Category: Plant and Soil Sciences
The future of urban forests
October 21, 2024 Written by Nya Wynn | Photos courtesy of Jeremy Wayman
The viability of our world’s forests is constantly threatened by climate change, urbanization and invasive species. Department of Plant and Soil Sciences Ph.D. student Jack Levy-Diedrich investigates urban forests and what they will look like in the future.
“Urban forests are really important in cities, they provide a ton of biodiversity and they give people in cities all this accessibility to nature,” Levy-Diedrich said. “But they’re under threat from invasive plants.”
Levy-Diedrich’s doctoral research, under the guidance of Tara Trammell, John Bartram Associate Professor of Urban Forestry, focuses on the communities of plants in urban forests and the kinds of seeds present in the soils. Using this data, Levy-Diedrich and his team can get a glimpse at what these forests might look like in the future.
“One of Jack's dissertation chapters is focused on cataloging all of the vegetation in each forest he visits,” Trammell said. “This includes the herbaceous plants all the way up through the woody plants, and studying multiple points within a forest, multiple forests in a city and multiple cities.”
By doing this cataloging on various scales, they can see where invasive plants frequently pop up and where they’re making the biggest impact on these forests at a larger scale.
Another aspect of his research required Levy-Diedrich to inventory the types of seeds found in the soils of these forests. While he traveled to forest locations to catalog the plant communities, he also took samples of the soil and brought these soil samples back to UD. Then Levy-Diedrich placed the soil samples in UD’s Fischer Greenhouse and allowed whatever seeds contained in the soil to grow.
By doing this, Levy-Diedrich analyzes what invasive species may flourish in the event of a forest disturbance. A forest disturbance could include a tree coming down or human activity that clears an area of the forest from whatever may be growing there already, leaving an open space for invasives to creep in.
“If we see a lot of invasive plants growing out of the soil samples from a particular area, we can predict that these invasive species may move in and germinate in the event of a forest disturbance,” Levy-Diedrich said.
Looking into what invasives may come onto the scene after a forest disturbance can help influence forest management efforts and legislation around plant nurseries.
“Our research can impact decisions made by parks and recreation departments and other environmental entities about what to plant in public spaces,” Levy-Diedrich said. “It could also help inform what kind of low cost interventions could be made to redirect some of the negative changes that we might see in urban forests.”
This sector of his dissertation research will round out next summer. Levy-Diedrich will return to all these forest locations in an attempt to verify his predictions about forests based on the seed banks.
The final piece of his research focuses on studying canopy gaps in forests. Naturally, trees die in the forest and form gaps over time as they age out. This is typically good for forests, as it allows for diversity of structure and age of the species within the forest. However, because of the growing population of deer and invasive plants in a lot of urban forests, tree seedlings can struggle to grow into the canopy in these gaps before they are browsed by deer or outcompeted by invasive plants.
This is where Levy-Diedrich comes in. He is spearheading the first field-based study focused on forest gaps in urban forest patches. According to Levy-Diedrich, analyzing the gap conditions is very important when it comes to assessing the future health of a forest.
“These forests do a ton to reduce urban temperatures in the neighborhoods around them and a lot of that is dependent on tree cover,” he said. “If we don't have as much forest cover, there is an ecosystem on the ground that might be degraded, and all the services that these forests provide to the city are going to be degraded as well.”
Although he makes it look easy, this research is no small feat. In order to collect all this data, Levy-Diedrich has to travel across five different states within FRAME: FoRests Among Managed Ecosystems that spans from Springfield, Massachusetts to Raleigh, North Carolina, multiple times a year.
Throughout the five cities in the FRAME network, Levy-Diedrich visited 125 different locations to identify plants and collect soil samples to form his seed bank.
“It takes a lot of work to do that much plant identification alone,” Trammell said. “In addition to all that, the seed bank work was surprisingly intense, because he had thousands of plants come up in the greenhouse that he had to identify.”
Learning about the different native and non-native species present in urban forests can help dictate forest management, what should and should not be planted in cities and even predict the viability of a forest.
“We’ve done so much destruction and damage to the landscape in cities and suburban areas, but these forests are some of the only areas in this very urban context where a lot of the native biodiversity can grow,” Levy-Diedrich said. “That's one of the big reasons that I care a lot about these forests and why I like to be in them.”