Remnant trees and landscape structure influence avian frugivores visitation in forest restored sites in Taiwan

Background/Question/Methods

Human exploitation is the major threat to forests worldwide, many of the forests were altered into farmlands and plantations and result in severe habitat degradation and compelling need of restoration. Among restoration strategies that accelerate natural regeneration of native trees, seed source is often the most critical limiting factor. Previous studies suggest remnant trees in restored sites and nearby landscape structure could affect seed rain of native trees by attracting avian frugivores. However, knowledge of the effects of remnant trees and landscape structure on avian attraction has been limited, and the interactions between remnant trees and landscape structure remain unclear. We monitored avian frugivore visitation in 30 forest restored sites within Experimental Forest of National Taiwan University in Taiwan. These sample sites were at the early stage of restoration, all of them had been restored within 5 years. The avian frugivores visitation pattern of these sites, where located in different landscape structure and degrees of remnant trees was analyzed by Generalized Linear Model and Canonical Correlation Analysis.

Results/Conclusions

Avian frugivore species richness and visitation rate were positively correlated with remnant tree species diversity, and the visitation rate was also correlated with remnant tree coverage. However, this effect of remnant trees differed as landscape structure changed. In area dominated by native forests, this effect was more prominent, and the frugivore species richness was also positively correlated with remnant tree coverage and foliage volume in the restored sites. In area dominated by tree plantations, the effect of remnant tree was very limited, very few avian frugivore species visited the restored sites and the visitation rate decreased with percentage of plantation area in nearby landscape. Frugivore species differed in their responses to remnant trees and landscape structure. Alcippe morrisonia preferred dense remnant trees, Hypsipetes leucocephalus and Heterophasia auricularis visited restored sites with very few remnant trees, and restored sites within plantations were mainly visited by shrub frugivores. Our results suggest that coverage and species diversity of remnant trees promote avian frugivore visitation in restored sites within native forests. However, in restored sites within plantations, mainly shrub frugivores visit and these species have limited ability to disperse seeds of native trees, and more active efforts are needed to restore these degraded lands.