Chapter 7: Trees and Ecology

The Earth may not be a spaceship but an organism, and the trees may be its lungs.– Michael Pollan


Ecology is the study of interrelated patterns, processes, interactions, and relations of flora, fauna, and ecosystems/habitats, including biotic and abiotic factors. Ecology is all plants, animals, and micro-organisms functioning together with the environment in complex and dynamic ways to create system balance. Forests and woodlands support the most biodiversity of plants and animals of all land-based habitats. Above and below ground, trees create micro-environments and microclimates. This is fairly obvious for tree communities but also true for individual trees, though the effects may be smaller and harder to see.

Historically, people have treated trees as individuals, especially in human built environments. A shift is needed to think about and treat trees as communities instead. Research in many disciplines supports this assertion and continues to provide new evidence of the interconnectedness of trees to each other and to other life forms in the community (plant, animal, insect, and fungi).[1] In many cases there is reliance or symbiosis occurring where one species cannot live or function without another. Thus, removal, treatment, or impact on one species affects other(s), and the effects ripple through the entire community. Species diversity within a community supports a web of complex relationships and creates checks and balances leading to resiliency and sustainability of the community.

Community balance is not, however, static over time. In the long historical view, ecosystems change gradually, interrupted by occasional events such as earthquakes or hurricanes. However, today’s reality is one of increasing urbanization and rapid climate change, requiring a new level of understanding of and management help for the trees in our cities and forests.

This chapter considers the significance of trees to the ecological balance in Virginia. The discussion of ecology is expanded beyond just interactions between naturally occurring organisms. It also considers the broader picture of biological, physical, social, and economic factors which together describe the reality for those organisms (including people and trees). The goal is to equip the tree steward with conceptual and resource tools to understand the context within which trees grow, including the regional differences across the state.

Learning Objectives

  1. Understand the definitions of key words in the fields of ecology and sustainability study.
  2. Understand the concept of Healthy Tree Cover.
  3. Understand the roles of the forester, the urban forester and the arborist.
  4. Be able to discuss factors which influence Healthy Tree Cover.
  5. Be aware of methods to improve Healthy Tree Cover.
  6. Be aware of regional differences within Virginia.
  7. Be aware of climate change dynamics as they affect the trees and tree cover in forests and urban areas.
  8. Understand the ecological situation in the student’s home region in enough depth to help improve Healthy Tree Cover through VCE outreach.

REVIEW: VCE Master Gardener Handbook 2015 (9/18 update)

  • Chapter 19: Water Quality and Conservation
  • Chapter 20: Habitat Gardening for Wildlife

 Definitions and Discussion

This section lays out the significant terms tree stewards should understand when considering trees as a part of ecological programs and activities. The terms and definitions are interrelated and build upon each other in many ways. The diagram below is one way to organize these different elements. The root zone reflects how important it is for each of these concepts that activity be based upon proper research, well-designed education, and consistent communication.

tree flow chart with buzz words about trees and environment: Biomes, phenology, disturbances, change, resilience, climate, mesoclimate, microclimate, natural communities, human changes, ecosystems and services, sustainable ecology, silviculture, urban forestry, arborculture. at the base of the tree, a box reads research, education, communication
Figure 7-1 Ecological Terminology Tree. (Courtesy Carol King)

Ecology is the study of the interrelationships between individual organisms and groups of organisms and between living organisms and the abiotic features of their environment.[2] It is important to note that relationships of many sorts, among many organisms and factors, influence ecological systems (ecosystems for short). Often, we think of the natural environment as a peaceful, serene coexistence: a poetic, romantic view. The reality is that the balance in a healthy ecosystem is achieved as an equilibrium among constant pushing and pulling by all the inhabitants. Dr. Doug Tallamy talks about a healthy garden as “a dynamic community of interacting organisms.”[3]

Biome is defined as any of the world’s major ecosystem types (terrestrial or aquatic), typically described in terms of dominant life forms and physical characteristics. Biomes are especially useful to look at for the adaptations the life forms make to survive in their surroundings.[4] The US Temperate Deciduous Forest Biome is a descriptor for the forest coverage of most of the eastern part of the United States. Broadly speaking, precipitation varies from 28 to 60 inches, evenly throughout the year. Freezing or near-freezing temperatures occur annually, and there are four distinct seasons.[5] Forest regions in the Eastern US are shown in the map available below, from an expert analysis in 2006. The cited paper notes that “continuing environmental change will be an issue for future research.” Virginia is in the Mesophytic and Southern Mixed regions, which include oaks and pines as significant species in a large and diverse list of tree species. More detailed descriptions of these regions can be found at Virginia Tech’s CNRE Forest Outreach (FORSite).[6]

For a map of forest regions, please see the National Park Service Eastern Deciduous Forest page:

Phenology is the “study of seasonal events, such as when plants produce leaves, flowers and fruit, when leaves fall, the arrival and departure of migrant species, nest-building, hibernation, etc.”[7] The significance of this field of study comes in the inter-relationships between different organisms within a biome: many plants depend on pollinators that hatch or arrive when the flowers are in bloom. Similarly, insect life cycle dates may be significant for birds who depend on them to feed their young. When timing changes occur to some parts of a phenological chain but not to all, then species disruption is likely. Logically, phenological disruption effects will be seen with annual and perennial plants (and their associated animals) before longer-lived species such as trees, but this is a concern for all species considering the rate of urbanization and climate change.

Disturbances in nature are more the norm than the exception, with frequency and destructiveness on the rise. Storms cause flooding, mudslides and erosion which kill trees. Winds make trees grow strong trunks but can also damage them. Forest fires cause detrimental cascading effects on soils and wildlife. Yet the absence of smaller, regular fires can also be a disturbance. For example, such fires allow the longleaf pine to sprout its seeds and to outcompete plants which are not fire resistant.[8] Human intervention is definitely a form of disturbance, such as concrete infrastructure projects that cause ecosystem fragmentation and degradation, with severe impact on trees. Sometimes the disruption can be in seemingly ‘green’ realms of activity: trees get harvested, in some cases almost to extinction, while others are shipped and grown around the world, well out of their original ecosystems. Multiple disturbances can compound the ecosystem impact and start destructive cycles that are hard to stop.

Along with disturbances, ecological systems are distinguished by the pervasiveness of change: not just a busy hum of constant tedium, but also an unending drama of skirmishes between creatures large and small struggling to stay alive and prosper in the face of shifting circumstances. One of the more important aspects of an ecological system is its resilience, or ability to handle the changes and recover/move on from disturbances. While the foregoing has always been true, data trends indicate more severe and frequent disruptive weather events; which may mean the acceleration of change patterns over the past or the decline of species and ecosystems that cannot adapt and thus are not resilient.

Climate is defined as the weather conditions experienced in a particular location averaged over a long period of time. In the United States, this is generally 30 years, adjusted every 10 years.[9] Trees are major components in soil, air and water cycles, and thus are important for overall climate stability.

Climate Change, according to the National Oceanic and Atmospheric Administration (NOAA), is “a significant and persistent change in an area’s average climate conditions or their extremes.”[10] The primary components of climate change are temperature, precipitation and sea level rise.[11] Looking deeper, the combination of these effects means both drought and floods; erosion and other soil detriments; increasing wildfires and invasive pest issues; and challenges to the natural adjustments by trees in terms of genetic pools, reproduction patterns and migration.[12]

Mesoclimate is the weather of a neighborhood or a city as modified by local influences of buildings, terrain, bodies of water, wind, and cloud cover.[13] This can lead to significant differences in the survivability of plants on the margins of their hardiness zones, water tolerances, etc. Many of the benefits/ecosystem services which trees provide, especially in the built environment, are actually improvements to the local mesoclimate or mitigation of its extremes (i.e. cooling of heat islands or moderating flooding). As climate changes continue to pose unprecedented challenges, management strategies at the mesoclimate level will have increased significance.

Microclimate is the same thing as mesoclimate but in a very small space. For example, a cold-sensitive tree can survive in a colder climate when it is planted against a sunny wall and screened from cold winter winds. Every site (home landscape, school yard, city park, etc.) has microclimates created by sun/shade exposure, wind, soils, water, buildings or other factors.

Natural Community is a usually recurring grouping of live organisms which co-exist and interact, taken together with their physical environment and ecological processes.

  • The Natural Communities of Virginia Classification of Ecological Groups and Community Types, from the Virginia Department of Conservation and Recreation is a catalog of the significant naturally-occurring ecological communities across the state. This resource gives tremendous insight into what lives together and where.[14]
  • The Digital Atlas of Virginia Flora is a searchable database which lists the vascular plants in Virginia and displays where they are found in the state.[15] For example, the maps below show each county where the white oak, Quercus alba is found (figure 7-2) and where the Bald Cypress, Taxodium distichum is found (figure 7-3). The database will also give a listing of plant species found within a specific county or city.
  • Flora of Virginia is a 2012 publication that documents and contains detailed descriptions of all 3,164 species of plants found in Virginia.[16] The last such catalog for Virginia was published in 1762!
map shows the entire state of Virginia highlighted to show white oak distribution
Figure 7-2 White Oak Distribution (shown in blue). White oaks are distributed throughout the whole state.


eastern half of state shaded to show bald cypres distribution
Figure 7-3 Bald Cypress Distribution (shown in blue). Bald Cypress distribution covers only the lower East coast, extending as far to the interior as Brunswick county.

Human Changes alter the natural communities in many ways. It is critical that we understand both the natural ecosystems and how human development has altered them. As an example (referring back to Chapter Six), urban soils are unlike any naturally developed soil, yet city-dwellers and planners must deal with their ecological consequences.

Ecosystem Services is a term describing services (also called benefits) provided by the environment, especially trees and tree communities. These services are grouped into four broad categories:[17]

  • Provisioning – products from ecosystems including food, drinking water, medicinal products, fuel wood, jobs, timber and drinking water.
  • Regulating – such as climate regulation, disease regulation, pollination, migratory wildlife, water quality, and water supply, soil health and stabilization.
  • Supporting – carbon dioxide and oxygen cycles, cycling of nutrients (N & C), genetics, pollinators & beneficial insects, energy transformation, formation of soil, beneficial insect and migratory species habitat, primary production/connection of ecosystems and resiliency/sustainability.
  • Cultural – nonmaterial benefits people gain from ecosystems including: recreation, spiritual benefits, aesthetic enjoyment, education, reduced violence, seasons, memorials, mental and physical health, community engagement, and historical and cultural benefits.

Sometimes these services are assessed in dollar terms. Examples include: when coastal communities apply for grants to plant riparian buffer zones to reduce the impacts of erosion and flooding, when cities assess the value of tree canopy for stormwater management and heat island moderation, or when trees increase property value and reduce crime. Often, though, people do not understand or value these services, especially when making cost/benefit planning decisions.[18] Some developing fields of study, such as the role the amount of tree canopy or specific tree species play in urban stormwater management, show where more scientific research and modeling are needed to refine urban tree policies.[19]

Sustainable Ecology is a term describing a state in which the interrelationships between living organisms and their environments are so balanced that long term stability is not sacrificed for present productivity and vice versa. In other words, it means using natural resources wisely in the short term so that the resources continue to be available in the long term. Trees are among the most significant contributors to sustainable ecology, in urban, suburban and rural settings. As an example, the Digital Atlas of Virginia Flora lists nine life support processes essential for the continuation of life on Earth, of which two are inextricably tied to trees: Land-System Change and Biosphere Integrity.[20]

Silviculture and Forestry are terms used to describe the science of developing, caring for and cultivating forests, as well as managing trees for timber production. The two terms are not synonymous, but the differences are a subject of another book. There is considerable discussion among foresters about ecological forestry (among a number of similar phrases), meaning practices which:

  • Recognize the intrinsic value of forests in balance with larger ecosystems
  • Understand that forests must provide for human social and economic needs
  • Plan for the long term with scientific data and location-specific experience[21]

Arboriculture is the study and practice of caring for trees and other woody plants in the human built landscape.[22][23] This usually means a focus on individual trees or those in settings without natural forest surroundings. Examples are home landscapes, city street trees and trees in school yards, cemeteries and public venues. Arborists specialize in helping trees adapt to and survive in the built environment, including extensive research into best selection, planting and establishment practices, soil analysis and mitigation, long-term maintenance and risk assessment.

Urban Forestry is the management of trees and associated plants in urban and suburban areas, including both naturally occurring and planted trees. The focus is on the larger populations of trees rather than individual specimens. Examples include the tree canopies in public parks, green spaces and natural areas. Municipal tree managers, tree officers and city/county arborists engage in urban forestry as they work with civil engineers, public works departments, government agencies, educational institutions and the public to improve the built environment by preserving or planting trees and other woody plants.[24][25]  Urban forestry involves maximizing the value of tree-related ecosystem services.

Healthy tree cover is an informal concept proposed for the purposes of this manual. In the terminology tree graphic at the beginning of this section, the entire canopy of the tree represents healthy tree cover. The concept can be applied for individual city trees, a grove in a park, a forest stand or any density of trees in between, and it is an integral part of a region’s sustainable ecology. What is the human footprint, and are enough trees there to moderate that footprint, provide services, and maintain the system balance? This concept does not intend to promote a goal of full tree cover everywhere, since not all soils, mesoclimates, biomes, plant communities, etc., are appropriate for a full forest of trees. What it does mean is that any situation under discussion should be considered dynamic, and that the tree cover shares in its overall health and sustainable balance. For example, it could mean planning management schemes which value slower growth and lower maintenance of trees and other plantings.[26][27] Pursuing a goal of healthy tree cover will help localities react to challenges such as extreme weather, sea level rise/land subsidence, pest threats, soil/air/water pollution , heat island, and other physical, economic and social factors.

Ecological Factors of Significance to Healthy Tree Cover

“And yet trees, nature’s largest and longest-lived creations, play an extraordinarily important role in our cityscapes. They are not only critical to public and individual health but are also the dominant component of what is now called green infrastructure, defining space, mitigating storm water, cooling the air, soothing our psyches, and connecting us to nature and to our past.” Jill Jonnes, Urban Trees[28]

This section is meant to encourage discussion. It does not reflect any one research source or discipline among the many to be found under the search topic Ecology. The focus is on arboriculture, urban forestry and forest management, but crossovers of topics into storm water management, air quality, carbon sequestration, etc., are inevitable as everything is connected as part of an ecosystem/community. A salient point here is that trees influence, as well as are influenced by, these ecological factors such that there is interdependency, with consequences for urban ecosystem function and the well-being of people.

Tree Stewards are encouraged to perform outside research into the ecological factors which have the greatest relevance to their own local needs and priorities. As a means of identifying problems which EMG Tree Stewards can usefully try to address, this section considers factors grouped by their causal origins: natural biotic and abiotic, plus human-connected, as part of the overall environment in which the trees live.

Natural Biotic Factors

Biotic agents and factors in tree success or failure are discussed from a variety of perspectives in Chapters Six, Eight, Ten and Eleven. Among the important considerations for ecological sustainability are species site suitability, mature size, and maintenance needs; also diversity of species and urban forest pressures/issues.[29][30]

Endangered species are generally considered as part of the larger ecology, though any one species (plant or animal) may occupy a small specialized niche in its ecosystem. Species become endangered when they do not survive ecosystem changes or when part of the ecosystem they depend on is changed or removed. The world is seeing an increase in the number of plant and animal species experiencing extinction threats, both as individual species and as part of larger ecosystems. Recognition of the interconnectedness of ecosystems (thinking of plants as communities versus individuals), informed higher-level planning and policies, and support for and encouragement of good plant choices and habitat care, can keep these situations from becoming worse.

Invasive species is a huge and serious topic in the world of trees and ecology.

  • Invasive trees (for example, tree of heaven, mimosa, chinaberry, and Bradford pear) and invasive plants like bamboo, kudzu, and Chinese wisteria, threaten the balance of ecosystems.
  • Invasive pests (insects and diseases) threaten valuable tree species (for example emerald ash borer, Lymantria dispar, Asian ambrosia beetle, crape myrtle bark scale, Dutch elm disease, chestnut blight).

The US Department of Agriculture maintains a National Invasive Species Information Center, and the USDA Natural Resources Conservation Service has a website dedicated to Introduced, Invasive and Noxious Plants. In Virginia, the Department of Conservation and Recreation (DCR) maintains an Invasive Species List which indicates (for plants) the degree of threat in different parts of the state. It’s recommended that students become familiar with at least the DCR website to get the most recent information for Virginia. (

Natural Abiotic Factors

Abiotic factors are the non-living parts of the environment that can influence trees and ecosystems. Abiotic factors include sunlight, soil, temperature, water and people’s actions and practices. Extreme weather events and disturbances such as tornados, floods, snowstorms, and droughts may act as super-abiotic factors which require larger-scale reactions. As an example, there are fairly recent tree-planting campaigns or incentive programs for towns in which large storms have removed a significant number of trees all at once.

Sunlight is necessary for photosynthesis, which is the process plants use to convert carbon dioxide and water to oxygen and sugar. We breathe the oxygen and the sugar then becomes food for the plants and ultimately food for people and animals. Simply put, without the sun and photosynthesizing plants we could not live. Tree ecosystems accumulate large amounts of biomass, which correlates to large stores of energy, rapid growth, resilience, sustainability.

Soil is one of the fundamental factors in defining the biological components of any ecological system. This is most evident in forested or other natural lands. The parent material, or underlying rock, determines the soil order. When it comes to urban and suburban lands, though, the soil can be seriously compromised through cutting/filling, mixing, compaction, pollutants and nutrient issues. Chapter Six discusses soils in detail.

Temperature can be influenced by building reflection and heat radiation, sunlight, elevation, prevailing winds, nearby water, and season. Consult the USDA’s Plant Hardiness Zone Map and the American Horticultural Society’s Plant Heat Zone Map to see the temperature parameters for your location. These zones have shifted over the last several decades, generally trending warmer. EMGs should be alert to further changes.

virginia usda zones
Figure 7-5 Virginia USDA Hardiness Zones.
To look up a USDA plant zone by zip code, see:
Cold hardiness zones are commonly listed on plant tags and in plant descriptions. Some regions of Virginia are more prone to certain kinds of extreme seasonal weather, especially hurricanes near the coast and blizzards in the mountains. Chapter Eleven discusses these as well as other storm-related phenomena. It is worth noting that prevailing winds affect ambient temperature and can result in plant shapes that are one-sided or ‘sheared’ near a coastline, on a mountain ridge, or in wind tunnels created by buildings. Trees that grow at higher altitudes and colder climates can be adversely affected by rising annual temperatures, particularly if they have limited migration options. The balsam fir, found now at higher elevations in Virginia, is a case in point.[31]

Water is life. All living organisms need water. Plants must have water to grow. Water form, amount, and quality are considerations. Is water in the form of floods, tidal currents, or precipitation (rain, snow, hail)? Obviously, some forms are more damaging than others. Is the amount average, extreme, or seasonal? Virginia receives fairly consistent precipitation in the form of rain spread throughout the year, averaging about 45 inches per year, in addition to occasional extreme water events like hurricanes, nor’easters, and flooding. When considering annual rainfall and frequency of storms, it is important to be aware of historic data. Scientific research and modeling will also help inform decision-making and planning.

Water quality also impacts trees. Whether water is fresh, salty/brackish, or polluted runoff influences which species grow, where and how well. Trees are water regulators, intercepting and absorbing rainfall, removing particulates from rainfall, transpiring water back into the atmosphere, softening the impact of rainfall on the ground, storing large amounts of water, reducing runoff, recharging ground water sources, preventing erosion, and moderating flooding. Thanks to Chesapeake Bay publicity, there is increasing recognition of the relationship between watershed activities (especially activities that affect tree canopy amount) and water quality. So, this manual reminds tree stewards about Virginia’s watersheds as shown below.

For a map of Virginia’s watershed regions, see DCR:

Factors from Humans in Aggregate and Over Time

“Humans are the only creatures in this world who cut the trees, make paper out of them, then write SAVE THE TREES on it.” Anonymous

Land Use is usually categorized as urban, agricultural, industrial, forest or natural grassland. Further refinements may split out city center or suburban from urban, heavy or light industry, managed forest (multiple species) from timber crops (monocultures) or highly productive agricultural regions. These categories are useful at high level planning.

When forming and executing tree cover plans, the focus is more at the level of watersheds, cities, counties, and neighborhoods. Considerations include: percent of impervious surfaces (pavement, buildings), open space with pervious surface (lawn, park, sports field), or space with some amount of tree and shrub cover. This level of information is most valuable to government and citizen planning groups. EMGs often assist with city tree inventories to help officials make informed decisions.

One consideration which is frequently overlooked is the importance of green corridors between areas of vegetative cover for the preservation of biological diversity.[32]The idea is to use small amounts of vegetated land to connect larger vegetated areas. For example, a riparian buffer corridor through residential properties that connects two larger city park areas, or an old railroad right of way that’s been vegetated and also has a walking and biking trail that connects a park to a wildlife refuge. These small connecting green corridors can have a significant positive impact on tree canopy cover and animal species movement and habitat if properly planned. On the scale of forests, the principle of contiguity is even more important for tree survival, as fragmented landscapes complicate species migration and reproduction.[33]

At the even more focused level of neighborhoods and individual properties, canopy cover impacts the variety of habitat types available to different plant and animal species. In nature, there are gradual shifts from forest to grassland to rock or shore, creating a variety of habitats. In the built environment, the transition zones are more numerous and usually more abrupt. Individual homeowners can positively affect the ecological balance by planting canopy layers to create transition zones.[34] If the patchwork of individual landscapes and gardens becomes connected, the total amount of edge habitat increases and benefits many plant, animal, and insect species which may be stressed or struggling.[35] Land use areas, connecting corridors, and transition zones often cross individual property, city/county and even state lines and should be considered carefully when planning at any level.

Pollution is everywhere: air, water, and soil. Point source pollution has mostly been addressed through regulations. Non-point source pollution consists of all the little actions that everyone does that collectively cause problems over time. Non-point source pollution is much harder to regulate and is often addressed through educational and incentive programs, since the end goal is behavior change.

Healthy tree cover is an integral part of pollution prevention and air, land, and water reclamation and remediation efforts. Some examples:

  • Tree canopies intercept particulates in the air
  • Tree canopies absorb carbon dioxide and release oxygen
  • Tree roots absorb pollutants in runoff or in the soil and internal tree systems break pollutants down into harmless components
  • Tree roots in conjunction with soil and soil microbes adsorb pollutants or break them down through chemical reactions into usable or harmless components.

Population is an obvious factor in considering healthy tree cover in the human built environment. This includes humans, domesticated animals (cats and dogs) and wildlife (geese and deer most notably). Human population directly impacts the amount of impervious surface which reduces the amount of space for trees; yet at the same time increases the need for more canopy cover.

Population density influences other factors that impact trees and ecology, depending on location and history. Some examples include:

  • Industrial activity causing heavy logging for fuel, export or development
  • Income distribution reflected in more trees in the more affluent neighborhoods
  • Educational achievement levels which hopefully lead to informed decisions
  • Political movements which understand and support the value of trees
  • Communication networks which can enable action to increase healthy tree canopy

Looking at secondary effects of human population concentrations due to domesticated animals, cats prey on song birds whose populations are already stressed because of insufficient or inappropriate plants to support the insects and caterpillars they feed on. Dogs, along with geese, especially overpopulations of non-migrating wild geese, contribute greatly to the bacterial and nutrient pollution found in runoff. These effects are intensified when there is no tree canopy to slow the rainfall and people don’t scoop the poop. Overpopulations of deer, especially at the suburban/rural interface, stress the ecosystem. Deer over browse vegetation which can shift species diversity and distribution in an ecosystem. They rub new antlers damaging young trees and eat young tree seedlings, which can significantly reduce the overall number of trees that grow in an area.

Transportation networks (rail, road and river) are essential for the movement of people and goods. They are influenced by trade routes, topography, military and industrial activity, political boundaries, and population centers. These networks physically disrupt the land. They cut open swaths through forested areas and sever green corridors isolating forested areas. If the transport grid is dense enough, the green space may disappear altogether.

Other human factors include: history, economics, technical knowledge, academic research, commercial practices, governmental policies, and professional development.

One of the great challenges in ecological planning is to bridge the gap between local experience and a larger reality. This bridging works both ways, so national and international scientific studies may inform and influence local efforts, if those studies adequately reflect specific local conditions. The availability and applicability of knowledge is an important human factor. It does no good to make a scientific discovery or prove an ecological concept if no one knows about it or is able or willing to apply it.

The state of a community’s tree cover is dependent on the actions of city/county planners, project engineers and designers, builders, landscapers and other professionals who are often motivated by economics rather than science. The reality of contracts, labor, and cost often dictate tree management. Some cities have departments and crews that manage the city’s trees, some cities hire private contractors to do the work, while other cities have no budget for tree management at all. In general, people do not like change and, therefore, resist it. This attitude makes it challenging when it comes to changing how people see the value of trees, how trees have been managed historically, the practices that have been or are being used, and the policies governing trees. Climate change concerns should raise awareness of the value of trees and increase public support for trees. Climate change should also bring more aspects of urban trees into development discussions and planning.

Professionals impact trees. The term professional indicates some level of expertise. Some who call themselves “professional” are not. They sell and perform tree “services” that are uninformed, unnecessary, incorrect, and detrimental to trees. Everyone knows that topping trees is wrong, yet the practice persists because of so-called “professionals” promoting it to make a dollar. Real tree and landscape professionals are up to date on research and appropriate practices. They are generally certified or licensed and attend regular training to maintain their certifications and licenses.

Examples of professional organizations, certifications and licenses related to trees include:

  • Trees Virginia (Virginia Urban Forest Council) and the regional Northern Virginia (NOVA) and Southeast Virginia (SEVA) Urban Forest Roundtables,
  • Mid Atlantic Chapter of the International Society of Arboriculture’s (MAC-ISA) Certified Arborist,
  • Virginia Nursery & Landscape Association’s Virginia Certified Horticulturist (VCH),
  • Chesapeake Bay Landscape Professional (CBLP) Certified Professional.
  • Virginia Pesticide Applicator through the Virginia Department of Agriculture and Consumer Services

Improving Healthy Tree Cover

Healthy tree cover is in jeopardy because of:

  • Development/urban sprawl/transportation routes/pollution
  • Undervaluation as a resource with multiple benefits
  • Inadequate protection policies and failure to anticipate problems
  • Uninformed plant selection and placement
  • Inappropriate maintenance practices
  • Insufficient replanting policies/efforts
  • Neglected forest without active management
  • Lack of invasive species management

Examples of ripple impacts on healthy tree cover:

  • Removing an “undesirable” tree from a stand of trees leaves a hole in the overall canopy cover. This can stress the surrounding trees, leaving them vulnerable to pests or storm damage, especially wind damage. Note that removing invasive trees means preserving the desirable trees around it, regardless of shorter term holes in the stand.
  • When ecosystem-appropriate undergrowth is removed, habitat is destroyed. The insects, birds, and other animals that pollinate trees or disburse tree seeds no longer do so.
  • When there is no leaf litter or mulch over tree roots, soil conditions are not as favorable for fungi communities which help tree roots absorb nutrients and water. Un-mulched soil is dryer and hotter which stresses tree roots.
  • Removing standing dead trees which are not posing threats removes habitat for many cavity nesting birds and animals.
  • Removing fallen trees prevents them from decaying and providing the rich organic matter where replacement tree seeds germinate.
  • Fertilizer applications that are excessive or at the wrong time promote lush new growth which may attract pests or be susceptible to heat, cold or drought.
  • Chemically treating one insect pest on a tree may kill numerous other beneficial insects leaving the tree and other plants in the community susceptible to other insect pests which normally would have been kept in check naturally.
  • An herbicide sprayed for broadleaf weeds can be absorbed by tree roots close to the soil surface or through thin bark on the tree trunk causing tree damage or even death.

It takes a long time for a tree to mature and reach capacity for the benefits it can provide. If you lose one mature tree, how long will it take before one or even several smaller trees provide same/equal services/benefits? Chapter Three introduced the National Tree Benefits Calculator, which is a very easy online tool to express the dollar value of a tree’s ecosystem services:

The first step in improving healthy tree cover is to know what is there in whatever space you are dealing with. Chapter Three also discusses the iTree tool, which has made a huge difference in cities’ abilities to assess their current tree inventory and canopy condition.[36] Chapters Four and Five cover identifying trees, which comes with experience and practice. Knowing what is there includes who as well: It’s equally important to know all the stakeholders involved in any tree inventory or survey, how trees connect to them, and what the goals are.

Planning needs to: include private and civic partners, seek investment in trees, and ensure that projects are financially and physically sustainable.[37] As discussed in the previous section, it is important to take as wide a view as possible of the factors which will influence the outcome of a project. All parts of a plan need to consider and strive for interconnectedness and resilience. This means making plant choices with context and understanding of which plants belong together, the location conditions, the user goals and capabilities and potential future changes in local conditions. Plants, especially trees, can no longer be thought of as landscape decoration. Think community! Promote, plan, and plant more communities of trees with appropriate layers of shrubs and groundcovers.[38][39] This may mean educating people on the benefits of plant communities versus individual trees. It may also mean helping people understand that plant communities look, act, and feel different than what they may be used to. For example, a buffer area looks very different than mowed grass to the water’s edge. A plant community looks very different than individual plants surrounded by large beds of sterile mulch.

Reforestation or restoration opportunities can be coordinated at the city, county, or state levels. Are there any projects in progress or planned for your area? Who is coordinating it and how can you support or participate? Reforestation/restoration is a long process with many stages before a healthy ecosystem is formed. Are there specific times in the process or specific activities (planting, monitoring, invasive species control, pest scouting) you can assist with? An example is: a local waterworks department purchased an 11 acre abandoned home site near the headwaters of a river draining into a reservoir. The plan was to demolish the structures, remove the septic tanks and debris (recycling the metal and tires), eradicate the invasive plants, and replant with 4500 native tree seedlings. The end result, from waterworks’ view, is a cleaner reservoir; but the benefits to the whole ecosystem will go well beyond that.[40]

Tree preservation is important during planning of any construction project and as part of a larger resource conservation program. Successful tree preservation requires knowledge of the species, individual tree and site conditions, stakeholders involved, and construction practices and policies. Inspection and enforcement during the construction period is essential. The end result can definitely be worthwhile if there is enough space and public support.9 Unfortunately, it is often “easier” to remove a tree and replant if possible after the construction. A cost analysis could be performed comparing the value of the existing tree’s ecosystem services versus the time it would take a newly planted tree to provide the same value and services.

Everyone (governments, institutions, companies, organizations and individuals) can do a better job of tree selection, planting and long term care on both private and public lands. Distribute science-based information. Teach. Conduct demonstrations. Become active in homeowner’s associations, civic leagues, and planning and review boards that impact your community. Support improved communication and better coordination between homeowner groups, environmental groups, private companies, and city planners, engineers and urban foresters/arborists.

One example is an initiative from the California-based Urban Tree Foundation (UTF) that created a series of Planting Details and Specifications based on best science. These include specifications on planting, mulching, and irrigation systems, as well as inspection criteria, in an effort to insure that trees are in good condition before planting and during establishment. The documents are available in PDF format and also in a format ready to use in engineers’ and contractors’ Computer-Aided Design (CAD) programs. They are free and may be obtained from the International Society of Arboriculture:

Nursery production and availability is another area that can be improved. Tree growers and sellers respond to market demands, but often the public doesn’t know what it wants or what is appropriate for their planting sites. This has meant a fairly limited range of tree species available to the public. Also, counties and cities can establish lists of trees approved for planting (including natives), but the supply has to be available or people will get discouraged and not plant them. The Arbor Day Foundation and a number of forward-thinking nurseries are broadening the choices beyond the standard red maples, dogwoods, and Leyland cypress trees. Remember, though, it can take 5 to7 years to produce a “saleable” size tree. Consider the Virginia Department of Forestry’s state nurseries as a resource for tree seedlings:

Opportunities for engagement to improve healthy tree cover through VCE activities:

  • Develop a list of nurseries and garden centers in your area that sell trees, especially those that sell native or hard to find species. Provide the list when people ask “Where to find…”
  • Insert one “tree fact” into the handouts or onto the agenda for each city council meeting. It might be best to focus on facts that have a dollar value or direct impact on the specific community. TREEmendous tree facts!
  • Make a point to introduce yourself to your local city/county arborist/forester. Ask about their background, programs, plans, and opportunities for partnerships or support. Go prepared to BRIEFLY discuss VCE & Tree Stewards. Take small VCE “gifts” (pencil, mug, set of VCE tree pubs, agent and tree steward contact information, etc.) when you go. People remember these things.
  • Offer a short program on trees to your civic league, Ruritans, book club, church, etc. Find a way to make the presentation connect to them. For example, trees on the church grounds which are in the Bible, or statistics on trees in the neighborhood preventing crime and raising property values.
  • Ask to assist in tree inventories for the city, military installations, the neighborhood, cemeteries, etc.
  • Demonstrate pruning, planting, pest ID at garden centers, garden club meetings, etc.
  • Offer to conduct the tree sections of the scouting curriculum.
  • Lead “lunch and learn” tree tours at city offices (during lunch breaks), parks, cemeteries, etc.
  • Install tree trails at local parks, businesses, schools, retirement communities, community centers, etc.
  • Develop short presentations for the local MG speaker’s bureau.
  • Find out what other organizations are doing tree related activities and see where MGTS can fit in and support them (Master naturalists, native plant societies, wildlife groups).
  • Have a VCE TS educational display at Earth Day or Arbor Day.
  • Order tree seedlings from the Virginia Department of Forestry nursery and coordinate giveaways.
  • Make large tree price tags that list the species, dollar value, and services provided and hang these on trees at various activities (i.e. how many birds supported, how much runoff prevented, how much shade provided, how much trees speed up recovery from illness or positively impact people with ADHD).
  • Set up a “good mulch bad mulch” demonstration.
  • Work with elementary school teachers (appropriate grade and SOL) to do leaf morphology, identification, and a collection, explain why some leaves change color and fall off while others don’t.
  • Volunteer to make a “Value of Trees” or “How Do Trees Benefit Our City” brochure.
  • Make a traveling “Tree ID” or “Tree Insect ID” display.
  • Distribute the VCE pub on recommended trees for under utility lines to city planners.
  • Write a grant proposal for tree related community projects.
  • Research information about trees improving downtown/shopping areas and distribute to businesses.
  • Find out what the city policy on street tree replacement is and work to make replacements happen if they are not.
  • Become familiar with local tree ordinances, who they apply to, and who enforces them. Work to educate citizens on them or to make changes if necessary.
  • Work with a youth group to make tree art (rubbings, drawings, sculptures, etc.) and get it displayed at the local community center or library.
  • Organize a canoe/kayak trip to look at trees along waterways or shorelines.
  • Identify any “champion or big” trees in your locality and look for specimens to submit. Bring attention to these unique local trees. Also, offer to measure these trees to keep records up to date. Ref.: Virginia’s Big Tree program.
  • Coordinate a unique tree tour of your locality. This could be for adults and/or children, scavenger hunt/passport to find trees with reward for visiting them all.
  • Incorporate trees into geocaching activities.
  • The Virginia Department of Forestry has many youth educational booklets and items (rulers, erasers, stickers, posters, etc.) that can be used for programs for scouts, school, environmental clubs and other youth groups.

Specific Tree Considerations by Region

One of the goals of this manual is to encourage VCE MG Tree Stewards to develop local knowledge to help positively impact Healthy Tree Cover in their own counties, cities and neighborhoods. There are commonalities among neighboring locales, and tree stewards are encouraged to share their efforts and experiences. This manual proposes a model for regional descriptions, being an unusual combination of altitude, weather, economic activity, land use, government and population density. The Guidebook to Virginia’s Historical Markers, Third Ed (2007) divides the state into six Cultural and Geographical Regions which address most of these factors, yet are socially, climatically and economically compact. The authors were able to make a reasonably thorough description of the Eastern Virginia region (since that’s where we live). We tried to frame some basic conceptual elements for the other regions, but tree stewards who reside in those regions are best equipped to expand upon these beginnings.


virginia eco regions
Figure 7-7 Eco-Cultural Regions Notations by Carol King

Each regional description should try to answer these questions:

  1. What distinguishes this region from others? Think both in terms of natural characteristics and human history.
  2. What are the basic climate parameters? Are there any significant mesoclimates?
  3. What are the ranges of altitude, geology, and soil type and pH?
  4. What are the major water features and/or issues?
  5. What are the main land uses and/or industries?
  6. What are the major tree species (genera, families): think native, introduced and invasive?
  7. What are the most significant stresses, both on human communities and on the trees?

Eastern Virginia: Primarily consists of the land east of the fall lines of the main rivers (Potomac, Rappahannock, York and James). Subregions are the Northern Neck, Middle Peninsula, Hampton Roads, Chesapeake Bay borders, the Eastern Shore, the Dismal Swamp, Chowan River drainage and the outer cape of Virginia Beach. This is a region of rivers and marshes overlaid by substantial and growing population development. As the first part of Virginia settled by English colonists, history is on display all over, though the economic dynamics of the fall line meant that the political center of gravity moved from this region by 1800. Today, port operations, shipyards and military installations make up a large part of the economic activity. NASA space research has long been a part of the economic picture and is now complemented by commercial space launches. At the same time, watermen still fish and harvest oysters. The counties bordering North Carolina are well suited to peanut production and also grow a lot of cotton and soybeans. This region has the second largest population in Virginia, principally in the Hampton Roads area.

Many of the waterways are tidal and saltwater, at least in part. Mesoclimates can vary considerably along the major rivers along with the large effects of residential and agricultural development resulting from waterfront attraction and discharge convenience, respectively. Significant regulation and public support is directed toward measures to improve the health of the Bay and the many rivers. In addition, the combination of sea level rise and the subsidence of the lands bordering the Bay leads to significant concerns for future high tides, storm surges and hurricanes. Trees which are not tolerant of these conditions may be expected to decline, with a corresponding need to plant resilient species along with appropriate shrubs, grasses, groundcovers and self-seeding annuals.

Temperatures fall in the USDA Cold Hardiness Zones 7b to 8a. The Eastern Shore, Virginia Beach/Norfolk and the Lower Peninsula have mostly moved into 8a, with the 7b zone farther inland. Hard freezes (10 to 20 degrees Celsius) are possible but not often or enduring. First frost may be early November or not until January, so the soil does not generally freeze solidly. Thus, winter dormancy in trees may be compromised by the odd warm days, and trees (especially young ones with thin bark) are susceptible to freeze cracks and sunscald.

Soils are mostly ultisols (strongly acidic clay), with pockets of sand, plus calcareous ravines in the York County area. Some mollisols (floodplain soils) are found in Norfolk. Tree cover is largely oak and loblolly pines, with magnolias, eastern redcedars, hickories and hollies interspersed. Swamps have several kinds of cypresses, especially along the North Carolina border. The only major stands of longleaf pine (Pinus palustris) are located around the town of Zuni, though conservation plantings are occurring the SE area, such as Poquoson. Species with notable presence at the northern end of their range are live oak (Quercus virginiana), Bald Cypress (Taxodium distichum), and southern magnolia (Magnolia grandiflora).

Northern Virginia: Small in area and number of political entities, Northern VA is densely populated and heavily developed. It is also home to the wealthiest cities and counties in the state. European arrivals in the early to mid 18th century established plantations and trading networks, especially around the fall line of the Potomac River. Much of the surrounding area remained largely agricultural until the post-WWII growth of the federal government; after that, suburban development has gradually solidified into a near –continuous urban center, except for the ends of the region in Loudoun and Stafford Counties. Cold Hardiness zones are 6b to 7a, hospitable to many temperate plant species, but there are great challenges represented by altered urban soils, heat island effects and management of storm water from impervious surfaces.

Northern Piedmont, Valley and Western Mountains: This region is noted particularly for its geography, being a series of river valleys separated by mountains from northeast to southwest. The history of modern settlement started in the early 18th century and continued as the region was a popular migration and transport route between Pennsylvania and the Carolinas. The very busy I-81 corridor continues this pattern. The Shenandoah River is the major water feature, flowing toward its juncture with the Potomac. It is a rich agricultural area set among large forest reserves in the George Washington National Forest. Where it intersects the Appalachian Mountain range, it is host to an unusually diverse forest floor biosphere (for example, millipedes and ferns). There is some very interesting geology, including caverns, the Natural Bridge formation, and hot springs. Tourism for both historical attractions and the natural wonders is an important part of economic life. Cold Hardiness zones are 5b to 7a, largely varying with the altitude, and even including a bit of 5a in the extreme western edge. A wide variety of mesoclimates can be expected due to abrupt changes in altitude and also exposure to (or shelter from) winter winds and snows.

Central Virginia and the Central Piedmont: The east-central part of the state derives its identity from the early history of development proceeding up the rivers from the earliest settlements to the limits of riverine navigation at the various fall lines. Subsequent consolidation of political government and industrial production in the Richmond area was reflected in the transportation grids, particularly during the tumultuous years of the Civil War. The area remained largely agricultural except for Richmond and Petersburg until fairly recent years, when the suburbs of Richmond began to push out. This region has the third largest population in the state, just a little less than the Eastern Region. The James River is the major water feature, along with its tributaries. Cold Tolerance zones are 7a and 7b, but with heat island effects in the two large cities.

Southern Piedmont and the Blue Ridge: Most of this region is a counterpart in elevation, terrain and soil to the center around Richmond, but without the extensive political and industrial history. Its past has been one of tobacco, timber and textiles. The land rises gently in elevation from the fall lines of the rivers to the beginnings of the Blue Ridge Mountains. The Roanoke River drains most of this region.

Southwest Virginia: Mountains, valleys, ridges and plateaus dominate this relatively sparsely settled, economically challenged region. The Blue Ridge Mountains dominate the terrain, as does the very busy I-81 corridor. Colonial settlements began in the mid 18th century and have been mostly motivated by the migratory route through the Cumberland Gap. Railroads were an engine of growth after the Civil War, into the 20th century, which facilitated the timber and coal industries. Textile mills were also an economic boon for a while. The decline in coal production has had significant economic and social impact on this region. On a cultural note, this region has a strong musical legacy, stemming from its earliest immigrant folk heritage. Cold Hardiness zones are 6a and 6b, and different mesoclimates due to changes in elevation and wind exposure are common.

Review Questions

  1. List some examples of changes or disturbances that impact tree communities.
  2. What is an ecosystem service?
  3. What is the difference between arboriculture and urban forestry?
  4. What are some steps to improve the health of local tree cover?
  5. What is the most common tree in your locality? Why is this so?


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