Initial beaked hazel growth responses following protection from ungulate browsing

Abstract

Beaked hazel (Corylus cornuta Marsh) dominates the understory of many Boreal Mixedwood forests in central Alberta including those in Elk Island National Park, where this species demonstrates a high tolerance to browsing. This research quantified changes in beaked hazel stem morphology (total twig length and number) and leaf and twig biomass of current annual growth, both inside and outside 4 newly established exclosures during the growing seasons of 1999 and 2000. At 2 sites, leaf and twig current annual growth of beaked hazel shrubs recently protected from herbivory increased significantly (P < 0.05) by 85 to 114% relative to that of browsed shrubs. At another site, the removal of browsing changed the morphology of beaked hazel shrub growth (P < 0.05), with protected shrubs producing 26% more twigs that were shorter in aggregate length by 27%. The final site exhibited no significant (P > 0.05) changes in current annual growth at the individual shrub stem level, potentially due to intense intra-specific competition. These results indicate that at several locations in the Park, the recent history of intense browsing appears to be limiting the annual growth of beaked hazel, including browse production. Despite the general increase in growth of individual beaked hazel stems, however, no changes in production were evident at the community level (P > 0.05) with the removal of browsing after 2 years. Protection from browsing did increase average beaked hazel height by 40% over the same period.