Populus forest characterization in Elk Island National Park relative to herbivory, prescribed fire, and topography

Abstract

Wild ungulate herbivory and prescribed fire can modify the vegetational characteristics of Populus forest plant communities and alter their potential to meet conservation objectives. Effective management of these areas depends on understanding the impact of these disturbances across natural landscapes. Our objective was to quantify various overstory and understory plant community characteristics in the Populus forests in and around Elk Island National Park, Alberta, under different disturbance regimes. Vegetation from 36 sites, stratified by four topographic positions and three historical treatment combinations of fire and native ungulate herbivory, were sampled. In these sites, we quantified tree density, basal area and cover, understory species richness and diversity, shrub density and height, as well as grass, forb, and browse annual net primary production (ANPP). Although tree canopy characteristics were similar under all three disturbances, small-diameter trees (< 5 cm) were nearly absent within the Park. The reference area outside the Park had greater browse-leaf and -twig ANPP, as well as shrub height, but lower grass ANPP. Inside the Park, burned areas had greater shrub density and ANPP of grass and forb components. Topographically, tree stand basal area, cover, and shrub height were greatest on the northern slope, as was browse-leaf ANPP. Species diversity and richness were relatively greater on the toe slope. Within the plant community variables examined, the disturbances and positions frequently interacted, particularly the burned treatment with the crest position and level of herbivory with the south-facing and north-facing slopes. The structure, composition, and ANPP of Populus forest in Elk Island National Park has been significantly affected by both ungulate herbivory and prescribed burning. These factors, along with topography, influence the vegetation and are consequently important for management of the park's habitat and ungulate populations. Key words: ANPP, national park, prescribed fire, structure, topography, ungulate herbivory.