COS 127-3 - Assessing forest composition change in the wildland-urban interface of the northeastern United States

Abstract: Forest composition can rapidly change due to climate change, disturbance, and human interventions. The wildland-urban interface (WUI)—locations where forests and other wilderness are adjacent to or intermixed with developed land—provides a unique opportunity to study how forest composition responds to urban development. Here, we aimed to assess how forest composition and composition change varies across different WUI change classes in the northeastern United States (US). We used two decades of remeasurements of Forest Inventory and Analysis (FIA) plots from the US Department of Agriculture Forest Service and WUI change classes developed from housing density data from the US Census Bureau (old-WUI, housing density threshold reached pre-1990; new-WUI, threshold reached 1990-2010; and non-WUI, low housing density across all recent censuses). We identified five major forest communities using latent Dirichlet allocation, a hierarchical Bayesian model originally developed for text mining which models how species cooccurrences in plots form communities like how word cooccurrences in sentences form topics. Mixed-effects models showed that fir-spruce and maple-beech-birch occurred at higher mean proportion and were more often the dominant community type in FIA plots than maple-oak, hemlock-ash, or pine-spruce communities. These two communities also occurred more often in non-WUI forests than old- or new-WUI forests. Plot remeasurements showed the mean proportion of maple-oak and maple-beech-birch significantly increased, fir-spruce and pine-spruce significantly decreased, and hemlock-ash did not significantly change over time. However, rates of change between remeasurements did not vary significantly among WUI change classes in both mean proportion of any individual community and multivariate change across all communities. Large differences in community composition but similar rates of change between WUI and non-WUI forests suggest that urbanization often acts as an abrupt driver of change in northeastern US forests, rapidly shifting forests from one community type to another, rather than a gradual or continuous driver of change that impacts the rate of community turnover.