Native Prairie Plants Research Articles

The Effect of Nitrogen, Phosphorus, and Potassium Fertilizers on Prairie Biomass Yield, Ethanol Yield, and Nutrient Harvest

Native prairie plants can be managed to provide biomass for cellulosic ethanol production; however, there is inadequate information in northern latitudes regarding the effects of fertilizers on biomass and ethanol yields. We evaluated biomass yield, land ethanol yield (theoretical ethanol production per unit area), and nutrient harvest in grasslands managed across a gradient of nitrogen (N), phosphorus (P), and potassium (K) fertilizers at three locations in MN, USA, from 2008 to 2009. The Austin and Lamberton locations were planted with a mixture of prairie plants, while the Rosemount location was solely switchgrass (Panicum virgatum L.). Model-based estimations of agronomically optimum nitrogen rates (AONRs) for land ethanol yield were determined for five of six site-year environments. Five response functions were modeled for land ethanol yield, each predicting a unique AONR with varying degrees of confidence. The linear plateau function was best-supported for four of six environments. Agronomically optimum nitrogen rates ranged from 61 to 87 kg N ha−1 and, on average, yielded 3,160, 2,090, and 3,180 L ethanol ha−1 at Austin, Lamberton, and Rosemount, respectively. On average, predicted ethanol yields increased 52 % when fertilized at AONRs compared to yields without fertilizer. Phosphorus and K fertilizers did not affect land ethanol yield. Nitrogen, P, and K removed during biomass harvest increased with N fertilization and averaged 31, 6, and 20 kg ha−1 at the AONRs. Nitrogen use efficiency declined with N fertilization during drier years. Modest rates of N fertilizer (between 60 and 90 kg N ha−1) can maximize cellulosic ethanol production in established northern latitude grasslands. Soil P and K should be monitored as nutrients are removed during repeated biomass harvests.

The Role of an Urban Tallgrass Prairie Remnant in Conservation: A Case Study in Central Iowa (USA)

Although more than 85% of Iowa (USA) was covered by tallgrass prairie at the time of settlement by Europeans in the early 19th century, less than 0.1% remains. The Richard W. Pohl State Preserve at Ames (IA) High School, surrounded on three sides by structures, roads, and other development, protects 4 ha of tallgrass prairie. The preserve, commonly referred to as Ames High Prairie (AHP), was grazed but never plowed under private ownership until its acquisition by the Ames School District in 1959. Although considered for development as a parking lot or football field in the 1960s, the residents of Ames voted in 1970 to award The Nature Conservancy (TNC) a 49-year lease to the property (until 2019). This preserve, almost completely open in the 1930s, has been subject to numerous threats, including encroachment by woody plants, entry of non-native and invasive plant species associated with human activity, and erosion associated with storm water runoff, sewer line repair, foot and bike traffic, and major flood events. Recent management activities at AHP, conducted by volunteer land stewards, high school and college students, TNC summer interns, and private contractors, has consisted of controlled burns, cutting and herbicide treatment of encroaching woody plants, manual removal and herbicide treatment of invasive herbaceous plants, and sowing of seeds (collected on site) into reopened areas. Three vascular plant inventories of the 8.9 ha preserve (1966, 1995, current study) have documented the occurrence of 465 taxa (329 native) at AHP, including 5 Iowa special concern species. This flora includes 147 native prairie plant taxa, which ranks 8th in comparison with the 26 other (and mostly larger) prairies protected as state preserves in Iowa. As a vegetation remnant, AHP protects tallgrass prairie taxa and their gene pools, maintains an example of historically abundant (but now scarce) tallgrass prairie vegetation, and provides citizens an opportunity to experience prairie.

Comparison of an autumn biomass harvest with a spring prescribed burn in restored native grass fields

Wildlife managers use spring prescribed burns to set back succession in managed grasslands throughout the prairie pothole region. Yet, prescribed burns are expensive and weather dependent. Autumn biomass harvest of native prairie plants may also simulate natural disturbances and help prevent the invasion of woody species. As such, biomass harvest can be an attractive management option that can augment, and in some cases, replace spring burning programs. We compared vegetation characteristics (vegetation ht and density, and residual litter depth) and changes to the plant community (e.g., species richness, relative abundance of native and exotic plant species) in restored native grasslands of Minnesota, during 2007–2009, in response to spring prescribed burns and autumn biomass harvest. We used a randomized block design to control for site-to-site variability, and compared treatments using mixed models that accounted for this source of variation as well as within-plot repeated measures. This framework also allowed us to consider additional variables (e.g., Julian date, yr effects) thought to influence response patterns, and also additional fields that were treated with an autumn biomass harvest during the same time period. Vegetation characteristics exhibited substantial site-to-site and temporal variability, but, with the exception of litter depths, vegetation characteristics were largely similar in biomass harvest and burned subplots. We conclude that autumn biomass harvests deserve more consideration as a potential grassland management tool. © 2013 The Wildlife Society.

The Effect of Biochar on Native and Invasive Prairie Plant Species

AbstractBiochar, a carbon-rich product formed by the incomplete combustion of biomass, has been shown to improve soil quality and increase crop growth but has not been evaluated in prairie ecosystems. We assessed the response of a native perennial grass, big bluestem, and an invasive herbaceous perennial, sericea, to biochar amendments in two greenhouse experiments in 2010 and 2011. In the first experiment, big bluestem and sericea were grown in monoculture; the main treatments were soil type (silt, sand), percent biochar (0%, 1%, 2%, and 4%) and nitrogen (0 and 10 g N m−2). Big bluestem growth was increased by the addition of biochar, particularly in the sand soil. In contrast, sericea growth was either not affected or decreased when biochar was added to the soil, particularly at the higher biochar rates. Adding N to the soil appeared to increase sericea growth in the presence of biochar and the silt soil, which suggests that biochar may have reduced N availability. A replacement series was used in the second experiment to evaluate the effect of biochar on competition between the two species. Main treatments were biochar rates (0% and 2%), nitrogen rates (0 and 10 g N m−2) and the following big bluestem to sericea ratios: 6 : 0, 4 : 2, 3 : 3, 2 : 4, and 0 : 6. After 180 d, big bluestem height and biomass were significantly greater in biochar-amended soils than in unamended soils. However, sericea height and biomass were unaffected by biochar amendments and the addition of biochar did not alter competitive outcomes. Competition between big bluestem and sericea was asymmetrical; sericea reduced the growth of big bluestem but big bluestem had relatively little effect on the growth of sericea. Our research suggests that biochar has the potential to increase the growth of big bluestem and may be a useful tool for prairie restoration.

Geology and Topography Effects on Exotic Plant Distribution in a Semiarid Mima Mound Prairie in Eastern Washington

Native prairie plant communities are among the most endangered habitats due to extensive agricultural use and exotic species invasion. Understanding how species composition, particularly of exotic species, varies with environment is essential for management and preservation of these communities. In semi-arid prairies, plant establishment is often heterogeneous across the landscape and depends on the patchy availability of resources across environmental gradients. We studied how soil geologic substrate, topography, and grazing history relate to patterns of native and exotic plant distribution in a semiarid Mima mound prairie in eastern Washington. We analyzed the relationship between native and exotic species richness and abundance on 61 Mima mounds in a prairie underlain by two types of soil geologic substrate (glacial alluvium and basalt) where half of each had been grazed recently. We found that exotic species richness and cover were lowest and native species cover was highest on mounds underlain by basalt bedrock that had experienced recent grazing; on sites underlain by glacial alluvium there was little difference between more and less recently grazed mounds. Moreover, we found that exotic abundance was greatest at the top of Mima mounds compared to the sides; the opposite was true for native species. Our findings indicate that geologic substrate and grazing history may interact to determine plant distribution in semi-arid prairie communities. This study demonstrates that land managers aiming to restore native plant communities need to consider the synergistic effects of multiple environmental factors in order to focus restoration funding and effort.

The impact of habitat fragmentation on fitness-related traits in a native prairie plant,Chamaecrista fasciculata(Fabaceae)

Loss and fragmentation of the native prairies in the Midwestern United States have resulted in isolated and smaller habitats and populations. The populations remaining in these prairies are expected to show a decline in the extent of genetic variation and an increase in genetic drift load (accumulation of deleterious recessive alleles due to genetic drift) in fitness-related traits. Using complementary greenhouse experiments, we tested whether these expected changes have occurred in the native annual prairie plant Chamaecrista fasciculata. In the first experiment, open pollinated C. fasciculata seeds from 12 prairie fragments representing a range in area of habitat were grown in competition with Schizachyrium scoparium to determine if there are changes in plant vigour with changes in fragment size and corresponding changes in population size. Plants from smaller prairie fragments exhibited a slight but significant decline in biomass, suggesting an increase in genetic drift load. In the second experiment, a formal genetic crossing design of four prairie fragment populations was used to estimate quantitative genetic diversity and genetic drift load. We did not find extensive quantitative genetic variation, but we did find a strong effect of genetic drift load on five traits in this experiment. Our overall conclusion is that a decline in relative-fitness traits in smaller prairie fragments is probably associated with fixation of deleterious alleles due to more isolated and smaller populations, i.e. genetic drift load.

Soil quality improvement under an ecologically based farming system in northwest Missouri

AbstractEcologically based farming conserves and improves the soil resource and protects environmental quality by using organic or natural resources without the application of synthetic chemicals. Soil quality assessment indicates the ability of management systems to optimize soil productivity and to maintain its structural and biological integrity. Our objective was to evaluate the effect of ecologically based management on biochemical characteristics of soil [soil quality indicators (SQI)] as an assessment of soil quality. The study was conducted on an ecologically based farming enterprise established on gently sloping soils of Sharpsburg silt loam (fine montmorillonitic, mesic Typic Argiudolls) in Clay County, Missouri, which was previously under conventional corn and soybean production. The transition to organic farming began in 1995, which included a primary management strategy to restore soil organic matter consisting of the establishment of native prairie plants and the application of composted vegetative residues and litter from horse and laying hen operations. Soils were collected at 0–10cm depths from sites under organic production (orchard and vegetable), managed prairie/pasture and from adjacent unmanaged fields during 2003–2008 for soil quality assessment. Soil organic carbon (SOC) and water-stable soil aggregates were considerably increased by up to 60 and 72%, respectively, in organic production sites compared with tilled cropland by the fifth year of assessment. Organically managed systems and restored prairie sites significantly increased (P<0.05) soil enzyme activities compared with unmanaged grass and tilled cropland. For example, dehydrogenase and glucosaminidase activities increased by 60 and 73%, respectively, under organic vegetables compared with tilled cropland. Soil enzyme activities were significantly correlated with SOC content (rvalues up to 0.90,P<0.001). The results of the soil quality assessment suggest that ecologically based management successfully restored biological activity of silt loam soils previously under intensive conventional agriculture. The system practiced at the study sites illustrates how resources internal to the farm (i.e., composts) can be used to manage soil productivity.

Carbon exchange by establishing biofuel crops in Central Illinois

Perennial grass biofuels may contribute to long-term carbon sequestration in soils, thereby providing a broad range of environmental benefits. To quantify those benefits, the carbon balance was investigated over three perennial grass biofuel crops – miscanthus ( Miscanthus × giganteus), switchgrass ( Panicum virgatum) and a mixture of native prairie plants – and a row crop control (maize–maize–soy) in Central Illinois, USA, during the establishment phase of the perennial grasses (2008–2011). The eddy covariance technique was used to calculate fluxes of carbon dioxide and energy balance components, such as latent and sensible heat fluxes. Whereas maize attained the highest maximal carbon uptake rates, the perennial grasses had significantly extended growing seasons, such that their total carbon uptake rivaled that of corn in the second growing season and greatly exceeded that of soy in the third growing season. To account for the removal of carbon through harvest, net ecosystem exchange of carbon (NEE) was combined with estimates of yields, resulting in the net ecosystem carbon balance (NECB). After 2.5 years, NECB for the maize/soybean plot was positive (a source of carbon), while the grasses were a sink of carbon. Continuous measurements over the next years are required in order to confirm whether miscanthus, switchgrass and prairie can sustain a long-term sink of carbon if managed for biofuels, i.e., if harvested annually.

Restoration of Agricultural Fields to Diverse Wet Prairie Plant Communities in the Willamette Valley, Oregon

Abstract Restoring highly degraded sites in Oregon's Willamette Valley to diverse native prairie plant communities is an important component of regional conservation strategies. However, creating or reassembling desired native plant communities is a tremendous challenge for restoration practitioners, and useful practical approaches are needed. Here, we describe an implementation strategy we developed for restoring intensively managed agricultural sites to native wet prairie that integrates relevant scientific research and lessons learned from previous restoration experience, with a particular focus on sequencing disturbance, colonization, and competitive actions to achieve desired outcomes. Then, we report vegetation monitoring results from four projects where we used this implementation strategy to assess if progress is being made to achieve our two a priori project objectives: (1) establishing a plant community with 50 or more native plant species, and (2) establishing a plant community with > 70% absol...

Shifts in the flowering phenology of the northern Great Plains: Patterns over 100 years

Climate change is associated with phenological shifts in an increasing number of organisms worldwide. However, accurate estimates of these shifts are dependent on long-term data sets that include phenological observations from before annual average temperatures began to rise. We compared the first flowering times of native prairie plants between 2007 and 2010 with historical data recorded by O. A. Stevens from 1910 to 1961. By merging climate variable data from the same time period, it also was possible to correlate first flowering dates with associated climate variables. Over the past 100 years, spring temperatures in the Red River Valley near Fargo, North Dakota, USA, have increased, and growing seasons have lengthened significantly. Seventy-five percent of the 178 species observed by Stevens had flowering times that were sensitive to at least one variable related to temperature or precipitation. Over the past 4 yr, 5% to 17% of the species observed have significantly shifted their first flowering time either earlier or later relative to the previous century. The results of this study indicate that as spring temperatures in the northern Great Plains have increased and the growing season has lengthened, some spring flowering species have advanced their first flowering time, some fall species have delayed their first flowering, and some species have not changed. Given the importance of flowering timing for reproductive success, the changing climate in the Great Plains is expected to have long-term ecological and evolutionary consequences for native plant species.

The effect of temperature and water potential on seed germination of poly-cross side-oats grama (Bouteloua curtipendula (Michx.) Torr.) population of Canadian prairie

There is increasing interest in using native prairie plants for revegetation and pasture in the drier regions of the Canadian prairies. An experiment was conducted to determine the effects of simulated dry conditions and temperature on seed germination of side-oats grama grass (Bouteloua curtipendula (Michx.) Torr.). Over a 21d period, germination was studied in five growth chambers with constant temperatures of 15, 20, 25, 30 and 35°C and water potentials of –1.2, –0.9, –0.6, –0.3 and 0.0 MPa at each temperature. Seeds used in the study were bulk harvested seeds from a nursery established from 12 collections across Canadian prairie. More than 85% of the seeds germinated within 5 days at water potentials of 0.0 or –0.3 MPa when temperature was 25-35°C, but the percentage was reduced in solutions of lower than –0.6 MPa. Even though seed germination was reduced at lower water potential, 35% of seed germinated in a solution of –1.2 MPa, at 25-35°C. The final germination was highest at 25-35°C, intermediate at 20°C, and lowest at 15°C. Side-oats grama grass can germinate at low water availability, and if the growth condition is favourable, the majority of the seeds finish germination within a week. However, a temperature at or higher than 25°C is critical to improve total seed germination.

Forage Yield, Nutritive Value, and Elemental Composition of Ten Native Prairie Plant Species

Native prairie plants have the potential to provide nutritious summer forage in grazing systems. Ten native prairie species (five perennial grasses, three legumes, and two forbs) were grown for three years and harvested annually in August to measure the herbage mass, nutritive value, and elemental composition of each species. Black-eyed susan (Rudbeckia hirta L.) yielded the most biomass in 2008 (2.9 tons/acre), but by 2010 native, warm-season grasses and oxeye sunflower [Heliopsis helianthoides (L.) Sweet] were the highest yielding (3.8 tons/acre). While neutral detergent fiber (NDF) concentrations of some prairie grasses exceeded 65%, potentially limiting available energy, crude protein levels in all ten species were high enough to maintain nonlactating cows. Concentrations of eleven elements were also adequate for nonlactating cows, with only sodium levels below minimum livestock requirements. Yield, nutritive value, and nutrient analyses suggest that many native prairie plants with minimal management can provide a high quantity of forage with reasonable quality during peak summer months when an abundance of cool-season forage may be lacking.

The importance of soil microorganisms for maintaining diverse plant communities in tallgrass prairie

According to the "Janzen-Connell hypothesis," soil microorganisms have the potential to increase plant community diversity by mediating negative feedback on plant growth. Evidence for such microbe-driven negative feedback has been found in a variety of terrestrial systems. However, it is currently unknown how general this phenomenon is within most plant communities. Also unknown is the role of mutualists in generating such feedback: do they decrease the influence of soil-mediated negative feedback on plant fitness or do they increase its effect by proliferating with plant hosts to which they give the least benefit? • We investigated soil-microbe-mediated feedback via a series of reciprocal transplant experiments in the greenhouse using soil from a restored tallgrass prairie and native tallgrass prairie plant species. • We found that negative feedback was very common but that mutualists (arbuscular mycorrhizal fungi) influence plant growth in opposition to the overall negative feedback trend. • Widespread microbially mediated negative feedback indicates that plant community diversity and composition in tallgrass prairie are dependent on soil microorganisms. Native soil microorganisms should be considered in restoration efforts of tallgrass prairie and, potentially, other native plant communities.

Relationships among leaf damage, natural enemy release, and abundance in exotic and native prairie plants

The Enemy Release hypothesis holds that exotic plants may have an advantage over native plants because their specialized natural enemies are absent. We tested this hypothesis by measuring leaf damage and plant abundance for naturally-occurring plants in prairies, and by removing natural enemies in an enemy exclusion experiment. We classified plants as invasive exotic, noninvasive exotic, or native, to determine if their degree of invasiveness influenced their relationships with natural enemies. Our field surveys showed that invasive exotic plants generally had significantly lower levels of foliar damage than native species while there was no consistent pattern for noninvasive exotics compared to natives. The relationship between damage and abundance was different for exotic and native plants: foliar damage decreased with increasing abundance for exotic plants while the trend was positive for native plants. While these results from the field surveys supported the Enemy Release Hypothesis, the enemy exclusion experiment did not. There was no relationship between a species’ status as exotic or native and its degree of release from herbivory. Pastinaca sativa, the invasive exotic in this experiment, experienced gains in leaf area and vegetative biomass when treated with pesticides, indicating substantial herbivore pressure in the introduced range. These results show that foliar damage may not accurately predict the amount of herbivore pressure that plants actually experience, and that the Enemy Release hypothesis is not sufficient to explain the invasiveness of P. sativa in prairies.

Anthracnose disease of switchgrass caused by the novel fungal species Colletotrichum navitas

In recent years perennial grasses such as the native tallgrass prairie plant Panicum virgatum (switchgrass) have taken on a new role in the North American landscape as a plant-based source of renewable energy. Because switchgrass is a native plant, it has been suggested that disease problems will be minimal, but little research in this area has been conducted. Recently, outbreaks of switchgrass anthracnose disease have been reported from the northeastern United States. Incidences of switchgrass anthracnose are known in North America since 1886 through herbarium specimens and disease reports, but the causal agent of this disease has never been experimentally determined or taxonomically evaluated. In the present work, we evaluate the causal agent of switchgrass anthracnose, a new species we describe as Colletotrichum navitas ( navitas = Latin for energy). Multilocus molecular phylogenetics and morphological characters show C. navitas is a novel species in the falcate-spored graminicolous group of the genus Colletotrichum; it is most closely related to the corn anthracnose pathogen Colletotrichum graminicola. We present a formal description and illustrations for C. navitas and provide experimental confirmation that this organism is responsible for switchgrass anthracnose disease.

Comparison of damage to native and exotic tallgrass prairie plants by natural enemies

We surveyed the prevalence and amount of leaf damage related to herbivory and pathogens on 12 pairs of exotic (invasive and noninvasive) and ecologically similar native plant species in tallgrass prairie to examine whether patterns of damage match predictions from the enemy release hypothesis. We also assessed whether natural enemy impacts differed in response to key environmental factors in tallgrass prairie by surveying the prevalence of rust on the dominant C4 grass, Andropogon gerardii, and its congeneric invasive exotic C4 grass, A. bladhii, in response to fire and nitrogen fertilization treatments. Overall, we found that the native species sustain 56.4% more overall leaf damage and 83.6% more herbivore-related leaf damage when compared to the exotic species. Moreover, we found that the invasive exotic species sustained less damage from enemies relative to their corresponding native species than the noninvasive exotic species. Finally, we found that burning and nitrogen fertilization both significantly increased the prevalence of rust fungi in the native grass, while rust fungi rarely occurred on the exotic grass. These results indicate that reduced damage from enemies may in part explain the successful naturalization of exotic species and the spread of invasive exotic species in tallgrass prairie.

Response to Comment on "Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass"

We discovered that biofuels from low-input high-diversity mixtures of native perennial prairie plants grown on degraded soil can provide similar bioenergy gains and greater greenhouse gas benefits than current corn ethanol produced from crops grown in monoculture on fertile soil with high inputs. Russelle et al .'s technical concerns are refuted by a substantial body of research on prairie ecosystems and managed perennial grasslands.

Natural Recolonization of Cultivated Land by Native Prairie Plants and its Enhancement by Removal of Scots Pine, <em>Pinus sylvestris</em>

A combination of native and introduced plants colonized abandoned cultivated land with adjacent relict prairie and savanna in the Rice Lake region of southern Ontario. After 71 years, the native colonizers included 86 species found in regional prairie relicts, but much of the area was also colonized by introduced Scots Pine, Pinus sylvestris, which apparently spread from an adjacent planting. The pines formed expanding patches of dense growth that excluded other species. Removal of the invasive Scots Pine from a 200 m2 plot within the abandoned land led to colonization 17 years later by 36 native species characteristic of the prairie, savanna and sand barrens of the region. Included in this group of native prairie colonizers were keystone species such as Andropogon gerardii, Carex siccata, Ceanothus americanus, Comptonia peregrina and Quercus velutina. Areas where patches of Scots Pine had been allowed to continue growing were either devoid of vegetation or had a sparse understory of introduced species and Poison Ivy (Rhus radicans). These observations support the concepts of (1) protecting islands of native dry ground flora which can serve as sources for recolonization and (2) protection of old field and particularly recently cultivated land adjacent to protected native grassland to allow natural restoration. The fact that keystone native species were able to colonize the area from which the introduced Scots Pines had been removed suggests that the pines are aggressive competitors that occupy space to the exclusion of the native species. Scots Pine is thus a driver of ecological change in degraded ecosystems. Management including removal of Scots Pine to support native plant biodiversity is strongly supported.

Predicting Plant Extinction Based on Species‐Area Curves in Prairie Fragments with High Beta Richness

Abstract: Species‐area relationships and island biogeography theory are commonly used to predict how species richness will decline with fragmentation. There are a variety of largely untested assumptions in these approaches, including the assumptions that populations are distributed uniformly before fragmentation, and that local extinctions are due to effects of small population sizes. If populations are not distributed uniformly, then populations can be abundant locally but rare globally. This would cause extinction rates to be smaller than predicted. We tested extinction theory by developing estimates of the number of plant species that should be present in small tallgrass prairie fragments and then testing the uniformity assumption by partitioning species richness into α (within site) and β (among site) components in Iowa prairies. Many more native prairie plant species were present in surveys of prairie fragments (491) than was predicted based on theory (27–207). A large proportion (75%) of the total species richness was β richness. We suggest that the high proportion of β richness was responsible for the shallow species‐area slopes and the lower than expected number of species losses and that a better understanding of what determines β diversity will improve predictions of fragmentation effects on richness of plants. We also suggest that plants in prairie remnants may be best conserved by protecting different prairie types rather than by protecting a few large areas containing a single prairie type.

Soil Heterogeneity Effects on Tallgrass Prairie Community Heterogeneity: An Application of Ecological Theory to Restoration Ecology

AbstractSpatial heterogeneity of resources can influence plant community composition and diversity in natural communities. We manipulated soil depth (two levels) and nutrient availability (three levels) to create four heterogeneity treatments (no heterogeneity, depth heterogeneity, nutrient heterogeneity, and depth + nutrient heterogeneity) replicated in an agricultural field seeded to native prairie species. Our objective was to determine whether resource heterogeneity influences species diversity and the trajectory of community development during grassland restoration. The treatments significantly increased heterogeneity of available inorganic nitrogen (N), soil water content, and light penetration. Plant diversity was indirectly related to resource heterogeneity through positive relationships with variability in productivity and cover established by the belowground manipulations. Diversity was inversely correlated with the average cover of the dominant grass, Switchgrass (Panicum virgatum), which increased over time in all heterogeneity treatments and resulted in community convergence among the heterogeneity treatments over time. The success of this cultivar across the wide range of resource availability was attributed to net photosynthesis rates equivalent to or higher than those of the native prairie plants in the presence of lower foliar N content. Our results suggest that resource heterogeneity alone may not increase diversity in restorations where a dominant species can successfully establish across the range of resource availability. This is consistent with theory regarding the role of ecological filters on community assembly in that the establishment of one species best adapted for the physical and biological conditions can play an inordinately important role in determining community structure.