Temporal trait plasticity predicts the growth of tropical trees

Questions: Linking tree growth dynamics to functional traits and neighborhood conditions that are measured at a single time point gives limited insights into the direction of forest structural and functional change. We used trait and neighborhood data collected at different time points for each individual tree of 15 Ficus species to test how trait (temporal trait plasticity) and neighborhood crowding change over time, and to test how their temporal change affects individual growth rate. We asked the following questions: (i) how do traits, neighborhood crowding, and growth of individual trees change over time; (ii) are functional traits and neighborhood crowding temporally consistent in their association with growth rate of individuals; and (iii) do temporal trait plasticity and changes in neighborhood crowding better predict the relative growth rate of individuals compared to using only a single snapshot of traits and neighborhood crowding?. Location: Xishuangbanna Tropical Seasonal Rainforest, southwest China. Methods: We collected traits (specific leaf area [SLA], leaf area (LA), leaf dry matter content [LDMC], leaf chlorophyll, leaf thickness, and leaf succulence) at two time points (2010 and 2017) for 472 individuals of 15 Ficus species. We used linear mixed-effect models to test the effect of temporal trait plasticity and neighborhood crowding on the relative growth rate of individuals. Results: We found that the temporal change in trait values predicts the growth rate of individuals better compared to static trait values in the initial and final censuses. We found significant temporal changes in individual traits suggesting a shift in ecological strategies from being acquisitive to conservative. A difference in neighborhood crowding between the two census years was also observed, indicating that the neighborhood effect on growth might also change over time. Conclusions: Our results in general highlight the need to consider the temporal dimension of traits and biotic interactions, as our results suggest that growth–trait relationships may vary between time points, allowing us to understand the demographic response of species to temporal environmental change through functional traits.