Seed limitation during early forest succession in a rural landscape on Chiloé Island, Chile: implications for temperate forest restoration.

Abstract

Re-establishment of native forest species in rural landscapes may be conditioned by the proximity of seed sources, the post-disturbance composition of successional patches and the seed dispersal patterns of frugivores. Knowledge of seed dispersal rates into early seral communities, and how these are influenced by the structural and compositional characteristics of these communities is still quite poor. We used an observational approach to quantify the seed rain and seed limitation (SL) (proportion of sites to which seeds were not dispersed) of woody species during two growing seasons in three early successional shrublands with contrasting species composition and attractiveness to frugivores on Chiloé Island, Chile. We compared species immigration based on dispersal types (bird- vs. wind dispersed) and life-form (shrubs vs. trees). Concomitantly, we used an experimental approach to test whether artificial perches would relieve SL and enhance seed dispersal and seedling establishment of fleshy-fruited species. Most seeds collected were of pioneer shrubs already present in the early successional sites. Few (5%) were from trees appearing only in the surrounding second-growth forest. Density of seeds from fleshy-fruited trees and shrubs was seven times higher in the seral community most attractive to frugivores, whereas density of seeds from wind-dispersed trees was similar among communities. Artificial perches significantly increased the density and species richness of seeds from fleshy-fruited trees in all communities, but the magnitude of the facilitation effect depended on the ecological context of each seral community. Seed rain enhancement was higher in the community less attractive to frugivores. Seedling recruitment, however, remained low even under perches, indicating that additional constraints act during seed germination and/or seedling survival and growth. Synthesis and applications. Forest succession in this rural landscape may be delayed or arrested by extremely low seed rain, despite the proximity (<100 m) of seed sources in older forest patches. Although artificial perches significantly enhance inputs of bird-dispersed tree seeds into shrublands, especially where fleshy-fruited pioneer species are absent from the seral community, they do not overcome other site-related barriers to establishment, as the lack of shaded places and limited soil drainage. Thus, in some ecological contexts, multiple approaches, such as direct seeding or planting, and the use of nurse plants, may be required to enhance seed rain and seedling establishment of fleshy-fruited species.

Key words

• barriers
• biodiversity
• characteristics
• communities
• conservation
• constraints
• diets
• direct sowing
• dispersal
• drainage
• ecology
• environmental protection
• forests
• fruits
• germination
• herbivores
• land use
• landscape
• nurse trees
• pioneer species
• rain forests
• recruitment
• regeneration
• restoration ecology
• scrublands
• secondary forests
• seed dispersal
• seed germination
• seed sources
• seedlings
• seeds
• shrubs
• soil
• species diversity
• species richness
• survival
• trees
• wind
• woody plants