Ozone exposure affects tree defoliation in a continental climate

Area of Science:

• Environmental Science
• Forest Ecology
• Atmospheric Chemistry

Background:

• Ground-level ozone (O3) causes visible leaf injury, reduces photosynthesis, and impacts tree growth and carbon sequestration.
• Tree crown defoliation is a critical indicator of forest health and vitality.
• Previous studies often used manipulative experiments, which may not reflect real-world environmental conditions.

Purpose of the Study:

• To investigate the role of ozone concentration and related metrics (AOT40, POD0) in causing crown defoliation in temperate Romanian forests.
• To assess the influence of ozone in conjunction with nitrogen pollutants, climate, and orographic conditions.
• To apply non-linear modeling approaches for a comprehensive analysis.

Main Methods:

• Utilized Random Forest and Generalised Regression Models for non-linear data analysis.
• Evaluated ozone concentration, AOT40 (Accumulated Ozone exposure over a Threshold of 40 ppb), and POD0 (Probability of Defoliation) metrics.
• Incorporated data on nitrogen pollutants, climatic factors, and orographic conditions specific to Romanian forests.

Main Results:

• Ozone concentration and AOT40 were identified as more significant factors affecting crown defoliation than meteorological parameters in the studied Romanian forests.
• POD0 levels consistently remained below critical thresholds, indicating a negligible impact on crown defoliation under the investigated conditions.
• The non-linear modeling approach provided insights into the complex interactions influencing forest health.

Conclusions:

• Ozone pollution, particularly its concentration and accumulated exposure (AOT40), plays a crucial role in forest crown defoliation in Romania.
• While other factors were considered, ozone metrics emerged as dominant drivers in this specific temperate forest ecosystem.
• The findings highlight the importance of monitoring and managing ozone levels to protect forest health and vitality.