The Vegetation Transition Magnitude (VTM) layer represents the relative magnitude of change applied to a pixel during the LANDFIRE (LF) vegetation update process. This layer provides information regarding disturbance type and the resulting impact on vegetation life-form or tree canopy cover.
The mapping process integrates annual disturbance layers. The effect of these disturbances on the vegetation are modeled or predicted using tables linking pre-disturbance existing vegetation type, height, and cover and possible disturbance types and severities with post-disturbance existing vegetation type, height, and cover. Forested vegetation tables are informed by computer simulations in the Forest Vegetation Simulator (FVS) while non-forest vegetation is informed by a series of simple rule-sets generated for each map zone. The tables spatially link vegetation and disturbance to assign existing vegetation, height, and cover. A code is assigned to unique combinations of disturbance type and change magnitude, which is expressed either in a change of vegetation life-form or a change in tree cover.