|HOME SCHEDULE AUTHOR INDEX SUBJECT INDEX|
The edge paradox: Investigating the impacts of multiple and novel disturbances on forest ecosystem thresholds.
Parry Hecht, Brooke1, Vogt, Kristiina2, 1 Yale University, New Haven, CT2 University of Washington, Seattle, Washington
ABSTRACT- Edges have been considered potentially sensitive locations for detecting ecosystem response to anthropogenic and natural disturbances. The current paradigm is that plant responses to stress are amplified at ecotones, and that edges such as the treeline will be among the first to respond to climate change. However, previous edge studies have not been designed to examine ecosystem level resistance and resilience characteristics in response to multiple disturbances. For example, it is not clear how the function of the forest limit at the boreal-arctic ecotone changes when there is an overlay of human land use on climatic disturbances. We assessed the resistance characteristics of plant communities at the boreal-arctic forest limit in landscapes with existing and long-term legacies of human land use. It was hypothesized that the existence of multiple disturbances and land use legacies at the forest limit would decrease the resistance of the edge to disturbance, such that it would be less able to sustain its acquisition of limiting nutrients. It was also hypothesized that the accumulation of disturbance factors in the landscape could shift the location of functional thresholds through space. Research plots were established at the Betula pubescens forest limit and at 50m and 100m in elevation below the forest limit in Iceland. Plots were manipulated by the addition of sugar, with the aim of immobilizing soil nitrogen. Site response to the sugar disturbance was tracked by measuring foliar carbon and nitrogen, relative foliar chlorophyll content, leaf area, and leaf weight. The results of this research suggest that structural edges can have varying functional roles in the landscape, that functional thresholds are not necessarily associated with the structural edge, and that patterns associated with the treeline zone can change or disappear as legacies of disturbance accumulate in an ecosystem.
Key words: treeline, threshold, edge, disturbance