Abstract
Abstract. 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 (ca. 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), 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). 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 south-east Asia and Central and South America at similar elevations and temperatures, and of the same magnitude as in tropical lowland forest of these 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 an attempt to quantify the C stock and sink strength of tropical montane forests and how they may differ among continents.
Highlights
Tropical forests store 40–50 % of the carbon (C) in terrestrial biomass (Phillips et al, 1998; Lewis et al, 2009) and account for one-third of global terrestrial net primary productivity (Saugier et al, 2001; Malhi et al, 2014b), thereby contributing significantly to the global C cycle and climate
Plots 13–15 located at ca. 500 m lower elevation compared to the others had a mean air temperature of 15.5 ± 0.06 ◦C and an annual precipitation of 3016 ± 63 mm during the same period
The daily mean soil temperatures were similar to the air temperatures, but with lower mean diurnal amplitudes (1.9 ◦C in the soil compared to 6.1 ◦C in air)
Summary
Tropical forests store 40–50 % of the carbon (C) in terrestrial biomass (Phillips et al, 1998; Lewis et al, 2009) and account for one-third of global terrestrial net primary productivity (Saugier et al, 2001; Malhi et al, 2014b), thereby contributing significantly to the global C cycle and climate. In addition to their influence on climate, tropical forests provide other important ecosystem services such as food, wood products, erosion control, biodiversity protection and water regulation (Costanza et al, 1997; Alamgir et al, 2016). Despite of being the world’s second largest tropical forest block, African tropical forests have drawn little attention in terms of C cycling research compared to their counterparts in South America and southeast Asia (Lewis et al, 2009; Malhi et al, 2013a, b)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
