Table_2_Aboveground Deadwood Biomass and Composition Along Elevation and Land-Use Gradients at Mount Kilimanjaro.docx

Deadwood is an important structural and functional component of forest ecosystems and biodiversity. As deadwood can make up large portions of the total aboveground biomass, it plays an important role in the terrestrial carbon (C) cycle. Nevertheless, in tropical ecosystems and especially in Africa, quantitative studies on this topic remain scarce. We conducted an aboveground deadwood inventory along two environmental gradients—elevation and land use— at Mt. Kilimanjaro, Tanzania. We used a huge elevation gradient (3690 m) along the southern slope of the mountain to investigate how deadwood is accumulated across different climate and vegetation zones. We also compared habitats that differed from natural forsts in land-use intensity and disturbance history to assess anthropogenic influence on deadwood accumulation. In our inventory we distinguished coarse woody debris (CWD) from fine woody debris (FWD). Furthermore, we calculated the C and nitrogen (N) content of deadwood and how the C/N ratio varied with decomposition stages and elevation. Total amounts of aboveground deadwood ranged from 0.07 ± 0.04 to 73.78 ± 36.26 Mg ha–1 (Mean ± 1 SE). Across the elevation gradient, total deadwood accumulation was highest at mid-elevations and reached a near-zero minimum at very low and very high altitudes. This unimodal pattern was mainly driven by the corresponding amount of live aboveground biomass and the combined effects of decomposer communities and climate. Land-use conversion from natural forests into traditional homegardens and commercial plantations, in addition to frequent burning, significantly reduced deadwood biomass, but not past selective logging after 30 years of recovery time. Furthermore, we found that deadwood C content increased with altitude. Our study shows that environmental gradients, especially temperature and precipitation, as well as different anthropogenic disturbances can have considerable effects on both the quantity and composition of deadwood in tropical forests.

枯木质残体（Deadwood）是森林生态系统与生物多样性的重要结构与功能组成部分。由于枯木质残体可占地上总生物量的较大比例，其在陆地碳（C）循环中发挥着关键作用。然而，针对热带生态系统，尤其是非洲区域的相关定量研究仍较为匮乏。本研究在坦桑尼亚乞力马扎罗山沿海拔与土地利用两条环境梯度开展了地上枯木质残体调查。研究依托该山南坡跨度达3690米的海拔梯度，探究枯木质残体在不同气候与植被带的积累规律。同时，本研究对比了土地利用强度与干扰历史不同于天然林的生境，以评估人类活动对枯木质残体积累的影响。本次调查中，我们将木质残体区分为粗木质残体（CWD）与细木质残体（FWD）两类。此外，我们测定了枯木质残体的碳与氮（N）含量，并分析了碳氮比随分解阶段与海拔的变化规律。地上枯木质残体总储量介于0.07±0.04至73.78±36.26 Mg ha⁻¹之间（均值±标准误1 SE）。沿海拔梯度，枯木质残体总积累量在中海拔区域达到峰值，而在极低与极高海拔处则接近零值。这种单峰分布格局主要受地上活生物量的对应水平，以及分解者群落与气候的综合作用所驱动。天然林向传统家庭菜园与商业人工林的土地利用转型，加之频繁的火烧，均显著降低了枯木质残体生物量；但经过30年恢复期的既往选择性择伐则未产生此类影响。此外，我们发现枯木质残体的碳含量随海拔升高而增加。本研究表明，环境梯度（尤其是温度与降水梯度）以及不同类型的人为干扰，均可对热带森林中枯木质残体的储量与组成产生显著影响。