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Biomass and nutrient distribution in a Chinese-fir plantation chronosequence in Southwest Hunan, China
Forest Ecology and Management 105 Ž1998. 209–216
Biomass and nutrient distribution in a Chinese-fir plantation chronosequence in Southwest Hunan, China Hongjun Chen
)
Department of Forest Soils, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China Received 4 February 1997; accepted 23 September 1997
Abstract Biomass and nutrient distribution were measured in a Chinese-fir plantation chronosequence in Southwest Hunan. Total tree biomass of 3, 6, 11, 17, 21 and 27-year-old stands was 38, 52, 118, 163, 173 and 269 trha, respectively. Biomass of understorey vegetation was the smallest, less than 1 trha, and there was an irregular change with stand age, while litter increased with stand age from 0.87 for the 3-year-old to 6.91 trha for the 27-year-old. Biomass of stemwood was the highest, accounted for 58% of the stand, while nutrient content in stemwood was relatively small, 18% of N, 27% of P, 13% of K, 15% of Ca and 13% of Mg accumulated in total trees. The highest nutrient concentration was found in needles and understorey vegetation and the lowest was in stemwood. The content in needles was from 0.9 for the 3-year-old to 6.9 trha for the 27-year-old. Needle content accounted for 48% of N, 41% of P, 48% of K, 42% of Ca and 42% of Mg accumulated in total trees. The amount of nutrients was K ) Ca ) N ) Mg ) P in the 3- and 6-year-old, N ) Ca ) K ) Mg ) P in the 11and 17-year-old, N ) K ) Ca ) Mg ) P in the 21-year-old, and Ca ) N ) K ) Mg ) P in 27-year-old stand. Phosphorus content was the lowest and Mg second to the lowest in all stands. q 1998 Elsevier Science B.V. Keywords: Cunninghamia lanceolata ŽLamb.. Hook; Nutrient content; Nutrient concentration; Understorey vegetation; Litter
1. Introduction Chinese-fir Ž Cunninghamia lanceolata., an important native conifer, has been widely planted for more than 1000 years and used for a variety of wood products ŽWu, 1984.. Planting area has reached 6 million ha and accounted for 24% of all forested land in China ŽYu, 1988.. Its plantation productivity has remarkably declined because of deterioration of physical, chemical and biochemical activity, and nu)
Corresponding author.
trient depletion in soil ŽSheng, 1992; Fang, 1987. which resulted from successive cropping, short rotation and whole-tree harvest. This problem has become the great concern of Chinese forest soil and ecological scientists so far. Increasing wood yield is one of the main goals of modern forestry by proper practices, such as fertilising, selecting superior stock, and matching the species to the site. Undoubtedly growing the yield of species will increase nutrient drain from the site and alter its productivity. The growing awareness of the important role of biomass and nutrient patterns in
0378-1127r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 1 1 2 7 Ž 9 7 . 0 0 2 8 4 - 3
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H. Chen r Forest Ecology and Management 105 (1998) 209–216
forest ecosystems makes it increasingly necessary to understand and direct plantation nutrient management and related practices. There are considerable studies on biomass and nutrient distribution in a stand chronosquence, including Chinese-fir ŽPan et al., 1981., Douglas-fir Ž Pseudotsuga menziesii ŽMirb.. Franco. ŽTurner, 1981., balsam fir Ž Abies balsamea ŽL.. Mill. ŽSprugel, 1984., loblolly pine Ž Pinus taeda L.. ŽSwitzer and Nelson, 1972., radiata pine Ž Pinus radiata D. Don. ŽMadgwick et al., 1977., Scotch pine Ž Pinus sylÕestris L.. ŽOvington, 1957., lodgepole pine Ž Pinus contorta spp. latifolia ŽEngelm. ex Wats.. Critchfield. ŽPearson et al., 1987., paper birch Ž Betula papyrifera Marsh. ŽWang et al., 1996., trembling aspen Ž Populus tremuloides Michx.. ŽRuark and Bockheim, 1988. and other species. Although some researchers ŽPan et al., 1981, 1983; Hui et al., 1989; Ye and Jiang, 1983; Zhong and Hsiung, 1993; Xue, 1996; Nie, 1993. studied biomass and nutrient distribution in Chinese-fir plantations in order to elevate its productivity, little information is available on biomass and nutrient distribution during its stand development, except for the study ŽPan et al., 1981.. These results were not consistent with each other and it is hard to assess these findings because of the different sites and different stand ages. In this study, biomass and nutrient distribution in a Chinese-fir stand chronosquence were investigated on the same and typical site of its central growing area. The trends of biomass and nutrient distribution in the stand with the different development stages can be well presented and assessed each other. The objective of this study is Ža. quantify the potential nutrient drain from whole tree harvesting, Žb. to decide optimum application rate for the maximum yield, and Žc. to provide nutrient management strategies for maintaining the sustainability of its plantation in Southwest Hunan.
2. Study site The studied sites were located at Diling Forest Farm Ž1098 42X E and 26809X N. in Tongdao County, Southwest Hunan. It lies between the Yunnan– Guizhou Plateau and the Nanlin Mountains and is
Table 1 Soil properties in Chinese-fir plantations Items
Mean
Min.
Max.
pHŽH 2 O. pH ŽKCl. Organic Matter Žgrkg. Total N Žgrkg. Total P Žgrkg. Available N Žmgrkg. Available P Žmgrkg. Available KŽmgrkg. Exchangeable Ca Žcmolrkg. Exchangeable Mg Žcmolrkg.
4.78 3.46 15.4 0.59 0.14 61 0.6 47 1.89 0.95
4.52 3.20 7.7 0.45 0.08 32 0.1 34 1.03 0.84
4.92 3.59 35.0 0.98 0.23 142 1.6 59 3.17 1.20
one of the central growing area of Chinese-fir. This area has a subtropical monsoon climate with mean annual temperature of 16.38C, frost-free period of about 298 days per year, and mean annual rainfall of 1192–1744 mm occurring most in spring and summer and least in winter. The soil has an average depth of more than 1 m, and was red earth derived from shale. The gravel content in soil was relatively low. Its elevation was 350–450 m. The aspect is eastern and the slope is 18–258. The soil properties for Chinese-fir plantation are listed in Table 1 ŽChen and Li, 1996.. The representative understorey vegetation in stands was dominated by Boehmeria grandifolia Wedd., Rhododendron simssii Planch, Miscanthus floridulus ŽLabill.. Warb., Lespedeza bicolor Turcz., Broussonetia kaempferi Sieb., Echinochloa crusgalli ŽL.. Beauv., Artemisia argyi Levl. et Vant. etc. ŽChen and Li, 1993..
3. Methods 3.1. Biomass of Chinese-fir, understorey Õegetation and litter The studied plantations were selected from a population of pure Chinese-fir stands on the same site index ŽSl 16. and were classified by stand age in March 1996. They were established by the Diling Forest Farm and have been managed by the standard of fast growing and high yield plantation. The age sequence included was 3, 6, 11, 17, 21 and 27-yearold stands. The span of age sequence exceeded Chinese-fir’s rotation of cutting in this region, where it was usually about 25 years ŽWu, 1984..
H. Chen r Forest Ecology and Management 105 (1998) 209–216
The biomass of individual tree was measured in March and April 1996, using procedures outlined by Alban et al. Ž1978.. Three Ž20 = 20 m. replicated plots were established in each stand in an age sequence. Within the plots, tree height, and DBH were measured on all trees. Three dominant trees in each plot were harvested for biomass estimate and nutrient analysis. Fresh weight of all tree components was determined in the field. After falling, all branches with needles and twigs attached, which included a few dead branches in older stands, were removed from main stem and weighed fresh. All needles were separated from branches. Branch biomass included dead branches. All roots of the dominant trees greater than 2 mm were hand excavated. The soil particles attached the roots were removed. Root biomass included 15 cm stumps. Subsamples of stemwood Žcutting into small chips., stembark, branch, needle and root were oven-dried at 708C for 48 h to determine field moisture content. Fresh weights were converted into dry weights by moisture content. The biomass of understorey vegetation and litter were collected from three 1 m2 , randomly located points in each replicate of each stand. The three samples were individually weighed fresh in the field, oven-dried and re-weighed to estimate their biomass. 3.2. Chemical analysis The samples of tree components, understorey vegetation and litter in each stand was composited for chemical analysis, respectively. These samples were ground to pass through a 20 mesh screen after drying at 708C for 48 h. After 0.5 g of subsamples were digested by nitric–perchloric acid, total N concentration was determined by semi-micro Kjeldahl method, total P was determined colorimetrically by molybdate blue and total K by flame photometry ŽAgriochemistry Commission and Soil Science Society of China, 1983.. Calcium and Mg were assayed by an atomic absorption spectrophotometer ŽAgriochemistry Commission and Soil Science Society of China, 1983.. Nutrient content Žkgrha. of tree components was determined as the product of total biomass of each component and nutrient concentration of that component.
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3.3. Regression analysis and biomass estimation Regression coefficients for biomass equations were estimated using non-linear model procedure. Allometric models of the form, Y s aŽDBH 2 ) H . b , where Y is ovendry mass Žkg., DBH Ž1.3 m above ground level. is in cm and tree height Ž H . in m, were used to develop the equations for tree biomass components of the 54 sample trees. The equations were solved for all trees surveyed in the plots, giving estimates of biomass for five tree components: stemwood, stembark, branch, needle and root ŽTable 2.. Although some researchers used tree height ŽFeng and Chen, 1983. or DBH ŽWang et al., 1996. as independent variables for predicting the biomass of tree components, this model form, Y s aŽDBH 2 ) H . b , was useful in predicting the biomass of Chinese-fir components. The result was consistent with previous work ŽPan et al., 1981..
4. Results 4.1. Regression equations The equations are shown in Table 2. Allometric models, expressing dry weight of individual component as a function of DBH and H, had high R 2 values and accounted for 90%, 96%, 90%, 90% and 93% of variance in stemwood, stembark, branch, needle and root, respectively. 4.2. Biomass pattern in ecosystems of different ages In general, total biomass in the stand increased with stand age through 37.96 trha for the 3-year-old
Table 2 Equations for component biomass of sample trees Component
Equations
R2
n
Stemwood Stembark Branch Needle Root
Y s 0.0293ŽDBH 2 ) H . 0.9593 Y s 0.0154ŽDBH 2 ) H . 0.8824 Y s 0.000012ŽDBH 2 ) H .1.1770 Y s 0.0255ŽDBH 2 ) H .1.3508 Y s 0.0122ŽDBH 2 ) H . 0.9765
0.896 0.964 0.903 0.903 0.934
54 54 54 54 54
H. Chen r Forest Ecology and Management 105 (1998) 209–216
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Table 3 Biomass accumulation Žtrha. of Chinese-fir plantation in a chronosequence of 3, 6, 11, 17, 21, 27 in Southwest Hunan, China
litter, stembark, branch and root. Compared to a whole tree, nutrient concentration of understorey vegetation and litter was relatively high ŽTable 4.. There was an irregular change of nutrient concentration of tree components, understorey and litter with stand development ŽTable 5.. Total nutrient content in biomass by expressing the product of nutrient concentration and dry weight of each component are shown in Table 6. Generally, total nutrient content increased with stand age from 77.95 kgrha for the 3-year-old to 605.90 kgrha for the 27-year-old for N, from 18.51 kgrha to 38.20 kgrha for P, from 90.95 kgrha to 329.21 kgrha for K, from 91.05 kgrha to 637.91 kgrha for Ca, and from 41.08 kgrha to 162.14 kgrha for Mg ŽTable 6.. There was no remarkable trend in nutrient content of understorey vegetation with stand age, while the accumulation of nutrient in litter changed from 6.46 to 67.48 for N, 0.11 to 4.36 for P, 4.14 to 38.52 for K, 7.23 to 40.51 for Ca and 6.40 to 22.55 kgrha for Mg, as stand age increased ŽTable 6.. Needles accumulated the greatest percentage and understorey vegetation did the smallest on a weight basis of all the nutrients. Although needle biomass represented less than 13% of total tree ŽTable 3., this component accounted for 48% of N, 41% of P, 48% of K, 42% of Ca, and 42% of the Mg accumulated in Chinese-fir. In contrast, stemwood biomass represent 58% of total tree ŽTable 3., while this component accounted only for 18% of N, 27% of P, 13% of K, 15% of Ca, and 13% of Mg accumulated in trees. Like the allocation of their biomass, there was an increasing trend in the nutrient contents of stembark, branch and root with stand age increased ŽTables 3 and 6..
Component Stand ageŽyears. 3 Stemwood Stembark Branch Needle Root Understory Litter Total
6
11
17
21
27
18.76 22.62 61.31 109.21 113.35 185.87 4.53 7.03 16.55 18.49 17.41 29.11 4.76 6.67 12.07 10.04 11.93 17.34 5.33 9.18 18.63 17.51 18.11 17.16 4.58 6.95 9.31 8.07 11.97 19.34 0.36 0.37 0.51 0.42 0.41 0.38 0.87 1.34 1.90 2.78 5.39 6.91 39.19 54.16 120.28 166.52 178.57 276.11
to 268.82 trha for the 27-year-old stand ŽTable 3.. Obviously, tree biomass was greatly higher than that of understorey vegetation and litter, and comprised 97–98% of total biomass in these plantations. Of the total biomass, the greatest amount was in stemwood which increased rapidly with stand age. The least was in understorey vegetation, less than 0.5 trha Žexcept for 0.51 trha at 11 years.. Litter biomass was only higher than that of understorey vegetation. The increment of needle biomass was higher in earlier stage than in later years and varied little from the 11-year-old to the 27-year-old. There was an increasing trend in the biomass of stembark, branch and root with stand age ŽTable 3.. 4.3. Nutrition accumulation and distribution in stands Nutrient concentration changed considerably among all the components. Nitrogen and P in needles and K, Ca and Mg in understorey vegetation were highest and lowest in stemwood, and intermediate in
Table 4 Nutrient concentration Ž% of dry weight. of Chinese-fir components, understorey vegetation, litter for all stand age combined Component
N
P
K
Ca
Mg
Stemwood Stembark Branch Needle Root Understory Litter
0.080 Ž0.01. 0.253 Ž0.04. 0.424 Ž0.07. 1.047 Ž0.10. 0.268 Ž0.03. 1.018 Ž0.10. 0.931 Ž0.09.
0.013 Ž0.00. 0.026 Ž0.00. 0.040 Ž0.00. 0.094 Ž0.01. 0.029 Ž0.00. 0.087 Ž0.01. 0.038 Ž0.01.
0.041 Ž0.01. 0.211 Ž0.03. 0.281 Ž0.03. 0.680 Ž0.05. 0.281 Ž0.04. 0.719 Ž0.08. 0.559 Ž0.05.
0.057 Ž0.01. 0.419 Ž0.04. 0.128 Ž0.03. 0.785 Ž0.10. 0.297 Ž0.04. 0.825 Ž0.19. 0.813 Ž0.12.
0.018 Ž0.00. 0.098 Ž0.04. 0.203 Ž0.02. 0.292 Ž0.03. 0.131 Ž0.03. 0.775 Ž0.06. 0.673 Ž0.09.
Values within parentheses are standard error of mean.
H. Chen r Forest Ecology and Management 105 (1998) 209–216 Table 5 Nutrient concentration Ž% of dry weight. of Chinese-fir components, understorey vegetation and litter in all stands in Southwest Hunan, China Age
Component
N
P
K
Ca
Mg
3
Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter
0.05 0.15 0.16 0.68 0.15 1.26 0.74 0.09 0.26 0.33 0.84 0.25 0.92 0.66 0.08 0.12 0.53 1.32 0.32 0.62 0.93 0.06 0.31 0.48 1.13 0.27 0.96 1.32 0.13 0.36 0.54 1.25 0.29 1.20 0.97 0.07 0.32 0.40 1.07 0.33 1.15 0.98
0.02 0.03 0.05 0.16 0.05 0.05 0.01 0.01 0.04 0.04 0.10 0.03 0.09 0.02 0.01 0.02 0.04 0.09 0.02 0.10 0.02 0.01 0.03 0.04 0.08 0.03 0.10 0.07 0.02 0.02 0.05 0.07 0.03 0.09 0.04 0.01 0.02 0.03 0.07 0.01 0.10 0.06
0.04 0.17 0.27 0.85 0.19 1.08 0.48 0.04 0.32 0.25 0.72 0.22 0.85 0.43 0.03 0.20 0.17 0.50 0.31 0.60 0.57 0.03 0.26 0.34 0.71 0.30 0.68 0.76 0.07 0.16 0.37 0.71 0.47 0.57 0.55 0.03 0.16 0.29 0.59 0.19 0.54 0.58
0.05 0.39 0.32 0.54 0.20 0.82 0.83 0.07 0.58 0.50 0.94 0.27 0.48 1.35 0.04 0.33 0.50 0.76 0.39 0.31 0.81 0.07 0.33 0.36 0.70 0.24 0.57 0.66 0.04 0.38 0.48 0.56 0.45 1.39 0.65 0.07 0.50 0.40 1.21 0.24 1.37 0.59
0.01 0.07 0.17 0.25 0.12 0.89 0.74 0.01 0.06 0.16 0.24 0.10 0.75 0.76 0.03 0.31 0.29 0.38 0.18 0.50 0.90 0.01 0.05 0.15 0.22 0.07 0.87 0.85 0.02 0.05 0.25 0.32 0.23 0.92 0.47 0.02 0.05 0.20 0.35 0.09 0.72 0.33
6
11
17
21
27
11- and 17-year-old, N ) K ) Ca ) Mg ) P in the 21-year-old, and Ca ) N ) K ) Mg ) P in the 27year-old ŽTable 6.. Phosphorus content was the lowest and Mg content was next lowest in all the stands.
Table 6 Nutrient contents Žkgrha. of stands in an age sequence in Southwest Hunan, China Nutrient Component Stand age Žyears.
N
P
K
Ca
Mg
There were the highest accumulation of N, P, Mg in needles in the 11-year-old, of K in the 6-year-old, and of Ca in the 27-year-old stand ŽTable 6.. The amount of nutrients was K ) Ca ) N ) Mg ) P in the 3- and 6-year-old, N ) Ca ) K ) Mg ) P in the
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Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total
3
6
11
17
21
27
9.72 6.84 7.61 36.00 6.80 4.52 6.46 77.95 3.76 1.56 2.34 8.34 2.21 0.19 0.11 18.51 8.21 7.62 12.92 45.42 8.77 3.87 4.14 90.95 9.76 17.79 15.35 28.80 9.16 2.96 7.23 91.05 2.17 3.14 7.67 13.05 5.46 3.19 6.40 41.08
19.91 18.21 22.28 77.30 17.51 3.42 8.79 167.42 2.94 2.53 2.53 9.55 1.95 0.32 0.28 20.10 9.05 22.64 30.42 133.95 20.39 3.14 5.79 225.38 15.16 40.84 33.62 86.29 18.90 1.79 18.14 214.74 2.94 4.10 10.47 21.66 6.95 2.79 10.14 59.05
49.05 19.80 63.97 246.29 29.79 3.18 17.63 429.73 6.13 3.31 4.83 16.77 1.86 0.49 0.37 33.76 18.39 33.10 20.52 93.15 28.86 3.08 10.85 207.95 24.52 54.62 60.35 141.59 36.31 1.60 15.30 334.29 18.39 51.31 35.12 70.79 16.76 2.54 17.00 211.91
69.89 57.13 49.92 197.69 22.11 4.01 36.61 437.36 10.12 4.62 3.74 14.01 2.74 0.42 1.92 37.57 28.39 47.89 35.05 124.50 24.45 2.87 21.22 284.37 79.72 60.83 37.13 122.57 18.96 2.40 18.30 339.91 13.11 9.43 15.08 38.52 5.25 3.66 23.70 108.75
147.36 62.68 94.01 226.38 34.50 4.93 52.00 621.86 24.71 3.80 5.73 11.86 3.31 0.36 2.17 51.94 84.79 27.49 43.62 127.93 56.73 2.32 29.83 372.71 47.15 65.88 57.50 102.16 53.76 5.71 34.79 366.91 27.20 8.36 30.06 58.68 27.51 3.76 25.40 180.97
126.39 92.86 69.01 182.93 62.86 4.37 67.48 605.90 9.29 4.95 4.86 11.84 2.51 0.39 4.36 38.20 53.90 46.28 50.11 101.42 36.94 2.04 38.52 329.21 124.53 145.55 69.36 207.12 45.64 5.20 40.51 637.91 29.74 14.56 34.83 59.72 17.99 2.75 22.55 162.14
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5. Discussion 5.1. The approaches Due to the lack of the long-term background data concerning studied stands, the variations in sites and practical measures could exist, and to examine stand development through an age sequence ŽSprugel, 1984. may result in inaccurate conclusions, although they could be controlled by carefully selecting samples. The drawbacks of the approach were enumerated by some researchers ŽCrowell and Freedman, 1994.. Root biomass may also be slightly smaller than its real amount in stands because of collection difficulty. Generally, since average trees can reflect the stand nutrient capital, they are used to estimate biomass and nutrient content in a stand and to develop biomass regression equations ŽAlban et al., 1978.. In this study, since the optimum application rate based on the maximum yield of the stand in this region—target yield—was to be determined, dominant trees were selected to estimate biomass and nutrient content. Although this likely led to an overestimate of standing nutrient content of the whole plantation, this approach could ensure that there would be enough fertiliser to be applied to these plantations if our recommendation would be decided. This procedure for biomass estimate in order to decide application rate for the maximum yield is still studied further. 5.2. Biomass and nutrient content distributions Total biomass of Chinese-fir stands increased with stand age, as has been reported in previous studies ŽPan et al., 1981, 1983.. Because Chinese-fir is a self-thinning species and dead branches always keep on tree stem, the amount of litter was smaller ŽTable 3.. In the study, the stage of stand development should be noted ŽArmson, 1977.. Although many studies showed that nutrient concentration decreased with stand age ŽVan Hook et al., 1982; Wright and Will, 1958., this rule was no found in this study. As a stand grew and developed, nutrient allocation varied rapidly ŽTable 3.. In the earlier stage of development, nutrient contents in needles and branches comprised a larger proportion of total tree nutrient than
in later years ŽTable 6., although their biomass accounted for a lesser portion. The result was supported by a number of investigation ŽSwitzer et al., 1968; Pan et al., 1981, 1983; Wang et al., 1996; Xue, 1996.. In short rotations a greater proportion of the stand development period was taken up with the development of needles which were the most nutrient-rich portion of the biomass produced ŽArmson, 1977.. The main change in nutrient distribution was the flux, which can be expressed quantitatively as the amount of a nutrient element and its rate of transfer from soil to tree biomass. The amount of nutrients in needle biomass was more important for tree growth than that of other components of tree, which was only a small proportion except for in stemwood ŽTable 6., and some of which was often removed from forest sites because of harvesting. Early thinning practice should aim to leave the branch attaching needles on the site so that residual tree nutrition can be improved by reduced competition and the addition of nutrients to forest floor. Understorey vegetation may also be important in improving soil fertility and play a key role in nutrient cycling processes ŽLittle and Shainsky, 1995., because of fast decomposition and retention of nutrients in soil. 5.3. Implications of different harÕest intensity If these stands, for example, 27-year-old stand, were harvested more nutrients would be extracted from the sites if the entire aboveground trees were taken than if only the boles were removed. The nutrient drain rate of N, P, K, Ca and Mg by the former was 2.4, 2.4, 2.9, 2.2 and 3.5 times as many as by the later ŽTable 6.. The nutrient removal Ž471 N, 30.5 P, 251 K, 546 Ca and 26 Mg kgrha. by aboveground tree harvesting in 27-year-old stand ŽTable 6. was smaller than in 40-year-old spruce stand, and greater than in 40-year-old red pine and jack pine stand in North-central Minnesota, USA ŽAlban et al., 1978.. By combining data on tree height and condition of the existing stand, with a knowledge of nutrient requirements of following species, one can assess the probability that additional nutrient removals in a whole-tree harvest will prove detrimental to site productivity ŽHendrickson et al., 1987.. Some scientists reported that nutrient removal
H. Chen r Forest Ecology and Management 105 (1998) 209–216
from forest land reduced the growth of succeeding trees ŽLutz and Chandler, 1946.. Previous agricultural use of sandy soils in eastern North America led to poor growth of subsequently planted red pine, which could be corrected by K fertilisation ŽLeaf et al., 1975; Wittwer et al., 1975.. In infertile soils in Europe where a high percentage of total nutrients was contained in the vegetation, harvesting this vegetation resulted in reduced growth of subsequent forest stands ŽRennie, 1957.. In Australia and New Zealand, the second rotation of P. radiata ŽD. Don. has frequently produced lower yields than the first ŽKeeves, 1966; Whyte, 1973.. In some cases this has been proved to be due to nitrogen deficiency ŽStone and Will, 1965.. The incidence of nutrient depletion can be expected to increase as more intensive forest management removes more nutrients though shorter rotations, and more complete tree utilisation ŽAlban et al., 1978.. The findings provided support for the general practice of bole-only harvesting. For wholetree utilisation, the nutrient supplying potential of the site need to be quantified, and then will be adjusted by species selection, fertilisation, adjustment of rotation length, and other management strategies.
Acknowledgements I would like to thank Mr. Lu Youjun for his reliable and patient assistance in the field; two anonymous reviewers for helpful comments on the manuscript. This study was funded by the Scientific and Technological funding, CAF.
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IUFRO-Conference Effects of Environmental Factors on Tree and Stand Growth. Dresden, Germany, pp. 311–317. Crowell, M., Freedman, B., 1994. Vegetation development in a hardwood-forest chronosequence in Nova Scotia. Can. J. For. Res. 24, 260–271. Fang, Q., 1987. Effect of Chinese fir successive cropping on soil fertility and tree growth. Sci. Silvae Sinicae 23 Ž4., 389–397, Žin Chinese.. Feng, Z.W., Chen, C.Y., 1983. Studies on the production of young Chinese fir communities. Acta Ecol. Sinica 3 Ž2., 119–130, Žin Chinese.. Hendrickson, O.Q., Burgess, D.M., Chatarpaul, L., 1987. Biomass and nutrients in Great Lakes–St. Lawrence forest species: implications for whole-tree and conventional harvest. Can. J. For. Res. 17, 210–218. Hui, G.Y., Luo, Y.W., Zhang, X.L., 1989. A study on the productivity of Chinese-fir plantation at hilly area in Dagang Mt., Jiangxi Province. Sci. Silvae Sinicae 25 Ž6., 564–569, Žin Chinese.. Keeves, A., 1966. Some evidence of the loss of productivity with successive rotation in P. radiata in Southeast of South Australia. Aust. For. 30, 51–63. Leaf, A.L., Leonard, R.E., Wittwer, R.F., Bickelhaupt, D.H., 1975. Four-year growth response of plantation red pine to potash fertilization and irrigation in New York. For. Sci. 21, 89–96. Little, S.N., Shainsky, L.J., 1995. Biomass and nutrient distributions in Central Oregon second-growth ponderosa pine ecosystems. Res. Pap. PNW-RP-481. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Portland, OR, 17 pp. Lutz, H.J., Chandler, R.F., 1946. Forest Soils. Wiley, New York. Madgwick, H.A.I., Jackson, D.S., Knight, P.J., 1977. Aboveground dry matter, energy, and nutrient contents of trees in an age series of Pinus radiata plantations. N.Z. J. For. Sci. 7, 445–468. Nie, D.P., 1993. A comparison of the productivity and nutrient cycling of Chinese-fir plantation in different site conditions. For. Res. 6 Ž6., 643–649, Žin Chinese.. Ovington, J.D., 1957. Dry-matter production by Pinus sylÕestris L. Ann. Bot. N.S. 21, 287–314. Pan, W.C., Tian, D.L., Li, L.C., Gao, Z.H., 1981. Studies on nutrient cycling in Chinese fir plantation: I. Output composition and nutrient trends in different age stands. J. South China For. Coll. 1, 1–21, Žin Chinese.. Pan, W.C., Tian, D.L., Lei, Z.X., Kang, W.X., 1983. Studies on nutrient cycling in Chinese fir plantation: II. Nutrient content, accumulation rate and biocycling of a quick-growth stand in hill. J. South China For. Coll. 3, 1–16, Žin Chinese.. Pearson, J.A., Knight, D.H., Fahey, T.J., 1987. Biomass and nutrient accumulation during stand development in Wyoming lodgepole pine forests. Ecology 68 Ž6., 1966–1973. Rennie, P.J., 1957. Uptake of nutrients by timber forest and its importance to timber production in Britain. Q. J. For. 51, 101–115. Ruark, G.A., Bockheim, J.G., 1988. Biomass, net primary production, and nutrient distribution for an age sequence of Populus tremuloides ecosystems. Can. J. For. Res. 18, 435–443.
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Sheng, W.T., 1992. Soil degradation and its control techniques for timber plantations in China. In: Sheng, W.T. ŽEd.., Research on Site Degradation of Timber Plantation. Chinese Science and Technology Press, Beijing, pp. 15–19 Žin Chinese.. Sprugel, D.G., 1984. Density, biomass, productivity, and nutrient-cycling changes during stand development in wave-regenerated balsam fir forests. Ecol. Monogr. 54, 165–186. Stone, E.L., Will, G.M., 1965. Nitrogen deficiency of second generation radiata pine in New Zealand. In: Youngberg, C.T. ŽEd.., Proceeding of the 2nd N. Am. For. Soils Conference, pp. 117–139. Switzer, G.L., Nelson, L.E., Smith, W.H., 1968. The mineral cycle in forest stands. In: Forest Fertilization: Theory and Practice. Tessessee Valley Authority, Muscle Shoals, pp. 1–9. Switzer, G.L., Nelson, L.E., 1972. Nutrient accumulation and cycling in loblolly pine plantation ecosystems: the first twenty years. Soil Sci. Soc Am. Proc. 36, 143–147. Turner, J., 1981. Nutrient cycling in an age sequence of western Washington Douglas-fir stands. Ann. Bot. ŽLondon. 48, 159– 169. Van Hook, R.I., Johnson, D.W., Mann, L.K., 1982. Environmental effects of harvesting forests for energy. For. Ecol. Manage. 4, 79–94. Wang, J.R., Zhong, A.L., Simard, S.W., Kimmins, J.P., 1996.
Aboveground biomass and nutrient accumulation in an age sequence of paper birch in the Interior Cedar Hemlock zone, British Columbia. For. Ecol. Manage. 83, 27–38. Whyte, A.G.D., 1973. Productivity of first and second crops of Pinus radiata on the Mountere gravel soils of Nelson. N.Z. J. For. 18, 87–103. Wittwer, R.F., Leaf, A.L., Leonard, R.E., Bickelhaupt, D.H., 1975. Biomass and chemical composition of fertilized andror irrigated Pinus resinosa Ait. plantations. Plant Soil 42, 629– 651. Wright, T.W., Will, G.M., 1958. The nutrient content of Scots and Corsican pines growing on sand dunes. Forestry 31, 13–25. Wu, Z.L., 1984. Chinese-fir. Forestry of China Publications, Beijing Žin Chinese.. Xue, L., 1996. Nutrient cycling in a Chinese-fir stand on a poor site in Yishan, Guangxi. For. Ecol. Manage. 89, 115–123. Ye, J.Z., Jiang, Z.L., 1983. The biomass and its structure in Chinese-fir stand in South Jiangsu hill. Acta Ecol. Sinica 3 Ž1., 7–14, Žin Chinese.. Yu, X.T., 1988. The research of Chinese-fir in China. J. Fujian Coll. For. 8, 203–220, Žin Chinese.. Zhong, A.L., Hsiung, W.Y., 1993. Evaluation and diagnosis of tree nutritional status in Chinese-fir plantations, Jiangxi, China. For. Ecol. Manage. 62, 245–270.
Biomass and nutrient distribution in a Chinese-fir plantation chronosequence in Southwest Hunan, China Hongjun Chen
)
Department of Forest Soils, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China Received 4 February 1997; accepted 23 September 1997
Abstract Biomass and nutrient distribution were measured in a Chinese-fir plantation chronosequence in Southwest Hunan. Total tree biomass of 3, 6, 11, 17, 21 and 27-year-old stands was 38, 52, 118, 163, 173 and 269 trha, respectively. Biomass of understorey vegetation was the smallest, less than 1 trha, and there was an irregular change with stand age, while litter increased with stand age from 0.87 for the 3-year-old to 6.91 trha for the 27-year-old. Biomass of stemwood was the highest, accounted for 58% of the stand, while nutrient content in stemwood was relatively small, 18% of N, 27% of P, 13% of K, 15% of Ca and 13% of Mg accumulated in total trees. The highest nutrient concentration was found in needles and understorey vegetation and the lowest was in stemwood. The content in needles was from 0.9 for the 3-year-old to 6.9 trha for the 27-year-old. Needle content accounted for 48% of N, 41% of P, 48% of K, 42% of Ca and 42% of Mg accumulated in total trees. The amount of nutrients was K ) Ca ) N ) Mg ) P in the 3- and 6-year-old, N ) Ca ) K ) Mg ) P in the 11and 17-year-old, N ) K ) Ca ) Mg ) P in the 21-year-old, and Ca ) N ) K ) Mg ) P in 27-year-old stand. Phosphorus content was the lowest and Mg second to the lowest in all stands. q 1998 Elsevier Science B.V. Keywords: Cunninghamia lanceolata ŽLamb.. Hook; Nutrient content; Nutrient concentration; Understorey vegetation; Litter
1. Introduction Chinese-fir Ž Cunninghamia lanceolata., an important native conifer, has been widely planted for more than 1000 years and used for a variety of wood products ŽWu, 1984.. Planting area has reached 6 million ha and accounted for 24% of all forested land in China ŽYu, 1988.. Its plantation productivity has remarkably declined because of deterioration of physical, chemical and biochemical activity, and nu)
Corresponding author.
trient depletion in soil ŽSheng, 1992; Fang, 1987. which resulted from successive cropping, short rotation and whole-tree harvest. This problem has become the great concern of Chinese forest soil and ecological scientists so far. Increasing wood yield is one of the main goals of modern forestry by proper practices, such as fertilising, selecting superior stock, and matching the species to the site. Undoubtedly growing the yield of species will increase nutrient drain from the site and alter its productivity. The growing awareness of the important role of biomass and nutrient patterns in
0378-1127r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 1 1 2 7 Ž 9 7 . 0 0 2 8 4 - 3
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forest ecosystems makes it increasingly necessary to understand and direct plantation nutrient management and related practices. There are considerable studies on biomass and nutrient distribution in a stand chronosquence, including Chinese-fir ŽPan et al., 1981., Douglas-fir Ž Pseudotsuga menziesii ŽMirb.. Franco. ŽTurner, 1981., balsam fir Ž Abies balsamea ŽL.. Mill. ŽSprugel, 1984., loblolly pine Ž Pinus taeda L.. ŽSwitzer and Nelson, 1972., radiata pine Ž Pinus radiata D. Don. ŽMadgwick et al., 1977., Scotch pine Ž Pinus sylÕestris L.. ŽOvington, 1957., lodgepole pine Ž Pinus contorta spp. latifolia ŽEngelm. ex Wats.. Critchfield. ŽPearson et al., 1987., paper birch Ž Betula papyrifera Marsh. ŽWang et al., 1996., trembling aspen Ž Populus tremuloides Michx.. ŽRuark and Bockheim, 1988. and other species. Although some researchers ŽPan et al., 1981, 1983; Hui et al., 1989; Ye and Jiang, 1983; Zhong and Hsiung, 1993; Xue, 1996; Nie, 1993. studied biomass and nutrient distribution in Chinese-fir plantations in order to elevate its productivity, little information is available on biomass and nutrient distribution during its stand development, except for the study ŽPan et al., 1981.. These results were not consistent with each other and it is hard to assess these findings because of the different sites and different stand ages. In this study, biomass and nutrient distribution in a Chinese-fir stand chronosquence were investigated on the same and typical site of its central growing area. The trends of biomass and nutrient distribution in the stand with the different development stages can be well presented and assessed each other. The objective of this study is Ža. quantify the potential nutrient drain from whole tree harvesting, Žb. to decide optimum application rate for the maximum yield, and Žc. to provide nutrient management strategies for maintaining the sustainability of its plantation in Southwest Hunan.
2. Study site The studied sites were located at Diling Forest Farm Ž1098 42X E and 26809X N. in Tongdao County, Southwest Hunan. It lies between the Yunnan– Guizhou Plateau and the Nanlin Mountains and is
Table 1 Soil properties in Chinese-fir plantations Items
Mean
Min.
Max.
pHŽH 2 O. pH ŽKCl. Organic Matter Žgrkg. Total N Žgrkg. Total P Žgrkg. Available N Žmgrkg. Available P Žmgrkg. Available KŽmgrkg. Exchangeable Ca Žcmolrkg. Exchangeable Mg Žcmolrkg.
4.78 3.46 15.4 0.59 0.14 61 0.6 47 1.89 0.95
4.52 3.20 7.7 0.45 0.08 32 0.1 34 1.03 0.84
4.92 3.59 35.0 0.98 0.23 142 1.6 59 3.17 1.20
one of the central growing area of Chinese-fir. This area has a subtropical monsoon climate with mean annual temperature of 16.38C, frost-free period of about 298 days per year, and mean annual rainfall of 1192–1744 mm occurring most in spring and summer and least in winter. The soil has an average depth of more than 1 m, and was red earth derived from shale. The gravel content in soil was relatively low. Its elevation was 350–450 m. The aspect is eastern and the slope is 18–258. The soil properties for Chinese-fir plantation are listed in Table 1 ŽChen and Li, 1996.. The representative understorey vegetation in stands was dominated by Boehmeria grandifolia Wedd., Rhododendron simssii Planch, Miscanthus floridulus ŽLabill.. Warb., Lespedeza bicolor Turcz., Broussonetia kaempferi Sieb., Echinochloa crusgalli ŽL.. Beauv., Artemisia argyi Levl. et Vant. etc. ŽChen and Li, 1993..
3. Methods 3.1. Biomass of Chinese-fir, understorey Õegetation and litter The studied plantations were selected from a population of pure Chinese-fir stands on the same site index ŽSl 16. and were classified by stand age in March 1996. They were established by the Diling Forest Farm and have been managed by the standard of fast growing and high yield plantation. The age sequence included was 3, 6, 11, 17, 21 and 27-yearold stands. The span of age sequence exceeded Chinese-fir’s rotation of cutting in this region, where it was usually about 25 years ŽWu, 1984..
H. Chen r Forest Ecology and Management 105 (1998) 209–216
The biomass of individual tree was measured in March and April 1996, using procedures outlined by Alban et al. Ž1978.. Three Ž20 = 20 m. replicated plots were established in each stand in an age sequence. Within the plots, tree height, and DBH were measured on all trees. Three dominant trees in each plot were harvested for biomass estimate and nutrient analysis. Fresh weight of all tree components was determined in the field. After falling, all branches with needles and twigs attached, which included a few dead branches in older stands, were removed from main stem and weighed fresh. All needles were separated from branches. Branch biomass included dead branches. All roots of the dominant trees greater than 2 mm were hand excavated. The soil particles attached the roots were removed. Root biomass included 15 cm stumps. Subsamples of stemwood Žcutting into small chips., stembark, branch, needle and root were oven-dried at 708C for 48 h to determine field moisture content. Fresh weights were converted into dry weights by moisture content. The biomass of understorey vegetation and litter were collected from three 1 m2 , randomly located points in each replicate of each stand. The three samples were individually weighed fresh in the field, oven-dried and re-weighed to estimate their biomass. 3.2. Chemical analysis The samples of tree components, understorey vegetation and litter in each stand was composited for chemical analysis, respectively. These samples were ground to pass through a 20 mesh screen after drying at 708C for 48 h. After 0.5 g of subsamples were digested by nitric–perchloric acid, total N concentration was determined by semi-micro Kjeldahl method, total P was determined colorimetrically by molybdate blue and total K by flame photometry ŽAgriochemistry Commission and Soil Science Society of China, 1983.. Calcium and Mg were assayed by an atomic absorption spectrophotometer ŽAgriochemistry Commission and Soil Science Society of China, 1983.. Nutrient content Žkgrha. of tree components was determined as the product of total biomass of each component and nutrient concentration of that component.
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3.3. Regression analysis and biomass estimation Regression coefficients for biomass equations were estimated using non-linear model procedure. Allometric models of the form, Y s aŽDBH 2 ) H . b , where Y is ovendry mass Žkg., DBH Ž1.3 m above ground level. is in cm and tree height Ž H . in m, were used to develop the equations for tree biomass components of the 54 sample trees. The equations were solved for all trees surveyed in the plots, giving estimates of biomass for five tree components: stemwood, stembark, branch, needle and root ŽTable 2.. Although some researchers used tree height ŽFeng and Chen, 1983. or DBH ŽWang et al., 1996. as independent variables for predicting the biomass of tree components, this model form, Y s aŽDBH 2 ) H . b , was useful in predicting the biomass of Chinese-fir components. The result was consistent with previous work ŽPan et al., 1981..
4. Results 4.1. Regression equations The equations are shown in Table 2. Allometric models, expressing dry weight of individual component as a function of DBH and H, had high R 2 values and accounted for 90%, 96%, 90%, 90% and 93% of variance in stemwood, stembark, branch, needle and root, respectively. 4.2. Biomass pattern in ecosystems of different ages In general, total biomass in the stand increased with stand age through 37.96 trha for the 3-year-old
Table 2 Equations for component biomass of sample trees Component
Equations
R2
n
Stemwood Stembark Branch Needle Root
Y s 0.0293ŽDBH 2 ) H . 0.9593 Y s 0.0154ŽDBH 2 ) H . 0.8824 Y s 0.000012ŽDBH 2 ) H .1.1770 Y s 0.0255ŽDBH 2 ) H .1.3508 Y s 0.0122ŽDBH 2 ) H . 0.9765
0.896 0.964 0.903 0.903 0.934
54 54 54 54 54
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Table 3 Biomass accumulation Žtrha. of Chinese-fir plantation in a chronosequence of 3, 6, 11, 17, 21, 27 in Southwest Hunan, China
litter, stembark, branch and root. Compared to a whole tree, nutrient concentration of understorey vegetation and litter was relatively high ŽTable 4.. There was an irregular change of nutrient concentration of tree components, understorey and litter with stand development ŽTable 5.. Total nutrient content in biomass by expressing the product of nutrient concentration and dry weight of each component are shown in Table 6. Generally, total nutrient content increased with stand age from 77.95 kgrha for the 3-year-old to 605.90 kgrha for the 27-year-old for N, from 18.51 kgrha to 38.20 kgrha for P, from 90.95 kgrha to 329.21 kgrha for K, from 91.05 kgrha to 637.91 kgrha for Ca, and from 41.08 kgrha to 162.14 kgrha for Mg ŽTable 6.. There was no remarkable trend in nutrient content of understorey vegetation with stand age, while the accumulation of nutrient in litter changed from 6.46 to 67.48 for N, 0.11 to 4.36 for P, 4.14 to 38.52 for K, 7.23 to 40.51 for Ca and 6.40 to 22.55 kgrha for Mg, as stand age increased ŽTable 6.. Needles accumulated the greatest percentage and understorey vegetation did the smallest on a weight basis of all the nutrients. Although needle biomass represented less than 13% of total tree ŽTable 3., this component accounted for 48% of N, 41% of P, 48% of K, 42% of Ca, and 42% of the Mg accumulated in Chinese-fir. In contrast, stemwood biomass represent 58% of total tree ŽTable 3., while this component accounted only for 18% of N, 27% of P, 13% of K, 15% of Ca, and 13% of Mg accumulated in trees. Like the allocation of their biomass, there was an increasing trend in the nutrient contents of stembark, branch and root with stand age increased ŽTables 3 and 6..
Component Stand ageŽyears. 3 Stemwood Stembark Branch Needle Root Understory Litter Total
6
11
17
21
27
18.76 22.62 61.31 109.21 113.35 185.87 4.53 7.03 16.55 18.49 17.41 29.11 4.76 6.67 12.07 10.04 11.93 17.34 5.33 9.18 18.63 17.51 18.11 17.16 4.58 6.95 9.31 8.07 11.97 19.34 0.36 0.37 0.51 0.42 0.41 0.38 0.87 1.34 1.90 2.78 5.39 6.91 39.19 54.16 120.28 166.52 178.57 276.11
to 268.82 trha for the 27-year-old stand ŽTable 3.. Obviously, tree biomass was greatly higher than that of understorey vegetation and litter, and comprised 97–98% of total biomass in these plantations. Of the total biomass, the greatest amount was in stemwood which increased rapidly with stand age. The least was in understorey vegetation, less than 0.5 trha Žexcept for 0.51 trha at 11 years.. Litter biomass was only higher than that of understorey vegetation. The increment of needle biomass was higher in earlier stage than in later years and varied little from the 11-year-old to the 27-year-old. There was an increasing trend in the biomass of stembark, branch and root with stand age ŽTable 3.. 4.3. Nutrition accumulation and distribution in stands Nutrient concentration changed considerably among all the components. Nitrogen and P in needles and K, Ca and Mg in understorey vegetation were highest and lowest in stemwood, and intermediate in
Table 4 Nutrient concentration Ž% of dry weight. of Chinese-fir components, understorey vegetation, litter for all stand age combined Component
N
P
K
Ca
Mg
Stemwood Stembark Branch Needle Root Understory Litter
0.080 Ž0.01. 0.253 Ž0.04. 0.424 Ž0.07. 1.047 Ž0.10. 0.268 Ž0.03. 1.018 Ž0.10. 0.931 Ž0.09.
0.013 Ž0.00. 0.026 Ž0.00. 0.040 Ž0.00. 0.094 Ž0.01. 0.029 Ž0.00. 0.087 Ž0.01. 0.038 Ž0.01.
0.041 Ž0.01. 0.211 Ž0.03. 0.281 Ž0.03. 0.680 Ž0.05. 0.281 Ž0.04. 0.719 Ž0.08. 0.559 Ž0.05.
0.057 Ž0.01. 0.419 Ž0.04. 0.128 Ž0.03. 0.785 Ž0.10. 0.297 Ž0.04. 0.825 Ž0.19. 0.813 Ž0.12.
0.018 Ž0.00. 0.098 Ž0.04. 0.203 Ž0.02. 0.292 Ž0.03. 0.131 Ž0.03. 0.775 Ž0.06. 0.673 Ž0.09.
Values within parentheses are standard error of mean.
H. Chen r Forest Ecology and Management 105 (1998) 209–216 Table 5 Nutrient concentration Ž% of dry weight. of Chinese-fir components, understorey vegetation and litter in all stands in Southwest Hunan, China Age
Component
N
P
K
Ca
Mg
3
Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter Stemwood Stembark Branch Needle Root Understory Litter
0.05 0.15 0.16 0.68 0.15 1.26 0.74 0.09 0.26 0.33 0.84 0.25 0.92 0.66 0.08 0.12 0.53 1.32 0.32 0.62 0.93 0.06 0.31 0.48 1.13 0.27 0.96 1.32 0.13 0.36 0.54 1.25 0.29 1.20 0.97 0.07 0.32 0.40 1.07 0.33 1.15 0.98
0.02 0.03 0.05 0.16 0.05 0.05 0.01 0.01 0.04 0.04 0.10 0.03 0.09 0.02 0.01 0.02 0.04 0.09 0.02 0.10 0.02 0.01 0.03 0.04 0.08 0.03 0.10 0.07 0.02 0.02 0.05 0.07 0.03 0.09 0.04 0.01 0.02 0.03 0.07 0.01 0.10 0.06
0.04 0.17 0.27 0.85 0.19 1.08 0.48 0.04 0.32 0.25 0.72 0.22 0.85 0.43 0.03 0.20 0.17 0.50 0.31 0.60 0.57 0.03 0.26 0.34 0.71 0.30 0.68 0.76 0.07 0.16 0.37 0.71 0.47 0.57 0.55 0.03 0.16 0.29 0.59 0.19 0.54 0.58
0.05 0.39 0.32 0.54 0.20 0.82 0.83 0.07 0.58 0.50 0.94 0.27 0.48 1.35 0.04 0.33 0.50 0.76 0.39 0.31 0.81 0.07 0.33 0.36 0.70 0.24 0.57 0.66 0.04 0.38 0.48 0.56 0.45 1.39 0.65 0.07 0.50 0.40 1.21 0.24 1.37 0.59
0.01 0.07 0.17 0.25 0.12 0.89 0.74 0.01 0.06 0.16 0.24 0.10 0.75 0.76 0.03 0.31 0.29 0.38 0.18 0.50 0.90 0.01 0.05 0.15 0.22 0.07 0.87 0.85 0.02 0.05 0.25 0.32 0.23 0.92 0.47 0.02 0.05 0.20 0.35 0.09 0.72 0.33
6
11
17
21
27
11- and 17-year-old, N ) K ) Ca ) Mg ) P in the 21-year-old, and Ca ) N ) K ) Mg ) P in the 27year-old ŽTable 6.. Phosphorus content was the lowest and Mg content was next lowest in all the stands.
Table 6 Nutrient contents Žkgrha. of stands in an age sequence in Southwest Hunan, China Nutrient Component Stand age Žyears.
N
P
K
Ca
Mg
There were the highest accumulation of N, P, Mg in needles in the 11-year-old, of K in the 6-year-old, and of Ca in the 27-year-old stand ŽTable 6.. The amount of nutrients was K ) Ca ) N ) Mg ) P in the 3- and 6-year-old, N ) Ca ) K ) Mg ) P in the
213
Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total Stemwood Stembark Branch Needle Root Understory Litter Total
3
6
11
17
21
27
9.72 6.84 7.61 36.00 6.80 4.52 6.46 77.95 3.76 1.56 2.34 8.34 2.21 0.19 0.11 18.51 8.21 7.62 12.92 45.42 8.77 3.87 4.14 90.95 9.76 17.79 15.35 28.80 9.16 2.96 7.23 91.05 2.17 3.14 7.67 13.05 5.46 3.19 6.40 41.08
19.91 18.21 22.28 77.30 17.51 3.42 8.79 167.42 2.94 2.53 2.53 9.55 1.95 0.32 0.28 20.10 9.05 22.64 30.42 133.95 20.39 3.14 5.79 225.38 15.16 40.84 33.62 86.29 18.90 1.79 18.14 214.74 2.94 4.10 10.47 21.66 6.95 2.79 10.14 59.05
49.05 19.80 63.97 246.29 29.79 3.18 17.63 429.73 6.13 3.31 4.83 16.77 1.86 0.49 0.37 33.76 18.39 33.10 20.52 93.15 28.86 3.08 10.85 207.95 24.52 54.62 60.35 141.59 36.31 1.60 15.30 334.29 18.39 51.31 35.12 70.79 16.76 2.54 17.00 211.91
69.89 57.13 49.92 197.69 22.11 4.01 36.61 437.36 10.12 4.62 3.74 14.01 2.74 0.42 1.92 37.57 28.39 47.89 35.05 124.50 24.45 2.87 21.22 284.37 79.72 60.83 37.13 122.57 18.96 2.40 18.30 339.91 13.11 9.43 15.08 38.52 5.25 3.66 23.70 108.75
147.36 62.68 94.01 226.38 34.50 4.93 52.00 621.86 24.71 3.80 5.73 11.86 3.31 0.36 2.17 51.94 84.79 27.49 43.62 127.93 56.73 2.32 29.83 372.71 47.15 65.88 57.50 102.16 53.76 5.71 34.79 366.91 27.20 8.36 30.06 58.68 27.51 3.76 25.40 180.97
126.39 92.86 69.01 182.93 62.86 4.37 67.48 605.90 9.29 4.95 4.86 11.84 2.51 0.39 4.36 38.20 53.90 46.28 50.11 101.42 36.94 2.04 38.52 329.21 124.53 145.55 69.36 207.12 45.64 5.20 40.51 637.91 29.74 14.56 34.83 59.72 17.99 2.75 22.55 162.14
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5. Discussion 5.1. The approaches Due to the lack of the long-term background data concerning studied stands, the variations in sites and practical measures could exist, and to examine stand development through an age sequence ŽSprugel, 1984. may result in inaccurate conclusions, although they could be controlled by carefully selecting samples. The drawbacks of the approach were enumerated by some researchers ŽCrowell and Freedman, 1994.. Root biomass may also be slightly smaller than its real amount in stands because of collection difficulty. Generally, since average trees can reflect the stand nutrient capital, they are used to estimate biomass and nutrient content in a stand and to develop biomass regression equations ŽAlban et al., 1978.. In this study, since the optimum application rate based on the maximum yield of the stand in this region—target yield—was to be determined, dominant trees were selected to estimate biomass and nutrient content. Although this likely led to an overestimate of standing nutrient content of the whole plantation, this approach could ensure that there would be enough fertiliser to be applied to these plantations if our recommendation would be decided. This procedure for biomass estimate in order to decide application rate for the maximum yield is still studied further. 5.2. Biomass and nutrient content distributions Total biomass of Chinese-fir stands increased with stand age, as has been reported in previous studies ŽPan et al., 1981, 1983.. Because Chinese-fir is a self-thinning species and dead branches always keep on tree stem, the amount of litter was smaller ŽTable 3.. In the study, the stage of stand development should be noted ŽArmson, 1977.. Although many studies showed that nutrient concentration decreased with stand age ŽVan Hook et al., 1982; Wright and Will, 1958., this rule was no found in this study. As a stand grew and developed, nutrient allocation varied rapidly ŽTable 3.. In the earlier stage of development, nutrient contents in needles and branches comprised a larger proportion of total tree nutrient than
in later years ŽTable 6., although their biomass accounted for a lesser portion. The result was supported by a number of investigation ŽSwitzer et al., 1968; Pan et al., 1981, 1983; Wang et al., 1996; Xue, 1996.. In short rotations a greater proportion of the stand development period was taken up with the development of needles which were the most nutrient-rich portion of the biomass produced ŽArmson, 1977.. The main change in nutrient distribution was the flux, which can be expressed quantitatively as the amount of a nutrient element and its rate of transfer from soil to tree biomass. The amount of nutrients in needle biomass was more important for tree growth than that of other components of tree, which was only a small proportion except for in stemwood ŽTable 6., and some of which was often removed from forest sites because of harvesting. Early thinning practice should aim to leave the branch attaching needles on the site so that residual tree nutrition can be improved by reduced competition and the addition of nutrients to forest floor. Understorey vegetation may also be important in improving soil fertility and play a key role in nutrient cycling processes ŽLittle and Shainsky, 1995., because of fast decomposition and retention of nutrients in soil. 5.3. Implications of different harÕest intensity If these stands, for example, 27-year-old stand, were harvested more nutrients would be extracted from the sites if the entire aboveground trees were taken than if only the boles were removed. The nutrient drain rate of N, P, K, Ca and Mg by the former was 2.4, 2.4, 2.9, 2.2 and 3.5 times as many as by the later ŽTable 6.. The nutrient removal Ž471 N, 30.5 P, 251 K, 546 Ca and 26 Mg kgrha. by aboveground tree harvesting in 27-year-old stand ŽTable 6. was smaller than in 40-year-old spruce stand, and greater than in 40-year-old red pine and jack pine stand in North-central Minnesota, USA ŽAlban et al., 1978.. By combining data on tree height and condition of the existing stand, with a knowledge of nutrient requirements of following species, one can assess the probability that additional nutrient removals in a whole-tree harvest will prove detrimental to site productivity ŽHendrickson et al., 1987.. Some scientists reported that nutrient removal
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from forest land reduced the growth of succeeding trees ŽLutz and Chandler, 1946.. Previous agricultural use of sandy soils in eastern North America led to poor growth of subsequently planted red pine, which could be corrected by K fertilisation ŽLeaf et al., 1975; Wittwer et al., 1975.. In infertile soils in Europe where a high percentage of total nutrients was contained in the vegetation, harvesting this vegetation resulted in reduced growth of subsequent forest stands ŽRennie, 1957.. In Australia and New Zealand, the second rotation of P. radiata ŽD. Don. has frequently produced lower yields than the first ŽKeeves, 1966; Whyte, 1973.. In some cases this has been proved to be due to nitrogen deficiency ŽStone and Will, 1965.. The incidence of nutrient depletion can be expected to increase as more intensive forest management removes more nutrients though shorter rotations, and more complete tree utilisation ŽAlban et al., 1978.. The findings provided support for the general practice of bole-only harvesting. For wholetree utilisation, the nutrient supplying potential of the site need to be quantified, and then will be adjusted by species selection, fertilisation, adjustment of rotation length, and other management strategies.
Acknowledgements I would like to thank Mr. Lu Youjun for his reliable and patient assistance in the field; two anonymous reviewers for helpful comments on the manuscript. This study was funded by the Scientific and Technological funding, CAF.
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