Dieback Disease Increases Short-Term Spatial Heterogeneity and Litterfall Inputs in Forests Dominated by a Long-Lived Foundation Species

Abstract Litterfall, a key ecosystem process linking vegetation dynamics, carbon flux, and nutrient cycling, can be substantially altered by disease. However, effects of disease on both its production and spatial distribution are not well understood. We examined the effects of a dieback disease on leaf litterfall in forests dominated by a susceptible foundation tree species Agathis australis (kauri). Using leaf litterfall data and mapped trees from stands of varying successional stages and disease severity, we parameterised a spatially explicit Bayesian inverse model to estimate species-specific leaf litter production and dispersal for eight focal species as functions of tree size, distance from trunk, and disease severity. Kauri tree-level litterfall initially increased with disease severity but declined sharply after severe canopy loss. Due to the dominance of kauri, stand-level litterfall production mirrored effects of the disease at kauri tree-level litterfall, across all successional stages. On average, healthy stands produced 129.2 g m −2 year −1 less than a stand undergoing branch dieback and 142.7 g m −2 year −1 more than a stand with severe canopy dieback. Kauri’s distinct litter-dispersal pattern drives heterogeneous litterfall distribution, and its stand-level litterfall dominance, arising from structural prominence rather than high tree-level productivity, further amplifies this pattern. As kauri dominance increases with succession and dieback induces additional leaf shedding, stand-level heterogeneity and spatial variation in nutrient inputs intensify. These findings highlight the potential for kauri dieback to reshape litter inputs in ways that alter nutrient cycling and future succession, underscoring the need for management strategies that address ecological impacts beyond mortality.