Kathryn A. Yurkonis

Aggregating Species at Seeding May Increase Initial Diversity during Grassland Reconstruction

Because the distances over which plants interact can be relatively short, the extent to which individuals interact with conspecific and heterospecific neighbors during the initial phases of grassland reconstruction may affect local species diversity and invasibility. To determine whether aggregating conspecific individuals at seeding (while controlling seed density) can be used as a technique to improve tallgrass prairie establishment, we used a greenhouse experiment with four native tallgrass prairie species (functional diversity controlled) seeded at three evenness levels into potting soil. We randomly assigned species to one (random) or a group of four (aggregated) fixed locations in an 8 × 8 grid (16 cm × 16 cm with 2 cm spacing) and subsequently seeded half of the communities with the non-native cool-season grass intermediate wheatgrass (Thinopyrum intermedium). After the equivalent of one growing season (four months), aggregated communities were more diverse and had a marginally greater proportion of legumes than random communities. Initial species pattern did not affect community invasibility, but invaded communities were less diverse and more dominated by the native cool-season grasses. Our results suggest that some tallgrass prairie species may benefit from initial conspecific aggregation and confirm that interactions that determine diversity, but not necessarily invasibility, during grassland establishment occur over short (cm-scale) distances. Aggregating seeds of conspecific species within the grassland reconstruction process may be used as a technique to improve diversity in grassland reconstruction sites and future projects need to consider whether these initial responses can be replicated and maintained within field-scale projects.

Can We Reconstruct Grasslands to Better Resist Invasion

Non-native, invasive plant species pose a challenge for land-management practitioners because of their potentially adverse effects on restoration success (reviewed in D’Antonio & Meyerson 2002) and the perception that reconstructed grasslands will harbor invasive species source populations (addressed in Hirsh et al. 2013, this issue). Many studies have addressed factors that help to make some communities more resistant to invasion than others (reviewed in Hector et al. 2001) and this special issue highlights several studies that have applied these concepts in a restoration context. However, as several authors in this issue point out, a deeper understanding on how planted community structure affects invasion is needed to improve restoration practices. The propagule pool within sites and additional propagule pressure from the surrounding matrix pose challenges for practitioners as they work to establish and maintain grasslands. Early in the reconstruction process, practitioners take steps to mitigate effects of the propagule bank accumulated from often decades of agricultural production and many techniques (such as cover crops and chemical control) are used to mitigate effects of the local propagule pool before and during establishment. Non-native, invasive species pose an additional threat to successfully established plantings as a result of secondary invasions stemming from subsequent disturbance, management, or environmental fluctuations (Alpert et al. 2000). In a recent study, over 80% of the seed bank in established reconstructions contained non-native and potentially invasive plant species (S. Rossiter and K.A. Yurkonis, unpub. data) which could establish after soil disturbance or severe drought (Yurkonis and Meiners 2006). Managing these secondary invasions is more challenging due to difficulties associated with targeting a specific species in an established community and may require site re-seeding efforts. While successful techniques exist to manage initial and subsequent populations of invasive plant species, resistance may be best maximized by investing in seed mixes and seeding regimes tailored to the mechanisms that contribute to grassland invasion resistance. This special issue outlines several approaches designed to maximize desired species establishment and minimize undesired species in newly developed grasslands. These approaches mainly center around manipulating focal plant density and richness (DiAllesandro et al. 2013, Goldblum et al. 2013, Nemec et al. 2013, this issue). While these factors certainly affect invasion resistance, there are other ways in which invasion resistance arises and understanding these effects offers opportunities for developing new, more effective management approaches. Future experimental plantings need to further address: 1) how resident plant identity and interactions contribute to invasion resistance; 2) how sown species pattern affects invasion resistance; and 3) whether soil biota can be manipulated to improve invasion resistance.

Effects of the Epichloë fungal endophyte symbiosis with Schedonorus pratensis on host grass invasiveness.

Initial studies of grass–endophyte mutualisms using Schedonorus arundinaceus cultivar Kentucky-31 infected with the vertically transmitted endophyte Epichloë coenophiala found strong, positive endophyte effects on host-grass invasion success. However, more recent work using different cultivars of S. arundinaceus has cast doubt on the ubiquity of this effect, at least as it pertains to S. arundinaceus–E. coenophiala. We investigated the generality of previous work on vertically transmitted Epichloë-associated grass invasiveness by studying a pair of very closely related species: S. pratensis and E. uncinata. Seven cultivars of S. pratensis and two cultivars of S. arundinaceus that were developed with high- or low-endophyte infection rate were broadcast seeded into 2 × 2-m plots in a tilled, old-field grassland community in a completely randomized block design. Schedonorus abundance, endophyte infection rate, and co-occurring vegetation were sampled 3, 4, 5, and 6 years after establishment, and the aboveground invertebrate community was sampled in S. pratensis plots 3 and 4 years after establishment. Endophyte infection did not enable the host grass to achieve high abundance in the plant community. Contrary to expectations, high-endophyte S. pratensis increased plant richness relative to low-endophyte cultivars. However, as expected, high-endophyte S. pratensis marginally decreased invertebrate taxon richness. Endophyte effects on vegetation and invertebrate community composition were inconsistent among cultivars and were weaker than temporal effects. The effect of the grass–Epichloë symbiosis on diversity is not generalizable, but rather specific to species, cultivar, infection, and potentially site. Examining grass–endophyte systems using multiple cultivars and species replicated among sites will be important to determine the range of conditions in which endophyte associations benefit host grass performance and have subsequent effects on co-occurring biotic communities.

Across species-pool aggregation alters grassland productivity and diversity

Abstract Plant performance is determined by the balance of intra‐ and interspecific neighbors within an individuals zone of influence. If individuals interact over smaller scales than the scales at which communities are measured, then altering neighborhood interactions may fundamentally affect community responses. These interactions can be altered by changing the number (species richness), abundances (species evenness), and positions (species pattern) of the resident plant species, and we aimed to test whether aggregating species at planting would alter effects of species richness and evenness on biomass production at a common scale of observation in grasslands. We varied plant species richness (2, 4, or 8 species and monocultures), evenness (0.64, 0.8, or 1.0), and pattern (planted randomly or aggregated in groups of four individuals) within 1 × 1 m plots established with transplants from a pool of 16 tallgrass prairie species and assessed plot‐scale biomass production and diversity over the first three growing seasons. As expected, more species‐rich plots produced more biomass by the end of the third growing season, an effect associated with a shift from selection to complementarity effects over time. Aggregating conspecifics at a 0.25‐m scale marginally reduced biomass production across all treatments and increased diversity in the most even plots, but did not alter biodiversity effects or richness–productivity relationships. Results support the hypothesis that fine‐scale species aggregation affects diversity by promoting species coexistence in this system. However, results indicate that inherent changes in species neighborhood relationships along grassland diversity gradients may only minimally affect community (meter) – scale responses among similarly designed biodiversity–ecosystem function studies. Given that species varied in their responses to local aggregation, it may be possible to use such species‐specific results to spatially design larger‐scale grassland communities to achieve desired diversity and productivity responses.

A Resource-Based Approach to Assessing Interseeding Success in Reconstructed Tallgrass Prairies

Interseeding is a common method used to increase species richness within established reconstructed grasslands. This process depends upon the ability of the practitioner to produce resource conditions that facilitate seedling emergence in systems where such emergence is often limited. We tested effects of a mowing disturbance on interseeding success by seeding a mix of 10 common tallgrass prairie species into 1-m2 plots within two warm-season grass dominated grasslands. We clipped the vegetation on a subset of the plots once or repeatedly and measured environmental variables including litter depth, soil surface light, soil moisture, and soil nitrate within the first growing season. While clipping consistently increased soil surface light, seeded species emergence varied in response to measured environmental resources between sites. In the lowland site, emergence over two growing seasons was primarily explained by microsite and early season light availability. In the more recently burned upland site, emergence was primarily limited by later season light conditions associated with clipping. Despite this variation, seed additions increased plot-scale species richness irrespective of clipping effects mainly as a result of high establishment of wild bergamot (Monarda fistulosa) in both sites. It appears that effects of season-long defoliation management on seedling emergence depend on microsite conditions at seeding and we conclude that soil surface and established vegetation management are necessary when interseeding to increase grassland species richness.

Restoring and managing grasslands for the future

Blakesley and Buckley combined their extensive scientific and practical experience to produce a comprehensive guide to UK grassland restoration and management as part of the Pelagic Publishing conservation handbook series. In Grassland Restoration and Management the authors thoroughly review the many challenges associated with grassland management and produce a good reference for those planning their own restoration activities. While restoration activities are often plant focused, Blakesley and Buckley encourage practitioners to take a taxonomically broad approach to restoration activities. The text begins with an extensive description of their regional flora and fauna (Chapters 1 and 2). The first chapter summarizes the types of UK grasslands and, while thorough, is less likely to be of interest to an international audience. The second chapter reviews the wildlife associated with these communities and uniquely moves beyond assessing vertebrate responses to include an extensive discussion on invertebrate and fungal responses to grassland management. While this chapter is also regionally specific, it serves as a good example for items to consider when listing restoration goals that move beyond defining target plant and vertebrate responses. The remainder of the text outlines aspects of vegetation, nutrient, and species management in impoverished and restored sites (Chapters 3–6). Chapter 3 reviews grazing, cutting, and herbicide application practices with helpful decision trees on how to select among alternative actions. This chapter is a must read for those managing grasslands elsewhere in the world and will be especially useful for those considering non-traditional grazers (e.g. horses and sheep). The chapter presents several items to consider (e.g. animal welfare clauses, defining handling areas) when developing Memoranda of Understandings around conservation grazing practices, and I look forward to using this as a resource when developing grazing agreements for our own lands. Chapter 4 specifically outlines threats and challenges associated with grassland management including considering effects of climate change and soil fertility. Chapter 5 answers these concerns by addressing management opportunities in these areas. While some of the content is repetitive between these chapters, together they provide a perspective on the actions that can be taken to mitigate challenges that extend beyond what species to select and how to seed them within a restoration. This is particularly relevant with their discussion of climate change effects and soil biota management in grasslands (Chapters 4 and 5). Practitioners are increasingly tasked with addressing climate change within management plans, but determining how to definitively address these concerns is K. Yurkonis (&) University of North Dakota Biology Department, Grand Forks, ND 58202, USA e-mail: Kathryn.Yurkonis@und.edu