Tropical tree growth sensitivity to climate is driven by species intrinsic growth rate and leaf traits

Abstract

A better understanding of how climate affects growth in tree species is essential for improved predictions of forest dynamics under climate change. Long‐term climate averages (mean climate) drive spatial variations in species’ baseline growth rates, whereas deviations from these averages over time (anomalies) can create growth variation around the local baseline. However, the rarity of long‐term tree census data spanning climatic gradients has so far limited our understanding of their respective role, especially in tropical systems. Furthermore, tree growth sensitivity to climate is likely to vary widely among species, and the ecological strategies underlying these differences remain poorly understood. Here, we utilize an exceptional dataset of 49 years of growth data for 509 tree species across 23 tropical rainforest plots along a climatic gradient to examine how multiannual tree growth responds to both climate means and anomalies, and how species’ functional traits mediate these growth responses to climate. We show that anomalous increases in atmospheric evaporative demand and solar radiation consistently reduced tree growth. Drier forests and fast‐growing species were more sensitive to water stress anomalies. In addition, species traits related to water use and photosynthesis partly explained differences in growth sensitivity to both climate means and anomalies. Our study demonstrates that both climate means and anomalies shape tree growth in tropical forests and that species traits can provide insights into understanding these demographic responses to climate change, offering a promising way forward to forecast tropical forest dynamics under different climate trajectories.

Temperature, nutrient availability, and species traits interact to shape elevation responses of Australian tropical trees

“…With respect to the field collections, the Australian Wet Tropics in general is characterized by MAP approaching and exceeding 2,000 mm (Turton et al, 1999), a range in which foliar δ 13 C in tropical rainforests is largely insensitive to MAP (Leffler and Enquist, 2002;Diefendorf et al, 2010). In a recent analysis, it was shown that mean climatological water deficit was not a significant predictor of tree growth rates across forests in the Australian Wet Tropics similar to those that we sampled (Bauman et al, 2022a). Furthermore, sap flow measurements at lowland, midelevation, and high elevation sites in the Australian Wet Tropics indicated that transpiration at the tree level is largely unresponsive to seasonal variations in soil moisture (McJannet et al, 2007;Binks et al, 2022).…”

“…Field campaigns to collect plant functional traits (LMA, foliar δ 13 C and δ 15 N) of exposed canopy branches of focal Flindersia species (a minimum of 2 individuals per site) were conducted in four locations (Supplementary Table 1) across a range in elevation, using standard trait measurement protocols (Cornelissen et al, 2003). Data from a previous trait campaign (Bauman et al, 2022a) were also added to this analysis (n = 16 individuals across five sites for the focal species).…”

“…Such large intraspecific variation has been attributed to increase in species' water-use efficiency with increasing elevation and its inherent adaptive plasticity to variable environmental conditions (Cordell et al, 1998;Peri et al, 2012). Studies have also reported variation in foliar δ 13 C with other environmental attributes such as precipitation, soil nutrients, solar radiation, and VPD (Vitousek et al, 1990;Chen et al, 2017;Zou et al, 2019;Bauman et al, 2022a). Variation in foliar δ 13 C with elevation can also result from the influence of leaf morphology (leaf thickness or LMA, for example), which leads to longer diffusion pathways for CO 2 into the leaf and decreases the internal-to-ambient CO 2 concentration ratio (c i /c a ) and hence causes enrichment of foliar δ 13 C in montane flora (Körner et al, 1986;Prentice et al, 2014).…”

“…Similarly, the availability of soil nutrients, such as N and P, can also change as a function of elevation, both because of changes in temperature-driven mineralization rates, and inherent litter decomposability (Salinas et al, 2011). Together, these environmental factors are all recognized as major drivers of tropical tree growth and selective filters for plant functional traits (Rapp et al, 2012;Cheesman et al, 2018;Bauman et al, 2022a). Trends in functional traits observed across elevation may therefore result from, to varying degrees, changes in temperature, vapor pressure deficit, soil nutrients, species turnover, and the interaction of these factors (Read et al, 2014;Fahey et al, 2016).…”

“…Higher LMA can increase the leaf internal resistance to CO 2 diffusion, thereby reducing chloroplastic CO 2 concentrations during photosynthesis (Cernusak et al, 2013), resulting in an increase in the foliar δ 13 C (Vitousek et al, 1990;Li et al, 2009). Increased LMA can also lead to increased leaf N and P concentrations per unit leaf area, which can confer increased leaf photosynthetic capacity, further decreasing discrimination against 13 C (Bauman et al, 2022a). Nevertheless, decreases in foliar δ 13 C with increasing elevation have been reported in some cases (Sah and Brumme, 2003), and could be related to lower leaf-to-air vapour pressure deficits (VPD) with increasing elevation, resulting in an increased ratio of intercellular to ambient CO 2 concentrations (c i /c a ) through opening of stomata (Cernusak et al, 2013;Chen et al, 2017).…”