title: Disentangling herbivore impacts on Populus tremuloides: a comparison of native ungulates and cattle in Canada's Aspen Parkland.
abstract: Ungulates impact woody species' growth and abundance but little is understood about the comparative impacts of different ungulate species on forest expansion in savanna environments. Replacement of native herbivore guilds with livestock [i.e., beef cattle (Bos taurus)] has been hypothesized as a factor facilitating trembling aspen (Populus tremuloides Michx.) encroachment into grasslands of the Northern Great Plains. We used a controlled herbivory study in the Parklands of western Canada to compare the impact of native ungulates and cattle on aspen saplings. Native ungulate treatments included a mixed species guild and sequences of herbivory by different ungulates [bison (Bison bison subsp. bison), elk (Cervus elaphus) then deer (Odocoileus hemionus); or deer, elk, then bison]. Herbivory treatments were replicated in three pastures, within which sets of 40 marked aspen saplings (<1.8 m) were tracked along permanent transects at 2-week intervals, and compared to a non-grazed aspen stand. Stems were assessed for mortality and incremental damage (herbivory, leader breakage, stem abrasion and trampling). Final mortality was greater with exposure to any type of herbivore, but remained similar between ungulate treatments. However, among all treatments, the growth of aspen was highest with exposure only to cattle. Herbivory of aspen was attributed primarily to elk within the native ungulate treatments, with other forms of physical damage, and ultimately sapling mortality, associated with exposure to bison. Overall, these results indicate that native ungulates, specifically elk and bison, have more negative impacts on aspen saplings and provide evidence that native and domestic ungulates can have different functional effects on woody plant dynamics in savanna ecosystems.
authors: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada, Edward.bork@ales.ualberta.ca.
authors: Edward W
authors: EW
authors: Bork
authors: Cameron N
authors: CN
authors: Carlyle
authors: James F
authors: JF
authors: Cahill
authors: Rae E
authors: RE
authors: Haddow
authors: Robert J
authors: RJ
authors: Hudson
mesh_terms: D000416:Alberta; D000704:Analysis of Variance; D000818:Animals; D016164:Bison / Q000502:physiology*; D002417:Cattle / Q000502:physiology*; D003670:Deer / Q000502:physiology*; D017753:Ecosystem; D060434:Herbivory / Q000502:physiology*; D016014:Linear Models; D011156:Population Density; D011157:Population Dynamics; D032107:Populus / Q000502:physiology*; D013045:Species Specificity
references: Ecology. 2011 Aug;92(8):1626-36
references: 21905429
references: Oecologia. 1999 Aug;120(2):287-294
references: 28308091
references: Oecologia. 1989 Mar;78(4):443-457
references: 28312172
references: Glob Chang Biol. 2013 Apr;19(4):1188-96
references: 23504895
references: Science. 2011 Sep 23;333(6050):1753-5
references: 21940896
references: J Anim Ecol. 2010 Mar;79(2):372-82
references: 20039982
references: Ecol Appl. 1993 Nov;3(4):631-643
references: 27759299