A project of
International Urban Dendrochronology Project
About UTEN
The Urban Tree Ecophysiology Network (UTEN) is an international network of researchers studying the growth and environmental responses of urban trees across different cities and climatic regions worldwide.
UTEN brings together researchers investigating how urban trees respond to environmental conditions and environmental stressors across a range of urban environments.
The Dendrochronology Project
As part of this effort, UTEN researchers are conducting a collaborative dendrochronology study across multiple cities worldwide. The project examines how different tree species respond to drought, heat, and other urban stressors through the analysis of annual growth rings. Dendrochronology enables researchers to reconstruct how climate and environmental conditions have influenced tree growth over time and to compare tree responses across different urban contexts.
Why Dendrochronology?
Several methods are available to assess the condition of urban trees, but dendrochronology is still rarely used in this context. By analyzing a single core sample, researchers can:
Reconstruct Growth History
Measure annual tree ring width to understand year to year growth dynamics.
Assess Drought Stress
Differentiate between earlywood and latewood and use additional proxies such as blue intensity to estimate wood density and drought related stress.
Determine Species Plasticity
Perform wood anatomical analyses to uncover species specific responses to urban conditions.
Utilize Stable Isotopes (δ¹³C)
Measure stable carbon isotope ratios in annual rings to evaluate changes in water use efficiency and physiological responses to environmental stress.
Estimate Longevity and Carbon Allocation
Determine tree age and improve estimates of carbon allocation in urban trees.
How Are Trees Sampled?
The study uses increment coring, a standard scientific sampling method widely used in forestry and dendrochronology research. A single core sample is collected from each selected tree using a 5 mm increment borer. Sampling is performed close to breast height (1.3 m), aiming to reach the pith whenever possible.
Each sample is labelled and accompanied by metadata, including GPS coordinates, tree diameter at breast height, tree height when possible, and notes regarding tree condition and surrounding conditions.
Is the Procedure Safe?
Scientific studies have demonstrated that, when performed according to accepted professional protocols, increment coring does not negatively affect tree growth, vitality, structural integrity, or mortality.
Healthy trees naturally isolate and seal the small sampling wound through a process known as compartmentalization, preserving their structural integrity and physiological function.
The UTEN protocol follows established best practices, including:
• Using a narrow 5 mm increment borer.
• Sampling during the active growing season.
• Avoiding sampling during periods of severe drought.
• Avoiding the use of artificial plugs or wound fillers.
Scientific References
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Portier, J., Shackleton, R. T., Klesse, S., et al. (2024). No evidence that coring affects tree growth or mortality in three common European temperate forest tree species. European Journal of Forest Research, 143, 129–139.
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Van Mantgem, P. J., & Stephenson, N. L. (2004). Does coring contribute to tree mortality? Canadian Journal of Forest Research, 34, 2394–2398.
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Shigo, A. L. (1984). Compartmentalization: a conceptual framework. Annual Review of Phytopathology, 22, 189-214.
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Maeglin, R. R. (1979). Increment cores: How to collect, handle, and use them. USDA Forest Service, Forest Products Laboratory. General Technical Report FPL 25.
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Smith, K. T. (1999). On the Menace of Coring: Wounding and Compartmentalization Responses in Living Trees. USDA Forest Service Research Brief.
Contact
Urban Tree Ecophysiology Network (UTEN)
Dr. Yakir Preisler
Ella Fraiman, MSc
Research Coordinator
Green City Research Center
List of cities
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Turin, Italy
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Minneapolis, MN, USA
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Sacramento, CA, USA
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Washington DC Area, USA
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Tel Aviv, Israel
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Berlin, Germany
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Tandil, Argentina
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Junín, Argentina
Frequently Asked Questions (FAQ)
What is the scientific question of this study?
The study aims to better understand how urban trees respond to environmental stressors such as drought, heat, and urban conditions across different cities and climatic regions worldwide.
The project focuses on approximately seven target genera and compares trees growing in two different urban environments: street trees and park trees.
The study also compares tree responses across different cities and climatic zones.
Is there a control group?
Urban environments are highly variable, and several approaches are used as reference conditions.
These include:
• Published studies of the same species growing in natural environments.
• Comparisons between trees growing in parks and trees growing along streets.
• Comparisons between species growing in their natural habitat and the same species growing in different cities as non native species.
This study also represents a first step toward a broader urban dendrochronology study that will improve our understanding of the factors influencing annual ring development in urban environments.
What information can be obtained from tree cores?
Tree cores can provide information about:
• Urban tree vitality.
• Annual ring width growth dynamics.
• Tree age.
• Sensitivity to climatic conditions.
• Sensitivity to growing conditions, such as differences between street and park environments.
• Variability in responses to changing climate.
• Water use efficiency.
How is this information measured?
Tree ring samples are analyzed together with background information collected for each site.
This information may include:
• Planting conditions.
• Local climate records.
• Historical precipitation records dating back to the planting date of the trees.
• Additional information provided by local collaborators.
Annual growth is assessed using Basal Area Increment (BAI) and annual tree ring width measurements after cross dating.
Tree age is determined using established dendrochronological tools and software that allow annual rings to be cross dated with temperature and precipitation records.
Future phases of the project, depending on funding availability, may include stable carbon isotope analysis (δ¹³C). This analysis can be used to calculate annual water use efficiency.
How will this research benefit municipalities and land managers?
Once we understand past growth patterns, the main limiting factors affecting tree development, and the environmental conditions to which specific species are most sensitive, we will be better able to plan for the future.
This information may help support:
• Selection of tree species adapted to future climate conditions.
• Improved treatment of trees that are sensitive to stressors such as water limitation and limited root volume.
The strength of this international study lies in its ability to compare trees growing across many cities and geographic locations while providing insights into future climate conditions.
What practical outcomes may emerge from this research?
Understanding what trees have experienced during the past 20 to 30 years can provide valuable information for future planning.
For example, previous municipal activities such as road construction, root damage, and soil compaction may leave measurable signatures in tree growth.
By identifying these impacts, municipalities may become more aware of the effects that infrastructure work can have on trees and take greater care to avoid damaging root systems during future projects.