Biotic and abiotic controls on tree colonization in three early successional communities of Chiloé Island, Chile

Abstract

Most studies of tree regeneration are limited to particular environments and may not capture variation in the biotic or abiotic factors that regulate recruitment at larger spatial scales. Critical processes such as competition and facilitation can vary spatially, along gradients in resource availability and environmental stress, and temporally, with plant development. We examined patterns of natural tree recruitment and experimentally followed germination and seedling survival of five tree species (pioneer to late seral) in three early successional communities of contrasting bio-physical environments in a rural landscape on Chiloé Island, Chile. We quantified natural recruitment of juveniles and saplings and assessed relationships between tree density and local environment. We used a removal experiment to test the influence of early successional vegetation on seed germination and early survival of tree species. In each community, seeds and seedlings were placed in paired experimental plots from which vegetation was removed or left intact (control). To identify potential correlates of germination and seedling survival, we measured light transmittance and soil properties in each plot. In all communities, established vegetation had either a positive or neutral effect on germination and/or survival although responses varied among life stages and species. Germination and survival were correlated with the lower levels of light in controls, consistent with negative correlations between natural tree densities and light. Vegetation cover was not dense enough to facilitate survival of late successional species, but not too dense to inhibit survival of shade-intolerant or mid-tolerant species. Among communities, natural densities of juveniles were greatest under conditions where experimental germination rates were highest. Seedling height growth was lowest in the community characterized by waterlogged soils, consistent with the naturally low transition rate from juveniles to saplings and a negative correlation between density of shade-intolerant trees and soil moisture. Synthesis. Our experiments indicate strong, mostly positive controls (facilitation) on tree recruitment in early seral shrublands with differing bio-physical environments. Benefits of shading are manifested at different stages in the life history. However, community context is critical: variation in seasonal patterns of soil moisture may explain spatial variation in the density and size structure of natural tree recruitment. © 2010 The Authors. Journal of Ecology © 2010 British Ecological Society.