CHANGES IN STRUCTURE OF A BOREAL FOREST COMMUNITY FOLLOWING INTENSE HERBIVORY BY MOOSE

Abstract

Herbivores have influenced the structure, biomass, and species composition of vegetation in heavily browsed or grazed areas. The introduction of moose (Alces alces) to Newfoundland in 1878 and 1904, and the subsequent closure of hunting with the establishment Gros Morne National Park in 1973 have resulted in current moose densities in excess of 4.0 moose/km². We hypothesized that browsing by moose has changed the plant species composition, the availability of browse, and influenced forest successional patterns. Browse use, availability, and species diversity indices in 1996 were compared to results of browse surveys conducted during 1977 in Gros Morne National Park, Newfoundland. In the Park, mean pellet group counts from surveys during 1996 were significantly greater than those of surveys in 1977, and were also greater than in sites located outside park boundaries (P = 0.001 and P = 0.017, respectively). In 1996, the mean browsing intensity was significantly greater than that of 1977. Significant differences (P < 0.001) occurred among proportions of available browse species between 1977 and 1996 at all sites. Species preferred by moose in 1977 decreased in availability  by 1996 while species not browsed or browsed infrequently in 1977 increased in abundance.  Selection of browse species by moose changed with changing availability of forage. Mean indices of species diversity in 1977 were significantly greater (P < 0.01) than species diversity indices at the same sites in 1996. No significant difference was found between mean indices for 1977 and 1996 in sites of low moose density located outside the Park boundaries. Data suggest that moose have changed species composition, the proportion of available browse remaining, and hence have influenced forest successional patterns within Gros Morne National Park.