 33. 1927.
Acta
The root system of birch
(Betula verrucosa). Acta forestalia fennica
.
41.
1934.
LaRue, C. D. Root grafting in trees. American
Journal of Botany 21:121-126. 1934.
Root grafting in tropical trees.
Science
115:296.
1952.
Ljubic, F. P.
Interrelation of root systems of
individual plants of . robur and of other
woody species in the 'nest' method of
establishing plantations. Doklady Akademii
Nauk SSSR 97:535-53g. 1954.
(Abstracted
in Forestry Abstracts 16: no. 2951. 1955)
McMinn, R, G,
Interim report on studies on the
characteristics and ecology of the root system
of second growth Douglas-fir. Victoria, B.C.
(Unpublished report)
March 1954.
2.
Molotkov, P. I. Sap movement in the waterconducting system of trees and interconnectiois
between root grafted trees.
Botaniceskij
Zurnal 41:407-409. 1956.
(Abstracted in
Forestry Abstracts 1: no. 212. 1957)
Newins, N. S. The natural root grafting of
conifers.
Proceedings of the Society of
American Foresters 4:394-404.
1916.
Nikitin, I. N.
New ideas in silviculture in the
light of 'Micurinist agrobiology'.
Lesnoe
(Abstracted
in
J-Iozjajstvo 5:13-].
1952.
Forestry Abstracts 16: no. 2952.
1955)
.
New points on the biology of
some tree species and stands. Lesnoe
Hozjajstvo
195g. (Abstracted in
Forestry Abstracts 20: no. 1456. 1959)
11:l-20.
Oregon Forest Research Center, Corvallis.
Report, 1960.
39 p.
Page, F.
Living stumps.
67-690.
1927.
Annual
Journal of Forestry. 25:
92
Pemberton, C0 C0 Living stumps of trees.
Forests 26:614-616.
1920.
American
. Overgrowth of stumps of conifers.
Canadian Field Naturalist
1921.
35:gl-7.
Rahteenko, I. N. On the transfer of mineral
nutrients from one plant to another owing to
interaction between their root systems.
Botaniceskij Zurnal 43:695-701.
(Abstracted in Forestry Abstracts 20:
l95.
no.
1433.
1959)
Rushmore, F. N. Sodium arenite in spaced ax
cuts:
an effective stand improvement
technique.
Journal of Forestry 56:195-200.
l95.
3.
Safar, J. Natural root grafting.
Its biological
and economic significance in some root
relations of trees. Sumarski List 79:56357g. 1955. (Abstracted in Forestry
Abstracts l: no. 211.
1957)
Stoddard, E. N. and A. E. Dimond, The chemotherapy
of plant diseases.
Botanical Review 15:
345-376.
1949.
U. S. Dept. of Agriculture.
Forest Service.
Synopsis of present inforation concerning
Poris weirii root rot in Douglas-fir.
Portland, Ore., April 1955, 2 p.
(Pacific
Northwest Forest and Range Experiment Station
Research Note no. 116)
Annual report, 1959. Northeastern
.
Forest Experiment Station. Upper Darby,Pa.,
1960. 7 p.
The occurrence of root-grafting,
Wachter, H.
particularly in Pseudotsuga menziesii (Mirb.)
(a compilation of literature). Master's
paper.
Corvallis, Oregon State University,
1962.
99 p.
Yli-Vakkuri, P.
Studies of organic root-grafts
between trees in Pinus sylvestris stands.
Acta forestalia fennica 60:1-117. 1953.
(Abstracted in Forestry Abstracts 16: no. 231.
1955)
93
44.
Yount, W. L.
Longevity of the oak wilt fungus in
oak roots as related to spread through root
grafts.
Plant Disease Reporter 39:256-257.
1955.