HORIZON is a landscape-level application of the stand-level ecosystem management model FORECAST. It is a raster-based, GIS-type (Geographic Information System) model in which the ecosystem development over time is simulated - stand dynamics, succession, and a variety of plant population, plant community and ecosystem processes - by FORECAST. Input GIS layers define topography to permit the development of a DEM (digital elevation model), roads, streams and any other permanent site or tree growth potential (e.g. site index) features that contribute to the definition of site quality. The map is populated by trees and other vegetation, snags, coarse woody debris, soil organic matter and soil fertility measures by running FORECAST for each site type polygon in a "setup" mode. These runs describe for each site type a history of ecosystem development, plant growth and disturbance events that collectively define the starting condition of each site-level ecosystem (polygon). A set of site-specific management strategies is then defined, and HORIZON is run for the desired length of time. The results for the entire area and for the individual polygons are then presented in graphical and tabular form, utilizing the graphical and tabular utilities of FORECAST for the individual polygons/cutblocks, and HORIZON graphical and tabular summaries for the entire area.