Christopher "Grant" Tolley, MF

2010 TRI Fellow in Panama

Functional convergence or niche differentiation? An analysis of foliar nutrient content of secondary succession plant communities in a former agricultural landscape in Panama

The evidence for the economic importance and ecosystem services provided by tropical secondary forests continues to mount. However, secondary succession is extremely varied and the mechanisms that determine secondary forest structure and function are not fully understood. This study investigates the mechanisms that drive the composition and structure of tropical secondary plant communities in an abandoned cattle pasture and agricultural landscape in Panama by quantifying the differences in evolutionary life strategy between tree species as indicated by foliar macronutrient allocation. The synthesis and allocation of macronutients to leaf tissue by plants has led to a diversity of strategies and corresponding trade-offs that can be conceptualized as leaf economics. Understanding how these plant nutrient investments vary between species, plant functional types, and the communities of different biomes is critical for determining how nutrient fluxes and community composition are shaped by land-use history and potential future disturbances like climate change. This study goes one step further by examining the influence of age and species composition on foliar nutrient levels during tropical secondary succession and combining foliar nutrient data with four plant functional traits generally recognized as indicators of life strategy to determine if levels of inter- and intra-specific variation in foliar nutrients in abundant species indicate merely functional convergence or suggest niche differentiation. Specifically, leaf functional traits were collected from 65 species along 56 transects in 28 sites of varied successional age and analyzed for foliar nutrient content (C, N, C:N, P, N:P), specific leaf area (SLA), foliar lignin, foliar cellulose, and wood density. From these data, the following questions were investigated:

1) How do foliar nutrients vary among species and with successional age and, therefore, what do these levels reveal about the mechanisms of secondary forest assemblage?

2) How are foliar nutrients associated with four other plant traits commonly associated with life strategy (SLA, foliar lignin, foliar cellulose, and wood density)?

Fieldwork was conducted at the Agua Salud Project in Panama, a joint research project between the Smithsonian Tropical Research Institute (STRI), the Panama Canal Authority (ACP), and the Panamanian Ministry of the Environment (ANAM). The results of this research will enhance our understanding of the mechanisms that determine community composition and function of tropical secondary forests.