Canopy gap disturbance restructures growth-mortality trade-offs of dominant canopy species in the understory

Vertical stratification in forests leads to distinct growth-mortality trade-offs, while canopy gap disturbance plays a crucial role in reshaping forest structure. However, how canopy gap disturbance influences growth-mortality trade-offs across vertical strata remains poorly understood. In this study, we selected 27825 individuals belonging to 27 dominant canopy species from a 20-ha subtropical evergreen broad-leaved forest dynamics plot, classified them into vertical strata, and quantified their growth and mortality rates in gap and non-gap areas. Our results revealed a pronounced growth-mortality trade-off among canopy species in the understory. Compared with non-gap quadrats, canopy species in gap quadrats exhibited significantly higher growth rates, while the slope of the growth-mortality trade-off in the understory remained unchanged. Among canopy species with explicitly increased growth rates in the understory of gap quadrats, shade-tolerant species experienced a pronounced increase in mortality. These findings suggest that canopy gap disturbances primarily promote the growth of canopy species in the understory, while increased mortality of shade-tolerant saplings, due to their limited adaptation to high-light environments, drives the restructuring of the growth-mortality trade-offs at the community level. Our study identifies a previously underappreciated mechanism shaping the tree growth-mortality trade-off and offers guidance for understory sapling planting following forest management interventions.