Grazing exclosures reveal divergent patterns of change in bunchgrass grasslands of Western Canada

Thirty-six long-term (14–83 years) cattle grazing exclosures and adjacent grazed pastures spanning a climatic gradient from cooler–wetter to warmer–drier growing seasons in south-central British Columbia were compared for temporal vegetation change. Trajectories of temporal vegetation change from non-metric multidimensional scaling were mostly scattered for the grazed areas, but more directed toward the dominant grasses, primarily rough fescue (Festuca campestris) or Kentucky bluegrass (Poa pratensis), for the exclosures. Plant community differences, detected only after 10 years of grazing exclusion, were primarily due to structural shifts in overall species cover related to growth increases of the dominant grasses inside exclosures. Species richness remained unchanged between the first and last sampling dates in both grazed areas and exclosures, with both treatments showing moderate degrees (15%–30%) of turnover in species composition. Shannon diversity declined in both treatments as a result of the structural changes in species cover. The results highlight the value of repeated monitoring of long-term exclosures for assessment of grassland resiliency to grazing. Further studies of the interaction of grazing and climate are needed for a more complete understanding of the ongoing vegetation change.

Reductions in foliar Hemiptera in portions of a fescue grassland invaded by Smooth Brome (Bromus inermis)

Fescue grassland in Canadian prairie is characterized by Plains Rough Fescue (Festuca hallii), but the introduced exotic grass, Smooth Brome (Bromus inermis), is expanding therein. Hemiptera play an important role as herbivores in vegetation. In an invaded fescue grassland in Manitoba, 52 plant species had a combined average cover of 216%. Kentucky Bluegrass (Poa pratensis), another exotic grass, was most abundant at 64%, followed by B. inermis at 21% and the native grass F. hallii at 18%. Across 47 random sample points, B. inermis cover ranged from 0% to 180%. At these points, 2445 specimens of Hemiptera were collected by sweep net and divided into 99 morphologically distinct species. Bromus inermis cover had negative correlations with Hemiptera species richness and diversity, but not with abundance and biomass of Hemiptera. However, B. inermis cover was negatively correlated with abundance of two individual species of Hemipteran leafhoppers in the family Cicadellidae: Doratura stylata and Diplocolenus configuratus. Total graminoid cover had no significant correlation with any of the above Hemiptera variables. We conclude that feeding requirements deter some phytophagous Hemiptera from entering sections of fescue grassland invaded by B. inermis. In this way, invasion by B. inermis can be expected to modify ecosystem function by increasing feeding pressure on neighbouring natural vegetation and other introduced species.

Horse ranching increases biodiversity in a foothills parkland prairie in northern Kananaskis Country, western Alberta

Vascular plant biodiversity was evaluated in two adjacent sections of a continuous prairie glade. One section has been subject to moderate grazing by feral horses (Equus ferus caballus) in late summer and fall for the past 25 years, while the other has been protected. From 28 June to 2 July 2009, we recorded cover for all vascular plants present in ten 1-m2 quadrats along five transects in each section. We calculated biodiversity measures, including species richness, evenness, and Shannon-Wiener and Simpson’s diversity indexes. Horse grazing did not affect richness but significantly increased evenness. Grazing increased the Shannon-Wiener index, but did not affect the Simpson’s index. Cover and frequency values for most species differed significantly between the two sites. Mountain Rough Fescue (Festuca campestris Rydberg) dominated the non-grazed site but several shorter grasses and different forbs dominated the grazed site. The plant community in the grazed areas can be seen as an earlier seral stage of the fescue community with a different contingent of plant species. Light grazing in part of the prairie glade increased overall plant diversity so that it provided more diverse animal habitat.