Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale, Michigan, USA

Abstract

Large mammalian herbivores can influence the dynamics and structure of ecosystems by selectively removing tissues of specific plant species. The plant community composition can be altered as animals feed on some species but not others, changing the biomass, production, and nutrient cycling of an entire ecosystem. We used four paired moose (Alces alces) exclosures and browsed plots (built between 1948 and 1950) on Isle Royale, Michigan, to examine the influence of moose on aboveground biomass, production, and annual litterfall of boreal vegetation in 1987. Tree biomass was significantly greater (X = 230 vs. 150 Mg/ha, df = 3, P < .05), shrub biomass was significantly less (X = 1.9 vs. 3.1 Mg/ha, P < .05), and herb biomass was significantly less (X = 0.2 vs. 0.8 Mg/ha, P < .05) in exclosures than in browsed plots. Tree production was greater in exclosures than in browsed plots (X = 7.9 vs. 5.0 Mg.ha—1.yr, P = .05), but there was no difference in the production per unit biomass between exclosures and browsed plots. Shrub production in exclosures was similar to that of browsed plots (X = 3.5 vs. 2.3 Mg.ha—1.yr—1, P < .05), despite total vegetation biomass differences between paired plots. There was significantly greater herb litter produced in the browsed plots than in the exclosures (X = 0.7 vs. 0.1 Mg.ha—1.yr—1, P < .05). Moose browsing prevented saplings of preferred species from growing into the tree canopy, resulting in a forest with fewer canopy trees and a well—developed understory of shrubs and herbs. In addition, browsing may have altered the eventual balance of white spruce (Picea glauca) was balsam fir (Abies balsamea), causing an increase in the former and a decrease in the latter. Thus, browsing by moose influences in long—term structure and dynamics of the boreal forest ecosystem, which has important implications for forest ecosystem management, especially where the population dynamics of moose are regulated.

Relationships between the species composition of forest field‐layer vegetation and environmental drivers, assessed using a national scale survey

“…Wild ungulates are important in determining forest field layer structure across a wide range of ecosystems (e.g. Mcinnes et al 1992;Augustine & McNaughton 1998). They can facilitate the long-distance dispersal of a large number of plant species (Vellend et al 2003;Eycott et al 2004), but are often associated with a decline of palatable species (Augustine & DeCalesta 2003;Kirby 2001).…”

“…Thus, while an understanding of forest spatial dynamics is important, buffer zones and provision of appropriate exclosures in areas of significant species loss (e.g. Mcinnes et al 1992;Cooke 2002), or desired expansion (Romagosa & Robison 2003;Palmer et al 2004;Truscott et al 2004) may prove as, or more, significant to the delivery of conservation objectives.…”

“…2004), with successional development (He et al . 2002) and direct management, including coppicing (Mason & MacDonald 2002) and grazing by wild ungulates or livestock (Mcinnes et al . 1992;Garin et al .…”

Opposing plant community responses to warming with and without herbivores

“…Vertebrate herbivores in particular may be of key importance to plant community response to warming because they influence plant biomass, soil nutrient dynamics, and species composition of plant communities (14)(15)(16). In high latitude systems, experimental evidence indicates that both small and large mammalian herbivores play an important role in structuring plant communities through selective foraging that not only reduces the abundance of preferred species but also alters competitive interactions among plant species (17,18).…”

Moose Foraging in the Temperate Forests of Southern New England

“…Only stems that were unequivocally browsed (i.e., torn and ragged) were recorded as "yes", and no distinction was made between recent and old browsing; thus, our browsing surveys likely reflected a browsing history that extended back months and even years (McInnes et al 1992). Moose also strip bark from the trunks of saplings and pole-sized trees and walk on or pull down small trees to browse the nutritious leading shoots, breaking stems .…”