Northern Great Plains Grasslands Research Articles

422 Mineral Content of Invaded Grassland Forages Is Affected By Precipitation and Management

Abstract Mineral content of grazed forage influences overall health, growth and reproduction of cattle and promotes maximum cattle productivity. However, grassland mineral content may not always meet cattle requirements throughout the grazing season and can be affected by precipitation of the season. Most of the Northern Great Plains grassland is invaded by exotic perennial grass species that have a uniform growth habit and response to precipitation. Growth habitat can be controlled by grazing or mowing, which may alter mineral content. No studies have examined the combined effects of mowing and drought on forage mineral concentration of invaded grassland. Therefore, the objective of this study was to determine mineral concentration of forage in rangeland pastures in seasons of low compared with normal precipitation and mowing status and model recommendations for mitigating low mineral content. This study was conducted at the Northern Great Plains Research Laboratory in Mandan, North Dakota USA. Pastures were sampled across several years and pasture locations, with enclosed plots mowed or not mowed in April, to simulate early season mobgrazing or clipping. Quarter- meter quadrats were taken every two weeks of the grazing seasons from plots in each pasture, one year dry and the other normal. Samples were analyzed for macrominerals and trace minerals via ICP-aa spectroscopy. Forage mineral content was analyzed as a completely randomized design using the MIXED procedure of SAS (SAS 9.4, Cary, NC). Total ash content was different by year (P = 0.0053) but not affected by mowing (P = 0.21). Potassium and phosphorus were not different due to mowing, nor effected by precipitation. Calcium was affected by mowing (P = 0.0065) and tended be affected by precipitation (P = 0.11). Zinc, copper, molybdenum, manganese and iron were all found to be significantly affected by precipitation (P < 0.001). When applied to a beef nutrient requirement model, Ca and P were generally adequate to meet recommended amounts for lactating cows based on a May-calving 1,200-pound cow most months of the season but did not meet needs of a 1400 lb. cow and calf. Forage phosphorus content was significantly less in June of each year, but adequate the rest of the season, suggesting targeting phosphorus supplementation for only the least months would save on mineral costs. Understanding forage mineral fluctuations across the grazing season may provide producers with tools to make the best supplementation strategies and use the most appropriate mineral formulations to maximize performance and reduce input cost.

Invasive grass and litter accumulation constrain bee and plant diversity in altered grasslands

Ecologists consider biological invasions one of the primary drivers of global change. Many remaining grasslands in North America have extensive invasions of exotic grass species that have replaced native plant species. In the Northern Great Plains, exotic cool-season grasses Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), paired with human alterations to the landscape and historical disturbance regimes, have resulted in functionally and structurally altered grassland plant communities. These changes may extend to impact species that rely on these plant communities, such as bees. Bees are ecologically diverse and serve important pollinator roles but are at risk from the loss and change of floral and nesting resources in plant communities. Our objectives were to determine whether Kentucky bluegrass and smooth brome alter the bee and forb species richness in invaded Northern Great Plains grasslands and how litter accumulation, grass cover, the amount of bare ground, and forb species richness interact with bee functional traits. To do this, we surveyed 67 grassland sites from 2017 to 2020 with two bee-sampling methods (268 netting and bee bowl surveys total) and vegetation cover surveys at each site. We collected 20,559 bees from 201 bee species and observed 249 forb and shrub species in vegetation surveys. Bee richness and Shannon diversity were associated with greater forb richness while forb richness was significantly lower with thicker litter depths and higher with a greater coverage of all grasses other than Kentucky bluegrass and smooth brome. Bee trait analyses showed varying relationships with plant community variables. Of these, litter depth and Kentucky bluegrass cover were associated with lower ground-nesting bee abundance while small-bodied bee abundance was positively associated with increasing bare ground. While our results support the close relationship between bee and plant diversity, we also found litter depth, in particular, contributed to the structure of these two communities. Specifically, Kentucky bluegrass and smooth brome are two exotic grass species associated with thatch-forming litter layers, especially under idle management that appear to simplify bee and forb communities. Our results make apparent the importance in maintaining structural and compositional diversity in invaded grasslands to support diverse bee communities.

Short-Term Vegetation Response to Bulldozed Fire Lines in Northern Great Plains Grasslands

A bulldozed fire line is a fire-suppression technique that limits fire movement by altering fuel continuity through vegetation removal and mineral soil exposure. The ecological impacts of a bulldozed fire line may exceed the effects of the fire itself through lasting changes in the soil and vegetation properties; however, little research has been performed to quantify these impacts in grassland systems. In this study, we compared vegetation properties among burned, unburned, and bulldozed fire line conditions on two August 2012 grassland wildfires in Montana. Standing biomass, by growth form, was quantified in 2013 and 2014, and compared using a generalized linear model. Perennial grass production was significantly reduced, while annual grass and annual forb biomass increased in response to the fire line treatment. Shrub and total vegetation standing crop were reduced in response to the fire line in 2013; however, the treatment effects were diminished by 2014. The burned and unburned treatments were generally similar within two years post-fire. The loss of perennial grasses and invasion of competitive annual grasses such as cheatgrass (Bromus tectorum L.) may limit the vegetation recovery of the fire line and promote further invasion of annual grasses into these systems. The marginal impact of the fires on these plant communities suggests the need to limit the use of ad hoc bulldozed fire lines as a suppression activity. If a bulldozed fire line is constructed, we suggest limiting soil disturbance by restricting blade depth to remove only surface vegetation and restricting bulldozer use to flat slopes, even if working with the contour, and incorporating re-seeding as part of or immediately after fire line construction.

Gatekeepers of transformation: private landowners evaluate invasives based on impacts to ecosystem services

AbstractBiological invasions are not new, yet the anthropogenic drivers of global change have produced unprecedented ecological novelty through the expansion of invasive species. Private landowners play an important role in determining the trajectory of ecological transformations driven by invasives. Using the northern Great Plains of the USA as a case study, we examined private landowners' role as gatekeepers for an invasive species. We employed a factorial vignette survey experiment to understand how the impacts of an unnamed invasive grass modeled on Kentucky bluegrass (Poa pratensis L.) were related to landowners' acceptance of the species. We also explored the relationship between landowners' acceptance of the invasive grass and their management intention to reduce/control the species. Each landowner evaluated multiple vignettes that randomly varied based on how a novel grass species expanding in rangelands would affect provisioning services (season of forage availability, forage quality, forage quantity), regulating services (floral resources for pollinators, water infiltration and availability), and supporting services (grassland bird diversity, grass diversity). Acceptability was strongly associated with landowners' management intentions, and the status of all seven services was related to acceptability. Reductions to any ecosystem service reduced the acceptability of the invasive grass species; however, only increases in forage quality, forage quantity, and water regulation were related to increased acceptability of the invasive. Scenario modeling shows that landowners displayed greater sensitivity to losses in a suite of ecosystem services than to equivalent gains. Scenarios specific to ecosystem service trade‐offs and Kentucky bluegrass invasion indicate that ecological losses may need to be severe before individual landowners change their management practices to reduce/control the species. Given the high thresholds for individual behavioral change, engaging private landowners in collaborative management efforts, whether to control an invasive grass or guide management toward co‐existence, may be helpful to conserve desired biodiversity and the flow of ecosystem services from northern Great Plains grasslands.

Kentucky Bluegrass Invasion in the Northern Great Plains and Prospective Management Approaches to Mitigate Its Spread.

Kentucky bluegrass (Poa pratensis L.) is one of the most aggressive grasses invading Northern Great Plains (NGP) grasslands, resulting in substantial native species losses. Highly diverse grasslands dominated by native species are gradually transforming into rangelands largely dominated by non-native Kentucky bluegrass. Several factors potentially associated with Kentucky bluegrass invasions, including high propagule pressure, thatch formation, climate change, and increasing nitrogen deposition, could determine the future dominance and spread of Kentucky bluegrass in the NGP. Because atmospheric CO2 is amplifying rapidly, a C3 grass like Kentucky bluegrass might be photosynthetically more efficient than native C4 grasses. As this exotic species shares similar morphological and phenological traits with many native cool-season grasses, controlling it with traditional management practices such as prescribed fire, grazing, herbicides, or combinations of these practices may also impair the growth of native species. Thus, developing effective management practices to combat Kentucky bluegrass spread while facilitating the native species cover is essential. Modifying traditional techniques and embracing science-based adaptive management tools that focus on the ecological interactions of Kentucky bluegrass with the surrounding native species could achieve these desired management goals. Enhancement of the competitiveness of surrounding native species could also be an important consideration for controlling this invasive species.

Fire controls annual bromes in northern great plains grasslands—Up to a point

Concern about the impacts of two invasive annual brome grasses (cheatgrass and Japanese brome, Bromus tectorum L. and B. japonicus Thunb. ex Murray) on the mixed-grass prairie of North America's northern Great Plains (NGP) is growing. Cheatgrass is well known west of the NGP, where replacement of fire-intolerant, native sagebrush steppe by fire-prone, exotic annual grasslands is widespread. Consequently, fire is often not considered as a tool for controlling annual bromes. This should not be the case in the NGP, where mixed-grass prairie is adapted to frequent fires. Fire's efficacy may vary with the degree of invasion, though; suppressing postfire annual brome populations or enhancing the native plant community may improve postfire annual brome control in highly invaded areas. To test this, we performed an experiment at two sites to evaluate the relative effectiveness of prescribed fire alone, fire followed by imazapic application and fire followed by native seeding across a pretreatment invasion gradient of annual brome-to-native species cover ranging from 0.05 to 2.35. Fall-prescribed fire alone greatly reduced annual bromes, but by the second yr after treatment the effect was significant only at invasion ratios < 1.2. Postfire imazapic application reduced annual bromes even further than fire alone, but only for 1 yr at the less invaded site and only at invasion ratios > 1.2 in yr 2 at the other site. Native species cover and total species richness responded positively to all treatments, but the degree of their response varied along the invasion gradient, between sites, with time since treatment and among treatments. Also, at one site, fire yielded a lagged stimulation of short-lived, exotic forbs. Seeding had little effect. Fire is an effective tool for reducing annual bromes in the NGP at lower invasion levels, but more tools are needed for long-term, effective control at highly invaded sites.

Using ecoacoustics metrices to track grassland bird richness across landscape gradients

Ecoacoustics is an emerging field that allows inferences about biodiversity trends and ecosystem health. Several acoustic indices have been developed for fast, automated assessments of ecosystem condition and are often used to assess changes in species richness/diversity across space or time. However, studies have reported inconclusive relationships between acoustic indices and species richness/diversity and the conclusions regarding “best” performing index differ between ecosystems. Here we assess the use of acoustic indices, using birds as a proxy for ecosystem health in a Northern Great Plains grassland system. We recorded soundscapes during bird morning chorus at 47 sites for 12–14 consecutive days and used these data to assess the accuracy of four acoustic indices (i.e. Bioacoustic Index; Acoustic Evenness Index; Acoustic Diversity Index; and Acoustic Complexity Index). We compared indices to bird richness derived from a trained ornithologist listening to sound recordings. The Bioacoustic Index (BI) and Acoustic Complexity Index (ACI) had the absolute highest correlation with bird richness in Northern Great Plains systems. Where Bioacoustic Index had a positive correlation and Acoustic Complexity Index had a negative correlation with grassland birds. The latter had the opposite direction from the ‘theoretical’ prediction. We further explored the relationship between indices and landscape gradients with known influences on bird diversity to further validate each index. We also discuss implications of acoustic indices as a tool for monitoring grassland birds. We found BI model outcomes align with known relationships between grassland birds and spatial covariates, whereas ACI did not concur these trends. We discuss these outcomes in relation to habitat-specific bird biophonic characteristics and provide possible explanations for differences between studies.

The greening of the Northern Great Plains and its biogeochemical precursors.

Vegetation greenness has increased across much of the global land surface over recent decades. This trend is projected to continue-particularly in northern latitudes-but future greening may be constrained by nutrient availability needed for plant carbon (C) assimilation in response to CO2 enrichment (eCO2 ). eCO2 impacts foliar chemistry and function, yet the relative strengths of these effects versus climate in driving patterns of vegetative greening remain uncertain. Here we combine satellite measurements of greening with a 135year record of plant C and nitrogen (N) concentrations and stable isotope ratios (δ13 C and δ15 N) in the Northern Great Plains (NGP) of North America to examine N constraints on greening. We document significant greening over the past two decades with the highest proportional increases in net greening occurring in the dries and warmest areas. In contrast to the climate dependency of greening, we find spatially uniform increases in leaf-level intercellular CO2 and intrinsic water use efficiency that track rising atmospheric CO2 . Despite large spatial variation in greening, we find sustained and climate-independent declines in foliar N over the last century. Parallel declines in foliar δ15 N and increases in C:N ratios point to diminished N availability as the likely cause. The simultaneous increase in greening and decline in foliar N across our study area points to increased N use efficiency (NUE) over the last two decades. However, our results suggest that plant NUE responses are likely insufficient to sustain observed greening trends in NGP grasslands in the future.

Looking to the future: key points for sustainable management of northern Great Plains grasslands

The grasslands of the northern Great Plains (NGP) region of North America are considered endangered ecosystems and priority conservation areas yet have great ecological and economic importance. Grasslands in the NGP are no longer self‐regulating adaptive systems. The challenges to these grasslands are widespread and serious (e.g. climate change, invasive species, fragmentation, altered disturbance regimes, and anthropogenic chemical loads). Because the challenges facing the region are dynamic, complex, and persistent, a paradigm shift in how we approach restoration and management of the grasslands in the NGP is imperative. The goal of this article is to highlight four key points for land managers and restoration practitioners to consider when planning management or restoration actions. First, we discuss the appropriateness of using historical fidelity as a restoration or management target because of changing climate, widespread pervasiveness of invasive species, the high level of fragmentation, and altered disturbance regimes. Second, we highlight ecosystem resilience and long‐term population persistence as alternative targets. Third, because the NGP is so heavily impacted with anthropogenic chemical loading, we discuss the risks of ecological traps and extinction debt. Finally, we highlight the importance of using adaptive management and having patience during restoration and management. Consideration of these four points will help management and restoration of grasslands move toward a more successful and sustainable future. Although we specifically focus on the NGP of North America, these same issues and considerations apply to grasslands and many other ecosystems globally.

Experimentally derived nitrogen critical loads for northern Great Plains vegetation.

The critical load concept facilitates communication between scientists and policy makers and land managers by translating the complex effects of air pollution on ecosystems into unambiguous numbers that can be used to inform air quality targets. Anthropogenic atmospheric nitrogen (N) deposition adversely affects a variety of ecosystems, but the information used to derive critical loads for North American ecosystems is sparse and often based on experiments investigating N loads substantially higher than current or expected atmospheric deposition. In a 4-yr field experiment in the northern Great Plains (NGP) of North America, where current N deposition levels range from ~3 to 9kg N·ha-1 ·yr-1 , we added 12 levels of N, from 2.5 to 100kg N·ha-1 ·yr-1 , to three sites spanning a range of soil fertility and productivity. Our results suggest a conservative critical load of 4-6kg N·ha-1 ·yr-1 for the most sensitive vegetation type we investigated, badlands sparse vegetation, a community that supports plant species adapted to low fertility conditions, where N addition at this rate increased productivity and litter load. In contrast, for the two more productive vegetation types characteristic of most NGP grasslands, a critical load of 6-10kg N·ha-1 ·yr-1 was identified. Here, N addition at this level altered plant tissue chemistry and increased nonnative species. These critical loads are below the currently suggested range of 10-25kg N·ha-1 ·yr-1 for NGP vegetation and within the range of current or near-future deposition, suggesting that N deposition may already be inducing fundamental changes in NGP ecosystems.

Ranching Sustainability in the Northern Great Plains: An Appraisal of Local Perspectives

On the Ground • In eight counties in Montana, South Dakota, and Nebraska characterized by high levels of intact Northern Great Plains grassland habitat, ranchers observe the following sustainability challenges: • Land prices and lack of land for purchase • Profitability • Family succession and community change (depopulation) • Notably, they do not anticipate extensive cropland conversion in the western edge of the Northern Great Plains. • We observed differences in the experience of these challenges based on the ranch ownership lifecycle. • In response, we recommend that conservation and government programs focused on sustainable ranching should adopt a framework for strategy and program evaluated based on the lifecycle framework. • Assisting emerging ranchers, according to this research effort, will demand more than coming up with loan funds or extra forage. Rather it will mean rethinking the existing pathway that operators follow on the route from emerging to established ranchers. • In addition, conservation and government programs and future research should address the impacts and patterns of land agglomeration in the Northern Great Plains.

Woody Encroachment in Northern Great Plains Grasslands: Perceptions, Actions, and Needs

ABSTRACT: The United States Northern Great Plains (NGP) has a high potential for landscape-scale conservation, but this grassland landscape is threatened by encroachment of woody species. We surveyed NGP land managers to identify patterns in, and illustrate a broad range of, individual managers' perceptions on (1) the threat of woody encroachment to grasslands they manage, and (2) what management practices they use that may influence woody encroachment in this region. In the 34 surveys returned, which came from predominantly public lands in the study area, 79% of responses reported moderate or substantial woody encroachment. Eastern redcedar (Juniperus virginiana) and Rocky Mountain juniper (Juniperus scopulorum) were the most problematic encroachers. Thirty-one survey respondents said that prescribed fire was used on the lands they manage, and 64% of these responses reported that controlling woody encroachment was a fire management objective. However, only 18% of survey respondents using prescribed fire ...

Soil organic carbon, nitrogen and phosphorus thirteen years after abruptly disturbing Northern Great Plains grassland

Thirteen years after cultivating native grassland and establishing continuous wheat (Triticum aestivum L.) and wheat–fallow rotations in southern Alberta, surface soil total N levels were 15% lower, and nitrate (60–90 cm) concentrations were 2.5- and 17-fold greater, than native grassland. Wheat–fallow, even without fertilization, markedly enhanced potential nitrate loss through the root zone.

Grazing improves C and N cycling in the Northern Great Plains: a meta-analysis.

Grazing potentially alters grassland ecosystem carbon (C) and nitrogen (N) storage and cycles, however, the overall direction and magnitude of such alterations are poorly understood on the Northern Great Plains (NGP). By synthesizing data from multiple studies on grazed NGP ecosystems, we quantified the response of 30 variables to C and N pools and fluxes to grazing using a comprehensive meta-analysis method. Results showed that grazing enhanced soil C (5.2 ± 4.6% relative) and N (11.3 ± 9.1%) pools in the top layer, stimulated litter decomposition (26.8 ± 18.4%) and soil N mineralization (22.3 ± 18.4%) and enhanced soil NH4+ (51.5 ± 42.9%) and NO3− (47.5 ± 20.7%) concentrations. Our results indicate that the NGP grasslands have sequestered C and N in the past 70 to 80 years, recovering C and N lost during a period of widespread grassland deterioration that occurred in the first half of the 20th century. Sustainable grazing management employed after this deterioration has acted as a critical factor for C and N amelioration of degraded NGP grasslands and about 5.84 Mg C ha−1 CO2-equivalent of anthropogenic CO2 emissions has been offset by these grassland soils.

Preserving prairies: understanding temporal and spatial patterns of invasive annual bromes in the Northern Great Plains

AbstractTwo Eurasian invasive annual brome grasses, cheatgrass (Bromus tectorum) and Japanese brome (Bromus japonicus), are well known for their impact in steppe ecosystems of the western United States where these grasses have altered fire regimes, reduced native plant diversity and abundance, and degraded wildlife habitat. Annual bromes are also abundant in the grasslands of the Northern Great Plains (NGP), but their impact and ecology are not as well studied. It is unclear whether the lessons learned from the steppe will translate to the mixed‐grass prairie where native plant species are adapted to frequent fires and grazing. Developing a successful annual brome management strategy for National Park Service units and other NGP grasslands requires better understanding of (1) the impact of annual bromes on grassland condition; (2) the dynamics of these species through space and time; and (3) the relative importance of environmental factors within and outside managers' control for these spatiotemporal dynamics. Here, we use vegetation monitoring data collected from 1998 to 2015 in 295 sites to relate spatiotemporal variability of annual brome grasses to grassland composition, weather, physical environmental characteristics, and ecological processes (grazing and fire). Concern about the impact of these species in NGP grasslands is warranted, as we found a decline in native species richness with increasing annual brome cover. Annual brome cover generally increased over the time of monitoring but also displayed a 3‐ to 5‐yr cycle of reduction and resurgence. Relative cover of annual bromes in the monitored areas was best predicted by park unit, weather, extant plant community, slope grade, soil composition, and fire history. We found no evidence that grazing reduced annual brome cover, but this may be due to the relatively low grazing pressure in our study. By understanding the consequences and patterns of annual brome invasion, we will be better able to preserve and restore these grassland landscapes for future generations.

Application of the photosynthetic light-use efficiency model in a northern Great Plains grassland

Abstract The light-use efficiency (LUE) model of photosynthesis is widely used to estimate ecosystem photosynthesis and net primary production from remote sensing measurements. The fraction of absorbed photosynthetically active radiation ( f APAR ) is a dominant term in this model, and it is fundamentally important for model calculations of ecosystem productivity across large areas. The LUE term is sometimes considered a constant, but may be best represented as a variable scalar under stress conditions. The main objective of this study was to better understand factors influencing f APAR , its relationship with seasonal variation in canopy greenness (Normalized Difference Vegetation Index (NDVI)), and the consequences of potential seasonal changes in the NDVI- f APAR relationship for LUE model calculations of ecosystem photosynthesis in a semi-arid grassland. We used two approaches to determine f APAR , (i) direct incoming and outgoing radiation measurements above and below the canopy, and (ii) an inversion approach based on incident photosynthetically active radiation and the light response curve of net ecosystem productivity measured by eddy covariance at low light levels. The two approaches resulted in f APAR values that were very strongly correlated during the initial development of the canopy until peak leaf area index (LAI) was reached. During this time, a strong linear relationship also occurred between f APAR and NDVI calculated from spectral reflectance measurements of the grassland canopy. After peak LAI, there was hysteresis in the NDVI– f APAR relationship, and the two f APAR estimates diverged. Light-use efficiency model calculations of ecosystem photosynthesis made using f APAR values were strongly correlated with chamber CO 2 exchange measurements during the initial development of the canopy leaf area. After peak LAI, a stress function, based on either soil moisture or vapour pressure deficit (VPD) measurements, was necessary to reduce quantum yield and model calculations of ecosystem photosynthesis during periods of relatively low soil moisture and higher VPD later in the growing season. Both stress functions were similarly effective in improving the correlation between modeled and measured ecosystem photosynthesis values, and indicated reduced LUE under late season conditions. Modulating LUE based on the Photochemical Reflectance Index or the Water Band Index (both proposed as possible indicators of LUE) was not effective to improve the correlation between modeled and measured ecosystem photosynthesis values in this ecosystem.

Response of plant biomass and soil respiration to experimental warming and precipitation manipulation in a Northern Great Plains grassland

The interacting effects of altered temperature and precipitation are expected to have significant consequences for ecosystem net carbon storage. Here we report the results of an experiment that evaluated the effects of elevated temperature and altered precipitation, alone and in combination, on plant biomass production and soil respiration rates in a northern Great Plains grassland, near Lethbridge, Alberta Canada. Open-top chambers and rain shelters were used to establish an experiment in 2011 with two temperature treatments (warmed and control), each combined with three precipitation treatments (minus 50%, ambient (no manipulation), and plus 50%). A smaller experiment with only the two temperature treatments was conducted in 2012, a year with less rain than 2011. Our objectives were to determine the sensitivity of plant biomass production and soil respiration to temperature and moisture manipulations, and to test for direct and indirect effects of the environmental changes on soil respiration rates. The experimental manipulations resulted primarily in a significant increase in air temperature in the warmed treatment. There were no significant temperature or precipitation treatment effects on soil moisture content. Aboveground biomass was not significantly affected by the experimental manipulations, but the warmed plots of the ambient precipitation treatment showed an increase in root biomass relative to the control plots in 2011. The warmed treatment increased the cumulative loss of carbon in soil respiration (July–September) compared to the control by 497gCm−2 during 2011, and by 185gCm−2 during 2012. This higher soil respiration rate in both years was not directly caused by significant differences among treatments in soil temperature or soil moisture, but was likely an indirect result of increased carbon substrate availability in the warmed relative to the control treatment.

Interacting controls on productivity in a northern Great Plains grassland and implications for response to ENSO events

In this study we investigated the causes of annual variability in peak aboveground biomass production, net ecosystem productivity (NEP) and gross ecosystem productivity (GEP) during an 8-year period (1999–2006) in a northern Great Plains grassland near Lethbridge, Alberta, Canada. In particular, we tested for a significant relationship between growing season precipitation and productivity and determined whether soil moisture carry-over from the previous fall–winter could alter this relationship. We also investigated the interaction between soil moisture availability and temperature in controlling grassland productivity. There was a very strong correlation between total precipitation input and average soil moisture content during the May–October growing season. However, the growing season average soil moisture contents in 2003 and 2006 were very similar to those recorded in 1999, despite lower than normal precipitation occurring in these 2 years. This resulted from a positive difference between precipitation and evapo-transpiration that allowed significant soil moisture to be carried-over from the previous fall–winter during both 2003 and 2006. Strong logistic relationships were observed between soil moisture and annual productivity based on data from all years except 2003 and 2006, years which had higher productivity than was predicted from the logistic regression. Interaction between temperature and soil moisture explained this difference. Productivity values in 2003 and 2006 were high compared with 1999, a year with approximately the same soil moisture content, and this resulted from the higher average growing season temperatures that were apparent in 2003 and 2006. Analysis of weather records indicated that precipitation in the month of June was significantly higher during El Niño years than during La Niña years in Lethbridge. During the study period, aboveground biomass, NEP and GEP were generally higher in El Niño years and lower in La Niña years because of associated variation in summer precipitation.

Plant Richness-Biomass Relationships in Restored Northern Great Plains Grasslands (USA)

We investigated plant richness-biomass relationships in tall grass (Field 1, 12 years) and mixed grass (Field 2, 5 years) restoration experiments located in the northern Great Plains grasslands (USA). They were organized as randomized factorial experiments with fertilization rates (N or P) and number of species as factors. Results were as follows: (1) above ground biomass (AGB) increased and year-to-year variability declined with plant species and functional form richness. (2) AGB was higher when the species had various combinations: (a) high relative growth rates, root density, root surface area, N or P uptake rates, and N use efficiency; (b) low root-to-shoot ratio and root plasticity. (3) Biomass stability was positively related to high root surface area in Field 1 and N use efficiency and P uptake rates in Field 2. (4) Invasion of nonseeded species declined with plant species and functional form richness.

Factors Affecting Revegetation of Oil Field Access Roads in Semiarid Grassland

We assessed vegetation recovery on access roads removed after well abandonment in an active oil‐producing region of northern Great Plains grasslands. We compared extant vegetation on 58 roads, restored 3–22 years previously, to records of species seeded on each and to adjacent, undisturbed prairie, to evaluate main differences between the restored and adjacent community and to explore patterns in the restored plant community over time. The restored plant community was dominated by low richness of seeded non‐native and native grasses and forbs, whereas adjacent prairie had numerous, abundant native graminoids and shrubs and higher richness of native forbs. Cover of seeded species on roads was double that of colonizing species. Disparity in cover of dominant native grasses between the adjacent community and relatively narrow restored roadway suggests that conditions for germination and survival in roadbeds are poor. This is at least partly due to persistence of seeded species. Differences in restored plant composition over time were best explained by changes in species seeded, from non‐natives to natives, and secondarily by successional shifts from ruderal to perennial non‐seeded species. Of the 30 species seeded at least once on these roads, only 10 were commonly used. The long‐term influence of seeding choices in grassland road restorations implies that improvements in these practices will be critical to reversing ecological impacts of roads.