Our first objective of this study was to test predictions of the competitive release hypothesis that the presence of large grazers (bison) on tallgrass prairie reduces canopy density, increases available light, and increases the growth, reproduction, and cover of forb
Fire season and prairie forb
richness in a 21year experiment.
There was also less perennial grass and forb
cover in the Northwest area.
Virginia pepperweed (Lepidium virginicum) was the dominant forb
the majority of the time (six quadrats).
Cattle diets in tall forb
communities on mountain rangelands.
Studies in less mountainous habitats have found moose consume larger proportions of forbs
(25%, LeResche and Davis 1973; 70.
The one obstacle in converting a meadow consisting chiefly of fescue to one of native grasses and forbs
is information regarding species that might be appropriate substitutes (N.
Look for them before the grass and the forbs
get too tall.
Vegetative features Baird's Chestnut-collared Sparrow Longspur Mean vegetation height (cm) 14-30 15-23 Maximum height (cm) 30-43 unknown Visual obstruction reading (cm) 6-21 6 Forb
cover (%) 25 6-18 Shrub cover (%) 1-20 [less than or equal to] 3 Bare ground (%) unknown 1-15 Litter depth (cm) <4 2 Vegetative features Dickcissel Mean vegetation height (cm) 20-98 Maximum height (cm) 150 Visual obstruction reading (cm) 14-82 Forb
cover (%) 3-60 Shrub cover (%) [less than or equal to] 11 Bare ground (%) [less than or equal to] 16 Litter depth (cm) [less than or equal to] 5
The increase in forb
cover on treatment Plow, however, was unexpected.
Univariate results of the five study regions combined indicate that Bachman's Sparrows occupied areas with relatively low mean values ([less than] 34%) for percent woody cover, percent forb
cover, and tree density, but higher values ([greater than] 58%) in percentages of ground cover, grass cover, and litter cover (Table 1).
On average, forb
species with wider leaves occupied shadier, siltier microsites [ILLUSTRATION FOR FIGURE 4 OMITTED], as expected from between-habitat comparisons elsewhere and from economic theory (Givnish 1987, 1988).