Edward A. Vasquez

Salt tolerance and osmotic adjustment of Spartina alterniflora (Poaceae) and the invasive M haplotype of Phragmites australis (Poaceae) along a salinity gradient.

An invasive variety of Phragmites australis (Poaceae, common reed), the M haplotype, has been implicated in the spread of this species into North American salt marshes that are normally dominated by the salt marsh grass Spartina alterniflora (Poaceae, smooth cordgrass). In some European marshes, on the other hand, Spartina spp. derived from S. alterniflora have spread into brackish P. australis marshes. In both cases, the non-native grass is thought to degrade the habitat value of the marsh for wildlife, and it is important to understand the physiological processes that lead to these species replacements. We compared the growth, salt tolerance, and osmotic adjustment of M haplotype P. australis and S. alterniflora along a salinity gradient in greenhouse experiments. Spartina alterniflora produced new biomass up to 0.6 M NaCl, whereas P. australis did not grow well above 0.2 M NaCl. The greater salt tolerance of S. alterniflora compared with P. australis was due to its ability to use Na(+) for osmotic adjustment in the shoots. On the other hand, at low salinities P. australis produced more shoots per gram of rhizome tissue than did S. alterniflora. This study illustrates how ecophysiological differences can shift the competitive advantage from one species to another along a stress gradient. Phragmites australis is spreading into North American coastal marshes that are experiencing reduced salinities, while Spartina spp. are spreading into northern European brackish marshes that are experiencing increased salinities as land use patterns change on the two continents.

Nitrogen Enhances the Competitive Ability of Cheatgrass (Bromus tectorum) Relative to Native Grasses

Abstract Invasion by cheatgrass and the associated high fire frequency can displace native plant communities from a perennial to an annual grass driven system. Our overall objective of this study was to determine the potential to favor desired native perennial bunchgrasses over annual grasses by altering plant available mineral nitrogen (N). In the first study, we grew cheatgrass and three native bunch grasses (native grasses were combined in equal proportions) in an addition series experimental design and applied one of three N treatments (0, 137, and 280 mg N/kg soil). Regression models were used to derive the effects of intra- and interspecific competition on individual plant yield of cheatgrass and the native bunch grasses (combined). In our second study, we compared the absolute growth rate of the four plant species grown in isolation in a randomized complete block design for 109 days under the same soil N treatments as the competition study. Predicted mean average weight of isolated individuals increased with increasing soil N concentrations for both cheatgrass and the three native perennials (P < 0.05). Biomass of cheatgrass and its competitive ability increased with increasing soil N concentrations (P < 0.0001) compared to the combined native bunchgrasses. However, the greatest resource partitioning occurred at the 137 mg N/kg soil N treatment compared to the 0 (control) and 280 mg N/kg soil treatments, suggesting there may be a level of N that minimizes competition. In the second study, the absolute growth of cheatgrass grown in isolation also increased with increasing N levels (P  =  0.0297). Results and ecological implications of this study suggest that increasing soil N leads to greater competitive ability of cheatgrass, and that it may be possible to favor desired plant communities by modifying soil nutrient levels. Nomenclature: Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) A. Love PSSP6; Idaho fescue, Festuca idahoensis Elmer FEID; needle and thread, Hesperostipa comata (Trin. and Rupr.) Barkworth HECO26; cheatgrass, Bromus tectorum L BRTE.

Applying Ecologically Based Invasive-Plant Management

Abstract The need for a unified mechanistic ecological framework that improves our ability to make decisions, predicts vegetation change, guides the implementation of restoration, and fosters learning is substantial and unmet. It is becoming increasingly clear that integrating various types of ecological models into an overall framework has great promise for assisting decision making in invasive-plant management and restoration. Overcoming barriers to adoption of ecologically based invasive-plant management will require developing principles and integrating them into a useful format so land managers can easily understand the linkages among ecological processes, vegetation dynamics, management practices, and assessment. We have amended a generally accepted and well-tested successional management framework into a comprehensive decision tool for ecologically based invasive-plant management (EBIPM) by 1) using the Rangeland Health Assessment to identify ecological processes in need of repair, 2) amending our framework to include principles for repairing ecological processes that direct vegetation dynamics, and 3) incorporating adaptive management procedures to foster the acquisition of new information during management. This decision tool provides a step-by-step planning process that integrates assessment and adaptive management with process-based principles to provide management guidance. In our case-study example, EBIPM increased the chance of restoration success by 66% over traditionally applied integrated weed management in an invasive-plant–dominated ephemeral wetland ecosystem. We believe that this framework provides the basis for EBIPM and will enhance our ability to design and implement sustainable invasive-plant management and restoration programs.

Creating Invasion Resistant Soils via Nitrogen Management

Abstract Invasion by annual grasses, such as cheatgrass, into the western U.S. sagebrush-steppe is a major concern of ecologists and resource managers. Maintaining or improving ecosystem health depends on our ability to protect or re-establish functioning, desired plant communities. In frequently disturbed ecosystems, nutrient status and the relative ability of species to acquire nutrients are important drivers of invasion, retrogression, and succession. Thus, these processes can potentially be modified to direct plant community dynamics toward a desired plant community. The overall objective of this review paper is to provide the ecological background of invasion by exotic plants and propose a concept to facilitate the use of soil nitrogen (N) management to achieve desired plant communities that resist invasion. Based on the literature, we propose a model that predicts the outcome of community dynamics based on N availability. The model predicts that at low N levels, native mid- and late-seral species are able to successfully out-compete early-seral and invasive annual species up to some optimal level. However, at some increased level of N, early-seral species and invasive annual grasses are able to grow and reproduce more successfully than native mid- and late-seral species. At the high end of N availability to plants, the community is most susceptible to invasion and ultimately, increased fire frequency. Soil N level can be managed by altering microbial communities, grazing, mowing, and using cover crops and bridge species during restoration. In these cases, management may be more sustainable since the underlying cause of invasion and succession is modified in the management process. Nomenclature: Cheatgrass, Bromus tectorum L. BROTE.

Principles for Ecologically Based Invasive Plant Management

Abstract Land managers have long identified a critical need for a practical and effective framework for designing restoration strategies, especially where invasive plants dominate. A holistic, ecologically based, invasive plant management (EBIPM) framework that integrates ecosystem health assessment, knowledge of ecological processes, and adaptive management into a successional management model has recently been proposed. However, well-defined principles that link ecological processes that need to be repaired to tools and strategies available to managers have been slow to emerge, thus greatly limiting the ability of managers to easily apply EBIPM across a range of restoration scenarios. The broad objective of this article is to synthesize current knowledge of the mechanisms and processes that drive plant community succession into ecological principles for EBIPM. Using the core concepts of successional management that identify site availability, species availability, and species performance as three general drivers of plant community change, we detail key principles that link management tools used in EBIPM to the ecological processes predicted to influence the three general causes of succession. Although we acknowledge that identification of principles in ecology has greatly lagged behind other fields and recognize that identification of ecological principles and the conditions in which they hold are still being developed, we demonstrate how current knowledge and future advances can be used to structure a holistic EBIPM framework that can be applied across a range of restoration scenarios.

Using rangeland health assessment to inform successional management.

Abstract Rangeland health assessment provides qualitative information on ecosystem attributes. Successional management is a conceptual framework that allows managers to link information gathered in rangeland health assessment to ecological processes that need to be repaired to allow vegetation to change in a favorable direction. The objective of this paper is to detail how these two endeavors can be integrated to form a holistic vegetation management framework. The Rangeland Health Assessment procedures described by Pyke et al. (2002) and Pellant et al. (2005) currently are being adopted by land managers across the western United States. Seventeen standard indicators were selected to represent various ecological aspects of ecosystem health. Each of the indicators is rated from extreme to no (slight) departure from the Ecological Site Description and/or the Reference Area(s). Successional management identifies three general drivers of plant community change: site availability, species availability, and species performance, as well as specific ecological processes influencing these drivers. In this paper, we propose and provide examples of a method to link the information collected in rangeland health assessment to the successional management framework. Thus, this method not only allows managers to quantify a point-in-time indication of rangeland health but also allows managers to use this information to decide how various management options might influence vegetation trajectories. We argue that integrating the Rangeland Health Assessment with Successional Management enhances the usefulness of both systems and provides synergistic value to the decision-making process. Interpretive Summary: Integrating the Rangeland Health Assessment with Successional Management enhances the usefulness of both systems and provides synergistic value to the decision-making process. Successional management provides a science-based management system based on the causes of vegetation dynamics. Rangeland Health Assessment provides a method for determining which causes of succession are most likely directing dynamics, and leads managers to those ecological processes most likely in need of repair. Thus, management can be tailored to specially address those causes and processes with the highest probability of directing vegetation on a favorable trajectory. Besides the clear economic advantage of lower management inputs associated with using the rangeland health assessment to identify which primary causes of succession are most likely directing dynamics, integrating Rangeland Health Assessment also has the advantage of avoiding unnecessary management inputs and has the additional advantage of minimizing unintended negative impacts on ecological processes.

Landscape-scale rehabilitation of medusahead (Taeniatherum caput-medusae)-dominated sagebrush steppe.

Abstract Producers facing infestations of invasive annual grasses regularly voice the need for practical revegetation strategies that can be applied across broad landscapes. Our objective was to determine the potential for scaling up the single-entry approach for revegetating medusahead-infested rangeland to broader, more heterogeneous landscape-scale revegetation of winter annual grass–infested rangeland. We hypothesized, when applied on a highly variable landscape scale, the combination of imazapic and seeding would provide highest abundance of perennial grasses and lowest amount of annual grasses. Treatments included a control, seeding of crested wheatgrass (‘Hycrest’) and Sandbergs bluegrass, spraying (60 g ai ha−1 imazapic), and a simultaneously applied combination of spraying and seeding. The HyCrest and Sandbergs bluegrass seeding rates were 19 and 3.4 kg ha−1, respectively. The treatments were applied to large plots (1.4 to 8 ha) and replicated five times, with each replication located in different watersheds throughout southeastern Oregon. This study shows that the single-entry approach can be scaled up to larger landscapes, but variation within establishment areas will likely be high. This procedure should reduce the costs over multientry treatment applications and make revegetating annual grass–infested rangeland across landscapes more affordable. Nomenclature: Imazapic, medusahead, Taeniatherum caput-medusae (L.) Nevski, crested wheatgrass, Agropyron cristatum (L.) Gaertn. × Agropyron desertorum Gaertn. ‘Hycrest’, Sandbergs bluegrass, Poa secunda J.S. Presl Management Implications: Managing invasive annual grass infestations on a large scale remains a major impediment for successful rangeland restoration. The high cost of treatments and low percentage of success often keep managers from initiating management plans where large-scale infestations are present. In this experiment, we utilized a single-entry treatment of herbicide application and seeding on landscape-scale plots of medusahead- and cheatgrass-infested rangeland. We were interested in determining whether this method would provide acceptable levels of control for the invasive grasses and establishment of desired species. Our results suggest that the one-pass system might be a suitable method for restoring invasive annual grass infestations and lower the cost of treatment by completing an herbicide application and seeding in a single entry into the field.

Functional Group Responses to Reciprocal Plant Litter Exchanges between Native and Invasive Plant Dominated Grasslands

Abstract Manipulating plant litter to direct successional trajectories is rarely considered as a management strategy. Our objective was to determine the influence of litter from an intact native plant community on a community dominated by an invasive species within the same habitat type as well as the influence of litter from a community dominated by an invasive species on an intact native plant community. We hypothesized that litter amount, type (source), and fragment size would influence various functional groups within a native plant community differently than within a weed-dominated plant community. We used reciprocal plant litter exchanges between native and invasive plant–dominated grasslands to gain an initial understanding of litters influence on the density and biomass of native grasses, native forbs, common St. Johnswort, and downy brome. Common St. Johnswort was not influenced by any treatment. Native grass density increased with application of low (454 g/m2) amounts of litter where the grasses were subordinate to common St. Johnswort, and adding native plant litter to the weedy site nearly doubled native grass biomass. Low amounts of finely fragmented litter and high amounts of coarse litter induced native forbs to produce about twice the biomass as found in the non–litter-amended controls. Our study suggests that plant litter may be a component of vegetation that can be managed to shift the plant community toward those plants that are desired. Nomenclature: Downy brome, Bromus tectorum L., common St. Johnswort, Hypericum perforatum L.

Invasive Plants on Rangelands: A Global Threat

he Rangeland Invasive Species Committee is a diverse group who seek to serve the SRM and the public by focusing attention, sharing knowl-edge, and communicating about rangeland inva-sive species. As a committee, we envision that the joint meeting of SRM and Weed Science Society of America in 2010 will provide an ideal opportunity to sponsor a special issue of