Topography in tropical forests enhances growth and survival differences within and among species via water availability and biotic interactions

Topography is associated with variation in soil water, biogeochemical properties and climate, which drive diversity by filtering species and promoting niche differences. However, the potential for topography to promote fitness differences and diversity among tree species and populations remains poorly tested in tropical rainforests, especially at small spatial scales in everwet climates.

We reciprocally transplanted tree seedlings between ridge and riparian sites and manipulated neighbour abundance and water availability to assess growth and survival differences both among species and between populations within species in response to changes in biotic interactions and soil water gradients associated with topographic heterogeneity.

Seedling growth rates were higher on the ridge, but probability of survival was lower on the ridge than the riparian site. Topography also altered growth and survival responses to water availability such that seedlings in the inundated soils in the ripar...