Grazing history versus current grazing: leaf demography and compensatory growth of three alpine plants in response to a native herbivore (Ochotona collaris)

Abstract

Summary 1We measured leaf births, leaf deaths and leaf length of three alpine perennial species, Kobresia myosuroides , Erigeron humilis and Oxytropis nigrescens , from sites with different grazing histories (strong or weak) in response to two levels of current season grazing (present or absent) by collared pikas ( Ochotona collaris ), a small lagomorph, in the south-west Yukon. 2 All three species appeared to tolerate the removal of 58-61% of summer leaf production under natural conditions. Grazing history, which was defined by the location of plants located either < 2 m or > 6 m from boulderfields with a history of occupation by pikas, was the most significant factor determining shifts in leaf births and leaf deaths following herbivory. 3 The only detectable influence of current season herbivory for any measured species was a reduction of leaf length of Kobresia . 4 A comparison of historically grazed with historically ungrazed plants indicated several changes in leaf demography and morphology. Kobresia leaves were generally shorter and had higher rates of production of new leaves. Oxytropis had higher rates of new leaf production. Erigeron had fewer leaf births throughout the summer, but showed a large and highly significant delay in the timing of leaf senescence. 5 These responses can be largely understood as strategies to avoid the predictable intensive late season foraging that is characteristic of pikas. Morphological mechanisms allow these species to tolerate and, more importantly for the herbivore, persist under heavy and chronic grazing.

Evidence for Selective Caching by Arctic Ground Squirrels Living in Alpine Meadows in the Yukon

“…Approximately 100 species of vascular plants have been recorded at our site, with communities dominated by Salix spp., Carex consimilis, and Dryas octopetala (McIntire and Hik, 2002). Ground cover at the site was a mosaic of unvegetated boulder fields (36%); patches of moss, lichens, and bare ground (37%); and vascular plants (27%).…”

“…Ground cover at the site was a mosaic of unvegetated boulder fields (36%); patches of moss, lichens, and bare ground (37%); and vascular plants (27%). Daily surface temperatures from June to August range from below 0˚C to +40˚C (McIntire and Hik, 2002).…”

Influences of chronic and current season grazing by collared pikas on above-ground biomass and species richness in subarctic alpine meadows

“…In addition, there was little reason to expect a strong grazing gradient outward from talus for either species (squirrels do not live within talus and marmots roam substantially further than pikas; see Rocky Mountain equivalent species in Barash 1973). As the dominant grazer in all the selected sites was the collared pika, we attributed the effects of exclosures to removal of pika grazing, as described by McIntire and Hik (2002).…”

“…McIntire and Hik (2002) showed that different seasonal patterns of leaf production, leaf mortality and leaf births exist among species, demonstrating potential mechanisms for changing plant community composition and biomass within a season. In spite of these criteria, most studies examining plant response to herbivory have addressed a single level of grazing intensity by a natural herbivore (e.g., fenced or not; Cargill and Jefferies 1984;Paige and Whitham 1987;Frank and McNaughton 1993;Hulme 1996), or multiple levels under simulated, modeled or unnatural herbivory (Williamson et al 1989;Hik and Jefferies 1990;Brown and Stuth 1993;Ouellet et al 1994;Bergelson et al 1996;Nilsson et al 1996).…”

Sheep camping influences soil properties and pasture production in an acidic soil of New South Wales, Australia

“…One typical feature of grazing activity is spatial heterogeneity (Haynes and Williams 1999;McIntire and Hik 2002). Animals select particular landscape features for resting and ruminating (Pratt et al 1986), such as beneath trees and hedges, around gateways and water troughs, on areas away from roadsides and on ridges and hillcrests on hill country farms (Haynes and Williams 1999;Rowarth et al 1992).…”