Effects of cattle grazing on diversity in ephemeral wetlands

Change season/timing of livestock grazing: freshwater marshes

A replicated, randomized, paired, controlled study in 2000–2003 of ephemeral pools in a grassland in California, USA (Marty 2005) found that dry season and wet season grazing had similar effects on relative cover of grasses and native plants, and on native plant richness. In three of three years, pools had similar cover of grasses relative to forbs regardless of the grazing season (dry-season-grazed: grass cover 46–55% of forb cover; wet-season-grazed: grass cover 48–54% of forb cover) and had similar cover of native plants relative to non-natives (data not reported). Over three years, pools experienced statistically similar changes in native plant richness regardless of the grazing season (dry-season-grazed: 0.5–1.0 more species/0.25 m²; wet-season-grazed: 0.6 fewer to 1.2 more species/0.25 m²). Methods: In 2000, six pairs of plots were established on a ranch grazed October–June for >100 years. Between 2000 and 2003, one plot/pair was grazed in the dry season (October–November and April–June) and one plot/pair was grazed in the wet season (December–April). All plots were grazed by 1 cow-calf pair/2.4 ha. Cattle access was controlled by electric fences. Each spring between 2001 and 2003, vegetation was surveyed in three pools/plot and in adjacent upland. Pools were 70–1,130 m² and dry when surveyed.

(Summarised by: Nigel Taylor)

Water: Use seasonal grazing

A replicated, randomized, controlled study in 2000–2003 in wet alpine meadows in central California, USA, found that pools in continuously grazed plots were wet for longer and dried out less frequently than those in seasonally grazed plots. Water availability: The maximum time that pools were wet was higher in continuously grazed plots, compared to seasonally grazed plots (115 vs 65–78 days). During a particularly dry year, pools in continuously grazed plots dried less frequently than those in seasonally grazed plots (1 vs 2 drying episodes).  Methods: Eighteen plots were established in 2000, each with three pools (70–1,130 m²) and nine times more dry land than pool. Areas were either grazed continuously or seasonally (dry: October–November; wet: April–June). Before the experiment, the area had been grazed for at least 100 years.

Reduce intensity of livestock grazing: freshwater marshes

A replicated, randomized, paired, controlled study in 2000–2003 of ephemeral pools in a grassland in California, USA (Marty 2005) found that seasonally grazed pools typically had similar relative cover of grasses and native plants to continuously grazed pools, and experienced similar changes in native plant richness. In six of six comparisons over three years, seasonally and continuously grazed pools had similar cover of grasses relative to forbs (seasonal: grass cover 46–55% of forb cover; continuous: 34–48%). In three of six comparisons, seasonally and continuously grazed pools had similar relative cover of native plants relative to non-natives. In the other three comparisons, seasonally grazed pools had lower relative cover of native plants than continuously grazed pools (data not reported). Finally, over the three years, seasonally and continuously grazed pools experienced statistically similar changes in native plant species richness (seasonal: 0.6 fewer to 1.2 more species/0.25 m²; continuous: 0.7–1.8 more species/0.25 m²). Methods: In 2000, eighteen plots were established (in six sets of three) on a ranch grazed for >100 years. In each set, one plot was grazed in the dry season, one was grazed in the wet season, and one was grazed throughout both seasons. Plots were grazed by 1 cow-calf pair/2.4 ha. Access to the seasonally grazed plots was controlled by electric fences. Each spring between 2001 and 2003, vegetation was surveyed in three pools/plot and in adjacent upland. Pools were 70–1,130 m² and dry when surveyed.

(Summarised by: Nigel Taylor)

Exclude or remove livestock from historically grazed freshwater marshes

A replicated, randomized, paired, controlled study in 2000–2003 of ephemeral pools within a grassland in California, USA (Marty 2005) found that excluding cattle increased the dominance of grasses, but reduced the dominance and richness of native plants. In the final two of three years, pools fenced to exclude cattle had greater relative grass cover (83–104% of forb cover) than pools that remained grazed (34–48% of forb cover). In three of three years, exclusion pools had lower relative cover of native vs non-native plants than grazed pools (data not reported). Over the three years, native species richness was stable or declined in exclusion pools (1.3 fewer to 0.1 more species/0.25 m²) whilst it increased in grazed pools (0.7–1.8 more species/0.25 m²). Methods: In 2000, six pairs of plots were established on a ranch grazed for >100 years. In each pair, one plot was fenced to exclude cattle whilst the other remained grazed (October–June; 1 cow-calf pair/2.4 ha). Each spring between 2001 and 2003, vegetation was surveyed in three dried-up pools (and adjacent upland) in each plot. Pools were 70–1,130 m². Ungrazed pools were dry for longer than grazed pools. This study was based on the same experimental set-up as (9), but monitored it for less time.

(Summarised by: Nigel Taylor)

Water: Exclude grazers

A replicated, randomized, controlled study in 2000–2003 in wet in alpine meadows in central California, USA (same study as (5)), found that pools in plots from which cattle were excluded were wet for less time than those with two of three grazing regimes, and they dried more frequently than those in plots with one of three grazing regimes. Water availability: The maximum time that pools were wet was lower in ungrazed plots, compared to grazed plots, for two of three grazing regimes (65 vs 78–115 days), but not compared to plots that were grazed in the wet season. During a particularly dry year, pools in ungrazed plots dried more frequently than those in continuously-grazed plots, but not seasonally-grazed plots (2 vs 1 drying episodes). Methods: Eighteen plots were established in 2000, each with three pools (70–1,130 m²) and nine times more dry land than pool. Areas were grazed continuously or seasonally (dry: October–November; wet: April–June). Before the experiment, the area had been grazed for at least 100 years.

Other biodiversity: Use seasonal grazing

A replicated, randomized, controlled before-and-after study in 2000–2003 in wet grassland in central California, USA, found that the number of aquatic invertebrate species and native plant species, and the cover of native and exotic plants, varied between plots grazed at different times, in some comparisons. Invertebrates: There were more aquatic invertebrate species in pools in continuously-grazed plots, compared to seasonally-grazed plots, in one of three years (14 vs 11–12 species). Plants: The number of native plant species in pool edges declined more in 2001–2003 in wet-season grazed, compared to continuously or dry-season grazed plots (pool edges: 0.5 fewer species vs 1–1.8 more species). Changes within pools and on the surrounding dry land did not differ between plots with different grazing timings. There was a higher relative cover of native species in pool edges and surrounding dry land in continuously grazed plots, compared to seasonally grazed plots (pool edges: 72% vs 53–58%; dry land: 31% vs 17–18%). There was no difference in relative coverage of native species within pools between grazing timings. There was lower cover of exotic grasses in continuously grazed plots compared to dry- and wet-season grazed plots in dry land but not in other habitats (52% vs 69–84%). Methods: Eighteen plots were established in 2000, each with three pools (70–1,130 m²) and nine times more dry land than pool. Areas were grazed continuously or seasonally (dry-season: October–November; wet-season: April–June). Before the experiment, the area had been grazed for at least 100 years.

Other biodiversity: Exclude grazers

A replicated, randomized, controlled, before-and-after study in 2000–2003 in wet alpine meadows in central California, USA (same study as (22)), found fewer aquatic invertebrate species, and greater declines in the number of native plant species, in plots from which cattle were excluded, compared to grazed plots. Lower native-plant cover and higher exotic-grass cover was found in ungrazed plots, compared to grazed plots. Invertebrates: There were fewer aquatic invertebrate species in pools in ungrazed plots, compared to pools in grazed plots, in one of three years (10 vs 11–14 species). Plants: The number of native plant species in pool edges and surrounding dry land declined more in 2001–2003 in ungrazed plots, compared to grazed plots (pool edges: 1.3 fewer species vs 0.5 fewer to 1.8 more species; dry land: 0.5 fewer vs 1–1.2 more). Changes within pools did not differ between ungrazed and grazed plots. There was lower relative cover of native species in pool edges and surrounding dry land in ungrazed plots, compared to grazed plots (pool edges: 40% vs 54–72; dry land: 13 vs 18–31). There was no difference in relative cover of native species within pools between ungrazed and grazed plots. There was higher cover of exotic grasses in ungrazed and dry-season-grazed plots, compared to continuously-grazed and wet-season-grazed plots (84–86% vs 52–70%). Methods: Twenty-four plots were established in 2000, each with three pools (70–1,130 m²) and nine times more dry land than pool. Areas were either continuously or seasonally grazed by cattle (dry season: October–November; wet season: April–June), or grazers were excluded. Before the experiment, the area had been grazed for at least 100 years.