Landscape effects on structure and species composition of tabonuco forests in Puerto Rico: Implications for conservation

Abstract

We studied the structure and species composition of nine residual forest stands of Dacryodes excelsa (tabonuco), a dominant vegetation type in the moist and wet lower montane forests of the Caribbean. The stands were scattered over three different landscapes with different degrees of anthropogenic disturbance: forested, shade coffee, and tobacco. We compared our results with data from undisturbed stands inside a protected and forested landscape to see how the type of landscape that surrounded them affected the structure and species composition of the residual forest stands. In the process we sought conservation lessons that would help restore degraded tabonuco forests to original conditions. Tree density, basal area, and species density all increased with elevation. We found 98 tree species, including 50 of the 83 species that we identified as belonging to undisturbed tabonuco forests (including 13 of 18 endemic tree species), 41 tree species not reported for undisturbed tabonuco forests, eight primary forest species, and six introduced species. When ordered by species Importance Value by site, the stands in nine sites separated into three general groups corresponding to landscape type: (1) Heavily used for tobacco production. (2) Shade coffee, and (3) Forested. The importance of introduced species increased, and the abundance of tabonuco forest indicator species and endemic species decreased with increased anthropogenic disturbances. When restoring tabonuco forests, it is necessary to understand the landscape forces that influence the species composition of these forests. It appears that particular species combinations are natural outcomes of the level of anthropogenic activity in the landscape and reversing those tendencies might be impractical or too costly.