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Coppice growth and water relations of silver maple
Biomassand Bioenergy Vol. 5, No. 5, pp. 317-323,1993 Printedin Great Britain. All rights reserved
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0961-9534/93 $6.00+ 0.00
c 1993 PergamonPress Ltd
GROWTH AND WATER SILVER MAPLE*
RELATIONS
OF
W. C. AsHBY,t D. F. BREsNAN,tll R. K. KJELGREN,$~~ P. L. ROTH,$ J. E. PREECE~ and
C. A. HUE~MAN~ TDepartment of Plant Biology, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. IDepartment of Plant and Soil Science, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. SDepartment of Forestry, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. lIPresent address: Department of Forestry, Kansas State University, Manhattan, KS 66506, U.S.A. YPresent address: Department of Plant, Soil and Biometrology, Utah State University, Logan, UT 843224820, U.S.A. (Received I2 May 1993; revised received 24 August 1993; accepted 25 August 1993)
Abstract-Trees of silver maple (Acer saccharinurn L.) planted in southern Illinois were cut at rootstock ages 2, 3, and/or 4 years. In all plantings a single main stem was the predominant growth form prior to initial harvest. The predominant post-harvest growth form was numerous coppice stems. The cumber of coppice stems per tree and percent tree survival decreased with greater stand density. Coppice growth, as measured by the number of stems and the height of the tallest stem, increased progressively with the number of harvest cycles. This growth was supported by a progressively older root system, and developed from an increasing number of cut stem bases. About 60% of the coppice were tall stems, over one-half the height of the tallest stem. Trees of the southernmost origin, from Mississippi, with high establishment rates had the highest dry weight production of two-year provenance coppice growth (equivalent to 59.5 Mg ha-’ ‘2 year-‘, or 13.2 ton acre-’ year-‘). The northernmost trees, from central Ontario, had low establishment rates and the lowest stand biomass. Dormant season macronutrient cropping losses were estimated related to biomass yield. Foliage density and stem elongation were greater in first-year coppiced compared to uncoppiced trees. Water relations of coppice growth differed from that of uncoppiced trees in both the first and the second year after harvest. Keywor&eBiofuels feedstock, foliage density, leaf water potential, nutrient cropping, provenance, rootstock, sprout growth, stomata1 conductance, woody biomass.
together with rapidly accreting soil organic matter (humus) significantly contribute to carbon storage. Silver maple (Acer saccharinurn L.) is well adapted for biomass production.’ It is one of the fastest growing temperate-zone trees and has been selected as a priority species by the Biofuels Feedstock Development Program of the U.S. Department of Energy’s Oak Ridge National Laboratory.* Our objectives were to evaluate coppice growth and water relations of silver maple as affected by provenance (origin of seed) and management, including planting density and number and duration of cutting cycles. Comparisons were made within and among different plantings.
1. INTRODUCTION
The ability of trees in a plantation to regenerate by coppice (sprout growth) after stem harvest is an important feature of successful biofuels feedstock production programs. Coppice potential varies with tree species, age and past history, size of an established root system, and with available moisture, nutrients and other environmental resources. Coppicing as a production system differs from other agricultural practices. Successive harvests can be made from one planting. The sprout growth after each biomass harvest is supported by an established root system. Rapid development of a renewed canopy suppresses weed competition. The canopy and surface litter of coppice growth quickly protect a planting site from erosion. The maturing root systems
2. METHODS
2.1. Plantation establishment and growth *Research performed under Subcontract No. 86X95908(3 with Oak Ridge National Laboratory under Martin Marietta Energy Systems, Inc. Contract DE-ACOS84OR21400 with the U.S. Department of Energy.
Three silver maple plantations were established near Carbondale in southern Illinois as part of an ongoing project to identify and select 317
W. C. ASHBKef ul.
318
Table I. Planting management and coppice growth after harvest of silver maple with differing root and stem ages Age (years) root stem
Planting distance (cm)
No. of trees
Tree density” (trees. haa’)
Coppice height No. of (m) stems
I. Minimal management (Commercial seedlings) 3 (1990) 4
I I
90x180
89 89
5500 5500
1.2 2.7
9.4 16.4
2.4 2.6 3.2
8.9 13.7 17.7
II. High-level management (Peoria seed) 3 (1989) 4 5
1 1
30x30
1
21 21 21
52,000 52,000 52,000
III. Provenance plantation (10 provenances from seed) 3 (1990) 4
1 2
15 X 15
1679 1520
191,000 173,000
1.1 1.8
5.0 5.8
“Approximate within-plot tree density, excluding aisles, at time of harvest. 5500 trees ha-’ approximates 2200 trees/acre. Planting areas were for I 195 m2, II 12 ml, and III 90 m2. Plantings I and II were not replicated. Data of planting III are analyzed in Table 2.
superior trees for biomass production in the Midwest region of the United States. All plots were on Hosmer silt loam soil as affected by post-settlement land uses. Hosmer is a fine-silty, mixed, mesic Typic Fragiudalf upland silt loam slightly to strongly acid with depth. The plantations differed in origin of plant materials, number and spacing of trees and management (Table 1). A 1987 planting of commercial seedlings from Tennessee had minimal management after establishment. Plant tissues were harvested in this study at 2-week intervals during spring and fall of the first year for nutrient analyses by the A & L Laboratories of Memphis, TN. A 1986 planting of seed from Peoria, Illinois received a high level of management including weeding, irrigation and fertilization. A third planting, 1987, included seeds from 10 provenances throughout silver maple’s native range.3 Randomized plots within blocks of this site were densely planted at 15 x 15 cm spacing with 100 seed spots each. An initial, two-year, high level of management in this planting included mulch, irrigation and fertilization. Data were taken yearly for all trees in all plantations on height of the tallest stem and number of stems after coppicing. On the provenance plots basal caliper was also taken, Stem form in the provenance study was classified based on presence and vigor of basal stem(s), presence or absence of lateral growth, and dieback or mortality using a modification of
Melick’s system.4 Stem weights of the provenance study were taken at 2 years, and at 4 years as two-year coppice growth. Ten trees (40 trees per provenance) were taken on a transect across each plot within a planting block. The plots were 30 cm apart (vs. 15 cm for the trees) and edge effects were commonly not evident. At harvest, trees in each of the plantations were cut with hand pruning shears or hand saw to 1Ocm stumps (except as noted) between November and May while the trees were dormant or in early leaf, and coppice stems were allowed to grow for one to three years. In one study 50 trees each were cut in November and in February, and in another study trees were cut at 5 cm, 10 cm, or 25 cm height. In each study the number and vigor of stems in the following year or years were determined. Coppice production data from the provenance study were processed using the SAS General Linear Models Procedure.’ Coppice growth compared to non-coppiced trees was measured for trees from three clustered provenances. Since the non-coppiced block was not replicated, all data were collected from a non-coppiced row in one plot and in an adjacent row of a coppiced plot of each provenance for a total of six plots. Stem elongation was measured, with yearly growth distinguished by the terminal bud scars, on ten stems randomly selected within each plot during 1989 and 1990. These trees were also used in a waterrelations study.
Coppice growth and water relations of silver maple
Foliage density was estimated by the light interception method of Lang6 based on the percent transmission of solar radiation beneath a canopy for a range of solar zenith angles. Transmission was measured with an integrating quantum sensor (model SF-80 Sunfleck Ceptometer, Decagon Inc., Pullman, WA) on the surface beneath the canopies. Solar zenith angles for 37.7” latitude and 89.2” longitude corresponding to the sampling times were calculated using the algorithm of Flint and Childs.’ 2.2. Water relations Stomata1 conductance was measured with a steady-state porometer (model 1600, Li-Cor Inc., Lincoln, NE) on the abaxial surface of five fully illuminated, randomly selected leaves within each plot following the precautions noted by McDermitt.* Sampling was carried out sequentially after dew evaporation at dawn until late afternoon. Leaf water potential was measured predawn, and concurrent with stomatal conductance using a Scholander-type pressure chamber (Arimad II, Arimad Corp., Israel) on three randomly selected leaves per plot. Samples were collected following the precau-
319
tions of Meyer and Reicosky,’ stored in an aluminum foil envelope,” and measured within an hour. The diurnal water-relations data were averaged by plot and fourth-order curves of the mean values over time then fitted.5 Each term in the model was tested for significance at alpha = 90% through backwards elimination until an order appropriate for the data was reached. Once the correct model was determined, pair-wise comparisons of the timeadjusted means within the provenance and coppicing treatments were made. 3. RESULTS
3.1. Coppice growth
Silver maples sprouted vigorously when cut back regardless of seed source or stump height. Trees cut in November had significantly more coppice stems in May than those cut in February; by summer no differences were evident in either stem number or height. None of these minimal-management trees, nor any of the highlevel management trees, died following successive harvests. Mortality both before and after
Table 2. Coppice growth within the silver maple provenance plantation, with provenances grouped by tree density. All trees had a 4-year-old rootstock and 2-year-old stems Provenance origin
Trees per plot” (#)
Coppice per tree (#)
Coppice growth per tree height caliper weight (m) (cm) (g)
Biomass per plotb (kg)
1.3 1.3 ns
228 165 ns
2.6 IO.1 **
I.6 1.5 1.1 1.2 I.0 ns
451 339 130 102 114 ns
4.1 3.7 1.6 1.4 2.0 ns
I .3ab
217 223 126 I31 115 ns
12.6ab l3.4a 7.9c 8.5bc 8.Oc *
Meam for provenance deity groups Lower density Higher density Significance
13’ 63d **
7.0 4.1 **
1.8 ns
Lower density provenances GB-Grand Bend, ONT NH-Boscawen VT-Burlington SSM-S. Ste. Marie, ONT PA-Montrose Significance
9 I1 12 I4 I8 ns
9.la 8.lab 5.7c 6.2bc 6.2bc
1.9 1.7 I.5 1.4 1.3
Higher den&y provenances ILC-Carbondale, IL MS-Starkville IA-Ames WI-Madison ILM-Murphysboro, IL Significance
58 60 63 65 71 ns
4.8 4.2 3.9 4.0 3.6 ns
l
1.5
tlS
I .9b 2.2a 1.6c 1.7bc I .8bc **
1.5a l.lc 1.3bc 1.2bc **
‘Plots were I50 by l5Ocm and were planted to 100 seed spots. bCalculated as mean number of trees per plot times weight per tree. Mean plot weight was 8.8 kg, equivalent to 29.7 Mg ha-’ .2 year-‘. cEquivalent to 57,778 trees ha-’ average plot density. dBquivalent to 279,999 trees ha-’ average plot density. “Grand B end is near Detroit, and relatively southern among these provenances. Provenance values significantly different at the 5% (*) level, or 1% (**) level, or not significantly different (ns). Duncan grouping means within a column with the same letter, or no letter, are not significantly different at a = 0.05. Rounded-off values lead to apparent discrepancies in calculated values.
W. C. ASHBYet al.
320
[II 0
GB
NH VT SSM PA Provenance State
aSee Table number
Tall stems Short stems
2 for provenance of trees
) l/2 - ( l/2
heqht height
ILC MS IA and/or Citya identification
of tallest of tallest
WI
stem stem
ILM
and mean
per plot.
Fig. 1. Number of tall and short coppice stems per tree related to tree density and to provenance. Number of trees per plot (density) increases greatly from GB on the left to ILM on the right.
harvesting was found in the closely-spaced provenance plots (Table 2, Fig. 1). Provenances with relatively low density of surviving trees prior to harvest had the greatest number of coppice stems after harvest (Fig. 1). Tall stems (> l/2 height of tallest stem) consistently predominated, and averaged about 60% of number of total coppice stems per tree. The numbers of short stems (G l/2 height of tallest stem) were less closely related to plot density. One main stem was the predominant stem form throughout the provenance plantation prior to the first harvest. The Illinois, Wisconsin, Iowa or Mississippi provenances that had the highest percentages of pre-harvest trees with one main stem did not have unusually high percentages of tall coppice shoots. Within a provenance the number of tall coppice stems per tree after harvest was correlated (r = 0.83) with the number of trees having one main stem prior to harvest. The number of coppice stems increased after harvest in all the studies with increasing age of the rootstock remaining after harvest (Table 1). Coppice height growth was also greater with increasing age of the root system, whether after successive cuttings or with longer periods between harvests of coppice stems. Stems were at least 1 m tall in the first year after cutting, and commonly reached or exceeded 2 m. Trees cut at 5 cm rather than the usual 1Ocm showed a reduction in number of sprouts, and those cut at 25 cm sprouted from the lower and middle rather than the upper part of the stems. Because of differences in seedling establish-
ment and survival in the provenance study,-’ the provenances were separated into two groups of 5 provenances each: those of higher densities with 58-71 trees per plot, and those of lower densities with 9-18 trees per plot. Mean number of stems, height, caliper and tree weight of the 4 plots per provenance varied both within the high- and the low-density provenance groups and between the groups (Table 2). Coppice height and caliper differed highly significantly among the higher density provenances; number of coppices per tree and tree weight did not. Trees were taller in the higher density provenances with an R2 of 0.82, and a C.V. of only 7%. Among the lower-density provenances with 9-18 trees per plot the number of coppice stems differed significantly (Table 2) and mean height, caliper and tree weight did not. There were fewer tall coppice stems with increasing density. The harvested dry weight of two-year coppice dormant stems in the provenance study were converted to plot weights by multiplying mean plot number of trees and individual tree weights (Table 2). The northernmost provenance, Sault Ste. Marie, Ontario, with the least heavy trees and the second lowest number had lowest biomass per plot, equivalent to 6.4 Mg * ha-’ .2 year-‘. The Mississippi provenance with the third heaviest trees and many more trees per plot had the highest biomass, equivalent to 59.5 Mg . ha-’ * 2 year-‘, or 13.2 ton . acre-’ . year-‘. Estimated nutrient cropping based on dormant-season stem analyses and the mean two-year biomass yield of all the
Coppice growth and water relations of silver maple
321
Table 3. Stem elongation and foliage density for silver maple from three provenances Yearly stem elongation 1989 1990 non-C copb non-C cop (m) (m) Cm) Cm)
1987-88 non-C’ (m)
Provenance Illinois Pennsylvania Wisconsin
2.52 2.47 2.04
0.76 0.55 0.12
1.52 1.24 1.36
0.66 0.52 0.79
1.43 0.95 1.17
Foliage density non-C (m2.
m-3)
1.15 1.23 1.19
(m2~~-‘)
4.92 5.12 4.47
“Non-C is a non-coppice stem. bCop is a coppice stem.
provenances was 48 kg 1ha-’ (42 lb. acre-‘) for phosphorus, 148 for potassium, 175 for calcium and 21 kg. ha-’ for magnesium. Stem elongation of the coppiced trees in the provenance study was, for two years, nearly double that of the non-coppiced trees (Table 3). Overall elongation in the coppiced trees was less during the second year of growth (1990) than during the first year after cutting. Foliage density within the volume defined by plot area and stem height was substantially greater in the coppiced trees as a result of a large number of leaves occurring along a much shorter length of stem than in the non-coppiced trees. 3.2. Water relations The coppiced trees experienced significantly different water relations than did the non-
Cop
2
coppice growth in the first year (1989). Relative water relations were more variable in 1990. Less water stress for the coppice growth in 1989 was shown by the higher predawn water potential (Fig. 2). During the day (dawn to dusk) the coppice shoots had significantly lower leaf water potential in 1989, and greater stomata1 conductance in July 1989 but not in August during a continued drought (Table 4). In 1990 with more rain the only significant difference was lower leaf water potential by the non-coppiced trees in August. Among provenances the southern Illinois trees had lower diurnal leaf water potential in August 1989 and lower stomata1 conductance in 1990 than did the trees from Wisconsin, with those from Pennsylvania intermediate in response. The Wisconsin trees had the least and
1990
Non-C
0 . 111. D v Penn 0 n Wise.
-0.2
60
2
40
.CI
t’
c
a +J
-0.4
E : c, g
-0.6 0.0
L
% 3
-0.2
F a 2
-0.4
iI -0.6
June
July
August
Fig. 2. Predawn leaf water potential, data points in MPa, for coppiced and non-coppiced silver maple from three provenances, Illinois, Pennsylvania and Wisconsin, in 1989 and 1990. Data bars are rainfall in mm.
W. C.
322
A~HBY
ef al.
Table 4. Time-adjusted means of diurnal stomata1 conductance and diurnal leaf water potential for silver maple with provenances averaged across treatment, and coppiced and non-coppiced treatments averaged across provenance, from four dawn-to-dusk sampling dates Diurnal stomata1 conductance 1989 1990 July July Aug Aug (mmol”) (mmola) (mmol”) (mmol”) Provenance Illinois Pennsylvania Wisconsin Significance
228 223 255 ns
104 118 106 ns
185b 223a 237a *
147b 193a 186a
Treatment Coppiced Non-coppiced Significance
373 98 *
183 36 ns
225 205 ns
181 169 ns
l
Diurnal leaf water potential 1989 1990 July July Aug Aug (MPa) (MPa) (MPa) (MPa) -0.52 -0.55 -0.44 ns
- 1.31b - 1.21b - 1.02a
-0.60 -0.40 *
-1.28 -1.08 +
l
-1.42 - 1.38 -1.47 ns
-1.52 -1.42 - 1.41 ns
- 1.40 -1.44 ns
-1.37 -1.54 *
Provenance values signficantly different at the 5% (*) level, or not significantly different (ns). Duncan grouping means within a column with the same letter, or no letter, are not significantly different at a = 0.05. “mm01 . rnm2. s-l.
the Illinois trees the greatest growth.
coppice
stem
4. DISCUSSION
Juvenile silver maple regenerates rapidly and vigorously by coppice stems.” Rootstocks in all three plantings sent up one to many stems after harvest. Tree mortality, if any, and number of coppice stems varied with both rootstock density and age. There is a complex relationship between spacing and coppice production cycles. ‘2-‘4Pre-harvest stem form was less immediately useful as a predictor of type of coppice growth than plot tree density. Differences in coppice production related to provenance alone were not evident in our studies. The increasing number of stems with increasing number of coppice cycles can be explained in part by the successively greater number of stem bases capable of sending up new stems. In three cycles we did not exhaust this resprout potential for the planting with high-level management. In fact the vigor improved with increased age of the root system and there was no mortality within the timeframe of our study. Geyer” reported that yield of silver maple did not deteriorate even after 5 or 6 cuts during an S-year period. These findings are in contrast to those with other species such as Populus that had reduced yields and increased mortality with multiple harvests.14 Several factors affect individual tree dry weights, including timing of harvest cycle,13 tree density and age of rootstocks. We feel that the
fewer coppice stems of the central or southern, more dense provenances than of the northern provenances may have been affected more by the differential survival and crowding than by inherent growth potential. The intensity of above-ground competition for closely-planted trees can be minimized by tree harvests at short intervals. Kopp et al.” stated that height growth of 7-year-old silver maple seed sources appears to be under stronger genetic control than stem number. Any planting method can give widely varying numbers of trees during the life of a plantation. Our use of seed was no exception. The importance of population size, and tree vigor, was demonstrated by the range of our two-year provenance harvest values from 59.5 to 6.4 Mg . ha-’ .2 year-‘. Major differences in individual tree height, caliper and weight were associated with the yield differences. The importance of root-shoot ratios was shown both by the greatly increased coppice vs. non-coppice stem growth and by the differing water relations. Early-season water stress by the coppiced compared to the non-coppiced trees would clearly be reduced because of the absence of stems with transpiring leaf area. Leaf area following coppicing of other species increased rapidly during the season from reinvigorated stem growth. I6 A consequent lower, denser leaf crown would increase boundary-layer resistance.17 In contrast, the non-coppiced trees had for a longer period of time more ventilated leaf canopies. Drought effects were less apparent in the second-year water relations data.
Coppice growth and water relations of silver maple 5. SUMMARY
This study documented the coppicing ability and productive capacity of silver maple from many sources related to management. Biomass production was relatively unaffected by differences in harvesting during the dormant season. Mineral nutrient cropping losses were indicated. Coppice regrowth was more vigorous and less affected by drought stress than was growth of non-coppiced trees. Two areas of concern remaining are the stocking rate effects on individual tree and tree plot weights, and properly matching specific tree clones or provenances to regional or site climatic/environmental factors to exploit genetic variability in growth performance. With these accomplished, silver maple will become an even more valuable asset in the biofuel energy strategy of the U.S.A.
REFERENCES 1. W. J. Gabriel, Acer saccharinurn L. Silver maple. In S&s of North America 2. Hardwoods. Agric. Handb. 654, pp. 7&77. U. S. Department of Agriculture, Washington, DC (1990). 2. L. L. Wright, J. H. Cushman and P. A. Layton, Expanding the market by improving the resource. Biologue 6(3), 12-19 (1989). 3. W. C. Ashby, D. F. Bresnan, P. L. Roth, J. E. Preece and C. A. Huetteman, Nursery establishment, phenology and growth of silver maple related to provenance. Biomass and Bioenergy 3(l), l-7 (1992). 4. R. Melick, Measurements-what, when, how, why? In Proc. Seruicewide Genetics Workshop, pp. 476485. U.
5. 6. 7. 8.
9.
323
S. Department of Agriculture Forest Service, Charleston, SC (1983). SAS Institute, Inc., SAS User’s Guide: Statistics 1985 edition. SAS Institute, Carey, NC (1985). A. R. G. Lang, Simplified estimate of leaf area index from transmittance of the sun’s beam. Agric. For. Meteorol. 41, 179-186 (1985). A. Flint and S. Childs, Calculation of solar radiation in mountainous terrain. Agric. Meteor. 40,233-249 (1987). D. K. McDermitt, Sources of error in the estimation of stomata1 conductance and transpiration from porometer data. HortScience 25, 1538-1548 (1990). W. Meyer and D. Reicosky, Enclosing leaves for water potential measurement and its effect on interpreting soil-induced water stress. Agric. Meteor. 35, 187-192
(1985). 10. H, Karhc and H. Richter, Storage of detached leaves
and twigs without changes in water potential.
New
Phytol. 83, 379-384 (1979). 1 I. W. A. Geyer, Spacing and cutting cycle influence on short rotation silver maple yield. Tree Planters Notes 29(l), 5-7, 26 (1978). 12. H. E. Kennedy, Jr, Influence of cutting cycle and
spacing on coppice sycamore yield. U. S. Department of Agriculture, Forest Service, Southern Forest Experiment Station Research Note SO-193, 3 pp. (1975). 13. W. A. Geyer, Growth, yield, and woody biomass characteristics of seven short-rotation hardwoods. Wood Sci. 13(4), 2099215 (1981). 14. T. Strong, Rotation length and repeated harvesting influence Populus coppice production. U. S. Department of Agriculture, Forest Service, North Central Forest Experiment Station Research Note NC-350, 4 pp. (1989). 15. R. F. Kopp, W. A. Geyer and W. R. Lovett, Silver maple seed sources for increased biomass production. North J. Appl. For. 5, 180-184 (1988). 16. T. J. Blake and T. J. Tschaphnski, Role of water
relations and photosynthesis in the release of buds from apical dominance and the early reinvigoration of decapitated poplars. Physiol. Plan. 68, 287-293 (1986). 17. P. Jarvis and K. McNaughton, Stomata1 control of transpiration: Scaling up from leaf to region. Adu. Ecol. Res. 15, l-49 (1986).
COPPICE
0961-9534/93 $6.00+ 0.00
c 1993 PergamonPress Ltd
GROWTH AND WATER SILVER MAPLE*
RELATIONS
OF
W. C. AsHBY,t D. F. BREsNAN,tll R. K. KJELGREN,$~~ P. L. ROTH,$ J. E. PREECE~ and
C. A. HUE~MAN~ TDepartment of Plant Biology, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. IDepartment of Plant and Soil Science, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. SDepartment of Forestry, Southern Illinois University at Carbondale, Carbondale, IL 62901, U.S.A. lIPresent address: Department of Forestry, Kansas State University, Manhattan, KS 66506, U.S.A. YPresent address: Department of Plant, Soil and Biometrology, Utah State University, Logan, UT 843224820, U.S.A. (Received I2 May 1993; revised received 24 August 1993; accepted 25 August 1993)
Abstract-Trees of silver maple (Acer saccharinurn L.) planted in southern Illinois were cut at rootstock ages 2, 3, and/or 4 years. In all plantings a single main stem was the predominant growth form prior to initial harvest. The predominant post-harvest growth form was numerous coppice stems. The cumber of coppice stems per tree and percent tree survival decreased with greater stand density. Coppice growth, as measured by the number of stems and the height of the tallest stem, increased progressively with the number of harvest cycles. This growth was supported by a progressively older root system, and developed from an increasing number of cut stem bases. About 60% of the coppice were tall stems, over one-half the height of the tallest stem. Trees of the southernmost origin, from Mississippi, with high establishment rates had the highest dry weight production of two-year provenance coppice growth (equivalent to 59.5 Mg ha-’ ‘2 year-‘, or 13.2 ton acre-’ year-‘). The northernmost trees, from central Ontario, had low establishment rates and the lowest stand biomass. Dormant season macronutrient cropping losses were estimated related to biomass yield. Foliage density and stem elongation were greater in first-year coppiced compared to uncoppiced trees. Water relations of coppice growth differed from that of uncoppiced trees in both the first and the second year after harvest. Keywor&eBiofuels feedstock, foliage density, leaf water potential, nutrient cropping, provenance, rootstock, sprout growth, stomata1 conductance, woody biomass.
together with rapidly accreting soil organic matter (humus) significantly contribute to carbon storage. Silver maple (Acer saccharinurn L.) is well adapted for biomass production.’ It is one of the fastest growing temperate-zone trees and has been selected as a priority species by the Biofuels Feedstock Development Program of the U.S. Department of Energy’s Oak Ridge National Laboratory.* Our objectives were to evaluate coppice growth and water relations of silver maple as affected by provenance (origin of seed) and management, including planting density and number and duration of cutting cycles. Comparisons were made within and among different plantings.
1. INTRODUCTION
The ability of trees in a plantation to regenerate by coppice (sprout growth) after stem harvest is an important feature of successful biofuels feedstock production programs. Coppice potential varies with tree species, age and past history, size of an established root system, and with available moisture, nutrients and other environmental resources. Coppicing as a production system differs from other agricultural practices. Successive harvests can be made from one planting. The sprout growth after each biomass harvest is supported by an established root system. Rapid development of a renewed canopy suppresses weed competition. The canopy and surface litter of coppice growth quickly protect a planting site from erosion. The maturing root systems
2. METHODS
2.1. Plantation establishment and growth *Research performed under Subcontract No. 86X95908(3 with Oak Ridge National Laboratory under Martin Marietta Energy Systems, Inc. Contract DE-ACOS84OR21400 with the U.S. Department of Energy.
Three silver maple plantations were established near Carbondale in southern Illinois as part of an ongoing project to identify and select 317
W. C. ASHBKef ul.
318
Table I. Planting management and coppice growth after harvest of silver maple with differing root and stem ages Age (years) root stem
Planting distance (cm)
No. of trees
Tree density” (trees. haa’)
Coppice height No. of (m) stems
I. Minimal management (Commercial seedlings) 3 (1990) 4
I I
90x180
89 89
5500 5500
1.2 2.7
9.4 16.4
2.4 2.6 3.2
8.9 13.7 17.7
II. High-level management (Peoria seed) 3 (1989) 4 5
1 1
30x30
1
21 21 21
52,000 52,000 52,000
III. Provenance plantation (10 provenances from seed) 3 (1990) 4
1 2
15 X 15
1679 1520
191,000 173,000
1.1 1.8
5.0 5.8
“Approximate within-plot tree density, excluding aisles, at time of harvest. 5500 trees ha-’ approximates 2200 trees/acre. Planting areas were for I 195 m2, II 12 ml, and III 90 m2. Plantings I and II were not replicated. Data of planting III are analyzed in Table 2.
superior trees for biomass production in the Midwest region of the United States. All plots were on Hosmer silt loam soil as affected by post-settlement land uses. Hosmer is a fine-silty, mixed, mesic Typic Fragiudalf upland silt loam slightly to strongly acid with depth. The plantations differed in origin of plant materials, number and spacing of trees and management (Table 1). A 1987 planting of commercial seedlings from Tennessee had minimal management after establishment. Plant tissues were harvested in this study at 2-week intervals during spring and fall of the first year for nutrient analyses by the A & L Laboratories of Memphis, TN. A 1986 planting of seed from Peoria, Illinois received a high level of management including weeding, irrigation and fertilization. A third planting, 1987, included seeds from 10 provenances throughout silver maple’s native range.3 Randomized plots within blocks of this site were densely planted at 15 x 15 cm spacing with 100 seed spots each. An initial, two-year, high level of management in this planting included mulch, irrigation and fertilization. Data were taken yearly for all trees in all plantations on height of the tallest stem and number of stems after coppicing. On the provenance plots basal caliper was also taken, Stem form in the provenance study was classified based on presence and vigor of basal stem(s), presence or absence of lateral growth, and dieback or mortality using a modification of
Melick’s system.4 Stem weights of the provenance study were taken at 2 years, and at 4 years as two-year coppice growth. Ten trees (40 trees per provenance) were taken on a transect across each plot within a planting block. The plots were 30 cm apart (vs. 15 cm for the trees) and edge effects were commonly not evident. At harvest, trees in each of the plantations were cut with hand pruning shears or hand saw to 1Ocm stumps (except as noted) between November and May while the trees were dormant or in early leaf, and coppice stems were allowed to grow for one to three years. In one study 50 trees each were cut in November and in February, and in another study trees were cut at 5 cm, 10 cm, or 25 cm height. In each study the number and vigor of stems in the following year or years were determined. Coppice production data from the provenance study were processed using the SAS General Linear Models Procedure.’ Coppice growth compared to non-coppiced trees was measured for trees from three clustered provenances. Since the non-coppiced block was not replicated, all data were collected from a non-coppiced row in one plot and in an adjacent row of a coppiced plot of each provenance for a total of six plots. Stem elongation was measured, with yearly growth distinguished by the terminal bud scars, on ten stems randomly selected within each plot during 1989 and 1990. These trees were also used in a waterrelations study.
Coppice growth and water relations of silver maple
Foliage density was estimated by the light interception method of Lang6 based on the percent transmission of solar radiation beneath a canopy for a range of solar zenith angles. Transmission was measured with an integrating quantum sensor (model SF-80 Sunfleck Ceptometer, Decagon Inc., Pullman, WA) on the surface beneath the canopies. Solar zenith angles for 37.7” latitude and 89.2” longitude corresponding to the sampling times were calculated using the algorithm of Flint and Childs.’ 2.2. Water relations Stomata1 conductance was measured with a steady-state porometer (model 1600, Li-Cor Inc., Lincoln, NE) on the abaxial surface of five fully illuminated, randomly selected leaves within each plot following the precautions noted by McDermitt.* Sampling was carried out sequentially after dew evaporation at dawn until late afternoon. Leaf water potential was measured predawn, and concurrent with stomatal conductance using a Scholander-type pressure chamber (Arimad II, Arimad Corp., Israel) on three randomly selected leaves per plot. Samples were collected following the precau-
319
tions of Meyer and Reicosky,’ stored in an aluminum foil envelope,” and measured within an hour. The diurnal water-relations data were averaged by plot and fourth-order curves of the mean values over time then fitted.5 Each term in the model was tested for significance at alpha = 90% through backwards elimination until an order appropriate for the data was reached. Once the correct model was determined, pair-wise comparisons of the timeadjusted means within the provenance and coppicing treatments were made. 3. RESULTS
3.1. Coppice growth
Silver maples sprouted vigorously when cut back regardless of seed source or stump height. Trees cut in November had significantly more coppice stems in May than those cut in February; by summer no differences were evident in either stem number or height. None of these minimal-management trees, nor any of the highlevel management trees, died following successive harvests. Mortality both before and after
Table 2. Coppice growth within the silver maple provenance plantation, with provenances grouped by tree density. All trees had a 4-year-old rootstock and 2-year-old stems Provenance origin
Trees per plot” (#)
Coppice per tree (#)
Coppice growth per tree height caliper weight (m) (cm) (g)
Biomass per plotb (kg)
1.3 1.3 ns
228 165 ns
2.6 IO.1 **
I.6 1.5 1.1 1.2 I.0 ns
451 339 130 102 114 ns
4.1 3.7 1.6 1.4 2.0 ns
I .3ab
217 223 126 I31 115 ns
12.6ab l3.4a 7.9c 8.5bc 8.Oc *
Meam for provenance deity groups Lower density Higher density Significance
13’ 63d **
7.0 4.1 **
1.8 ns
Lower density provenances GB-Grand Bend, ONT NH-Boscawen VT-Burlington SSM-S. Ste. Marie, ONT PA-Montrose Significance
9 I1 12 I4 I8 ns
9.la 8.lab 5.7c 6.2bc 6.2bc
1.9 1.7 I.5 1.4 1.3
Higher den&y provenances ILC-Carbondale, IL MS-Starkville IA-Ames WI-Madison ILM-Murphysboro, IL Significance
58 60 63 65 71 ns
4.8 4.2 3.9 4.0 3.6 ns
l
1.5
tlS
I .9b 2.2a 1.6c 1.7bc I .8bc **
1.5a l.lc 1.3bc 1.2bc **
‘Plots were I50 by l5Ocm and were planted to 100 seed spots. bCalculated as mean number of trees per plot times weight per tree. Mean plot weight was 8.8 kg, equivalent to 29.7 Mg ha-’ .2 year-‘. cEquivalent to 57,778 trees ha-’ average plot density. dBquivalent to 279,999 trees ha-’ average plot density. “Grand B end is near Detroit, and relatively southern among these provenances. Provenance values significantly different at the 5% (*) level, or 1% (**) level, or not significantly different (ns). Duncan grouping means within a column with the same letter, or no letter, are not significantly different at a = 0.05. Rounded-off values lead to apparent discrepancies in calculated values.
W. C. ASHBYet al.
320
[II 0
GB
NH VT SSM PA Provenance State
aSee Table number
Tall stems Short stems
2 for provenance of trees
) l/2 - ( l/2
heqht height
ILC MS IA and/or Citya identification
of tallest of tallest
WI
stem stem
ILM
and mean
per plot.
Fig. 1. Number of tall and short coppice stems per tree related to tree density and to provenance. Number of trees per plot (density) increases greatly from GB on the left to ILM on the right.
harvesting was found in the closely-spaced provenance plots (Table 2, Fig. 1). Provenances with relatively low density of surviving trees prior to harvest had the greatest number of coppice stems after harvest (Fig. 1). Tall stems (> l/2 height of tallest stem) consistently predominated, and averaged about 60% of number of total coppice stems per tree. The numbers of short stems (G l/2 height of tallest stem) were less closely related to plot density. One main stem was the predominant stem form throughout the provenance plantation prior to the first harvest. The Illinois, Wisconsin, Iowa or Mississippi provenances that had the highest percentages of pre-harvest trees with one main stem did not have unusually high percentages of tall coppice shoots. Within a provenance the number of tall coppice stems per tree after harvest was correlated (r = 0.83) with the number of trees having one main stem prior to harvest. The number of coppice stems increased after harvest in all the studies with increasing age of the rootstock remaining after harvest (Table 1). Coppice height growth was also greater with increasing age of the root system, whether after successive cuttings or with longer periods between harvests of coppice stems. Stems were at least 1 m tall in the first year after cutting, and commonly reached or exceeded 2 m. Trees cut at 5 cm rather than the usual 1Ocm showed a reduction in number of sprouts, and those cut at 25 cm sprouted from the lower and middle rather than the upper part of the stems. Because of differences in seedling establish-
ment and survival in the provenance study,-’ the provenances were separated into two groups of 5 provenances each: those of higher densities with 58-71 trees per plot, and those of lower densities with 9-18 trees per plot. Mean number of stems, height, caliper and tree weight of the 4 plots per provenance varied both within the high- and the low-density provenance groups and between the groups (Table 2). Coppice height and caliper differed highly significantly among the higher density provenances; number of coppices per tree and tree weight did not. Trees were taller in the higher density provenances with an R2 of 0.82, and a C.V. of only 7%. Among the lower-density provenances with 9-18 trees per plot the number of coppice stems differed significantly (Table 2) and mean height, caliper and tree weight did not. There were fewer tall coppice stems with increasing density. The harvested dry weight of two-year coppice dormant stems in the provenance study were converted to plot weights by multiplying mean plot number of trees and individual tree weights (Table 2). The northernmost provenance, Sault Ste. Marie, Ontario, with the least heavy trees and the second lowest number had lowest biomass per plot, equivalent to 6.4 Mg * ha-’ .2 year-‘. The Mississippi provenance with the third heaviest trees and many more trees per plot had the highest biomass, equivalent to 59.5 Mg . ha-’ * 2 year-‘, or 13.2 ton . acre-’ . year-‘. Estimated nutrient cropping based on dormant-season stem analyses and the mean two-year biomass yield of all the
Coppice growth and water relations of silver maple
321
Table 3. Stem elongation and foliage density for silver maple from three provenances Yearly stem elongation 1989 1990 non-C copb non-C cop (m) (m) Cm) Cm)
1987-88 non-C’ (m)
Provenance Illinois Pennsylvania Wisconsin
2.52 2.47 2.04
0.76 0.55 0.12
1.52 1.24 1.36
0.66 0.52 0.79
1.43 0.95 1.17
Foliage density non-C (m2.
m-3)
1.15 1.23 1.19
(m2~~-‘)
4.92 5.12 4.47
“Non-C is a non-coppice stem. bCop is a coppice stem.
provenances was 48 kg 1ha-’ (42 lb. acre-‘) for phosphorus, 148 for potassium, 175 for calcium and 21 kg. ha-’ for magnesium. Stem elongation of the coppiced trees in the provenance study was, for two years, nearly double that of the non-coppiced trees (Table 3). Overall elongation in the coppiced trees was less during the second year of growth (1990) than during the first year after cutting. Foliage density within the volume defined by plot area and stem height was substantially greater in the coppiced trees as a result of a large number of leaves occurring along a much shorter length of stem than in the non-coppiced trees. 3.2. Water relations The coppiced trees experienced significantly different water relations than did the non-
Cop
2
coppice growth in the first year (1989). Relative water relations were more variable in 1990. Less water stress for the coppice growth in 1989 was shown by the higher predawn water potential (Fig. 2). During the day (dawn to dusk) the coppice shoots had significantly lower leaf water potential in 1989, and greater stomata1 conductance in July 1989 but not in August during a continued drought (Table 4). In 1990 with more rain the only significant difference was lower leaf water potential by the non-coppiced trees in August. Among provenances the southern Illinois trees had lower diurnal leaf water potential in August 1989 and lower stomata1 conductance in 1990 than did the trees from Wisconsin, with those from Pennsylvania intermediate in response. The Wisconsin trees had the least and
1990
Non-C
0 . 111. D v Penn 0 n Wise.
-0.2
60
2
40
.CI
t’
c
a +J
-0.4
E : c, g
-0.6 0.0
L
% 3
-0.2
F a 2
-0.4
iI -0.6
June
July
August
Fig. 2. Predawn leaf water potential, data points in MPa, for coppiced and non-coppiced silver maple from three provenances, Illinois, Pennsylvania and Wisconsin, in 1989 and 1990. Data bars are rainfall in mm.
W. C.
322
A~HBY
ef al.
Table 4. Time-adjusted means of diurnal stomata1 conductance and diurnal leaf water potential for silver maple with provenances averaged across treatment, and coppiced and non-coppiced treatments averaged across provenance, from four dawn-to-dusk sampling dates Diurnal stomata1 conductance 1989 1990 July July Aug Aug (mmol”) (mmola) (mmol”) (mmol”) Provenance Illinois Pennsylvania Wisconsin Significance
228 223 255 ns
104 118 106 ns
185b 223a 237a *
147b 193a 186a
Treatment Coppiced Non-coppiced Significance
373 98 *
183 36 ns
225 205 ns
181 169 ns
l
Diurnal leaf water potential 1989 1990 July July Aug Aug (MPa) (MPa) (MPa) (MPa) -0.52 -0.55 -0.44 ns
- 1.31b - 1.21b - 1.02a
-0.60 -0.40 *
-1.28 -1.08 +
l
-1.42 - 1.38 -1.47 ns
-1.52 -1.42 - 1.41 ns
- 1.40 -1.44 ns
-1.37 -1.54 *
Provenance values signficantly different at the 5% (*) level, or not significantly different (ns). Duncan grouping means within a column with the same letter, or no letter, are not significantly different at a = 0.05. “mm01 . rnm2. s-l.
the Illinois trees the greatest growth.
coppice
stem
4. DISCUSSION
Juvenile silver maple regenerates rapidly and vigorously by coppice stems.” Rootstocks in all three plantings sent up one to many stems after harvest. Tree mortality, if any, and number of coppice stems varied with both rootstock density and age. There is a complex relationship between spacing and coppice production cycles. ‘2-‘4Pre-harvest stem form was less immediately useful as a predictor of type of coppice growth than plot tree density. Differences in coppice production related to provenance alone were not evident in our studies. The increasing number of stems with increasing number of coppice cycles can be explained in part by the successively greater number of stem bases capable of sending up new stems. In three cycles we did not exhaust this resprout potential for the planting with high-level management. In fact the vigor improved with increased age of the root system and there was no mortality within the timeframe of our study. Geyer” reported that yield of silver maple did not deteriorate even after 5 or 6 cuts during an S-year period. These findings are in contrast to those with other species such as Populus that had reduced yields and increased mortality with multiple harvests.14 Several factors affect individual tree dry weights, including timing of harvest cycle,13 tree density and age of rootstocks. We feel that the
fewer coppice stems of the central or southern, more dense provenances than of the northern provenances may have been affected more by the differential survival and crowding than by inherent growth potential. The intensity of above-ground competition for closely-planted trees can be minimized by tree harvests at short intervals. Kopp et al.” stated that height growth of 7-year-old silver maple seed sources appears to be under stronger genetic control than stem number. Any planting method can give widely varying numbers of trees during the life of a plantation. Our use of seed was no exception. The importance of population size, and tree vigor, was demonstrated by the range of our two-year provenance harvest values from 59.5 to 6.4 Mg . ha-’ .2 year-‘. Major differences in individual tree height, caliper and weight were associated with the yield differences. The importance of root-shoot ratios was shown both by the greatly increased coppice vs. non-coppice stem growth and by the differing water relations. Early-season water stress by the coppiced compared to the non-coppiced trees would clearly be reduced because of the absence of stems with transpiring leaf area. Leaf area following coppicing of other species increased rapidly during the season from reinvigorated stem growth. I6 A consequent lower, denser leaf crown would increase boundary-layer resistance.17 In contrast, the non-coppiced trees had for a longer period of time more ventilated leaf canopies. Drought effects were less apparent in the second-year water relations data.
Coppice growth and water relations of silver maple 5. SUMMARY
This study documented the coppicing ability and productive capacity of silver maple from many sources related to management. Biomass production was relatively unaffected by differences in harvesting during the dormant season. Mineral nutrient cropping losses were indicated. Coppice regrowth was more vigorous and less affected by drought stress than was growth of non-coppiced trees. Two areas of concern remaining are the stocking rate effects on individual tree and tree plot weights, and properly matching specific tree clones or provenances to regional or site climatic/environmental factors to exploit genetic variability in growth performance. With these accomplished, silver maple will become an even more valuable asset in the biofuel energy strategy of the U.S.A.
REFERENCES 1. W. J. Gabriel, Acer saccharinurn L. Silver maple. In S&s of North America 2. Hardwoods. Agric. Handb. 654, pp. 7&77. U. S. Department of Agriculture, Washington, DC (1990). 2. L. L. Wright, J. H. Cushman and P. A. Layton, Expanding the market by improving the resource. Biologue 6(3), 12-19 (1989). 3. W. C. Ashby, D. F. Bresnan, P. L. Roth, J. E. Preece and C. A. Huetteman, Nursery establishment, phenology and growth of silver maple related to provenance. Biomass and Bioenergy 3(l), l-7 (1992). 4. R. Melick, Measurements-what, when, how, why? In Proc. Seruicewide Genetics Workshop, pp. 476485. U.
5. 6. 7. 8.
9.
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S. Department of Agriculture Forest Service, Charleston, SC (1983). SAS Institute, Inc., SAS User’s Guide: Statistics 1985 edition. SAS Institute, Carey, NC (1985). A. R. G. Lang, Simplified estimate of leaf area index from transmittance of the sun’s beam. Agric. For. Meteorol. 41, 179-186 (1985). A. Flint and S. Childs, Calculation of solar radiation in mountainous terrain. Agric. Meteor. 40,233-249 (1987). D. K. McDermitt, Sources of error in the estimation of stomata1 conductance and transpiration from porometer data. HortScience 25, 1538-1548 (1990). W. Meyer and D. Reicosky, Enclosing leaves for water potential measurement and its effect on interpreting soil-induced water stress. Agric. Meteor. 35, 187-192
(1985). 10. H, Karhc and H. Richter, Storage of detached leaves
and twigs without changes in water potential.
New
Phytol. 83, 379-384 (1979). 1 I. W. A. Geyer, Spacing and cutting cycle influence on short rotation silver maple yield. Tree Planters Notes 29(l), 5-7, 26 (1978). 12. H. E. Kennedy, Jr, Influence of cutting cycle and
spacing on coppice sycamore yield. U. S. Department of Agriculture, Forest Service, Southern Forest Experiment Station Research Note SO-193, 3 pp. (1975). 13. W. A. Geyer, Growth, yield, and woody biomass characteristics of seven short-rotation hardwoods. Wood Sci. 13(4), 2099215 (1981). 14. T. Strong, Rotation length and repeated harvesting influence Populus coppice production. U. S. Department of Agriculture, Forest Service, North Central Forest Experiment Station Research Note NC-350, 4 pp. (1989). 15. R. F. Kopp, W. A. Geyer and W. R. Lovett, Silver maple seed sources for increased biomass production. North J. Appl. For. 5, 180-184 (1988). 16. T. J. Blake and T. J. Tschaphnski, Role of water
relations and photosynthesis in the release of buds from apical dominance and the early reinvigoration of decapitated poplars. Physiol. Plan. 68, 287-293 (1986). 17. P. Jarvis and K. McNaughton, Stomata1 control of transpiration: Scaling up from leaf to region. Adu. Ecol. Res. 15, l-49 (1986).