Social and ecological dimensions of forest stewardship in Pacific islands

Abstract

Forests face loss and degradation globally, yet they are essential for human and planetary health, hence their conservation and restoration are imperative. Tropical forests, particularly on islands, host high levels of biodiversity and endemism, and experience multiple threats due to climate change, invasive species, and other anthropogenic drivers of change. Major research gaps on tropical island forest conservation and restoration include establishing a better understanding of how human dimensions are incorporated into forest conservation efforts; the most effective methods to manage non-native species; and the impacts of climate change. In this thesis, I addressed these gaps by examining social and ecological aspects of forest conservation and restoration (together called stewardship) in two Pacific Island archipelagos: the Hawaiian Islands, and the Southern Line Islands. The main question being asked is: what are the drivers and limitations that promote or hinder the success of conservation and restoration? I used a combination of document analysis, interviews, vegetation surveys, and comparisons to historic studies to address: 1) What is the range of types of organizations focusing on terrestrial ecosystem stewardship in Hawaiʻi and how do these organizations incorporate human dimensions into their approaches and discourse? 2) What underlying values drive restoration practitioners and how do they define restoration success? 3) What restoration techniques affect metrics of restoration success in Hawaiian mesic forests? 4) How is vegetation of currently uninhabited islands affected by land-use history and an extreme El-Niño Southern Oscillation (ENSO) event, and what does this mean for restoration in the context of climate change? I found that organizations in Hawaiʻi incorporated the human dimensions in diverse ways, with no clear trends with respect to organization type; that all organizations involved local communities; and that the majority of organizations included cultural aspects in stewardship. Restoration practitioners in Oʻahu’s Waiʻanae mountains were motivated by a passion to protect and restore the unique and imperiled species and ecosystems of Hawaiʻi. I found that some of their measures of success were achieved, including native species predominance in the midstory of the restoration sites. Removing non-native trees by total cutting or girdle treatments led to better metrics of restoration success than the selective cutting of trees, but removal of non-native species alone was not sufficient to support native species regeneration in the understory. Furthermore, time since initiation of restoration, out-planting density, and weeding frequency did not affect indicators of restoration success over the timeframe of the restored forests that were studied (4-14 years post-initiation of restoration). In the Southern Line Islands, changes in species richness were noted on all islands since the historic studies, with a reduction in species richness found for most islands due to the disappearance of some non-native species which had been cultivated previously. There was some evidence of drought post-ENSO, with implications for the plant communities facing climate change. Taken together, the findings provide a breadth of knowledge on social and ecological factors which can support effective terrestrial ecosystem stewardship in Pacific Islands and other similar tropical ecosystems.