Neighbor defoliation regulates Canada thistle (Cirsium arvense) in pasture by mediating interspecific competition

Competitive exclusion ofCirsium arvensein pasture: a simulated neighbour grazing-height experiment

“…In summary, the results of these two experiments align with those of other simulated grazing experiments (Eerens et al 2002;Cripps et al 2010;De Bruijn et al 2010) that indicate that competition from sown pasture species can regulate population growth in C. arvense. They lead to the inference that, under grazing systems where C. arvense itself is avoided (e.g.…”

“…6). These results support the idea that deferred grazing or highintensity/low-frequency rotational grazing systems where the grazed neighbours of the weed have time to recover and compete, can reduce the presence of C. arvense in a pasture as was demonstrated in natural field populations of the weed in Alberta, Canada (De Bruijn et al 2010).…”

“…1, 1-12, http://dx.doi.org/10.1080/00288233.2014 manipulated the height of neighbouring pasture plant species show that shoot density and biomass in C. arvense decreases with increasing height of the simulated grazed pasture sward (Eerens et al 2002;Cripps et al 2010). A sensitivity of C. arvense to competition is also illustrated in a field experiment conducted in Alberta, Canada where the weed's year-end biomass was lowest (4% of sward biomass) when neighbouring pasture species were not trimmed (a simulated deferred grazing regime) and highest (35% of sward biomass) when the neighbours were trimmed frequently to a low level during the growing season (a simulated set-stocking grazing regime) (De Bruijn et al 2010).…”

“…The trimmings were discarded. C. arvense was not trimmed in any of the treatments in order to simulate completely selective grazing (De Bruijn et al 2010) and neither component was trimmed in the 'Hay' treatment in order to simulate a system in which grazing does not occur.…”

Divergent effects of defoliation intensity and frequency on tiller growth and production dynamics of Pascopyrum smithii and Hesperostipa comata

“…RS with repeated grazing in a growing season is based on the premise that pasture regrazing would be beneficial if defoliation stimulates compensatory plant responses (McNaughton, ). Indeed, grazing does not universally compromise grass productivity (e.g., De Bruijn & Bork, ; De Bruijn, Bork, & Grekul, ; Donkor, Bork, & Hudson, , ) and may maximize the latter at some optimal frequency and intensity (Turner, Seastedt, & Dyer, ). A recent investigation in the Mixed Grass prairie of western Canada suggests that high‐intensity–low‐frequency defoliation may lead to greater production than areas exposed to high‐intensity–high‐frequency defoliation, although both remained lower than areas where defoliation was deferred to the end of the growing season (Bork, Broadbent, & Willms, ).…”