A new study has found that ozone pollution is having a significant impact on the survival of tree species across the United States. The research, published in the Journal of Geophysical Research: Atmospheres, is the first to measure how ozone exposure affects mature trees in real-world conditions.
The study was led by Nathan Pavlovic, lead geospatial data scientist at Sonoma Technology Inc., and Charles Driscoll, University Professor of Environmental Systems and Distinguished Professor in the College of Engineering and Computer Science at Syracuse University.
Driscoll explained what sets this research apart from previous studies. “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.”
Driscoll also emphasized why it is important to look at tree survival rates rather than just growth rates: “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.”
Pavlovic discussed regional differences found by their research: “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.”
The findings come as discussions continue about possible changes to current EPA air quality standards related to ozone levels. Driscoll said: “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 [since]the initiation of Clean Air Act[,]the EPA has not had the political will to establish meaningful secondary standards that differ from primary standards.This is despite the importanceof ecosystem 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.”
Looking ahead, Pavlovic described future research directions: “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.”
