The effects of cattle grazing on flora and fauna in the Kissimmee River valley, Florida.
Peter G. David and David Black
South Florida Water Management District, West Palm Beach, FL
The impacts of cattle grazing on plant communities, small mammals, and herpetofauna were studied on a section of drained Kissimmee River floodplain. Six approximately 1.5 ha fenced exclosures were constructed in semi-improved pasture for replicate treatment of 3 grazed and 3 control (ungrazed) sample sites. Small mammals and herpetofauna were sampled from October 1996 through July 2001 using Sherman live traps and drift fences accompanied by funnel traps. Plant species occurrence, percent cover, herbaceous height and shrub height were recorded on random 1 m quadrats for two baseline and four post-treatment samples. One hundred plant species were recorded during the study period, including 25 exotic species. Bahia grass (Paspalum notatum) occurred most frequently in over 76% of the plots with a mean coverage of 52%. Comparisons of baseline and post-treatment data showed that cattle grazing had a significant effect on vegetation height (P > 0.001) and shrub coverage (P > 0.01), and shrub height (P > 0.01). Repeated measurements were used to determine the possible effect of grazing on plant species over time. Percent coverage of the native Andropogon virginicus declined significantly (P > 0.0001) between baseline and treatment while percent cover was significantly higher (P > .01) in the control plots compared to the grazed plots. Percent occurrence and cover of the exotic Bahia grass was significantly lower (P > 0.0001) in the control plots than in the grazed plots. Results for other exotic and native plant species varied. Chi-square contingency tables (2 X 2) showed that proportions of cotton rats (Sigmodon hispidus) and harvest mouse (Reithrodotomys humulis) were significantly lower (P > 0.001) in grazed exclosures. However, least shrew (Cryptotis parva) and those herpetofauna captured in large enough numbers for analysis, appeared to be unaffected by grazing. Analysis of covariance using small mammal trap rates over time also indicated greater declines (P > 0.0001) of cotton rats in the grazed plots as compared to the control plots. Harvest mouse trapping rates showed similar declines although no significant differences were detected. Decline of important food species for cotton rats such as Andropogon virginicus might help explain the effects of grazing. The reduction in shrub and herb percent cover might also explain the proportional differences in numbers of harvest mouse; a species that prefers advanced old field succession. On heavily grazed pastures, reduction of plant food and cover may have resulted in fewer small mammals while most herpetofauna species and the insectivorous least shrew appeared to be unaffected by grazing.
Peter G. David: South Florida Water Management District, Dupuis Management Area, 23500 SW Kanner Highway, Canal Point, FL 33438
Phone (561) 924-5310, fax (561) 924-5114 fax, .