Wetlands more vulnerable to invasives as climate changes

In the battle between native and invasive wetland plants, a new Duke University study finds climate change may tip the scales in favor of the invaders -- but it’s going to be more a war of attrition than a frontal assault.

“Changing surface-water temperatures, rainfall patterns and river flows will likely give Japanese knotweed, hydrilla, honeysuckle, privet and other noxious invasive species an edge over less adaptable native species,” said Neal E. Flanagan, visiting assistant professor at the Duke Wetland Center, who led the research.  

Increased human disturbances to watersheds and nutrient and sediment runoff into riparian wetlands over the coming century will further boost the invasive species’ advantage, the study found.

“It’s death by a thousand small cuts. Each change, on its own, may yield only a slight advantage for invasive species, but cumulatively they add up,” said co-author Curtis J. Richardson, director of the Duke Wetland Center and professor of resource ecology at Duke’s Nicholas School of the Environment.

If left unchecked, over time these change will reduce the diversity of plants found in many wetlands and could affect the wetlands’ ability to mitigate flooding, store carbon, filter out water pollution and provide habitat for native wildlife, the authors said.

The scientists published their peer-reviewed findings this week in the journal Ecological Applications.

The study, funded by the U.S. Environmental Protection Agency (EPA), is the first large-scale field experiment to simulate how future environmental changes linked to global warming and land-use change will affect plant communities in major river systems in the U.S. Southeast.

It was conducted using plant species and biomass surveys, continuous real-time measurements of water levels and water temperatures, and statistical modeling of long-term plant abundance and growing conditions at 24 riparian floodplain sites in North Carolina and Virginia over a three-year period.

The Intergovernmental Panel on Climate Change (IPCC) projects that surface-water temperatures in the Southeast will increase by 1 to 5 degrees Celsius by the year 2100. Increased evaporation will reduce surface water base flows, while a 5 percent to 30 percent increase in precipitation, mostly in the form of intense storms, will cause pulsed hydrology -- sudden, short-term rises -- in water levels.  

As these changes occur, the annual timing of when wetland soils warm up in spring will fluctuate and may no longer be synchronized with when river levels drop, Flanagan said.

This de-synchronization will affect all floodplain plants, but the natural phenotypic plasticity of invasive species allows them to adapt to it better than native species, which need both exposed soil and warmer temperatures to germinate.

As native species’ germination rates decline, invasives will move in and fill the void, their increased abundance fueled by high levels of nutrients flowing into the wetlands in runoff from upstream agriculture and other disturbances.  

"These findings underscore the need for us to better understand the interaction between climate, land use and nutrient management in maintaining the viability of native riparian plant communities," Richardson said.

“What makes this study so novel is that we used a network of natural, existing riparian wetlands to simulate the long-term impacts of IPCC-projected changes to water temperature and flow over the coming century,” Richardson added.

Eighteen of the 24 wetlands used in the study were located downriver from dams or power plants built at least 50 years ago, he said. Ten of these wetlands were classified as warm sites, because water discharged back into the river by the upstream dam or power plant was heated by steam turbines or pulled from higher in a reservoir, where water temperatures were warmer.

Eight wetlands were classified as cold sites because the upstream dams pulled their outflow water from deeper in reservoirs, where temperatures were more than 5 degrees Celsius cooler than at warm sites.

“This allowed us to simulate the effect of long-term changes in water temperatures on native and invasive species abundance,” Richardson said.  All 18 dams regulated their outflow of water, allowing the team to simulate the effects of projected lower base flow and increased storm flows. Six wetlands in the study were located on undammed rivers and served as control sites.

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What quails can teach us about the gait of dinosaurs

The motion scientists from Jena University had quails walking through a high speed X-ray installation and measured the power at work in their legs.

Motion scientists and zoologists at Jena University are studying the gait of birds. In the Proceedings of the Royal Society B the team published the first detailed analysis of the bipedal gait of quails. The scientists analyzed the effect of the birds' posture  on the movement of their legs and on their stability when they walk.

Dinosaurs did it. Human beings and monkey do it. And even birds do it. They walk on two legs. And although humans occupy a special position amongst mammals as they have two legs, the upright gait is not reserved only for humans. In the course of evolution many animals have developed the bipedal gait -- the ability to walk on two legs.

"Birds are moving forward on two legs as well, although they use a completely different technique from us humans," Dr. Emanuel Andrada from the Friedrich Schiller University in Jena (Germany) says. Human beings keep their upper bodies generally in an upright position and the body's center of gravity is directly above the legs. The bodies of birds on the other hand are horizontally forward-facing, which appears to be awkward at first glance. Hence the motion scientist analyzed -- together with colleagues -- which effect this posture has on the movement of their legs and on their stability when they walk.

To this end the team had quails walking through a high speed X-ray installation at varying speeds. While the installation monitored the movements of the animals meticulously, the scientists were able to measure the power at work in their legs. From this data, the Jena research team could develop a computer model of the whole motion sequence, which served to simulate and analyze the stability and the energy balance in connection to different gaits.

As it turned out, the birds use the so-called "grounded running" style when they move quickly -- this is a running style in which at least one leg is always touching the ground. "Even when running quickly, short periods of flight phases occur only very rarely between the individual steps," Prof. Dr. Reinhard Blickhan, Chair of Motion Science at Jena University explains. But this is extremely energy consuming for the animals because the body's center of gravity lies distinctly in front of their legs -- due to the horizontal posture. "The animals have to constantly balance out their own bodies in order to prevent falling forwards," says Blickhan.

But this huge effort is worthwhile as the researchers discovered with the help of their computer model. "Unlike the legs of humans which gather energy like two coil springs and use it directly to move forwards, the bird's legs work in addition like dampers or shock absorbers." In order to prevent falling forwards or to permanently accelerate their movement, the birds practically have to brake all the time. This happens while the bird leg is working like a spring damper: Energy is withdrawn from the leg, but the amount of energy is the same that was invested in the hip to stabilize the trunk via the turning moment.

"This apparent wasting of energy is the price for a very stable posture during locomotion, especially on an uneven terrain," Blickhan summarizes the result of this study.

After these newly presented results, the Jena researchers anticipate interesting times ahead. They also want to test the gait of other birds with the help of the computer model they developed. And the scientists even want to analyze the locomotion of dinosaurs -- the direct forebears of today's birds. "It is not clear yet how two-legged species like Allosaurus or Tyrannosaurus Rex really moved forward," says Dr. Andrada. But it is assumed by now that they also ran with their upper bodies thrust forwards horizontally -- due to biomechanical advantages.

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