Pitt et al. measured the effects of cattle grazing on lodgepole pine (Pinus contorta) seedlings in seeded clearcut areas at different stocking rates (AU days/ha) and grazing pressures (AU/Mg per ha). Most damage to lodgepole pine seedlings occurred during the first and second years of the study. After this time cattle browsed and trampled significantly less tree seedlings, possibly because of the increased size of the trees in these later years. During the first year of the study, as stocking rate and grazing pressure increased, basal scarring and browsing of tree seedlings increased, however, only grazing pressure was still related to seedling damage after the first year of the study. The authors concluded that grazing pressure (AU/Mg per ha) was a better predictor of lodgepole pine seedling damage in this system and that grazing pressures greater than 12.0 AU/Mg per ha caused significant damage to seedlings, however, they caution that grazing pressure thresholds may not be the same for all systems and that these should be determined before grazing is applied in timber production areas.
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