LB 31-260 - Assessment of masting behavior in a tropical wet forest in Puerto Rico.

Evald Maceno, Miguel Leon, and Jess K. ZimmermanProject title: Assessment of masting behavior in a tropical wet forest in Puerto Rico.Abstract: Large pulses of seed production occur in many tree species every few years in many forest types. Masting behavior in trees is hypothesized to be driven a variety of factors, including resources allocation predator satiation, disturbance and weather patterns. This study examines the interannual patterns of reproduction in the Luquillo Experimental Forest in Puerto Rico focusing on evidence of masting behavior and potential explanations. We analyzed 30+ years (1992-2022) of fruit and seed production records in the 16- ha Luquillo Forest Dynamics Plot using 120 0.5 m2 traps visited biweekly. The community was composed of 70 species of shrubs, trees, and climbers of various types. We included only those species found in 5 % or more of the traps to ensure more than one individual was sampled. We used the coefficient of variation (CV > 1) to identify potential masting species in the community. Our findings indicated that more than 50 % of the community exhibit masting behavior by this standard. No species, however, exhibited negative autocorrelation of seed production, indicative of synchronized endogenous (i.e., resource-based) reproductive cycles. This suggests an importance of disturbance events or other environmental triggers of masting behavior. We then identified years of high seed production in individual species using the deviation from long-term mean method. All species exhibited masting by this standard, even those with a CV < 1. However, only a handful of peaks among species fell within four years of major disturbance events (two strong hurricanes [1998. 2017], and one major drought [2015]) thus disturbance did not seem to be a major driver of masting behavior. Overall, pairwise synchronicity among all species was positively skewed. However, this appeared to be a result of a general negative trend in reproduction in many species rather than synchronized masting behavior. This may be because of hurricane Hugo (1989) before the start of the time series. This was the first major hurricane to strike the region in 57 years, before the most recent ones, thus having lagged effects on the entire community. Beyond this, we suggest that other, unidentified environmental conditions may be critical to triggering peaks of seed production in this tropical forest.