QUANTIFYING THE IMPACT OF VEGETATION ON EROSION PROCESSES ALONG THE NIAGARA ESCARPMENT IN THE HAMILTON REGION OF SOUTHERN ONTARIO

Landforms have a significant influence on vegetation growth and development, and vegetation in turn is a regulator of landform evolution. The Niagara Escarpment of southern Ontario is a striking geomorphological landform that extends over 700 km from the Niagara Gorge northward to the Bruce Peninsula of Lake Huron. The City of Hamilton is bisected by the escarpment which divides the lower Lake Ontario and downtown core from upper residential and commercial areas above. Numerous access roads crossing the escarpment have provided a link between these city areas. However, the frequency of large rockfalls and debris slides from the exposed escarpment face has resulted in reoccurring road closures in recent years and has prompted the city to seek information on the processes affecting escarpment erosion and slope stability.

Little is currently known about how vegetation growth contributes to erosion processes operating on the escarpment face. However, plants play a key role in weathering regolith in the critical zone, which varies as a function of hydraulic conditions, vegetative architecture, and substrate structure. Extreme weather events contribute to biomechanical weathering and fracture widening processes by increasing external forces on tree boles, resulting in root stretching and dislocation. This presentation will identify the vegetation characteristics of a selected area of the escarpment in the Hamilton region and its relationship to bedrock lithology, fracture spacing, slope, and aspect. Particular attention will be given to the effect of vegetation growth in bedrock fractures and quantification of chronic wind forcing on tree stands using accelerometers to measure the tilt of tree boles during canopy sway in response to wind gusts. In addition, a methodology for determining qualitative relationships between lithological and vegetation characteristics that may be applied to other areas of the escarpment will be outlined. While this research is still in the initial stages of data collection, observational data suggest the existence of a strong relationship between vegetation growth, lithologic characteristics, and erosion potential as evident by the extensive penetration of roots through bedrock disconformities and fractures along the escarpment.