Forest Ecology and Management, 13 ( 1 9 8 5 ) 2 2 3 - - 2 3 3 223 Elsevier Science Publ ishers B.V., A m s t e r d a m - - P r in t ed in The N e t h e r l a n d s

BIOMASS PRODUCTION AND NUTRIENT ACCUMULATION IN SEEDLING AND COPPICE HARDWOOD PLANTATIONS

R.F. WITTWER' and J.W. STRINGER

Department of Forestry, University of Kentucky, Lexington, KY 40546 (U.S.A.) 'Present address: Department of Forestry, Oklahoma State University, Stillwater, OK 74078, U.S.A.

(Accepted 20 June 1985)

ABSTRACT

Wittwer, R.F. and Stringer, J.W., 1985. Biomass production and nutrient accumulation in seedling and coppice hardwood plantations. For. EcoL Manage., 13: 223--233.

Total biomaas and contents of N, P, K, Ca, Mg and Mn in above-ground tree com- ponents of five deciduous species were determined in closely-spaced (0.9 X 0.6 m) 5-year- old plantations of seedling origin and 5-year~)Id coppice stands regenerated after the seedling harvest. Species evaluated were: a Populus hybrid, Platanus occidentalis L., Alnus glutinosa L., Betula nigra L., and Fraxinus pennsylvanica Marsh. In seedling stands, total biomass of Alnus glutinosa and the Populus hybrid was significantly greater than for the other species. In coppice stands, total biomass of Alnus glutinosa was significant- ly greater. The proportion of total biomass in bole components increased and in crown components decreased in coppice stands as compared to seedling stands. This resulted in relatively more Ca and less N, P, and K in above-ground tree components of the coppice stands. Leaf area index for each species in the seedling stands generally ranked in the same order as total biomass.

INTRODUCTION

Worldwide demand for wood products is increasing; at the same time society is placing more diverse demands on forested land. Recreation and watershed uses of forest land will take precedence over wood production in some areas. Large areas of prime hardwood forests are being converted to other uses, for example, agriculture, urban and industrial development and utility rights-of-way. These factors have motivated foresters to seek methods of maximizing production on lands that are available for forestry purposes.

Establishment of closely-spaced hardwood plantations harvested on short rotations (1--10 years) to increase fiber production has been evaluated by several investigators and Cannel and Smith (1980) have reviewed yields resulting from use of these silvicultural systems. Species--site relationships, rotation age--stand density interactions and cultural treatments exert strong

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influences on biomass production (Wittwer and Immel, 1978; Wittwer et al., 1978; Fege, 1981). Impor tant attributes of suitable species include: rapid juvenile growth, efficient dry mat te r product ion in terms of water and nutrient inputs, crown characteristics to maximize interception of solar radiation, and ease of regeneration by coppicing (Fege, 1981). Based on these characteristics, promising genera for short rotat ion forestry include Alnus, Platanus, Populus, Betula, and Fraxinus. The s tudy reported herein examined biomass and nutr ient accumulat ion, leaf area, and coppice re- generation potential for five species representing these genera on a produc- tive bottomland site.

STUDY AREA

The study is located within the floodplain of the Ohio River in western Kentucky. The deep, well-drained softs formed in alluvium from sedimentary rocks, glacial till, and loess. The area has been mapped as Ashton silt loam, a fine-silty, mixed, mesic, Mollic Hapiudalf (Cox, 1974). Natural fertility and available water-holding capacity are high.

The area has a temperate climate with warm, humid summers and mod- erately cold winters. Average length of the frost~free period is about 190 days, extending from mid-April to late October. Annual precipitation averages 113 cm and is fairly wen distributed th roughout the year. Native forests contain Liriodendron tulipifera L., Fagus grandifolia Ehrh., Liquid- ambar styraciflua., and various species of Acer, Carya, and Quercus.

MATERIALS AND METHODS

Seedling stand

Three replicate plots of five species, each containing six rows, 0.9 m apart, with ten seedlings (s temwood cuttings for the hybrid poplar), spaced 0.6 m apart in each row were studied. The species included American syca- more (Platanus occidentalis L.,), European alder (Alnus glutinosa L.), river birch (Betula nigra L.), green ash (Fraxinus pennsylvanica Marsh.) and a hybrid poplar (Populus sp.). The exact origin of the poplar is unknown. Cuttings were acquired from the Kentucky Division of Forestry which pro- duces several hybrids described by Stout and Schreiner (1933). These hy- brids include representatives of sections Aigeiros and Tacamahaca.

In late August, near the end of the fifth growing season, height and dia- meter (ground level) were measured on the center two rows of each plot. Survival counts were made on the entire plot. Four sample trees, selected to represent the range of sizes present, were cut near the groundline and re- moved from each replicate plot. Sample trees were separated into biomass components , weighed and taken to the laboratory for drying at 65 ° C, and re- weighed. All remaining trees on each plot, excluding the border rows, were

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harvested and weighed to determine total green weight on an area basis. These data were used in conjuct ion with the sample tree data to estimate oven-dry biomass of each componen t part on an area basis.

Total leaf areas (single surface) of the four sample trees from one plot of each species were measured with a Li-Cor ® portable area meter. A predic- tion equation was determined for each species using {tree diameter-squared) × (height) as the independent variable. Leaf areas were predicted for all trees in the center two rows on each plot and converted to an area basis. Subsamples of the tree material were ground in a Wiley mill, dry ashed (450°C) and taken up in 1 N HCI. Phosphorus was determined by colori- metry with molybdenum blue color development and K, Ca, and Mn, by atomic absorption. Nitrogen concentrat ions were determined by the Kjel- dahl procedure.

Weighted average chemical concentrat ions were computed by summing the elemental contents of the four sample trees on each plot, for each ele- ment and biomass component , and dividing by the combined weight of the biomass for that component . Elemental contents o f tree components on each replicate plot were determined by multiplying each biomass value by the appropriate weighted average chemical concentration. These data were subjected to analysis of variance procedures, and when significance {0.05 level) was indicated means were compared by Duncan's multiple range test.

Coppice stand

Five growing seasons after the seedling harvest coppice stands regenerated on the s tudy plots were evaluated. Hybrid poplar plots had been invaded by a heavy cover of vines and weeds, especially Japanese honeysuckle (Loni- cera japonica) during the coppice rotation. Due to high tree mortality, this species was excluded from further study. The number of living stems per roots tock was determined on the center two rows of each plot. In nearly all cases, there was a single dominant sprout on each rootstock, and total height measurements were made on these stems. Survival counts were con- ducted on all rows. Methods for determinat ion of biomass production and nutrient accumulation were identical to those used to evaluate seedling stands. Stem diameter and leaf area were no t evaluated in the coppice stands.

Soils

Five composi te soil samples collected from the surface 20 cm of each replicate plot at the time o f the seedling harvest were analyzed for total N by the Kjeldahl method, available P by molybdenum blue color develop- ment after extract ion with Bray No. 1 extractant, and exchangeable K, Ca, and Mg by atomic absorption following extract ion with 1 N, pH 7.0, NH4OAc. Mean values were pH, 7.3; total N, 0.2%, available P, 12 ppm,

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exchangeable K, 95 ppm; exchangeable Ca, 2000 ppm and exchangeable Mg, 400 ppm.

RESULTS

Mensuration data

The species differed in growth, in both the seedling and coppice stands (Table 1). European alder and hybrid poplar seedlings were about three times taller than green ash, the lowest ranking species. On a nearby river terrace site with lower fertility and available moisture, total height of 4-year- old seedlings ranked as follows: hybrid poplar > American sycamore > Euro- pean alder > river birch > green ash (Wittwer and Immel, 1978). The better growth of European alder on the floodplain site in the present study may have been due to the more favorable moisture conditions. Franklin (1977) reported that the species is expected to grow better than native hardwoods on wet sites in the southeastern United States. As would be expected, dominant stems in the coppice stands were taller than in the seedling stands. Relative species rankings in the coppice stands were similar to the seedling stands. Relative ranking of basal diameters in the seedling stands was similar to height growth.

Survival of the seedling stands ranged from 80 to 98% at the end of five growing seasons. This is generally above the range observed in 4-year-old seedling stands on an adjacent river terrace site (Wittwer and Immel, 1978). European alder showed the largest reduction in survival, from 88 to 69%, during the coppice rotation. Survival decreases during the 5-year coppice rotation were negligible for sycamore, river birch, and green ash. Green ash

TABLE I

Mensuration data for 5-year-old seedling (S) and 5-year-old coppice (C) stands

Species Height (m) Diameter a Survival (%) S

S C (cm) S C

Sprouts/ rootstock C

European alder 5.7a b 6.3a 6.0a 88a 69ab 2.7 Hybrid poplar 5.5a ND c 5.3a 85a ND ND American sycamore 3.4b 4.2b 3.7b 80a 78bc 1.6 River birch 2.6hc 3.4b 3.4bc 86a 85cd 2.8 Green ash 1.8c 2.9b 2.6c 98a 92d 1.5

aMeasured near ground level. bMeans within a column followed by the same letter are not significantly different at the 0.05 level. CND = no data collected in coppice stands.

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maintained the highest survival throughout the 10-year s tudy period, com- prised of the 5-year seedling rotat ion and the 5-year coppice rotation. This may be related to the relatively slower growth of individual stems of this species, resulting in less compet i t ion in these closely-spaced stands.

The average number of dominant stems per roots tock is an indication of the relative sprouting ability of each species; however, these data may be confounded by other factors, such as growth rates of individual stems and survival rates for rootstocks. For example, the low survival (69%) for Euro- pean alder rootstocks and decreased stand density is associated with a high number of dominant stems per rootstock.

Biomass

Biomass of the various components varied considerably among species (Table 2). In the seedling stands, biomass of European alder and hybrid poplar, for each component and the total tree, exceeded the o ther three species. The same trend was generally true in the coppice stand except for foliage. There were fewer differences among the various species for foliage in the coppice stands. Total tree biomass in the coppice stands ranged from 29% (European alder) to 127% (green ash) greater than in the seedling stands. The differences were even greater for bolewood, the componen t of most interest from a utilization viewpoint, ranging f rom 42% (European alder) to 162% (green ash). Species with lower total biomass as seedlings had larger percentage increases in the coppice stands and yield differences be- tween species decreased in the coppice rotation. This suggests tha t species found to be more productive during a seedling rotat ion may not have the same relative advantage during two or more cutting cycles with a coppice silvicultural system.

L e a f area - - seedl ing s tand

Leaf product ion is related to the production of other biomass compo- nents since leaf surface area is the basis of photosynthet ic activity. Attain- ment and maintenance of opt imum leaf areas is essential to maximizing productivity. Average leaf area per tree (single surface) in the seedling stand ranged f rom 4.0 m 2 for hybrid poplar to a low of 1.3 m 2 for green ash when sampled in late August (Table 3). Four-year-old Popu lus 'Tristis No. 1' planted at a 0.6 × 0.6 m spacing have been found to have 7.06 m 2 per tree when fertilized and irrigated (Isebrands et al., 1977).

The average leaf area of individual trees is a funct ion of spacing and density for the specific stand, and the most commonly used measure of leaf product ion is leaf area index (LAI), which is the ratio of the total leaf sur- face area o f a stand to ground surface area. The LAI values (single surface) for these stands ranged from 6.2 to 2.2 m~/m ~. The relative ranking for the five species was hybrid poplar ~ European alder > American sycamore >

bO

{30

TABLE

2

Biomass b

y species and c

omponent part for 5-year-old seedling (S) and 5-year-old co

ppic

e (C

) stands

Species

Foliage (t/ha)

Bran

ches

(t/ha)

Bole

bark

(t/ha)

Bolewood (t/ha)

Tota

l (t/ha)

S C

S C

S C

S C

S C

E uropean

alder

3.1a a

2.5a

10.0

a 9.5a

5.9a

8.4a

32.2

a 45

.7a

51.2

a 66

.1a

Hybrid

poplar

3.1a

ND b

7.6b

ND

6.1a

ND

24.9

a ND

41.7

a ND

American

sycamore

1.9b

2.

lab

2.5c

4.1b

1.

3b

2.2b

9.

8b

15.9

b 15

.5b

24.3

b Ri

ver

birch

1.3b

1.

4b

2.4c

3.1b

1.

0b

1.4b

4.

7b

8.1c

9.

4b 14

.0c

Green

ash

1.9b

2.5a

1.8c

4.4b

0.

8b

2.0b

3.

7b

9.7b

c 8.

2b

18.6

bc

aMeans within a column f

ollo

wed by the

same letter are no

t significantly different at the 0.0

5 level.

bND = no data collected in cop

pice

stands.

TABLE 3

Leaf area data for 5-year-old seedling stands a

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Species Average leaf area Leaf area per t ree index (ms ) (m2/m ~)

Hybrid poplar 4.0a b 6.2a European alder 3.0ab 4.7ab Amer ican sycamore 2.0b 2.8b River birch 1.7b 2.5b Green ash 1.3b 2.2b

aLeaf area data are for single surfaces only. bSpecies means wi th in a co lumn fo l lowed by ferent at the 0.05 level.

the same let ter are not s ignificantly dif-

river birch > green ash. This is similar to the ranking from total biomass with the exception of European alder biomass exceeding that of hybrid poplar. LAI results are within the range found by other investigators for similar stands. Cumulative LAI in a 5-year-old, 0.6 × 0.6 m spaced plan- tation of Populus 'Tristis No. 1' was 7.3 m2/m 2 , however, leaf fall had started in June, and when top growth finished by mid-August, the equiva- lent of 1.2 to 1.5 LAI had already fallen, thus LAI at any point in time was below the cumulative total (Zavitkovski, 1981).

Chemical contents

Since total above-ground biomass varied significantly for the five species (Table 2) it is not surprising that chemical contents of these tree components also varied in the seedling (Table 4) and coppice stands (Table 5). The high N content of European alder can be attributed to two factors, the higher total biomass and the higher N concentrations in the various components of this N-fixing species. Differences in distribution of total biomass among component parts in the seedling and coppice stands resulted in differences in total content of some elements that did not parallel differences in total biomass. For example, biomass of the coppice stands ranged from 29 to 127% greater than in the seedling stands for the various species, while Ca content ranged from 75 to 396% greater. This is probably due to a greater proportion of bolewood, a component relatively high in this element, in the coppice stands. Conversely, contents of N, P, and K, major elemental constituents of foliage, did not increase in the coppice stands in the same proportion as did total biomass since foliar biomass in the coppice stands was not appreciably greater than in the closely-spaced seedling stands. The high Mn concentrations in European alder and river birch resulted in high stand content for these species relative to their above-ground biomass.

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TABLE 4

Total above-ground chemical content by species and component part in 5-year-old seedling stands

Species Chemical contents (kg/ha)

N P K Ca Mg Mn

Foliage European alder 98a 5.3abc 18b 33b 15.7a 0.61a Hybrid poplar 59b 9.0a 41a 51a 18.7a 0.19b American sycamore 33bc 4.2bc 15b 16c 5.2b 0.10b River birch 25c 2.9c 10b 18c 6.6b 0.80a Green ash 35bc 7.6ab 22b 10c 3.6b 0.05b

Branches European alder 97a 6.6a 36a 46a 7.1b 1.00a Hybrid poplar 38b 7.7a 22b 53a 9.5a 0.14b American sycamore 9c 2.2b 5c 10b 1.8c 0.03b River birch l l c 1.gb 4c 12b 2o0c 0.17b Green ash 7c 1.4b 5c 7b 1.0c 0.02b

Bole bark European alder 64a 4.2b l l b 31a 4.6a 0.85a Hybrid poplar 38b 6.1a 23a 34a 8.5a 0.14b American sycamore 7c 1.3c 4bc 9b 1°4c 0.03b River birch 7c 0.7c 2c 8b 0.8c 0.11b Green ash 5c 0.6c 3bc 6b 0.9c 0.02b

Bolewood European alder 97a 10.3b 38a l l a 5.6ab 0.72a Hybrid poplar 36b 18.4a 37a 17a 9.1a 0.22b American sycamore 14c 9.6b 16b 4b 4.3bc 0.06b River birch 9c 4.9c 6b 2b 3.6bc 0.13b Green ash 7c 2.5c 6b 2b 1.0c 0.02b

Total tree European alder 356a 26.4b 103a 121a 33.0b 3.18a Hybrid poplar 171b 41.2a 123a 155a 45.8a 0.69bc American sycamore 63c 17.3bc 40b 39b 12.7c 0.22c River birch 52c 10.4c 22b 40b 13.0c 1.21b Green ash 54c 12.1e 36b 25b 6.5c 0.11c

Species means for each element and component followed by the same letter are not significantly different at the 0.05 level.

Nutrient demand

Most or all of the total above-ground biomass is likely to be harvested with this type of silvicultural system. Therefore chemical contents of these biomass components represent probable nutr ient removals. Assuming that a unit of biomass for any species has equal utilization value, a comparative measure of nutrient demand is indicated by the quanti ty of nutrients re-

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TABLE 5

Total above-ground chemical content by species and component part in 5-year-old coppice stands

Species Chemical content (kg/ha)

N P K Ca Mg Mn

Foliage European alder 81a 4.3a 16a 32a 9.8a 0.63a American sycamore 40b 5.6a 18a 27a 6.0a 0.17a River birch 35b 3.9a l l a 17a 5.6a 0.34a Green ash 45b 10.4a 23a 33a 6.8a 0.16a

Branches European alder 70a 4.9a 2Sa 60a 6.4a 2.00a American sycamore 12b 3.0a 7b 20b 3.4ab 0.13b River birch 17b 2.5a 7b 21b 2.5b 0.23b Green ash 15b 3.1a 13ab 26b 3.5ab 0.13b

Bolebark European alder 82a 4.0a 24a 127a 8.1a 1.04a American sycamore 11b 2.2ab 7b 49ab 3.1b 0.09b River birch 11b 0.9b 3b 24b 1.4b 0.12b Green ash 13b 0.9b l l a b 30b 2.6b 0.09b

Bole wood European alder 99a 0.5a 32a 40a 10.6ab 1.70a American sycamore 23b 16.9b 32a 21b 13.8a 0.29b River birch 12b 7.5c 8a 8c 6.6ab 0.30b Green ash 15b 7.0c 15a 10c 4.7b 0.19b

Total tree European alder 332a 13.7a 100a 259a 34.9a 5.37a American sycamore 86b 27.7a 64ab l17b 26.3ab 0.68b River birch 75b 14.8a 29b 70b 16.1a 0.99b Green ash 88b 21.4a 62ab 99b 17.6b 0.57b

Species means for each element and component followed by the same letter are not significantly different at the 0.05 level.

moved per unit of biomass (Wittwer and Immel, 1980). This value varies characteristically by element, and differs between species by a factor of 3--4-fold for some elements (Table 6).

American sycamore ranks lowest in terms of N potentially removed in the harvested biomass, and European alder ranks lowest for P, K, Ca, and Mg. Although European alder ranks high in terms of N removed in the har- vested biomass, it should be recognized that a portion of the N content of this species represents fixation from atmospheric sources and should not be viewed as higher N demand in comparison with the other species. Euro- pean alder also was found to rank low in nutrient demand based on this ratio in a similar study involving these same species on an adjacent site

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TABLE 6

Nutrient content per unit biomass in total above-ground tree components a

Species Nutrient content (g) : biomass (kg)

N P K Ca Mg Mn

European alder 5.9 0.3 1.7 3.2 0.6 0.07 Hybrid poplar b 4.1 1.0 3.0 3.7 1.1 0.02 American sycamore 3.7 1.1 2.6 3.9 1.0 0.02 River birch 5.4 1.1 2.2 4.7 1.2 0.09 Green ash 5.3 1.2 3.7 4.6 0.9 0.09

alncludes combined seedling and coppice stands except for hybrid poplar. bData from seedling stand only.

(Wittwer and Immel, 1980). River birch and green ash rank high in terms of nutrient demand per unit of biomass product ion since a relatively larger proportion of the total biomass in these slower-growing species is comprised of crown components with typically higher chemical concentrations for most elements.

CONCLUSIONS

During the 10-year study period (5-year-old seedling stand plus 5-year- old coppice regrowth) European alder produced significantly more total above-ground biomass. Hybrid poplar ranked high during the seedling ro- tation, but evaluation of this species was discontinued when the coppice plots were invaded by heavy herbaceous competit ion. Coppice stands pro- duced from 29% (European alder) to 127% (green ash) more biomass than the seedling stands, given a 5-year growth period for each. Leaf area index at the end of the fifth growing season in the seedling stands ranged from 2.2 to 6.2 m2/m 2, and the ranking by species generally followed the trend for total biomass.

Assuming that a given quantity of biomass for any species has equivalent utilization value, European alder appears to be a preferred species on this site in view of its nutrient content and potential nutrient removals that would result from total tree harvesting. Content of P and K, per unit of bio- mass, for the combined seedling and coppice product ion of this species ranked lowest. Nitrogen content and potential removals for European alder ranked high; however, a portion of this N resulted from fixation and does not represent higher demands on the site in comparison with the other species. Absolute nutrient removals could be reduced considerably by not removing foliage or small branch components from the site, an approach suggested by other authors (Hansen and Baker, 1979).

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ACKNOWLEDGEMENTS

The inves t igat ion r e p o r t e d in this p a p e r (84 -8 -162) is in c o n n e c t i o n wi th a p ro jec t o f the K e n t u c k y Agr icu l tu ra l E x p e r i m e n t S t a t i on and is pub l i shed wi th approva l o f the Direc tor . J o u r n a l Art ic le No . J - 4 6 0 9 o f the O k l a h o m a Agricul tural E x p e r i m e n t S ta t ion , O k l a h o m a S ta te Univers i ty . T h e ass is tance o f F.R. E l l ingswor th and M.J. I m m e l , f o r m e r g r a d u a t e s tuden t s , and O.W. H i n t o n and R. Schaefer , Wi l l ame t t e Indus t r ies , is g ra te fu l ly a c k n o w l e d g e d .

REFERENCES

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Fege, A.S., 1981. Silvicultural principles and practices in short rotation energy forestry in temperate zones. International Energy Agency, Forestry Energy, Planning Group B -- Growth and Production. College of Forestry, Univ. Minnesota, St. Paul, MN, 101 pp.

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Hansen, E.A. and Baker, J.B., 1979. Biomass and nutrient removal in short rotation intensively cultured plantations. In: Proceedings -- Impact of Intensive Harvesting on Forest Nutrient Cycling, 13--16 Aug. 1979, Syracuse, NY. SUNY College of Environ. Sci. For., Syracuse and U.S. Dep. Agric. For. Serv., Northeast For. Exp. Stn, pp. 130--151.

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Stout, A.B. and Schreiner, E.J., 1933. Results of a project in hybridizing poplar. J. Hered., 24: 216--229.

Wittwer, R.F. and Immel, M.J., 1978. A comparison of five tree species for intensive fiber production. For. Ecol. Manage., 1: 249--254.

Wittwer, R.F. and Immel, M.J., 1980. Chemical composition of five deciduous species in four-year-old, closely-spaced plantations. Plant Soil, 54: 461--467.

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Zavitkovski, J:, 1981. Structure and seasonal distribution of litteffall in young plantations of Populus 'Tristis No. 1'. Plant Soil, 60: 409--422.