VDDT/TELSA -- Vegetation Disturbance Dynamics Tool/Tool for Exploratory Landscape Scenario Analyses

DESCRIPTION

As described in "A Risk Based Comparison of Potential Fuel Treatment Tradeoff Models", VDDT was developed to support the Interior Columbia River Basin Assessment. This tool simulates changes in vegetative composition and structure using disturbance probabilities and successional pathways data. VDDT has been recently enhanced to enable more realistic modeling of infrequent large scale disturbances such as stand replacement wildland fires.

VDDT models typically apply to Potential Vegetation Types (PVT). For each PVT succession classes are defined according to the cover type and structural stage combinations that exist. In the absence of disturbance, vegetation progresses (grows) from one succession class to the next. This time-dependent progression is referred to as a successional pathway. Natural or man- caused disturbances also affect vegetation.

In VDDT disturbances are defined for each succession class according to type (e.g. wildland fire, harvest, etc.), succession class destination, probability of occurrence, and the relative ages for which each probability applies. For each year of the simulation, VDDT cycles through the landscape, generates a random number, and determines whether each landscape unit merely gets a year older, moves to a new succession class, or has a disturbance applied to it.

VDDT models have been built for several areas outside the Columbia basin. The Siuslaw NF in Oregon's Coast range has developed models that apply to both public and private lands in northwest Oregon. Past studies have assumed that private lands are harvested at some fixed rotation age (e.g. 50 years). In the Siuslaw model, private land harvest probabilities vary according to the class of owner and stand age. This results in a more realistic projection of the condition of intermingled private land. The Siskiyou and Shasta-Trinity NFs are using VDDT to project vegetative conditions in areas including wildlife reserves to depict the consequence of active intervention versus passive management.

The ESSA Technologies Web site contains in depth information on VDDT, including:

• general model description;
• landscape characterization;
• model operation and output;
• user-defined data requirements;
• model documentation;
• model users, and system requirements.

This site also allows users to download the VDDT model.

TELSA is a spatially explicit extension to VDDT that simulates forest succession, natural disturbances, and forest management activities. It is designed to simulate up to 250,000 ha landscape units and has been applied successfully to simulate the dynamics of 116,000 ha landscape. At the core of the process is a tool with which to simulate multiple scenarios, each characterized by different assumptions about management actions and natural disturbances. Since wildfires and other natural disturbance events that affect vegetation dynamics are inherently unpredictable, the model can use multiple stochastic simulations of each scenario to provide estimates of the mean, range and variability of the selected performance indicators.

The ESSA Technologies Web site provides detailed information regarding TELSA, including:

• model description;
• data requirements;
• model output;
• technical requirements, and,
• point of contact.

SCALE AND AREAS OF APPLICATION

SURVEY COMMENTS

No survey respondents mentioned using VDDT/TELSA.

BENEFITS (PROS)

COSTS (CONS)

RECOMMENDATIONS