Talking Trees

In this Friday episode of Talking Trees, we celebrate the legacy and ongoing impact of the International Society of Arboriculture (ISA)—the world’s leading organization dedicated to advancing the profession of arboriculture.

We explore:

• The history of ISA, which celebrated its 100th anniversary in 2024
• The evolution of its scientific journal from the Journal of Arboriculture to Arboriculture & Urban Forestry (AUF)
• The transition of AUF to open access in 2022, expanding its reach and influence in global tree care and research
• ISA’s core mission: promoting education, certification, research, and professional development in arboriculture
• The journal’s role in supporting urban forestry as cities increasingly invest in green infrastructure

As the field of arboriculture grows in importance, ISA continues to serve as a pillar of knowledge and community, connecting practitioners and researchers worldwide.

Background information:

• Celebrating 50 Years of Arboriculture & Urban Forestry:Journal of Arboriculture | Arboriculture & Urban Forestry.pdf
• International Society of Arboriculture > Who We Are

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In this Thursday episode of Talking Trees, we explore the emerging and complex connections between exposure to trees and green spaces and the risk of cancer, particularly breast cancer. While research is still developing, recent studies have started to uncover possible protective effects of urban greenery on human health.

We discuss:

• A multi-regional study from Spain suggesting lower breast cancer risk among women living near urban green spaces, compared to higher risk near agricultural areas
• A systematic review analyzing global data, revealing inconsistent but potentially protective links between greenspace exposure and various cancer outcomes
• The challenges of isolating environmental vs. lifestyle factors in cancer risk assessments
• Why tree-filled environments might contribute to stress reduction, better air quality, and increased physical activity, all of which may influence long-term health outcomes
• The importance of urban tree planning not only for ecology but for public health strategies

This episode highlights how trees may play a subtle but meaningful role in supporting human health—and how more research is needed to fully understand their therapeutic potential.

Background information:

• O’Callaghan-Gordo et al. 2018. Residential proximity to green spaces and breast cancer risk_ The multicase-control study in Spain (MCC-Spain).pdf
• Sakhvidi et al. 2022. Exposure to greenspace and cancer incidence, prevalence, and mortality_ A systematic review and meta-analyses.pdf

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In this Wednesday episode of Talking Trees, we investigate the powerful and often underestimated role of lightning in the life and death of trees. Lightning not only causes physical damage but may also shape tree evolution and biodiversity over time.

We explore:

• How lightning strikes affect tree aging, decay processes, and habitat creation
• The ecological significance of lightning-damaged trees as microhabitats for biodiversity
• Current technical standards for lightning protection, including components, installation procedures, and long-term maintenance
• When and why to install lightning protection systems in high-value or ecologically important trees
• Insights from arboricultural and engineering practices that help reduce tree loss due to strikes

Lightning is not just a destructive force—it’s a natural phenomenon deeply intertwined with forest dynamics and arboricultural care.

Background information:

• 2003 - The possible role of lightning in the tree evolution and biodiversity - Fay.pdf
• KnŪöka 2.1 Final.pdf
• SPPK A02 006_2015Ochrana_Blesk_FINAL_AOPK.pdf

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In this Tuesday episode of Talking Trees, we focus on the often underappreciated but absolutely essential role of the Groundie—the ground worker in tree care operations. Inspired by Jeff Jepson’s book Groundie, we explore what it takes to thrive in this demanding position.

We discuss:

• The core responsibilities of a ground worker during tree work operations
• Why the job is both physically intense and mentally engaging
• The reality of high turnover versus the deep satisfaction for those who commit to the craft
• How the role of a groundie provides the foundation for climbing arborists and safe, efficient teamwork
• Why Jepson’s book is a valuable introduction for those entering the field of arboriculture

This episode celebrates the Groundie not as a stepping stone, but as a profession in its own right, rich in skills, pride, and purpose.

Background information:

• Excerpt from “Groundie” by Jeff Jepson: The Role of the Ground Worker….At a Glance. - Sherrilltree

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In this Monday episode of Talking Trees, we uncover the hidden world beneath our feet—the soil microbiota that supports and sustains urban street trees. This episode dives into the crucial roles played by bacteria, fungi, and other microorganisms living in the rhizosphere and within tree tissues.

We discuss:

• How microbial communities affect tree nutrition, immunity, and resilience
• The constant biochemical communication between roots and microbes
• The importance of endophytes and rhizospheric organisms in supporting tree health
• Why moving beyond an anthropocentric perspective helps us appreciate the complexity of urban tree ecosystems
• How this knowledge can inform better urban tree care and soil management strategies

Street trees are not isolated individuals but hubs in a vibrant, living underground network. Recognizing their microbial allies is key to sustaining greener, healthier cities.

Background information:

• SUELO, ÁRBOL URBANO Y VECINOS INVISIBLES.pdf

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In this Friday episode of Talking Trees, we celebrate the remarkable career of Dr. Mark Johnston, a pioneer in urban forestry whose life’s work has shaped tree care across the UK and beyond. Drawing from his autobiographical reflections in the 2024 TREES e-book, this episode offers a personal and professional journey through decades of dedication to arboriculture.

We explore:

• Mark’s early life and how his passion for trees developed
• His academic and professional path across London, Wales, and Northern Ireland
• Key projects and collaborations that influenced urban forestry policy and education
• The intersection of social values, politics, and green infrastructure
• Insights on how urban forestry has evolved—and where it’s going next

Listeners will be inspired by Mark’s commitment to trees, communities, and sustainable cities.

Background information:

• Planting Ideas in the Urban Forest (https://markjohnstontrees.com/free-ebook/)
• https://markjohnstontrees.com

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Episode Summary (English):

 In this Saturday episode of Talking Trees, we examine the devastating impact of Chalara fraxinea (Hymenoscyphus fraxineus), the fungal pathogen behind ash dieback in Europe. We explore the spread, symptoms, and susceptibility factors affecting Fraxinus excelsior and other ash species, including findings from Ukraine, Poland, and Lithuania.

We discuss:

• How the ash dieback pathogen and emerald ash borer are compounding damage in Eastern Europe
• The potential role of bud burst timing in ash resistance, with earlier-bursting clones showing greater survival
• The presence of wood-inhabiting fungi, like Armillaria cepistipes, in weakened trees, and their possible role in secondary decline
• The importance of phenological and genetic traits in breeding programs for resilient ash populations

This episode highlights current scientific insights into ash decline and disease ecology, offering a hopeful look at strategies for future forest resilience.

Background information:

• Davydenko et al. 2022. Invasion of Emerald Ash Borer Agrilus planipennis and Ash Dieback Pathogen Hymenoscyphus fraxineus in Ukraine - A Concerted Action.pdf
• Przybylski et al. 2024. Spring's Signal_ Can Bud Burst Timing Enhance Resistance to Ash Dieback in Europe_.pdf
• Wood-inhabiting_fungi_in_stems_of_Fraxin.pdf

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In this Thursday episode of Talking Trees, we examine one of the most contentious questions in urban arboriculture: who should bear the cost of protecting trees? Focusing on legal and planning frameworks in the United States, the episode explores how local tree protection ordinances can spark conflict between environmental goals and private property rights.

We discuss:

• The concept of regulatory takings and its legal implications for tree protection
• The case of Canton Township and its failed legal defence of mitigation fees
• The risks of poorly designed or overly rigid tree ordinances
• How municipalities can create more balanced, defensible policies that benefit both the public and property owners
• Ethical considerations in distributing the responsibilities and costs of environmental stewardship

This episode offers a thought-provoking look at the intersection of law, urban planning, and tree protection policy.

Background information:

• Who Should Pay to Protect Trees Tree Protection Regulatory Takings and Unconstitutional Conditions.pdf

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In this Wednesday episode of Talking Trees, we dig into the science and practice of tree injections, also known as vegetative endotherapy. This method of delivering substances directly into a tree's vascular system is transforming plant care, especially in managing pests and diseases.

We explore:

• The history and development of endotherapy techniques
• Types of injection systems: trunk opening, interface, and direct injection
• The most common uses: applying insecticides, fungicides, and nutrients
• Practical considerations such as dosage, tree species suitability, and seasonal timing
• Benefits and limitations of injections compared to foliar sprays and soil treatments

With insights from recent research, this episode highlights how tree injections are emerging as a sustainable, targeted approach in arboriculture and urban forestry.

Background information:

• The endotherapy | Endoterapia Vegetal
• Tree Injection - an overview | ScienceDirect Topics.pdf
• Tree injection - Wikipedia
• Why Tree Injection? - Tree Care Industry Magazine
• agriculture-13-01465-v2.pdf

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In this Tuesday episode of Talking Trees, we ascend into the practical world of structural substrates and their critical role in supporting healthy urban trees, especially in areas with paved surfaces and compacted soils.

We focus on Cornell University’s CU-Structural Soil® system, an engineered soil blend combining crushed stone and uncompacted soil to provide a load-bearing yet root-friendly environment. This innovation allows trees to thrive beneath sidewalks, plazas, and roads without compromising infrastructure stability.

Topics include:

• Challenges of urban soil compaction
• Benefits and function of structural substrates
• Key features of CU-Structural Soil® and its practical applications
• Installation, irrigation, and tree species considerations
• Examples from real-life urban projects

This episode is a must for arborists, urban planners, and landscape architects looking to enhance tree health in dense city environments.

Background information:

• Guía Suelos Estructurales Universidad de Cornel.pdf

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