OOS 30-4 - An overview of the influences of biotic and abiotic factors on the tree species community of the Luquillo Forest Dynamics Plot in Puerto Rico

The Luquillo Forest Dynamics Plot (LFDP) is a 16-ha plot located in subtropical wet forest in northeastern Puerto Rico. It serves as a living laboratory to observe tree species interactions and effects on forest community composition and structure in the context of multiple disturbance factors, including historical land use legacies, severe hurricanes, and more recently, droughts. Since 1990 we have collected data on self-supporting woody seedlings and trees, plant pathogens, and fungal communities, among other taxa, and have conducted analyses to explore the effects of their interactions on tropical forest dynamics and successional processes. Examination of abiotic and biotic factors associated with above-ground pathogens and the foliar damage they cause on tree seedlings revealed that interspecific variation in tree species abundance leads to differences in the magnitude and type of damage tropical tree seedlings experience. Tree species of intermediate abundance host a greater richness of generalist and specialist enemies, and suffer higher levels of foliar damage, relative to common tree species. The relationships between tree seedling damage and enemies appears to be mediated by arbuscular mycorrhizal fungi (AMF), which vary in abundance and diversity between early vs mid- and late-successional tree species. Interactions of tree seedlings with AMF diversity can also counteract negative effects of foliar damage on seedling mortality, thereby fostering tree species coexistence at the community scale.

Other LFDP research on the role of historical land use and hurricanes in shaping seedling phylogenetic and functional community structure highlighted the importance of both the abiotic environment (e.g., light availability, soil type, topography), and biotic interactions such as with conspecific species on post-disturbance forest recovery. Heterogeneity in soil moisture is a main driver of seedling survival and plays a central role in buffering or exacerbating impacts of climate fluctuations on forest regeneration. Modeling the effects of hurricane damage and neighborhood competitive interactions for species representing a variety of life history strategies has helped our understanding of the complex relationships among tree size, growth, and survival under different abiotic regimes, and the biotic interactions of hurricane-induced stem damage and tree crowding. Results from a forest simulator suggested that over time historical land use and hurricane disturbance will generate novel forest communities with a mixture of early and late successional forest species. Our findings provide important insights about the interplay of abiotic and biotic interactions that can help us forecast the long-term effects of climate change on tropical forests.