The curious case of maile: lessons in ecotypes, population viability and restoration

Abstract

The harvest of non-timber forest products (NTFPs) is a major economic and cultural activity in many tropical forests. The continued availability of NTFPs is not only essential for conservation of the plant species, but also for the livelihoods of millions of people worldwide and accessibility of resources for cultural practices. Incorporating culturally significant plants in restoration may increase success rates through partnership with local communities. The Hawaiian Islands are model study sites to examine the following key concerns in restoration: ecotypic variation, critical factors in establishment and survival, and population dynamics and persistence. Maile is a culturally prominent native Hawaiian NTFP liana with declining populations, and ideal species for addressing restoration concerns for other species in Hawaiʻi and elsewhere. This study demonstrated significant differences in maile growth, survival, and seed germination rates between populations and in variable light, in a common garden experiment. These results support evidence of ecotypic variation in maile. Degree of climatic congruence between source and restoration sites appeared to be an important predictor of performance. The effects were physiologically and economically significant, and may have both short and long term effects on restoration success. Substrate treatments used in maile reestablishment experiments showed significantly higher survival in soil than in coarse woody debris. Moisture and nitrogen availability were lower in coarse woody debris than in soil, and may be correlated with the drier than average annual precipitation study year. Coarse woody debris may offer long-term benefits, such as safe sites, that deserve consideration. Wild maile populations were projected to either remain stable or decline, and appeared to be sensitive to precipitation changes. Restored maile populations were projected to not persist in the long term, with the open canopy population having the lowest population growth rate. However, elasticity and life table response experiments analyses pinpointed key strategies, e.g., increasing juvenile and adult survival, to achieving success in restoration. This study emphasized the importance of demographic comparisons between wild and restored populations. The results from these studies can serve to increase sustainability of NTFPs through guided restoration methodologies that can extend to other Hawaiian species and beyond.