The Path Landscape Model(Path) is a simulation modeling environment built on state-and-transition modeling concepts that simulates future landscape conditions given current conditions and a set of probabilistic disturbance events. Path is built upon ESSA's VDDT simulation program and can be used to evaluate the potential long-term outcomes of different management strategies.
Path relies on S/T models where each state can be mapped on the landscape and each transition has been quantified by being assigned a probability of occurring. Once the current condition of the states has been mapped on the landscape, that information becomes the initial conditions for the scenario modeling.
Often more than one S/T model is needed to capture the ecological dynamics of a landscape. In these cases, the landscape is stratified based on biophysical and management attributes. Each stratum has a vegetation model associated with it that identifies the full suite of possible vegetation states and transitions between them. Transitions between states may be driven by natural processes such as succession and disturbance or by anthropogenic changes such as management actions. Within each stratum, the landscape is divided up into small polygons, and Monte Carlo simulation methods are used to determine if and when a transition happens to each polygon and if a transition occurs, then determines the new state. At the end of each time step, information on the states is collected and the simulation continues.
Outputs of the scenario models can be displayed to allow for comparison and ranking of management alternatives at the level required for decision making. Path can be used to evaluate both predictions and uncertainty, or levels of confidence in model predictions. For example, results to be displayed could include map, tabular and graph summaries of: current and future vegetation; current and future wildlife habitat condition; and model inputs (location and proposed timing of management activities). Results in tabular form can be easily exportable to other applications such as MS Excel and statistical software.
Currently, Path is a non-spatial form of landscape analysis. Non-spatial approaches treat each individual simulation polygon independently and track the only the frequency of vegetation states over time and not their configuration on the landscape. These models require fewer inputs than spatially explicit ones and are faster to simulate on a computer. Spatial models can provide additional information, such as the implications of alternative management strategies for the fragmentation of wildlife habitat or the comparison of alternative spatially explicit rules about where management actions may or may not occur. ESSA is currently working on implementing a spatially-explicit version of Path.
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