Mon, Aug 02, 2021:On Demand
Background/Question/Methods
ʻŌhiʻa (Metrosideros polymorpha) accounts for 50% of all trees on Hawai'i Island. Rapid ʻŌhiʻa Death (ROD) caused by the primary fungal pathogen Ceratocystis fimbriata threatens Hawaiʻi's ʻŌhiʻa forests statewide and has caused stand level mortality across approximately 140,000 hectares of ʻŌhiʻa forest on Hawaiʻi Island. Here we present results of research to determine manifestation of Ceratocystis-induced Rapid ʻŌhiʻa Death (i.e., ROD) – its distribution, patterns, and impacts - across Hawaiʻi Island. We established 250 ROD monitoring plots to characterize forest stands in which ROD is occurring and to determine ʻŌhiʻa annual mortality rates within those forests.
Results/Conclusions Where C. lukuohia-infected trees were detected, ʻŌhiʻa annual mortality rates averaged 9%. Results indicated that younger, smaller stature ʻŌhiʻa stands exhibited lower annual rates of mortality (i.e., 4 to 5%) compared to older, larger stature ʻŌhiʻa stands (i.e., 12 to 13%). Mortality rates were also lower in ʻŌhiʻa stands on young stands growing on young lava flows compared to rates on older flows. Mortality rates decreased with increasing elevation and increased with increasing mean annual temperature (MAT). Annual mortality rates also increased with increasing mean annual precipitation (MAP) and increasing evapotranspiration (ET). ʻŌhiʻa seedling recruitment was rare or absent within most plots measured; ʻŌhiʻa seedlings were completely absent from 182 inventory plots, or 80% of all plots. Plots containing ʻŌhiʻa seedlings were found in the upper elevations of ohia forest range and were absent from lower elevation plots where non-native invasive species were prevalent. Result from this research will help inform additional critically needed ROD management efforts.
Results/Conclusions Where C. lukuohia-infected trees were detected, ʻŌhiʻa annual mortality rates averaged 9%. Results indicated that younger, smaller stature ʻŌhiʻa stands exhibited lower annual rates of mortality (i.e., 4 to 5%) compared to older, larger stature ʻŌhiʻa stands (i.e., 12 to 13%). Mortality rates were also lower in ʻŌhiʻa stands on young stands growing on young lava flows compared to rates on older flows. Mortality rates decreased with increasing elevation and increased with increasing mean annual temperature (MAT). Annual mortality rates also increased with increasing mean annual precipitation (MAP) and increasing evapotranspiration (ET). ʻŌhiʻa seedling recruitment was rare or absent within most plots measured; ʻŌhiʻa seedlings were completely absent from 182 inventory plots, or 80% of all plots. Plots containing ʻŌhiʻa seedlings were found in the upper elevations of ohia forest range and were absent from lower elevation plots where non-native invasive species were prevalent. Result from this research will help inform additional critically needed ROD management efforts.