UNIVERSITY OF CALIFORNIA, SANTA CRUZ. Restoration strategies to control non-native grasses and forbs in California coastal prairie BACHELOR OF ARTS

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1 Chan 1 UNIVERSITY OF CALIFORNIA, SANTA CRUZ Restoration strategies to control non-native grasses and forbs in California coastal prairie A senior Thesis submitted in partial satisfaction of the requirements for the degree of BACHELOR OF ARTS In ENVIRONMENTAL STUDIES By Robert Gorbon Chan April 2011 ADVISOR: Karen D. Holl, Environmental Studies ABSTRACT: California coastal prairie has been heavily impacted by anthropogenic degradation. One of the biggest obstacles to the restoration of California coastal prairies is the presence of introduced exotic species. Research is needed to evaluate the efficiency of different strategies to control exotic forbs and grasses for restoration. I set up a factorial experiment comparing several weed control treatments including one-time (1 ) tarping, two-time (2 ) tarping, topsoil scraping, herbicide, and a control (no treatment) crossed with mulching and not mulching. I measured percent cover of non-native forbs, native grasses, non-native grasses, and bare ground. My results suggest that herbicide, 1 tarping, and 2 tarping in combination with mulch are the most effective methods to reduce exotic forbs and grasses. Concerns about introducing chemicals into the environment and labor requirements leads to the conclusion that 1 tarping with mulch is the most viable weed control method for restoration of California coastal prairie on the Central Coast. KEYWORDS: Restoration, Central Coast, Herbicide, Grassland, Tarping I claim the copywrite to this document but give permission for the Environmental Studies department at UCSC to share it with the UCSC community. Student signature Date

2 Chan 2 Restoration strategies to control non-native grasses and forbs in California coastal prairie Introduction Anthropogenic degradation has transitioned the composition of California s grassland from native grasses to an assemblage mainly of non-native grasses of Eurasian origin (Barbour et al. 1993). This shift began in the nineteenth century and has negatively impacted the conservation of native species and ecosystem function (Stromberg et al. 2007). Research and restoration efforts now focus on mitigating or reversing these anthropogenic impacts to conserve remaining native species and restore ecosystem function (Symstad 2006). Further research has focused on evaluating the efficiency of different strategies effective at an increasing scale for restoration in California grassland. Dominance of non-native grasses and forbs pose the largest obstacle to the restoration of degraded grasslands found in California (Humphreys 1997). Restoration of grasslands requires the active manipulation of existing non-native vegetation with the addition of native species (Whisenant 1999). For my thesis I evaluated different strategies to reduce exotic forb and nonnative grass cover values to facilitate the addition of native grass species. Treatments to control exotic forbs and non-native grasses were selected because of their relative ease of application and ability to be applied on a larger scale. Five treatments were applied for this study, 1 tarping, 2 tarping, topsoil scraping, herbicide and control (no treatment) crossed with a mulch or no mulch treatment. Herbicide is considered to be the most cost effective method for large scale grassland restoration (DiTomaso et al. 2007). However, reservations exist concerning the introduction of chemicals into the environment. Due to these concerns, an herbicide with active ingredient glyphosate was selected for this experimenr because of glyphosate s rapid breakdown in the

3 Chan 3 environment. Glyphosate is a widely used herbicide common for broad-spectrum weed control (Franz et al. 1997). Glyphosate, a systemic herbicide, is applied post emergence directly to plants. Systemic herbicides move into the vascular system of plants, affecting the above and below ground systems of each plant. Use of glyphosate should be minimized because its use increases the likelihood of creating glyphosate tolerance in undesirable plants (Franz et al. 1997). Topsoil scraping has been demonstrated to facilitate the growth of Nassella pulchra and Danthonia californica, native perennial bunchgrasses, in California coastal prairie (Buisson et al. 2006, Buisson et al. 2008). This treatment is best suited to degraded locations where a native seed bank is not present (Buisson et al. 2008). Topsoil scraping is the mechanical scraping of the top 5 10 cm of soil. Scraped soil can be removed from the site, or segregated onsite to contain the emergence of non-native plants. However, topsoil scraping is an intensive restoration method which impacts local soil conditions and hydrology (Buisson et al. 2008). Solarization has been demonstrated to be an efficient method to control invasive species in hot arid regions (El-Keblawy and Al-Hamadi 2009). As a restoration strategy, it is attractive because of its low maintenance, relative low cost, and the fact that it does not rely on chemical agents. There has been little published research on solarization in climates which are not characterized to be arid. In sub-optimal conditions for solarization (cool air temperature and high cloud cover), the use of black plastic tarp (tarping), instead of clear plastic tarps has been practiced with success (Stapleton 2000). For tarping, non-transparent black polyethylene plastic sheets are used to block the plants below from absorbing light. A shading period of roughly 6-8 weeks has been tested in unpublished studies with positive results. All vegetation is killed under the tarps in the shading process. Consideration about the positives and negatives of tarping must be taken into account when native vegetation is present.

4 Chan 4 Mulch was included as a cross treatment because it increases seedling growth by dampening temperature extremes, increases bioaccumulation of organic matter, and reduces competition from weeds (Stromberg et al. 2007). Mulch increases the level of available nitrogen in the landscape which disfavors natives more adapted to lower nitrogen levels in the soil (Buisson et al. 2006). However, mulch is important in suppressing the emergence of exotic forbs and grasses and the competition they exert on native species. My research tested the effectiveness of 1 tarping, 2 tarping, herbicide, topsoil scraping, and a control crossed with mulch or no mulch treatment in reducing background vegetation. Reductions in background vegetation facilitate the re-introduction of native species (Whisenant 1999). I hypothesized that topsoil scraping would be the most effective method, followed by 2 tarping, herbicide, 1 tarping, and control (no treatment) being the least effective treatment. Methods The study was conducted on the terrace lands of the University of California's Younger Lagoon Natural Reserve. The terrace lands were degraded by intensive agricultural use and subsequent invasion of exotic forbs and non-native grasses. Currently the presence of native plants is limited to Coyote brush, Baccharis pilularis. Coyote brush was not present in experimental plots. The terrace lands were historically likely to have been California coastal grassland composed of native perennial bunch grasses interspersed with wetlands and coastal scrub (D Antonio et al. 2007). The University of California Santa Cruz s Long Range Development Plan for its Marine Sciences Campus was certified by the California Coastal Commission on 7 January From this certification, UC Santa Cruz is mandated to restore the terrace lands surrounding its Marine Sciences Campus to 25% native vegetation (Holl et al. 2010). Currently the site is dominated by non-native annual grasses. My study investigates what

5 Chan 5 restoration strategy would be the most effective in reaching this goal. Research plots were established on California coastal prairie adjacent to south facing coastal bluffs. All plots were mowed before the application of each treatment and the area was fenced off using chicken wire and wooden stakes to reduce herbivory and trampling. Each treatment was tested in a 5 5 m plot. Plots were separated from neighboring treatments and the non-treated surrounding area by a 0.5 m buffer. The five treatments: 1 tarping, 2 tarping, topsoil scraping, herbicide and control were crossed with mulch or no mulch treatment by dividing each plot into two subplots measuring 2.5 5m. One subplot had mulch applied, while the other subplot did not. This experiment was set up as a randomized complete block design where each set of treatments was replicated in five blocks. Construction of the block design began with mowing on August 2010, with the hay created allowed to fall in place. 2 tarping treatment was initiated immediately thereafter. Plots were irrigated in August for 18 days to stimulate the emergence of the non-native seed bank. 10- ml black polyethylene sheets were placed on the soil surface following irrigation, and a 20-cm trench was dug to bury the edges of each 5 5 meter tarp. Sand bags were used to secure the tarps against onsite winds and other disturbances. Four sand bags were placed on each corner and a single sand bag was placed at the center of each plot. The 10-ml tarps and sand bags were kept in place for a period of seven weeks and were removed on 21 October tarping plots were then left exposed to the environment for a period of 18 days. This 18 day period was planned to coincide with local rainfall to stimulate the emergence of non-native forbs and grasses. The second application of the 2 tarping treatment was conducted simultaneously with the application of 1 tarping on 8 November Tarps laid for 1 tarping and the second application for 2 tarping were kept in place for nine weeks until the tarps removal on 10

6 Chan 6 January Mulch was applied after tarping in January directly before planting. The herbicide treatment relied on two applications of Round-up, a commercially available herbicide. Round-up was applied on 18 November 2010 and again on 5 January Round-up was applied using a hand-operated sprayer at a diluted rate of 88.7-ml per plot or 3.5-ml per square meter. Mulch was applied after the last herbicide application before planting. Topsoil scraping was carried out in a single day, 27 October A small bulldozer was used to remove roughly 5-10 cm of topsoil. The soil was placed to the north of the scraped plots, and was smoothed out to be consistent with the landscape. Mulch was applied consistent with mulch applied to other treatments. The entire experimental area was fenced off to exclude herbivory and trampling. Mammal traps were placed in the field to remove any mammals inside the enclosed area. Wood chip mulch was applied to half of each plot. Wood chip mulch was supplied by the University of California, Santa Cruz campus. Mulched was applied with a rake to a thickness of ~2 cm before planting. Seeds of Nassella pulchra, Elymus glaucus, Hordeum brachyantheum, and Bromus carinatus, all native grasses, were collected beginning in summer Native grass seeds were first seeded in trays at University of California, Santa Cruz greenhouses. After sprouting from trays, the sprouts were transferred to cone-tainers. Plants were then out planted into the study site after a period of hardening in the greenhouses located at Long Marine Lab campus. Vegetation cover was measured in four m quadrats in each plot. Cover values were measured in 5% cover classes for non-native grasses, exotic forbs, bare ground, sorrel (Oxalis), thistles (most commonly Italian thistle Carduus pycnocephalus and Bull thistle Cirsium

7 Chan 7 vulgare), and wild radish (Raphanus sativus). Quadrats were placed 0.5 m from the buffers separating each plot and were spaced in 1 meter intervals to run the length of the subplot. Measurements were taken three times: 10 January 2011, 20 February 2011, and 13 April I focus here on the results from the last round of data collection (13 April 2011), since those were taken at the peak of the growing season. I conducted all analyses using JMP. I analyzed the various cover values using a two-way ANOVA with weed control treatment, mulch, and their interaction term in the model. I used a Tukey analysis to compare differences among the five weed control treatments. Results Treatments and mulch exhibited a significant interactive effect on non-native grass and forb cover as well as bare ground cover (Table 1). 2 tarping, 1 tarping, and herbicide treatments in combination with mulch had the lowest non-native grass and forb cover as well as the highest percent bare ground (Figure 1, Table 1). Herbicide without mulch was the most effective treatment by itself at reducing non-native grass and forb cover (Figure 1). Control and topsoil scraping were the least effective treatments on their own. Non-native grass and forb cover was the highest in control and topsoil scraping plots. Topsoil scraping was ineffective as a weed control method; results from topsoil scraping were similar to the control. Mulch had a significant interactive effect between applied treatments and the mulch treatment. Mulch had a stronger effect in less effective treatments (Figure 1, Figure 2, Figure 3). Mulch also showed a strong effect on native grass cover; all mulched treatments had the highest native grass cover (Figure 3, Table 1). Trends in forb cover were explained mostly by thistle cover (Figure 2). Mulch had a strong effect on thistle levels, all treatments crossed with mulch yielded equal results (Figure 2).

8 Chan 8 Oxalis cover was reduced by 2 tarping and herbicide with and without mulch. No treatment was effective on Raphanus sativus (Figure 2). Treatment Mulched Treatment*Mulched Non- native Grass Cover 54.6(<0.0001) 359.6(<0.0001) 11.4(<0.0001) Non- native Forb Cover 40.1(<0.0001) 83.4(<0.0001) 5.5(0.0003) Bare Ground 30.1(<0.0001) 182.4(<0.0001) 4.3(0.0025) Oxalis Cover 16.1(<0.0001) (.9918) 4.8(0.0010) Thistle Cover 5.5(0.0003) 61.7(<0.0001) 3.2(0.0148) Raphanus sativus Cover 2.3(0.0561) 0.73(0.3947) 0.37(0.8303) Native Grass Cover 11.1(<0.0001) 10.6(0.0013) 1.5(0.2032) Table 1. F(P) values for ANOVA of the effects of treatments, mulch, and the treatment*mulch interaction on herbaceous cover.

9 Chan 9 Figure 1. Cover values from top to bottom; Non-native grass, Non-native Forb, and Bare ground. Values are means ± 1 SE. Means are not significantly different for the same letters.

10 Chan 10 Figure 2. Cover values from top to bottom for; Oxalis, Thistle, and Raphanus sativus. Values are means ± 1 SE. Means are not significantly different for the same letters.

11 Chan 11 Figure 3. Cover values for Native grasses. Values are means ± 1 SE. Means are not significantly different for the same letters. Discussion Herbicide, 2 tarping, and 1 tarping in combination with mulch were the most effective restoration strategies. In conjunction with mulch, they were the most effective treatments in reducing exotic cover, retaining bare ground, and promoting native growth. These results mimic the results of other studies on the use of herbicide, black plastic tarping, mowing, and disking for restoration (Marushia and Allen 2011, Enloe et al. 2005) 2 tarping and 1 tarping had similar weed control effects. Both 2 tarping and 1 tarping with mulch do not have statistically differentiable cover values for non-native vegetation or native grasses. The first application of tarps for 2 tarping was ineffective. The concurrent tarping period between 1 tarping and 2 tarping from 8 November 2010 to 10 January 2011 was more influential in controlling forbs and non-native grasses. This is supported by another

12 Chan 12 study on tarping which noted tarping timed to coincide with California s fall rains to be particularly successful (Marushia and Allen 2011). Herbicide without mulch was the most effective of any treatment by itself in reducing non-native grass cover. This mirrors another case study in perennial grassland restoration which has shown the benefits of using glyphosate to control exotic plants (Enloe et al. 2005). Herbicide by itself was particularly effective at controlling non-native grasses and thistle (Figure 1, Figure 2). A broad herbicide was appropriate for the study site because of the site s limited existing native plant species. If the site had endemic plant species, herbicide would not have been appropriate. Herbicide was noted to inhibit growth of out-planted native grasses. Plots treated with herbicide had the lowest native grass cover values (desilva 2011). Application of glyphosate herbicide should be limited to reduce the risk of glyphosate resistance and to minimize negative effects of residual chemicals to native plants (DiTomaso et al. 2007; Cornish and Burgin. 2005). As a restoration strategy, topsoil scraping was ineffective. Results from topsoil scraping were similar to control. Background vegetation cover in scraped plots was not measurably different from control plots. This goes against past success with topsoil scraping in coastal prairie (Buisson et al. 2006, Buisson et al. 2008), although this can mostly be explained by different site conditions. Vegetation cover in topsoil scraping plots could be contributed to physically lowering the soil profile. Topsoil scraping plots were observed to be flood for multiple days during the rainy season. This flooded state may have increased exotic seed dispersal into scraped plots or promoted growth of exotic seedlings. High forb cover values in topsoil scraping plots also suggest that non-native forbs benefited from the disturbance to soil (Figure 1, Shiffman 2007). No measurements were taken relating to the existing seed bank of the

13 Chan 13 site, but quantifying the existence of the non-native seed bank could be of interest of future studies. Mulch reduced background vegetation cover values and increased bare ground values (Figure 1, Figure 2). This effect was more pronounced in treatments which were less effective (Table 1). The most pronounced effect of mulch was noted in thistle cover. All treatments crossed with mulch did equally well in suppressing thistle cover (Figure 2). This reduction in thistle cover is responsible the majority of forb cover reductions. Mulch reduces seed germination of weeds and thereby reduces competition on natives (Stromberg et al. 2007). Mulch s negative effects on native seed germination were negligible in this first year of study because no native grasses or forbs were present in experimental plots before the planting of native grasses for this study. Future studies could compare recruitment rates of native grasses in mulch and no mulch plots as planted native grasses begin to generate a native seed bank. It appeared tarping was made less effective because of soil disturbance on the margins of each plot. Soil displaced from burying the edges of the tarps resulted in small ditches around the perimeter of each tarping plot after the tarps were removed. These ditches became sources of significant creeping forb growth which may in turn have increased forb cover inside the tarping plots. When mulch was applied, it was spread to the buffer, reducing the negative effective of weedy buffers on tarping plots. Alternative treatments are needed to control Raphanus sativus. All weed control methods tested did not have an effect on Raphanus sativus cover. Raphanus was present on the study site before the implementation of any treatment. Treatments either failed to exhaust the existing Raphanus seed bank or were unable to prevent Raphanus seed dispersal from sources outside of the experiment.

14 Chan 14 For restoration purposes, 1 tarping with mulch is a viable alternative to herbicide with mulch and represents the best weed control strategy. 2 tarping with mulch did not yield better results than 1 tarping with mulch. As a strategy for coastal prairie restoration, 1 tarping makes the most sense because of its smaller labor, material, and time commitments. Herbicide with mulch can be an alternative to 1 tarping in landscapes which are not flat or where tarps cannot be securely fixed. Future study of the site will yield interesting results. I speculate that the strategies studied will become less effective over time in reducing exotic vegetation cover after their initial application. Where native grass growth is the highest, out planted native grasses, given their density may out compete invasive forbs and grasses (Middleton et al. 2010). However, without active manipulation, plots may return to an equilibrium community of exotic grasses and forbs (D Antonio et al. 2007). One point of interest would be the introduction of a mowing regime, which has been shown to control exotic annuals when correctly timed (DiTomaso et al. 2007). With proper management, 1 Tarping is a viable technique for restoration in California coastal prairie, with less negative environmental impacts than herbicide use and less effort than multiple tarping periods. Literature Cited Barbour, M., B. Pavlik, F. Drysdale, and S. Lindstrom California s Changing Landscape, California Native Plant Society, Sacramento. Buisson, E., S. Anderson, K. D. Holl, E. Corcket, G. F. Hayes, A. Peeters, and T. Dutoit Reintroduction of Nassella pulchra to California coastal grasslands: Effects of topsoil scraping, plant neighbor scraping and grazing. Applied Vegetation Science, 11: Buisson, E., K. D. Holl, S. Anderson, E. Corcket, G. F. Hayes, F. Torre, A. Peteers, and T. Dutoit Effect of seed source, topsoil scraping, and plant neighbor scraping on restoring

15 Chan 15 California coastal prairies. Restoration Ecology Vol. 14 Issue 4, Cornish, P. S. and S. Burgin Residual effects of glyphosate herbicide in ecological restoration. Restoration Ecology Vol. 13, No D Antonio, C. M., C. Malmstrom, S. A. Reynolds, and J. Gerlach Ecology of invasive non-native species in California grassland. Pages in M. R. Stromberg, J. D. Corbin, and C. M. D Antonio (eds) California Grasslands: Ecology and Management. University of California Press, Berkeley, CA. desilva, T Effect of different exotic control strategies on growth and survival of native grasses in coastal prairie habitat. Senior Thesis: UC Santa Cruz DiTomaso, J. M., S. F. Enloe, and M. J. Pitcairn Exotic plant management in California annual grasslands. Pages in M. R. Stromberg, J. D. Corbin, and C. M. D Antonio (eds) California Grasslands: Ecology and Management. University of California Press, Berkeley, CA. El-Keblawy, A. and F. Al-Hamadi Assessment of the differential response of weeds to soil solarization by two methods. Weed Biology and Management, 9: Enloe, S. F., J. M. DiTomaso, S. B., Orloff, and D. J. Drake Perennial grass establishment integrated with clopyralid treatment for yellow starthistle management on annual range. Weed technology 19: Franz, J. E., M. K. Mao, J. A. Sikorski Glyphosate A Unique Global Herbicide. American Chemical Society Monograph, 189: 1-17, Holl, K. D., T. Hylnad, B. Largay, and L. Stratton Enhancement and Protection of Terrace Lands at Younger Lagoon Reserve. Humphreys, L. R The Evolving Science of Grassland Improvement. Cambridge University Press, Cambridge. Lulow, M. E Restoration of California native grasses and clovers: the roles of clipping, broadleaf herbicide, and native grass density. Restoration Ecology Vol. 16, No. 4, Marushia, R. G. and E. B. Allen Control of exotic annual grasses to restore native forbs in abandoned agricultural land. Restoration Ecology Vol. 19, No. 1, Middleton, E. L., J. D. Bever, and P. A. Schultz The effect of restoration methods on the quality of the restoration and resistance to invasion by exotics. Restoration Ecology Vol. 18, No. 2, Schiffman P. M Ecology of native animals in California grasslands. Pages

16 Chan 16 in M. R. Stromberg, J. D. Corbin, and C. M. D Antonio (eds) California Grasslands: Ecology and Management. University of California Press, Berkeley, CA. Stapleton, J. J Soil solarization in various agricultural production systems. Crop Protection, 19: Stromberg, M. R., C. M. D Antonio, T. P. Young, J. Wirka, and P. R. Kephart California grassland restoration. Pages in M. R. Stromberg, J. D. Corbin, and C. M. D Antonio (eds) California Grasslands: Ecology and Management. University of California Press, Berkeley, CA. Symstad, A. J Does biodiversity-ecosystem function science apply to prairie restoration? Ecological Restoration, Vol. 26 Issue 2, Whisenant, S. G., Repairing Damaged Wildlands. Cambridge University Press, Cambridge..