Photo: Native prairie, East Texas. Copyright 2017 Delena Norris-Tull
Grazing & Revegetation to Manage Noxious Weeds
Sheley, et al., 1996, propose that livestock can be used to assist in revegetation with desired species by adding native plant seed to the hay.
In an extensive review of the research on grazing, Sheley, et al., 2011, found that little research has been conducted on the long-term success of grazing in controlling weeds and restoring native species. “In general, when grazing is limited to periods when weedy species are most susceptible to defoliation and desirable plants are largely dormant, the impact of grazing on desirable vegetation can be minimized and benefit of grazing for weed control maximized…. If weedy and desirable vegetation have comparable forage quality, grazing animals largely will consume plants in proportion to their abundance.” Thus, grazing is more affective in areas with relatively high densities of invasive species. If weeds have low forage value, grazing may have a greater negative impact on desirable vegetation. But it is difficult to predict the impact of grazing on desirable species. More research, with close monitoring, is needed.
Sheley, et al, 2011, concluded that, “To be successful, prescribed grazing will likely need to be carried out indefinitely.” Prescribed grazing with “sheep and goats can be economically profitable in well-managed operations or they can serve as additional revenue sources in cattle operations.” But grazing is most effective if carried out prior to invasive plant seed production, and then repeated multiple times during the growing season.
Hayes and Holl, 2011, compared various methods of managing disturbance regimes to determine which, if any, may encourage the growth of native species. They chose three prairie sites in the coastal area of California that were already highly invaded. They examined changes in vegetation composition in the three sites over 10 years. The treatment methods were: no disturbance, grazing, and clipping (mowing, at diverse frequencies) with and without litter removal. They also compared seeding with eight native species to no seeding.
The three sites had the following characteristics: each had been grazed by cattle since the 1950s, but two sites had not been grazed in the 1990s; each contained characteristic native prairie species, had gentle slopes, had sandy loam soils, and had long-term conservation protection status. All sites had probably been surface tilled using a harrow.
Hayes and Holl, 2011, fenced a large area on each site, to exclude cattle and feral pigs during the study. They measured vegetation inside and outside the enclosures. At each site, cattle grazed outside the enclosures. They compared diverse cattle stocking rates. They collected rainfall data for each site. They recorded species in each site using corner grids. In years 5 and 6, 2003 and 2004, they seeded eight native species, two native perennial grasses (Danthonia californica and Nassella pulchra) and two native annual forbs (Castilleja exserta ssp. exserta and Gilia capitata), and one perennial native forb (Sisyrinchium bellum) into various plots on two sites. They seeded with Calandrinia ciliata, Eschscholzia californica, and Lupinus nanus (native forbs) in 2004 only. They compared vegetation cover, focusing on plant guilds to analyze the effect of diverse disturbance regimes on vegetation communities.
Hayes and Holl, 2011, found that “Because vegetation rarely differed in plots with and without litter removal, [they] pooled data from these two treatments and focused on comparing no disturbance, grazing and the three clipping frequencies…. For vegetation community analysis, [they] used only data from unseeded plots in order to test whether managing disturbance regimes alone could shift the balance from exotic to native guilds.” And they “compared individual species abundance in seeded and unseeded plots which were managed identically (clipping and raking).”
Hayes and Holl, 2011, found that “Total cover… was relatively constant over time and across treatments… [At two sites] exotic annual grass…cover was significantly higher in plots with no treatment.” At the third site, exotic annual grass “cover was higher in grazed plots 2 years out of 10, but otherwise there were no differences across treatments… “Exotic annual forbs… were a substantial component of the vegetation at all three sites, although populations fluctuated greatly among years… This guild generally had opposite clipping response to that of the” exotic annual grasses. At one site, exotic annual forb “cover was consistently much lower in the no-disturbance treatment in years 2 to 10.” “Exotic perennial forbs…clipping response varied across sites.” These plants “were generally less common in grazed and no-disturbance plots at [one site], whereas” exotic perennial forb cover was lower in grazed plots in some years at another site. In the third site, exotic perennial forb “cover differed across treatments, but declined significantly in all treatments over time.”
Hayes and Holl, 2011, found variable results with comparisons of seeded and non-seeded plots. Overall, seeding had little impact on improving native perennial grasses. At the beginning of the study, most plots had low cover by native plants. These California grasslands typically have long-lived seed banks, but these sites “had been lightly tilled historically and grazed for many decades,” thus It seemed likely that the native seed banks had been degraded over time. “Native perennial and annual forbs had <5% cover in all treatments at all sites in most years, and their abundance did not change consistently over time with two exceptions. At [one site] E. californica had 28% cover in no-disturbance plots in the year 1 and steadily declined to <5% by year 5. Similarly, [at another site] Madia sativa covered >5% of [several] plots in the first 3 years…, but was rarely recorded after year 4.”
Hayes and Holl, 2011, concluded that, “Clipping generally shifted community dominance from exotic annual grasses to exotic annual forbs, rather than consistently favoring native species. At one site, perennial [native] grass cover decreased in the no-disturbance plots, but only after 4 years. Litter removal had minimal impact… Grazing had a highly variable effect on the abundance of different plant guilds….Seeding increased abundance of only two [Nassella pulchra and S. bellum] of eight native species.”
“Our results indicate that even the resource-intensive approach of introducing [native] propagules along with managing disturbance regimes does not guarantee native species establishment and that maintaining and restoring broader suites of native species in invaded grasslands is extremely challenging….It is highly probable that landscape-level management…of varied disturbance regimes in locations where native species are already present will provide the most positive results.”
This study appears to present a challenge to the successional management system proposed by Sheley, et al., 1996, at least in sites where a reserve of native seed has been depleted. As with so much else that these reports reveal, much more research is needed, to determine effective methods of managing invasive plants and restoring native vegetation.
References:
Links to additional Innovative Solutions:
Grazing & Revegetation to Manage Noxious Weeds
Sheley, et al., 1996, propose that livestock can be used to assist in revegetation with desired species by adding native plant seed to the hay.
In an extensive review of the research on grazing, Sheley, et al., 2011, found that little research has been conducted on the long-term success of grazing in controlling weeds and restoring native species. “In general, when grazing is limited to periods when weedy species are most susceptible to defoliation and desirable plants are largely dormant, the impact of grazing on desirable vegetation can be minimized and benefit of grazing for weed control maximized…. If weedy and desirable vegetation have comparable forage quality, grazing animals largely will consume plants in proportion to their abundance.” Thus, grazing is more affective in areas with relatively high densities of invasive species. If weeds have low forage value, grazing may have a greater negative impact on desirable vegetation. But it is difficult to predict the impact of grazing on desirable species. More research, with close monitoring, is needed.
Sheley, et al, 2011, concluded that, “To be successful, prescribed grazing will likely need to be carried out indefinitely.” Prescribed grazing with “sheep and goats can be economically profitable in well-managed operations or they can serve as additional revenue sources in cattle operations.” But grazing is most effective if carried out prior to invasive plant seed production, and then repeated multiple times during the growing season.
Hayes and Holl, 2011, compared various methods of managing disturbance regimes to determine which, if any, may encourage the growth of native species. They chose three prairie sites in the coastal area of California that were already highly invaded. They examined changes in vegetation composition in the three sites over 10 years. The treatment methods were: no disturbance, grazing, and clipping (mowing, at diverse frequencies) with and without litter removal. They also compared seeding with eight native species to no seeding.
The three sites had the following characteristics: each had been grazed by cattle since the 1950s, but two sites had not been grazed in the 1990s; each contained characteristic native prairie species, had gentle slopes, had sandy loam soils, and had long-term conservation protection status. All sites had probably been surface tilled using a harrow.
Hayes and Holl, 2011, fenced a large area on each site, to exclude cattle and feral pigs during the study. They measured vegetation inside and outside the enclosures. At each site, cattle grazed outside the enclosures. They compared diverse cattle stocking rates. They collected rainfall data for each site. They recorded species in each site using corner grids. In years 5 and 6, 2003 and 2004, they seeded eight native species, two native perennial grasses (Danthonia californica and Nassella pulchra) and two native annual forbs (Castilleja exserta ssp. exserta and Gilia capitata), and one perennial native forb (Sisyrinchium bellum) into various plots on two sites. They seeded with Calandrinia ciliata, Eschscholzia californica, and Lupinus nanus (native forbs) in 2004 only. They compared vegetation cover, focusing on plant guilds to analyze the effect of diverse disturbance regimes on vegetation communities.
Hayes and Holl, 2011, found that “Because vegetation rarely differed in plots with and without litter removal, [they] pooled data from these two treatments and focused on comparing no disturbance, grazing and the three clipping frequencies…. For vegetation community analysis, [they] used only data from unseeded plots in order to test whether managing disturbance regimes alone could shift the balance from exotic to native guilds.” And they “compared individual species abundance in seeded and unseeded plots which were managed identically (clipping and raking).”
Hayes and Holl, 2011, found that “Total cover… was relatively constant over time and across treatments… [At two sites] exotic annual grass…cover was significantly higher in plots with no treatment.” At the third site, exotic annual grass “cover was higher in grazed plots 2 years out of 10, but otherwise there were no differences across treatments… “Exotic annual forbs… were a substantial component of the vegetation at all three sites, although populations fluctuated greatly among years… This guild generally had opposite clipping response to that of the” exotic annual grasses. At one site, exotic annual forb “cover was consistently much lower in the no-disturbance treatment in years 2 to 10.” “Exotic perennial forbs…clipping response varied across sites.” These plants “were generally less common in grazed and no-disturbance plots at [one site], whereas” exotic perennial forb cover was lower in grazed plots in some years at another site. In the third site, exotic perennial forb “cover differed across treatments, but declined significantly in all treatments over time.”
Hayes and Holl, 2011, found variable results with comparisons of seeded and non-seeded plots. Overall, seeding had little impact on improving native perennial grasses. At the beginning of the study, most plots had low cover by native plants. These California grasslands typically have long-lived seed banks, but these sites “had been lightly tilled historically and grazed for many decades,” thus It seemed likely that the native seed banks had been degraded over time. “Native perennial and annual forbs had <5% cover in all treatments at all sites in most years, and their abundance did not change consistently over time with two exceptions. At [one site] E. californica had 28% cover in no-disturbance plots in the year 1 and steadily declined to <5% by year 5. Similarly, [at another site] Madia sativa covered >5% of [several] plots in the first 3 years…, but was rarely recorded after year 4.”
Hayes and Holl, 2011, concluded that, “Clipping generally shifted community dominance from exotic annual grasses to exotic annual forbs, rather than consistently favoring native species. At one site, perennial [native] grass cover decreased in the no-disturbance plots, but only after 4 years. Litter removal had minimal impact… Grazing had a highly variable effect on the abundance of different plant guilds….Seeding increased abundance of only two [Nassella pulchra and S. bellum] of eight native species.”
“Our results indicate that even the resource-intensive approach of introducing [native] propagules along with managing disturbance regimes does not guarantee native species establishment and that maintaining and restoring broader suites of native species in invaded grasslands is extremely challenging….It is highly probable that landscape-level management…of varied disturbance regimes in locations where native species are already present will provide the most positive results.”
This study appears to present a challenge to the successional management system proposed by Sheley, et al., 1996, at least in sites where a reserve of native seed has been depleted. As with so much else that these reports reveal, much more research is needed, to determine effective methods of managing invasive plants and restoring native vegetation.
References:
- Hayes, G.F., & Holl, K.D. (2011). Manipulating disturbance regimes and seeding to restore mesic Mediterranean grasslands. Applied Vegetation Science, 14: 304-315.
- Sheley, R.L., Svejcar, T.J., & Maxwell, B.D. (Oct.-Dec., 1996). A theoretical framework for developing successional weed management strategies on rangeland. Weed Technology, 10 (4): 766-773.
- Sheley, R.L., James, J.J., Rinella, M. J., Blumenthal, D., & DiTomaso, J.M. (2011). Invasive plant management on anticipated conservation benefits: A scientific assessment. In D.D. Briske (Ed.) Conservation benefits of rangeland practices: Assessment, recommendation, and knowledge gaps. (pp. 293-336). USDA Natural Resources Conservation Service.
Links to additional Innovative Solutions: