Dry forest restoration and unassisted native tree seedling recruitment at Auwahi, Maui

Abstract

Efforts to restore highly degraded but biologically significant forests draw from a limited toolbox. With less than 10% of their former distribution remaining, Hawaiian dry forests, though critically endangered, remain important biological and cultural refugia. At restoration onset (1997), vegetation of restoration and control areas of degraded Auwahi dry forest, Maui Island, was similar, dominated by nonnative graminoids (restoration 78.3%; control 75.4%), especially Cenchrus ( Pennisetum ) clandestinus . In 2012, unrestored control area vegetation was basically unchanged. In contrast, in the restoration area in 2012, native shrub cover increased from 3.1% to 81.9%, and cover of nonnative graminoids declined from 75.4% to 3.3%. In 2012, nonplanted seedlings of 14 of 22 native tree species and six of seven native shrub species were observed in restoration plots; the majority (99%) were five native ( Dodonaea viscosa, Coprosma foliosa, Osteomeles anthyllidifolia, Chamaesyce celastoides, Nestegis sandwicensis ) and one nonnative species ( Bocconia frutescens ). By 2012, stem counts of native woody plants had increased from 12.4 to 135.0/100 m 2 , and native species diversity increased from 2.4 to 6.6/100 m 2 . By 2012, seven rare dry forest tree species, Charpentiera obovata, Nothocestrum latifolium, Ochrosia haleakalae, Pleomele auwahiensis, Santalum ellipticum, S. haleakalae , and Streblus pendulinus , had established seedlings and/or saplings within the restoration site, especially notable because natural reproduction is largely lacking elsewhere. Without development and implementation of appropriate management strategies, remaining Hawaiian dry forest will likely disappear within the next century. Multicomponent restoration incorporating ungulate exclusion, weed control, and outplanting as described here offers one strategy to conserve and restore tracts of high-value but degraded forests.