Survival and environmental filtering of angiosperm and conifer seedlings at range‐wide scales throughout temperate evergreen rainforests

Abstract Filtering of tree species drives forest community dynamics. Filters apply strongly at the seedling stage, where differential survival among species reflects species‐specific strategies, which vary along resource and environmental gradients. Strategies differ notably between conifers, which have generally conservative strategies that enable persistence, and angiosperms, which have a wide range of strategies to maximise growth. A quantitative understanding of how filters act to cause differential survival among and within species will strengthen our ability to forecast future forest communities. This understanding is needed at broad scales along multiple environmental gradients. Using a Bayesian hierarchical demographic model and repeated counts of canopy tree conifer and angiosperm seedlings, we used statistical inference to estimate range‐wide survival of 112 species from forest inventories across evergreen temperate rain forests in New Zealand that span multiple environmental gradients. We expected consistently higher seedling survival of conifers than angiosperms because of their contrasting survival–growth trade‐offs across environmental gradients (i.e. water deficit, minimum temperature, C:N ratio, canopy cover, understorey cover and basal area of tree ferns and palms). We further predicted that filtering (i.e. interspecific variance in survival at a site) should increase with environmental stress expressed through those major abiotic and biotic drivers. Range‐wide survival rates of conifer and angiosperm seedlings were similarly high and responded similarly across environmental gradients. Seedling survival decreased with canopy cover, but none of the other gradients strongly influenced seedling survival across large scales. Filtering decreased with canopy cover and increased with understorey cover, but was not influenced by other drivers. Synthesis . Systematic forest inventory data based on counts can be used to unlock survival rates of seedlings across multiple environmental gradients. Seedling survival is high across environmental gradients, likely because of overlap in resource‐use strategies of conifers and angiosperms within a community. Our results suggest that filtering during regeneration occurs through the differential ability of species to efficiently exploit low canopy cover or tolerate resource competition with understorey vegetation.