Riparian Meadow Response to Modern Conservation Grazing Management

Abstract

Riparian meadows occupy a small proportion of the public lands in the western United States but they provide numerous ecosystem services, including the production of high-quality forage for livestock grazing. Modern conservation management strategies (e.g., reductions in livestock stocking rates and adoption of new riparian grazing standards) have been implemented to better balance riparian conservation and livestock production objectives on publicly managed lands. We examined potential relationships between long-term changes in plant community, livestock grazing pressure and environmental conditions at two spatial scales in meadows grazed under conservation management strategies. Changes in plant community were not associated with either livestock stocking rate or precipitation at the grazing allotment (i.e., administrative) scale. Alternatively, both grazing pressure and precipitation had significant, albeit modest, associations with changes in plant community at the meadow (i.e., ecological site) scale. These results suggest that reductions in stocking rate have improved the balance between riparian conservation and livestock production goals. However, associations between elevation, site wetness, precipitation, and changes in plant community suggest that changing climate conditions (e.g., reduced snowpack and changes in timing of snowmelt) could trigger shifts in plant communities, potentially impacting both conservation and agricultural services (e.g., livestock and forage production). Therefore, adaptive, site-specific management strategies are required to meet grazing pressure limits and safeguard ecosystem services within individual meadows, especially under more variable climate conditions.

Keywords: Climate change; Livestock grazing; Long-term; Plant community monitoring; Public lands; Riparian meadows; United States Forest Service.

Fig. 1

Change in animal unit months (AUM) on public lands in eleven states in the western U.S. between 2000 and 2015. The lightest color represents slight positive to slight negative changes in AUMs. Darker colors represent increasingly negative changes in AUMs. Solid polygons represent lands administered by the Bureau of Land Management (BLM). Hatched polygons represent lands administered by the U.S. Forest Service (USFS). Data were sourced from BLM and USFS annual reports (Bureau of Land Management ; U.S Forest Service 2016)

Fig. 2

Location of allotment and meadow study areas. Light gray shaded areas represent National Forest lands in California. Dark gray shaded areas represent the allotments in the allotment scale analysis of changes in plant community and each allotment contains at least one long-term plant community monitoring site (n = 279). The inset shows a subset of monitoring sites that were selected for meadow scale analysis of changes plant community (n = 52)

Fig. 3

Long-term change (Δ) in allotment scale plant community metrics in 279 plant community monitoring plots in riparian meadows across California (n = 279). Metrics are species richness (S), diversity (H′), and the relative frequencies of forb, non-native, wetland obligate (OBL), and upland species (UPL). Dark lines represent the median. Top and bottom box boundaries represent the 75th and 25th percentiles, respectively. Top and bottom whiskers represent the 95th and 5th percentiles, respectively

Fig. 4

Allotment scale changes (Δ) in (a) species richness (S), (b) species diversity (H′), and the relative frequencies of (c) wetland obligate and (d) non-native species (%) by the 10-year cumulative allotment stocking rate (AUM/km²; n = 279). As indicated by the p values listed in each panel, no significant relationships were found between these plant community metrics and cumulative stocking rate at the allotment scale (Bonferroni-corrected p < 0.016)

Fig. 5

Allotment scale changes (Δ) in (a) species richness (S), (b) species diversity (H′), and the relative frequencies of (c) wetland obligate and (d) non-native species (%) by the 10-year average relative precipitation (percent of 30-year normal annual precipitation; n = 279). As indicated by the p values listed in each panel, no significant relationships were found between these plant community metrics and cumulative stocking rate at the allotment scale (Bonferroni-corrected p < 0.014). One apparent relationship (i.e., p < 0.1) was found between changes in wetland obligate species and relative precipitation

Fig. 6

Long-term trends (Δ) in meadow scale plant community metrics in 52 grazed meadows. Richness (S), diversity (H′), and the relative frequencies of forb, non-native, wetland obligate (OBL), and upland (UPL) species. Dark lines represent the median. Top and bottom box boundaries represent the 75th and 25th percentiles, respectively. Top and bottom whiskers represent the 95th and 5th percentiles, respectively

Fig. 7

Meadow scale changes (Δ) in the relative frequencies (%) of (a) non-native species, (b) wetland obligate species, and (c) forbs by precipitation as a percent of long-term normal levels (n = 52). The effect of precipitation was positive for wetland obligate species and negative for forbs (Bonferroni-corrected p < 0.016). There was an apparent (i.e., p < 0.1) positive effect of precipitation for non-native species. P values are presented for the effect of meadow relative precipitation (10-year average annual precipitation percent of 30-year normal annual precipitation) in each model

Fig. 8

Meadow scale changes (Δ) in species richness (S) and the relative frequency (%) of wetland obligate species and upland species by fecal density (n = 52). Fecal density had a significant negative effect of on changes in wetland obligate species (Bonferroni-corrected p < 0.016). The fecal density by relative precipitation interaction was significant for changes in upland species. There was an apparent (i.e., p < 0.1) negative effect of fecal density on changes in species richness. In panels a and b, p values are presented for the fecal density effect. In panel c, the p value shown is for the interaction of fecal density and relative precipitation and the line represents the effect of fecal density at the median relative precipitation value (81.7% of 30-year normal annual precipitation). The line has been clipped to the range of fecal densities observed at sites receiving approximately 81.7% relative precipitation