We investigated the impact of feral ungulate invasion and subsequent removal on three high-elevation (1450-2270 m) plant communities on Haleakalâ volcano, Maui, Hawai‛i. For bog communities, we used cover and frequency data from 380 permanently marked 1m² quadrats dispersed among five sites and surveyed before invasion (1973 & 1978), after invasion (1982-1986) and again after ungulate exclusion (1993, 2000 & 2007).  For cloud forest communities, we used cover and frequency estimates for groundlayer species from 700 1m² quadrats dispersed among 28 sites established in 1973 (before invasion), repeat sampled in 1980 (after invasion) and again in 2007 (after exclusion). For alpine scrub communities, we used estimates of cover and plant height from 110 permanently marked 100m² quadrats dispersed among 11 sites established in 1984 (six invaded and five not invaded) and repeat sampled in 2007 (after exclusion).  Change over time was assessed within each vegetation type using g-tests for individual species' frequencies and ANOSIM for community changes.

Results/Conclusions:

In bog and alpine scrub communities, feral ungulates had a dramatic influence on the vegetation, decreasing native plant cover and facilitating invasion by non-native plant species. Non-native species were less successful in invading cloud forest communities, though we did observe decreased frequencies in over 75% of the species in the original survey and increased dominance by a few generalist ferns. Following ungulate exclusion, bog plots originally dominated by Oreobolus furcatus were less associated with non-native species and more likely to return to pre-disturbance conditions than were plots originally dominated by Carex echinata. Though C. echinata itself recovered, it now shares dominance with the non-native species Holcus lanatus and Hypochoeris radicata which are apparently replacing native species like C. thunbergii and Calamagrostis expansa in these areas. Though native plant cover in alpine scrub communities also recovered, the dominance by the native shrub Styphelia tameiameiae appears to be increasing at the expense of other native species, including Deschampsia nubigena and Vaccinium reticulatum. Cloud forest communities showed no trend toward recovery, remaining degraded more than 25 years after ungulate exclusion. Collectively, our results demonstrate the efficacy of feral ungulate removal in protecting high-elevation vegetation on Haleakalâ, but suggest that recovery is uneven and will likely require active restoration to return these communities to their pre-disturbance composition and structure.