Effects of Long‐Term Ungulate Exclusion and Recent Alien Species Control on the Preservation and Restoration of a Hawaiian Tropical Dry Forest

Abstract

Although the destruction of tropical rain forests receives much attention, tropical dry forests are in general far more threatened and endangered. Eliminating grazing ungulates is often considered a key first step toward protecting these ecosystems, but few studies have investigated the long‐term effects of this technique. We examined the effects of ungulate exclusion from a 2.3‐ha native dry‐forest preserve on the island of Hawaii by comparing its present flora to the flora of an adjacent area subjected to continuous grazing since the preserve was fenced over 40 years ago. Relative to this adjacent area, the fenced preserve contained a more diverse flora with substantially greater coverage of native overstory and understory species. Until recently, however, regeneration of native canopy trees within the preserve appears to have been thwarted by a dominant herbaceous cover of alien fountain grass ( Pennisetum setaceum) and predation by alien rodent species. Our results indicate that although ungulate exclusion may be a necessary and critical first step, it is not sufficient to adequately preserve and maintain Hawaii's remaining tropical dry forest remnants. Our recent efforts to control the dominant alien species within the fenced preserve suggest that this practice may facilitate both the regeneration of native species and the colonization and potential invasion of new alien plants. Comparisons of seedlings of the dominant native canopy tree Diospyros sandwicensis growing in sites both dominated by and free of fountain grass suggested that fountain grass inhibits Diospyros seedling growth and photosynthesis but may increase survival if seedlings are protected from ungulates.

Gene flow among established Puerto Rican populations of the exotic tree species, Albizia lebbeck

“…Forest vegetation is scattered across a landscape that has been largely cleared for agriculture and cattle pastures. Exotic grasses cover much of the site, as is typical for tropical areas cleared of forest (Daehler, 1998;Cabin et al, 2001). Especially common is African Guinea Grass (Panicum maximum Jacq.…”

Native Species Regeneration Following Ungulate Exclusion and Nonnative Grass Removal in a Remnant Hawaiian Dry Forest

“…This decline represents a substantial loss of biodiversity because these forests were once described as the most diverse in the Hawaiian archipelago (Rock 1913). Currently, remnant dry forests have the highest proportion of endangered taxa among Hawaiian plant communities (Sakai et al 2002), and native species continue to decline within these remnants due to lack of natural regeneration (Cabin et al 2000, Litton et al 2006. Conservation of remnant dry forests is thus critical, and their successful restoration is likely to depend on overcoming barriers to natural regeneration.…”

Review of the Avifauna of the Tres Marías Islands, Mexico, Including New and Noteworthy Records

“…contrasts with the abundance of cycads and thick undergrowth still there in 1955and 1976, respectively (e.g., Stager 1957: plate 20, Wilson 1991, suggesting much degradation of the forest in the past few decades. It is well known that introduced goats (e.g., Cabin et al 2000, Dukes and Mooney 2004, Dixon 2011, Chynoweth et al 2013, cats (Medina et al 2011), and rats (Shiels et al 2014, ISSG 2016) devastate ecosystems and native species. These species have been successfully eradicated from other islands of western Mexico (Aguirre et al 2008), and we hope that similar efforts will be taken to ensure the continued well-being of the birds and other native wildlife of the Tres Marías Islands.…”