To understand how these ecosystems will respond to pressures from climate change, a new study examines what goes on under the forest floor
BUFFALO, NY – You can’t see it. But what goes on in a forest underground is very important to its fate.
In a new study, scientists conclude that the lateral flow of water through the ground can have an important influence on how riparian forests react to climate change. Models used to predict future forest plight typically don’t take this factor into account – but they should, researchers say.
“Groundwater has not received much attention and how the movement of water from one location to another underground can affect the chances of survival of plants, making some locations drier and others wetter,” says lead author Xiaonan Tai, PhD, assistant professor for biological sciences at the New Jersey Institute of Technology. “Groundwater is a hidden source of water for ecosystems that humans have neglected over the years: it’s very difficult to observe and quantify just because we can’t see it. The contribution of our new research is to start characterizing lateral groundwater processes and quantifying how much impact they can have on the future of forests. “
The study, published in Environmental Research Letters in July, builds on research topics Tai explored as a PhD student in geography at the University of Buffalo College of Arts and Sciences, where she completed her PhD in 2018.
The new paper focuses on incorporating information about subsurface hydrology into computer models that predict the future fate of forests.
“Our research will fundamentally change the way the Earth systems modeling community thinks about the impact of future climate change droughts on forests,” said Scott Mackay, PhD, UB Professor and Chair of Geography and Professor of Environment and Sustainability. “In essence, the various vegetation models today assume that the world is flat. Our model changes history by allowing water to move sideways under the surface while modeling the physiological responses of trees to the landscape. “
In addition to Tai and Mackay, the authors of the new study also include Martin D. Venturas, PhD, from the Universidad Politécnica de Madrid; Paul D. Brooks of the University of Utah; and Lawrence B. Flanagan, PhD, from the University of Lethbridge.
The research was funded by the US National Science Foundation.
The paper models potential future prospects for a poplar forest in Alberta, Canada, and focuses on a period of 20 years at the end of the 21st century. Alluvial forests are common ecosystems that are located next to a body of water such as a stream or pond.
Conventional wisdom has it that as the carbon dioxide levels in forests increase, tiny pores on leaves – called stomata – do not have to open as wide to absorb the carbon dioxide that plants need for photosynthesis. This in turn leads to a reduction in the water loss that occurs through the stomata.
However, the new study suggests that the amount of water saved for future use may not be as great as expected: “Once you introduce a lateral flow of water below the surface, there is still additional water saved, but that saved water doesn’t stay all local. ”says Tai. “Some of it will move away, and once it’s gone, plants won’t be able to use it in future droughts.”
Additionally, models that ignore horizontal water flow can overestimate other mortality risks, Mackay says.
“In the ground, water can move in all directions from areas with high water content to areas with low water content,” he says. “This is pronounced in mountain landscapes because water moves from high to low heights, and in the immediate vicinity of bodies of water such as those found in floodplains.
“The horizontal movement of the water makes places that would otherwise be very dry when the rain stops, more humid, while normally wet areas can afford to shed some water without harming the plants.”
The big message of the research? If scientists and politicians want to understand how riparian forests will fare in a warming world, they need to think more about hydrology and the difficult-to-see processes beneath the forest floor.
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