JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Weather patterns significantly influence annual vegetation, both within and between years. The impact of these weather patterns on standing crop, cover, and botanical composition were investigated during the years 1955-1973 inclusive. Standing crop increased as the growing season progressed from March to June, while cover declined. Erodium spp. Carduus pycnocephalus, Geranium spp. and Hypochoeris glabra all declined between these 2 calendar dates.Other annual species increased in botanical composition as the growing season progressed. Weather patterns primarily influenced total standing crop during the initial period of plant growth. Following germination, temperatures were typically warm and conducive to plant growth; drought at this time suppressed total standing crop. Consistent precipitation following fall germination, and again during the period of rapid plant growth in spring, contributes to a "grass year" in the annual type. The sequence of freezing temperatures in relation to phenology of developing grass seedlings determines the relative proportion of annual grass species from one year to the next. Botanical composition of Trifolium spp. and Medicago hispida depends upon mild autumn weather, particularly when such fall weather favors none of the annual grass species. Botanical composition of Erodium spp. positively correlated with weather patterns associated with dry fall conditions. Multiple regressions of standing crop on weather patterns produced useful guidelines for manipulating animal units to achieve complete utilization of available forage, particularly when these equations were implemented in seasonal stages.

Simple linear and muliple regressions were used to determine the contribution of operative temperature (Te), forage, and snow depth to moose (Alces alces) selection of canopy cover types. The number of degree-hours for which Te exceeded the thermal limit at which panting is required to dissipate metabolic heat contributed significantly to selection during summer (1 June – 15 September) and late winter (16 January – 15 April). Forage explained canopy cover selection in early winter (16 November – 15 January) and contributed significantly to the best equation describing habitat selection during late winter. Snow depth contributed to habitat selection in early winter but was not related to habitat selection during late winter. During summer, moose generally selected against sites where Te exceeded 30 °C, the thermal limit requiring panting to dissipate metabolic heat. During late winter, moose also generally avoided canopy covers where Te commonly exceeded 8 °C, the temperature at which panting is required to dissipate heat. During early winter, moose apparently suffered minimal heat stress, as Te remained below 0 °C; consequently, moose selected canopy cover types that provided comparatively high forage availability.

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Pastures grazed by sheep at moderate and 1%, 2-, and 2% times the moderate stocking rate from 1969-1973 were analyzed for relative changes in cover, herbage productivity, and botanical composition. All four pastures were less productive in 1973 than in 1969, but exhibited similar trends in cover and botanical composition regardless of grazing intensity. Only grazing at 2 '/z times the moderate stocking rate produced a residual decline in productivity following 1 year of rest from the grazing treatment. However, this decline in productivity was managerially negligible compared to other stocking rates, and would probably disappear within 2-3 years in response to the overriding influence of annual weather, especially precipitation, patterns. Hormay (1944) suggested that moderate stocking rates provided the best grazing technique in the annual type. Old vegetation left on the ground at the end of each grazing season would enhance soil fertility, provide progressively improved range condition, and ultimately promote high livestock weight gains. Grazing either greater or less than this moderate level would produce changes in both total herbage productivity and relative botanical composition.Heady ( 1958) postulated. that grazing occurred first on taller plant species, thereby increasing the relative proportion of shorter plant species. Alternatively, complete elimination of grazing animals encouraged taller annual plants relative to short plant species. Talbot et al. ( 1939), Talbot and Biswell ( 1942), and Jones and Evans (1960) all found that exclusion of grazing animals quickly led to grass dominance, particularly taller species, such as ripgut (Bromus rigidus). Biswell (1956) held the opinion that this increase in ripgut occurred at the expense of true clovers (Trifolium spp.) and bur-clover (Medicago hispida), with plant succession proceeding from forbs to soft chess (Bromus n&is), to wild oats (Avena spp.) to ripgut.Biswell (1956) hypothesized that the impact of grazing on botanical composition in the annual type operated primarily by altering the accumulation of mulch. Heady (1958, 1961) supported Biswell's hypothesis by demonstrating that mulch exceeding 700 pounds per acre in Northern California encouraged taller grasses such as soft chess and ripgut. With no mulch accumulation small, unpalatable forbs such as goldfields (Bueriu chrysostomu), smooth cat's ear (Hypochoeris glabra), and owl's clover (Orthocurpus eriunthus) proliferated. With small amounts of mulch, diminutive, low-forage-value grasses such as little quaking grass (Briza minor) and silver hairgrass (Aira caryophylfea) abounded. Annual fescues (Festuca spp.) Authors are assistant professor of' range ecology.

This research investigated the potential for using cattle grazing pressure (AU Mg-' ha-') and stocking rate (Animal Unit Days ha-') for predicting basal scarring and browsing of lodgepole pine (pinus conforta Dot@) seedlings on cutblocks in southern British Columbia from 1989 to 1992. Cattle browsing on lodgepole pine seedlings occurred almost exclusively during the fit 2 years of grazing. Browsing increased (P c 0.05; 3= 0.71) with increasing stocking rate only during the first year of grazing. Browsing increased with increasing grazing pressure in 1989 (P < 0.05; If = 0.38) and 1990 (P < 0.05; 9 = 0.39). Basal scarring peaked during the second year of grazing, but was correlated (P < 0.05; 8 = 0.79) with stocking rate only during the first year of grazing. Increasing grazing pressure was associated with higher (P < 0.05) basal scarring during all 4 years of the study, and likely better predicts trampling damage than does stocking rate, particularly during the first year of grazing. Basal scarring during 1989 generally increased to > 10% of sample trees when grazing pressure exceeded 12.0 AU Mg-' ha-'. This threshold grazing pressure value of 12.0 AU Mg-' had, however, cannot likely be extrapolated diitly to other sites. Grazing pressure values and associated basal scarring are unquestionably influenced by many factors (e.g., pasture size, kind of grazing animal, forage species, tree height, water availability, topography, and weather patterns during the grazing period). Nonetheless, our work provides evidence that grazing pressure provides a useful index for predicting the potential for trampling damage of lodgepole pine seedlings by cattle.