Karin M. Kettenring

Genetic diversity, reproductive mode, and dispersal differ between the cryptic invader, Phragmites australis, and its native conspecific

Genetic diversity and reproductive mode can control whether an introduced species becomes invasive. Here we use genetic tools to compare the non-native, invasive Phragmites australis to its native conspecific, P. australis subsp. americanus, in wetlands of Utah and southern Idaho. We found striking differences in genetic structuring, population diversity, and mode of reproduction between the two lineages. Non-native P. australis exhibited substantially more genetic homogeneity among populations, greater local genet richness, greater genetic diversity among individuals, and smaller average clone size compared to the native lineage. These findings suggest that non-native P. australis relies more heavily on sexual reproduction and disperses pollen and/or seeds more widely than native P. australis. We also found no evidence of hybridization between the two lineages, nor did we find evidence of local extirpations of native by non-native P. australis based on historical collection sites we revisited. Given the ability of non-native P. australis to disperse widely by seeds, we recommend careful monitoring of critical wetland habitat to detect new non-native P. australis invasions and incorporating new practices into Phragmites management that limit sexual reproduction.

Phragmites australis management in the United States: 40 years of methods and outcomes

We reviewed all available studies on Phragmites australis management in the United States. Our results show that there is a heavy emphasis on herbicides to manage Phragmites, relative to other methods, and a lack of information on what types of plant communities establish once Phragmites is removed. Our model of Phragmites establishment and reproduction describes the invasion as a symptom of watershed-scale land use and disturbance. We advocate more holistic approaches to control and management that focus on improving water quality and minimizing human disturbance to deter future invasion and improve resilience of native plant communities.

Application of genetic diversity–ecosystem function research to ecological restoration

Summary 1. Three common goals for restoration are (i) rapid plant establishment, (ii) long-term plant persistence and (iii) restoration of functioning ecosystems. Restoration practitioners often use cultivars optimized for rapid plant establishment under highly disturbed conditions to achieve the first goal; locally adapted genotypes are championed for the second because they can be well suited for local environmental conditions. Restoring functioning ecosystems is considered a loftier goal that practitioners struggle to achieve because we lack proven techniques. 2. Similar to the demonstrated benefits of species, functional and phylogenetic diversity for ecosystem functions (EFs), recent genetic diversity (GD)–ecosystem function (EF) experiments have shown that increases in plant GD can positively influence many different EFs. Would the introduction of diverse plant genotypes of a given species into a restoration enhance ecosystem functioning and the evolutionary potential of restored populations? 3. In this review, we first examine three propagule-sourcing approaches: cultivar, local adaptation and GD. Next, we raise questions that if addressed, could help practitioners implement a GD approach in restoration: (i) How might the selection, relatedness and arrangement of genotypes be optimized to restore functioning ecosystems, (ii) How do traits that affect an EF relate to neutral or adaptive diversity, more common measures of GD and (iii) at which spatial and temporal scales does GD influence EFs in restorations? 4. Synthesis and applications. Although each propagule-sourcing approach may be best suited for a particular restoration goal, each approach may simultaneously benefit other goals. Yet cultivars and locally adapted populations that have experienced artificial and/or natural selection may not possess the levels of diversity that will confer expected benefits to different ecosystem functions. Future research should determine the relative value of each approach (or a combination of approaches) for simultaneously achieving multiple restoration goals. Restoration experiments, where plant genetic diversity (GD) is manipulated and monitored over scales relevant to restoration, could reveal the true promise of a GD approach to restoration.

Moving from a regional to a continental perspective of Phragmites australis invasion in North America

Here we describe the results of a regional comparison of introduced Phragmites australis and two other P. australis lineages found in North America. The regional similarities and differences in introduced P. australis invasion highlight the importance of continental-scale studies for decoding plant invasions.

Biotic resistance, disturbance, and mode of colonization impact the invasion of a widespread, introduced wetland grass.

Disturbance and biotic resistance are important factors driving plant invasions, but how these factors interact for plants with different modes of colonization (i.e., sexual and asexual) is unclear. We evaluated factors influencing the invasion of nonnative Phragmites australis, which has been rapidly expanding in brackish tidal wetlands in Chesapeake Bay. We conducted a survey of naturally occurring small-scale disturbances (removal of vegetation and/or sediment deposition) across four plant communities; determined the effects of small-scale disturbance and biotic resistance on P. australis seedling and rhizome emergence; and tested the effects of size and frequency of small-scale disturbances on seedling emergence and survival of transplanted seedlings. The results of our study demonstrate that the invasion window for seeds is in disturbed areas in high-marsh plant communities that flood less frequently; seedling emergence in undisturbed areas was negligible. Establishment of shoots from rhizome segments was low in all plant communities. Disturbance size and frequency had no significant impact on seed germination and seedling survival. Our findings provide evidence that small-scale within-wetland disturbances are important for the invasion of the nonnative lineage of P. australis by seeds in brackish tidal wetlands in Chesapeake Bay. Efforts to reduce disturbances, large and small, in wetlands can be used to limit P. australis invasion by seed, but invasion by rhizome is still likely to occur across many plant communities irrespective of the presence of disturbance.

Developing Adaptive Capacity to Droughts: The Rationality of Locality

The Bear River is driven by a highly variable, snow-driven montane ecosystem and flows through a drought- prone arid region of the western United States. It traverses three states, is diverted to store water in an ecologically unique natural lake, Bear Lake, and empties into the Great Salt Lake at the Bear River Migratory Bird Refuge (BRMBR). People in the Bear River Basin have come to anticipate droughts, building a legal, institutional, and engineered infrastructure to adapt to the watersheds hydrologic realities and historical legacies. Their ways of understanding linked vulnerabilities has led to what might appear as paradoxical outcomes: farmers with the most legally secure water rights are the most vulnerable to severe drought; managers at the federal Bear River Migratory Bird Refuge engage in wetland farming and make unlikely political alliances; and, increased agricultural irrigation efficiency in the Bear River Basin actually threatens the water supply of some wetlands. The rationality of locality is the key to understanding how people in the Bear River Basin have increased their adaptive capacity to droughts by recognizing their interdependencies. As the effects of climate change unfold, understanding social-ecological system linkages will be important for guiding future adaptations and enhancing resilience in ways that appropriately integrate localized ecosystem capacity and human needs.

Carex seedling emergence in restored and natural prairie wetlands

Carex species, common dominants of wet meadows and widespread in ecosystems in the northern hemisphere, seldom naturally recolonize drained wetlands following hydrologic restoration. We conducted a seedling emergence experiment with five Carex species in restored and natural prairie wetlands to determine if recolonization is limited by the suitability of conditions for seed germination and seedling emergence. Seeds were sown unstratified in the fall or spring, or stratified in the spring, and seedling emergence was monitored for two field seasons. Seedling emergence was 3–360 times higher in restored compared with natural wetlands, regardless of seed treatments. In restored wetlands, a seed dormancy breaking treatment, whether in the field (fall, unstratified seeding) or in the lab (spring, stratified seeding), was important for seedling emergence. In both restored and natural wetlands, the majority of seedlings emerged within year one compared with year two of the study, indicating the importance of initial steps to optimize seedling emergence. Restored wetlands were drier than natural wetlands but seedling emergence was generally not related to soil moisture conditions. Our findings indicate that a recolonization lag can be overcome through direct seeding of these Carex species with an emphasis on appropriate seed pretreatment and timing of sowing.

The importance of roads, nutrients, and climate for invasive plant establishment in riparian areas in the northwestern United States

Natural and anthropogenic site characteristics play a role in determining the current distribution of invasive plant species. An understanding of these characteristics can be used to prioritize areas for monitoring and control efforts and to determine appropriate management actions to lower site invasion risk. We used species distribution models to look for attributes associated with invasion and to determine the extent to which these attributes varied across a suite of species. We modeled the presence-absence of 11 invasive plant species along riparian areas in the northwestern United States using the model Random Forests. We found that climate variables were most important for predicting species distributions across the large study area and factors related to nutrients, land cover, and disturbance had moderate importance. We also found that there was a general pattern related to invasion for almost all species. Invasion was more likely to occur at hotter, drier sites near roads in unforested areas. In addition, high nutrient levels and proximity to streams with lower baseflow values also generally increased the likelihood that at least one invasive species would be present. Examining patterns across a broad range of regions can help suggest general mechanisms of invasion as well as provide region-specific management recommendations.

Adaptive Wetland Management in an Uncertain and Changing Arid Environment

Wetlands in the arid western United States provide rare and critical migratory bird habitat and constitute a critical nexus within larger social-ecological systems (SES) where multiple changing land-use and water-use patterns meet. The Bear River Migratory Bird Refuge in Utah, USA, presents a case study of the ways that wetland managers have created adaptive management strategies that are responsive to the social and hydrological conditions of the agriculture-dominated SES within which they are located. Managers have acquired water rights and constructed infrastructure while cultivating collaborative relationships with other water users to increase the adaptive capacity of the region and decrease conflict. Historically, water management involved diversion and impoundment of water within wetland units timed around patterns of agricultural water needs. In the last 20 years, managers have learned from flood and drought events and developed a long-term adaptive management plan that specifies alternative management actions managers can choose each year based on habitat needs and projected water supply. Each alternative includes habitat goals and target wetland water depth. However, wetland management adapted to agricultural return-flow availability may prove insufficient as population growth and climate change alter patterns of land and water use. Future management will likely depend more on negotiation, collaboration, and learning from social developments within the SES than strictly focusing on water management within refuge boundaries. To face this problem, managers have worked to be included in negotiations with regional water users, a strategy that may prove instructive for other wetland managers in agriculture-dominated watersheds.

Cosmopolitan Species As Models for Ecophysiological Responses to Global Change: The Common Reed Phragmites australis

Phragmites australis is a cosmopolitan grass and often the dominant species in the ecosystems it inhabits. Due to high intraspecific diversity and phenotypic plasticity, P. australis has an extensive ecological amplitude and a great capacity to acclimate to adverse environmental conditions; it can therefore offer valuable insights into plant responses to global change. Here we review the ecology and ecophysiology of prominent P. australis lineages and their responses to multiple forms of global change. Key findings of our review are that: (1) P. australis lineages are well-adapted to regions of their phylogeographic origin and therefore respond differently to changes in climatic conditions such as temperature or atmospheric CO2; (2) each lineage consists of populations that may occur in geographically different habitats and contain multiple genotypes; (3) the phenotypic plasticity of functional and fitness-related traits of a genotype determine the responses to global change factors; (4) genotypes with high plasticity to environmental drivers may acclimate or even vastly expand their ranges, genotypes of medium plasticity must acclimate or experience range-shifts, and those with low plasticity may face local extinction; (5) responses to ancillary types of global change, like shifting levels of soil salinity, flooding, and drought, are not consistent within lineages and depend on adaptation of individual genotypes. These patterns suggest that the diverse lineages of P. australis will undergo intense selective pressure in the face of global change such that the distributions and interactions of co-occurring lineages, as well as those of genotypes within-lineages, are very likely to be altered. We propose that the strong latitudinal clines within and between P. australis lineages can be a useful tool for predicting plant responses to climate change in general and present a conceptual framework for using P. australis lineages to predict plant responses to global change and its consequences.