We present a vegetation succession model developed as part of the Across Trophic Level System Simulation (ATLSS) project, a multimodel designed to evaluate the potential effects of hydrologic restoration on various biotic components of the South Florida system. The model (VSMod) takes account of three of the most important factors driving succession in the Everglades: hydrology, fire and nutrients. VSMod has been developed to address scientific issues associated with the interaction of multiple environmental factors in the spatially-heterogeneous landscape of South Florida, to provide a standard basis to evaluate the impacts of alternative hydrologic plans on the vegetative landscape of the region, and to be linked to a variety of other ATLSS models for other trophic components.

VSMod is spatially explicit, generally operates at a spatial resolution of 500 m, and uses vegetation alliances based upon the Florida GAP map with a focus on the natural portions of the Everglades. The model time step is one year, though it takes account of within-year changes in hydrology, fire and nutrients. The model is framed as a Markov chain which specifies how the vegetation type within a particular 500 m landscape cell transitions from one year to the next. The transition rules depend upon the current vegetation type in the cell, the vegetation types in neighboring cells, the history of hydrology and fire in the cell and the nutrient changes in the cell. Each of these factors change from location to location and over time. Each vegetation type is characterized by its tolerance to the environmental factors, and the transition probabilities depend upon these tolerances. As long as environmental conditions are within the tolerance range for a vegetation type, that type will continue to occupy that site. When conditions are no longer appropriate for a vegetation type, there is a chance that a new type will occupy the site.

VSMod assumes that vegetation responds to hydroperiod as a measure of the hydrologic conditions. Transition probabilities depend upon whether hydroperiod is increasing or decreasing over certain time periods and the magnitude of this change. The model includes two general classes of fire, hot and cool, with differing effects on vegetation transition probabilities based upon the time since the last fire. VSMod also includes the effect of total phosphorus (TP) with a component that models the spatial spread of TP from various input sources. Interactions between the three environmental factors modify the transition probabilities between vegetation types.

We will present the application of VSMod to three hydrologic scenarios, making use of spatial output as well as percent cover summary time series to compare the scenarios. Additionally, we present the results of several different fire scenarios to illustrate how fire and hydrology interact in affecting the projected succession dynamics.

Contact Information: Scott M. Duke-Sylvester, The Institute for Environmental Modeling, University of Tennessee, 569 Dabney Hall, Knoxville, TN, 37996-1610 USA, Phone: 865-974-0223, Fax: 865-974-3067, Email: sylv@tiem.utk.edu

Lou Gross, University of Tennessee, The Institute for Environmental Modeling, 569 Dabney Hall, Knoxville, TN 37996-1610, Phone: 865-974-0223, Fax: 865-974-3076, Email: gross@tiem.utk.edu

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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