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a b s t r a c tA range of economic and societal issues has resulted from fossil fuel consumption in the transportation sector in the U.S. These include health related air pollution, climate change, dependence on imported oil, and other oil related national security concerns. Biofuels production from various lignocellulosic biomass types, such as wood, forest residues, and agriculture residues, have the potential to replace a portion of the total fossil fuel consumption. This study focused on locating biofuel facilities and designing the biofuel supply chain to minimise the overall cost. For this purpose, an integrated methodology was proposed by combining the Geographic Information System technology with simulation and optimisation modelling methods. The GIS-based method was used as a precursor for selecting biofuel facility locations by employing a series of decision factors. The identified candidate sites for biofuel production served as inputs for simulation and optimisation modelling. The simulation/optimisation model and identified locations provided an integrated decision support system for decision makers to determine the optimal cost, energy consumption, and emissions for candidate locations. This novel methodology development extends prior research.

Biological invasions are often exacerbated by disturbance or deviations from historic disturbance regimes. Dense understory layers of invasive exotic plants can alter successional trajectories, resulting in consequences that cascade through the biota. However, it is unclear if such layers are self-sustaining or maintained by chronic disturbances that asymmetrically depress native competitors. We examined the role of white-tailed deer (Odocoileus virginianus Zimm.) herbivory and drought on the permeability of recalcitrant understory layers dominated by the invasive exotic Microstegium vimineum (Trin.) A. Camus in 15 exclosures and 15 control plots from 1997 to 2006. This study was conducted in Cades Cove, Great Smoky Mountains National Park, Tennessee, USA. M. vimineum cover exhibited high inter- and intra-annual variation in both exclosures and controls, but displayed a significant correspondence to drought severity. Native species richness and the abundance of woody plants increased within exclosures, but not controls, following a drought-induced nadir in M. vimineum cover that occurred in 2000. By 2003, all height classes of native tree seedlings were present in exclosures and seedlings were advancing into the sapling layer (>or=50 cm tall). After 10 years, no tree seedling on a control plot had been able to attain and maintain a height >or=20 cm. Our results suggest that chronic herbivory inhibits state transitions that could occur in response to intermittent disturbances, which reduce the abundance of the invader. Consequently, recalcitrance is likely reinforced by chronic herbivory.