Remnant trees and surrounding vegetation determine avian frugivore visitation of restored forest sites in Taiwan

Abstract

Natural recovery is an important approach used in forest restoration in many parts of the world. The visitation of avian frugivores, a major source of seed rain in restored sites, is mainly controlled by bird assemblages in surrounding areas and their tendency to enter the restored sites. In this study, we examined the effects of remnant trees, surrounding vegetation, and seasons on avian frugivore visitation in 30 restored sampling plots and 15 edge sampling plots in subtropical Taiwan from 2013 to 2014. The results showed that both remnant trees and the surrounding vegetation were important in avian frugivore visitation of restored sites. Avian frugivores had a higher tendency to enter restored sites with diverse remnant trees and during the non-breeding season. An average of approximately 25% of the avian frugivore individuals in edge sampling plots entered the nearby restored sites within 15 min. Among three surrounding vegetation types, native forests had more frugivores than did conifer plantations. However, if the remnant trees had low species diversity, restored sites surrounded by native forests would have low frugivore visitation similar to restored sites surrounded by conifer plantations. We conclude that the species diversity of remnant trees is more important than the complexity of the surrounding vegetation in increasing avian frugivore visitation. Therefore, in order to promote increased seed rain at restored sites, it is important to maintain the species diversity of remnant trees. For restored sites with limited remnant trees or surrounded by conifer plantations, frugivore visitation would be low, and human intervention might be needed.