Island biogeography and restoration: The role of living fence islands as regeneration foci in the rehabilitation of degraded lands in Honduras

Two native 'living fence' tree species were evaluated for their ability to establish vegetatively and serve as forest 'regeneration foci' at three degraded sites in Pico Bonito National Park, Honduras. The 2-yr project tested island biogeography theory by evaluating whether greater island size and/or shorter distance to secondary forest (seed source) increased seed rain and seedling establishment in a 'sea' of abandoned pasture. 'Artificial' islands of three sizes (4, 16, 64m 2) and at two distances to secondary forest (20, 50m) were created by planting 2m tall stakes of Gliricidia sepium and Bursera simaruba, each in monoculture. Open pasture 'islands' served as controls and were delineated with flagpoles. Each island size was replicated four times at each site. A bird survey was undertaken to evaluate frugivore attractiveness to islands, and nine additional species were evaluated for their ability to establish vegetatively in a pilot study.; Gliricidia stake establishment was ∼100% at all sites; Bursera establishment ranged from 30--50%. Gliricidia stakes developed cover more rapidly and had greater cover values than Bursera. Greater initial DBH of stakes increased establishment success of both species. Planting at the onset of the dry season resulted in greater establishment for Bursera and more rapid cover development for Gliricidia. Of the nine other species evaluated, Erythrina berteroana, Erythrina fusca , and Jatropha curcas had high establishment success.; Artificial islands increased visitation by frugivores; during 47 observation hours, 160 visits were recorded to artificial islands compared to one to open pasture. A total of 144,140 seeds of 186 species were collected during the study; >80% of seeds were grasses. Tree seeds were predominantly early successional species. Distance to seed source did not affect seed rain of tree species into islands. Density and species richness of zoochorous-dispersed tree seeds were greater in artificial islands than open pasture. Large Gliricidia islands had greater zoochorous tree seed density than smaller islands.; A total of 543 seedlings of 41 species established in islands. Seedling number did not differ among island types, although a trend toward greater density was apparent in artificial islands. Species richness was greater in Gliricidia islands than in Bursera or open pasture islands. Seedlings were also quantified in a 1m strip surrounding artificial islands, suggesting that islands can expand into surrounding pasture over time. Lastly, artificial islands (notably Gliricidia) created a microenvironment more favorable for seedling establishment by reducing temperature and light extremes as compared to open pasture. Given the problems associated with rehabilitation of tropical pastures, artificial islands present a simple, non-labor intensive technique for facilitating forest regeneration.