Hawai'i conservation alliance

2010 Runner Up Best Student Poster Presentation

Temperature impacts on native wet forest structure and biodiversity in Hawai‘i

Darcey Iwashita 1, Creighton Litton1, Christian Giardina2
1University of Hawaii at Manoa, United States, 2Institute of Pacific Islands Forestry, USDA Forest Service, United States

Native-dominated montane wet forests in Hawai‘i are currently experiencing rising temperatures as a result of global climate change, with unknown effects on forest composition and structure. The objective of this study was to examine how native wet forest biodiversity and structure vary across a 5°C mean annual temperature (MAT; 13-18°C) gradient on the Island of Hawai‘i. It was hypothesized that biodiversity and basal area would increase with MAT due to greater resource availability and productivity at higher temperatures. Density was expected to be negatively correlated with MAT and basal area as a result of resource limitation and stand carrying capacity. Diameter size class distribution was hypothesized to not vary with MAT due to natural species range limits. Trees, saplings, and seedlings were quantified in nine 400 m2 plots in native-dominated forest stands across the MAT gradient. Tree species richness and the Shannon index for tree diversity were significantly and positively related to MAT. Basal area showed a weak positive relationship with MAT, with larger trees contributing to greater basal area at mid-MATs. Stand density and MAT were negatively correlated, although the trend was driven by the two dominant species. In line with density results, diameter size class distribution varied with MAT for the two dominant species, with a broader range of diameter size classes at lower MATs. These results indicate that MAT has a significant impact on biodiversity and forest structure in Hawai‘i and that rising temperatures can be expected to alter native Hawaiian montane wet forest composition and structure.