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Invasive species are one change agent that can impact natural areas and can interact with other ecosystem modifiers such as climate change and fire.�State-and-transition simulation models (STSMs) can provide information to resource managers about potential outcomes of management actions in the face of multiple, interacting change agents. These models divide the landscape into various states (such as uninvaded, low invasion, moderate invasion, high invasion) and simulate changes in states through time based on transitions that can be natural processes (such as growth and spread) or management actions (such as control). One of the major strengths of this tool is the ability to simulate and evaluate various �what if� scenarios. For example, a no management action scenario can provide information on how big a problem is while an unlimited management scenario can provide information on how much effort would be required to achieve long-term suppression. Scenarios can be explored to determine efficient combinations of management practices, both economically and ecologically, and to determine potential impacts of climate change and invasion effects on fire regimes.�We will present an example of these types of �what if� scenarios for buffelgrass (Cenchrus ciliaris) invasion in Saguaro National Park, Arizona, taking into account potential effects of climate change and buffelgrass alteration of the fire regime.