Advancing arboriculture through human and tree ecology

Abstract

This paper explores the significance of ecosystem functions in maintaining the health and balance of ecological systems, particularly in the context of planning, managing, and maintaining trees in landscape settings. It emphasises the multifaceted relationship between humans and trees, encompassing cultural, ecological, economic, and emotional connections, and underscores the value of traditional ecological knowledge alongside empirical science. By combining these two ways of knowing, along with social science insights into human health and well-being, future landscapes can be crafted to be sustainable, diverse, and functional. As urbanisation continues to shape landscapes globally, urban planners face the challenge of managing rapidly changing environments. Urban forestry and arboriculture have emerged to address these challenges, aiming to enhance environmental quality and human well-being. The concept of Nature-based Solutions (NbS) has gained traction, recognising the importance of integrating natural systems into urban planning to address environmental challenges while preserving functional ecosystems. This paper advocates for an enhanced understanding of tree and human ecology to navigate the complex relations between trees, people, and their environments. It calls for interdisciplinary collaboration, research, and education to inform policy, assess environmental impacts, and widen approaches to ecosystem management. By monitoring ecosystem health and collaborating across disciplines, arboriculturists and urban foresters can shape resilient practices for tree conservation and sustainable urban development. In conclusion, integrating tree ecology into urban planning and management practices is essential for ensuring the health, resilience, and sustainability of tree populations and the ecosystems they inhabit. By embracing a holistic understanding of trees and their environments, professionals can contribute to shaping future landscapes that support both human well-being and biodiversity.

Keywords:

• Tree Ecology
• Ecosystem Functions
• Traditional Ecological Knowledge (TEK)
• Urban Forestry
• Nature-based Solutions (NbS)
• Arboriculture

The human relationship with trees is characterised by a rich tapestry of cultural, ecological, economic, and emotional connections (Frediani, 2021; see Figure1). Trees are not only essential for human survival and well-being but have also held profound symbolic and spiritual significance in traditional ecological knowledge (TEK) or traditional knowledge (TK), in Indigenous human societies across the globe. In contrast, the study of trees using empirical science has only been advancing in recent centuries, with roots dating back to the early days of modern scientific inquiry. Empirical research in ecology, including tree ecology, began to gain significant momentum in the late 19th and early 20th centuries (Odum & Barret, 1980). Since then, a substantial body of social-ecological literature has steadily emerged, highlighting the pivotal role of trees in bolstering the health of human and biological ecosystems (Marselle et al., 2021). Trees are celebrated for their role in creating a more pleasant, healthier, and comfortable environment for citizens to live, work, and play in. These organisms play an essential role in the function and resilience underpinning natural ecosystems, through the provision of habitat, food, oxygen, carbon sequestration, soil formation and stabilisation, water regulation, nutrient cycling, and temperature regulation.

The past offers valuable insights into the intricate layers of a landscape’s history. In seeking to understand where and how communities of trees may have naturally propagated and grown, we learn to read the “old growth” woodlands, and their formative groves that have markedly changed since the Pleistocene advancement, which ended 11,700 years ago. Large vertebrates, as strong interactors in food webs, were lost from most ecosystems following the dispersal of modern humans from Africa and Eurasia, c. 300,000 to 200,000 years ago (Donlan et al., 2006). Knowledge in this context helps us to interpret the palimpsest that led up to the present landscapes and features, where “ancient woodland” and “ancient” and “veteran trees,” can be understood in the context of the modern cultural landscape (Rackham, 1990). It is a complex and diverse landscape modified multiple times by humans over recent millennia in the Holocene. Traces of former dynamic and diverse mosaics have shifted over time, which have been increasingly simplified and more recently mechanised in the pursuit of productivity. In doing so we seek to comprehend the prior actions of those who have worked with trees, can begin to interpret the agency of previous land owners who have each stewarded spaces, through a diversity of improved land uses that have come to be compounded as the cultural landscapes we have inherited today.

There is a rich history to unpick that includes the hunter gather harvest of famine foods in ancient times and the working of osier withies and bast fibres, fashioned into baskets, textiles and ropes. We have learned the importance of animal forage and pannage to the outputs of woodlands, and how harvesting of structural timbers for ships, bridges, and cathedrals often occurred in hedgerows and boundaries. This is because these areas were considered feudal property under forest law, until private landowners retained them through the 18^th and 19^th century improvement period, as their value was being replaced by iron and steel. These histories can be read in our heritage gardens, the agroforestry of our parks, farmland and orchards, as well as in our pre-enclosure hedgerows, fields, and woodlands (Augere-Granier, 2020; Çolak et al., 2023). They helped inform the character of our historic parklands and today help soften the hard architecture in our modern urban landscapes. Such a study reminds us not only of how productivity has been a constant force of change in the landscape, but also of what resilience means for the individual trees and woodlands that have subsequently survived such human induced land cover and land use changes over the course of their long histories.

Figure 1. This human ecological schema, represents a simplified socio-economic-environmental system with many component parts (rectangles) that interact within and across levels of tree governance and organisation. The overall boundary of the whole S-E system is the solid black line, and the subsystems are in light blue or green in each of the large grey rectangles. The large black arrow at the top indicates that the overall system state or behaviour “emerges” as a result of the interactions. The interactions noted are not exhaustive (e.g. reduced national, regional or local economic-outputs could spur changes to national land use policy with regional or local land cover implications). Rural landscapes and urban spaces that include or have the potential to include trees or woodlands must be examined from diverse perspectives to fully understand their interconnections. This includes ecological or conservation and environmental drivers, but equally from the corporate economic and social perspectives of the social system to ensure good governance and management is afforded at the local and regional planning levels © Kevin Frediani 2024.

Discerning the woods from the trees

We live in a rich era of information we can easily gain access to. Knowledge has been compiled during an urban and more recently technological transition, a modern phenomenon in human history, which has increasingly witnessed communities leaving the rural landscape – leaving behind embodied knowledge gathered over millennia, reframed as TEK and TK by ethnographers. Stories that originated in popular culture, which would have previously been valued and tacit as inherited wisdom beyond folktales, have been marginalised. There has been little consideration given to the ways in which people visualised and came to understand their environment and those of others. Conventional landscape studies focusing on post-roman periods are concerned with “material” landscapes – that is, the physical traces of people’s lives and occupations. The notion of “mental” landscapes, relating to the “superstructures of meanings and values” attached to these material remains, are less well explored, although commonplace in prehistoric studies.

Today, more than half of the world’s population are now living in urban areas, with higher populations found across most high-income countries – across Western Europe, the Americas, Australia, Japan, and the Middle East – where more than 80% of the population now reside (Ritchie et al., 2024). Learning to interpret this new and rapidly growing, homogenised approach to landscape is one of the challenges being led by urban professional planners. It is a fast growing profession, which is struggling to keep up with the fastest growing habitat on Earth today (United Nations 2015; Simkin et al., 2022), the urban habitat – representing 2% of the world’s land surface but using over 70% of the global natural resources (Grimm et al., 2008; McKinney 2006). As new urbanists with deep roots, we can help trace the origins of forms and landscapes we have transposed into our streets and parks, that became the 19^th century tree-lined boulevards of our industrialised urban streets, echoing the former tree-lined avenues in pre-industrial landed estates and then transposed across Europe and the global iterative western informed urban paradigm. This can help find a localised sense of new vernacular – which embraced the aesthetics of “place,” with the historic understanding of living heritage.

The concepts of arboriculture and urban forestry have evolved late in this timeline of urban growth, but have come of age, are professionally recognised and are now well placed to blend the historical and scientific knowledge with the new technological skills to help inform the planning of the future treescapes in a time of global change (Koch, 2000). From horticulturists to arboriculturists (UK), from foresters to urban foresters (US), urban forestry is increasingly being promoted to describe the planning, design and landscape management of populations of trees as part of Nature-based Solutions for our modern cities (Bell et al., 2005). The science and practice of the cultivation, establishment and management of amenity trees is practiced for the benefit of society (arboriculture), and single trees and tree populations are planned and managed in urban settings for the purpose of improving the urban environment (urban forestry). Both approaches are underpinned by the human perception of an aesthetic value as improved, that considers trees as features of a place, contributing to its attractiveness and comfort. This echoes its late 14th century etymology, where amenity (n.) meant a “quality of being pleasant or agreeable” to inhabitants. This reflects the notion that spaces only become places when imbued with emotion through the action and reactions of people and their environment. Where an important consideration for the conservation and development of biodiversity is to reflect the local ecological characteristics of the areas where the woodland, park or street trees are to be located (Gilbert, 1991). Biodiversity, in this context being valued not primarily for its intrinsic value but for its underpinning of urban ecosystem functions that are essential for human health and well-being.

Seeing the interconnection of the entire system

How land is used is deeply connected to the most critical issues of our time: sustainable development, economic development, reducing territorial inequalities and the rights of future generations. Awareness of this interconnection, leads onto the recognition that a wide range of top down policies shape how land is used and managed or conserved within the framework of land use and environmental planning systems being adopted globally (Tate et al., 2024). The human need to categorise and its cultural bias towards human made rather than natural features to value, is reflected in the concept of Natural Heritage, defined at the international level by UNESCO that allows for the designation of landscapes under the World Heritage Convention. It is an international instrument designed to protect the most extraordinary natural places on the planet, characterised by their natural beauty or outstanding biodiversity, ecosystem and geological values. It has an anthropocentric bias towards so called wilderness landscapes which lies at the heart of many forms of environmental ethics, and has been of particular significance in the US, and to deep ecology. It is a designation that reflects a view that wildernesses are untouched, pristine parts of the natural world, formed without human agency and to be protected from permanent human presence. Such cultural bias has meant that urban spaces are spaces neglected in environmental ethics until very recently. Whilst wilderness has been at the heart of environmental ethics since its very beginning, there have been barely any publications on urban environments to date (Brennan and Norva 2022).

The human need to classify and confer social constructs that become norms for society to adopt and embrace also helps to define human definitions of, and subsequent management of, cultural constructs such as “cultural heritage.” A significant definition that has recently been defined nationally is through the Levelling Up and Regeneration Bill (LURB) in the UK, which defines “any building, structure, other feature of the natural or built environment, which is of historic, architectural, archaeological or artistic interest.” Conduct as a way of acting, bearing or deportment, including providing direction or management or administration is after all pervasively a function of norms; where norms account for many apparent oddities or anomalies in human behaviour. Changes in norms might be the best way to improve social well-being where government inevitably has a significant role in norm management, including the definition and protection of trees, habitats and landscapes. As such, cultural heritage can be considered a key component of the wider environment when making planning decisions.

We are still only just understanding the incredible legacy of ancient trees in our rural and encapsulated urban environments that we have inherited. Our values are not yet reflected in their acknowledgement, so designation is lacking in the UK landscape and the collective social construct of “living heritage” is left wonton of protection, because of the way we designed our legal system. Individual trees still have no current standing: subsequently having no legal status, in and of themselves. This is a point unfortunately laid bare with the recent felling of the Sycamore Gap tree demonstrating that, the rights of life and death over an individual tree in the UK belong to whoever owns the land it is rooted in, with no regard paid to its intrinsic value as a living being or cultural or ecological amenity.

While there is no kind of legal understanding of a tree being a separate legal entity, which is causing loss of irreplaceable diversity in our rural landscapes, there is a growing trend to promote Nature-based Solutions into urban planning around the world with endorsement at the highest intergovernmental level. In 2020, IUCN launched the IUCN Global Standard for NbS, recognising them as providing holistic ecosystem-based approaches to providing “solutions based on nature use the power of functioning ecosystems as infrastructure to provide natural services to benefit society and the environment” (IUCN, 2022). Such an approach is aimed at addressing the imbalance in the human social and natural environmental systems and is informed through a better understanding of human ecology, which involves the interrelationships among people, other organisms and their environments. Adopting a human ecology lens, therefore, can potentially help capture and make sense of the complexity of a system, highlighting potential areas of stress and helping to direct opportunities for intervention that might otherwise not be understood. This helps to access the knowledge of the structure, function and processes that informed the current human settlements, which may be then subject to foresight, to better plan urban and rural trees in the face of the biodiversity and climate polycrisis (Hoyer et al., 2023; European Foresight Platform, 2024; Figure 2 above).

Figure 2. Foresight is a systematic, participatory, future-intelligence-gathering and medium-to-long-term vision-building process aimed at enabling present-day decisions and mobilizing joint actions. It can be envisaged as a triangle combining “Thinking the Future,” “Debating the Future” and “Shaping the Future.” Source JRC-IPTS © European Foresight Platform.

The idea of holistic “whole ecosystem” properties and measures has a long history in ecology. However, research into the ability of ecosystems to simultaneously provide multiple ecosystem functions and services (multifunctionality) has become increasingly common only in the last decade, as comprehensive datasets and model outputs from multidisciplinary, collaborative projects have become available. It provides the potential future integration of function habitat for wildlife and creates a more hospitable setting for many species at the landscape scale as well (Gilbert & Anderson, 1998). It enables a more complete understanding of the potential of establishing functional green and blue infrastructure for sustainable urban ecosystems. Such approaches require new skill sets and knowledge, because like all ecosystems, urban ecosystems are composed of biological components (plants, animals and other forms of life) and physical components (soil, water, air, climate and topography). These components interact with one another within a specified area and can be linked by extension to the rural landscapes beyond the political and administrative boundaries that currently define them.

Functional landscapes require scale. After all, ecosystems are transboundary in terms of the mapped human constructs of towns, cities, counties and even countries where individual species and their communities are found. In rural ecosystems this can be understood at the catchment or bioregional level that is informed by the physical and biological features of any dominant ecosystem. In the case of urban ecosystems, however, the biological complex also includes human populations, their demographic characteristics, their institutional structures, and the social and economic tools they employ. The physical complex includes buildings, transportation networks, modified surfaces (e.g. parking spaces, roofs and landscaping), and the environmental alterations resulting from human decision making. The physical components of urban ecosystems also include energy use and the import, transformation and export of materials. Such energy and material transformations involve not only beneficial products (such as transportation and housing) but also pollution, wastes and excess heat. Urban ecosystems are often warmer than other ecosystems that surround them, have less infiltration of rainwater into the local soil, and show higher rates and amounts of surface runoff after rain and storms. Heavy metals, calcium dust, particulates and human-made organic compounds (e.g. fertilisers, pesticides and contaminants from pharmaceutical and personal care products) are also concentrated in cities.

Practical consideration to help advance arboriculture and urban forestry

While arboriculturists and urban foresters work with individual and populations of trees, their approaches, areas of focus and the scale of operation overlap within what can be considered nested levels of practice and management. However, both can potentially differ when we consider a deeper understanding that could be attributed to tree ecology. This point of difference offers a new opportunity for individuals and organisational growth and development as arboriculture and urban forestry are asked to support the overseeing of a rapid transition of urban areas from a grey to green and blue sustainable development. There is a growing acknowledgement that foresight planning requires strategic partners with professional knowledge in the planning, implementation and management of Nature-based Solutions to come together and design, build and reshape cities as sustainable urban ecosystems. These include trees in urban areas that provide ecosystem services to the city residents and visitors, while also helping to conserve and maintain the ecological functions of the cultural landscapes they help create and the remaining open grown trees in our wider landscapes which include our revered ancient and veteran trees.

To help open the discussion of how this opportunity may be explored to support trees not only in the urban but also in the wider conservation landscape as living heritage in the rural landscapes, I will attempt to frame the subtly different approaches to knowing trees that arboriculturists/urban foresters and tree ecologists might be expected to assume. This is an exercise informed by a personal challenge made to me by Ted Green MBE, founder of the Ancient Tree Forum and prototype tree ecologist, who asked whether a better understanding of tree ecology might help add value to the professional development and potential growth of the arboricultural sector, while improving the open treescape he has spent so much of his professional life’s work on. The approach looks to compare and contrast the first principles of the knowledge that may be gleaned from an ecosystem services based tree and population approach to one that looks to adopt the wider ecosystem functions perspective. Given such an ecological framing, a tree ecologist could be expected to emphasise the broader ecological context and the interactions between trees, other organisms and their environment as a priority. Whereas it would be reasonable to expect the arboriculturist and urban forester to focus more on the optimal ecosystem services or benefits, that can be managed within human-resourced landscapes.

Table

Definitions: Ecosystem functions include the physicochemical and biological processes that occur within the ecosystem to maintain terrestrial life. Ecosystem services are the set of ecosystem functions that are linked to benefit human well-being (Kremen, 2005).

From this framing of disciplines, tree ecologists, arboriculturists and urban foresters all currently approach and work with trees in discrete ways which I will attempt to summarise, noting that this discussion has required broad generalisations to be made to elevate the points. However, the article is not seeking to undermine any profession but instead raise awareness of the opportunity and benefits that might arise by embracing tree and human ecology into the pedagogy that informs the current world view of the existing profession. The hope is to stimulate a discussion that others may contribute to in future issues of this journal.

Tree ecologist

Focus: Tree ecologists study trees within the broader context of ecosystems, focusing on their interactions with the environment, other organisms and the ecological roles they play.

Research: They investigate the physiological, ecological and biodiversity aspects of trees, examining their roles in nutrient cycling, carbon sequestration and their responses to environmental changes.

Scope: Their work involves understanding forests, woodlands and tree populations in natural settings, considering their relationships with soil, climate and other species.

Purpose: Tree ecologists contribute to conservation, sustainable forest management, and understanding the ecological functions of trees within ecosystems.

Arboriculturist

Focus: Professionals trained in the care, maintenance and management of individual trees, and populations of trees often in urban or suburban settings.

Practical Applications: They specialise in tree care practices, including pruning, planting, pest and disease management, risk assessment and tree preservation in urban landscapes.

Scope: Their work revolves around maintaining a healthy and diverse population of trees, critical to sustaining resilient delivery of tree benefits, and requires understanding on the whole community tree and woodland resource, including: species and age composition, distribution and health.

Purpose: The aim is to ensure the health and longevity of individual trees, and as part of a community, considering their role in enhancing urban landscapes, providing shade, improving air quality and supporting wellbeing as part of public amenity.

Urban forester

Focus: Urban foresters undertake the management of naturally occurring and planted trees and associated plants in urban areas.

Practical Applications: The practice of forest and natural resource management situated within developed areas (e.g. cities, towns and suburban areas) that involves the management of trees and other natural systems for the health and well-being of human society.

Scope: The urban forest comprises the design, planning and management of all the trees in the urban realm – in public and private spaces, along linear routes and waterways and in amenity areas. It contributes to green infrastructure and the wider urban ecosystem. It provides multiple benefits to human society, at scale, that are strategically planned and evaluated.

Purpose: Maintaining a healthy and diverse urban forest is critical to sustaining resilient delivery of these benefits, and requires understanding of the urban forest resource, including: species and age composition, distribution and health.

Initial thoughts and reflections

There is a need to recognise a difference between the approaches to tree care and management, based upon underpinning knowledge. While the professional name for tree care and management is for the profession, the underpinning knowledge base that informs their practices is intricately linked to the terms of reference we use to justify their work and outputs. This paper has identified a current focus of both arboriculture and urban forestry that is based upon the provision of ecosystem services, which are the set of ecosystem functions that are useful to humans. I argue that this presents not only a shortfall in the potential offer, but also a risk to the wider treescape we profess to care for. If we only focus on the services and benefits that trees provide through our work as professionals, we will bias the outputs towards the slow erosion of the self-sustaining functional ecosystems that underpin the wider ecosystem that our all-encompassing social system is embedded within. The limits to growth have been well made for over 50 years following the first study of the interconnected challenges of the world using one of the first computer models, in 1972. Their finding being reinforced in 2022 with the following challenge:

It is only collective action that reflects the interconnectedness and interdependence of the web of life, a holistic viewpoint and systems approach, will adequately address the issues we face as part of the planetary emergency.

Both transformative thinking and action is needed – which is what this paper hopes to foster with a final suggestion that we need to embrace an ecological engineering core to our methods, an environmental history underpinning our knowledge and a climate awareness through human ecology to see the whole landscape we work within. The use of terms like Nature-based Solutions (NbS), and the offsetting of biodiversity through initiatives such as Biodiversity Net Gain, are examples of the commodification of biodiversity which requires a balanced approach to ensure living functional systems are retained, protected and fostered. After all, biodiversity is not something we can replace and recreate anew with a 10% added value overnight, through the transfer of money or awarding of a contract – given we have yet to restore a single habitat on Earth, yet alone understand the complexity of trees and their habitat! We don’t even know the sum of diversity associated with an individual plant’s holobiont (Vandenkoornhuyse et al., 2015; Fuentes-Montemayor et al., 2022; Mesny et al., 2023). This emerging field of research has blossomed in recent decades, as scientists have been exploring the complex associations of the micro-organism such as bacteria and fungi, upon, within and around each individual plant. It is one thing to study these associations, and quite another to profess to understand how other organisms interact across a landscape scale, as we see the continual decline of birds, bats, moths and other macro-organisms which are associated with the landscapes we are looking to help manage.

The emerging role of tree ecology (tree ecologist)

Tree ecologists can play a multifaceted role in understanding, managing and conserving tree populations and their interactions within our current knowledge of the functional ecosystem. Key roles they might explore include:

• Research and study: Tree ecologists can conduct research to understand the biology, ecology and dynamics of trees within their ecosystems. This involves studying tree physiology, species interactions, biodiversity patterns and the impact of environmental factors on tree populations.

• Ecosystem management: They can contribute to the management and conservation of individual trees, as well as forests and woodlands. By studying tree ecology, as well as species composition, forest dynamics and ecosystem functions, they inform forest management practices, biodiversity conservation strategies and restoration efforts. From sustainable urban drainage systems to shelterwoods, the ecological engineering of landscapes requires holistic understanding of tree ecology if functional ecosystems are to be established and maintained.

• Environmental impact assessment: Tree ecologists assess the environmental impact of a range of factors on tree populations, such as climate change, land-use changes, pollution, and disturbances like flooding, wildfires or logging. They provide insights into how these factors affect tree health and ecosystem stability.

• Policy development: Their research findings often contribute to policy formulation related to tree conservation, land-use planning and sustainable resource management. They provide scientific input to support decisions that affect tree populations and ecosystems.

• Education and outreach: Tree ecologists often engage in education and outreach activities, sharing their knowledge with the public, policymakers, land managers and other stakeholders. They raise awareness about the importance of trees, promote conservation efforts and advocate for sustainable practices.

• Collaboration and interdisciplinary work: They collaborate with scientists from various fields, such as botany, ecology, climatology and soil science, to gain a holistic understanding of tree ecosystems. Interdisciplinary collaboration helps address complex ecological questions more comprehensively.

• Monitoring and assessment: Tree ecologists engage in monitoring tree populations and ecosystem health over time. By assessing changes in tree distributions, health and responses to disturbances, they contribute to long-term conservation strategies.

• Informing resilience: The diversity – function debate in ecology tackles the question of whether increased numbers of species enhance function. A common question within diversity – function research is: “‘Do communities with more species have more biomass production?’” Nested within this question is the issue of whether all species matter, or whether there are interchangeable groups of functionally equivalent species. An important question when we look to select and plan future treescapes that are adapted to the climate that is predicted to come.

As noted earlier, urban areas are the fastest growing ecosystem on Earth, with the development of cities leading to modifications to many aspects of the wider environment. On average, urban areas experience increased air, water, light and noise pollution, more impervious surfaces (e.g. buildings and paved roads), greater habitat loss and fragmentation, as well as more non‐native species compared to nearby non-urban habitats (McDonnell et al., 2009; Niemelä, 2011). As such, cities tend to be more similar to one another in their biotic and abiotic environmental characteristics than they are to nearby non-urban ecosystems (Groffman et al., 2014).

Knowledge of tree ecology has the potential to augment the roles of the arboriculturist and urban forester and progress new opportunities that are diverse and critical in maintaining the health, resilience and sustainability of individual trees, tree populations and the ecosystems they inhabit. This paper argues that professionals informed with this knowledge and world view could also contribute significantly to our future understanding of the intricate relationships between trees and their environments, helping to shape future practices that support the well-being of these vital organisms and their surrounding ecosystems.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Notes on contributors

Kevin Frediani

Kevin Frediani is an experienced manager and leader of change in the land use sector gained over 30 years. As Curator of Botanic Garden and Head of Grounds at Dundee University, he leads a team that conserves, educates, facilitates research, and delivers a sustainable green infrastructure across the university campuses, sports facilities, and Botanic Garden. He has a background in arboriculture, horticulture and sustainable land use as a curator, lecturer, and researcher. He is currently one of the Horizon Europe funded UrbanReleaf.EU project team enabling a citizen-powered data ecosystems to support cross-sectoral innovation and inform the political agenda for informed climate change adaptation and green infrastructure planning in urban environments.