Tropical rainforests – adapted to a thermally stable climate – may be particularly vulnerable to climate change but this hypothesis remains poorly evaluated due to data scarcity.
In a unique TRopical Elevation gradient Experiment in Rwanda – Rwanda TREE – we examine the sensitivity of tropical trees to warming and altered water supply. Multi-species plantations have been established at sites with large variation in climate, and with additional water and nutrient manipulation treatments applied at each site. We also study tree ecophysiology and ecosystem processes in permanent monitoring plots established in Nyungwe forest – one of Africa’s largest remaining tropical montane rainforests.
Our research in Rwanda TREE and Nyungwe is collaborative, involving researchers from the University of Rwanda (UR), the University of Gothenburg, and Rwanda Agriculture and Animal Resources Development Board (RAB). The scientific overall aim of our research is to:
Determine the climate and climate change sensitivity of tropical trees and forest processes.
More specifically, we explore:
Tree physiological and morphological responses and acclimation capacity to heat and drought
Mechanisms and processes controlling tree growth, mortality and climate-induced shifts in tree community composition
Re- and afforestation potential using native tree species
Carbon stocks and fluxes of tropical montane forests with different tree community composition (due to successional stage or climate)
The project has strong connections with stakeholders and policy makers within the forestry/agroforestry sector in Rwanda and the societal vision is to: Promote tree plantation with native species and tree/forest-based climate change adaptation and mitigation in Rwanda.
This is a 6-minute film about the Rwanda TREE project, also cut into smaller pieces shown at other places at this webpage.
This far, our published research (see papers under Publications) has shown that montane rainforests are very productive and contain more biomass and carbon than their counterparts in South America (Nsabimana 2009, Nyirambangutse et al. 2017, Cuni-Sanchez et al. 2021). We have shown that the photosynthesis of montane late-successional tree species is sensitive to increased temperature (Vårhammar et al. 2015, Dusenge et al. 2015, Mujawamariya 2021, Wittemann et al. 2022) and that the reduction in photosynthesis during the dry season is much stronger at warmer locations than at cooler places at higher elevation (Mujawamariya et al. 2018 and 2021). Moreover, the capacity of trees to acclimate photosynthetic biochemistry to warming is limited (Dusenge et al. 2021) and the heat tolerance threshold may be exceeded in late-successional species grown in a warmer climate (Tarvainen et al. 2022). We further found that leaf morphological responses to climate varies greatly among species and successional groups (Manishimwe et al. 2022) and that leaf respiration exhibits complete or over-compensatory acclimation to warming (Mujawamariya et al. 2021). Comparisons of early- and late-successional species have revealed contrasting photosynthetic nitrogen dependencies (Dusenge et al. 2015, Hasper et al. 2017, Ziegler et al. 2020) and traits controlling shade tolerance (Ntawuhiganayo et al. 2020). Our results have been used in several global meta-analyses (Lin et al. 2015, De Kauwe et al. 2016, Kumarathunge et al. 2019, Cuni-Sanchez et al. 2021, Crous et al. 2022, Ellsworth et al. 2022).
In ongoing research, we explore how photosynthetic heat tolerance/avoidance, leaf chemical and morphological traits and tree hydraulics influence tropical tree growth, mortality and community composition in a warmer and drier climate. Results of our research has important implications for tree plantation success, forest carbon storage and biodiversity in Rwanda and beyond.
Part of research team at a meeting at the Biology Department, University of Rwanda, in 2017.
From the left: Myriam Mujawamariya, Etienne Zibera, Johan Uddling, Aloysie Manishimwe, Elisée Bahati Ntawuhiganayo (MSc student), Félicien Uwizeye (MSc student), Donat Nsabimana, Bonaventure Ntirugulirwa, Göran Wallin.