Matt Dannenberg, assistant professor at the University of Iowa in the Geographical and sustainability sciences department, presented a science café discussion Thursday, April 24 at Fuel Café in Mount Vernon on how climate change impacts plants and water cycles.

Dannenberg has studied the global change of ecology, focused on the impact of climate change. As part of that research he has used data from satellites, as well as eco variance towers. He’s taken tree ring cores from a number of trees west of the Mississippi River to show the impact of drier and wetter years on trees in their lives.

“One of the questions I get asked is when you’re taking a core from a tree to collect tree rings, does that hurt the tree?” Dannenberg said “It is something that injures the tree after it happens, but I’ve taken cores from the tree in the next years, and the tree has already adapted and healed from the injury.”

One of the things he has found is that the scraggliest trees that look to cling life are some of the oldest.

Dannenberg said that one of the trends that is worrying is the increases in temperature and saturation vapor pressure in the atmosphere.

“What happens is these storms when they rain, they have more water vapor to rain out in these storms,” Dannenberg said. “The more intense the precipitation, it also takes more to fill.”

Dannenberg said while with climate change you see more intense rainfall events each year, you also see more impacts on dry and wet years. When an area experiences a dry year, that impact lasts longer.

When it comes to the rates of vaporation, it isn’t the level of humidity in the air that directs that impact, it is the vapor pressure deficit.

“Plant leaves have a high water pressure on their surface,” Dannenberg said. “Plants transpire water faster and evaporate water much quicker.”

One of the impacts of having more intense rain events is drainage tiles are not able to keep up with the amount of water that comes down in the storms.

“What we’ve found is that in the Missouri River basin, some of those tiles have seen 50 percent increases in their depth in the streams,” Dannenberg said. “A lot of the way we planned water resources, especially in western states was based on the weather in the early 20th century. Those conditions no longer apply, and we haven’t adapted to those change of conditions.”

Increased temperatures also has an effect on precipitation. The Midwest has seen precipitation increase by 40 to 50 percent in recent years.

Dannenberg said that the impact of climate change on trees and plants can be seen in plants, especially in drier years.

“Trees try to protect themselves from water loss, especially in drier years,” Dannenberg said. “They work to close and reduce the size of the opening in their leaves if things are too dry.”

By doing that, however, trees will also impact their ability to photosynthesize in order to protect water.

“What happens is all that water sticks to itself in the trees,” Dannenberg said.

Air outside the tree leaves has negative potential, and water wants to move outside those leaves.

If trees don’t close themselves to excessive water loss due to increased temperatures or dry seasons, the tree runs the risk of cavitating or dying.

This also means it can lengthen the time it takes for moisture in the soil to get to a trees xylem.

An audience member asked about why if carbon dioxide is increasing and contributing to global warming, why are trees or plants not growing faster?

Dannenberg said he and researchers are going to be studying what happens to plants in a high carbon dioxide environment this summer.

“What we expect to see happen as leaf temperatures go up and carbon dioxide increases, we’ll see more leaves transpiring water, and water in the soil gets drawn down faster,” Dannenberg said. “That means plants can die faster.”

Dannenberg’s research is funded through a mix of sources – some from the university, some from federal agencies. He said he is worried that some of those funding streams may disappear in the future, especially because of the focus on climate change related items.

Another area that may be impacted are the eco-variance towers, as many of those are manned or funded from other areas.

“Those are very expensive to operate and come with high personnel costs,” Dannenberg said. “If funding dries up, we could be at risk of losing some of those towers going offline in areas that would impact future data.”

Dannenberg said historical data is not one he is worried of disappearing, though.

A questioner asked if the evolution of plants could be observed.

“Because of how long it takes for evolutions to occur, that’s not likely,” Dannenberg said. “We see some adaptations plants make, but they aren’t keeping up consistently with the pace of change of our climate.”