), Monica l. Pokorny (Kc Harvey Environmental llc, Bozeman, Mt
Restoration Notes Restoration Notes have been a distinguishing feature of Ecological Restoration for more than 25 years. This section is geared toward introducing innovative research, tools, technologies, programs, and ideas, as well as providing short-term research results and updates on ongoing efforts. Please direct submissions and inquiries to the editorial staff (ERjournal@ aesop.rutgers.edu).
Can a Combination of Grazing, Herbicides, and Seeding Facilitate Succession in Old Fields?
Robert V. Taylor (corresponding author: The Nature Conservancy, Enterprise, OR 97828,
[email protected]), Monica L. Pokorny (KC Harvey Environmental LLC, Bozeman, MT), Jane Mangold (Montana State University, Bozeman, MT) and Nathan Rudd (Bureau of Reclamation, Boulder City, NV).
A
bandoned agricultural lands called “old fields” currently cover millions of hectares of land on nearly every continent. Studies of old fields indicate the effects of past cultivation on soils and vegetation may persist for hundreds of years (Dupouey et al. 2002, Fuhlendorf et al. 2002). Additionally, exotic species are often planted after final tillage, making it difficult for native species to recolonize. In arid shrub-steppes of the Pacific Northwest, many old fields remain dominated by exotic species decades after abandonment (Kulmatiski 2006). The Zumwalt Prairie in northeastern Oregon is one of the last large relicts of Pacific Northwest bunchgrass prairie. However, old fields comprise approximately 10% of the prairie. Zumwalt old fields are dominated by exotic perennial grasses that were bred for rapid reproduction, tolerance to high levels of livestock herbivory, and disease resistance. Zumwalt old fields are low in native plant species richness and lack biological soil crusts. Improving the ecological condition of old fields is a priority of local natural resource management entities (Wallowa Resources 2005) and The Nature Conservancy (Shephard and Taylor 2009). Augmentative restoration recognizes the positive ecological attributes intact within a plant community while seeking to restore key aspects of composition, structure, and function (Sheley et al. 2009). An augmentative approach can be used to meet specific land management goals while also improving cost effectiveness. Although Zumwalt old fields are dominated by exotic grasses, several factors favor their recolonization by native species, including their small size (10 % Canada thistle was mapped using GPS and GIS software (ESRI® Arcpad Version 7, Redlands, CA). The actionable stage when control of Canada thistle will be implemented by managers at the various locations is >10% canopy cover of thistle ( personal communication with USFWS personnel). The paired plots were analyzed with a paired T-test using a one-tailed test. A one-tailed test was used because we were only interested in testing whether the cover of Canada thistle in treated areas (spike) is lower than the control (non-spike). An arcsine square root transformation was used on the percentage data for the area covered by >10% cover of Canada thistle. An
30 25
x
Imax-N 0.2466 0.4363 1.9311 0.7170 0.1931 0.9931 1.0892 0.5721
τ 0.03 0.92 0.73 0.81 0.27 0.50 0.80 1.59
Imax-P 0.1083 0.1517 0.5538 0.3607 0.0456 0.3586 0.2979 0.1693
arcsine square root transformation is recommended to normalize proportion data ( percentage) with values 0.7 (Zar 2010). The cover of Canada thistle for the first two growing seasons after planting was significantly lower for the spike treatment compared to non-spike for the small plots at both locations (Ekre 2011: p = 0.001, t = 5.5 df = 5; Ekre 2012: p = 0.031, t = 2.37, df = 5) (CGREC 2011: p = 0.05, t = 2.0, df = 5; CGREC 2012: p = 0.03, t = 2.4, df = 5) (Figure 1). The large plots had the same trend as the small plots with significantly lower Canada thistle cover for the spike treatment compared to non-spike (2011: p = 0.014, t = 3.96, df = 3; 2012: p = 0.007, t = 4.94, df = 3)
x x
x x
15 10
0
PUE 114.99 98.14 121.61 97.03 158.57 87.56 113.30 110.46
x
20
5
NUE 63.31 39.42 38.93 44.66 46.58 41.75 49.59 36.70
y y
Ekre 2011
y
y y
y Ekre 2012
CGREC 2011 CGREC 2012
Large plot 2011
Large plot 2012
Plot locations and years Figure 1. Percent canopy coverage (± 1SD) of Canada thistle for the small plot locations at the Central Grassland Research and Extension Center (CGREC) and Ekre Grassland Preserve (Ekre) and the large plots at four different locations for the first two growing seasons after planting. Black bars represent non-spike treatments and gray bars represent spike treatments (CGREC is Central Grassland Research and Extension Center). Withinyear comparisons with different letters are significantly different (p < 0.05).
June 2013 Ecological Restoration 31:2 • 145
(Figure 1). The percent of the large scale plots covered by >10% Canada thistle was significantly lower ( p = 0.026, t = 3.11, df = 3) for the spike (5.4%, SD = 4) compared to the non-spike (32.7%, SD = 24.9) which was a six-times reduction in coverage. Here we show that the spike method used in this study is effective in reducing the cover of Canada thistle the first two years after planting. This result follows the proposed rationale that the planting of a high seed density of functionally similar forb species interferes with the establishment of Canada thistle. The most likely mechanism proposed for the reduced thistle establishment is that interspecific competition from the spiked species caused the reduction in Canada thistle. The species used in the spike had similar rooting and uptake characteristics to Canada thistle (Table 2) so there was symmetrical competition for belowground resources. Because a high density of spike seeds were used there is an increased probability that individuals would find sites conducive to fast establishment compared to the existing seed bank of Canada thistle. This fast establishment then allows for asymmetrical competition, an unequal division of resources between individuals and species, to occur (Freckleton and Watkinson 2001). Both forms of competition along with the higher number of spike species establishing due to high seed density would then produce a competitive environment that restricts the establishment of Canada thistle. This study only examined the first two growing seasons after planting. Most restorations require several more years of growth before the planted species express themselves and the plant composition becomes more stable and is less prone to large changes. However, here we show that by spiking a typical seed mix, the objective of developing a diverse native plant community can occur at the same time while also reducing Canada thistle establishment. The current need by managers to avoid control actions and the reduced value of restored grasslands from Canada thistle establishment prompted us to report the results from the first two years rather than wait several years for the outcomes of the eventual restored plant community. Managers would be justified in using the spike method from just the two years’ worth of results based on the strength of the effect size from both the precisely controlled small plot experiments and the large plots which represent effectiveness in a real world situation even though there is
uncertainty in what will be the eventual restored plant community. We anticipate that the native forbs used as spike species will eventually be reduced in their dominance in the following years of the restoration due to pathogens and predators along with normal successional forces resulting in a diverse native plant community. These experiments will continue to be monitored to determine the effects that spike species have on: 1) the establishment of other native species; 2) whether spike species either dominate or have reduced cover over time; and 3) whether the cover of Canada thistle changes. As the study continues, a cost comparison will be done between the costs of the spiked seed mix and the costs of reducing Canada thistle with herbicides. References Biondini, M. 2007. Plant diversity, production, stability, and susceptibility to invasion in restored Northern Tallgrass Prairies (United States). Restoration Ecology 15: 77–87. Freckleton, R.P. and A.R. Watkinson. 2001. Asymmetric competition between plant species. Functional Ecology 15: 615–623. Funk, J.L., E.E. Cleland, K.N. Suding and E.S. Zavaleta. 2008. Restoration through reassembly: Plant traits and invasion resistance. Trends in Ecology & Evolution 23: 695–703. Hodgson, J.M. 1968. The nature, ecology, and control of Canada thistle. Technical Bulletin of the United States Department of Agriculture, No. 1386. Washington, DC: United States Department of Agriculture. Lym, R.G. and C.A. Duncan. 2005. Canada thistle (Cirsium arvense L. Scop.). Pages 69–83 in C.L. Duncan and J.K. Clark (eds), Invasive Plants of Range and Wildlands and Their Environmental, Economic, and Societal Impacts. Lawrence, KS: Weed Science Society of America. McCain, K.N., S.G. Baer, J.M. Blair and G.W.T. Wilson. 2010. Dominant grasses suppress local diversity in restored tallgrass prairie. Restoration Ecology 18: 40–49. Natural Resources Conservation Service (NRCS). 2013. The PLANTS Database. U.S. Department of Agriculture, National Plant Data Team. plants.usda.gov Rowe, H.I. 2010. Tricks of the trade: Techniques and opinions from 38 experts in tallgrass prairie restoration. Restoration Ecology 18: 253–262. Zar, J.H. 2010. Biostatistical Analysis, 5th Ed. Upper Saddle River, NJ: Pearson Prentice-Hall.
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