Tsuga canadensis (Eastern Hemlock) forests are experiencing widespread mortality due to the invasive insect Adelges tsugae (Hemlock Woolly Adelgid). This study sought to document the community response to HWA across latitude. I selected two sensitive response groups—plants and ants— to use as biological indicators of ecosystem change to monitor differences along a natural gradient of Eastern Hemlock mortality among 3 forest types: relatively healthy Eastern Hemlocks, dead or dying Eastern Hemlocks, and hardwood stands. I sampled understory vegetation, ants, and soils at each site and compared sites using a linear mixed-model to discern the best predictors of species density. I also compared analyses of variances across forest types among response variables. There was an average two-fold increase in understory vegetation species density between Eastern Hemlock and hardwood forests; ant species density was not influenced by forest type. Analysis of variance comparisons for understory vegetation showed that forest type affects understory vegetation, a result which was attributable to differences in a few dominant plant species. The linear mixed-model showed that Eastern Hemlock density and latitude were important predictors for both ant and vegetation species densities; soil pH and stand density were predictors for vegetation species density, and litter depth was a predictor for ant species density. My findings show that large structural changes in Eastern Hemlock forest communities (induced by the effects HWA) alter a foundation ecosystem by shifting the composition of understory plant communities, but not ant communities.