The Arctic oscillation, climatic variability, and biotic factors influenced seedling dynamics in a Caribbean moist forest.

We assessed the influence of the Arctic oscillation (AO) on local climate (using data from 2004 to 2009), their influence and the effects of heterospecific density on seedling dynamics (from January 2006 to August 2009), using data from 120 25-m2 subplots established in a moist tropical forest over limestone in Jamaica. The AO index (AOI) had a positive nonlinear relationship with mean monthly rainfall and the number of days with rain. Also, there was a significant increase in mean monthly atmospheric temperature in 2006, which coincided with a global temperature increase. Overall, at the community level, as temperature increased, mortality increased and then decreased. Also, mortality was significantly lower in plots with higher densities and those that experienced the positive phase of the AO. The effect of the AO on relative growth rate (RGR) of height (RGRh) varied as the AOI increased from negative to positive, while the number of days with rainfall had a positive effect on recruitment. However, these relationships differed during three six-month and two 12-month sample periods. There was a drought during the first period (dry season) during the negative phase of the AO; consequently, mortality was highest during this period. As the AOI increased (negative to positive), both mortality and RGRh declined while recruitment increased, culminating in a high-recruitment event. In addition, as the number of days with rainfall increased, RGR of diameter (RGRd) values were more positive (indicating that moisture stress was alleviated). During the second period (wet season), mortality increased as seedling density increased (possibly due to increased competition). Additionally, elevated temperature had a significant negative effect on RGRh (again, possibly due to increased competition or due to elevated respiratory carbon loss at higher growth temperatures). After the first two censuses, temperature and the AO influenced dynamics marginally, and seedling heterospecific density became increasingly important (lower mortality at higher densities). At the population level, the number of days with rainfall was the most frequent predictor of dynamics followed by temperature, AO, density and rainfall, and they were largely beneficial.