APPROACHES TO DETERMINING VOLUME LOSSES DUE TO DWARF MISTLETOE ON A WESTWIDE BASIS-1/
David B. Drummond-2/ Abstract: Timber inventory data from three National Forests were evaluated to determine their suitability as a source of data which could be used to compute cubic-foot volume loss. These data indicate that while timber inventory
and forest survey represent the logical approach to the collection and storage of such information, existing data are not adequate to provide cubic-foot volume loss estimates
at this time. Results from a road-plot survey indicate that
the system can be used to estimate dwarf mistletoe incidence
and intensity in areas where all topographic aspects contain
adequate roads. pest complex on growth which will help establish priorities in management; (2) the documentation Information on forest insect- and disease- of the success or failure of silvicultural caused losses over large areas has usually been and/or direct control measures applied by the available only by extrapolating timber stand data timber manager (these estimates will assure that initially collected for other purposes. Few research support is provided for problems of attempts have been made to relate disease greatest concern to the timber manager); and (3) incidence to volume loss at a statewide level. the reduction in the amount of management by In the past,confidence limits could not be crisis--a syndrome often displayed by the Forest placed on national estimates of insect- and Service in its dealings with pests. Furthermore, disease-related losses, and they were often data of this nature will aid in allocating funds disregarded. To rectify this, we are attempting when needed. to assess loss from dwarf mistletoe and other forest pests over a statewide area. .To help in The estimates per se, if made for an entire planning and carrying out this attempt, the U.S. forest, state, or region, will be of little Forest Service organized a Loss Assessment direct value to the timber manager in dealing Working Group composed of forest pathologists. with specific stands. However, data from which such estimates were drawn would be of use to him At first glan~e~statewide
estimates
of if they were located in a common data base. forest insect- and disease-caused loss would appear to be of little benefit to the timber manager at the district .level. Indirect values to TIMBER INVENTORY AS A FUTURE the timber manager, however, include (1) the SOURCE OF LOSS DATA determination of long-term effects of a pest or Remote sensing techniques are coming into wide use, but dwarf mistletoes do not lend themselves well to detection using such tech- Ñ'~resente at the Symposium on Dwarf Mistletoe niques. In most areas, greatest losses are Control Through Forest Management, Berkeley, attributed to reduced growth, not mortality; Calif. April 11-13, 1978. consequently, these losses are often ignored. INTRODUCTION ?'survey
Plant Pathologist, Forest Insect and Disease Management Methods Application Group, USDA Forest Service, Davis, Calif. To measure the effects of dwarf mistletoes and other pathogens, data need to be collected over large areas, and data collection should be repeated a t specified intervals. This
r e e v a l u a t i o n i s most i m p o r t a n t . Growth l o s s
c a u s e d by f o r e s t p e s t s must b e s t u d i e d d u r i n g
t h e endemic p h a s e s o t h a t host-pathogen i n t e r a c t i o n s a t t h a t l e v e l can b e documented. I n
t h i s way, it can b e determined i f a p a r t i c u l a r
p e s t c a u s e s s u f f i c i e n t l o s s a t normal p o p u l a t i o n
l e v e l s t o a l t e r e x i s t i n g management s t r a t e g y .
Research h a s documented t h e e f f e c t s o f
m i s t l e t o e s on a stand-by-stand b a s i s (Baranyay
and S a f r a n y i k 1970; Hawksworth and Hinds 1964;
Weir 1916), and t h e s e r e s u l t s have been i n c o r p o r a t e d i n t o s i m u l a t i o n models f o r l o d g e p o l e
p i n e and s o u t h w e s t e r n ponderosa p i n e (Edminster
1977). These t o o l s can a i d i n e s t i m a t i n g l o s s
on a s t a t e o r r e g i o n a l b a s i s .
The Loss Assessment Working Group a g r e e d
t h a t t h e t i m b e r i n v e n t o r y would p r o v i d e t h e
b e s t way t o f u l f i l l t h e s e d a t a c o l l e c t i o n
r e q u i r e m e n t s ; however, e x i s t i n g t i m b e r i n v e n t o r y
d a t a a r e not adequate t o provide r e l i a b l e
d i s e a s e and i n s e c t i n f o r m a t i o n . G e n e r a l l y ,
i n f o r m a t i o n concerning p e s t s a v a i l a b l e i n t h e
inventory i s not adequate t o a s s e s s i n s e c t o r
d i s e a s e p r e s e n c e a t t h e s t a n d l e v e l , n o r i s it
s u f f i c i e n t l y consistent f o r estimates of
d i s e a s e l o s s o v e r l a r g e a r e a s . I n s e c t and
d i s e a s e i n f o r m a t i o n i n many r e g i o n a l i n v e n t o r i e s
c o n s i s t s of a s u b j e c t i v e e v a l u a t i o n o f o n l y
t h e "most damaging agent" observed on e a c h
p l o t t r e e . T h i s does n o t p e r m i t a c c u r a t e
d e t e r m i n a t i o n o f s p e c i f i c p e s t organisms
i n v o l v e d i n complexes o r t h e r e l a t i v e importance
o f o t h e r organisms endemic i n t h e a r e a . We
hope e v e n t u a l l y t o a l t e r s l i g h t l y t h e v a r i o u s
t i m b e r i n v e n t o r y methods t o improve t h e q u a l i t y
and q u a n t i t y o f p e s t d a t a c o l l e c t e d ; i n t h e
meantime, we hope t o g e n e r a t e l o s s e s t i m a t e s
by u s i n g s e v e r a l approaches.
I n t h e i n t e r i m , we a r e e v a l u a t i n g e x i s t i n g
dwarf m i s t l e t o e i n c i d e n c e d a t a , and where
possible, use those d a t a t h a t appear adequate
t o p r o v i d e a n i n t e r i m volume l o s s e s t i m a t e .
We a r e a l s o i n v e s t i g a t i n g methods o f r a p i d l y
a c q u i r i n g a c c u r a t e d a t a f o r a r e a s where e i t h e r
t i m b e r i n v e n t o r y a n d / o r dwarf m i s t l e t o e i n c i dence d a t a a r e n o t a v a i l a b l e , i - e . , p r i v a t e
and s t a t e ownerships.
T h i s p a p e r d e s c r i b e s a p p r o a c h e s used t o
e s t i m a t e l o s s e s due t o dwarf m i s t l e t o e s on
t h r e e N a t i o n a l F o r e s t s : t h e Medicine Bow i n
Wyoming, t h e P r e s c o t t i n Arizona, and t h e
Deschutes i n Oregon.
GATHERING LOSS ASSESSMENT
INFORMATION
Medicine Bow
N a t i o n a l F o r e s t , Wyoming
During 1977, a p i l o t p r o j e c t was conducted
on t h e Medicine Bow N a t i o n a l F o r e s t i n Wyoming.
The p u r p o s e o f t h i s s u r v e y was t o e v a l u a t e a n
e x i s t i n g t i m b e r i n v e n t o r y system t h a t i n c l u d e d
a dwarf m i s t l e t o e r a t i n g (Hawksworth 1 9 5 6 ) , i n
a d d i t i o n t o t h e "most damaging agent" e v a l u a t i o n
o f p l o t t r e e s . These t i m b e r i n v e n t o r y d a t a
were compared w i t h r e s u l t s o f a r o a d - p l o t
s u r v e y , c a r r i e d o u t by f o r e s t p a t h o l o g i s t s
d u r i n g t h e summer. The s u r v e y was i n t e n d e d t o
t e s t our a b i l i t y t o estimate green stand
p a r a m e t e r s and, a t t h e same t i m e , d e t e r m i n e i f
t i m b e r i n v e n t o r y crews a c c u r a t e l y e v a l u a t e d
t h e p r e s e n c e o f dwarf m i s t l e t o e .
Road P l o t Survey
The s u r v e y was s i m i l a r i n d e s i g n t o one
conducted by Hawksworth (19581, b u t w i t h some
m o d i f i c a t i o n s . The s t u d y c o n s i s t e d o f two
p a r t s . The f i r s t p a r t was a road r e c o n n a i s s a n c e
where t h e d i s t a n c e was r e c o r d e d a t any p o i n t
where a d e t e c t a b l e change i n f o r e s t t y p e , s i z e
c l a s s , o r dwarf m i s t l e t o e i n f e c t i o n l e v e l
occurred along t h e right-hand s i d e of t h e
road. Type maps were used t o e x c l u d e obvious
a r e a s o f non-lodgepole p i n e t y p e . Lodgepole
p i n e s t a n d s above 3,000 m e l e v a t i o n were a l s o
excluded because l o d g e p o l e p i n e dwarf m i s t l e t o e
does n o t o c c u r above t h i s e l e v a t i o n i n t h e
Medicine Bow N a t i o n a l F o r e s t (Hawksworth
1956). I n v e n t o r y d a t a were u s e d t o p r o v i d e
a c r e a g e e s t i m a t e s f o r l o d g e p o l e p i n e t y p e on
the forest.
Dwarf m i s t l e t o e i n f e c t i o n was r e c o r d e d a s
none, l i g h t , moderate, o r heavy. "Light"
indicated l e s s than one-third of t h e t r e e s i n
t h e s t a n d ' s predominant s i z e c l a s s were i n f e c t e d ;
"moderate" i n d i c a t e d o n e - t h i r d t o t w o - t h i r d s
were i n f e c t e d ; and "heavy" i n d i c a t e d t h a t
g r e a t e r t h a n t w o - t h i r d s o f t h e t r e e s were
i n f e c t e d . The s t a n d s were e v a l u a t e d t o a
d e p t h o f 1 c h a i n from t h e r o a d f o r mature
s t a n d s , and o n e - h a l f c h a i n i n p o l e , and s e e d l i n g
s t a n d s . The p e r c e n t a r e a o f l o d g e p o l e p i n e
t y p e a f f e c t e d by m i s t l e t o e was e s t i m a t e d by
determing t h e r a t i o o f m i l e s o f l o d g e p o l e p i n e
type with infected t r e e s present t o t h e t o t a l
number o f m i l e s o f l o d g e p o l e p i n e t y p e t r a v e r s e d .
The second p a r t o f t h e s u r v e y c o n s i s t e d
of e s t a b l i s h i n g variable-radius p l o t s a t
t h r e e - m i l e i n t e r v a l s a l o n g t h e road. P l o t s
were l o c a t e d 2 c h a i n s i n t o t h e f o r e s t a t
right-angles t o t h e road being traveled.
P l o t s were e s t a b l i s h e d on t h e right-hand s i d e
of t h e road; however, i f t h e p l o t was nontype, t h e n t h e l e f t s i d e of t h e road was used.
I f both s i d e s were non-type, t h e p l o t l o c a t i o n
was r e j e c t e d without replacement.
Basal a r e a was determined f o r 107 v a r i a b l e
p l o t s . Diameter a t b r e a s t height (DBH), and a
dwarf m i s t l e t o e r a t i n g (DMR), were recorded
f o r each t r e e 5 inches o r more i n diameter. A
one-one hundredth-acre (1/100) f i x e d p l o t was
a l s o e s t a b l i s h e d t o e v a l u a t e reproduction.
Trees g r e a t e r than 6 f e e t i n h e i g h t and l e s s
than 5 inches DBH were recorded and evaluated
f o r dwarf m i s t l e t o e . P l o t d a t a were combined
t o r e p r e s e n t approximately 70 h y p o t h e t i c a l
stands.
The RMYLD simulation model (Edminster
1977) was then used t o e s t i m a t e cubic-foot
volume l o s s f o r each stand, base,d on t h e
average dwarf m i s t l e t o e r a t i n g from t h e p l o t s
combined t o make up t h e s t a n d . This l o s s
e s t i m a t e was derived by making two consecutive
computer runs using t h e model, t h e f i r s t with
average D M R f s derived from t h e d a t a , and t h e
second with a l l DMR's converted t o zero t o
r e p r e s e n t non-infected s t a n d s . The l a t t e r
s i m u l a t e s growth over t h e next ten-year period
a s i f no dwarf m i s t l e t o e i n f e c t i o n e x i s t e d i n
the forest.
Timber Inventory
Ninety-two Stage I timber inventory p l o t s
had been e s t a b l i s h e d w i t h i n t h e lodgepole p i n e
type i n t h e Medicine Bow National Forest.
Region 2 timber inventory personnel provided a
summary o f t h e green s t a n d d a t a f o r t h e s e
p l o t s . From p r i n t o u t s , d a t a f o r t h e following
parameters were transposed t o a summary s h e e t
and were segregated by computer i n t o t h e
following c a t e g o r i e s :
S i t e index ( f i v e d t e g o r i e s )
Dwarf m i s t l e t o e i n f e c t i o n l e v e l (four
categories)
a.
b.
c.
d.
no i n f e c t i o n (0)
l i g h t (L) 1-60 percent of t r e e s
infected
moderate (M) 61-81 percent of
t r e e s infected
heavy (H) g r e a t e r than 81 percent
of t r e e s i n f e c t e d
Basal a r e a ( f i v e c a t e g o r i e s )
a.
b.
c.
d.
e.
0-50 f t . 2
51-100 f t . 2
101-150 f t . 2
151-200 f t . 2
g r e a t e r than 200 f t . 2
On t h e b a s i s of t h e s e c a t e g o r i e s , s i m i l a r
p l o t d a t a were segregated i n t o 65 h y p o t h e t i c a l
s t a n d s . The FNYLD s i m u l a t o r was used t o
e s t i m a t e growth l o s s i n t h e same way a s i t was
used f o r t h e survey.
Volume Loss Estimates
Incidence, a s used i n t h i s paper, r e f e r s
t o t h e presence o r absence of t h e pathogen on
t h e timber inventory o r survey p l o t , and does
not r e f l e c t an e v a l u a t i o n of d i s e a s e s e v e r i t y .
Table 1 compares incidence d a t a f o r t h e Medicine
Bow National Forest acquired from s e v e r a l
sources, r e v e a l i n g t h a t 47% of t h e Stage I
timber inventory p l o t s contained one o r more
m i s t l e t o e i n f e c t e d t r e e s . F i f t y - f i v e percent
of t h e lodgepole p i n e acreage represented by
those p l o t s contained m i s t l e t o e i n f e c t e d
t r e e s . The road survey conducted i n 1977
revealed t h a t 60.5 percent of t h e miles t r a v e r s e d
were a d j a c e n t t o m i s t l e t o e i n f e s t e d s t a n d s .
S i x t y percent of t h e p l o t s e s t a b l i s h e d i n
conjunction with t h e road survey contained
m i s t l e t o e i n f e c t e d t r e e s . Hawksworth's survey
conducted i n t h e mid-1950's r e p o r t e d t h a t 59
percent of t h e p l o t s on t h e Medicine Bow
National Forest contained m i s t l e t o e i n f e c t e d
trees.
The average volume derived from t h e Stage
I timber inventory was 2302 cubic f e e t p e r
a c r e ( t a b l e 1 ) . The 1977 road survey e s t i m a t e
was 2213 cubic f e e t p e r a c r e . These two
e s t i m a t e s a r e not s i g n i f i c a n t l y d i f f e r e n t .
A l l d a t a sources produced s i m i l a r e s t i m a t e s
of dwarf m i s t l e t o e incidence, and t h e p l o t
p o r t i o n o f t h e road survey and t h e Stage I
timber inventory produced comparable e s t i m a t e s
of average t o t a l cubic f o o t volume p e r a c r e .
A l a r g e discrepancy occurred i n t h e
acreage and corresponding volume l o s s e s t i m a t e s
f o r t h e d i f f e r e n t dwarf m i s t l e t o e s e v e r i t y
c a t e g o r i e s [ t a b l e 2 ) . The survey conducted by
trained forest pathologists resulted i n a
l a r g e r number of a c r e s w i t h i n t h e h i g h e r
s e v e r i t y c a t e g o r i e s of i n f e c t i o n and a concomit a n t i n c r e a s e i n volume l o s s .
These r e s u l t s i n d i c a t e t h a t while timber
inventory crews may be a b l e t o recognize dwarf
m i s t l e t o e incidence on inventory p l o t s , a s
Table '[--Incidence of dwarf m i s t l e t o e on t h e
Medicine Bow National F o r e s t .
Source
Parameter
Percent
Timber
Inv.
p l o t s with mistletoe
47.0
Timber
Inv.
acres with mistletoe
55.0
1977
Survey
miles with mistletoe
60.5
1977
Survey
p l o t s with mistletoe
60.0
Hawksworth' s
1958
Survey
p l o t s with mistletoe
59.0
Per Acre Volume Estimates:
T. I . Stage I
Road Survey P l o t s
2302.6 cu. f t .
2213.3 cu. f t .
r e v e a l e d by t h e c o n s i s t e n c y o f t h e r e s u l t s
shown i n t a b l e 1, t h e y s i g n i f i c a n t l y underest i m a t e t h e i n t e n s i t y o f t h e i n f e c t i o n . This
i s f u r t h e r i l l u s t r a t e d by t h e f a c t t h a t 34
p e r c e n t o f t h e acreage was r e p r e s e n t e d by
average dwarf m i s t l e t o e r a t i n g s o f 3.1 o r
g r e a t e r f o r t h e 1977 survey p l o t d a t a , while,
according t o t h e timber i n v e n t o r y d a t a , only 3
p e r c e n t o f t h e acreage contained s t a n d s t h a t
had average dwarf m i s t l e t o e r a t i n g s g r e a t e r
t h a n 3.1.
Timber Inventory Data
Dwarf m i s t l e t o e presence on p l o t t r e e s
was not recorded s e p a r a t e l y i n t h e F o r e s t
Service Region 3 timber inventory a s it was i n
Region 2; however, it was given precedence
over a l l o t h e r damaging agents i n t h e e v a l u a t i o n .
I f a t r e e displayed symptoms o r s i g n s o f more
than one damaging agent, one of which was
dwarf m i s t l e t o e , i t was recorded a s m i s t l e t o e
i n f e c t e d i n t h e "most damaging agent" column
of t h e inventory.
Therefore, a l l i n d i v i d u a l t r e e e n t r i e s
f o r ponderosa p i n e on t h e P r e s c o t t National
Forest t h a t d i d not d i s p l a y a dwarf m i s t l e t o e
i n f e c t i o n r a t i n g (1-6) i n d i c a t e d e i t h e r no
m i s t l e t o e o r some o t h e r damaging agent category.
Dwarf m i s t l e t o e i n f e c t i o n r a t i n g , n e t
volume and n e t growth p e r a c r e i n cubic f e e t
f o r each p l o t t r e e , and t h e p l o t b a s a l a r e a
and s i t e index f o r approximately 130 p l o t s
were summarized f o r t h e e n t i r e f o r e s t . T o t a l
volume p e r a c r e f o r t h e average p l o t t r e e was
averaged by s i t e c l a s s f o r a l l p l o t s with
i n f e c t e d t r e e s p r e s e n t . The same c a l c u l a t i o n
was made by s i t e c l a s s f o r a l l p l o t s without
i n f e c t e d t r e e s p r e s e n t . The d i f f e r e n c e between
t h e s e two f i g u r e s ( t a b l e 3) should r e p r e s e n t
t h e n e t d i f f e r e n c e i n volume o r growth o f t h e
average p l o t t r e e f o r t h a t p a r t i c u l a r s i t e
c l a s s . Our assumption was t h a t volume d i f f e r e n c e
r e s u l t e d p r i m a r i l y from m i s t l e t o e presence.
Data acquired from t h e P r e s c o t t National
Forest timber inventory show t h a t t h e only
s i g n i f i c a n t d i f f e r e n c e occurred i n t h e volume
of t h e average S i t e 1 p l o t t r e e ( t a b l e 3 ) .
Net volume was s i g n i f i c a n t l y lower f o r S i t e 1
plots containing infected t r e e s . Significant
d i f f e r e n c e s were expected f o r S i t e s I 1 and
111, but were not d e t e c t e d . No s i g n i f i c a n t
d i f f e r e n c e s were observed when a l l p l o t s ,
i r r e s p e c t i v e of s i t e , were combined; again,
s i g n i f i c a n t d i f f e r e n c e s were expected but d i d
not occur.
P r e s c o t t National F o r e s t , Arizona
Other approaches t o t h e g e n e r a t i o n o f
l o s s d a t a were attempted f o r t h e P r e s c o t t
National F o r e s t , Arizona, by u s i n g timber
i n v e n t o r y f i l e s and a 1970 dwarf m i s t l e t o e
survey conducted by t h e f o r e s t . The survey
was conducted i n a r e a s shown by an e a r l i e r
compartment examination t o c o n t a i n dwarf
mistletoe infected trees.
Although s i g n i f i c a n c e was noted f o r t h e
one category, our confidence i n t h e r e s u l t s i s
low and w i l l remain s o u n t i l they a r e v e r i f i e d .
I t i s p o s s i b l e t h a t s i t e e v a l u a t i o n was compromised i n t h e inventory a s a r e s u l t of u s i n g
t h e h e i g h t of dwarf m i s t l e t o e i n f e c t e d t r e e s
t o e s t a b l i s h s i t e . The most we could p o s s i b l y
i n f e r from t h e s e d a t a i s t h a t dwarf m i s t l e t o e
seems t o be lowering t h e p r o d u c t i v i t y o f t h o s e
a r e a s with good growth p o t e n t i a l .
Table 2--Annual cubic-foot volume loss estimates for the Medicine Bow National Forest, derived from Stage I Timber Inventory and 1977 plot surveys using RMYLD model. Dwarf Mistletoe
Severity Category
M's of Acres Represented 1 1977 Plot
Stage I
Survey
~ i m yI.
1
1
1
Annual Cubic Foot Volume Loss
Stage I
1
1977 Plot
~im: I.
survey
I
TOTAL Dwarf Mistletoe Survey D.
Basal Area Basal areas were used to describe A second source of information on dwarf stand density and calculate the DBH mistletoe-caused loss for the ponderosa pine of the tree of average basal area, type on the Prescott National Forest was parameters necessary to use with the available from a dwarf mistletoe survey conducted RMYLD simulator. during 1969 and 1970. The original data from this survey were furnished to Forest Insect Height was not available from the dwarf and Disease Management (FIGDM) personnel by the Forest. Region 3 FIGDM personnel summarized mistletoe survey data; however, the RMYLD these data, extracting the following parameters: simulator will insert a standard value for height if site is given. A.
Dwarf Mistletoe Level (DMR) The combined results of two separate complete runs using the RMYLD simulation model 1.
(0) = no infection
2.
(1-2)=low show that the annual cubic-foot volume loss estimates generated for the overstory and 3.
(3-4) = moderate
understory were 37,000 and 46,200, respectively 4.
(5-6) =heavy (table 4). These losses occurred on approxi- B.
Size Class (As defined in the original mately 6000 of 9300 infested acres. Dwarf mistletoe was present, but losses were not dwarf mistletoe survey, 1972) projected for approximately 3300 acres. 1.
2.
3.
C.
1to7in. 7.1 to 11.6 in. Greater than 11.6 in. Site Class (Region 3 uses three categories, as follows) 1.
2.
3.
Site 1: greater than 75 Site 2: 55-74 Site 3: 54 or less
Deschutes National Forest, Oregon A third approach to determine loss on a
Forest-basis is being attempted for the Deschutes National Forest, Oregon. For this Forest, we will estimate cubic-foot volume loss using growth parameters from existing inventory data. Table 3--Cubic-foot n e t growth and n e t volume p e r a c r e f o r t h e average p l o t t r e a ' i n
dwarf m i s t l e t o e non-infested and i n f e s t e d p l o t s from t h e P r e s c o t t National Forest.
Non-infested plotsL'
Infested plots?'
Difference
48.1
50.9
-2.8
I
Site I
NET GROWTH
S i t e I1
S i t e I11
Site I
NET VOLUME
S i t e I1
S i t e I11
I
Ñ Ponderosa p i n e only
2
'
2'
** S t a t i s t i c a l l y s i g n i f i c a n t a t
Column derived from 72 p l o t s
Column derived from 21 p l o t s
Region 6 timber management personnel w i l l
search timber inventory t a p e s f o r t h e Deschutes
National Forest, and r e t r i e v e and record t h e
following 10 parameters f o r each t r e e e n t r y :
P l o t number
Site class
Net growth i n cubic f e e t
Diameter a t b r e a s t height
Height ( s i t e t r e e s only)
Age
Crown c l a s s
Dwarf m i s t l e t o e r a t i n g
Tree h i s t o r y
Condition c l a s s
Net growth recorded on t h e f o r e s t ' s d a t a
t a p e i s a derived e n t r y . Actual observed n e t
growth f o r p l o t t r e e s i s a v a i l a b l e only from
t h e o r i g i n a l f i e l d d a t a cards on t h e f i r s t
t h r e e p o i n t s of a 10-point c l u s t e r p l o t . These
d a t a e n t r i e s have been r e t r i e v e d by hand, and
w i l l be appended t o t h e newly-produced d a t a
tape f i l e .
Volume l o s s e s t i m a t e s w i l l be made i n two
ways. The f i r s t w i l l provide estimates f o r
hypothetical s t a n d s by s i t e c l a s s and dwarf
m i s t l e t o e r a t i n g using a c t u a l measured n e t
volume growth a s t h e dependent v a r i a b l e . The
t o t a l number of e n t r i e s used f o r t h i s summary
w i l l be approximately 30 percent of t h e t o t a l
number of ponderosa p i n e t r e e s sampled during
t h e inventory. Since f u t u r e estimates cannot
r e l y on t h e manual t r a n s p o s i t i o n of f i e l d
records f o r d a t a i n p u t , t h e second e s t i m a t e of
growth l o s s volume w i l l come d i r e c t l y from t h e
1 percent l e v e l
F o r e s t ' s p l o t summaries. These w i l l c o n s i s t
of net growth f o r each p l o t by s i t e and by
average p l o t DMR using a l l individual t r e e
e n t r i e s . Growth l o s s estimates, derived i n
t h e s e two ways, w i l l then be compared t o
determine t h e r e l i a b i l i t y of t h e l a t t e r method.
REVISED APPROACH TO
GATHERING INFORMATION
The Dwarf Mistletoe Loss Assessment
Working Group met again i n January 1978,
reviewed t h e r e s u l t s reported i n t h i s paper,
and made several changes i n our approach t o
l o s s assessment.
The Group s t i l l was committed t o t h e
b e l i e f t h a t Forest Inventory and Forest Survey
systems remain t h e only f e a s i b l e way t o c o l l e c t
and s t o r e c e r t a i n i n s e c t - and disease-caused
l o s s information a p p l i c a b l e over l a r g e a r e a s .
However, our approach t o gathering i n t e r i m
data has changed. We a r e requesting t h a t each
Region update estimates t h a t were made i n 1975.
Many Regions have recent d a t a t h a t should
improve t h e r e l i a b i l i t y of t h e i r 1975 estimate.
Other Regions plan t o use t h e road survey
procedures previously discussed t o add t o
t h e i r d a t a base. Other sources may be consulted.
The Forest Survey u n i t of t h e P a c i f i c
Northwest Forest and Range Experiment S t a t i o n
i s p r e s e n t l y working with dwarf m i s t l e t o e
incidence d a t a f o r s t a t e and p r i v a t e lands i n
Washington and Oregon. This information has
been summarized a t t h i s Symposium. Data were
Table 4--Cubic-foot volume loss derived from the would be beneficial to most administrative RMYLD simulator using 1970 dwarf mistletoe levels, from the timber manager on the Ranger data from the Prescott National Forest. District to the U.S. Office of Management and Budget in Washington, D.C. This approach would require greater commitment by FIGDM personnel to training timber inventory crews, possibly even providing one well-trained Infested
Cubic-foot volume loss individual per crew for the insect and disease Acres
overstory understory total recognition portion of the inventory. This person need not be a professional, but could be a technician thoroughly trained in insect and disease recognition. LITERATURE CITED collected using Hawksworthls rating system. When they have completed their summary work, specialists in Regions 5 and 6 can use the incidence data to estimate volume loss. Baranyay, J.A., and L. Safranyik. 1970. Effect of dwarf mistletoe on growth and mortality of lodgepole pine in Alberta. Can. Dep. Fish and Forest. Publ. 1285, 19 p. Edminster, C.B. 1977. Computation of yield tables for even- aged and two-storied stands. USDA Forest Region 5 FIGDM personnel recently collected Serv. Res. Paper. Rocky Mountain Forest dwarf mistletoe incidence data for the San and Range Exp. Stn., Ft. Collins, Colo. Bernardino National Forest as part of the Pest Damage Inventory (PDI). These supplemental data were collected to determine whether or Hawksworth, F.G. not the RMYLD simulator could be used in 1958. Survey of lodgepole pine dwarf mistletoe Southern California. Other data from the on the Roosevelt, Medicine Bow, and Bighorn Pacific Southwest Forest and Range Experiment National Forests. Rocky Mountain Forest and Station will be consulted to determine how Range Exp. Stn. Paper 35, 13 p. suitable they are for making volume loss estimates for Region 5. Hawksworth, F .G
1956. Upper altitudinal limits of dwarf The diverse methods and data sources mistletoe on lodgepole pine in the central being used to make interim loss estimates Rocky Mountains. Phytopathology 46:561-562. illustrates the inconsistency in existing data from area to area. The diversity of approaches Hawksworth, F.G., and T.E. Hinds. points out the need to incorporate more complete 1964. Effects of dwarfmistletoe on immature insect and disease information in the regional lodgepole pine stands in Colorado. J. For. timber inventory systems and Forest Survey 62 :27-32.
wherever possible. The Dwarf Mistletoe Loss Assessment Working Group still believes that Weir, J.R. the timber inventory data base is the logical 1916. Mistletoe injury to conifers in the place to maintain data on insects and pathogens Northwest. U.S. Dep. Agric., Agric. Bull. which influence forest productivity. The data 360, 39 p. .