Witness Trees Project 2026 Fieldwork Campaign
Five years of monitoring trees for a more climate-resilient future
The Witness Tree Project is a long-term monitoring initiative that began in 2022 at the Trinity College Botanic Garden and expanded to the National Botanic Gardens in 2024. Each summer, researchers monitor 21 tree species to better understand how climate change is affecting tree health and resilience, while also investigating the important role these species play in retaining airborne pollutants in urban environments. The project has completed its 2026 summer fieldwork campaign this July.
This year’s fieldwork was led by Dr. Leticia Figueiredo Candido at the National Botanic Gardens, together with intern Julia and volunteers Blanka and Chiara. At the Trinity College Botanic Garden, the Research Assistant Msc. Richard Slevin led the field team, supported by interns Charles, and Antony and volunteers Liza, and Qudseya. Members of the Plant–Climate Interaction Lab, including Dr. Christos Chondrogiannis, Dr. Michelle Murray, and Dr. Miriam Słodownik, also contributed to data collection, continuing their involvement from previous years. A huge thanks to everyone who contributed to the data collection and continues helping the project.
During the campaign, researchers collected a range of physiological measurements to assess tree health and resilience. These included stomatal conductance, leaf temperature, and chlorophyll fluorescence. Leaf samples were also collected for carbon isotope (δ¹³C) analysis, with the goal of providing insights into long-term water-use efficiency and how trees respond to environmental stress.
In addition, leaf samples were collected to quantify the amount and chemical composition of particulate matter retained by different tree species, helping researchers evaluate the ecosystem service that urban trees provide by improving air quality. The team also collected herbarium specimens from all monitored species, creating a permanent historical record of the trees while providing valuable material for future studies, these specimens will be available at the Trinity College Dublin Herbarium.
The project’s genetic component also continued in 2026. This work, initiated in 2025 by Dr. Ailbhe Brazel, aims to identify molecular biomarkers associated with environmental responses in selected species, including alder, hazel, common oak, and maidenhair tree. This year’s sampling was carried out by Dr. Brazel together with research assistant James, continuing the development of this important aspect of the project.
The data collected during the 2026 campaign will contribute to the project’s long-term dataset, helping researchers better understand how urban trees respond to changing environmental conditions and informing evidence-based strategies for selecting resilient tree species for future cities.
Witness Tree Project – 2025 Update
Exploring the Role of Trees in Climate Change Mitigation Through Collaborative Research
The Witness Tree Project continues to play a crucial role in advancing research on climate change through its focus on long-lived trees, which act as natural sensors of environmental change. In 2025, the project has made significant strides with new research initiatives, collaborations, and the involvement of a growing team of dedicated experts, students, and volunteers.
This year, Dr Miriam Slodownik, the lead of the Witness Tree Project, was responsible for leading the team at the National Botanic Gardens, where she focused on key questions regarding urban trees and their capacity to improve air quality. The research investigates which tree species are most effective at capturing particulate matter (PM) and explores the leaf traits that support PM uptake, including leaf area and surface texture.
Dr Ailbhe Brazel led a new initiative this year, collecting leaf samples from four tree species — alder, hazel, common Oak, and maidenhair tree — to identify molecular biomarkers of environmental responses. This research aims to deepen our understanding of how trees respond to environmental stressors and contribute to enhancing urban air quality.
A central theme of this research includes:
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Which tree species captures the most particulate matter (PM)?
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How do Leaf Area Index (LAI), leaf angles, and leaf size affect PM uptake?
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What specific leaf traits help increase PM absorption per tree?
By linking leaf traits with air quality data, the project is providing valuable insights to inform urban planning decisions aimed at improving air quality in cities.
Charlotte Salter-Townsend, a Master’s student, was also involved, examining which species within the Witness Tree Project have the highest PM capturing capacity. Charlotte’s work focuses on understanding how traits like leaf area, trichome density, and leaf size influence PM capture, and how these traits may work together to enhance the tree’s ability to absorb particulate matter.
At the Trinity College Botanic Gardens, Dr Michelle Murray led a separate team focused on monitoring the health of trees in response to environmental stressors such as temperature fluctuations and urban heat islands. Dr Christos Chondrogiannis supported the team, contributing to field collection and data analysis.
This year, a group of dedicated volunteers contributed significantly to the success of the project. A huge thank you goes out to Sophie, Lucy, Phoebe, Yidan, Ríona and Ciaran for their invaluable help. Their hard work, enthusiasm, and commitment to the project have been essential to the progress made this year.
The project remains highly active on social media, particularly through its Instagram platform, where updates and findings from the ongoing research are shared. Recent posts highlight the involvement of students, volunteers, and researchers in this year’s activities, showing the critical role that community engagement plays in the success of the project.
