The forgotten forest: Ecosystem structure, function, and services of forested verges along interstates in Louisville, KY

Cities, and the interstates that connect them, alter the local environment by changing the microclimate, elevating pollutant deposition, introducing species, and disturbing ecosystems. How these multiple factors interact to affect natural areas within the urban environment and adjacent to interstates is important to understand. However, the vegetation communities along urban interstates are forgotten in urban and road ecology studies. In previously forested landscapes, remnant vegetation alongside urban interstates are "forgotten forests" that may be extremely beneficial in providing ecosystem services to society and habitat corridors for plant and animal species in the urban environment.The tree species composition of these forests was almost entirely native whereas exotic invasive species were more frequent in the understory (i.e., shrubs and vines). An exotic invasive shrub, Amur honeysuckle (Lonicera maackii), was the most important species explaining variation in woody vegetation composition. Amur honeysuckle may further enhance its own establishment by reducing native tree regeneration via lower light levels below honeysuckle shrubs, by increasing carbon reserves through an extended growing season, and by increasing nitrogen release from decaying honeysuckle litter during early spring before other species may access the nitrogen. The legacy of planting honeysuckle post-construction and disturbing soils during construction has lasting effects on the forest composition. Exotic species, including honeysuckle, were more prevalent and native tree regeneration was lower on disturbed soils. The combined impact of honeysuckle presence and soil disturbance diminished ecosystem services provided by these forests and the future ability of these forests to provide ecosystem services is expected to decline over time with the continued dominance of honeysuckle.Altered forest composition and diminished ecosystem services in locations where interstate construction activities occurred demonstrates the lasting effects of past human activity on forest composition. However, the existence of native stands along urban interstates provides hope that naturally regenerating forests can persist in the urban environment along interstate corridors. To promote the ability of native woody species to maintain their populations along forested highway verges, management needs to reduce exotic invasive species and to plant native species. These "forgotten forests" contribute many ecological services and they deserve recognition for their value.I examined forested verges along interstates in Louisville, KY and determined whether introduced plant species, disturbance legacy from interstate construction, current interstate impacts, or the surrounding urban context explained variation in woody plant composition and the underlying soil matrix. A primary production study and a decomposition experiment were conducted to assess the ecosystem function of these forests. The UFORE and CENTURY models were used to estimate ecosystem services (i.e., carbon storage and accumulation, pollutant removal) provided by these forest verges.