Modeling change in maximum growing space under projected climate scenarios in the Central Hardwood Forest using an ecosystem process model
Ecosystem process models have been successfully used to model forest response to climate change at a variety of scales. The results for individual tree species can be used to assess species establishment probability (SEP), which in turn reveals the trend of expansion or decline of each species under changing climates. Maximum growing space (MGS) or forest carrying capacity is also influenced by climate, specifically available moisture. MGS determines the maximum number of trees or biomass per unit area and in turn partially drives ecosystem type transition (e.g., forest, woodland, savanna, or prairie). Forest ecosystem dynamics can be better described using both SEP and MGS under changing climates. To date, MGS is relatively less studied than SEP. We used the ecosystem process model LINKAGES v2.2 to quantify changes of MGS in the Central Hardwood Forest region. We used soil and climate data as inputs to model forest succession and mortality as well as soil moisture and nutrient cycling. We used LINKAGES to model the maximum biomass, stem density, and basal area for 74 ecological subsections within the central interior broadleaf forest ecological province under current climate conditions and three statistically downscaled climate projections: CGCM3(T47)-A2, GFDL-A1fi, and PCM-B1. The GFDL-A1fi scenario projects a high increase in temperature with a decrease in precipitation, while the CGCM3(T47)-A2 scenario projects a more modest increase in temperature and decrease in precipitation. The PCM-B1 scenario has a small increase in temperature with an increase in precipitation.
There were only slight decreases or moderate increases of maximum site biomass, basal area, and average stem density over the entire study area under the PCM scenario; the greatest increases occurred in southern Indiana and Kentucky. Under both the GFDL and CGCM climate scenarios there was a decline in maximum site biomass and basal area over the entire study area. The largest reductions in maximum site biomass and basal area occurred under the GFDL scenario in the western most Central Hardwoods region (Ouachita Mountains and Ozark Highlands ecological sections), suggesting the possibility of transition from forest to woodland or savanna in these regions. These results will be used to parameterize the LANDIS PRO 7.0 forest landscape model to simulate changes in maximum available growing space at the subsection level and transition of ecosystem type at the site level over the next century under the three climate scenarios.