Changes in tree species abundance, forest composition and structure in response to climate change and disturbance in U.S. Central Hardwood Forests Region
Forest succession and disturbance will result in significant forest changes in the U.S. Central Hardwood Forest Region (CHFR). Projected climate change will further affect forest changes and consequently regional carbon dynamics. Projections of these changes have mainly relied on the niche and biogeochemical/ecophysiographical process models at regional scales. These models are limited in their ability to incorporate site-scale processes such as growth, mortality and competition and landscape-scale processes such as dispersal and tree harvest. We projected the forest changes in the CHFR in response to multiple interactive processes including forest growth and succession, dispersal, windthrow, and forest harvesting under alternative climate change scenarios. We coupled a forest landscape model (LANDIS PRO) and ecosystem model (LINKAGES II) to investigate how tree species abundance and forest composition and structure will change and the relative importance of climate change and disturbances in determining these changes over the next 300 years.
Forest composition and structure in CHFR gradually but substantially changed over time as a result of forest succession, disturbances, and climate change. Forest growth and succession was the primary driver of forest change in the short term (50-100 years). However, over the long-term (100-300 years), climate warming and altered precipitation patterns will have profound effects on forest composition. Northern species such as sugar maple and American beech may fare worse compared to current climate conditions, but southern species such as loblolly pine, yellow poplar, southern red oak and post oak may do better under the warming climates. The responses of forest changes varied among ecological section depending on soil nutrient and water regimes. The projected results showed that mesic upland forests were the most vulnerable. For example, temperate deciduous forests in ecological subsection such as Springfield Plateau, Ouachita Mountains, and Sandstone Mountain may transition to woodland and even savanna over the next 300 years. Disturbance especially forest harvesting significantly accelerated the decline of northern species and establishment of southern species.