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.
Harnessing botanical remedies for respiratory health
Plant-based cough syrup - a blend of tradition and science
Muhammad Siddiq, a PhD student, recently carried out a project exploring natural alternatives to synthetic cough syrups, with a focus on medicinal plants from the TCD Botanical Garden. This independent project, while separate from his doctoral research on plant chemistry and climate change, contributes to the broader conversation about the role of plants in healthcare.
Siddiq’s work focused on identifying plants with potential cough-relieving properties, drawing on both historical knowledge and scientific evidence. He highlighted five plants known for their medicinal value: Allium sativum (garlic), prized for its antibacterial and immune-boosting effects; Aloe vera, recognized for its soothing and anti-inflammatory properties; Equisetum hyemale (horsetail), a mild expectorant; Thuja occidentalis, traditionally used for respiratory congestion but requiring controlled use due to its thujone content; and Rubus armeniacus (blackberry), rich in antioxidants that help alleviate throat irritation.
Using these plants, Siddiq developed a natural cough syrup, blending garlic extract, aloe vera juice, horsetail infusion, blackberry syrup, and honey—an age-old natural remedy known for its preservative and throat-soothing properties. This simple yet effective formulation offers a plant-based alternative to commercial cough syrups and demonstrates the potential of botanicals in modern medicine.
Although separate from his PhD research, Siddiq’s work highlights the relevance of plant-based treatments in healthcare, bridging traditional knowledge with modern scientific validation. His project also emphasizes the value of locally available medicinal plants, many of which visitors to the TCD Botanical Garden can explore firsthand to learn about their historical and medicinal significance, both in Ireland and beyond.
by Muhammad Siddiq
New publication!
Functional traits of fossil plants
Led by Prof. McElwain, the ERC-funded TERRAFORM project team recently published a comprehensive review “Functional Traits of Fossil Plants” in the New Phytologist. The review took a unique approach, evaluating which extant plant traits offer the greatest promise for application to fossils through contemporary trait-based ecology. The focus was placed on plant functional traits and measurable properties of fossils that provide insights into the functioning of the plants in past environments.
Taking into consideration the limitations of a trait-based approach in palaeobotany, the team together with collaborators assessed over 30 extant traits in palaeobotany and ranked 26 paleo-functional traits based on taphonomic and methodological criteria that can potentially impact Earth system processes. The Tansley Review offers a new perspective on the study of extinct plants and brings insights into their functioning in the past.
The open-access publication is available online under this link.
Figures from the publication:
Figure 1. The methodological framework used to critically evaluate 30 contemporary plant traits (from Pérez-Harguindeguy et al., 2013) for their potential application to the plant fossil record as paleo-functional traits.
Figure 2. Examples of fossil plant functional traits.
Figure 3. Comparison of paleo-functional trait scores according to different weighting criteria.
Are plants Ecosystem Engineers?
Will Matthaeus presents a case to the International Biogeography Society in Prague
In the frosty early days of January, Dr Will Matthaeus went to Prague to deliver a talk at the Ecosystem Engineering Symposium organized by Kate Lyons and Amelia Villaseñor at the 11th Biennial Conference of International Biogeography Society (IBS). In a session covering everything from Edicarian bioturbation to anthropogenic impacts and rewilding—500 million years of ecosystem engineering—Will presented plants as a foundational aspect of terrestrial ecosystems and classic examples of ecosystem and landscape reorganization with plant evolutionary changes (e.g., ‘The Devonian Plant Hypothesis’). The earliest plants were little more than ‘green slime.’ These small, prostrate organisms that were limited to wet environments may still have impacted global ecosystems by altering atmospheric oxygen concentrations. Over the course of the evolutionary transformations that led from green slime to boreal forests and savannahs, plants have likely increased the diversity and maximum effect in their impact on ecosystems. Synthesis of paleo-plant traits, among other paleontological techniques, may provide insight into this function over periods of change, upheaval, and extinction in terrestrial environments that are informative for our future. However, understanding these changes requires expertise in a broad variety of disciplines; IBS meetings are a valuable opportunity for developing the frontiers of paleoecology through new collaborations.
How to bring extinct plants ‘Back to Life' - publication by Will Matthaeus and Jenny McElwain
How to bring extinct plants ‘Back to Life.’
An obvious question to many might be “why study plant fossils?” Of course, some people just think they are amazing on their own. But there are ways that plant fossils can help us understand how Earth’s different systems work together. One framework for this approach is described by the recent review A Systems Approach to Understanding How Plants Transformed Earth’s Environment in Deep Time by TERRAFORM postdoc Will Matthaeus and PI Jenny McElwain among others. First, the plant fossil record tells us that at least part of Earth has been covered by plants since they evolved nearly half-a-billion years ago, even though the climate has been very different at times. The fossil record also shows that plants have changed so much since their start that at times they may have been nearly alien to our modern eyes. Finally, using ecosystem process models to incorporate measurements from plant fossils with climate simulations, we can estimate how extinct plants may have performed in the climates they experienced hundreds of millions of years in the past. Reaching so far back requires the expertise of several different kinds of scientists all working closely together to carefully develop solutions to a diverse array of challenges, and will allow us to understand the whole story of how the Earth we know came to be.