NYUNGWE FOREST PLOTS

In addition to Rwanda TREE, we also conduct studies of tree ecophysiology and ecosystem processes in Nyungwe tropical montane rainforest located in south-western Rwanda, ranging from 1600 to 2950 m in elevation. Nyungwe forest was declared a national park in 2004. It covers an area of 1013 km2 and is the largest remaining middle-elevation montane rainforest in central Africa. At a meteorological station located at Uwinka (2465 m a.s.l. elevation), the average day and night air temperatures are around 16 and 14 °C, respectively.

Nyungwe forest hosts a large biodiversity, supporting approximately 1100 vascular plant species (of which 230 are trees), 280 bird species and is home to 13 species of primates. The forest contains various ecosystems, ranging from dense forest and bamboo groves to marshes. In late 2011 and early 2012, 15 permanent plots with a planimetric area of 0.5 ha (100 x 50 m) were established. The plots were arranged along a 32 km-long east–west transect at an elevation of ca. 1950 to 2500 m. Forest stands ranging from a dominance of early-successional to a dominance of late-successional species were included, but areas with recent and extensive disturbance were excluded. All individual woody plants with a breast height diameter ≥ 5 cm have been mapped and measured for estimation of C stock and productivity at repeated censuses. In addition, canopy and belowground processes such as photosynthesis, leaf and soil respiration and fine root production have been measured in campaigns.

Our research in Nyungwe, together with comparative studies on the same species at Arboretum of Ruhande, has shown that this montane rainforest is very productive and contain more biomass and carbon than its counterparts in South America and Asia (Nyirambangutse et al. 2017). It has also indicated that some tree species are physiologically very sensitive to increased temperature (Vårhammar et al. 2015, Dusenge et al. 2015, Ntawuhiganayo et al. 2020) and that the reduction in photosynthesis during the dry season is much stronger at warmer, lower-elevation locations than at higher elevation (Mujawamariya et al. 2018). Moreover, the research on photosynthesis has indicated that negative heat effects are considerably stronger in late- compared to early-successional species. This in turn suggests that a warmer climate with more pronounced droughts will not only affect individual species’ performance but also the tree community composition of tropical forests. These results from our research in Nyungwe forest greatly inspired the idea, proposal and design of Rwanda TREE!