Feral Herbivores Suppress Mamane and Other Browse Species on Mauna Kea, Hawaii

Abstract

Abundance, survival, and growth of mamane (Sophora chrysophylla) regeneration were determined inside and outside sheep exclosures located in heavily browsed portions of the mamane forest of Mauna Kea, Hawaii. Vegetational cover of other species was estimated. Mamane grew abundantly inside 16-year-old exclosures but was sparse outside. Height class distributions indicated that feral sheep prevented establishment of regeneration. Survival of seedlings and sprouts at 2-year-old exclosures was greater inside than outside. The largest difference between survival inside and outside was found where browsing pressure was greatest. Mamane reproduction exposed to browsing tended to be shorter than protected reproduction. Rate of height growth for protected mamane reproduction was significantly affected by exclosure location. Cover data for preferred browse species other than mamane indicated that 3 endemic grasses-Hawaiian bent (Agrostis sandwicense), he'u-pueo (Trisetum glomeratum), and Deschampsia australis, an endemic shrub-aheahea (Chenopodium oahuense), and an introduced forb-gosmore (Hypochoeris radicata)-were susceptible to browsing. On the basis of these findings, vegetation recovery should be rapid in most areas where feral sheep are eliminated or reduced.