OOS 16-6 - Dynamics of carbon cycling at temperate forest edges

Background/Question/Methods
Agriculture and urbanization have transformed much of the terrestrial environment into heterogeneous mosaics of fragmented ecosystems. Temperate forests are the most anthropogenically fragmented forest biome. In the northeast US, almost 25% of all forests are a mere 30m from a forest edge. Centuries of fragmentation have created a permanent shift in the microenvironment of a large and growing proportion of the global temperate forest area. With rising populations, expanding urban and agricultural areas, and ongoing deforestation, there is a critical need to understand fragmented forests as distinct ecosystems. In this presentation I will synthesize a suite of recent studies exploring dynamics of carbon cycling at temperate forest edges.

Results/Conclusions
Compared to the forest interior, forest edges are hotter and drier and experience increased light, atmospheric nitrogen deposition, and exposure to wind. In the tropics, these changes at the edge yield increased mortality and decreased tree growth rates. In the northeastern US, we find that forest edges adjacent to anthropogenic land covers show increases of 36.3% and 24.1% in forest growth and biomass, respectively, with no changes in mortality. While soil respiration typically increases with temperature, we find elevated rates of respiration at temperate forest edges in rural areas, but we find that respiration is suppressed at urban forest edges. At urban sites, respiration rates are 25% lower at the forest edge relative to the interior, likely due to extremely high temperature and aridity conditions near urban edges. Compared to intact forests, few experimental or observational studies have directly evaluated the confluence of environmental changes that occur in response to forest fragmentation. Any attempt to predict future forest responses to a changing climate must account for ongoing changes in the prevalence of forest edges and their differential responses to environmental change.