Growth and wood density predict tree mortality in Amazon forests

Abstract

Summary Tree mortality is an important process in forest ecology. We explored the extent to which tropical tree death is a predictable outcome of taxon and individual level properties by means of mixed‐species logistic regression, for trees ≥ 10 cm in diameter. We worked in two lowland forest regions with markedly different floristic composition and dynamic regimes – the high wood density, low‐mortality northeastern (NE) Amazon (in eastern Venezuela), and the low wood density, high‐mortality northwestern (NW) Amazon (in northern Peru). Among those genera that are shared between regions there were no detectable regional differences in mortality rates. This suggests that floristic compositional differences are a major driver of the twofold regional contrast in stand‐level mortality. In NE forests, mortality risk of individual trees is best predicted by low taxon‐level wood density, slow relative growth, and large size, reflecting phylogenetically determined life‐history strategy, physiological stress and senescence. In NW forests, trees with low wood density and slow relative growth are also at most risk, but probability of death is independent of tree size, indicating that senescence is unimportant in this region. Synthesis. This study shows that despite fundamental floristic and dynamic differences between the two Amazonian regions, mortality risk can be predicted with mixed‐species, individual‐based statistical models and that the predictors are remarkably similar, such that tree growth and wood density both play important roles.

After trees die: quantities and determinants of necromass across Amazonia

“…The NE Amazonian forests in our study are towards the higher end of the range, whereas the NW forests are close to the average for terra firma forests. Although the stem mortality rate (number of dead trees) in NE Amazonia was low (Chao et al, 2008b), there was high mortality mass input (amount of dead mass) ( Table 2). This pattern suggests that big trees died in the NE forests (see also Chao et al, 2008b) and necromass is closely related to mass-mortality rates rather than stemmortality rates.…”

“…Although the stem mortality rate (number of dead trees) in NE Amazonia was low (Chao et al, 2008b), there was high mortality mass input (amount of dead mass) ( Table 2). This pattern suggests that big trees died in the NE forests (see also Chao et al, 2008b) and necromass is closely related to mass-mortality rates rather than stemmortality rates. When using a larger sample of published terra firma studies, we find positive relationships between necromass and biomass (AGB coarse ), mortality mass input (I recent ), and plotlevel average living wood density (ρ BA j ).…”

Methods to estimate aboveground wood productivity from long-term forest inventory plots

“…Several authors have reported that stems grow at below-average rates in the years or months prior to mortality (Wyckoff and Clark, 2002;Bigler and Bugmann, 2003;Chao et al, 2008;Vasconcelos et al, 2012). Similarly, unobserved recruits that die may have lower than average taxon-level wood density, as this has been shown to be a predictor of mortality (Chao et al, 2008;Kraft et al, 2010). Both these factors may cause our assumed growth in CIC 2 to be too high, although we deal with this by using median growth estimates for the unobserved growth of known stems that die and of unobserved recruits, as explained above.…”

“…We assumed the diameter growth rate of unobserved recruits to be the median rate for dicotyledonous stems in the 10-19.9 cm size class. We chose this as a lower estimate than the size class mean growth rate or the mean growth rate of recruits, since stems are reported to have reduced growth in the months immediately prior to mortality (Chao et al, 2008). We assigned stem wood density as the same as the plot mean in that census.…”

Patterns and determinants of wood physical and mechanical properties across major tree species in China

“…The physical and mechanical properties of wood can affect the growth and development of woody plants by determining water conduction and mechanical support [46], and are closely linked with the morphological structure of individual [7], life-history strategy [8], resource competition [9], community dynamics [10] and the terrestrial ecosystem function of trees [11,12]. Therefore, exploring the physical and mechanical properties of wood and their driving factors can help us to further understand the structure and function of terrestrial ecosystems, and thus provide valuable information for predicting the responses of terrestrial ecosystems to global change.…”