Differential tree demography mediated by water stress and functional traits in a moist tropical forest

Climate-induced changes in tree mortality, recruitment and growth have been extensively observed in forests worldwide. However, there is still a lack of quantitative understanding regarding how tree demography responds to environmental factors, particularly different water conditions, and how plant functional traits contribute to interspecific differences in this response. Using data collected from a forest monitoring plot, meteorological observations and trait measurements on Barro Colorado Island in Panama-one of the most studied sites, we investigated the mortality, recruitment, growth and population dynamics of 165 tree species from 1990 to 2014 and examined the influence of functional traits in determining the interspecific differences in tree demography. We also employed parametric accelerated failure time models to assess the impact of environmental conditions, functional traits and individual tree characteristics on tree survival time. We find that water stress drives the temporal dynamics of tree demography. During the high water stress period, the increase in mortality rates and decrease in recruitment rates caused negative population changes for species. In contrast, the increase in recruitment rates and decline in mortality rates during the low water stress period positively affected the population of species. Wood density and P50 (xylem water potential at 50% loss of maximum hydraulic conductivity) are significantly correlated with species-level mortality, recruitment and growth rates, indicating that traits related to resource allocation and hydraulic safety dictate the interspecific differences in demographic rates. Our results demonstrate that water stress and traits related to resource allocation and hydraulic safety jointly mediate tree demography in this tropical forest. High mortality and low recruitment under high water stress may especially cause a decline in fast-growing species. Therefore, timely recovery of recruitment under favourable water conditions is crucial for the forest dynamics.Read the free Plain Language Summary for this article on the Journal blog.

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This study investigates the tree demography in Barro Colorado Island forest in Panama, focusing on the impact of water conditions and plant functional traits. It reveals that water stress is the main driver of tree dynamics, with negative population changes during high water stress and positive changes during low water stress. Wood density and P50 are found to be significantly correlated with tree mortality, recruitment, and growth rates, indicating the importance of resource allocation and hydraulic safety traits. Timely recovery of recruitment under favorable water conditions is crucial for forest dynamics.