Spatial Patterns of Tree Invasion in an Old Field: Implications for Restoration
Buschert, Karen Elizabeth
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In north-eastern North America, abandoned agricultural fields typically revert to forest after many decades of spontaneous succession. This process can be influenced in part by nearby available propagule sources and their natural patterns of dispersal. Ecological restoration encompasses understanding this natural process and how it may influence active or passive restoration efforts. This study attempts to determine the spatial and temporal patterns of establishing trees arising in an old field at 10 years post-cultivation and the implications of this process on restoration at rare and other similar sites. The 0.8 ha field is situated at rare, an ecological reserve in Cambridge, Ontario and is bordered by forest or hedgerow on all sides. Using Environmental Monitoring and Assessment Network (EMAN) protocols, vegetation sampling was completed in the field and adjacent forest and hedgerow. A complete tree inventory was undertaken in the field, followed by a sampling of potential seed sources in the forest and hedgerow. ESRI ArcMap, a Geographic Information System (GIS) was utilized for both spatial representation and spatial analysis. Research revealed that the application of geostatistics to ecological data here and elsewhere in the literature has some specific challenges which need to be overcome for analysis of spatial data. Currently, the old field shows early signs of woody plant invasion from the nearby forest. Both trees and shrubs have become established, though not yet dominant. The primary dispersal of these species follows spatial patterns based on method of dispersal (wind, nut, fruit and clonal) and there is a higher degree of clustering of all species closer to the forest edge. Invasive species such as Rhamnus cathartica and Rhamnus frangula have become established in the old field and may influence successional patterns. Implications for restoration include the creation of goals and objectives which incorporate these natural processes into a future management plan. Specific recommendations include: 1) Develop a management strategy for invasive species such as Rhamnus spp. which can detrimentally affect restoration goals; 2) Continue to monitor EMAN plots for the production of time-series data on the same site; 3) Identify sites with good regeneration potential based on spatial patterns identified in this research and collect additional information such as soil conditions, canopy cover, etc.; 4) Extend the current GIS database created for this thesis to become an inventory of natural and cultural features for the reserve. Advanced spatial analysis required a more extensive data set and/or custom programming.