岷江上游亚高山林区老龄林地上生物量动态变化

Dynamics of aboveground biomass of sub-alpine old-growth forest in the upper Minjiang River(UMR)

中国川西亚高山森林中的天然林大部分为成过熟的老龄林,对其生物量动态研究有助于了解其碳储量的动态变化规律。利用全国森林资源连续清查的27个固定样地数据,基于地上各器官生物量与树干胸径(D)和树高(h)的异速生长方程,估算了岷江上游亚高林山老龄林地上生物量密度的动态变化特征及其时空变化规律。结果表明,(1)从1988～2002年期间,老龄林地上生物量密度净增量为(27.311±15.580)Mg·hm-2,平均每年增长率为(1.930±1.091)Mg·hm-2·a-1,平均每年枯损率为(2.271±1.424)Mg.hm-.2a-1;(2)地上生物量变化受各径级保留木生长量、枯损量及进界生长量影响,其中20～40cm径级保留木生长量与生物量净增量最大,>80cm径级生物量增量最小,40～60cm和60～80cm径级生物量在调查期间净增量出现负增长。(3)岷江上游老龄林地上生物量动态变化具有时空异质性,同一样地在不同调查间隔期或同一调查期间不同样地间生物量变化不同,不仅有增量数值大小差异,还表现为生物量增量的正负差异。

Majority of the natural forests in UMR are mature and over-mature.Acturate estimation of the Biomass in the old-growth forests will help quatify actual carbon sequestration and carbon sink size.The allometric equations of the relationship between above-ground biomass（AGB）of various tree organs and diameter at breast height（DBH）and tree height,which are constructed on the 4 consecutive forest resource inventory data of 27 permanent plots,was used to explore the dynamics of the above-ground biomass density（AGBD）and its temporal and spatial variation of sub-alpine old-growth forest in UMR.The results showed：（1）the net increase in AGBD was（27.311±15.580）Mg·hm-2 while the mean annual growth rate and the mean annual mortality rate were（1.930±1.091）Mg·hm-2·a-1 and（2.271±1.424）Mg·hm-2·a-1 during 1988-2002,respectively.（2）the AGB depended largely on the growth and mortality rate of the remaining trees of different DBH classes and recruitment rate from one DBH class to another as well.The largest increment component of AGB came from DBH class at 20 cm to 40 cm,whereas the minimum increment component of AGB was above 80 cm.The net negative increment of AGB occurred at DBH ranging from 40-60cm to 60-80cm.（3）There were temporal and spatial variations of AGB in the alpine old-growth forests as AGB changed over time for the same sampling plot and AGB varied with location or sites for the same period.The variations not only reflected in numerical value but also in positive or negative biomass increment.