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Invasion by Tamarix (L.) can severely alter riparian areas of the western U.S., which are globally rare ecosystems. The upper Verde River, Arizona, is a relatively free-flowing river and has abundant native riparian vegetation. Tamarix is present on the upper Verde but is a minor component of the vegetation (8% of stems). This study sought to determine whether riparian vegetation characteristics differed between sites where Tamarix was present and sites where Tamarix was absent during the invasion of the upper Verde. We hypothesized that herbaceous understory and woody plant communities would differ between Tamarix present and absent sites. Our hypothesis was generally confirmed, the two types of sites were different....
Concern about spread of non-native riparian trees in the western USA has led to Congressional proposals to accelerate control efforts. Debate over these proposals is frustrated by limited knowledge of non-native species distribution and abundance. We measured abundance of 44 riparian woody plants at 475 randomly selected stream gaging stations in 17 western states. Our sample indicates that Tamarix ramosissima and Elaeagnus angustifolia are already the third and fourth most frequently occurring woody riparian plants in the region. Although many species of Tamarix have been reported in the region, T. ramosissima (here including T. chinensis and hybrids) is by far the most abundant. The frequency of occurrence of...
Alien plants invade many ecosystems worldwide, often having substantial negative effects on ecosystem structure and functioning. The apparent complexity of invasions has impaired the development of a predictive framework of alien plant spread. Such a framework requires both a conceptual understanding of the ecology of invasions and appropriate modelling tools. We demonstrate, using a simple conceptual model and illustrative examples from the literature, that a predictive understanding of invasions can be established. Potential modelling tools are reviewed by categorizing models of plant spread as either simple-demographic, spatial-phenomenological or spatial-mechanistic, based on the model's data inputs and outputs....
Biological invasions are a threat to ecosystems across all biogeographical realms. Riparian habitats are considered to be particularly prone to invasion by alien plant species and, because riparian vegetation plays a key role in both aquatic and terrestrial ecosystems, research in this field has increased. Most studies have focused on the biology and autecology of invasive species and biogeographical aspects of their spread. However, given that hydrogeomorphological processes greatly influence the structure of riparian plant communities, and that these communities in turn affect hydrology and fluvial geomorphology, scant attention has been paid to the interactions between invasions and these physical processes....
Aim The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long-term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass-dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods At two sites in...
Alien invasions typically reduce species richness of habitats, but few studies have examined their effects on species turnover, the difference in species composition between localities. Agropyron cristatum (L.) Gaertn. (crested wheat grass) has been planted on 6?10 million ha of North American prairie, and is invading native prairie. We studied the invasion of A. cristatum into native prairie by measuring species composition along a gradient from maximum to minimum A. cristatum abundance. As A. cristatum increased, the abundance of most common native species decreased, but one appeared to be unaffected (Bouteloua gracilis (H.B.K.) Lag.), and another (Poa sandbergii Vasey) increased. The effect of A. cristatum on...
Aim Biological invasions facilitate ecosystem transformation by altering the structure and function, diversity, dominance and disturbance regimes. A classic case is the grass–fire cycle in which grass invasion increases the frequency, scale and/or intensity of wildfires and promotes the continued invasion of invasive grasses. Despite wide acceptance of the grass–fire cycle, questions linger about the relative roles that interspecific plant competition and fire play in ecosystem transformations.Location Sonoran Desert Arizona Upland of the Santa Catalina Mountains, Arizona, USA.Methods We measured species cover, density and saguaro (Carnegiea gigantea) size structure along gradients of Pennisetum ciliare invasion...
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Predicting suitable habitat and the potential distribution of invasive species is a high priority for resource managers and systems ecologists. Most models are designed to identify habitat characteristics that define the ecological niche of a species with little consideration to individual species’ traits. We tested five commonly used modelling methods on two invasive plant species, the habitat generalist Bromus tectorum and habitat specialist Tamarix chinensis, to compare model performances, evaluate predictability, and relate results to distribution traits associated with each species. Most of the tested models performed similarly for each species; however, the generalist species proved to be more difficult...
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Many studies have quantified plant invasions by determining patterns of non-native species establishment (i.e. richness and absolute cover). Until recently, dominance has been largely overlooked as a significant component of invasion. Therefore, we re-examined a 6-year data set of 323 0.1 ha plots within 18 vegetation types collected in the Grand Staircase-Escalante National Monument from 1998 to 2003, including dominance (i.e. relative cover) in our analyses. We specifically focused on the non-native species Bromus tectorum, a notable dominant annual grass in this system. We found that non-native species establishment and dominance are both occurring in species-rich, mesic vegetation types. Therefore, non-native...
Altered hydrology of southwestern United States rivers has led to a decline in native cottonwood (Populus deltoides). Areas historically dominated by cottonwood have been replaced by invasive saltcedar (Tamarix chinensis). Restoration of historic hydrology through periodic flooding of riparian areas has been a means of restoring native species. However, due to similarity in germination requirements of cottonwoods and saltcedars, flooding may create an unwanted increase in the number of saltcedar seedlings. Therefore, we evaluated competitive aspects of these co-occurring species in an extant riparian habitat in the arid southwestern US. We measured effects of competition between cottonwood and saltcedar seedlings...
Land managers require landscape-scale information on where exotic plant species have successfully established, to better guide research, control, and restoration efforts. We evaluated the vulnerability of various habitats to invasion by exotic plant species in a 100,000 ha area in the southeast corner of Grand Staircase-Escalante National Monument, Utah. For the 97 0.1-ha plots in 11 vegetation types, exotic species richness (log10) was strongly negatively correlated to the cover of cryptobiotic soil crusts (r = −0.47, P < 0.001), and positively correlated to native species richness (r = 0.22, P < 0.03), native species cover (r = 0.23, P < 0.05), and total nitrogen in the soil (r = 0.40, P < 0.001). Exotic species...
A paradox of invasion biology is that even though native species are locally adapted to environmental conditions, nonnative species without this advantage often invade. Ecologists have advanced four main theories to explain why invaders are successful in some places and not others: biotic resistance, environmental resistance, human disturbance, and natural enemies. However, none of these theories alone can account for invasions by two trout species outside their native ranges in North America. Brook trout (Salvelinus fontinalis) are able to displace native cutthroat trout (Oncorhynchus clarkii) in the inland western US, but are themselves displaced by nonnative rainbow trout (O. mykiss) in the southeastern US. An...
Variable densities of an invasive species may represent variation in invasion resistance, due to variation in resource availability. This study determined whether low- and high-density cheatgrass (Bromus tectorum L.) patches within a shadscale-bunchgrass community of western Utah, USA, can be explained by variation in resource availability. It also explored the possible role of seed limitation and enemy pressure on invasion patterns. Two parallel field experiments were conducted:(1) increasing resources within low-density cheatgrass patches and, conversely (2) reducing resources within high-density cheatgrass patches. Treatments were applied at three life stages separately and across all stages. In low-density cheatgrass...
Annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of northern mixed-grass prairie, and have been shown to alter the structure and function of prairie ecosystems, including plant biomass production and litter decomposition. To build on previous findings, our objective was to model the impact of annual brome grasses on soil organic carbon storage as a step towards forecasting ecological change. Specifically, we measured differences in carbon storage between patches dominated by annual bromes and perennial grasses, in addition to evaluating key plant functional characteristics that impact carbon storage. Using the CENTURY model, we simulated high- and low-brome vegetation based on differences...
Accurate, time dependent control options are required to halt biological invasions prior to equilibrium establishment, beyond which control efforts are often impractical. Although invasions have been successfully modeled using diffusion theory, diffusion models are typically confined to providing simple range expansion estimates. In this work, we use a Susceptible/Infected cellular automaton (CA) to simulate diffusion. The CA model is coupled with a network model to track the speed and direction of simulated invasions across heterogeneous landscapes, allowing for identification of locations for targeted control in both time and space. We evaluated the role of the location of initial establishment insofar as it affected...
Question: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi-arid ecosystems where water is a limiting resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool-season annual grass that has successfully colonized much of the U.S. Great Basin? Location: Short-grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern...
A relatively small subset of exotic plant species competitively exclude their neighbors in invaded recipient communities but coexist with neighbors in their native habitat. Allelopathy has been argued as one of the mechanisms by which such exotics may become successful invaders. Three approaches have been used to examine allelopathy as a mechanism for invasion. The traditional approach examines exotic invasives in the same way that other native plants also suspected of allelopathic activities are studied. In this approach dose, fate, and replenishment of chemicals can provide powerful evidence for allelopathic processes. The bio-geographical approach often does not provide as much mechanistic evidence for allelopathy,...
1 Most theory and empirical research on exotic invasions is based on the assumption that problematic exotics are much more abundant in the regions where they invade than in the regions where they are native. However, the overwhelming majority of studies on exotic plants have been conducted solely within the introduced range. With few exceptions, ecologists know surprisingly little about the abundance, interaction strengths and ecosystems impacts of even the best-studied exotics in their native range. 2 We argue that taking a biogeographical approach is key to understanding exotic plant invasions. On a descriptive level, unambiguous quantification of distributions and abundances of exotics in native and introduced...
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Understanding species?environment relationships is important to predict the spread of non-native species. Yellow toadflax (Linaria vulgaris Mill.) is an invasive perennial recently found in the Flat Tops Wilderness of the White River National Forest on the western slope of the Colorado Rocky Mountains. We hypothesized yellow toadflax occurrence could be predicted from easily measured site characteristics. We used logistic regression with stepwise selection to generate a model to predict yellow toadflax occurrence on a particular plot based on that site?s physical characteristics. The experimental design was a paired-plot study in two locations using circular 1,018-m2 plots. Sixty-eight plots that did not contain...
The United States National Park Service was created to protect and make accessible to the public the nation?s most precious natural resources and cultural features for present and future generations. However, this heritage is threatened by the invasion of non-native plants, animals, and pathogens. To evaluate the scope of invasions, the USNPS has inventoried non-native plant species in the 216 parks that have significant natural resources, documenting the identity of non-native species. We investigated relationships among non-native plant species richness, the number of threatened and endangered plant species, native species richness, latitude, elevation, park area and park corridors and vectors. Parks with many...
map background search result map search result map Predicting yellow toadflax infestations in the Flat Tops Wilderness of Colorado Evaluating dominance as a component of non-native species invasions Modelling invasion for a habitat generalist and a specialist plant species Predicting yellow toadflax infestations in the Flat Tops Wilderness of Colorado Modelling invasion for a habitat generalist and a specialist plant species Evaluating dominance as a component of non-native species invasions