Invading species can extinguish native plants despite recent reports

Seed Daily via SPX: Ecologists at the University of Toronto and the Swiss Federal Institute of Technology Zurich (ETH Zurich) have found that, given time, invading exotic plants will likely eliminate native plants growing in the wild despite recent reports to the contrary.

A study published in Proceedings of the National Academy of Sciences (PNAS) reports that recent statements that invasive plants are not problematic are often based on incomplete information, with insufficient time having passed to observe the full effect of invasions on native biodiversity.

"The impacts of exotic plant invasions often take much longer to become evident than previously thought," says Benjamin Gilbert of U of T's Department of Ecology and Evolutionary Biology (EEB) and lead author of the study. "This delay can create an 'extinction debt' in native plant species, meaning that these species are slowly going extinct but the actual extinction event occurs hundreds of years after the initial invasion."

Much of the debate surrounding the threat posed to biodiversity by the invasions of non-native species is fueled by recent findings that competition from introduced plants has driven remarkably few plant species to extinction. Instead, native plant species in invaded ecosystems are often relegated to patchy, marginal habitats unsuitable to their nonnative competitors....

Crows on a cross at Pere Lachaise cemetery in Paris, with an invasive ailanthus in the background, shot by jphilipg, Wikimedia Commons via Flickr,  under the Creative Commons Attribution 2.0 Generic license

Pythons, lionfish and now willow invade Florida's waterways

University of Central Florida: Foreign invaders such as pythons and lionfish are not the only threats to Florida’s natural habitat. The native Carolina Willow is also starting to strangle portions of the St. Johns River.

Biologists at the University of Central Florida recently completed a study that shows this slender tree once used by Native Americans for medicinal purposes, may  be thriving because of water-management projects initiated in the 1950s. Canals were built to control  runoff and provide water for agriculture. The unintended consequence — stable water levels — allowed Carolina Willow to spread and thrive.

They now cover thousands of acres. Willows form impenetrable thickets that prevent boating and eliminate duck habitat. Willow thickets also use tremendous amounts of water, leaving less available for wildlife and people. The findings were published today in Restoration Ecology,  the peer-reviewed journal of the Society for Ecological Restoration. The St. Johns Water Management District funded the study.

While the trees previously were kept in check by natural annual flooding, they can now be found thriving in wetlands, swamps and marshes. Some trees grow as tall as 35 feet. The leaves of the tree contain salicin, which is the compound behind the pain-relieving effect of salicylic acid found in aspirin.

UCF professors Pedro F. Quintana-Ascencio and John Fauth worked with Kimberli Ponzio and Dianne Hall, scientists from the St. Johns River Water Management District, to run experiments that found ways to control the willow, which is taking over marshes in the upper St. Johns River basin....

St. John's River near Orange City, Florida, shot by Mwanner, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Invasive plant species may harm native grasslands by changing soil composition

Newswise: The future landscape of the American Midwest could look a lot like the past—covered in native grasslands rather than agricultural crops. This is not a return to the past, however, but a future that could depend on grasslands for biofuels, grazing systems, carbon sequestration, and other ecosystem services. A major threat to this ecosystem is an old one—weeds and their influence on the soil.

According to a study in the journal Invasive Plant Science and Management, when invasive plants spread, they can leave behind a “legacy” of alteration in the native soil. Even after an invading species has been controlled, its effects can inhibit the regrowth of native plant species. The causes of this process are still being investigated and may involve changes in soil food webs, soil microbial communities, and mutualistic fungi.

In the study, researchers tested soil conditions for changes in composition after three growth cycles of invasive plant species. Researchers looked for changes in colonization rates, diversity, and composition of arbuscular-mycorrhizal fungi (AMF).

Three exotic plant species—crested wheatgrass, smooth brome, and leafy spurge—were tested in a glasshouse experiment. These plants, all characterized as strong invaders, were grown in native soil collected from North Dakota grasslands. Native species, including western wheatgrass, little bluestem, and blue gramma, were also grown, and after three growth cycles, soil composition was compared among these treatments....

Grasslands in Inner Mongolia, shot by Shizhao, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Tracking invasive cheatgrass role in larger, more frequent Western fires

PhysOrg: New research that relied in part on satellite images suggests that cheatgrass, an invasive species brought west by settlers in the 1800s, is one cause for the larger, hotter and more frequent range fires experienced recently in the Great Basin of the American West. The arid region covers about 230,000 square miles (600,000 km) over much of Nevada and parts of Utah, Colorado, Idaho, California and Oregon.

Bethany Bradley, a biogeographer at the University of Massachusetts Amherst, brought her expertise in remote sensing and spatial analysis to the study, which was led by fire expert Jennifer Balch of Penn State University.

Bradley used data from NASA's Moderate Resolution Imaging Spectoradiometer from 2000 to 2009 to detect burned areas to create the first land cover map for the Great Basin area. With it, the two researchers and their colleagues combined data sets, matched fire dates and perimeters with land cover data to reach their conclusions, reported in the current online edition of Global Change Biology.

Bradley, Balch and colleagues say that over the past 10 years, cheatgrass fueled most of the largest fires, influencing 39 of the largest 50. Also, fires in grass-covered lands were on average significantly larger than the average fire size on lands dominated by other types of vegetation such as pinyon-juniper, montane shrubland and cultivated areas. Data also suggest that cheatgrass plays a role in more frequent fires.

"From 2000 to 2009, cheatgrass burned twice as much as any other vegetation," Balch says. "Although this result has been suspected by managers for decades," the authors note, "this study is the first to document recent cheatgrass-driven fire regimes at a regional scale."...

A 2007 fire outside San Diego, US Navy photograph