Drier, more seasonal climates strengthen coordination of hydraulic, leaf economic and reproductive strategies in subtropical forest tree communities

Trade‐offs relating to resource acquisition and conservation, reproduction and longevity generate considerable trait variation among co‐occurring tree species, yet little is known about how the nature and strength of these trade‐offs shift along gradients of resource availability. For rainforest and dry forest tree communities distributed across a continuous gradient of moisture availability in Australia's subtropics (600 to 2500 mm rainfall yr −1 ), we examined the coordination of hydraulic, leaf economic and reproductive traits using a metric of multi‐trait covariance and pairwise trait correlations. We hypothesized that trait coordination would be strongest at the dry and wet extremes of the moisture gradient, capturing strong moisture‐ and light‐driven trade‐offs, respectively. Overall trait covariance peaked in the driest sites and declined linearly along the regional moisture gradient, a trend also seen in the correlation of many trait pairs. In dry forests, stronger coordination of hydraulic and leaf economic traits captured a drought tolerance‐drought avoidance spectrum, while correlations involving seed size reflected a ‘stature–recruitment' trade‐off. Albeit far weaker, we found that shade‐tolerance and height‐driven constraints on hydraulic function drove some trait coordination in wetter, light‐limited sites. Our findings underscore the importance of interpreting trait‐based trade‐offs within the context of each site's resource availability. We established that moisture limitation places much stronger constraints on trait combinations than light limitation and identified key trade‐off axes that will likely become increasingly important under ongoing climate change.