SIMULATING EFFECTS OF FIRE ON NORTHERN ROCKY-MOUNTAIN LANDSCAPES WITHTHE ECOLOGICAL PROCESS MODEL FIRE-BGC

A mechanistic, biogeochemical succession model, FIRE-BGC, was used to investigate the role of fire on long-term landscape dynamics in northe rn Rocky Mountain coniferous forests of Glacier National Park, Montana , USA. FIRE-BGC is an individual-tree model-created by merging the gap -phase process-based model FIRESUM with the mechanistic ecosystem biog eochemical model FOREST-BGC-that has mixed spatial and temporal resolu tion in its simulation architecture. Ecological processes that act at a landscape level, such as fire and seed dispersal, are simulated annu ally from stand and topographic information. Stand-level processes, su ch as tree establishment, growth and mortality, organic matter accumul ation and decomposition, and undergrowth plant dynamics are simulated both daily and annually. Tree growth is mechanistically modeled based on the ecosystem process approach of FOREST-BGC where carbon is fixed daily by forest canopy photosynthesis at the stand level. Carbon alloc ated to the tree stem at the end of the year generates the correspondi ng diameter and height growth. The model also explicitly simulates fir e behavior and effects on landscape characteristics. We simulated the effects of fire on ecosystem characteristics of net primary productivi ty, evapotranspiration, standing crop biomass, nitrogen cycling and le af area index over 200 years for the 50,000-ha McDonald Drainage in Gl acier National Park. Results show increases in net primary productivit y and available nitrogen when fires are included in the simulation. St anding crop biomass and evapotranspiration decrease under a fire regim e. Shade-intolerant species dominate the landscape when fires are excl uded. Model tree increment predictions compared well with field data.