Individual study: Effect of cattle grazing season and burning on re-establishment of native grassland species at Sather Canyon, California, USA
Bartolome J.W., Fehmi J.S., Jackson R.D. & Allen-Diaz B. (2004) Response of a native perennial grass stand to disturbance in California's Coast Range Grassland. Restoration Ecology, 12, 279-289
California's native Coast Range grasslands have much diminished since European settlement some 200 years ago. A semi-natural pasture that potentially could be enhanced for native grassland plants had vegetation typical of California coastal grassland in eastern San Francisco Bay, but was dominated by annual non-native grasses (Mediterranean origin) with scattered stands of native perennial grasses. To assess the potential for enhancing native species, management was manipulated by grazing and burning.
Study site: The study took place at Sather Canyon, a 200 ha pasture under continuous cattle grazing. Annual plants tend to germinate with autumn rains, most growing until late spring.
Treatments: In spring 1993, fences were erected to create a split-plot design with 13 experimental units. Cattle grazing was initiated with three replicates (except for a fourth summer grazing replicate) of four treatments:
1) no grazing;
2) spring grazing;
3) summer grazing;
4) continuous grazing.
Grazing, other than continuous, was undertaken in a row of 30.5 x 30.5 m paddocks. One continuous grazing replicate was assigned to a paddock with the fencing partially removed, the other two were located randomly along the outside of the fencing. Spring grazing began in April 1993, 1994 and 1995 with several cows in each paddock until a residual dry matter level of 750 kg/ha was achieved. The summer treatment (July 1993, 1994 and 1995) was applied likewise. Grazing ended in 1996. In November 1993 and 1994, half of each paddock and a 15.2 m strip of the continuously grazed pasture were burned. This was intended to follow annual herb germination, but the first autumn 1993 rains were light and late, resulting in low pre-burn germination.
Monitoring: Permanent 5-m long transects were established within each unit to estimate plant species cover (line-point method) each spring before grazing commenced.
Four distinct plant groups emerged, two dominated by annual grasses and two by perennial grasses. Both annual groups were characterized by high Italian ryegrass Lolium multiflorum and soft brome Bromus hordeaceus cover but one had more annual grasses (Group 1) and the other more annual forbs (Group 2) as subdominants.
One perennial grass group was dominated by purple needlegrass Nassella pulchra (Group 3) and the other foothill needlegrass N.lepida (Group 4). They also had significant native perennial, California oatgrass Danthonia californica cover, with (non-native) L.multiflorum and ribwort plantain Plantago lanceolata also abundant (20-30% of total cover). There were no significant effects of burning on plant diversity.
Grazing removal resulted in a shift from more annual-dominated toward more perennial grass-dominated vegetation. All three perennial grasses responded favourably to the no-grazing treatment, both Nassella species increased gradually over time regardless of grazing treatment, and showed positive post-treatment response. Spring grazing appeared to have a generally positive effect on purple needlegrass cover (increasing over time under this treatment). Foothill needlegrass increase was greatest with grazing removal. Summer grazing caused a slight decline in California oatgrass cover, spring grazing had little effect, it increased with grazing removal.
Conclusions: In this study, temporary grazing removal increased cover of existing native perennial grasses.
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