During the last six years, large areas of healthy ??hi?a lehua trees (Metrosideros polymorpha) have died rapidly on Hawai'i Island. The fungus Ceratocystis fimbiata was routinely found associated with rapidly dying individuals of ??hi?a, Hawai'i's most widespread native tree. Pathogenicity of this fungus was proven, and M. polymorpha was recorded as a new host for C. fimbriata. Imagery of ??hi?a mortality obtained in 2012 revealed expanses of mortality greater than expected. ?hi?a mortality in field plots established within the study region averaged 39 percent. Mortality was comparable across size classes and forest compositions. Average annual ??hi?a mortality rates were 24 percent based on basal area and 28 percent based on stem density measures. The dearth of ??hi?a seedling recruitment and characteristic understory dominance of non-native species documented within the study’s research plots, coupled with the lethality of C. fimbriata to ??hi?a, suggest that these forests likely will be dominated by non-native species in the future in the absence of concerted active management.