Abstract
This paper describes a process to evaluate the ecological sustainability of fire-adapted ecosystems, using a case study based on ponderosa pine (Pinus ponderosa) forests. We evaluated ecological sustainability by: 1) using reference conditions and models to describe the historical range of natural variability; 2) using recent remote sensing-based mid-scale mapping of existing vegetation to describe current conditions; and 3) retooling the reference condition models to incorporate current natural and anthropogenic processes to project future conditions of ecosystems. Finally, we discuss a process for incorporating consequences of climate change. Using the Vegetation Dynamics Development Tool (VDDT), we constructed state-and-transition models (STM) for cold ponderosa pine bunchgrass systems of northern Arizona. We included historic and contemporary fire frequencies in the respective models, and integrated forest insect and disease events. For the contemporary model, we added anthropogenic transitions based on the types and frequencies of current management activities. We calculated the historic proportion of each vegetation state by averaging model outputs from multiple 1000 yr simulations. We summarized current conditions from remote-sensing based existing vegetation map data, and then used the contemporary model to generate out-year projections as expressions of current management practices. Finally, we generated ecological departure ratings based on disparities between current and historic conditions, and between projected and historic conditions. Our analysis indicated that fire suppression coupled with infrequent management activities contributed to already significant trends in departure from reference conditions. We concluded by recommending additional steps for evaluating the effects of climate change, as well as the effects of alternative management scenarios for addressing climate change issues.
Highlights
Introduction to the modeling softwareThe Vegetation Dynamic Development Tool (VDDT) (ESSA 2006) has been used by the National LANDFIRE program (Ryan et al 2006) and others such as The Nature Conservancy (TNC) (Smith 2006) to develop state-and-transition models and descriptions of reference conditions
A comprehensive evaluation of ecological sustainability includes the consideration of all natural resources including soil, water, and air, but here we focus on vegetation diversity and related ecological processes such as fire
Our findings indicate that current conditions and projected conditions in the ponderosa pine bunchgrass potential natural vegetation types (PNVTs) are approximately 97 % departed from reference conditions, as represented by an ecosystem condition class of 3
Summary
Introduction to the modeling softwareThe Vegetation Dynamic Development Tool (VDDT) (ESSA 2006) has been used by the National LANDFIRE program (Ryan et al 2006) and others such as The Nature Conservancy (TNC) (Smith 2006) to develop state-and-transition models and descriptions of reference conditions. We retooled these models to project future conditions for the ponderosa pine bunchgrass forest model by replacing historic probabilities and transitions with contemporary transitions and attendant frequencies that reflect current land management.
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