A new nationwide study reveals that ozone pollution—an invisible threat in the air—may be quietly reducing the survival chances of many tree species across the United States.
The research, published in the is the first to quantify how much ozone exposure harms mature trees under real-world conditions. The findings offer a new lens for policymakers and forest managers to protect trees—and the ecosystems they support—from the silent stress of ozone pollution.
Charles Driscoll
The research is led by Nathan Pavlovic, lead geospatial data scientist at Sonoma Technology Inc. and , University Professor of Environmental Systems and Distinguished Professor in the College of Engineering and Computer Science.
Below they answer five questions about the work and how it helps us understand tree health and ozone pollution.
What makes this study different from previous research on ozone and tree health?
CD: There are several key innovations in our paper. It is the most comprehensive study of ozone effects of trees ever conducted using a database representing about 85 species and 1.5 million trees over the coterminous U.S. This study involves the analysis of mature trees under the environmental conditions that they are experiencing. Most previous studies have involved controlled experiments using seedlings. This is the first study to use machine learning to characterize and quantify effects of ozone on many different tree species experiencing a range of environmental conditions over a large spatial scale.
Why is it important to understand how ozone affects tree survival, not just growth?
CD: Tree survival rates are arguably as important as tree growth. Decreases in survival of tree species make them more vulnerable to displacement by competing species, possibly resulting in shifts in species abundance and distributions and decreasing biodiversity.
Your findings show that western U.S. forests are especially vulnerable. What factors contribute to this regional risk?
Nathan Pavlovic
NP: This is an interesting observation and result. It is not clear what is driving this response. We speculate that our results suggest conifers are more sensitive to ozone than hardwoods due to the longer growing season for these species, which has been indicated in some other work. This could be an important driver for this regional response. Also, the response may be connected to limited water availability in the West, exacerbating the ozone response. The heightened sensitivity of tree species in the West is paired with higher ozone concentrations relative to the East. By contrast, we found limited evidence of impacts to trees from recent ozone concentrations in the East, a finding corroborated by other work that has been conducted on select trees at the regional level.
There is growing conversation about rolling back current EPA standards as it relates to air quality. How can your results inform national air quality standards or forest management practices?
CD:In the U.S. there are two sets of air quality standards, those set to protect human health called primary standards and those intended to protect public welfare. Public welfare is everything potentially impacted by air pollution beyond health. Public welfare includes crops, materials and ecosystems. Science has clearly demonstrated that trees and other items pertaining to public welfare have been impacted by air pollution. Nevertheless, in the 50+ years the initiation of Clean Air Act the EPA has not had the political will to establish meaningful secondary standards thatdifferfromprimary standards.This is despite the importanceofecosystem health for human well-being and the fact thattheformof standards to protecthuman-healthis often inappropriate to protect ecosystem structure and function.If the EPA tries to roll back air quality standards there will likely be considerable push back from many groups. But for ecosystem health concerns from air pollution, despite whatever happens it is unlikely this will be an important factor in decision making.
What are the next steps for your team in this line of research?
NP: As concentrations and sources of air pollution have shifted over recent decades, new sources of pollution have taken on increased importance. In addition to ozone, we have also assessed impacts of nitrogen and sulfur deposition on trees. There is much left to understand how the shift from primarily industrial and transportation sources to area sources including agriculture and wildfires may be affecting ecosystems. The sensitivity of trees to pollution from these sources is also dependent on heat and water stress. While we account for these factors in our models currently, there is more to learn about how these factors influence outcomes now and in the future.
To set up interviews or get more information about the work, please contact:
Daryl Lovell
Associate Director of Media Relations
University Communications
M315.380.0206
dalovell@syr.edu|
