Montane plant communities throughout the world have responded to changes in precipitation and temperature regimes by shifting ranges upward in elevation. Organisms that cannot disperse or adapt in situ to projected climate conditions are expected to decrease in distributional range and abundance. We sought to restore a degraded Hawaiian montane woodland ecosystem and enhance connectivity between existing subalpine woodlands and lower-elevation montane mesic forests, while increasing ecosystem tolerance to contemporary and future climate conditions. We collected seeds of three native montane plant species from source populations located above (2,500 m) and below (1,900 m) the restoration site. Seeds were germinated in a greenhouse and out-planted at eight plots spanning a 500-m elevation gradient. Recognizing that there may be a lag time between changes in climate and corresponding plant adaptation, we hypothesized that survival and growth of low-elevation origin plants would generally improve when planted at higher elevations, whereas, survival and growth of high-elevation origin plants would not improve when planted at lower elevations. We monitored climate conditions to determine the effects of temperature or rainfall on survival and growth after 20 weeks, and measured specific leaf area (SLA) to identify leaf characteristics that varied with environmental conditions.
Responses to changing precipitation and temperature regimes varied between species. We found that origin significantly affected survival and SLA in one species. There was greater survival of Dodonaea viscosa seedlings from high-elevation origin compared to low elevation across the entire gradient; however, due to lack of local availability, low-elevation seeds had been sourced from a more distant collection site 30 km away with precipitation similar to the high-elevation source location. We found no support for SLA variation, and high overall survival, in two other species along the gradient despite >1 m annual rainfall difference between source locations. Survival increased with elevation and soil moisture for Sophora chrysophylla, while it decreased for other species. Survival increased with increasing monthly temperature range for Chenopodium oahuense, particularly for low-elevation origin plants. Results support previous research that careful selection of micro-sites may provide suitable conditions for plants in a rapidly changing climate, although optimal conditions may vary at the species level. Additionally, results suggest that locally-sourced seed is important to ensure highest survival at restoration sites. Further experimentation on larger spatial and temporal scales may be necessary to determine the empirical responses of species and communities to changing climate in highly degraded montane ecosystems.