CoEB SEMINAR SERIES BY: Megan K Sullivan, PhD, Fulbright Scholar, Rwanda 2023-2024.

Recent studies on tropical tree phenology (e.g. the timing of life events such as flowering and fruiting in trees) show that climate and phenology are inextricably linked, highlighting the importance of studying phenological patterns as a key indicator of climate change. Studying these phenology patterns is not only important for understanding climate-plant relationships, but also to understand the cascading impacts that phenological shifts might have on other organisms,
such as animals that depend on fruit trees as a food source. Some studies from lowland tropical forests find that declines in fruit production over long time periods are associated with negative impacts on frugivorous wildlife. However, whether we will find similar drastic patterns in fruit production at other sites and cascading impacts on different wildlife species is unclear, because climate change can play out differently based on site-specific contexts and wildlife speciesspecific traits. To understand how fruit production has been changing over time in a diverse
montane tropical forest, we analyzed the long-term overall shifts in fruit production over time and shifts in seasonal fruiting peaks in Nyungwe National Park, Rwanda. Additionally, we explored patterns in chimpanzee movement and diet over time in the park, to see if changes in
chimpanzee movement or behavior was occurring concurrently with changes in fruiting patterns. Our analyses explore cascading impacts of fruit shifts on wildlife using more than two decades of tree crown phenology monitoring, and records of chimpanzee movement patterns and diet in
Nyungwe NP. We found that there was a gradual increase in fruit production over time in our
high-elevation forest ecosystem, the opposite pattern found in lowland forests. Additionally, we
observed changes in the timing of seasonal fruiting peaks over the study period – at the
beginning of the observation period, community-level fruiting peaks occurred during the dry
season (June-July), while in recent years fruiting peaks occurred in the wet season (April).
Looking at individual tree species, we saw that most species had stable fruit production over
time, and a few species had big or gradual increases in fruit production – and that some of these
species were important fruit species for chimpanzees. We are currently exploring how these
fruiting patterns are related to some key chimpanzee behaviors – such as movement patterns,
space use (e.g. exiting protected areas for crop-raiding), and frequency of hunting. Overall, our
study highlights how understanding tropical tree functioning can help us better predict key
impacts of climate change on tropical forest ecosystems, and how providing this information to
park managers can help better inform wildlife conservation strategies and protected area
management planning.