Celebrating and conserving the ecological richness of California's grasslands
Grasslands Research Highlights 

Grasslands are important subjects of ecological research and experimentation, and are studied from a wide variety of perspectives (e.g., native and invasive species; soils; management using fire, grazing, mowing, and herbicide application; ecological restoration). CNGA will regularly browse peer-reviewed books and scientific journal articles to provide highlights of recent grasslands research. Studies are organized by year of publication, and sorted within years by author's first name.

2020 Publications

Newbold, T., Oppenheimer, P., Etard, A. et al. Tropical and Mediterranean biodiversity is disproportionately sensitive to land-use and climate changeNat Ecol Evol (2020). https://doi.org/10.1038/s41559-020-01303-0


Global biodiversity is undergoing rapid declines, driven in large part by changes to land use and climate. Global models help us to understand the consequences of environmental changes for biodiversity, but tend to neglect important geographical variation in the sensitivity of biodiversity to these changes. Here we test whether biodiversity responses to climate change and land-use change differ among biomes (geographical units that have marked differences in environment and species composition). We find the strongest negative responses to both pressures in tropical biomes and in the Mediterranean. A further analysis points towards similar underlying drivers for the sensitivity to each pressure: we find both greater reductions in species richness in the types of land use most disturbed by humans and more negative predicted responses to climate change in areas of lower climatic seasonality, and in areas where a greater proportion of species are near their upper temperature limit. Within the land most modified by humans, reductions in biodiversity were particularly large in regions where humans have come to dominate the land more recently. Our results will help to improve predictions of how biodiversity is likely to change with ongoing climatic and land-use changes, pointing toward particularly large declines in the tropics where much future agricultural expansion is expected to occur. This finding could help to inform the development of the post-2020 biodiversity framework, by highlighting the under-studied regions where biodiversity losses are likely to be greatest.:

Science Daily Summary Article: Mediterranean and tropical biodiversity most vulnerable to human pressures. Date: September 14, 2020

Stuble KL, Young TP. Priority Treatment Leaves Grassland Restoration Vulnerable to Invasion. Diversity. 2020; 12(2):71. Full Text


Priority effects can be used to promote target species during restoration. Early planting can provide an advantage over later-arriving species, increasing abundance of these early-arrivers in restored communities. However, we have limited knowledge of the indirect impacts of priority effects in restoration. In particular, we do not understand how priority effects impact non-target species. Of particular conservation concern is how these priority effects influence establishment by non-native species. We use a field-based mesocosm experiment to explore the impacts of priority effects on both target and non-target species in California grasslands. Specifically, we seeded native grasses and forbs, manipulating order of arrival by planting them at the same time, planting forbs one year before grasses, planting grasses one year before forbs, or planting each functional group alone. While our study plots were tilled and weeded for the first year, the regional species pool was heavily invaded. We found that, while early-arrival of native grasses did not promote establishment of non-native species, giving priority to native forbs ultimately left our restoration mesocosms vulnerable to invasion by non-native species. This suggests that, in some cases, establishment of non-native species may be an unintended consequence of using priority treatments as a restoration tool

Groves, A.M., Bauer, J.T. & Brudvig, L.A. Lasting signature of planting year weather on restored grasslandsSci Rep 10, 5953 (2020). Open Access. Published: 06 April 2020.  https://doi.org/10.1038/s41598-020-62123-7. PDF


Ecological restoration — the rebuilding of damaged or destroyed ecosystems — is a critical component of conservation efforts, but is hindered by inconsistent, unpredictable outcomes. We investigated a source of this variation that is anecdotally suggested by practitioners, but for which empirical evidence is rare: the weather conditions during the first growing season after planting. The idea of whether natural communities face long-term consequences from conditions even many years in the past, called historical contingency, is a debated idea in ecological research. Using a large dataset (83 sites) across a wide geographic distribution (three states), we find evidence that precipitation and temperatures in the planting year (2–19 years before present) affected the relative dominance of the sown (native target species) and non-sown (mostly non-native) species. We find strong support for lasting planting year weather effects in restored tallgrass prairies, thereby supporting the historically contingent model of community assembly in a real-world setting.

Science Daily Article April 6, 2020

Buzhdygan, O.Y., Meyer, S.T., Weisser, W.W. et al. Biodiversity increases multitrophic energy use efficiency, flow and storage in grasslands. Nat Ecol Evol 4, 393–405 (2020). https://doi.org/10.1038/s41559-020-1123-8


The continuing loss of global biodiversity has raised questions about the risk that species extinctions pose for the functioning of natural ecosystems and the services that they provide for human wellbeing. There is consensus that, on single trophic levels, biodiversity sustains functions; however, to understand the full range of biodiversity effects, a holistic and multitrophic perspective is needed. Here, we apply methods from ecosystem ecology that quantify the structure and dynamics of the trophic network using ecosystem energetics to data from a large grassland biodiversity experiment. We show that higher plant diversity leads to more energy stored, greater energy flow and higher community-energy-use efficiency across the entire trophic network. These effects of biodiversity on energy dynamics were not restricted to only plants but were also expressed by other trophic groups and, to a similar degree, in aboveground and belowground parts of the ecosystem, even though plants are by far the dominating group in the system. The positive effects of biodiversity on one trophic level were not counteracted by the negative effects on adjacent levels. Trophic levels jointly increased the performance of the community, indicating ecosystem-wide multitrophic complementarity, which is potentially an important prerequisite for the provisioning of ecosystem services.

This research is from the Jena Experiment, a long-term grassland experiment in Germany looking at biodiveristy-ecosystem functioning. 

Would you like the significance in plain words? Read the Science Daily summary of this article

Cristian Román-Palacios, John J. Wiens. 2020. Recent responses to climate change reveal the drivers of species extinction and survival. Proceedings of the National Academy of Sciences Feb 2020, 117 (8) 4211-4217; DOI: 10.1073/pnas.1913007117


Climate change may be a major threat to biodiversity in the next 100 years. Although there has been important work on mechanisms of decline in some species, it generally remains unclear which changes in climate actually cause extinctions, and how many species will likely be lost. Here, we identify the specific changes in climate that are associated with the widespread local extinctions that have already occurred. We then use this information to predict the extent of future biodiversity loss and to identify which processes may forestall extinction. We used data from surveys of 538 plant and animal species over time, 44% of which have already had local extinctions at one or more sites. We found that locations with local extinctions had larger and faster changes in hottest yearly temperatures than those without. Surprisingly, sites with local extinctions had significantly smaller changes in mean annual temperatures, despite the widespread use of mean annual temperatures as proxies for overall climate change. Based on their past rates of dispersal, we estimate that 57–70% of these 538 species will not disperse quickly enough to avoid extinction. However, we show that niche shifts appear to be far more important for avoiding extinction than dispersal, although most studies focus only on dispersal. Specifically, considering both dispersal and niche shifts, we project that only 16–30% of these 538 species may go extinct by 2070. Overall, our results help identify the specific climatic changes that cause extinction and the processes that may help species to survive.

Science Daily Summary: University of Arizona. "One-third of plant and animal species could be gone in 50 years." ScienceDaily. ScienceDaily, 12 February 2020. <www.sciencedaily.com/releases/2020/02/200212150146.htm>.

Stuart Wagenius, Jared Beck, and Gretel Kiefer. 2020. Fire synchronizes flowering and boosts reproduction in a widespread but declining prairie species. PNAS. January 27, 2020. From the Echinacea Project.

Science Daily Interview with Author 


We address a critical conservation concern: the loss of native plant species in fire-dependent ecosystems. Reduced fire frequency in ecosystems such as the North American prairie contributes to local extinctions. The leading hypothesis is that woody and large herbaceous species outcompete other species in the absence of fire. However, alternative mechanisms have not been investigated. In our 21-y study of a model prairie plant, Echinacea angustifolia, we demonstrate that fires synchronize reproduction, leading to increased mating opportunities and improved reproduction. Fire synchronizes flowering both among and within years, nearly doubling seed production. These findings demonstrate a potentially widespread mechanism by which fire can enhance plant reproduction, promote population growth, and maintain plant diversity in fire-dependent ecosystems worldwide.

Bucharova, A., F Krahulec. 2020. “Native seed addition as an effective tool for post-invasion restoration.” Basic and Applied Ecology 43 (March 2020): 34-41.



Invasive plant species reduce biodiversity, alter ecosystem processes, and cause economic losses. Control of invasive plants is therefore highly desired by land managers and policy makers. However, invasive plant control strategies frequently fail, partly because management often concentrates only on the eradication of invasive plants and not on revegetation with native species that use the available resources and prevent reinvasion. In this study, we focused on the intracontinental invader Rumex alpinus L., which was introduced by humans from the Alps to the lower mountains of Central Europe, where it has spread to semi-natural meadows, suppresses local biodiversity, and reduces the quality of hay used as cattle fodder. The species can be effectively removed using herbicide, but this leaves behind a persistent seed bank. Without further treatment, the invader rapidly regenerates and reinvades the area. We supplemented the herbicide treatment by adding the seeds of native grasses. Addition of native-seed effectively suppressed the regeneration of the invader from the seed bank, reduced its biomass, and consequently, prevented massive reinvasion. While the invader removal was successful, the restored community remained species-poor because the dense sward of native grasses blocked the regeneration of native forbs from the seed bank. Nevertheless, the addition of native seed proved to be an effective tool in preventing reinvasion after the eradication of the invasive plant.

Zirbel, C. R., and Brudvig, L. A.. 2020. "Trait–environment interactions affect plant establishment success during restoration." Ecology 101(3):e02971. 10.1002/ecy.2971

Abstract [Full text is available for this article]

Establishment and persistence are central to community assembly and are determined by how traits interact with the environment to determine performance (trait–environment interactions). Community assembly studies have rarely considered such trait–environment interactions, however, which can lead to incorrect inferences about how traits affect assembly. We evaluated how functional traits, environmental conditions, and trait–environment interactions structure plant establishment, as a measure of performance. Within 12 prairie restorations created by sowing 70 species, we quantified environmental conditions and counted individuals of each seeded species to quantify firstyear establishment. Three trait–environment interactions structured establishment. Leaf nitrogen interacted with herbivore pressure, as low leaf nitrogen species established relatively better under higher herbivory than species with high leaf nitrogen. Soil moisture interacted with root mass fraction (RMF), with lowRMF species establishing better with low soil moisture and higherRMF species better on wetter soils. Specific leaf area (SLA) interacted with light availability, as lowSLA species established better under high light conditions and highSLA species under low light conditions. Our work illustrates how community assembly can be better described by trait–environment interactions than correlating traits or environment with performance. This knowledge can assist species selection to maximize restoration success.

2019 Publications

Beaury, E.M., Finn, J.T., Corbin, J.D., Barr, V. and Bradley, B.A. (2019), Biotic resistance to invasion is ubiquitous across ecosystems of the United States.Ecol Lett. doi:10.1111/ele.13446



The biotic resistance hypothesis predicts that diverse native communities are more resistant to invasion. However, past studies vary in their support for this hypothesis due to an apparent contradiction between experimental studies, which support biotic resistance, and observational studies, which find that native and non‐native species richness are positively related at broad scales (small‐scale studies are more variable). Here, we present a novel analysis of the biotic resistance hypothesis using 24 456 observations of plant richness spanning four community types and seven ecoregions of the United States. Non‐native plant occurrence was negatively related to native plant richness across all community types and ecoregions, although the strength of biotic resistance varied across different ecological, anthropogenic and climatic contexts. Our results strongly support the biotic resistance hypothesis, thus reconciling differences between experimental and observational studies and providing evidence for the shared benefits between invasive species management and native biodiversity conservation.

Kimberly J. Komatsu et al. 2019. Global change effects on plant communities are magnified by time and the number of global change factors imposed. PNAS. DOI: 10.1073/pnas.1819027116. Science Daily News Article 

Luong JC, Turner PL, Phillipson CN, Seltmann KC. 2019. Local grassland restoration affects insect communities. Ecological Entomology. https://doi.org/10.1111/een.12721

Abstract. 1. It is hypothesised that ecological restoration in grasslands can induce an

alternative stable state shift in vegetation. The change in vegetation influences insect

community assemblages and allows for greater functional redundancy in pollination and

refuge for native insect species.

2. Insect community assemblages at eight coastal California grassland sites were

evaluated. Half of these sites had undergone restoration through active revegetation

of native grassland flora and half were non-restored. Insects were collected from

Lupinus bicolor (Fabaceae) within 2 × 2-m2 plots in spring 2017. Lupinus bicolor is

a common native species that is used in California restoration projects, and home and

state landscaping projects.

3. Ordination demonstrated that insect community assemblages were different between

restored and non-restored sites. These differences were seen in insect functional groups

as well as taxa-specific differences and were found to be driven by environmental

characteristics such as non-native forb cover.

4. Functional redundancy of herbivores decreased at restored sites, while pollinators

became more redundant compared with non-restored sites. The assemblages of the

common species found at restoration sites contained more native insects than those found

at non-restored sites, including species such as Bombus vosnesenskii.

5. Local grassland restoration has the potential to induce an alternative stable state

change and affect insect community assemblages. Additionally, it was found that grassland

restoration can be a potential conservation tool to provide refugia for bumblebees

(Bombus), but additional studies are required to fully understand its broader applicability.

Uricchio, Lawrence H.  S. Caroline Daws, Erin R. Spear, and Erin A. Mordecai. 2019. Priority effects of nonhierarchical competition shape species composition in a complex grassland community. The American Naturalist 193 (2). 

Abstract. Niche and fitness differences control the outcome of competition, but determining their relative importance in invaded communities—which may be far from equilibrium—remains a pressing concern. Moreover, it is unclear whether classic approaches for studying competition, which were developed predominantly for pairs of interacting species, will fully capture dynamics in complex species assemblages. We parameterized a population-dynamic model using competition experiments of two native and three exotic species from a grassland community. We found evidence for minimal fitness differences or niche differences between the native species, leading to slow replacement dynamics and priority effects, but large fitness advantages allowed exotics to unconditionally invade natives. Priority effects driven by strong interspecific competition between exotic species drove single-species dominance by one of two exotic species in 80% of model outcomes, while a complex mixture of nonhierarchical competition and coexistence between native and exotic species occurred in the remaining 20%. Fungal infection, a commonly hypothesized coexistence mechanism, had weak fitness effects and is unlikely to substantially affect coexistence. In contrast to previous work on pairwise outcomes in largely native-dominated communities, our work supports a role for nearly neutral dynamics and priority effects as drivers of species composition in invaded communities.

More about this research: Knowing how invasive grasses compete could help preserve native grasslands, according to Stanford researchers. Stanford News, January 15, 2019, by Sophie Bates 

2018 Publications

Dass, Pawlok, Benjanim Z Houlton, Yingping Want and David Warlind. 2018. Grasslands more reliable carbon sink than trees. Environmental Research Letters, Volume 13, Number 7. PDF

LaForgia, Marina L.,  Marko J. Spasojevic,  Erica J. Case,  Andrew M. Latimer,  Susan P. Harrison. Seed banks of native forbs, but not exotic grasses, increase during extreme drought. (2018). Ecology 99 (4):896-903. 

Abstract: Extreme droughts such as the one that affected California in 2012–2015 have been linked to severe ecological consequences in perennial‐dominated communities such as forests. In annual communities, drought impacts are difficult to assess because many species persist through facultative multiyear seed dormancy, which leads to the development of seed banks. Impacts of extreme drought on the abundance and composition of the seed banks of whole communities are little known. In 80 heterogeneous grassland plots where cover is dominated by ~15 species of exotic annual grasses and diversity is dominated by ~70 species of native annual forbs, we grew out seeds from soil cores collected early in the California drought (2012) and later in the multiyear drought (2014), and analyzed drought‐associated changes in the seed bank. Over the course of the study we identified more than 22,000 seedlings to species. We found that seeds of exotic annual grasses declined sharply in abundance during the drought while seeds of native annual forbs increased, a pattern that resembled but was even stronger than the changes in aboveground cover of these groups. Consistent with the expectation that low specific leaf area (SLA) is an indicator of drought tolerance, we found that the community‐weighted mean SLA of annual forbs declined both in the seed bank and in the aboveground community, as low‐SLA forbs increased disproportionately. In this system, seed dormancy reinforces the indirect benefits of extreme drought to the native forb community.

Eviner, Valarie and Carolyn Malmstrom.  and Carolyn Malmstrom. 2018. California's native perennial grasses provide strong suppression of goatgrass and medusahead. Grasslands 28(1): 3-6. 

California's native grasses have the ability to suppress noxious weeds and prevent them from dominating grasslands when naturalized annual exotics, which can out-compete native grasses, are controlled. 

Maresh Nelson, S.B., Coon, J.J., Duchardt, C.J. et al. Contrasting impacts of invasive plants and human-altered landscape context on nest survival and brood parasitism of a grassland bird. Landscape Ecol 33, 1799–1813 (2018). https://doi.org/10.1007/s10980-018-0703-3


Controlling tall fescue within grasslands could benefit birds by increasing nest success.

This study found that nest survival declined with increasing tall fescue cover at nest sites for a Midwestern small grassland bird called a dickcissel. Tall fescue changes the vegetation structure making it less diverse to mat-like.

The researchers identified all the plants within a 16-foot radius of every dickcissel nest they found - all 477 of them - and the more tall fescue there was, the greater the chances of nest failure. No other plant in their surveys had significant predictive power.

Read the Eureka Alert Article Summary: Invasive forage grass leads to grassland bird decline/ October 19, 2018.

2017 Publications

Balachowski, Jennifer A. and Florence A. Volaire. 2017. Implications of plant functional traits and drought survival strategies for ecological restoration. Journal of Applied Ecology (online) DOI: 10.1111/1365-2664.12979.

The authors measured seasonal growth and foliar and root functional traits under non-limiting water conditions, followed by recovery after severe drought in four populations of Elymus glaucus.  Dehydration tolerance and summer dormancy were associated with a more conservative strategy (lower productivity, lower Specific Leaf Area and Specific Root Length), as well as earlier reproductive phenology. The authors discuss the implication that restored populations with superior drought survival may therefore be less competitive, and recommend further investigation to inform plant materials selection protocols and management practices

Gennet, Sasha, Erica Spotswood, Michele Hammond, James W. Bartolome. 2017. Livestock grazing supports native plants and songbirds in a California annual grassland. PLoS ONE 12(6) (June 14, 2017) : e0176367. https://doi.org/10.1371/journal.pone.0176367.

An 8-year study in central California finds livestock grazing can be compatible with or support grassland bird conservation. --Michele Hammond is a current serving on the CNGA Board of Directors. 

Hungate, Bruce A. , Edward B. Barbier, Amy W. Ando, Samuel P. Marks, Peter B. Reich, Natasja Van Gestel, David Tilman, Johannes M. H. Knops, David U. Hooper, Bradley J. Butterfield, Bradley J. Cardinale. 2017.  The economic value of grassland species for carbon storage. Science Advances: E1601880. 

Biodiversity confers economic value by enhancing carbon storage in grasslands, an economic argument for biodiversity conservation.

Vaughn, K.J., Biel, C., Clary, J.J. et al. 2011. California perennial grasses are physiologically distinct from both Mediterranean annual and perennial grasses.  Plant Soil (2011) 345: 37. https://doi.org/10.1007/s11104-011-0757-3

Gornish, Elise and Julea Shaw. 2017. Restoration manual for annual grassland systems in California. University of California ANR Publication 8575.  

Techniques to provide general direction to effectively improve grassland conditions in monetary and logistically feasible ways. Developed for practitioners of any experience level to inform grassland restoration, design and application. --Elise Gornish served on the CNGA Board of Directors in 2017. 

2015 Publications

Veldman, J.W., Buisson, E., Durigan, G., Fernandes, G.W., Le Stradic, S., Mahy, G., Negreiros, D., Overbeck, G.E., Veldman, R.G., Zaloumis, N.P., Putz, F.E. and Bond, W.J. (2015), Toward an old‐growth concept for grasslands, savannas, and woodlands. Frontiers in Ecology and the Environment, 13: 154-162. doi:10.1890/140270

We expand the concept of “old growth” to encompass the distinct ecologies and conservation values of the world's ancient grass‐dominated biomes. Biologically rich grasslands, savannas, and open‐canopy woodlands suffer from an image problem among scientists, policy makers, land managers, and the general public, that fosters alarming rates of ecosystem destruction and degradation. These biomes have for too long been misrepresented as the result of deforestation followed by arrested succession. We now know that grassy biomes originated millions of years ago, long before humans began deforesting. We present a consensus view from diverse geographic regions on the ecological characteristics needed to identify old‐growth grasslands and to distinguish them from recently formed anthropogenic vegetation. If widely adopted, the old‐growth grassland concept has the potential to improve scientific understanding, conservation policies, and ecosystem management.

2013 Publications

Azzari, G., M.L. Goulden, and R.B. Rusu. 2013. Rapid characterization of vegetation structure with a Microsoft Kinect sensor. Sensors 13(2): 2384–98. doi:10.3390/s130202384.

Bai, S., Q. Xu, and Y. Qin. 2013. Vibration driven vehicle inspired from grass spike. Scientific Reports 3:1851.

ABSTRACT: Searching and detecting in some harsh environments such as collapsed buildings, pipes, small cracks are crucial for human rescue and industrial detection, military surveillance etc. However, the drawbacks of traditional moving modes of current vehicles make them difficult to perform such tasks. So developing some new vehicles is urgent. Here, we report aSetaria viridis spike's interesting behavior on a vibrating track, and inspired by that phenomena we develop a concept for cargo delivery, and give a detailed discussion about its working mechanism. This vehicle can move on a wide range of smooth and rough surfaces. Moreover, its climbing capability in tilted and even vertical smooth pipe is also outstanding. These features make it suitable for search-rescue, military reconnaissance, etc. Finally, this vehicle can be reduced into micro/nano-scale, which makes it would play an important role in target-drug delivery, micro-electromechanical systems (MEMS).

Chaplin-Kramer, R., and M.R. George. 2013. Effects of climate change on range forage production in the San Francisco Bay Area. PloS One, 8(3): e57723. doi:10.1371/journal.pone.0057723

Concilio, A. L., M.E. Loik, and J. Belnap. 2013. Global change effects on Bromus tectorum L. (Poaceae) at its high-elevation range margin. Global Change biology, 19(1): 161–72. doi:10.1111/gcb.12032

Evett, R, & J.W. Bartolome. (2013). Phytolith evidence for the extent and nature of prehistoric California grasslands. The Holocene, 23(11) 1-6. doi:10.1177/0959683613499056

Californian grasslands have been radically transformed by cultivation and exotic species invasions that began with European settlement in 1769. Because native species contribute only a small percentage of total vegetation cover at most grassland sites in California today, there has been a long-standing controversy regarding the extent and composition of prehistoric grasslands. We used phytolith analysis of soil samples from 153 spatially diverse grassland sites currently cultivated or dominated by exotic annual grasses to provide the first direct evidence that, except for areas near the coast, grass was generally a minor component of the vegetation. Most of the arid, non-wetland Central Valley and surrounding foothills probably had very low grass cover. Combining our data with historical accounts of vegetation encountered by early explorers in California and relict analysis of native species in existing grassland patches, it appears that while the extent of prehistoric grassland was probably similar to the current extent of exotic annual grassland, most areas were likely dominated by a highly diverse assemblage of herbaceous species, composed largely of annual forbs adapted to exploit local environmental heterogeneity. Phytolith analysis should be routinely performed in California to guide grassland restoration efforts. The technique can also be used to reconstruct prehistoric vegetation of highly altered grassland ecosystems worldwide.

Fernandez-Going, B. M., and S. Harrison. 2013. Effects of experimental water addition depend on grassland community characteristics. Plant Ecology 214:777–786.

ABSTRACT: Plant community biomass and composition on low-productivity soils, such as serpentine, may be more resistant to climate change because they host stress-tolerant species that may respond slowly to change. These communities also host a number of endemic taxa that are of special interest because of their narrow distributions. In a 3-year study, we experimentally tested the response of serpentine and non-serpentine communities to water addition in spring. We also compared the responses of endemics and generalists to water addition, with and without biomass (competitor) removal. In the non-serpentine grassland, peak biomass was significantly greater in the water addition plots compared with control plots, but this effect depended on the year. In the serpentine grassland, there was no effect of water addition on biomass. Survival, biomass, growth rates, and seed production of soil endemics and generalists were all significantly reduced by competition, but were unaffected by water addition. Overall, endemics tended to perform better in serpentine soil and generalists in non-serpentine soil, suggesting that soil is an important factor for the establishment and survival of endemics and generalists. For endemics, the effect of biomass removal was stronger on non-serpentine soil, but for generalists this effect was similar on both soils, indicating that competition can be important in low-resource habitats. In conclusion, our results suggest that low-fertility plant communities may be slow to respond to changes in precipitation compared to communities on more fertile soil.

Mariotte, P., C. Vandenberghe, P. Kardol, F. Hagedorn, and A. Buttler. 2013. Subordinate plant species enhance community resistance against drought in semi-natural grasslands. Journal of Ecology 101:763–773.

ABSTRACT: According to the insurance hypothesis, more diverse plant communities are more likely to be resistant to drought. Whilst many experiments have been carried out to determine the effects of plant diversity on plant community insurance, the results are still contradictory. Here, we conducted a drought experiment where we tested whether the presence of subordinate species increases plant community insurance. In Swiss Jura grassland, we combined a removal experiment of subordinate species with a summer drought event using rainout shelters. Plant community composition was determined after the drought and based on biomass measurements; we estimated resistance, recovery and resilience of the plant community for each combination of treatments. Moreover, to assess drought impacts on water-use efficiency (WUE), we analysed carbon isotope ratios (13C values) in plant leaves of two dominants and two subordinates collected at the end of the drought period. We showed that subordinate species are more resistant to drought and increased community resistance by enhancing their above-ground biomass production during the imposed drought. These patterns were associated with decreased competitiveness of dominant species whose biomass decreased during drought. Significant increase in 13C values in plant tissue under drought indicated a better WUE for the measured species. Interestingly, the WUE was significantly higher in plots where subordinates were removed. Recovery and resilience were not affected by the summer drought, but the absence of subordinates reduced overall above-ground biomass in both watered and drought plots. Synthesis. We demonstrated that, independent of plant diversity, the presence of drought-resistant subordinate species increases plant community insurance against drought and, hence, is important for the functioning of grassland ecosystems.

McAdoo, J. K., B. W. Schultz, and S.R.  Swanson. 2013. Aboriginal precedent for active management of sagebrush-perennial grass communities in the Great Basin. Rangeland Ecology & Management, 66(3), 241-253.

ABSTRACT: Until recently, most contemporary ecologists have ignored or diminished anecdotal historical accounts and anthropologists' reports about aboriginal fire in the Great Basin. Literature review shows that Indians practiced regular use of fire for many purposes, including the obvious reasons of increasing the availability of desired plants, maintaining habitats for animals used as food, and driving game during hunts. Historical accounts of prehistoric anthropogenic firing, inferences from fire-scar data, and data regarding annual production capability of representative sagebrush (Artemisia spp.)-perennial grass ecological sites indicate that prehistoric conditions were neither fuel- nor ignition-limited. According to many sources, this "active management" by Indians was widespread, significant, and more common than lightning-caused fires, resulting in mosaic vegetation patterns that subsequently moderated the behavior of "natural fires." This interaction between Indian-burning and lightning fires may have strongly influenced the pre-Euro-American settlement vegetation of the Great Basin. At the very least, the landscape was a patchwork of areas altered by aboriginal people and areas shaped primarily by bio-physical processes. Based on this prehistoric precedent, current historically unprecedented conditions (fuel load and exotic weed invasion threats), and predicted climate change, contemporary active management of sagebrush-perennial grass communities is paramount. Restoration measures should be scientifically based and tailored to achieve ecological resilience and functionality in specific sites. Prescribed fire is not always ecologically appropriate or judicious, especially in Wyoming big sagebrush (A. tridentata spp. wyomingensis) communities, so managers should consider using other alternatives where an intentional low severity disturbance is deemed necessary. Properly planned active management would disrupt fuel continuity for lightning fires, ensure ecological process and successional integrity, and benefit multiple uses on a landscape scale.

McSherry, M. E., and M. E. Ritchie. 2013. Effects of grazing on grassland soil carbon: a global review. Global change biology 19:1347–57.

ABSTRACT: Soils of grasslands represent a large potential reservoir for storing CO2, but this potential likely depends on how grasslands are managed for large mammal grazing. Previous studies found both strong positive and negative grazing effects on soil organic carbon (SOC) but explanations for this variation are poorly developed. Expanding on previous reviews, we performed a multifactorial meta-analysis of grazer effects on SOC density on 47 independent experimental contrasts from 17 studies. We explicitly tested hypotheses that grazer effects would shift from negative to positive with decreasing precipitation, increasing fineness of soil texture, transition from dominant grass species with C3 to C4 photosynthesis, and decreasing grazing intensity, after controlling for study duration and sampling depth. The six variables of soil texture, precipitation, grass type, grazing intensity, study duration, and sampling depth explained 85% of a large variation (+/- 150gm2yr1) in grazing effects, and the best model included significant interactions between precipitation and soil texture (P=0.002), grass type, and grazing intensity (P=0.012), and study duration and soil sampling depth (P=0.020). Specifically, an increase in mean annual precipitation of 600mm resulted in a 24% decrease in grazer effect size on finer textured soils, while on sandy soils the same increase in precipitation produced a 22% increase in grazer effect on SOC. Increasing grazing intensity increased SOC by 67% on C4-dominated and C4C3 mixed grasslands, but decreased SOC by an average 18% in C3-dominated grasslands. We discovered these patterns despite a lack of studies in natural, wildlife-dominated ecosystems, and tropical grasslands. Our results, which suggest a future focus on why C3 vs. C4-dominated grasslands differ so strongly in their response of SOC to grazing, show that grazer effects on SOC are highly context-specific and imply that grazers in different regions might be managed differently to help mitigate greenhouse gas emissions. 

Ryals, R., & Silver, W. L. 2013. Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands. Ecological Applications 23(1): 46–59.

Setterfield, S. A, N. A Rossiter-Rachor, M. M. Douglas, L. Wainger, A. M. Petty, P. Barrow, I. J. Shepherd, and K. B. Ferdinands. 2013. Adding fuel to the fire: the impacts of non-native grass invasion on fire management at a regional scale. PloS One 8:e59144.

ABSTRACT: Widespread invasion by non-native plants has resulted in substantial change in fire-fuel characteristics and fire-behaviour in many of the world's ecosystems, with a subsequent increase in the risk of fire damage to human life, property and the environment. Models used by fire management agencies to assess fire risk are dependent on accurate assessments of fuel characteristics but there is little evidence that they have been modified to reflect landscape-scale invasions. There is also a paucity of information documenting other changes in fire management activities that have occurred to mitigate changed fire regimes. This represents an important limitation in information for both fire and weed risk management. Methodology/Principal Findings: We undertook an aerial survey to estimate changes to landscape fuel loads in northern Australia resulting from invasion by Andropogon gayanus (gamba grass). Fuel load within the most densely invaded area had increased from 6 to 10 t ha(-1) in the past two decades. Assessment of the effect of calculating the Grassland Fire Danger Index (GFDI) for the 2008 and 2009 fire seasons demonstrated that an increase from 6 to 10 t ha(-1) resulted in an increase from five to 38 days with fire risk in the 'severe' category in 2008 and from 11 to 67 days in 2009. The season of severe fire weather increased by six weeks. Our assessment of the effect of increased fuel load on fire management practices showed that fire management costs in the region have increased markedly (similar to 9 times) in the past decade due primarily to A. gayanus invasion. Conclusions/Significance: This study demonstrated the high economic cost of mitigating fire impacts of an invasive grass. This study demonstrates the need to quantify direct and indirect invasion costs to assess the risk of further invasion and to appropriately fund fire and weed management strategies.

Skaer, M. J., D. J. Graydon, and J. H. Cushman. 2013. Community-level consequences of cattle grazing for an invaded grassland: variable responses of native and exotic vegetation. Journal of Vegetation Science 24:332-343.

Vourlitis, G. L., & J.L. Kroon. 2013. Growth and resource use of the invasive grass, Pampasgrass (Cortaderia selloana), in response to nitrogen and water availability. Weed Science, 61(1): 117–125. doi:10.1614/WS-D-11-00220.1

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