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.

A distinct, non-native haplotype of the common reed Phragmites australis has become invasive in Atlantic coastal Spartina marshes. We compared the salt tolerance and other growth characteristics of the invasive M haplotype with 2 native haplotypes (F and AC) in greenhouse experiments. The M haplotype retained 50% of its growth potential up to 0.4 M NaCl, whereas the F and AC haplotypes did not grow above 0.1 M NaCl. The M haplotype produced more shoots per gram of rhizome tissue and had higher relative growth rates than the native haplotypes on both freshwater and saline water treatments. The M haplotype also differed from the native haplotypes in shoot water content and the biometrics of shoots and rhizomes. The results offer an explanation for how the M haplotype is able to spread in coastal salt marshes and support the conclusion of DNA analyses that the M haplotype is a distinct ecotype of P. australis. KEY WORDS: Salinity tolerance · Invasive species · Phragmites australis · Salt marshes Resale or republication not permitted without written consent of the publisherThe invasive, M haplotype of Phragmites australis overtopping the shorter, lighter green native form in the Delaware Estuary, USA. The M haplotype, a distinct variety introduced from Europe, has greater salt tolerance and greater ability to generate new shoots from rhizomes than native haplotypes.

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 5 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.

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.

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. Resumen Existe una necesidad sustancial e insatisfecha de un marco ecológico unificado y mecanístico que mejore nuestra habilidad para tomar decisiones y predecir cambios en la vegetación, que guie la implementación de acciones de restauración, y que promueva el aprendizaje. Resulta cada vez más claro que la integración de varios tipos de modelos ecológicos dentro de un macro general tiene un futuro promisorio en la toma de decisiones para el manejo y la restauración de áreas afectadas por plantas invasoras. La superación de las barreras que obstaculizan la adopción de pautas de manejo ecológicas de plantas invasoras requerirá el desarrollo de principios cuya integración en un formato útil permitirá a los decisores entender fácilmente las conexiones entre procesos ecológicos, la dinámica de la vegetación, las prácticas de manejo y la evaluación. Hemos actualizado un marco de manejo de sucesión ampliamente aceptado y corroborado y lo hemos transformado en una herramienta exhaustiva para el Manejo Ecológico de Plantas Invasoras (EBIPM) mediante 1) el uso de la Evaluación del Estado de Salud del Pastizal para identificar procesos ecológicos que requieren reparación, 2) la inclusión de principios para reparar procesos ecológicos que dirigen la dinámica de la vegetación, y 3) l...