Urbanization is one of the most powerful historically-altering forces on thriving trees across the globe, and therefore an extreme stress on their health. A new research paper finds that development in urban areas comes at a cost, uprooting the tree microbiome. This rich community of microorganisms is vitally important to tree health and growth. As cities grow outward, they exert tremendous stress on important ecosystems. This environmental stress wears urban trees down, inhibiting their capacity to perform the irreplaceable services they supply. Researchers, including Ph.D. candidate Katie Atherton, are investigating these impacts and exploring solutions to enhance the resilience of urban forests.
This rapid pace of urbanization is expected to increase the physical footprint of cities worldwide by twofold by 2050. In the United States, urbanization is projected to take over 20% of existing forest cover. Yet this shift will have profound impacts on the microbial life that trees depend on to thrive. This widespread change has a large detrimental impact on tree health. It also undermines the priceless ecosystem services that our trees deliver, from filtering air pollution to sequestering carbon.
Understanding the Tree Microbiome
The tree microbiome is primarily made up of bacteria and fungi that live in, on, or around the tree roots. Among these, ectomycorrhizal fungi are especially important for many woody plants, including oaks. These fungi help expand plant roots’ access to nutrients and water and increase plant defenses against environmental stressors.
Today, at least 20,000 fungal species can colonize the roots of living plants. Urbanization breaks those connections, changing the soil structure and introducing chemicals that are harmful to water quality. This disruption results in a loss of balance in the tree microbiome, which in turn has cascading effects on desired health and growth outcomes for trees.
Research indicates that when urban trees experience stress due to environmental changes, such as soil compaction and pollution, their associated microbiomes suffer. This results in compromised trees that are increasingly vulnerable to diseases, forming dieback, and eventual death. Thus, disentangling the urban tree microbiome’s complex dynamics is critical to informing approaches to bettering urban forestry practices.
The Role of Ectomycorrhizal Fungi
Ectomycorrhizal fungi are some of the most important symbionts for promoting the health and longevity of trees in an urban context. These complex fungi help their tree and shrub hosts weather extreme environments by increasing their capacity to uptake water and nutrients. That mutually beneficial relationship spares no resource, giving trees a completely interconnected advantage to shape their environment to their liking.
The disruption that comes with urbanization further stresses these positive relationships, leading to a loss of resilience for our trees. In their struggle against this environmental adversity, trees face an ultimate distinguishing factor. This painstaking effort throws their microbiomes out of whack, leading to increased death. Yet studies have found that by reintroducing ectomycorrhizal fungi, tree mortality in forested areas can be dramatically lowered.
Taken together, this finding opens up an exciting new opportunity for increasing the welfare of our urban forests. By adopting an urban microbiome approach to urban forestry policies, cities can better guarantee tree survival and pave the way for healthier and more diverse urban ecosystems. Providing and protecting trees’ connections to probiotic microorganisms is vital in strengthening their defenses against urban stressors.
Strategies for Resilient Urban Forests
Developing resilient and equitable green infrastructure in cities and metropolitan areas will be more important than ever. Moving forward, we need to prioritize how the tree microbiome should inform city planning and urban forestry policies. By recognizing the ecological significance of these microbial communities, urban planners and city leaders can adopt more effective planning and management practices that promote tree wellbeing.
According to recent Ph.D. research by Katie Atherton, it’s critical that we reverse the harmful impacts of urbanization on microorganisms. Her work continues to push for the integration of microbiome considerations into urban forestry initiatives, leading to healthier trees and ultimately, sustainable ecosystems. This forward-thinking technique significantly increases tree survival by up to 97%. It simultaneously improves the cultural and artistic experience of quality of life of urban dwellers.
Cities that invest in and protect their green spaces with science- and equity-based policies can maximize these green infrastructure benefits. Our existing urban tree canopy provides enormous benefits to our air pollution filtration and carbon capture, both crucial for fighting climate change. By encouraging beneficial tree microbiomes, municipalities can help their urban forests withstand the growing urban pressures of today and tomorrow.