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Increased wildfires and temperatures due to climate change are expected to have profound effects on forest productivity and nitrogen (N) cycling. Forecasts about how wildfire and climate change will affect forests seldom consider N availability, which may limit forest response to climate change, particularly in fire-prone landscapes. The overall objective of this study was to examine how wildfire and climate change affect long-term mineral N availability in a fire-prone landscape. We employed a commonly used landscape simulation model (LANDIS-II) in the New Jersey Pine Barrens, a landscape characterized by frequent small fires and fire-resilient vegetation. We found that fire had little effect on mineral N, whereas climate change and fire together reduced mineral N by the end of the century. Though N initially limited forest productivity, mineral N was no longer limiting after 50 years. Our results suggest that mineral N is resilient to fire under our current climate but not under climate change. Also, predictions that do not consider N limitation may underestimate short-term but not long-term productivity responses to climate change. Together these results illustrate the importance of including N dynamics when simulating the effects of climate change on forest productivity, particularly in fire-prone regions such as the New Jersey Pine Barrens. [ABSTRACT FROM AUTHOR]

Abstract: Changes in land use patterns in and around forests, including rural development and road building, have occurred throughout the United States and are accelerating in many areas. As a result, there have been significant departures from ‘natural’ or pre-settlement disturbance regimes. Altered disturbance regimes can shift composition and dominance in tree species communities, potentially affecting ecosystem functioning. We examined the potential consequences of various forest management practices and forest fragmentation on tree community composition. Both forest management and fragmentation are changing as land use changes within the New Jersey Pine Barrens (NJPB). The NJPB has and is continuing to experience rapid rural development and urbanization that are altering the types, frequency, and intensity of forest management, and are increasing forest fragmentation. In the NJPB, the size and frequency of wildfires have declined and the use of prescribed fires is limited to a small portion of the landscape. In addition, the expansion of roads and decline in total forested area – two common measures of fragmentation – may impede the ability of tree species to colonize available habitat. To assess the consequences of fire management and fragmentation on fire regimes and forest communities, we simulated forest landscape change using LANDIS-II, a stochastic, spatially dynamic forest succession model that simulates the growth of tree species cohorts (defined by species and age), dispersal and colonization, and mortality. Simulated fires are sensitive to fuel loads and fuel load continuity. We constructed scenarios to mimic the pre-colonial contiguous landscape with an estimated pre-colonial fire regime; scenarios of the current day landscape with current and potential fire management; and scenarios designed to highlight the effects of fragmentation. Our simulations indicate that relative to the pre-colonial landscape and fire regime, the landscape is changing from a pine-dominated to an oak-dominated state. However, within areas where prescribed burning remains a viable management option, a doubling of the mean annual area that is managed with prescribed burns may substantially push the system back towards pre-colonial conditions, although oaks will continue to retain a higher than pre-colonial dominance. Our results also indicate that aside from a reduction in the potential fire sizes, fragmentation does not appear to substantially alter forest successional dynamics. In summary, our simulations estimate the departure from pre-colonial conditions and indicate the potential for a limited restoration of these conditions. [Copyright &y& Elsevier]

Disturbance regimes within temperate forests can significantly impact carbon cycling. Additionally, projected climate change in combination with multiple, interacting disturbance effects may disrupt the capacity of forests to act as carbon sinks at large spatial and temporal scales. We used a spatially explicit forest succession and disturbance model, LANDIS-II, to model the effects of climate change, gypsy moth (Lymantria dispar L.) defoliation, and wildfire on the C dynamics of the forests of the New Jersey Pine Barrens over the next century. Climate scenarios were simulated using current climate conditions (baseline), as well as a high emissions scenario (HadCM3 A2 emissions scenario). Our results suggest that long-term changes in C cycling will be driven more by climate change than by fire or gypsy moths over the next century. We also found that simulated disturbances will affect species composition more than tree growth or C sequestration rates at the landscape level. Projected changes in tree species biomass indicate a potential increase in oaks with climate change and gypsy moth defoliation over the course of the 100-year simulation, exacerbating current successional trends towards increased oak abundance. Our research suggests that defoliation under climate change may play a critical role in increasing the variability of tree growth rates and in determining landscape species composition over the next 100 years.