ABIOTIC FACTORS
TOPOGRAPHY
Cattle are reluctant to graze on slopes exceeding 60% (Table 6.4). The numbers in the following table may be revised for various British Columbia conditions. Through experience cattle become acclimated to rugged terrain and are less reluctant to use steep slopes.
Table 6.4 Suggested reduction in cattle carrying capacity according to percentage slope.
|
% slope |
% reduction in carrying capacity |
|
0 - 10 |
no reduction |
|
11 - 30 |
30 |
|
31 - 60 |
60 |
|
> 60 |
100 (ungrazeable) |
DISTANCE FROM WATER
Cattle will rarely feed beyond a 2.5 km horizontal distance from water (Table 6.5). In rolling terrain, they will rarely feed at elevations greater than 70 m above water. Thus, the classic bull’s eye pattern of grazing develops where forage use is heaviest at the water source and decreases in concentric circles away from it. Herding can be used to obtain better distribution, but greater travel distances and rougher terrain will demand more energy expenditure (and perhaps sacrifice gain). Sheep are better able to utilize rugged terrain. They will readily walk from 3 to 5 km for water, though travel distance comes at the expense of energy (and possibly weight gain).
Table 6.5 Suggested reduction in carrying capacity given feeding distance from water.
|
Distance from water (km) |
% reduction in carrying capacity |
|
0-1.5 |
None |
|
1.5-3.0 |
50 |
|
>3.0 |
100 (ungrazeable) |
SHADE AND THERMAL COVER
Livestock prefer dry southern exposures in spring, switching to northern exposures, riparian and forested areas during hotter periods. In Montana, during August and September, approximately 80 percent of the forage used by livestock may come from riparian sites even though they often comprise less than 4 percent of the total acreage in a pasture.
