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2014

Native Establishment Success Influenced yb Spotted Knapweed ( stoebe) Control Method

Laurelin M. Martin Grand Valley State University

Neil W. MacDonald Grand Valley State University, [email protected]

Tami E. Brown Grand Valley State University

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ScholarWorks Citation Martin, Laurelin M.; MacDonald, Neil W.; and Brown, Tami E., "Native Plant Establishment Success Influenced by Spotted Knapweed (Centaurea stoebe) Control Method" (2014). Funded Articles. 15. https://scholarworks.gvsu.edu/oapsf_articles/15

This Article is brought to you for free and open access by the Open Access Publishing Support Fund at ScholarWorks@GVSU. It has been accepted for inclusion in Funded Articles by an authorized administrator of ScholarWorks@GVSU. For more information, please contact [email protected]. RESEARCH ARTICLE

Native Plant Establishment Success Influenced by Spotted Knapweed (Centaurea stoebe) Control Method Laurelin M. Martin, Neil W. MacDonald and Tami E. Brown

ABSTRACT frequently need to be controlled as part of efforts to reestablish native species on degraded sites. While the effectiveness of differing control methods are often reported, the impacts these methods have on the establishment of a native plant community are often unknown. To determine methods that effectively reduce spotted knapweed (Cen- taurea stoebe) while enhancing native species establishment, we tested 12 treatment combinations consisting of an initial site preparation (mowing, mowing + clopyralid, or mowing + ), in factorial combination with annual adult knapweed hand pulling and/or burning. We established 48 plots and applied site preparation treatments during summer 2008, seeded 23 native forbs and grasses during spring 2009, pulled adult knapweed annually from 2009–2012, and burned in the early spring 2012. During July of 2011 and 2012, percent cover of all species was visually estimated. By 2011, seeded species had established in all treatment plots, including plots that retained greater than 50% knapweed cover, indicating that native species successfully established despite knapweed dominance. Mowing alone had no longterm impacts on community development. Clopyralid favored non-native grass establishment, while glyphosate encouraged non-native forbs. Clopyralid had minimal impacts on native forb establishment, but did effectively control knapweed. Pulling reduced knapweed cover, increased non-native grass cover and enhanced native species establishment. Burn- ing had little impact, possibly due to low intensity and unseasonable weather. On the heavily invaded site we studied, combining the use of clopyralid with hand pulling effectively controlled knapweed and favored the establishment of seeded native grasses and forbs.

Keywords: community development, ecological restoration, invasive , Michigan prairie, native diversity

uccessful restoration often requires control efforts (D’Antonio and Mey- while also allowing for either unin- Sthe concomitant control of inva- erson 2002). hibited or accelerated restoration of a sive species, which otherwise will Control efforts targeting invasive native community. hinder the restoration effort, espe- species can also inhibit the develop- Spotted knapweed (Centaurea stoebe; cially on degraded land. Following ment of a native community (Erskine hereafter knapweed) has invaded over invasive plant establishment, resto- Ogden and Rejmánek 2005, Rinella et 2.9 million hectares in North America ration of a native plant community al. 2009, Ortega and Pearson 2011). (DiTomaso 2000) and can success- becomes very challenging (DiTomaso Successful control of one invasive fully invade plant communities on 2000). Invasive plants are capable of plant may open the community to both remnant and disturbed sites. altering ecosystem function (Weiden- further invasion or surges in domi- Following invasion, knapweed forms hamer and Callaway 2010), nutrient nance of other non-natives already peripherally enlarging monocultures cycles (Ehrenfeld et al. 2001, Allison present (Zavaleta et al. 2001, Ortega that seed profusely, have allelopathic and Vitousek 2004), and disturbance and Pearson 2011). Unfortunately, effects on susceptible species, and regimes (D’Antonio and Vitousek it is infrequent for studies targeting negatively impact ecosystem richness 1992, Brooks et al. 2004), resulting invasive species control to report on and diversity (Watson and Renney in a continuing need for longterm the effects of these treatments on the 1974, Schirman 1981, Tyser 1992, restored plant community (Reid et Sheley et al. 1998, Kedzie-Webb et Ecological Restoration Vol. 32, No. 3, 2014 al. 2009, Kettenring and Reinhardt al. 2001, Thorpe et al. 2009). While ISSN 1522-4740 E-ISSN 1543-4079 Adams 2011). Thus, it is highly desir- it is known that knapweed can be ©2014 by the Board of Regents of the able to determine which methods controlled using a variety of methods University of Wisconsin System. can be used to control invasive plants including application (Rice

282 • September 2014 ECOLOGICAL RESTORATION 32:3 et al. 1997), biological controls (Story reduced knapweed cover and increased average, is 369 mm (NCDC 2009). et al. 2006, but see Ortega et al. 2012), native species diversity, cover, and During the study, total precipita- and controlled burning (MacDonald floristic quality. These treatments tion from April through August et al. 2007), resurgence of knapweed included factorial combinations of was 386 mm during 2009, 381 mm is very likely without the formation mowing alone or mowing in combina- during 2010, 510 mm during 2011 of a competitive, native community tion with a single application of either and 302 mm during 2012, as deter- (Sheley et al. 1996), especially on sites a broadleaf-specific herbicide (clopy- mined from the Muskegon, Michi- in which seeds from previous infes- ralid), or broad-spectrum herbicide gan National Weather Service station tations are present in the seed bank (glyphosate), hand pulling of adult (NCDC 2014). Normal tempera- (Sheley et al. 1996, Carpinelli et al. knapweed, and burning. Based on our tures for the area are 18.3 °C in June, 2004). As diverse native plant com- review of published literature and pre- 21.1 °C in July, and 20.3 °C in August munities are more capable of resist- vious study in adjacent areas (Mac- (NCDC 2014). Temperature averages ing knapweed invasion (Kennedy et Donald et al. 2003, 2007), we hypoth- during the study for June, July and al. 2002, Bakker and Wilson 2004, esized: (1) a single mowing would August respectively were 18.9 °C, Maron and Marler 2007), it is impor- have little longterm impacts, (2) use 18.8 °C, and 19.9 °C for 2009, tant during any restoration project to of clopyralid would reduce knapweed 19.8 °C , 23.9 °C, and 23.9 °C for ensure that such diverse native systems cover and lead to increases in grass 2010, 19.7 °C, 24.1 °C, and 21.8 °C are reestablished. cover, (3) application of glyphosate for 2011, and 20.8 °C, 25.4 °C, and Targeting native plant establishment would reduce competition during 21.2 °C for 2012 (NCDC 2014). in combination with knapweed con- native species seedling establishment, Thus, while 2009 and 2010 experi- trol requires knowledge on how com- but allow for rapid knapweed resur- enced relatively normal weather, in munity development will be affected. gence, (4) pulling of adult knapweed 2011 there was above average precipi- For instance, the controlled burning would reduce knapweed cover, allow- tation, and in 2012, low precipitation of native, fire-adapted species stimu- ing for increased native species estab- and high temperatures led to a severe lates flower stalk production, facili- lishment due to decreased competi- drought conditions lasting from mid- tates seedling establishment, enhances tion, (5) controlled burns performed June through mid-October (NDMC productivity, and increases warm-sea- in mid-Spring would both reduce 2013). son grasses (Old 1969, Abrams et al. knapweed and increase native warm- Prior to establishment of the Bass 1986, Howe 1994, Maret and Wilson season grasses, (6) the broadleaf-spe- River Recreation Area, the site was 2005). In addition, carefully timed cific herbicide treatment (clopyralid) highly disturbed by extensive gravel burns can reduce knapweed cover would result in higher grass cover, mining in the mid-1900s (MacDon- and seed viability (Emery and Gross while the broad-spectrum herbicide ald et al. 2003), leaving a persistent 2005, MacDonald et al. 2007, Ver- (glyphosate) + pulling + burning treat- ruderal plant community infested by meire and Rinella 2009). Applying ment and the mowing + pulling + spotted knapweed (MacDonald et al. effective control methods, but rely- burning treatment would lead to the 2003, 2007, 2013). Knapweed was the ing on a remnant native seed bank highest native diversity. Within the dominant invasive plant at our study or colonization from nearby sites for context of these hypotheses, the goal site prior to the initiation of our study native species establishment may result of the restoration was to establish a with 60% to 70% cover based upon in communities with lower species diverse native plant community that the total pre-treatment knapweed den- richness (Heslinga and Grese 2010), would effectively resist reinfestation by sity (236 ± 16 m-2 SE, , MacDonald especially in isolated areas. Therefore, knapweed while providing opportuni- et al. 2013). Previous studies at this seeding with a diverse mix of native ties for active management to reinforce site demonstrated that native grass species immediately following control the trajectory toward the maintenance establishment and fire reintroduction treatment may facilitate native species of native species and processes. could successfully control knapweed establishment and competition with (MacDonald et al. 2003, 2007), but knapweed (Tyser et al. 1998). Methods these approaches resulted in a com- The objective of this study was to munity with very low native diversity. determine the most effective treatment Study Area The current study design expands on these works through the use of larger for increasing native plant diversity Our study site was within the Bass plots, incorporation of a more diverse while also reducing knapweed on an River Recreation Area, Ottawa invaded site in western Michigan, County, Michigan, US (43°00' 49" N, seed mix, application of different com- US. To achieve this aim, 12 different 86°01' 47" W). Typical precipitation binations of knapweed control treat- ments, and an extensive evaluation of treatment combinations were tested for the area, based on the 30-year to determine which would result in the developing community.

September 2014 ECOLOGICAL RESTORATION 32:3 • 283 Table 1.The twelve treatment combinations tested during study at Bass comprised a total of 60% of the mix, River Recreation Area, Ottawa County, MI, US. The treatment combinations and 18 native forbs, which made up represent a factorial arrangement of treatments in a randomized complete the remaining 40% of the mix (Table block design, including three levels of initial site preparation, two levels of pulling, and two levels of burning. 2). Pulling of adult, bolted knapweed on designated plots (n = 24) began in Levels of Treatment July of 2009 and continued annually Initial Site Preparation Pulling Treatment Burn Treatment n thereafter. Pulling entailed removing Mowed, 2008 None None 4 adult knapweed, including the tap- Mowed, 2008 None Burned, 2012 4 root, in advance of flowering to pre- Mowed, 2008 Knapweed pulling, Annually None 4 vent seed production and dispersal Mowed, 2008 Knapweed pulling, Annually Burned, 2012 4 within the plot with the aid of a hand- Mowed + clopyralid, 2008 None None 4 held weed puller (Ergonomic Hand Mowed + clopyralid, 2008 None Burned, 2012 4 Weeder, Item #2306, Shanghai Worth Mowed + clopyralid, 2008 Knapweed pulling, Annually None 4 Garden Products Co., Ltd., Shanghai, Mowed + clopyralid, 2008 Knapweed pulling, Annually Burned, 2012 4 Mowed + glyphosate, 2008 None None 4 156 China). Mowed + glyphosate, 2008 None Burned, 2012 4 Controlled burning of the desig- Mowed + glyphosate, 2008 Knapweed pulling, Annually None 4 nated plots (n = 24) took place on Mowed + glyphosate, 2008 Knapweed pulling, Annually Burned, 2012 4 April 2, 2012 (MacDonald et al. 2013). Unseasonably warm weather during March of 2012 resulted in Experimental Design bluegrass (Poa compressa). None of the advanced plant phenology causing In July, 2008, we established the field species included in the native seed us to burn earlier than is optimal for experiment using a randomized com- mix were present on the plots before knapweed control (Emery and Gross plete block design with a fully crossed the initiation of the experiment, with 2005, MacDonald et al. 2007). Fire factorial arrangement of 12 treatment the exception of a few scattered occur- temperature at ground level was mea- combinations and four replicate blocks rences of little bluestem (Schizachy- sured with pyrometers constructed for a total of 48 5 m by 5 m plots. The rium scoparium) and big bluestem using Tempilaq G® indicator solu- 12 treatment combinations consisted (Andropogon gerardii). In the summer tions (Tempil, South Plainfield, of three initial site preparation treat- of 2008, the entire site was mowed to NJ). These solutions were painted ments of mowing, mowing plus clopy- facilitate plot layout, reduce knapweed on ceramic tiles and melt at speci- ralid, or mowing plus glyphosate; seedfall prior to other treatments and fied temperatures. The 14 indicators each combined with or without hand ease herbicide application (Packard used ranged from 79 °C to 204 °C, at pulling and with or without burning and Mutel 1997). Randomly selected 14 °C intervals, and 232 °C to 316 °C, (Table 1). Buffers were mowed yearly plots were subsequently treated with at 28 °C intervals, as this has been in late June, with plots separated by a single application of the broad-spec- shown to include the ranges of tem- 2.5 m buffers, and blocks surrounded trum herbicide glyphosate (Roundup perature in controlled burns (Kennard by 5 m buffers. While there was no Concentrate Plus®, Monsanto, Marys- et al. 2005). Four pyrometers were true “control” treatment combination ville, OH), at a rate of 9.9 kg ae ha-1 installed per plot on the morning of in the sense of including plots with no (n = 16), or the broadleaf-specific the burns. Immediately following the treatments whatsoever, in the context herbicide clopyralid (Transline®, burns, the pyrometers were collected of this experiment the plots that were Dow AgroSciences, Indianapolis, and inspected to determine the high- only mowed once and did not receive IN), at a rate of 0.6 kg ae ha-1 (n = est temperature indicator that showed either pulling or burning can be con- 16). The remaining 16 plots did not signs of changing during the fire. receive any additional site preparation. sidered a control as a single mowing Plant Surveys was not expected to have any longterm These mowed-only plots allowed us impacts on community trajectory. to determine if native plants could In 2009 and 2010, we recorded the Prior to implementation of treat- be established simply by interseeding presence/absence of each grass and ments, all plots were dominated by following minimal site preparation. forb species in the seed mix on five spotted knapweed and other non- In the spring of 2009, we seeded 0.25 m2 frames randomly located on native grasses and forbs, including all plots at a rate of 22 kg ha-1 with a each plot. In 2011 and 2012, we visu- Kentucky bluegrass (Poa pratensis), mixture of native species representa- ally estimated percent cover of each quackgrass (Elymus repens), rabbitfoot tive of Michigan dry-mesic prairie, grass and forb species in each plot, clover (Trifolium arvense), sweetclo- dry sand prairie and oak barrens (Kost determining a plot estimate by aver- ver (Melilotus officinalis), and Canada et al. 2007). The seed mix included aging one cover estimate from each five native warm-season grasses, which of the four quarters of the plot. This

284 • September 2014 ECOLOGICAL RESTORATION 32:3 Table 2. Seeded species presence as a percent of the 48 total treatment plots at Bass River Recreation Area, Ottawa County, MI, US. Species are ordered in terms of presence during 2011. Column C corresponds to the coefficient of conservatism for each species specific to Michigan (MDNR 2001).

Family Species Common Name C 2011 2012 Poaceae Andropogon gerardii Big Bluestem 5 100.0% 97.9% Poaceae Schizachyrium scoparium Little Bluestem 5 100.0% 100.0% Poaceae Sorghastrum nutans Indiangrass 6 100.0% 100.0% Lamiaceae Monarda fistulosa Wild Bergamot 2 97.9% 95.8% Coreopsis lanceolata Lanceleaf Tickseed 8 93.8% 93.8% Lamiaceae Monarda punctata Spotted Beebalm 4 87.5% 66.7% Asteraceae Rudbeckia hirta Blackeyed Susan 1 83.3% 85.4% Apocynaceae Asclepias tuberosa Butterfly Milkweed 5 77.1% 62.5% Poaceae Elymus canadensis Canada Wildrye 4 43.8% 16.7% Asteraceae Ratibida pinnata Pinnate Prairie Coneflower 4 39.6% 29.2% Asteraceae Pseudognaphalium helleri Heller’s Cudweed 2 12.5% 18.8% Fabaceae Lupinus perennis Sundial Lupine 7 12.5% 0.0% Poaceae Panicum virgatum Switchgrass 4 12.5% 8.3% Asteraceae Solidago nemoralis Gray Goldenrod 2 10.4% 8.3% Asteraceae Coreopsis tripteris Tall Tickseed 7 8.3% 2.1% Fabaceae Lespedeza capitata Roundhead Lespedeza 5 6.3% 8.3% Verbenaceae Verbena stricta Hoary Verbena 4 2.1% 4.2% Asteraceae Coreopsis palmata Stiff Tickseed 10 2.1% 2.1% Asteraceae Helianthus occidentalis Fewleaf Sunflower 8 2.1% 2.1% Asteraceae Solidago speciosa Showy Goldenrod 5 2.1% 0.0% Asteraceae Solidago juncea Early Goldenrod 3 0.0% 0.0% Fabaceae Tephrosia virginiana Virginia Tephrosia 10 0.0% 0.0% Commelinaceae Tradescantia ohiensis Bluejacket 5 0.0% 0.0%

entailed dividing each 5 m by 5 m 2) D = 1-Σ pi2 plant communities. These methods plot into quarters, with two research- rely on coefficients of conservatism ers each estimating the cover of two (McCune and Grace 2002). As recom- specific to Michigan (MDNR 2001), quarters. During both years, each mended by Peet (1974), we used the ranging from zero, representing ubiq- researcher consistently examined the exponential of H' for analysis, as this uitous native species, to ten, represent- same two quarters within each plot. indicates the functional number of ing highly conserved native species To standardize visual estimates among species in the sample. Interpretations (Taft et al. 1997). FQI was calculated researchers, we referred to published of the results remain the same, with for each plot by multiplying the C area charts (Anderson 1986), and used higher values indicating higher diver- for the plot by the square root of the 0.1 m2 PVC frames as a standard area sity. Simpson’s index has a range from number of native species on the plot reference. Following data collection, zero, with a single species present, to (Packard and Mutel 1997). Native tree we calculated the relative percent one, maximum diversity (Peet 1974). and shrub species are not part of the cover ( pi ) of each species on each plot Estimates of percent cover have been target prairie community and were by dividing the summed total cover used successfully in previous studies excluded from FQI and C analysis. of each species by the summed total to calculate these diversity indices For analyses of community com- cover of the plot. (Potvin and Vasseur 1997, Tilman et position, we classified species into al. 1997), and avoid errors resulting one of six groups: non-native forbs, Data Analysis from miscounting clonal species if knapweed, non-native grasses, native Using the relative percent cover cal- density had been used. graminoids, native forbs, and tree/ culated for each year, we determined To evaluate community quality, we shrub species. The non-native forbs plot diversity using the Shannon index calculated the mean coefficient of con- group does not include knapweed. of diversity: servatism (C ), and a floristic quality As the dominant invasive species and index (FQI) for each plot to distin- a focus of our research, knapweed was

1) H' = -Σ pi log pi guish among treatment combinations classified independently. Following containing ubiquitous native plants this classification, we calculated the and Simpson’s index of diversity: and those containing species more relative percent cover for each group- likely to occur in undisturbed native ing by summing the relative percent

September 2014 ECOLOGICAL RESTORATION 32:3 • 285 cover of all species within that group. a trend toward lower gravel on plots lanceleaf tickseed quadrupled in aver- As the tree/shrub group accounted for assigned to the pulling treatments age relative cover from 0.2% to 0.8%, less than 0.4% relative cover in both (PERMANOVA; F = 3.19, p = 0.09). irrespective of treatment. years, we did not include it in subse- Since variation in gravel content could Both the FQI and C of the entire quent analyses. We performed simple affect soil moisture holding capacity site were increased by seeding. Vol- linear (Pearson) correlations among and thus plant response, when a sig- unteer native species found on site the remaining five groups, in addition nificant pulling effect was found, the had a C of 2.72 and an FQI of 13.6, to total grass cover (sum of non-native data were re-analyzed using gravel while including seeded native species grasses and native graminoids cover) as a covariate to ensure the apparent resulted in a C of 3.79 and an FQI using JMP 9.0.0 (n = 48; JMP v. 9.0, treatment effect was not related to of 26.0. SAS Institute, Cary, NC). In addition, underlying variation in soil properties. the most prevalent native seeded spe- Initial Site Preparation Effects cies were analyzed to determine if the Results Initial site preparation influenced both control treatments influenced their the diversity and quality of the plant establishment. Seeding Effects community, with lower diversity, but We analyzed the 2009 and 2010 In 2009, 20.8 ± 3.3% (mean ± SE) a higher C in clopyralid treatments native grass and forb presence data of 0.25 m2 frames sampled (averaged (Table 3, Table S1). Non-native spe- and 2011 diversity indices, FQI, C , across all treatment combinations) cies, including non-native grasses, non-native forbs, and knapweed and relative cover data using three had at least one seeded native grass levels of initial site preparation and species present, although no seeded exhibited the greatest response to site preparation (Figure 1, Table S2). The two levels of pulling, as there were no forbs were identified. In 2010, 32.9 ± burning effects prior to application of 3.8% of frames sampled had at least clopyralid-only treatment maintained this treatment and these effects were one seeded native grass species pres- low knapweed cover through four pooled with error. The 2012 diversity ent and 17.5 ± 2.8% of frames had years, while knapweed had resurged indices, FQI, C , and relative cover at least one seeded native forb species to near estimated pre-treatment levels on mowed-only and glyphosate-only data were analyzed using the full fac- present. The percent occurrence of treatments by 2011 (Figure 1, Table torial design, including the additional native grasses and forbs did not differ two levels of burning. As these data significantly among treatment com- S2). Clopyralid also consistently did not fully meet the assumptions of binations in either 2009 or 2010. We resulted in greater non-native grass a parametric ANOVA, analyses were observed native forbs and grasses on cover (Figure 1, Table S2). Glyphosate carried out using PERMANOVA, a all plots by three years after seeding, treatments contained the highest non- nonparametric, permutational analysis with 20 of the 23 seeded native spe- native forb cover in 2011 (29.4%), of variance (Anderson 2001, McArdle cies established on site (Table 2). By while non-native forb cover was lower and Anderson 2001, Anderson 2005), 2011, big bluestem, little bluestem, and similar on the clopyralid and using Euclidean distances. Prelimi- and Indiangrass (Sorghastrum nutans) mowed treatments (7.7% and 7.4% respectively; Figure 1, Table S2). nary analyses suggested block effects had established in every plot (Table 2). were small and including block terms Between 2011 and 2012, Indiangrass The initial site preparation also in the model would not greatly alter doubled in average relative cover from impacted the establishment of native species (Table 4). In 2012, big blue- results, so we pooled block effects with 1.8% to 3.6%. Coinciding with an stem had the highest relative percent error terms in the PERMANOVA. increase in average native grass cover PERMANOVA is not designed to between 2011 and 2012 from 11.9% cover in the glyphosate and clopy- allow a repeated measures analysis of to 15.1%, there was a significant nega- ralid treatments (Table 4, Table S3). While pinnate prairie coneflower had variance, so we ran separate analy- tive correlation between native and low establishment success, both this ses for each year. Post-hoc analyses non-native grass cover in 2012 (Pear- species and blackeyed Susan occurred were completed using nonparametric son correlation; r = - 0.47, p < 0.001). most prevalently on glyphosate treat- multiple comparison tests available Several forbs also had high frequency ments (Tables 2 and 4, Table S3). in PERMANOVA (Anderson 2005). of establishment, including butterfly Significance was accepted at p < 0.05 milkweed (Asclepias tuberosa), lanceleaf for all tests. Pulling Effects tickseed (Coreopsis lanceolata), wild In addition, based on soil testing bergamot (Monarda fistulosa), spotted Pulling resulted in lower Simpson’s performed at the onset of the study beebalm (Monarda punctata), pinnate diversity during 2012, but tended to (MacDonald et al. 2013), we found prairie coneflower (Ratibida pinnata), increase FQI. This effect, however, that while soil properties did not and blackeyed Susan (Rudbeckia hirta; became non-significant when gravel differ significantly among the differ- Table 2). Between 2011 and 2012, was included as a covariate (Table ent treatment combinations, there was 3, Table S1). In 2011, we observed

286 • September 2014 ECOLOGICAL RESTORATION 32:3 Table 3. Main effects means (SE) of site preparation and pulling treatments on Simpson’s diversity, Shannon diver- sity, mean coefficient of conservatism (C ), and Floristic Quality Index (FQI), at Bass River Recreation Area, Ottawa County, Michigan, US. Means followed by different letters differ significantly. Letters a, b indicate differences among initial site preparation treatments within a single year; x, y indicate differences between pulling treatments within a single year (p < 0.05). See Table S1 for test-statistics.

Initial Site Preparation Treatment Pulling Treatment Mow Clopyralid Glyphosate None Pulled Simpson’s Diversity 2011 0.61 (0.03) 0.54 (0.05) 0.63 (0.03) 0.58 (0.03) 0.60 (0.03) 2012 0.63 (0.03) a 0.44 (0.04) b 0.66 (0.03) a 0.63 (0.03) x 0.53 (0.03) y Shannon Diversity 2011 4.31 (0.26) 3.94 (0.39) 5.17 (0.44) 4.24 (0.29) 4.71 (0.33) 2012 4.37 (0.37) a 3.13 (0.26) b 5.33 (0.48) a 4.64 (0.37) 3.91 (0.33) C 2011 3.53 (0.07) ab 3.73 (0.13) a 3.34 (0.07) b 3.52 (0.06) 3.56 (0.10) 2012 3.61 (0.77) b 4.02 (0.12) a 3.64 (0.08) b 3.66 (0.08) 3.85 (0.10) FQI 2011 13.51 (0.46) 13.31 (0.33) 13.88 (0.42) 13.05 (0.25) 14.09 (0.37) 2012 12.66 (0.60) 12.87 (0.38) 13.18 (0.35) 12.23 (0.32) 13.57 (0.37)

a x c d z b y d z a x c z 100%

90%

80%

70%

60%

50% a Knapweed

Relative cover a x Non-Native Grasses 40% b y Non-Native Forbs y x Native Forbs 30% a x Native Graminoids a x 20% b

10%

0%

Treatment combination

Figure 1. Plant community composition as affected by site preparation and pulling at Bass River Recreation Area. Treatments that differ significantly p( < 0.05) are indicated by different letters: a, b, c, and d compare means for 2011; x, y and z compare means for 2012. Letters within the non-native grasses bars indicate differences among these treatments, letters above the knapweed bars indicate differences among these treatments. See Table S2 for exact p-values.

September 2014 ECOLOGICAL RESTORATION 32:3 • 287 Table 4. Main effects means (SE) of site preparation, pulling and burning treatments on native seeded species at Bass River Recreation Area, Ottawa County, Michigan, US. All values given represent relative percent cover. Means followed by different letters differ significantly. Letters a, b, c indicate differences among initial site preparation treatments within a single year; m, n indicate differences between pulling treatments within a single year; x, y indicate differences between burn treatments within a single year (p < 0.05). See Table S3 for test statistics.

Initial Site Preparation Treatment Pulling Treatment Burning Treatment Mow Clopyralid Glyphosate None Pulled None Burned % % % % % % % Big Bluestem 2011 0.77 (0.18) 1.06 (0.15) 1.05 (0.10) 0.81 (0.08) 1.11 (0.14) 0.99 (0.10) 0.93 (0.14) 2012 1.17 (0.19) b 1.83 (0.24) a 2.06 (0.31) a 1.37 (0.21) 2.00 (0.20) 1.74 (0.22) 1.63 (0.22) Butterfly Milkweed 2011 0.06 (0.02) 0.05 (0.01) 0.07 (0.02) 0.04 (0.01) n 0.08 (0.02) m 0.05 (0.01) 0.07 (0.01) 2012 0.04 (0.02) 0.10 (0.03) 0.11 (0.04) 0.04 (0.01) n 0.13 (0.03) m 0.06 (0.01) 0.10 (0.03) Spotted Beebalm 2011 0.60 (0.16) 0.32 (0.09) 0.42 (0.10) 0.24 (0.06) n 0.66 (0.11) m 0.49 (0.11) 0.41 (0.09) 2012 0.27 (0.11) 0.16 (0.05) 0.47 (0.14) 0.20 (0.06) 0.40 (0.10) 0.48 (0.09) x 0.12 (0.07) y Pinnate Prairie Coneflower 2011 0.02 (0.01) b 0.01 (0.01) b 0.08 (0.02) a 0.03 (0.01) 0.04 (0.01) 0.03 (0.01) 0.04 (0.01) 2012 0.01 (0.01) b 0.01 (0.01) b 0.10 (0.03) a 0.03 (0.01) 0.05 (0.02) 0.04 (0.01) 0.04 (0.02) Blackeyed Susan 2011 0.22 (0.04) b 0.11 (0.04) b 0.57 (0.15) a 0.19 (0.06) 0.41 (0.10) 0.27 (0.05) 0.33 (0.11) 2012 0.18 (0.04) b 0.07 (0.02) c 0.43 (0.11) a 0.15 (0.04) 0.30 (0.08) 0.25 (0.07) 0.21 (0.06) Little Bluestem 2011 0.86 (0.16) 0.57 (0.07) 0.58 (0.15) 0.50 (0.07) n 0.84 (0.22) m 0.72 (0.10) 0.62 (0.10) 2012 3.34 (0.82) a 1.37 (0.20) b 2.01 (0.40) ab 1.49 (0.24) n 2.99 (0.58) m 2.55 (0.56) 1.93 (0.33) higher native forb cover within the milkweed, spotted beebalm, and little Discussion pulling treatment as compared to bluestem exhibiting greater cover on treatments that did not include pull- the pulling treatments during at least Seeding Effects ing (6.3% compared to 2.3%; Figure one year of the study (Table 4, Table An unexpected finding in our study 1, Table S2), but this effect was less S3). Little bluestem had the greatest was the ease with which many seeded pronounced in 2012 (6.9% com- cover in the mowing-pulling treatment native species established on site. By pared to 3.9%). Knapweed cover was in 2012 (5.1%). While not significant seeding, we facilitated greater native reduced to less than 0.6% after three with gravel included as a covariate, forb diversity, which can assist in the years and to 0.06% after four years in there was also a trend toward higher prevention of knapweed reinvasion all pulling treatments (Figure 1, Table cover within pulling treatments for big (Sheley and Half 2006), and avoided S2). As adult knapweed was removed, bluestem during 2012, wild bergamot low recruitment that would have been the remaining knapweed cover rep- during 2011, and blackeyed Susan expected if we had relied on the native resented the presence of juveniles during both years (Table 4, Table S3). seed bank or outside colonization or seedlings. Pulling also resulted in (Heslinga and Grese 2010). We also Burning Effects greater non-native grass cover (Figure experienced fairly normal amounts 1, Table S2). Increases in non-native Average plot temperatures during the of precipitation in 2009, 2010, and grass cover corresponded to decreases 2012 burn ranged from < 79 °C to 2011. If we had experienced an in non-native forbs (Pearson correla- 159 °C. Burning resulted in lower C extreme drought earlier in the study tion; 2011: r = - 0.41, p = 0.004; 2012: compared to unburned treatments similar to the one experienced in 2012 r = - 0.50, p < 0.001), and knapweed (3.57 to 3.94, 2012; Table 3, Table after native species had successfully (Pearson correlation; 2011: r = - 0.67, S1); however, C had increased from established, seeding may have been less p < 0.001; 2012: r = - 0.58, p < 0.001). the 2011 mean values of 3.49 on successful. While the FQI of the entire Total grass cover had an increasing burned plots and 3.59 on unburned site remains lower than 35, which is negative correlation with knapweed plots. Burning also resulted in reduced the value considered indicative of a (Pearson correlation; 2011: r = - 0.77, spotted beebalm cover, while spot- plant community exhibiting floristic p < 0.001; 2012: r = - 0.83, p < 0.001). ted beebalm cover remained largely importance within Michigan (MDNR Pulling favored the establishment unchanged on unburned plots (Table 2001), it is higher than would have of seeded native species, with butterfly 4, Table S3). been achieved by relying on volunteer

288 • September 2014 ECOLOGICAL RESTORATION 32:3 species establishment alone (site FQI = whether competition with native have relatively low cover, however, 26.0 with seeded species, 13.6 without grasses will have any undesirable and will require more time to demon- seeded species). effects on native forbs. Sluis (2002) strate their competitive abilities. Once As with previous studies at this found that increases in big bluestem the native community becomes well knapweed-infested site (MacDonald dominance within prairie restorations established, it is expected to be more et al. 2003, 2007), big bluestem, little paralleled reductions in species rich- resistant to the resurgence of invasive bluestem, and Indiangrass established ness within 15 years, while Camill plants, including knapweed. successfully (Table 2). Competition et al. (2004) saw similar results three from these species should result in years into their restoration. After Initial Site Preparation Effects reduced knapweed cover over time. knapweed has been successful sup- Of the three initial site preparation Indiangrass, in particular, achieved pressed, however, utilization of meth- treatments tested, clopyralid had the uniform cover regardless of knapweed ods such as burning during varying most positive effect on the develop- control treatments, demonstrating its intervals and seasons can counteract ment of the native plant community. establishment and persistence even decreases in native diversity caused Clopyralid increased big bluestem within knapweed-dominated com- by competition from native grasses (Table 4) and non-native grass cover munities. The increasing negative (Howe 1994). (Figure 1), thereby helping to prevent correlation between total grass cover Although species that are sensitive knapweed resurgence. Use of broadleaf and knapweed is consistent with grass- to the allelopathic effects of knapweed herbicide to control non-native forbs induced suppression of knapweed can persist in knapweed-infested areas often results in increases in non-native (Lindquist et al. 1996, MacDonald (Perry et al. 2005), very little research grass cover (Sheley et al. 2004, Ortega et al. 2003). At the same time, a nega- has been published detailing which and Pearson 2011, Endress et al. 2012, tive correlation between non-native native forbs are capable of establish- Skurski et al. 2013). While we were grasses and native graminoids and ing in the presence of knapweed. We initially concerned that the persistence increasing native graminoid cover observed native forb establishment in of clopyralid in the soils would reduce (Figure 1) illustrate competition that all treatments, including those that forb establishment (DiTomaso 2000, may lead towards a transition from retained high knapweed cover (Table Enloe et al. 2005), we now believe the non-native grass-dominated to native 2). In addition, over 80% of the forbs longterm trajectory of this community graminoid-dominated communities. studied had established within three will trend towards a diverse blend of Similar results have been found by years of seeding (Table 2). In par- warm-season grasses and native forbs, Foster et al. (2007), in which sowing of ticular, butterfly milkweed, lanceleaf as opposed to the grass-dominated native and naturalized prairie species tickseed, wild bergamot, spotted bee- community we had originally pre- decreased non-native grass, including balm, and blackeyed Susan exhibited dicted. Clopyralid is particularly effec- the most common non-native grass relatively high cover, with lanceleaf tive against the families Fabaceae and species found during our study, Ken- tickseed having similar cover on all Asteraceae (Enloe et al. 2005), which tucky bluegrass. Endress et al. (2012) treatments indicating establishment includes knapweed, and 13 of the 18 found that while seeding native grasses success even in knapweed-dominated forb species seeded (Table 2). Of the into an invasive forb-dominated com- communities (Table 4). Several of species we seeded, only blackeyed munity lowered non-native grass cover these species share similar characteris- Susan exhibited reduced establish- within six years, cover of the domi- tics with knapweed, which may ensure ment on clopyralid treatments (Table nant invasive forb was unaffected. In greater competition with knapweed 4), consistent with this known sen- contrast, the native grasses seeded in as they continue to increase in cover sitivity. The relatively minor impact our study have been shown to reduce (Pokorny et al. 2005). Such was the of clopyralid on native forbs that we knapweed dominance to 2.1% of case with common yarrow (Achillea observed may have been related to total biomass or less through time millefolium), which shares similar the sand to loamy sand soil of our (MacDonald et al. 2007). phenology and rooting morphology study site (MacDonald et al. 2013), While native grass dominance is with knapweed and is more able to as clopyralid is lost rapidly from sandy likely to assist in knapweed suppres- resist knapweed invasion (Maron soils by leaching (Dow AgroSciences sion (MacDonald et al. 2003, 2007, and Marler 2007). Within our study, 2010, 2011). Baer et al. 2004, McCain et al. 2010), butterfly milkweed, wild bergamot, A single application of clopyralid this is not ideal given the goal of estab- spotted beebalm, and blackeyed Susan provided knapweed control for at lishing a diverse community. Although share a similar flowering season with least four years post-treatment, even there is no evidence of native forb knapweed (Gleason and Cronquist in the absence of pulling (Figure 1). As suppression within the establishment 1991), and all have proven to be suc- knapweed cover has been found to be stage of our study, it may be some cessful at establishing in the presence inversely related to diversity (Kedzie- time before we are able to determine of knapweed. Seeded native forbs still Webb et al. 2001), we anticipated

September 2014 ECOLOGICAL RESTORATION 32:3 • 289 greater diversity in treatments that (McCain et al. 2010). Yet, the ease forbs, similar to results found by Bosy had reduced knapweed cover. Yet, with which native grasses and forbs and Reader (1995). we believe that the non-native spe- established following such minimal Pulling increased the total cover cies presence within the community site preparation indicates that seed of native forbs and several individual remains too high for diversity indices limitations may be preventing natural species, including butterfly milkweed, to indicate either the longterm tra- recovery of some degraded sites (Foster spotted beebalm, and little bluestem jectory or the current condition of et al. 2007), and shows promise for the (Table 4), consistent with the trend the restoration. Despite the effective development of communities with this towards a higher FQI on the pulled knapweed control, clopyralid resulted treatment. As reported by MacDon- treatment (Table 3). We attribute the in communities with lower diversity ald et al. (2013), the single mowing higher establishment of native forbs on during 2012. The higher diversity had few effects on knapweed densities pulled plots to reduced competition within mowing and glyphosate treat- on mowed-only plots, with a total with knapweed, since pulling has been ments coincides with lower C and knapweed density of 251 ± 47 m-2 shown to substantially reduce knap- higher knapweed cover in the absence (mean ± SE) in 2010, and remaining weed density and biomass (MacDon- of pulling, and higher non-native forb at a comparable level in 2011 (218 ± ald et al. 2013). Knapweed, which can cover (Figure 1). 38 m-2). These values resemble total have detrimental impacts on native In contrast to the effectiveness of knapweed densities in untreated areas forb establishment and persistence clopyralid, in absence of pulling the of the study site measured in 1999 (Lesica and Sheley 1996, Maron and glyphosate-only treatment allowed (239 ± 16 m-2). In addition, mature Marler 2008), was highly dominant for rapid knapweed resurgence from knapweed densities measured on the prior to the initiation of our study. the seedbank (Figure 1). Glyphosate mowed-only plots in 2009 were 45.6 ± However, while we saw increases in in combination with seeding native 4.7 m-2. In comparison, mature knap- the establishment of native forbs and grasses may provide limited short- weed densities measured in untreated one native grass when knapweed was term success in terms of grass estab- areas in the vicinity of the study plots manually removed, we also saw estab- lishment and knapweed control. Pre- in summer, 2013, averaged 46.3 ± lishment and persistence of native vious studies have shown that in as 7.7 m-2 and comprised 82.3 ± 3.1% species even in treatments with high little as three years knapweed density (mean ± SE) of the total biomass knapweed cover. This indicates that may be greater than pre-herbicide (N.W. MacDonald, unpub. data). the allelopathic effects of knapweed treatment, ultimately resulting in low These comparisons demonstrate that (Thorpe et al. 2009) had little impact longterm grass establishment (Sheley mowed-only plots contained similar on native species establishment and et al. 2001). Glyphosate, in absence knapweed populations to untreated persistence on our study site. of pulling, also resulted in lower areas at the initiation of the study, It is possible that rather than elimi- grassy fuel, leaving greater unburned and that adult knapweed densities in nation of the non-native species, dis- areas within the plots (L.M. Martin, untreated areas did not spontaneously turbance caused by pulling encour- personal observation). Still, big blue- decline during the study period. aged seedling establishment; however, stem, pinnate prairie coneflower, and Skurski et al. (2013) found that a blackeyed Susan demonstrated higher Pulling Effects single manual removal of knapweed cover within the glyphosate treat- Pulling provided both effective knap- and replicated soil disturbance exhib- ment (Table 4), indicating a positive weed control (MacDonald et al. 2013) ited no difference in variables affected, change in the development of this and favored native grass and forb estab- with the exception of knapweed cover. community. However, it remains too lishment, in addition to encouraging This provides evidence that it was the early to know if the seeded native the development of grassy fuels that removal of knapweed, rather than the species will gain dominance within will facilitate future burns. Greatly disturbance, that facilitated native this developing community due to reduced knapweed cover was main- forb establishment within our study. the persistence of non-native species, tained throughout the study, resulting especially knapweed. in non-native grass-dominated com- Burning Effects After a single mowing, we saw no munities (Figure 1). In turn, high We believe that due to the extended major longterm impacts on the com- non-native grass cover helps prevent drought period experienced during munity trajectory, as was expected. knapweed resurgence (Lindquist et al. June and July 2012, the effects of Mowing allowed for comparable levels 1996) until the native grasses become our burn on the native community of seeded species cover as both herbi- dominant. Additionally, the decreases may be delayed. Differences between cide treatments, with the exception of in non-native forb cover associated burned and unburned sand prairies lower big bluestem cover (Table 4), with increases in non-native grasses, are less notable during drought years which should be temporary due to indicate that these grasses may be (Dhillion and Anderson 1994), and the dominant nature of this species competitively excluding non-native by reducing soil moisture (Anderson

290 • September 2014 ECOLOGICAL RESTORATION 32:3 1965), our burn may have exacer- been shown to assist in the establish- knapweed-infested site we studied bated the effects of low soil moisture ment of warm-season grasses in cool- as certain species established with- on productivity (Abrams et al. 1986, season grass dominated communities out intensive treatment, including Briggs and Knapp 1995, Bowles and (Doll et al. 2011), which would be big bluestem, blackeyed Susan, but- Jones 2013). In addition, burns con- beneficial in our pulling and clopyralid terfly milkweed, Indiangrass, lance- ducted during the early spring result treatments that are non-native grass leaf tickseed, little bluestem, spotted in lower soil moisture than mid- or dominated (Figure 1). We believe that beebalm, and wild bergamot. While late-Spring burns (Anderson 1965). future burns performed during this native species cover may be initially We believe that reduced soil moisture long-term study will result in greater low, increased native dominance may have accentuated lower spotted knapweed control and increased native will facilitate future management to beebalm cover on the burning treat- species establishment. gradually suppress knapweed. ments (Table 4), which contributed to • Although labor intensive, pulling of the lower C (Table 3). There also was Conclusions knapweed, in concert with seeding little change from 2011 to 2012 in native species, was an effective treat- spotted beebalm cover on unburned Our results show that the method used ment for reducing knapweed cover treatments (Table 4), indicating that for knapweed control played a large and increasing native grass and forb unlike many other seeded native spe- part in determining the development establishment. cies that increased in cover, spotted of a restored plant community. Hand • A single application of clopy- beebalm may be more susceptible to pulling of knapweed assisted in native ralid provided long-lasting con- drought stress. Other studies have plant community establishment. Both trol of knapweed and had less than found that burning encourages germi- clopyralid application and pulling expected impact on seeded species nation and flower stalk production in encouraged the accumulation of grassy establishment on this sandy site. native species (Kucera and Ehrenreich fuel loads, which will facilitate future • A single treatment with glypho- 1962, Old 1969, Maret and Wilson burns that may help to further con- sate resulted in rapid resurgence of 2005), increases warm-season grass trol knapweed, suppress other non- knapweed from the seedbank and dominance (MacDonald et al. 2007), native species, and encourage estab- increases in other non-native forbs. and that in combination with seed- lishment and dominance by native This approach would require inten- ing of native species, fire can promote species. However, the labor required sive follow-up control measures native species richness while decreas- for pulling may limit this treatment to prevent continued knapweed ing non-native richness (Suding and to small knapweed infestations, areas dominance. Gross 2006). pre-treated with a broadleaf-specific • Pulling of knapweed or a single While we had anticipated that burn- herbicide such as clopyralid, or areas application of clopyralid resulted in ing would reduce knapweed cover, where herbicide use would damage a communities dominated by non- none of the plots reached an aver- sensitive remnant native community. native grasses, which may prevent age fire temperature in excess of the Our use of a more diverse seed mix knapweed resurgence until seeded 200 °C that has been shown to reduce allowed for a greater number of poten- native grasses and forbs mature. knapweed germination rates in the tially competitive species to establish, • To be effective, burning needs to be laboratory (Abella and MacDonald which may further prevent knapweed carefully timed to optimize knap- 2000). Temperatures did exceed the from returning to the site. Seeding weed control and encourage native 107 to 143 °C that has been shown to with a mix of selected native species species. In this study, a low-inten- reduce knapweed germination under takes little time to implement, and sity early spring burn had minimal field conditions (Vermeire and Rinella produces a more desirable native plant effects on either knapweed or native 2009); however, weather conditions community over time as evidenced species cover. and timing were not optimal during by the increased FQI and C achieved • On sites that are heavily infested our burn (MacDonald et al. 2013). through seeding. Through time, the with spotted knapweed, initial treat- Despite the low intensity of the initial interactive effects of site preparation ment with a broadleaf-selective her- burn, several of the treatment combi- methods, pulling, and burning may bicide like clopyralid followed by nations should prove to be beneficial become more pronounced as the annual hand pulling to control during future prescribed burns due to native plant community continues to residual spotted knapweed would be their high grass cover. The non-native develop. most effective in controlling knap- weed and favoring the establish- grasses present within our study are Implications for Practice mainly cool-season grasses that should ment of seeded native grasses and be damaged by spring burns (Abrams • Seeding of selected native grasses forbs. et al. 1986), thereby reducing their and forbs following minimal site cover. Additionally, spring burning has preparation was worthwhile on the

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