Influence of overstory composition on understory colonization by native species in plantations on a degraded tropical site

Abstract

Patterns of understory colonization by native and naturalized trees and shrubs were evaluated in 4.5-year-old plantations of three exotic tree species, Casuarina equisetifolia, Eucalyptus robusta, and Leucaena leucocephala, on a de­graded coastal grassland site with reference to overstory com­position and understory environmental conditions. 19 second­ary forest species were established in the plantation understories (with a total area of 0.52 ha), while no natural regeneration occurred in unplanted, though protected, control areas. The majority of these species (90%) and the total seedling popula­tion (97%) were zoochorous, indicating the importance of frugivorous bats and particularly birds as facilitators of sec­ondary forest species colonization. Understory species rich­ness and seedling densities were affected significantly by overstory composition, the most abundant regeneration occur­ring beneath Leucaena and least under Casuarina. Understory colonization rates within mixed-species stands were interme­diate between those of single-species stands of the trees com­prising their overstories. Significant negative correlations were found between understory species richness and seedling den­sity, and forest floor depth and dry mass, especially for small-­seeded ornithochorous species. Higher colonization rates near the peripheries of plantation plots relative to plot interiors were due in part to roosting site preferences by frugivores, particularly bats. The study results indicate that overstory species selection can exert a significant influence on subsequent patterns of colonization by secondary forest species and is an important consideration in the design of plantations for 'catalyzing' succession on deforested, degraded sites.

Citation

Parrotta, John A. 1995. Influence of overstory composition on understory colonization by native species in plantations on a degraded tropical site. Journal of Vegetation Science 6(5): 627-636.