Photo: Kochia, southwest montana. © 2020 Delena Norris-Tull
Challenges in the restoration of a California grassland
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western,
September 2020.
A study by Buisson, et al., 2008, emphasizes the challenges of reintroducing native species in degraded grasslands that are already infested by exotic annual grasses and exotic forb species. They conducted a study to compare the effectiveness of various treatments on the reintroduction of the Nassella pulchra, a perennial bunchgrass native to the northern mediterranean coastal grasslands of California. The treatments were: grazing intensity (light grazing by native mammals or ungrazed); topsoil removal; and reduction of native and exotic plant neighbours.
24 experimental plots within a degraded grassland area were established. Half were planted with Nassella seeds, and half were planted with Nassella seedlings.
Results of growth from Nassella seeds: Buisson, et al., 2008, found that topsoil removal, which removed much of the soil nitrogen, had the greatest impact on the success of the growth and survival of Nassella from seeds, likely because seeds and adult plants of competing exotic species were removed along with the soil. Within plots that had been infested with exotic grasses prior to soil removal, 35% (+ or – 2%) of Nassella seeds sprouted and survived. Within plots with exotic forbs, 40% (+ or – 2%) of Nassella seeds sprouted and survived.
To test the impact of removal of nearby plants, they removed plants growing near the Nassella seeds by hand-pulling nearby native and exotic seedlings and clipping larger plants to the ground. Removal of neighbouring plants had little beneficial impact on the growth and survival of Nassella from seeds. In patches infested with exotic forbs, neighbouring plant removal only improved Nassella seed growth and survival from 37% to 42%. In patches infested with exotic grasses, removal of neighbouring plants near the Nassella seeds resulted in an increase in exotic grasses. In control plots, with both intact topsoil and intact neighbors, only 12% of Nassella seeds sprouted and survived.
In the plots with transplanted Nassella seedlings, in exotic grass patches, topsoil removal had the greatest success of survival of seedlings. Neighbour removal also had some success. “In exotic forb patches, topsoil removal x intact neighbours maximized transplant survival,” 28% compared to 11% in other treatments. This indicates that, if topsoil is removed, additional removal of exotic plant neighbours is not necessary. “In exotic grass patches, neighbour removal had a significant positive effect on transplant biomass... In exotic forb patches, topsoil removal x intact neighbours resulted in a marginal increase in transplant biomass.” They point out that previous studies have indicated that successful exotic species germinate earlier than native perennials, and exotic annual grasses can reduce water availability.
While moderate grazing by deer, rabbits, and gophers “did not have any detrimental effect on the reintroduced perennial native species, it did not have any direct or indirect positive effects either.” Thus, fencing to reduce herbivory would be unnecessary in similar conditions.
While topsoil removal is an extreme restoration tool that should only be undertaken with careful consideration, this study indicates that it may have a greater chance of success than other restoration methods within the California mediterranean grasslands. This study also indicates that restoration with native grass seeds can be a successful alternative to the more expensive transplant of seedlings.
Reference:
Links to additional Prairie Restoration projects:
Links to additional Rangeland Restoration practices:
Links to additional Innovative Solutions:
Challenges in the restoration of a California grassland
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western,
September 2020.
A study by Buisson, et al., 2008, emphasizes the challenges of reintroducing native species in degraded grasslands that are already infested by exotic annual grasses and exotic forb species. They conducted a study to compare the effectiveness of various treatments on the reintroduction of the Nassella pulchra, a perennial bunchgrass native to the northern mediterranean coastal grasslands of California. The treatments were: grazing intensity (light grazing by native mammals or ungrazed); topsoil removal; and reduction of native and exotic plant neighbours.
24 experimental plots within a degraded grassland area were established. Half were planted with Nassella seeds, and half were planted with Nassella seedlings.
Results of growth from Nassella seeds: Buisson, et al., 2008, found that topsoil removal, which removed much of the soil nitrogen, had the greatest impact on the success of the growth and survival of Nassella from seeds, likely because seeds and adult plants of competing exotic species were removed along with the soil. Within plots that had been infested with exotic grasses prior to soil removal, 35% (+ or – 2%) of Nassella seeds sprouted and survived. Within plots with exotic forbs, 40% (+ or – 2%) of Nassella seeds sprouted and survived.
To test the impact of removal of nearby plants, they removed plants growing near the Nassella seeds by hand-pulling nearby native and exotic seedlings and clipping larger plants to the ground. Removal of neighbouring plants had little beneficial impact on the growth and survival of Nassella from seeds. In patches infested with exotic forbs, neighbouring plant removal only improved Nassella seed growth and survival from 37% to 42%. In patches infested with exotic grasses, removal of neighbouring plants near the Nassella seeds resulted in an increase in exotic grasses. In control plots, with both intact topsoil and intact neighbors, only 12% of Nassella seeds sprouted and survived.
In the plots with transplanted Nassella seedlings, in exotic grass patches, topsoil removal had the greatest success of survival of seedlings. Neighbour removal also had some success. “In exotic forb patches, topsoil removal x intact neighbours maximized transplant survival,” 28% compared to 11% in other treatments. This indicates that, if topsoil is removed, additional removal of exotic plant neighbours is not necessary. “In exotic grass patches, neighbour removal had a significant positive effect on transplant biomass... In exotic forb patches, topsoil removal x intact neighbours resulted in a marginal increase in transplant biomass.” They point out that previous studies have indicated that successful exotic species germinate earlier than native perennials, and exotic annual grasses can reduce water availability.
While moderate grazing by deer, rabbits, and gophers “did not have any detrimental effect on the reintroduced perennial native species, it did not have any direct or indirect positive effects either.” Thus, fencing to reduce herbivory would be unnecessary in similar conditions.
While topsoil removal is an extreme restoration tool that should only be undertaken with careful consideration, this study indicates that it may have a greater chance of success than other restoration methods within the California mediterranean grasslands. This study also indicates that restoration with native grass seeds can be a successful alternative to the more expensive transplant of seedlings.
Reference:
- Buisson, E., Anderson, S., Holl, K.D., Crockett, E., Hayes, G.F., Peeters, A., Dutoit, T. (April, 2008). Reintroduction of Nasella pulchra to California coastal grasslands: Effects of topsoil removal, plant neighbour removal and grazing. Applied Vegetation Science, 11(2): 195-204.
Links to additional Prairie Restoration projects:
Links to additional Rangeland Restoration practices:
- Federal Goals for Rangelands
- Novel Ecosystems
- Sagebrush Steppe Restoration
- Revegetation with Native Plants
- Dogs as detectors of noxious weeds
Links to additional Innovative Solutions: