Invasion during Extreme Weather: Success and Failure in a Temperate Perennial Grassland

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1 University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln West Central Research and Extension Center, North Platte Agricultural Research Division of IANR 216 Invasion during Extreme Weather: Success and Failure in a Temperate Perennial Grassland James C. Han University of Nebraska-Lincoln, chengchouhan@huskers.unl.edu Stephen L. Young Cornell University, sly27@cornell.edu Follow this and additional works at: Part of the Agriculture Commons, Ecology and Evolutionary Biology Commons, and the Plant Sciences Commons Han, James C. and Young, Stephen L., Invasion during Extreme Weather: Success and Failure in a Temperate Perennial Grassland (216). West Central Research and Extension Center, North Platte. Paper This Article is brought to you for free and open access by the Agricultural Research Division of IANR at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in West Central Research and Extension Center, North Platte by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.

2 Invasion during Extreme Weather Success and Failure in a Temperate Perennial Grassland James c. Han and Stephen 1. Young ABSTRACT-Invasive and native plant species compete for resources in similar pools, with disturbances often favoring the invader. Yet, increased climate variability may be shifting the competitive edge back toward the natives. We conducted field studies in perennial grasslands to determine the effects of clipping and drought on resource availability (light and moisture) and subsequent establishment of Carduus nutans. We measured light penetration and soil moisture content in C. nutans monoculture, clipped and non clipped grassland with C. nutans, and bare ground control plots. We also tracked phenology of the invader and grasses. Our studies revealed that light was a limiting resource in normal precipitation years; removing biomass (e.g., clipped grassland plots) allowed C. nutans to successfully establish, while not removing biomass (e.g., nonclipped grassland plots) resulted in premature death. Similarly, soil moisture was a limiting resource when light was abundant; a lack of precipitation in the second year reduced grass growth, which opened the canopy and allowed adequate light for C. nutans seedlings that also died prematurely under extremely low soil moisture levels. We found that C. nutans was unable to compensate for the low light and soil moisture in offsetting, yet consecutive seasons and failed to establish in a nonclipped grassland. The emergence of C. nutans in a temperate perennial grassland is not a sure sign of success. Ifleft undisturbed, C. nutans seedlings may eventually die without having a significant impact on grasses. Key Words: Carduus nutans, climate change, clipping, drought tolerance, extreme weather events, fitness, grazing, invasion resistance, musk thistle, plant plasticity, resource competition I ntrod uction Invasive plant species in grasslands of temperate regions have modified biotic communities and altered natural cycles with increasing frequency (Charles and Dukes 27). In order to prevent negative impacts from invasive plant species, the focus of many restoration efforts has been on the creation of diverse grassland communities that provide a barrier against invasion (Berlinger and Knapp 1991; Bottoms and Whitson 1998). This approach provides a good base for understanding competition for resources by native and invasive plant species, including those in temperate regions (Pokorny et al. 25). Access to available resources is important for invasive plant species (Thomas et al. 22; Maron and Marler 27). Moreover, spatiotemporal resource acquisition by native and invasive plant species is considered to be a key factor in invasion success (Zavaleta and Hulvey 27). Manuscript received for review, ; accepted for publication, 3/ Great Plains Research 26 (Fall 216): Copyright 216 by the Center for Great Plains Studies, University of Nebraska-Lincoln Invasive plant establishment is often due to niches in plant communities that are created by variations in phenologies and traits (Godoy and Levine 214; MacDougall et al. 29). Wolkovich and Cleland (21) argue that many invasive plants adapt quickly to changes in the environment through altered phenology (Le., plasticity), thus making them better competitors for limited resources in niches (Hooper and Dukes 21, Fargione and Tilman 25). Over time, the change in phenology could be considered a fitness advantage that allows for invasive plants to become established and eventually dominate resident plant species (MacDougall et al. 29; Chesson 2). In grasslands, a well-established perennial grass community can preempt belowground space by extending roots (Blank and Morgan 212) and depleting resources to the detriment of the invader (Milbau et al. 25). However, disturbance can reduce resistance by a perennial grassland community as openings in the canopy create niches that allow invasive plant species to establish (Feldman et al. 1968). Overgrazing is a disturbance that can lead to invasive plants establishing 93

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