Can a Tree Live Forever?
Trees are by nature healthy and resilient. They can “potentially” live a long time. A 2021 Scientific American piece by Robin Lloyd declares “Trees Have the Potential to Live Indefinitely.” It summarizes the findings of an article entitled “On Tree Longevity” by Gianluca Piovesan and Franco Biondi in the August 2020 New Phytologist. Lloyd quotes Biondi, “Trees can indeed live indefinitely, but this does not happen.” Eventually a living (biotic) or non-living (abiotic) thing ultimately kills them. Sad for the planet, since an older tree stores more carbon than a younger tree. Piovesan and Biondi observe that there is “no genetic evidence of aging in extremely old trees’ meristem.” The meristem is tissue whose cells divide, thus generating new cells and, therefore, growth. Apical meristems are located at the tips of branches and roots and in buds. The vascular cambium is a meristem and produces the diameter growth of the trunk, branches, and roots.
One study of the lifespan of street trees indicates that the ideal life span of a white oak is 600 years, and that the average life of a red maple in Illinois forests is 75 to 150 years. It suggests that trees planted in groupings in the landscape may survive 50 years longer than those planted in a pit beside a sidewalk. In fact, the United States Department of Agriculture study found that the average urban tree lives between 19 and 28 years. For a documented list of very old trees see the Wikipedia article “List of oldest trees” and the Virginia Big Tree Program’s Lifespans of Common Trees in Virginia. Clearly, trees do not live forever and different trees have different lifespans.
The focus of this article is disease, but below we will also explore factors that can compromise any tree’s longevity potential. Often alone, without companions, and not always in a setting they would naturally choose, it is important to appreciate that sometimes our plantings compel trees to live a life for which they did not evolve.
History Shows Us Just How Stressful a Tree’s Life Can Be
All living things, including trees, contract diseases. Stress in its many forms sets the stage for a tree’s decline. Trees become ill because of the intersection of specific vulnerability, environmental factors, and the existence of a pathogen. More on this later. Sometimes all factors come perfectly together to create an arboreal nightmare on a grand scale. Among recent history’s most interesting and instructive tree tragedies are the tribulations of Hevea brasiliensis, the rubber tree, and Castanea dentata, the American chestnut.
Henry Ford wanted to own the production of one of the most critical materials for his vehicles: rubber. He hoped to do some social good as well for Amazon residents. He established two plantations in the Amazon – Fordlândia (1928) and Belterra (1934) — with mass plantings and superb supporting facilities. But once the rubber trees had taken hold they were attacked by a diversity of challenges. In his Business History Review article “Rubber in Brazil: Dominance and Collapse, 1876-1945” Randolph R. Resor writes, “Caterpillars and sauba ants, red mires, black crust, yellow scale, lace bugs (a pest unknown in Amazonia before the start of the Ford plantation) and South American leaf blight [the fungus Microcyclus ulei] weakened and killed many trees.” (p. 364) The dangers of monoculture were apparent: “When trees were scattered through the Amazon rain forest, a pest that would attack one tree would not necessarily attack another. But in close proximity on the Ford plantation, the . . . trees provided an easy target.” (p. 364) The disease causes leaves to spot, and as the spots increase in number, leaves wither and fall. Although Ford’s effort faced many challenges, the greatest challenge was nature. After substantial investment, the land was sold back symbolically to the Brazilian government in 1945 for only $244,700. Today most rubber is grown in Southeast Asia. If the South American leaf blight (SALB) travels there, there will be an existential natural rubber crisis. Natural rubber remains in demand. Perhaps there are some resistant trees in the Amazon or a resistant variety might be developed.
Until the early 20th century, many of America’s forests were dominated by the American chestnut. Chestnuts fed animals and people, the wood was durable, fine grained and easily worked, and its bark was used in the tanning industry. Before the 20th century, perhaps as many as one out of four trees in the eastern United States was a chestnut. Some mature trees were known to reach heights exceeding 100 feet, with diameters of more than 10 feet. As early as 1893 the tree came under attack by the fungus. Limbs, branches, and twigs were killed by sunken or open cankers, which began as reddish brown bark patches. Leaves on affected branches withered and turned brown. The fungus was observed in 1904 and was described and named in a scientific bulletin two years later. The disease spread rapidly across all ranges. By 1911 much had been learned. Today we know the parasitic fungus as Cryphonectria parasitica, formerly Endotria parasitica, and in 1905 as Diaporthe parasitica. Then as now, the fungus emitted both summer and winter spores. Sticky summer spores attached themselves to animals and birds, people, and things and were carried from tree to tree. Diseased lumber spread the disease. And the wind carried winter spores great distances. Virginia forests were hit hard. To find a home, the spores needed only to find a microscopic break in a tree’s bark caused by insects, woodpeckers, or natural occurrences. Richard Powers’ novel The Overstory describes the chestnut’s plight. This remarkable book was awarded the Pulitzer Prize for Fiction in 2019, was shortlisted for the Man Booker Prize, and received the William Dean Howells Medal.
Pennsylvania was the first state to fight the chestnut blight. In 1911, it was the site of a large conference focused on how to repel the invader. The argument that any action was hopeless — the correct conclusion — was not accepted, and instead, the trees were attacked with saws to prevent spread. It was soon discovered that the blight had entered the United States on Japanese chestnut tree nursery stock. Unfortunately, what was not a tree killer in Asia was a killer in America. Early on, it was observed that Chinese and Japanese varieties survived the blight, and breeding became a reasonable response. The backcrossing of resistant Chinese trees with the American chestnut, rather than the eradication of struggling and ultimately doomed survivors, is now pursued. There are also genetic engineering efforts underway. Once again, nature has proved to be a formidable foe. Fungi, bacteria, and viruses and their vectors are, after all, just doing what comes naturally. To understand this crisis is greater detail, see especially George H. Hepting’s Journal of Forest History article “Death of the American Chestnut,” Chestnuts and the Introduction of Chestnut Blight, Forest Pathology’s Chestnut Blight and A New Hope, and the Virginia chapter of The American Chestnut Foundation’s Warren Laws’ presentation The American Chestnut: The Tree that Made America.
High profile challenges remain. Insects alone can wreak devastation and death. Currently, the North American ash is under attack by two wood-boring insects, the emerald ash borer and the Asian longhorned beetle. Dutch elm disease continues with us, the fungus having entered the country during World War I from Europe, but probably originating in Asia. Vectors are the European elm bark beetle and the American elm bark beetle. And climate change is expected to impact forest health in the future. Large and localized change will have an impact, one paper contends: disease outbreaks will become more difficult, host resistance to pathogens may be overcome, and warmer winters may allow pathogens and insects to overwinter more successfully. A warmer/wetter climate will encourage foliar and rust diseases in particular. With climate change, some diseases may travel north and/or to higher elevations.
Why Trees Get Sick
For a tree to contract a disease, an intersection of factors must come together: the environment must be conducive to disease, there must be a pathogen (disease-causing organism) present, and the species must be susceptible. This is known as the disease triangle. For an insightful and concise discussion of the disease triangle, see Leonard J. Franci’s consideration. If one element is missing or removed, a tree will neither contract nor sustain a disease. Of course, there must be a way for the pathogen to infect the tree. The pathogen can be carried by a living organism, a vector, or carried by wind, water, or another means. Insects are the usual vectors (and sometimes pathogens can grow within them), although their role may be simply to make a hole in the tree’s defenses, allowing the pathogen entry through other means. Pathogens are bacteria, fungi, viruses, mycoplasmas and spiroplasmas (bacteria), and parasitic plants as well as nematodes.
Bacteria are one-celled microorganisms; they cannot reproduce on their own, but grow by cell division. A cell grows to twice its initial size and then divides in two. Bacteria can be spread by every imaginable means. Fungi are microscopic and are neither plants nor animals. They belong to the kingdom Fungi. Mold is a microscopic fungal growth that spreads on damp or decaying organic matter. Fungi reproduce by spores and gather nutrients from their host plant. They can lay dormant in adversity waiting for the return of favorable conditions. Even smaller than bacteria and fungi, viruses are submicroscopic and depend on living organisms for food and reproduction. They replicate only within an organism’s cells. Among their modes of spread are fungi, insects, nematodes, seed, and soil. Finally, plant-feeding nematodes are microscopic worms and one of the planet’s most abundant creatures. Nematodes puncture cell walls to feed and parasitize a tree’s roots. The vast majority of plant diseases — including tree diseases — are fungal.
The other two sides or factors of the disease triangle are the host and the environment. Hosts can vary in their susceptibilities. A pathogen that will impact one tree will often have no effect whatsoever on another. For a disease to be contracted, the environment must be conducive to its development. Temperature and moisture extremes as well as nutritional deficiencies can create a conducive environment. Air quality can also be an issue as well as air movement. Injuries the tree has sustained can be determinative as well as planting practices, such as monoculture, as in the case of the rubber tree, which is discussed above. Finally, the duration of alignment between pathogen, host, and environment can be critical. Variations in the intensity of the factors represented by the triangle’s sides, and duration of alignment, will determine the severity of an infection. Stress caused by biotic and abiotic factors weaken a tree’s response to infection.
Recognizing a Sick Tree
Does my tree have a disease? In most instances, you will recognize relatively quickly that something is wrong. A definition of “disease” suggests how easy this should be: “Any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury. A diseased organism commonly exhibits signs or symptoms indicative of its abnormal state.” (Burrows, William and Dante G. Scarpelli “disease“. Encyclopaedia Britannica.) In other words, look for the unusual or atypical. Of course, to recognize an abnormality, one must be familiar with a tree’s normal appearance.
Sick Trees Usually Look Sick
Mushrooms growing at the tree’s base indicate decay, as does crumbling or soft wood. Fungal infections present as unusual patches on leaves that look powdery, furry, or fuzzy. Fungal infections can also cause wilting: foliage will yellow, plant parts will droop, and defoliation will occur early. Sometimes an infected tree will produce an excessive crop of seeds and have small leaves. Fungal and bacterial diseases present as spots on bark and leaves. Leaf and growing tip damage that appears suddenly is an indication of disease. Branches that are drooping, dead, or dying can be the result of a tree’s struggle with a disease. Wilting leaves can be an indicator of disease — not drought related, — if they appear on only a portion of a tree. Fungi can cause root rot, affecting both hardwoods and conifers, presenting as yellow leaves, dead branches, stunted growth, and droop and wilt. Fungi can also result in cankers on both hardwoods and conifers, presenting as deep lesions on woody parts. In advanced stages twigs or branches can be girdled, leaves will drop, wilt, and the portion of the branch farthest from the trunk may die. See Sharon M. Douglas’ Recognizing Tree Diseases and Stress Factors.
For a cornucopia of ailing tree images, there is no better place to search than the Bugwood Image Database System. Here you’ll find leaves, trunks, branches, and stems in all stages of despair. Bugwood is a grant-funded effort, started in 1994 by the University of Georgia’s Center for Invasive Species and Ecosystem Health. One of its components is devoted to forestry. As a whole, the system holds more than 318,161 high quality images and is superbly searchable. Excellent images are also available in Tree and Forest Health Guide: A Handbook for the Diagnosis of Urban and Rural Forest Disturbances.
Trees Are Not Defenseless
While your tree may be sick, it likely is fighting back. Its struggle will not always end in success, but it will literally not go down without a fight. Like all living things, trees store and use energy and they have special reserves to deal with illness. A tree’s first line of defense is the bark on its trunk and branches and the waxy cuticle on its leaves. Breaching or compromising these is a serious matter. Pathogens can enter through cracks or wounds as well as through the pores on the epidermis of leaves and stems (these pores are known as stomata, and are required for photosynthesis).
Trees engage in chemical warfare. Their defensive chemicals have antibiotic qualities; they inhibit the attacker’s growth or prevent it entirely by making plant tissue inedible. This is also a response to insect feeding. Plant cells recognize the invader by its molecular pattern and then respond on a cellular level. Chemicals are produced that make the cell environment toxic, and alkalization occurs, creating flavonoids or alkaloids, which are antimicrobial. When the sapwood (the soft outer layers of recently-formed wood containing functional vascular tissue), located between the bark and heartwood (the dense inner part of a tree trunk), is attacked, the tree begins to grow rapidly to close the wound. This process can be characterized as a balancing act or hedging between defense and regeneration. The pathogen may have entered through damage incurred from engagement with something as mundane as wind, pruning (do not cut into the fungicide producing branch collar, cut outside of it), or an insect. These events are evident in structures on the tree’s limbs and trunk and are remembered with knots and blemishes in lumber. Once the decayed area is closed, the tree saturates the isolated area from the inside and kills the fungus. This process is known as “compartmentalization of decay in trees” or CODIT.
At CODIT’s core is the fact that while trees cannot repair cells, they have a prodigious ability to generate new ones. Discussions of the process are plentiful and available in various levels of detail, basic discussions are provided by Paul Hetzler’s How trees protect themselves from wounds, disease and pests (including us) and Matt Candeias’ How Trees Fight Disease; but a thorough discussion, with excellent graphics, is found in Alex L. Shigo’s “Compartmentalization of Decay in Trees.” As noted, the process begins with the tree walling off the decaying area; the tree then chemically changes the structure of the diseased cells, and new walls of more resistant cells are built around the diseased area. Four chemical walls are constructed: two circular, one radial, and one horizontally flat. Simultaneously, the tree continues to grow, the disease tissue is isolated and starved, and then chemically attacked. Note that the healing cover by itself does not determine the resulting level of decay. Hetzler points out that CODIT responses vary by species: poplars and willows have a very weak response, red oak and soft maple a middling response, but hard maple and white oak respond vigorously. Because of a diversity of stress factors, landscape trees — especially urban trees — respond with less vigor than forest trees. Scientists also think that trees can warn one another of approaching insect and disease challenges, enabling them to ramp up their defense. Unfortunately, if the fungus has moved through the sapwood into the heartwood, the battle is eventually lost. Even then, the tree can live on for a long time. Peter Wohlleben explains how in The Hidden Life of Trees:
“But even if the fungus lives and makes itself at home inside the tree, all is not lost. True, the fungus can get stuck into the wood without further hindrance, but it takes its time. A whole century can pass before everything is consumed and turned to mush. Even this won’t make the tree the slightest bit less stable, because the fungus cannot expand into the wetter outer rings of living sapwood. In extreme cases, the tree gets hollowed out like a stovepipe. And just like a pipe, the tree remains stable . . . The outer growth rings, which are still active, transport water up the trunk and, therefore, are much too wet for fungi.” (pp. 160-161)
In the simplest terms, a tree dies when it can no longer feed itself — absorb and use water/moisture, nutrients, and sunlight in sufficient quantity — and/or when its structural integrity is “morbidly” compromised. Remember though, trees are tough: they can generally live with a pathogen or recover from a disease.
Know the Patient
So far we’ve approached the topic largely conceptually. Now for the practical. If your tree looks sick it is best to identify the tree. This will allow you to visit reference sources that will suggest a choice of probable problems and corresponding responses. As a practical matter, you should know the identity of the plants for which you are responsible. It facilitates caring for them. Tree identification can proceed through a diversity of channels: books, websites, and apps.
The best book for identifying Virginia trees is Common Native Trees of Virginia: Identification Guide (Virginia Department of Forestry, 2020). It is available in print and free online. On a computer, you can try Tree Identification, Virginia Tech. On your phone, load and use the excellent app Virginia Tech Tree Identification. There is also the Purdue Tree Doctor app, which briefly suggests management options. Among other approaches are the excellent Virginia Tech “factsheets.” Using information from the Virginia Department of Forestry and the Virginia Tech Dendrology Department (dendrology is the scientific study of trees), the Charlottesville Area Tree Stewards (CATS) have prepared the excellent introduction to tree identification Getting to Know Trees. The organization also regularly holds tree identification Zoom classes as well as walks. Slides from the recent winter tree identification presentation are available online. They will instruct you in tree identification strategies.
Help Can Be On the Way
The Virginia Department of Forestry’s Help with Sick Trees is a guide to identifying what ails your tree. Recommended steps or options are sending a “sample” to the Department, contacting your local Department forester, or consultation of the excellent Tree and Forest Health Guide: A Handbook for the Diagnosis of Urban and Rural Forest Disturbances. This is the place to begin. This guide is beautifully illustrated and is organized first by biotic pests: insects, animals, and diseases. Under diseases will be found subcategories for rust, root issues, cankers, foliage, and vascular issues. For each type of problem, there is a list of host trees, signs and symptoms, timing, management, and other specifically applicable information. Abiotic issues are also covered: separate sections cover such issues as girdling roots, wind, air pollution, and soil pH. These abiotic considerations are important because they can weaken a tree, making it susceptible to biotic challenges. Once you identify the tree under consideration, you can use the “Host Tree Species Index” to find the pests and diseases potentially affecting the tree.
The standard treatment for many years has been chemicals. For guidance on chemical use, refer to VCE’s Home Grounds & Animals: 2023 Pest Management Guide. It covers insects and diseases. This guide is an expansive, detailed, and practical collection of information. It is the place to turn first for information on all aspects of chemical application as well as storage and disposal of pesticides. In the section titled “Diseases of Landscape Trees”, Table 4.3 lists the tree, and beneath it, potential diseases with corresponding pesticides (by common name), and then recommendations for chemical control, cultural control, and precautions and remarks. A cultural control includes such things as the recommendation to burn or bury fallen leaves or to prune affected branches below a canker and then remove the branches from the area. In some of the tree sections, extensive guidance is given. The introduction to the section is very useful.
If you’d like to address the problem more holistically, an Integrated Pest Management (IPM) approach is recommended. Elements of this approach for trees focused explicitly on disease will include correct pruning, inspection for bark injuries, protecting trunks from mower and trimmer damage, removing debris beneath trees, appropriate mulching materials and application, irrigation as needed, preventing soil erosion or compaction, regular and through monitoring and record keeping, the biological control or elimination of harmful insects, and the use of organic pesticides. Critical to any IPM program is the reduction of pesticide use. In addition, mycomhizal fungus might be added to improve both mineral nutrient and water absorption and, if appropriate, protective wrap might even be considered at time of planting. The selection of problem-free trees as new additions is also wise and is considered below. For more about IPM, consider the Piedmont Master Gardener Garden Shed article “Integrated Pest Management.” See also Virginia Cooperative Extension’s An Introduction to Integrated Pest Management. Whether or not pursuing an IPM approach, the Garden Shed article “Pesticide Storage and Disposal” deserves review. Finally, the VCE Pest Management Guide includes a concise and very useful IPM section.
At any point in the process of recognizing a problem and identifying its cause, you may wish to contact an arborist. Size alone suggests that dealing with a tree disease is far more challenging than combating pests or diseases plaguing a rose bush. Begin by visiting the Department of Forestry’s page Hire a Certified Arborist. One criteria for selecting an arborist is to be certain the person you’ve selected is certified by the International Society of Arboriculture (ISA). To find a certified arborist, search under the ISA website’s utility Find an Arborist. (Located at the bottom of the page.)
An Ounce of Prevention is Worth a Pound of Cure
“Hindsight is always 20/20”: but it is generally true that “An ounce of prevention is worth a pound of cure.” A thriving healthy tree, planted correctly and in an appropriate setting, is most likely to be resilient, defending itself well from all insults. A piece by the University of Illinois Extension advises planting the right tree in the right place, not planting trees too deep, correct pruning, appropriate mulching, reducing girdling roots, spacing trees for their mature size, and staking only when necessary. After considering these key points, the Department of Forestry’s Tree Care is a good first overview.
To start from the beginning, which may well not be where you are, select a tree for planting that will enjoy its environment, “right tree, right place.” See the Charlottesville Area Tree Stewards’ (CATS) Right Tree/Right Place and the Right Tree/Right Place Tree List. Problem-free Trees for Virginia Landscapes, noted above, is helpful as well as Common Native Trees of Virginia. Also valuable are the tree sections of Piedmont Native Plants: A Guide for Landscapes and Gardens. See also CATS’ Suggested Native Tress for the Piedmont and Charlottesville’s Tree Packet as well as the current Charlottesville Master Tree List.
Once a tree and site are selected, plant it carefully. Virginia Cooperative Extension’s Planting Trees is concise but comprehensive and the CATS Tree Planting Guide and the video Planting a Tree Bare Root should be consulted. Also, check out the Department of Forestry’s Planting Trees. See also Say NO to Volcano Mulching! The moisture trapped by over-mulching encourages bacteria.
One of the most important things you can provide throughout a tree’s life is wise pruning. Pruning can play an extremely important role in disease prevention. For instance, rubbing branches, which may quickly damage bark, invite vector and consequently disease infiltration. See the slides from a CATS presentation How to Prune Landscape Trees (Young Landscape Tree Pruning). Adventitious growth wastes a tree’s energy. Lack of airflow may also be an issue. Proper fertilization during a tree’s earliest years and fertilization if an appropriately selected tree begins to struggle can also be helpful. See the VCE’s Fertilizing Landscape Trees and Shrubs – Basic. And while planting masses of the same species is aesthetically pleasing, the dangers inherent in monoculture – at least in extreme cases – may be lurking.
Friends of Trees
A wealth of valuable information is readily available, and there are local and state organizations that will help you in your tree efforts. Some already mentioned include the Charlottesville Area Tree Stewards (CATS), Piedmont Master Gardeners (PMG), and, of course, the Virginia Department of Forestry (VDOF). Call the PMG help desk (where you can receive guidance regarding a Virginia Tech diagnostic service and the Plant Disease Diagnostic Form) or consult Forestry’s Home Owner Assistance for Urban and Community Forestry. Virginia Tech offers Dr. Dendro (“Dr. Dendro will answer any of your tree related questions.”). To contact the Virginia Department of Forestry forester for your area, see Find a Forester. And, as previously noted, to hire an arborist, visit Forestry’s Hire a Certified Arborist.
Sources
Featured Image: Dogwood anthracnose (the fungus Discula destructiva), a symptom close-up. Photo: Penn State Department of Plant Pathology & Environmental Microbiology Archives, Penn State University, Bugwood.org, CC BY-NC 3;0 US.
Core Sources
Help with Sick Trees. Virginia Department of Forestry.
Home Grounds & Animals: 2023 Pest Management Guide. Publication 456-018. Virginia Cooperative Extension. See Diseases of Landscape Trees, 4-11 and Insects of Trees, Shrubs, Annuals, and Perennials, 4-29.
Homeowner Assistance for Urban and Community Forestry. Virginia Department of Forestry.
Insects and Diseases. Virginia Department of Forestry.
Tree and Forest Health Guide: A Handbook for the Diagnosis of Urban and Rural Forest Disturbances. Virginia Department of Forestry.
Additional Sources
The American Chestnut Foundation (TACF). Virginia Chapter.
American Chestnut: The Tree That Made America. Video slide presentation for the Virginia Native Plant Society by Warren Laws, former president of the Virginia chapter of The American Chestnut Foundation.
Bugwood Image Database System.
Chestnut Blight and A New Hope. Forest Pathology.
Chestnuts and the Introduction of Chestnut Blight. By Dr. Sandra L. Anagnostakis. Department of Plant Pathology and Ecology, The Connecticut Experiment Station.
Charlottesville Area Tree Stewards. The website provides a wealth of information.
Charlottesville’s Tree Packet. Neighborhood Development Services Department, City of Charlottesville, 2021. Includes the current master tree list as well as guidance on planting and maintenance.
Challenges to Sustainable Forests: Disease & Insects. Slide Presentation. Virginia Tech.
Common Forest Disease Problems. University of Arkansas Research and Extension, Cooperative Extension Service.
“Compartmentalization of Decay in Trees.” By Alex L. Shigo. USDA Forest Service, 1985.
“Death of the American Chestnut.” By George H. Hepting. Journal of Forest History, vol. 18, no. 3 (July, 1974), pp. 60-67.
“Developing Blight-Tolerant American Chestnut Trees.” By Powell, William A., Andrew E. Newhouse, and Vernon Coffey. Cold Spring Harbor Perspectives in Biology, vol 11, no.7 (1 Jul;y 2019).
The Disease Triangle: A Plant Pathological Paradigm Revised. By Leonard J. Franci. Department of Plant Pathology, North Dakota State University. The American Phytopathogical Society (APS).
Disease Types. Forest Pathology.
Diseases. University of Maryland Extension. Enter trees or the specific tree or topic in the search box.
Diseases in Hardwood Tree Plantings. By Paula M. Pijut. Hardwood Tree Improvement and Regeneration Center, Northern Research Station USDA Forest Service and Department of Forestry and Natural Resources, Purdue University.
Fertilizing Landscape Trees and Shrubs – Basic. Virginia Cooperative Extension.
Fertilizing Trees and Shrubs. Clemson Cooperative Extension.
Forest Health. Southern Regional Extension Forestry. Provides information on plants, insects, diseases, and other factors. Also provides accessible resources under headings for publications, webinars, and other resources. The Southern Regional Extension Forestry (SREF) Forest Health Program was created in 2015 by Drs. David Coyle and William Hubbard with support from the USDA Forest Service – Forest Health Protection Unit, the Southern Group of State Foresters, and the University of Georgia’s – D.B. Warnell School of Forestry and Natural Resources and the College of Agriculture and Environmental Sciences.
Forest Tree Diseases and Climate Change. By Susan Frankel, Jennifer Juzwik, and Frank Koch. The Climate Change Resource Center, United States Department of Agriculture (USDA).
The Hidden Life of Trees: What They Feel, How They Communicate; Discoveries From A Secret World. By Peter Wohlleban. Greystone Books, English translation 2016; originally in German 2015.
How Long Should I Expect My Tree to Last? By Scott A. Sjolander. Penn State Extension.
How Trees Fight Disease. By Matt Candeias. In In Defense of Plants, 23 January 2018. (A discussion of CODIT).
How trees protect themselves from wounds, disease and pests (including us). By Paul Hetzler. North Country Public Radio (NCPR).
Hybrid American Chestnuts. Penn State College of Agricultural Sciences.
Increase life span of urban trees. Illinois Extension.
[Insects:] Trees and Shrubs. University of Maryland Extension.
An Introduction to Integrated Pest Management. Virginia Cooperative Extension.
International Society of Arboriculture (ISA). See Find an Arborist.
Lifespans of Common Trees in Virginia. Virginia Big Tree Program, Virginia Cooperative Extension.
“On Tree Longevity.” By Gianluca Poovesan and Franco Biondi. New Phytologist (December 2020).
The Overstory. By Richard Powers. W.W. Norton & Company, 2018.
Parasitic Plants. Forest Pathology.
“Pesticide Storage and Disposal.” By Penny Fenner-Crisp. The Garden Shed, vol. 5, no. 11 (November 2019). Piedmont Master Gardeners.
Piedmont Master Gardeners. Help Desk.
“Planting a New Tree.” By David K. Garth. The Garden Shed, vol. 1, no. 11 (November 2015). Piedmont Master Gardeners.
Problem-free Trees for Virginia Landscapes. Publication 450-237. By Mary Ann Hansen, Alex Niemiera, and Eric Day. Virginia Cooperative Extension.
Purdue Tree Doctor. App. Available at app stores for Android and iPhone. Purdue University Extension. See online searchable program named Purdue Plant Doctor.
Recognizing Tree Diseases and Stress Factors. By Dr. Sharon M. Douglas. Department of Plant Pathology and Ecology, Connecticut Agricultural and Experiment Station.
“Recovery of American chestnut characteristics following hybridization and backrcross breeding to restore blight-ravaged Castanea dentata.” By Diskin, Matthew, Kim C, Steiner, and Frederick V. Hebard. Forest Ecology, vol 223 (2006), pp. 439-447.
Revitalization of the Majestic Chestnut: Chestnut Blight Disease. By Sandra L. Anagnostakis. Connecticut Agricultural Experiment Station.
“Rubber in Brazil: Dominance and Collapse, 1876-1945.” By Randolph R. Resor. The Business History Review, vol. 51, no. 51 (Autumn, 1977), pp. 341-366.
Tree and Shrub Insects. University of Minnesota Extension.
Tree Identification. Virginia Department of Forestry.
Tree Pruning Essentials. By Lindsey Purcell. Purdue Extension. This is an outstanding and comprehensive introduction.
Tree Pruning for the Landscape. Webinar. Purdue Extension.
Trees Have The Potential to Live Indefinitely. By Robin Lloyd. Scientific American (24 December 2021).
Virginia Tech Dendrology. Virginia Tech. Tree identification searchable database.
Virginia Tech Tree Identification. App. Available at app stores for Android and iPhone. For an introduction, see the YouTube video. The Web is rich in tree identification videos.
