| Accumulation of forest biomass provides the basis for material cycle and energy flow in ecosystems.It determines the stability and species deversity of ecosystem,and plays an important role in global carbon cycle.Investigations on the determinants of forest biomass is not only important for seeking the mechanisms how ecosystems work,but also crucial for restoring the degraded forests and predicting the carbon budget of forests.This research focuses on several typical pine forests,larch forests and oak forests in China.Field measurement data(including stand age,aboveground biomass,canopy density,etc.)on 118 pine forest stands,126 larch forest stands and 159 oak forest stands have been collected from published literatures.Eight climatic indices,including mean annual temperature(MAT),mean annual bio-temperature(BT),mean annual potential evapotranspiration(APE),warmth index(WI),coldness index(CI),mean annual precipitation(MAP),humidity index(HI)and mean annual actual evapotranspiration(AE),are selected to describe the climatic effect on aboveground biomass(AGB).Mutiple statistical analyses are conducted for stands at three levels of canopy density(0.2?1.0,0.2?0.7 and 0.7?1.0).The relationships among AGB,stand age and climate are established,and the best regression equations and dominant climatic factors are obtained.We also analyze the effects of stand age and climate on AGB,and discuss the underlying ecophysiological reasons responsible for the different dominant climatic factors with different forest types.Moreover,the spatial data of dominant climatic factors are used to predict the potential patterns of AGB and carbon sequestration for each forest type.The main results are listed as following:(1)With the canopy density at 0.2-0.7,the determination coefficients(R2)of the relationships among stand age,climate and AGB for Pinus forest,Pinus tabulaeformis forest,Pinus massoniana forest,Larix forest,Larix gmelini forest,Larix kaempferi forest,Quercus forest and Quercus liaotungensis forest are 0.517,0.412,0.519,0.519,0.000,0.764,0.201 and 0.205 respectively.With the canopy density at 0.7?1.0,the determination coefficients are 0.855,0.851,0.819,0.781,0.849,0.833,0.605 and 0.755.With the canopy density at 0.2?1.0,the determination coefficients are 0.668,0.746,0.738,0.409,0.573,0.447,0.202 and 0.319.In comparison,the regression equations are best fitted at the canopy density level 0.7?1.0.(2)With the canopy density at 0.7?1.0,the explanatory powers of stand age on AGB of Pinus forest,Pinus tabulaeformis forest,Pinus massoniana forest,Larix forest,Larix gmelini forest,Larix kaempferi forest,Quercus forest and Quercus liaotungensis forest are 58.8%,69.3%,68.4%,30.9%,26.9%,56.3%,32.3%and 41.5%respectively.Among all the climatic factors considered,AE,MAP,CI,CI,AE,CI,AE and MAP are found as the dominant factors determining AGB for these forest types.Their explanatory powers are 26.7%,15.8%,13.5%,47.2%,58.1%,27.0%,28.2%and 34.0%.After fixxing the effect of stand age,the partial correlation coefficients between AGB and these climatic factors are 0.806,0.717,0.654,0.826,0.891,0.786,0.646 and 0.762.(3)With the canopy density at 0.7?1.0,if stand age is treated as the unique fact to predict AGB,the mean relative errors are 13.3%,4.5%,3.6%,21.2%,20.6%,3.6%,5.7%and 3.5%for Pinus forest,Pinus tabulaeformis forest,Pinus massoniana forest,Larix forest,Larix gmelini forest,Larix kaempferi forest,Quercus forest and Quercus liaotungensis forest respectively,and the mean absolute values of relative errors are 35.1%,19.2%,16.6%,42.4%,47.2%,14.6%,20.5%and 17.6%.If both stand age and dominant climatic factor are used to predict AGB,the mean relative errors are 4.2%,2.1%,2.1%,6.0%,5.6%,1.0%,2.8%and 1.5%respectively,and the mean absolute values of relative errors are 20.9%,12.0%,11.7%,21.7%,18.2%,6.3%,15.4%and 10.8%.Thus taking both stand age and climate into consideration could predict AGB much better than merely considering stand age.(4)In the study area of each forest type,the potential AGB exhibits different patterns with the changes of stand age and dominant climatic factors.AGB of Pinus forest decreases from southeast to northwest,and the 20-,60-,and 100-year-old forests can sequester 14.6,30.4 and 37.8 Pg C respectively.AGB of Pinus tabulaeformis forest decreases from southeast to northwest,and the 20-,40-,and 60-year-old forests can sequester 2.30,4.95,6.50 Pg C.AGB of Pinus massoniana forest decreases from south to north,and the 15-,35-,and 55-year-old forests can sequester 4.03,6.88,8.40 Pg C.AGB of Larix forest decreases from south to north,and the 30-,90-,and 150-year-old forests can sequester 10.7,17.2,20.3 Pg C.AGB of Larix gmelini forest decreases from east to west,and the 30-,90-,and 150-year-old forests can sequester 3.18,5.12,6.02 Pg C.AGB of Larix kaempferi forest decreases from south to north,and the 20-,40-,and 60-year-old forests can sequester 6.28,9.75,11.8 Pg C.AGB of Quercus forest decreases from southeast to northwest,and the 30-,60-,and 90-year-old forests can sequester 6.58,9.56,11.3 Pg C.AGB of Quercus liaotungensis forest decreases from southeast to northwest,and the 40-,65-,and 90-year-old forests can sequester 0.99,1.85,2.43 Pg C.In this study,the dominant factors determining AGB of forests are selected,and accurate prediction equations for AGB are established.We also estimate the potential AGB and carbon sequestraion at the distribution areas of each forest type.This research is of great value in seeking the mechanisms of forest biomass accumulation,restoring the degraded forests and planning forestation for carbon sink. |
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