Data from: Carbon stocks and dynamics at different successional stages in an Afromontane tropical forest

As a result of different types of disturbance, forests are a mixture of stands at different stages of ecological succession. Successional stage is likely to influence forest productivity and carbon storage, linking the degree of forest disturbance to the global carbon cycle and climate. Although tropical montane forests are an important part of tropical forest ecosystems (c. 8 %, elevation > 1000 m a.s.l.), there are still significant knowledge gaps regarding the carbon dynamics and stocks of these forests, and how these differ between early (ES) and late successional (LS) stages. This study examines the carbon (C) stock, relative growth rate (RGR), and net primary production (NPP) of ES and LS forest stands in an Afromontane tropical rainforest using data from inventories of quantitatively important ecosystem compartments in fifteen 0.5 ha plots in Nyungwe National Park in Rwanda. The total C stock was 35 % larger in LS compared to ES plots due to significantly larger above ground biomass (AGB; 185 and 76 Mg C ha−1 in LS and ES plots, respectively), while the soil and root C stock (down to 45 cm depth in the mineral soil) did not significantly differ between the two successional stages (178 and 204 Mg C ha−1 in LS and ES plots, respectively). The main reasons for the difference in AGB were that ES trees had significantly lower stature and wood density compared to LS trees. However, ES and LS stands had similar total NPP (canopy, wood and roots of all plots ~ 9.4 Mg C ha−1) due to counterbalancing effects of differences in AGB (higher in LS stands) and RGR (higher in ES stands). The AGB in the LS plots was considerably higher than the average value reported for old-growth tropical montane forest of Southeast Asia and central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of different regions. The results of this study highlight the importance of accounting for disturbance regimes and differences in wood density and allometry of tree species dominating at different successional stages in attempts to quantify the C stock and sink strength of tropical montane forests and how it may differ among continents.受不同类型干扰影响，森林由处于不同生态演替（ecological succession）阶段的林分混合组成。演替阶段（successional stage）可能影响森林生产力与碳储量，进而将森林干扰程度与全球碳循环及气候相联系。尽管热带山地森林（tropical montane forests）是热带森林生态系统（tropical forest ecosystems）的重要组成部分（约占8%，海拔高于1000米a.s.l.），但学界对这类森林的碳动态（carbon dynamics）与碳库（carbon stocks），以及其在早期演替（ES）与晚期演替（LS）阶段间的差异仍存在显著认知空白。 本研究依托卢旺达尼亚恩圭国家公园内15块0.5公顷样地的定量重要生态系统组分调查数据，探究了非洲山地热带雨林中早期演替与晚期演替林分的碳（C）储量、相对生长速率（RGR）及净初级生产力（NPP）。 研究结果显示，晚期演替样地的总碳储量较早期演替样地高出35%，这一差异源于地上生物量（AGB）的显著不同：晚期演替与早期演替样地的AGB分别为185与76 Mg C ha⁻¹；而矿质土壤（mineral soil，深度至45厘米）及根系碳储量在两类演替阶段间无显著差异，二者对应值分别为178与204 Mg C ha⁻¹。 造成地上生物量差异的核心原因为，早期演替树木的株高与木材密度（wood density）均显著低于晚期演替树木。不过，早期演替与晚期演替林分的总净初级生产力相近（所有样地的冠层、木质部及根系碳通量约为9.4 Mg C ha⁻¹），这是由于地上生物量（晚期演替林分更高）与相对生长速率（早期演替林分更高）的差异产生了抵消效应。 晚期演替样地的地上生物量显著高于东南亚、中美洲及南美洲同海拔、同温度条件下的原始热带山地森林平均水平，且量级与不同区域的热带低地森林相当。 本研究结果强调，在量化热带山地森林的碳储量与汇强度（sink strength），以及不同大陆间的差异时，需考量干扰制度（disturbance regimes）、不同演替阶段优势树种的木材密度与异速生长（allometry）差异。