Trees help protect Iowa against climate change, researchers say. But we need more of them

Iowa weather is getting hotter, wetter and more extreme — and trees will be critical for mitigating the dangerous impacts of climate change, according to a 2022 Iowa Climate Statement released Wednesday.

This summer alone, heat waves, record temperature highs and a derecho barreled through Iowa.

Trees help reduce the effects of these extreme weather events by providing shade, sucking up water and offsetting carbon emissions. But tree canopies in Iowa — decimated during the 2020 derecho — need to be sustained and expanded.

That’s why Iowa researchers decided to focus on trees and their benefits in this year’s climate statement, they said on a Wednesday press call.

“Many of the trees that we plant today will be living well into the 22nd and even 23rd centuries,” said David Courard-Hauri, a Drake University professor of environmental science and sustainability. “Trees provide us with an opportunity and an obligation to think about what our state will be like then, and how we can ensure their survival in a very different climate from the one we've gotten used to.”

The climate statement was endorsed by 203 science faculty and researchers, spanning 33 colleges and universities across Iowa. Previous statements include focuses on electric infrastructure and COVID-19.

Climate change

Climate change will likely bring increased humidity, warmer nights and wetter winters to Iowa — which could lead to more floods and droughts.

Thirty-nine climate projections models from the Intergovernmental Panel on Climate Change found that Iowa will be much warmer in a high-emissions future, said Jerry Schnoor, co-director of the University of Iowa’s Center for Global and Regional Environmental Research.

In Des Moines, for example, the number of days with temperatures over 95 degrees is projected to increase from 3.6 days per year to 95 days per year by 2081. By the end of the century, the city could experience up to 45 days per year that have a heat index over 106 degrees.

“The heat and humidity will be oppressive,” Schnoor said. “Such heat waves would create a huge problem for trees and Iowa as we move to midcentury and beyond.”

Changing climate is causing tree-growing seasons to shift, said Jan Thompson, a professor of natural resource ecology and management at Iowa State University.

With warmer springs, trees begin growing sooner, and they become dormant later due to warmer falls. If this seasonal shift grows large enough, it could cause a mismatch of life cycle timings for pollinators — which are essential to a tree’s natural seed reproduction, Thompson said.

Plant processes critical for a tree’s survival and growth — like photosynthesis — also are heavily influenced by climatic conditions. Higher temperatures cause the rates of these processes to increase. But extreme temperatures can cause some to decline, which can create imbalances that weaken the tree. This makes them more susceptible to destructive pests like the emerald ash borer.

Other forest disturbances, like fires, also are more likely with increased temperatures and decreased moisture. Iowa is already starting to see more fires on the landscape, Thompson said.

“The recipe isn’t good for long-lived species that can’t get up and walk away,” she said.

How trees help

In spite of the climatic challenges, trees act as lines of defense against climate change, said Heather Sander, a UI associate professor of geographic and sustainability sciences.

They absorb large volumes of water during periods of intense rainfall, which will likely become more common and frequent in Iowa, Sander said. This helps decrease flooding in fields, streets and waterways. Their roots also hold soil in place and prevent erosion.

Trees help cool the air when they release water from their leaves in a process called transpiration. Their canopies also shade the land underneath. Higher tree concentrations can help reduce energy usage and bills in cities experiencing the urban heat island effect, which is when cities replace natural land cover with surfaces that retain heat, like pavement and buildings.

With its extreme tree loss, Cedar Rapids will experience worse urban heat island effects for a projected 10 to 20 years, Schnoor said.

“The shading and cooling provided by trees will help to reduce this heat and provide respite from it, particularly for those without access to air conditioning,” Sander said.

Trees also provide general ecosystem benefits, including wildlife habitat, clean air and aesthetic enhancements for communities.

“To preserve these benefits and to address the many challenges climate change is going to pose to Iowans, Iowa needs to take care of its trees and forests,” Sander said.

More trees needed

Even before the 2020 derecho, Iowa wasn’t keeping up with its tree planting, Thompson said. Now — spurred by the derecho — communities are “stepping it up.”

Cedar Rapids’ $37 million ReLeaf plan, for instance, aims to plant more than 42,000 trees on public land over 10 years. As of the derecho’s two-year anniversary, city staff, contractors and Trees Forever volunteers have planted at least 2,470 trees along streets and in parks.

Planting trees is a great first step, but keeping them alive is most important.

Caring for them means watering newly planted trees and mature trees during times of drought, Sander said. Trees also must be pruned to keep them strong against high winds. And planting a variety of species helps promote resilience against invasive pests.

“Without those trees, the effects of climate change on our health and well-being will be far greater,” Sander said.

Although they store carbon and offset emissions, trees cannot single-handedly defeat climate change. Global carbon-dioxide emissions rose to 36.3 billion tonnes in 2021, according to the International Energy Agency.

“Trees are not going to solve the problem. They may help us adjust, particularly to climate change, but we can't just count on trees to fix our problem for us,” Sander said. “What we need to do is reduce emissions.”

Brittney J. Miller is an environmental reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com