Long-term grazing study in spring-fed wetlands reveals management tradeoffs

Published source details Allen-Diaz B., Jackson R.D., Bartolome J.W., Tate K.W. & Oates L.G. (2004) Long-term grazing study in spring-fed wetlands reveals management tradeoffs. California Agriculture, 58.
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This study is summarised as evidence for the following.

	Action	Category
	Water: Use fewer grazers Action Link
	Water: Exclude grazers Action Link
	Soil: Exclude grazers Action Link
	Other biodiversity: Use fewer grazers Action Link
	Other biodiversity: Exclude grazers Action Link

Water: Use fewer grazers

A replicated, randomized, controlled study in 1992–1996 in grazed wetlands in northern California, USA, found no differences in nitrate levels or pH between plots grazed by cattle at light or moderate intensities. Nutrients: There was no difference in nitrate levels or pH in surface water in lightly grazed plots, compared to moderately grazed plots (data not reported). Methods: Three meadows were studied. Three watersheds in each were randomly assigned to a grazing intensity: one with cattle excluded, one with light grazing (leaving 800–1,000 pounds of residual dry matter at the end of the season), and one with moderate grazing (leaving 600–700 pounds). Samples were taken from both the spring and along the creek in each watershed. Water samples were taken monthly.
Water: Exclude grazers

A replicated, randomized, controlled study in 1992–1996 in grazed wetlands in northern California, USA, found no differences between ungrazed and cattle-grazed plots in nitrate or pH levels in surface water. A separate three-year experiment (1999–2001) found higher nitrate levels in streams in ungrazed plots, compared to grazed plots. Nutrients: A five-year experiment found no differences between ungrazed and grazed plots in nitrate or pH levels in surface water (data not reported). A three-year experiment found higher nitrate levels in streams in ungrazed plots, compared to grazed plots (81–1,200 vs 23–100 micromoles). Methods: A five-year experiment from 1992–1996 was established in three meadows. Within each meadow, three watersheds were randomly assigned to one grazing intensity: cattle excluded, light grazing (leaving 800–1,000 pounds of residual dry matter at the end of the season), or moderate grazing (leaving 600–700 pounds). Samples were taken from the spring and along the creek in each watershed. The second experiment was in 1999–2002 in marshy areas in four meadows. Two plots were established in each meadow: one ungrazed and one with moderate grazing. Water samples were taken monthly.
Soil: Exclude grazers

A replicated, randomized, controlled study in 1999–2001 in grazed wetlands in northern California, USA, found lower methane production in plots from which grazers were excluded, compared to cattle-grazed plots. Greenhouse gases: Methane production was lower in ungrazed plots, compared to grazed plots (2.6 vs 8.5 mg CH₄–C/m²/hr). Methods: Experimental plots were established in four grazed wetlands in 1999, with cattle excluded from one plot, but not from another plot, in each wetland. Methane emissions were measured monthly in March–September 2002.
Other biodiversity: Use fewer grazers

A replicated, randomized, controlled study in 1992–2002 in grazed wetlands in northern California, USA, found more families of aquatic insects in streams in lightly, compared to moderately, grazed plots. There were no differences in the number of plant species or the relative cover of native and non-native species, although diversity and community composition in one of two habitats did differ between grazing intensities and total plant cover was lower in moderately grazed plots. Invertebrates: There were more families of insects in streams in lightly grazed plots, compared to moderately grazed plots (data not provided). Plants: There were no differences in the number of plant species or the relative cover of native and non-native species (data not reported). Diversity relative to before the experiment was higher in lightly grazed plots, compared to moderately grazed plots. Plant community composition varied between lightly and moderately grazed plots along creeks, but not at springs, in wetlands (data reported as ordination scores). Plant cover at the end of the experiment was higher in lightly grazed, compared to moderately grazed, plots (data not provided). Methods: Three meadows were studied, with three watersheds in each randomly assigned to a grazing intensity: one with cattle excluded, one with light grazing (leaving 800–1,000 pounds of residual dry matter at the end of the season) and one with moderate grazing (leaving 600–700 pounds). Samples were taken from both the spring and along the creek in each watershed. Insects were surveyed every three months in one year. Plants were surveyed each June using line transects.
Other biodiversity: Exclude grazers

A replicated, randomized, controlled study in 1992–2002 in grazed wetlands in northern California, USA, found more families of insects in streams in ungrazed plots, compared to grazed plots, in a ten-year experiment. Plant diversity was lower at one of two grazing intensities. In a separate three-year experiment, diversity decreased in plots from which cattle were removed, but not in grazed plots. Invertebrates: There were more families of insects in streams in ungrazed plots, compared to grazed plots (data not reported). Plants: In a ten-year experiment, there was no difference in the number of plant species, or the relative cover of native and non-native species, in ungrazed plots, compared to grazed plots (data not reported). Lower plant diversity was found after the experiment, compared to before, in ungrazed plots, compared to lightly grazed plots (but not moderately grazed, plots). Plant community composition differed between plots with or without grazers along creeks, but not at springs (data reported as ordination scores). Plant cover at the end of the experiment was higher in ungrazed plots, compared to moderately grazed plots but not lightly grazed plots (data not reported). In a separate three-year experiment, plant diversity decreased in ungrazed plots, but not in grazed plots. Methods: The ten-year experiment from 1992–2002 was established in three meadows. Within each, three watersheds were randomly assigned to one of three grazing intensities: cattle excluded, light grazing (leaving 800–1,000 pounds of residual dry matter at the end of the season), or moderate grazing (leaving 600–700 pounds). Samples were taken from both the spring and along the creek in each watershed. The three-year experiment was in 1999–2002 in marshy areas within four meadows. Two plots were established in each: one ungrazed and one with moderate grazing. Insects were surveyed every three months in one year. Plants were surveyed each June using line transects.