The influence of native plant characteristics and site conditions on restoration approaches in grass-invaded remnant Hawaiian dry forests

Tropical dry forests are one of the most endangered forest types worldwide.  In Hawaii, lowland dry forests presently cover less than 10% of their original area, and most remaining forests are threatened by invasive species.  Conservation and restoration of remnant dry forests is critically important since they contain over 25% of the endangered taxa in the Hawaiian flora.  Barriers to restoration of degraded dry forests include: grazing by non-native ungulates, altered fire regimes, lack of seed sources, and competition from invasive grasses.  Invasive grasses in particular have proven to block regeneration of native plants even when sites are protected from ungulate grazing and fire.  To assess grass effects on native species, we developed field-based restoration experiments within remnant native forest stands invaded by African fountain grass (Pennisetum setaceum) at the Kaupulehu dry forest preserve on the island of Hawaii.  Our results indicate that grass invasion alters ecosystem processes and initiates strong competition with native species for water.  Successful restoration in invaded sites with limited native seed sources requires a range of top-down and bottom-up approaches including: grass removal, shading and introduction of native species.  Furthermore, native species responses to restoration treatments are often highly species specific.  To increase our ability to generalize restoration approaches to other sites, we assessed the potential for using resource capture related traits (i.e. morpho-physio-phenological characteristics) of native species to predict their response to restoration treatments.  Our results suggest this approach may be useful for designing efficient restoration prescriptions across a range of site conditions.