资源环境科技发展态势分析平台

When public lands were surveyed in the U.S., "witness trees" were often recorded to facilitate the relocation of property boundaries, and these records provide a snapshot of forest conditions prior to Euro-American settlement and land clearing. This study utilizes witness trees and present-day plot data to explore long-term vegetation changes at a regional scale. Landscape classes for a 5000 km(2) study area in Appalachian Ohio were defined by slope, aspect, topographic position, soil pH, and available water capacity. Cluster analysis and ordination revealed topo-edaphic patterns in the presettlement (c. 1800) and present-day forests, based on 5765 witness trees and 3249 contemporary trees occurring on 547 Forest Inventory and Analysis (FIA) subplots. Mesophication is evident, as the oak-hickory presettlement forest is now dominated by maple-poplar. Size-class analysis suggests the presettlement forest also experienced mesophication following xeric conditions of the preceding centuries. In both presettlement and contemporary forests, ridges form distinctive communities compared to slopes and valleys, although topographic distinctiveness is now more prevalent. Several taxa revealed changes in site affinities over the past two centuries; shifts in their realized niches suggest mesophication acts through diverse individualistic responses to a multiple set of interacting drivers. Specifically, regionally documented changes in land use, drought, N deposition, and fire at the time of the original surveys lead to altered competitive relationships.