Ms. 5647
Plant and Soil 79, 343-351 (1984).
© 1984 Martinus Niihoff/Dr W. Junk Publishers, The Hague. Printed in the Netherlands.
Litterfall and nutrient returns in red alder stands in western
Washington
M. A. RADWAN, CONSTANCE A. HARRINGTON and J. M. KRAFT
'
Forestry Sciences Laboratory, U.S. Forest Service, Olympia, WA 98502, USA
Received 21 September 1983. Revised January 1984
Key words Alnus rubra Aluminum Annual returns Essential elements Litterfall
Leaf litter Nitrogen Nutrients Red alder
Summary
Litterfall was collected over 1 year from eight natural stands of red alder growing on
different sites in western Washington. The stands occurred at various elevations and on different
soils, and differed in age, basal area, and site index. Most litterfall was leaf litter (average 86
percent). Amounts of litterfall lind leaf litter varied significantly (P < 0.05) among the sites.
Average weights of litterfall and leaf litter in kg ha-1 yr-1, were 5150 and 4440, respectively.
Weight of leaf litter was not significantly (P < 0.05) related to site index, stand age, or basal
area. The sites varied significantly (P < 0.05) in concentrations of all elements determined in
the leaf litter, except Zn. Average chemical concentrations were: N, 1.98 percent; P, 0.09 per­
cent; K, 0.44 percent; Ca, 1.01 percent; Mg, 0.21 percent; S, 0.17 percent; S04 -S, nil; Fe, 324
ppm; Mn, 311 ppm; Zn, 53 ppm; Cu, 13 ppm; and AI, 281 ppm. There were significant correla­
tions between some stand characteristics and concentrations of some clements, and among the
different chemical components of the leaf litter. Important correlations were found between
stand age and P concentration (r = -0.84, P < 0.01); weight of leaf litter and P concentration
(r = 0.74, P < 0.05); weight of leaf litter and K concentration (r = 0.71, P < 0.05); concen­
trations of N and S (r
=
0.81, P < 0.05); and concentrations of Fe and AI (r
=
0.98, P <
0.01). Returns of the different elements to the soil by leaf litter varied among the different
sites. Average nutrient and Al returns, in kg ha-' yr -1, were: N, 82; Ca, 41; K, 19; Mg, 8 ;
S, 7 ; P, 4; Fe, 1 ; Mn, 1 ; AI, I:Zn, 0.2, and Cu, < 0.1.
Introduction -
Red alder (Alnus rubra Bong.) is the major hardwood tree species in
the Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) region of
the Pacific Northwest. The N2 -fixing ability of alder and its
effect on physical and chemical properties of the soil have been
studied1,8,1l, lS, 16,17, as have the production, composition, and some
chemical -properties of litterfa111 , 9,16 ,18, 20. The latter studies, however,
have not been complete. For example,' past work included only one
report on the effects of site quality and stand density on litterfall pro­
duction. Most chemical investigations were also confined to determin­
ations of N, with only two reports on P, K, Ca, and Mg, and one study
on Mn. III addition, concentrations and amounts of other essential ele­
ments in the litterfall have not been reported.
This study, therefore, was carried out to determ!ne: ( l ) production
of litterfall by different stands of red alder; (2) relationships among the
344
RADWAN,HARRINGTON AND KRAFT
different chemical components of the leaf litter, and between the
chemicals and selected site and stand characteristics; and (3) annual
returns of important macro- and micro-nutrients and Al by leaf litter.
Aluminum was included because of its potential phytotoxic effects.
Materials and methods
Site selection and measurement of stand variables
Eight natural stands of red alder located within 60 km of Olympia,in western Washington,
were chosen for study. Site selection was made to assure representation of a range in soil con­
ditions and site quality. All stands were 23 to 30 years old,well stocked,free from signs of past
disturbance,and had at least 94 percent of their basal area in red alder.
Four to six O.OI-ha plots were established in each stand. Stem diameter at breast height
(1.3 m) was determined for all trees on the plots. Basal area was calculated from this infor­
mation to provide a measure of stocking.
At each site, six healthy, dominant or codominant trees with no evidence of past top
damage were selected to determine site index. Tree heights and ages were determined and site
index at 50 years was calculated according to Worthington et a/19 •
Collection of litterfall
Litterfall collections were begun in January 1979 and continued through December 1979.
The litterfall was gathered on traps raised from the ground and equipped with fine-mesh nylon
screens to provide for drainage. Each trap had a collecting surface of 0.4 m2,and six traps were
placed at random within each stand. Shrub and herbaceous vegetation in the immediate vicinity
of the traps was clipped to ensure that the trap surfaces were not blocked and to reduce con­
tamina tion of the alder litter by litter of other species. Traps were emptied weekly in the
autumn,but over longer,irregular intervals at other times. The weekly collections were made to
reduce nutrient losses by leaching during the period when most litterfall is deposited. At each
collection,non-alder litter,if any,was removed from the traps and discarded. Contents of two
traps in each site were bulked at each collection,resulting in three composite samples for each
of the eight stands.
The litterfall samples collected were air dried at room temperature. Branches and stem
material more than 1 em in diameter were discarded. Each sample was separated into its com­
ponents of cones, twigs,and leaves,and each component was weighed. Total production and
composition of the litterfall were calculated. Only leaf litter was saved for chemical analysis.
Other components were discarded because they represented minor proportions of the litterfall.
Processing and chemical analysis of leaf litter
Samples of leaf litter were dried to constant weight at 65°C and ovendry weights were cal­
culated. Subsamples of the leaf litter were ground to 40 mesh and stored in closed containers
at -10°C until analyzed.
Total N was determined by the standard micro-Kjeldahl procedure3
•
Other analyses were
carried out as follows: total S and S0 -S . (extracted with 0.6N HCl) by the turbidimetric
4
method of Butters and Chenery4,:P by the molybdenum blue technique6 ; and K,Ca,Mg,Fe,
Mn,Zn,Cu,and Al by standard atomic absorption methods13 • The annual returns of chemicals
determined were calculated from concentrations in and weights of the leaf litter.
Statistical analysis
Total litterfall, leaf litter, elemental concentrations in leaf litter,and annual returns from
leaf litter by element were each analyzed for differences among stands using a nested analysis of
variancel4. Before analysis,data were transformed to arc-sine if necessary. All possible relation­
ships between the leaf litter variables plus the stand variables (I.e., age, basal area, and site
index) were evaluated by computing simple correlation coefficients (r): In addition,stepwise
345
LlTTERF ALL AND NUTRIENT RETURNS IN RED ALDER
multiple regression -analyses were run with litterfall, leaf litter, ot percent leaf litter in litterfall
as the dependent variables, and age, basal area, and site index as the independent variables.
Stand averages, based on untransformed variables, were used in the correlation and regression
analysis. In all analyses, P .;; 0.05 was used to judge statistical significance.
Results and discussion
Stand characteristics
The alder sites studied varied greatly in many of their key physical,
soil, and plant properties (Table 1). Elevation was highest (550m) at
site 5 and lowest ( l 25 m) at site 7 where a perched water table was
present during the winter. The sites represented six different soil types.
The stands were 23 to 30 years old and averaged 26.5 years. Basal area
varied from 25.8 m2/ha to 42.3 m2/ha, and site productivity, expressed
as site index, ranged from 24.0 m -at site 5 to 33.1 m at site 4. Associ­
ated vegetation on most sites was composed mainly of a variety of
shrubs and herbs with occasional presence of other tree species, such as
Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock
(Tsuga heterophylla (Raf.) Sarg.), western redcedar (Thuja plicata Donn
Table 1. Selected characteristics of eight sites of red alder
Site number
and general
Soil
location
1 . Brooklyn
2. Porter
Basal
Stand
area
age
at 50 years
(m2/ha)
(year)
(m)
series
Associated plant
·
species
Zenker
Oregon grape, cascara.
42.3
Bunker
Redcedar, hemlock, salal,
Site index
31.7
27
30
28.5
41.1
25
31.0
39.7
23
33.1
30.7
25
24.0
Vine maple, salmonberry.
39.8
30
24.5
Skunk cabbage, redcedar,
25.8
29
27.2
34.7
24
26.3
28.9
swordfern, Oregon grape,
Sitka spruce. .
3. Hell Creek
Bunker
Douglas-fir, hemlock,
swordfern, salmonberry,
devil's club.
4. Gibson Creek Boistfort
Douglas-fir, vine maple,
salmonberry, devil's club.
5. Wedekind
Katula
Douglas-fir, blackberry,
big-leaf maple.
6. Capitol Peak
Bunker/
Bolstfort
7. Jones Mill
Mukilteo
red elderberry, swordfern,
big-leaf maple.
8. Vail
Everett Nettle, redcedar.
·
Ol'egon grape, Berberis aquifoliumj cascara, Rhamnus purshianaj redcedar, Thula plicataj
hemlock, Tsuga heterophyllaj swordfern, Polystichum munitumj salal, Gaultheria shal/onj
Douglas-fir, Pseudotsuga mensiesii; vine maple, Acer circinatum; red elderberry, Sambucus
racemosa; salmonberry, Rubus spectabilis; big-leaf maple, Acer macrophyllum; blackberry,
Rubus ursinus; skunk cabbage, Lysichitum americanum; nettle, Urtica dioica; devll's club,
Oplopanax horridum j Sitka spruce, Picea sitchensis.
346
RADWAN, HARRINGTON AND KRAFT
ex D. Don), big-leaf maple (Acer macrophyllum Pursh), and Sitka
spruce (Picea sitchensis (Bong.) Carr.) in some stands.
Litterfall
Litterfall weight varied significantly (P < 0.05) among the different
sites, ranging from 4 I 70 to 6 I 00 kg ha-1 yr-1 (Table 2). Average weight,
5 I 50 kg ha-1 yr-1 , is lower than that found in one study 20, but very
similar to annual weights reported for red alder by others 9•16• Our lit­
terfall weights are also within ranges estimated for other deciduous
trees of the temperate region throughout the world, including other
Alnus species 2• However, as expected, values for red alder exceeded
those determined for conifers. in the Pacific Northwest and else­
where7•1 2•
Leaf litter was the principal component of litterfall; it ranged from
82.0 to 91.1 percent of the total. Others have reported that alder leaf
litter comprised 60 to 90 percent of total litter9 • 20. The leaf litter pro­
duced, litterfall weight, and percent leaf litter in litterfall were not cor­
related with stand age, basal area, or site index, taken individually or in
combination (i.e., mUltiple regression). The absence of any significant
relation between quantity of leaf litter and site productivity is consis­
tent with an earlier observation with red alder ih western Oregon20 ; it
may be related to the species' ability to fix atmospheric nitrogen.
The other components of the litterfall collected - twigs and cones ­
were only minor, and averaged 11.8 percent and 2.1 percent, respec­
tively. Litterfall of red alder collected earlier in western Oregon con­
tained 28 percent branches and twigs and 3 percent catkins20 . Differen­
ces in methodology were probably responsible for the different results.
Table 2. Litterfall of eight stands of red alder *
Stand number and
Litterfall components
general location
Cones
Twigs
Leaves
Total
Percent
litterfall
leaf litter
- Airdry weight (kg ha-t yr-t) _
1. Brooklyn
60
350
2. Porter
30
440
4. Gibson Creek
30
470
3. Hell Creek
5. Wedekind
6. Capitol Peak
7. Jones Mill
8. Vail
Average
30
92.0
5250
91.0
4950
5450
90.8
700
3980
4800
730
606
5000
6100
950
680
220
530
370
108
%
5150
4780
0
120
4740
4400
4230
3420
4440
5380
81.8
4910
86.2
4170
82.0
5150
82.9
82.0
86.1
*Values are averages of three sUbsamples each. Ovendry weights of leaf litter (kg ha-t yr-t)
for stands 1 to 8 were, respectively: 4410,4440, 4100,4600,3940,3700,3180, and 4650
(average, 4130).
347
LlTTERF ALL AND NUTRIENT RETURNS IN RED ALDER
Elemental concentrations in leaf litter
With the exception of Zn, concentrations of each of the elements
determined in the leaf litter varied significantly (P < 0.05) among the
eight sites (Table 3). The widest ranges occurred in K (0.18 percent to
0.64 percent), Ca (0.65 percent to 1.40 percent), Fe (93 ppm to 854
ppm), Cu (8 ppm to 15 ppm), and Al (75 ppm to 669 ppm). In addition,
the highest concentrations of Fe and Al and the lowest levels of K and
Cu occured in the leaf litter collected from site 7, the site with an
organic soil and a high water table. The exact cause of these differences
is not clear. However, K deficiency of trees growing on organic soils is
not uncommon if the soils were derived from poor parent material.
Average concentrations of the various elements are shown in Table 3.
S04 -S was practically nil in all samples; sulfate (uncombined S) pro­
bably was low in the N-rich leaves, and could also have leached from
the leaf litter before it was collected. Concentrations of P, K, Ca, and
Mg are generally within the ranges determined for leaf litter of other
hardwood speciess. Compared with red alder litterfall previously
reported9, our values for leaf litter are higher in P, lower in K, and
about the same in N, Ca, and Mg. There is no literature available for
comparing the other elements in leaf litter of red alder.
Compared with elemental concentrations in mature leaves of red
alder from western Washington, average concentrations in leaf litter are
generally lower in N, P, and K, but higher in the remaining elements,
Table 3. Concentration of nutrients and aluminum in leaf litter from eight different stands of
*
red alder
Stand number and general location
1
Brooklyn
2
Porter
Element
N
P
1.89
1.96
3
Hell
2.29
0.08
0.09
0.10
Ca
0.65
0.90
0.99
S
0.15
0.16
0.18
K
Mg
Fe
0.54
0.21
93
0.64
0.23
105
5
4
Wedeklnd
Gibson
Creek Creek
0.44
0.20
149
2.04
%
2.17
0.10
0.10
0.36
0.47
0.18
0.23
0.82
1.00
0.18
164
ppm
0.20
409
Mn
219
337
364
399
308
Cu
12
15
15
14
14
Zn
Al
60
92
57
76
57
90
47
130
52
405
6
7
Peak
Mill
Capitol Jones
1.96
0.06
0.41
1.07
0.19
1.73
1.98
0.09
1.23
1.40
1.01
0.16
0.17
0.18
0.20
178
854
54
46
156
1.80
0.10
0.14
12
Average
0.06
0.18
320
8
Vail
0.51
0.21
640
0.44
0.21
324
231
311
311
81
11
13
669
50
632
53
281
*Concentrations are calculated on a weight basis. Values are averages of three sub-
samples each.
348
RADWAN, HARRINGTON AND KRAFT
especially Ca, Fe, Mn, and AI*. The limited comparison between alder
leaves and litterfall presented by others 9is also in agreement with our
assessment. Increased levels of some elements from leaves to leaf litter
may be caused by depositions in the leaves as they mature on the trees.
On the other hand, lower values in the leaf litter compared with leaves
are probably due to movement of nutrients into the trees before the
leaves fall and leaching from the leaves on the ground before the leaves
are collected. Our litterfall was collected more frequently than in pre­
vious studies9, 16,20 in order to minimize leaching losses. Some leaching
still occurred as evidenced by detection of most elements studied in
leachates collected from some of the litterfall samples. There were some
significant correlations between stand characteristics and concentra­
tions of certain elements, and among the different chemical com­
ponents of the leaf litter (Table 4). Among the more important cor­
relations found is the relationship between stand age and P concentrations
(r =- 0.84, P< 0.01), indicating a decrease of P as the trees age.
Results from other studies* support this trend and point to the impor­
tance of P in the nutrition of red alder in a manner similar to that with
other N2-fixing plants10. Important positive correlations found were
between leaf litter and percent P (r = 0.74, P < 0.05), between leaf
litter and percent K(r=0.71, P<0.05), between N and S (r=0.81, P<
0.05), and between Fe and Al (r=0.98, P<O.O I ). Relations between
leaf litter and P and K indicate importance of these elements to produc­
tion of red alder. Relationships between N and S and between Fe and Al
Table 4. Significant correlations between the different study variables
Correiation
Correia tion
Stand age
Basal area
liS.
liS.
coefficient
percent P in leaf litter
ppm Fe in leaf litter .
Ovendry leaf litter
Ovendry leaf litter
Ovendry leaf litter
liS.
liS.
liS.
Percent N in leaf litter
Percent N in leaf litter
Percent K in leaf litter
ppm Fe in leaf litter
litterfall produced
percent K in leaf litter
percent P in leaf litter
liS.
liS.
liS.
liS.
percent S in leaf litter
ppm Cu in leaf litter
ppm Zn in leaf litter
ppm Cu in leaf litter
ppm Fe in leaf litter vs. ppm Al in leaf litter
ppm Fe in leaf litter vs. ppm Zn in leaf litter
ppm CU in leaf litter
ppm CU in leaf litter
liS.
liS.
ppm Mn in leaf litter
ppm Al in leaf litter
-0.89
P-value
<0.01
-0.75
<0.05
0.71
<0.05
0.81
<0.05
0.74
<0.05
0.98
<0.01
0.90
0.74
0.82
-0.79
<om
<0.05
<0.05
<0.05
0.71
< 0.05
-0.75
<0.05
0.71
<0.05
* Unpublished data by DeBell and Radwan, on file at the USDA Forest Service Forestry
Sciences Laboratory, 3625 9yd Avenue, S. W.,Olympia, Wash. U. S. A. 98502
LlTTERFALL AND NUTRIENT RETURNS IN RED ALDER
349
similar to those found in other plants, and indicate concomitant
changes in concentrations of the elements involved. Additional signifi­
cant correlations are listed in Table 4. The importance of these relation­
ships, however, is not immediately apparent.
Nutrient and aluminum returns to the soil from leaf litter
Returns of the different elements to the soil by leaf litter differed
among the different sites by element (Table 5), and trends closely fol­
lowed those of leaf litter production (Table 2) and concentrations of
the different elements (Table 3). As might be expected, N was the ele­
ment returned to the soil in the largest amounts. Obviously, N returns
were determined by N concentration and weight of leaf litter. In
addition, concentrations of P, K, and S apparently affected N returns
since these elements were related to production of leaf litter and to N
concentration (Table 4). On average, N returns were 82 kg ha-1 yr -1 ;
this compares with earlier estimates (in kg ha-1 yr-1) of 11216 and 989
for red alder litterfall, 19 for leaf litter of hardwood species incapable
of N2 -fixationS, and 36 for conifer litterfall16 Average annual contri­
butions of other elements through the leaf litter are shown in Table 5.
Previously published estimates for these elements are: Ca, 63; K, 39;
Mg, 13; and P, <0.2 for red alder litterfall9; Ca, 36; K, 32; Mg, 6; P,
2; and Mn, 1 for leaf litter of red alder18; and Ca, 73; K, 15; Mg, 10;
and P, 4 for leaf litter from non-N2 -fixing hardwoodss .
Clearly through deposition of leaf litter alone (i.e., not including
additions by nodules, dead roots, etc.), red alder returned to the soil
•
Table 5. Nutrient and aluminum returns to the soil from the leaf litter of eight different stands
of red alder
*
Stand number and general location
Chemical
element
N
P
K
Ca
Mg
S
Fe
Mn
Zn
Cu
Al
Brooklyn
83.7
3.3
24.0
28.7
9.0
6.3
0.4
1.0
0.3
<0.1
0.4
3
4
Creek
Creek
87.0
5
6
7
Peak
Mill
93.3
kg ha-I yr-I
93.7
85.7
72.7
55.3
84.0
81.9
28.3
17.7
16.7
18.7
15.0
6.0
23.7
18.8
10.3
8.0
9.3
6.7
2
Porter
4.0
40.0
7.0
0.5
1.5
0.2
<0.1
0.3
Hell
4.0
40.7
7.3
0.6
1.5
0.2
<0.1
0.4
Gibson Wedekind
4.0
45.7
8.3
8.0
0.8
1.8
0.2
<0.1
0.6
* Values are averages of three subsampJes each.
4.0
32.3
7.7
1.6
1.2
0.2
<0.1
1.6
Capitol Jones
2.3
2.0
39.7
39.0
6.3
4.3
1.2
0.7
0.7
0.2
<0.1
0.6
6.3
2.7
0.2
<0.1
2.1
8
Vail
Average
4.7
3.5
65.3
41.4
7.3
6.8
1.5
1.3
10.0
3.0
0.2
8.5
1.3
0.2 <0.1 <0.1 2.9
1.1
350
RADWAN,HARRINGTON AND KRAFT
substantial amounts of N (55 to 94 kg ha-1 yr -1 ). Returns of other ele­
ments were smaller, but still constituted considerable contributions to
the pool of nutrients in surface soil and may help in maintaining soil
fertility. Amounts of Al returned were not large enough to constitute
any toxicity hazard. Nitrogen returns mostly represent additions to the
soil through biological fixation of atmospheric N; this undoubtedly
enriches the soil with this important element. As with other hardwoods,
however, returns of other elements represent redistribution within the
ecosystem. This may also improve site productivity by bringing the
nutrients to surface soil and into the root zone where they may be
available for succeeding crops.
Such potential benefits from alder, however, should not obscure the
fact that the species has its own nutritional requirements for growth
and development, and that the trees accumulate many nutrients in the
wood. N returns from alder, therefore, would not be signigicant unless
the site has sufficient amounts of nutrients other than N to meet the
trees own requirements for healthy growth. Similarly, benefits to com­
panion or succeeding crops from redistribution by alder of elements
other than N would not accrue unless amounts of these elements in the
upper soil layers were already limiting, and if removal of nutrients
during harvest of the alder crop did not accelerate nutrient depletion at
the site. It is evident, therefore, that the net impact of red alder on site
productivity, still unknown, deserves much attention in future studies.
Acknowledgements We thank the U. S. Department of Energy,Biomass Energy Technology
Division,Short Rotation Woody Crops Program for funds which helped support this research.
We also thank J. E. Wilcox,D. W. Johnson,and R. L. Deal for their assistance with the various
phases of the study.
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20 Zavitkovski J and Newton M 1971 Litterfall and litter accumulation in red alder stands in
western Oregon. Plant and Soil 35,257-268.
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