Stewarding forests with climate change in mind

Minnesota's climate is projected to become warmer and wetter with more extreme weather events. Fewer days below freezing will mean more habitat for insects and diseases that infect trees. A greater number of hot days will affect moisture levels in soil while more extreme storms may lead to longer floods. Trees that grow in floodplain forests, such as eastern cottonwoods, are adapted to withstand seasonal flooding, but changes in flood timing and length may hinder the establishment of new seedlings.

Such impacts are predicted to negatively impact some tree species in our area, including black willow, eastern cottonwood, and silver maple. Other species, such as hackberry, American elm, bur oak, and swamp white oak, may see an increase in habitat that matches their needs.

Silviculture is known as "the art and science" of maintaining forests for a variety of needs and values, for example, planting trees and shrubs to provide wildlife habitat and protect the river from erosion. Adaptive silviculture means attempting to prepare for and respond to the impacts of climate change on forests. At a given site, is it more effective to put energy into bolstering forest species' abilities to persist through change, facilitating changes that may help the ecosystem adapt, or some strategy in between? The Adaptive Silviculture for Climate Change network is testing these approaches to help inform forest management across the country.

Floodplain forests are forests that reside in areas prone to flooding, typically along rivers and near other bodies of water. They provide a number of benefits to those who live near them. They act as water filters, by slowing the movement of water across soil that would otherwise be swept into the river as sediment. They take up carbon dioxide and other pollutants from the air. Forests along the river support a large mix of animals, including insects, birds, reptiles, and mammals. As the Twin Cities area sees an increasing number of days above 100 degrees Fahrenheit, urban forests are critical to people's health and wellbeing. Finally, these places are unique, interesting, and fun to explore!

Understanding how to best support floodplain forests through challenges like warming temperatures, insect outbreaks, and extreme weather will allow us to continue to enjoy them for decades to come.

In 2019, a group of collaborators met to discuss plans for this project, including which tree species to test. The partners chose trees from hardiness zones 4,5, and 6 according to their chances of survival, their ecological relationships, and social preferences. Each of the tree species in the study has some flood tolerance and most are found growing in lowland and riparian areas.

Another factor that came up was whether certain species from southern areas were already growing in the Twin Cities as street trees. To maintain the appearance of Crosby Farm Regional Park that visitors are used to seeing, the project partners selected only deciduous trees. They also considered whether southern-adapted tree species would have associations with fungi that would be necessary to their survival or characteristics that would cause them to outcompete other plants growing in the forest.

At the beginning and end of each growing season, researchers collect data on the survival and growth of each tree in the experiment. They are also studying the vegetation that is growing in the plots, including control plots, which are fenced-in areas of the same size as the other plots where no trees were planted. Soil moisture and temperature readers that are installed on-site are providing insight into the climate conditions in the plots. Volunteers and the research team are tracking the phenology of a subset of the trees in the experiment, or the timing of annual life cycle events, like buds leafing out or leaves changing color. This information will help us understand how the trees are relating to the timing of seasons, which is shifting due to climate change.

As the study continues over the next several years, other collaborators may sign on to ask other questions, about insects or soil microbes, for example. One place to watch for research updates is the ASCC network's "News" page.

In the long-term, we hope to learn which treatments best meet the management goals for this floodplain forest ecosystem. We hope to provide information that land managers can use to adapt their techniques as climate change creates new pressures in forest ecosystems like those in Crosby Farm Regional Park. At the end of the study's third growing season in 2022, we hope to have preliminary data about which trees are establishing and what other vegetation is most prevalent in the gaps left by felled, infected ash trees.

As the first urban site in the ASCC network, this experiment has also been an opportunity to engage community members around climate adaptation and forest science. The public is invited to participate in this work through education and volunteering opportunities.

Become a member: Like all our work, this effort to learn how to better steward floodplain forests in a changing climate is made possible in part by our financial supporters. Learn how to become a sustaining member of Mississippi Park Connection or make a one-time donation to support this important climate change work.

Volunteer: There are a number of ways to give your time to this project by collecting data and maintaining the research plots. You can learn about available opportunities on our volunteer page or email our volunteer coordinator at volunteer@parkconnection.org for more information.