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Plants & Animals

Plants and animals—key building blocks of natural communities—face ecological threats that natural resource managers and volunteers are tasked with stewarding.

In many natural areas, non-native invasive plants and problem insects are threatening the natural communities.

Non-native invasive plants such as kudzu can smother natural vegetation and destroy habitat needed by native animals. Non-native insects such as the gypsy moth can kill mature trees.

Non-native diseases, such as chestnut blight and Dutch elm disease, are also a problem for natural communities in parks and other natural areas. Native plants and animals have little or no immunity to these foreign pathogens.

A big shift in population dynamics of a native species can also cause trouble. A population spike of white-tailed deer can be catastrophic to other animals and plants in natural communities.

Some plants and animals have already become extinct. Others have been extirpated in particular areas, meaning they can no longer be found there, although they still live in other locations. Park staff work to identify and protect species of concern.

Non-Native Invasive Plants

Non-native invasive plants are species that reproduce and out-compete native plants in areas where they themselves are not native. They often degrade habitat for wildlife as well.

Explore this section:

How Did Non-Native Invasive Plants Get Here?

Coming from places as far flung as England, Japan, and Iran, most of these plants were brought to the United States in the nursery trade as special new introductions. No one knew they'd be such a problem! (Not all non-native plants sold in nurseries cause headaches in the long-run, but these ones do.)

Most, unfortunately, are still available at plant nurseries and are commonly planted in gardens and backyards.

Why Do They Do So Well in the Wild?

Characteristics that may make certain non-native plants valuable to gardeners make them aggressive invaders or naturalizers if they make it into the wild, easily thriving and reproducing. Some of their competitive advantages over native plants include the following:

Many Lack Natural Predators in the United States

In their native environment, most plants have natural predators like insects, diseases, hungry animals, and/or enterprising people that keep their growth in check. Non-native plants may lack these specific natural controls in their new environment. Kudzu, known to Americans as “the vine that ate the South,” does not grow out of control in its homeland of Japan.

Many Have Longer Growing Period

Many non-native invasive plants green up earlier in the spring, remain green longer in the fall, or are green all winter. For example, non-native wildflowers that produce their greenery early in the spring can shade out native wildflowers that get going a bit later.

Evergreen non-natives such as Japanese honeysuckle and English ivy can grow bigger and faster because they benefit from a longer growing season than native deciduous plants. The downside to sporting green leaves in winter instead of going dormant, however, is the possibility of damage by freezing winter storms. This risky trait also puts at greater risk the shrubs or trees on which evergreen vines climb. The weight of ice or snow on the climbers’ leaves can be enough to break the supporting plants.

Many Are Shade Tolerant

Many non-native invasives (like garlic mustard, porcelain-berry, Japanese barberry, winged burning-bush, privets, linden arrow-wood and other viburnums, and oriental bittersweet) grow not only along trails, where volunteer weed-pullers can more easily find and remove them, but in the shady interior of forests.

Many Grow Quickly

Non-native plants such as mile-a-minute weed grow quickly, shading out and choking out other plants. Porcelain-berry, Chinese wisteria and kudzu vines can overcome entire forests. Japanese stiltgrass can shade out entire forest floors.

Many Are Profuse Seeders

Garlic mustard and Japanese stiltgrass each generously reseed themselves, making a dense groundcover in no time. Brilliant red berries of linden arrow-woodattract birds and get dispersed in the woods through their droppings, as do the berries of oriental bittersweet, and of English ivy grown vertically. The profuse purple blooms of princess-tree promptly turn into pods filled with thousands of tiny wind-borne seeds. All of this spells trouble for nearby woods, unless their berries and flowers are harvested and used for indoor decorations before their seeds are carried away by birds, animals, wind, and streams (or dumped by landscapers into the wild).

Many Reproduce Aggressively Even Without Seeds

The reproducing bulblets and tubers of lesser celandine multiply underground and dislodge easily with a slight disturbance or flood, re-settling wherever they’re taken. Vines like oriental bittersweet, English ivy, and Japanese honeysuckle can run for great distances on and under the forest floor, putting down new roots at short intervals. Tree-of-heaven sends up a forest of saplings from one original root.

You Can Make a Difference!

Most parks and natural areas have plenty of opportunities for volunteers to work in the park to help protect the natural communities there. Contact your local park or natural area for more information.

When you’re visiting a park, you can help keep natural communities healthy by being observant and sharing what you see with park staff.

Have a smart phone? You can make a difference wherever you go! Get the app, and locate/photograph infestations of non-native plants for www.eddmaps.org (Early Detection & Distribution Mapping System).

You can also help parks and natural areas from the comfort of your own backyard. You can avoid planting non-native plants that tend to be invasive.

Or if you do, you can maintain them to keep them from reproducing and spreading (Ecobit: Don’t Let Your Ivy Climb).

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Non-Native Invasive Insects / Animals

Insects play a valuable role in natural communities. They provide food to birds and other animals, and they help break down organic matter. But non-native insects can devastate entire natural communities.

Chances are good that the insects that have successfully hitched rides around the world to reach other continents and become big problems are pretty robust. But it's not guaranteed that in their home continent they have a reputation as a pest. Why?

Explore this section:

Two bluish gray caterpillars with red and blue spots
Gypsy moth caterpillars are destructive, each one eating up to one square foot (929 square cm) of leaves per day!

Dennis Wilkinson / Flickr / June 2012 / Creative Commons BY-NC-SA

Insect Pests

Gypsy Moth

(Lymantria dispar) can defoliate whole forests of oak or other favored trees. If a population explosion is combined with drought, or if it occurs two or more years in a row, the insects can weaken and indirectly kill many or even most of the oaks in a forest.1 Gypsy moth defoliation and mortality can create extensive sunlit openings in the forest canopy, allowing understory trees such as red maple to grow.2 In combination with over-browsing of oak seedlings by deer and the presence of non-native invasive plants, large opening such as these can result in a complete shift in forest canopy composition.

Brown moth.
An adult male gypsy moth.

Jenn Forman Orth / Flickr / January 2013 / Creative Commons BY-NC-SA

National Park Service and U.S. Forest Service staff fight the gypsy moth with insecticides, a naturalized fungus that infects gypsy moth caterpillars, and parasitic wasps. Oak trees’ natural cycles of mast-fruiting also help prevent gypsy moth overpopulation.

Gypsy moth caterpillars are hairy and have distinctive markings: five pairs of blue dots on the back near the head, followed by six pairs of red dots.3 They do not build webs, as do the native eastern tent caterpillar and fall webworm, which rarely kill trees.4

Native to Europe and Asia, the gypsy moth became established in America in the late 1800s, and reached the mid-Atlantic region a century later.

Tree trunk missing its bark, and etched with dense, winding lines.
Emerald ash borers (Planipennis agrilus) bore paths just below the bark of ash trees (Fraxinus spp.).

Pat Heathzib / Flickr / May 2010 / Creative Commons BY-NC-SA

Emerald Ash Borer

The emerald ash borer (Agrilus planipennis) could be as devastating to ash trees in the U.S. as the chestnut blight was to American chestnut a century ago.

This half-inch long, Asian metallic green beetle is a relative newcomer to America. First found in 2002 in Michigan, the emerald ash borer spread among ash trees quickly, often hitching rides on infested firewood and nursery stock. By 2009, it had reached twelve states including Virginia and Maryland, and two Canadian provinces, killing hundreds of millions of trees.

As they feed, emerald ash borer larvae make S-shaped tunnels just under the bark of ash trees, destroying the trees’ circulatory system, or cambium. Emerging adults make D-shaped exit holes in the bark (flat on top, rounded on the bottom). Trees typically die within two years.5

Researchers are working to identify and develop biological control agents for emerald ash borer.

Large black beetle with white spots and long black and white antennae.
Asian long-horned beetle (Anoplophora malasiaca).

Changhua Coast Conservation Action / Flickr / June 2009 / Creative Commons BY-NC-SA

Asian Long-Horned Beetle

The Asian long-horned beetle (Anoplophora glabripennis) is a large and extremely destructive beetle that was probably imported from East Asia in wooden packing material in the 1990s.

Live adults have been destroyed in warehouses around North America. By 2008, tree infestations had been discovered in New York, Illinois, New Jersey, Massachusetts, and Ontario, Canada.6 7

Host trees include maple, box-elder, elm, birch, American sycamore, and willow. The Asian long-horned beetle’s larvae tunnel through the tree’s vascular system and heartwood, eventually killing it.

Round hole in a section of a branch.
Asian longhorned beetle (Anoplophora grabripennis) exit hole.

sallaha / Flickr / October 2010 / Creative Commons  BY-NC-SA

Tree infestations are recognized by the large round exit holes (at least the diameter of a ball-point pen, and sometimes dime-sized) that the beetle creates in the bark of large upper branches.8

The white-spotted, glossy black bodies of these winged adult beetles are ¾–1 ½ inches long. Their black-and-white banded antennae are up to four inches long! They should not be confused with the duller whitespotted sawyer which attacks conifers.

Infested trees must be cut down (after the first frost kills adult beetles) and chipped or burned to prevent spread. Early detection is crucial for beating the Asian long-horned beetle. You can help; visit the website beetlebusters.info to get started.

Small pale yellow and black larva on the underside of a half-eaten leaf.
A viburnum leaf beetle (Pyrrhalta viburni) on a skeletonized viburnum leaf.

dogtooth77 / Flickr / May 2009 / Creative Commons BY-NC-SA 2.0

Viburnum Leaf Beetle

The viburnum leaf beetle (Pyrrhalta viburni) is a serious pest of viburnum plants in Canada and the northeastern U.S.9

This Eurasian beetle arrived in the United States in the early 1990s. By 2008, it had been documented in New England, New York, New Jersey, Pennsylvania, Ohio, Michigan as well as Ontario and the Canadian Maritime Provinces.

Cornell University has set up a citizen science project to help track the spread of this beetle.10

The adult is a tiny brown adult beetle the size of a matchstick head. It lays eggs in imperfect rows of chewed holes underneath younger twigs in summer and until the first frost.

Small gold-colored beetle on a partially eaten leaf.
An adult viburnum leaf beetle, a dangerous pest for viburnum shrubs.

Ettore Balocchi / Flickr / August 2007 / Creative Commons BY 2.0

In spring, tiny pale larvae emerge to feast on viburnum leaves, eating their way through three stages of change, and leaving behind skeletons of leaf veins. Then they crawl down the plant to build a cocoon in moist soil. Later in the summer, the adults emerge, find undamaged leaves, and eat little oblong bullet-holes through them.11 Repeated infestation can kill the plants.

The most effective control of this pest is to prune and destroy egg-infested twigs from late fall to early spring. Beneficial insects like ladybug larvae and adults and even certain stinkbugs feed on the viburnum leaf beetle or its larvae.

Sirex Woodwasp

The sirex woodwasp (Sirex noctilio) is a pest of pine trees and other conifers. It arrives in the United States in pallets of wood from infested trees.

By 2014, sirex woodwasp had been found in New York and Pennsylvania, and scattered areas in Michigan, Connecticut, New Jersey, and Vermont. The first woodwasp was found in Indiana in 2002. It is considered a particular threat to plantations of pines in the southeastern United States.

When laying their eggs, female sirex woodwasps inject a fungus and irritating mucus into weakened or stressed pine trees. The fungus feeds their larvae, and further weakens the tree. In other countries where it is an invasive pest, the woodwasp often attacks loblolly trees on pine plantations.

Symptoms include a lightening or yellowing of the tree crown (sometimes reddish-brown), beads or streams of resin dripping from tiny holes in the bark, larvae tunnel in the wood, and exit holes.12

You Can Make a Difference!

"An ounce of prevention is worth a pound of cure." The sooner someone notices telltale signs of an insect invasion and speaks up, the better chance there is of controlling it. Whether it's in your own neighborhood or in a park, resource managers need your set of eyes to help keep a vigilant watch for these insect pests!

Some of the insects, such as the viburnum leaf beetle13 and the Asian long-horned beetle14, are the subject of citizen science projects designed to track their spread.

When visiting a park, you can help keep natural communities healthy by being observant and sharing what you see with park staff. (Ecobit: An Extra Set of Eyes)

Citations

  1. US Department of Agriculture Forest Service. 2003. Gypsy moth in North America.
  2. Abrams MD. 1998. The red maple paradox: what explains the widespread expansion of red maple in eastern forests? BioScience. 48:355-364
  3. Schuster J, Nixon PL. 2008. Focus on Plant Problems: Gypsy Moth.
  4. Bessin RIC. 2007. Eastern tent caterpillar. accessed March 3, 2009
  5. US-Department-of-Agriculture-Forest-Service, Michigan-Department-of-Agriculture, et al. 2008. Emerald ash borer.
  6. USDA Animal and Plant Health Inspection Service. 2017. Asian longhorned beetle.
  7. Canadian-Food-Inspection-Agency. 2008. Asian longhorned beetle - Anoplophora glabripennis.
  8. USDA Animal and Plant Health Inspection Service. 2017. Asian longhorned beetle.
  9. Citekey 408 not found
  10. Cornell University. 2016. Viburnum Leaf Beetle.
  11. Cornell University. 2016. Viburnum Leaf Beetle.
  12. USDA Animal and Plant Health Inspection Service. 2008. Proposed Program for the Control of the Woodwasp Sirex noctilio F. (Hymenoptera: Siricidae) in the Northeastern United States.
  13. Cornell University. 2016. Viburnum Leaf Beetle.
  14. USDA-Animal-and-Plant-Health-Inspection-Service. 2014. Asian longhorned beetle.


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Diseases of Plants and Animals

Bacteria and fungi (together with insects) play an important role in natural communities because they help break down material from dead plants into nutrients that benefit living plants. But non-native bacterial, viral and fungal pathogens can kill entire populations of plant species that have no natural resistance.

Explore this section:

Where Do Plant Diseases Come From?

Many of the most threatening plant diseases spreading in the U.S. today were brought there on plants or wood products from around the world. (In the same way, some of the most threatening plant diseases spreading in Asia today were brought there from the U.S.!)

Plant Diseases

Chestnut Blight

American chestnut was once the dominant tree in mid-Atlantic hardwood forests—comprising as much as 35 percent to 50 percent and sometimes more of the canopy.1 2

Today, there are virtually no mature American chestnuts remaining in these forests.

What killed the chestnuts? A fungus called chestnut blight (Cryphonectria parasitica).

Before the blight, the fast-growing American chestnut provided foliage, fruits, and living wood as food for bears, turkeys, and native insects and many more animals. Its dependable, abundant crops of chestnuts were an important food for Native Americans, and later, European immigrants who incorporated them into Christmas traditions.

It easily survived wildfires and outbreaks of native insects and diseases. Its durable, high quality wood was widely used in construction and carpentry. But since the 1930s, it has all but disappeared. Store-bought chestnuts today come from European stock or hybridized strains.

The chestnut blight fungus was apparently unwittingly brought to the U.S. on highly resistant Japanese and/or Chinese chestnut trees in the late 1800s, and spread undetected for many years throughout the U.S. via the nursery trade.

The fungus enters wounds on the tree and grows in and under the bark, forming cankers on the stems. The tree eventually dies back to the roots. Chestnut blight is easily spread on the feet of any insect or other animal that walks across the cankers.3

In some cases the roots continue to send up sprouts, which succumb to the fungus before they are old enough to reproduce. After the loss of American chestnut, drought-tolerant oaks appear to have increased where American chestnuts once grew.4 5 Oaks can host the fungus without getting sick, so there is a continual source of the fungus to infect new chestnut sprouts.

Scientists are working to develop blight controls and to breed a resistant strain of American chestnut, with the goal of restoring the majestic chestnut to eastern forests of North America.

Butternut Canker

Butternut canker (Sirococcus clavigignenti-juglandacearum) is currently eliminating entire populations of butternut trees (also called white walnut) throughout its range in the United States.

The origin of the fungus is unknown, but it was probably introduced from outside the United States in the mid 1900s.6

Infected trees typically have dead branches or a dying top. Cracked, sunken, discolored bark may ooze black inky fluid in spring, or appear sooty with whitish margins in summer. Where the bark has come loose, dark oval stains may be visible on the wood beneath.7 Controls currently do not exist.8

Rain splash and wind (and possibly insects and other animals) spread the spores to other butternut trees and to black walnut. However, black walnut, which is related to butternut and overlaps part of its geographic range, appears to be resistant to the fungus.

Butternut has prized edible nuts. Never a very common tree, butternut is becoming hard to find. Since some trees in the U.S. seem to display resistance, there is hope that the species can outlive the disease.

Dogwood Anthracnose

Dogwood anthracnose (Discula destructive) is a fungus that appeared simultaneously on both coasts of the United States in the mid-1970s, origin unknown.

It forms purple-rimmed tan blotches on the leaves, and cankers on the twigs of our beautiful flowering dogwood. Lower branches often die first, and the trunk may produce a lot of sprouting as a last-ditch (but ill-fated) attempt to survive.9

Healthy trees may be able to survive a bout with the fungus, but trees stressed from drought or other problems can die within a few years—sometimes within months. Early removal of infected parts may help the tree survive (taking care to disinfect the pruning tools with rubbing alcohol between cuts).

The spores of the fungus can be splashed by rain or carried by other means, such as insects, birds, and pruning tools. Some trees seem to be resistant.

Flowering dogwood trees are valued for their beauty in early spring and because their fall berries feed many birds.

Dutch Elm Disease

Dutch elm disease (Ophistoma ulmi) is a fungal disease from Asia, not Holland. Its common name comes from the fact that it was first described by Dutch scientists, not many years before it arrived in North America in about 1930.

It can affect all of our native elm species, and has swept through much of the United States, killing a majority of the elms formerly present. The fungus is moved from infected elm trees to healthy ones by spores carried on the elm bark beetle. The disease can also be passed from tree to tree by their interlocking roots.10

When the elm bark beetle comes to feed and reproduce in the trunk of a tree, it drops fungal spores, which the tree attempts to quarantine by closing off newly-infected parts of its circulatory system—effectively shutting off the flow of water and nutrients to any limb that depends on that part of the tree’s vascular system.

The visual result is a tree with individual dead branches with brown, wilted leaves. As the fungus spreads, this symptom eventually progresses throughout the tree and kills it.

One option in the battle against Dutch elm disease is to inoculate individual elm trees against the fungus—an expensive option at $100 per tree.

To decrease the risk of attracting elm bark beetles (which move the fungal spores from tree to tree), elm trees can also be pruned of their dead branches—but it should be done in winter when there is no smell of fresh sap to attract more elm bark beetles. Elm bark beetles are more attracted to weak and stressed elm trees, so watering elm trees during a dry summer helps deter the beetles.

Elms growing within 50 feet of one another risk infecting each other through their roots. Trenching around a tree exhibiting early symptoms will help to protect nearby trees. It is critical to the survival of other elms that trees infected with Dutch elm disease be immediately destroyed, so that the elm bark beetles cannot continue to reproduce in its trunk; some estimates suggest that, left in place, a diseased tree can release upwards of 400,000 beetles within two years!11

Elm Yellows (or Elm Phloem Necrosis)

Elm yellows is caused by a bacteria that is spread by a sap-sucking insect, the leaf hopper. Unlike Dutch elm disease, elm yellows typically affects the entire crown of an elm tree all at once, turning the leaves yellow in late summer and causing them to drop prematurely.12 Trees may develop witch's broom—dense sprouts in tiny patches in the crown.

By the time symptoms have appeared, the tree is infected systemically, and may die right away, or within a year or two. When infected, the inner bark of several species of elms develops the odor of wintergreen; that of slippery elm acquires the smell of maple syrup.13

Beech Bark Disease

Beech bark disease (Nectria coccinea var. faginata or Nectria galligena) arrived in the United States around 1890, and is slowly spreading throughout the eastern part of the country, killing large American beech trees. Beech bark disease has been found in Virginia forests14 and Maryland forests.15

It is a canker disease caused by a fungus that enters trees through tiny wounds in the bark, killing patches of inner bark. If enough cankers form, ringing the entire tree trunk, the tree will die.16

The wounds by which the fungus enters are created by a yellow beech scale insect that inserts its needle-like mouth to feed on the inner bark. This scale should not be confused with the generally harmless beech blight aphid.

American beech plays an important role for wildlife, providing food—beechnuts—and den habitat for numerous animals.

There is currently no cost-effective way to manage this disease in a large forest stand. Fortunately, there are some American beech trees that seem to have less feeding injury from the beech scale. These resistant trees suffer less of an attack by the fungus. Over time, the offspring of these healthy trees may be able to replace the trees that succumb to beech bark disease.17

Sudden Oak Death

The origin of sudden oak death (Phytophthora ramorum) is uncertain, but it appeared on the west coast of the U.S. in the mid 1990s. Natural resource managers everywhere should be watchful for early signs of the disease because of nationwide shipments in 2004 of millions of potentially infected host plants (rhododendrons and camellias) from west coast nurseries. The pathogen prefers cool, moist air, putting drier natural communities at lesser risk.

The pathogen weakens the oak tree, causing reddish or black bleeding ooze from lesions on the bark, and later a rapid browning of the leaves. It renders the tree vulnerable to bark beetle and fungus invasions.18

Many plant species can host the sudden oak death pathogen without dying. Unfortunately, this creates an ongoing source for the air-borne pathogen.19 Such hosts include many ornamental nursery plants as well as forest trees and shrubs such as mountain laurel, azaleas, rhododendrons, viburnums, witch hazel, and Solomon's plume.20

Hikers, researchers, and horses may unintentionally move spores from one forest to another, unless care is taken to clean their shoes, hooves, tires, equipment, etc. when leaving an infected area, especially in areas of muddy soil.

Various chemical treatments, including injections to the tree trunk, can be used preventatively in an area known to be at risk of an epidemic, or with very early detection. Laboratory tests show northern red oak and southern red oak to be highly susceptible to the disease.21 The pathogen prefers cool, moist air.

You Can Make a Difference!

"An ounce of prevention is worth a pound of cure." The sooner someone notices telltale signs of plant disease outbreak and speaks up, the better, whether it's in your own neighborhood or in a park! Parks keep a vigilant watch, and ask visitors to do the same, so that suspected disease outbreak can be identified early and curbed where possible.

When visiting a park, you can help keep natural communities healthy by being observant and sharing what you see with park staff. (Ecobit: An Extra Set of Eyes)

Citations

  1. Shreve E. 1910. The ecological plant geography of Maryland; coastal zone; eastern shore district.
  2. Nerurkar JD. 1974. Plant communities on a quartzite ridge in Chester County, Pennsylvania. Proceedings of the Pennsylvania Academy of Science . 48:101-106
  3. Anagnostakis S. 1997. Chestnuts and the Introduction of Chestnut Blight.
  4. Keever C. 1973. Distribution of major forest species in southeastern Pennsylvania. Ecological Monographs. 43:303-327
  5. Overlease WR. 1978. A study of forest communities in southern Chester County, Pennsylvania. Proceedings of the Pennsylvania Academy of Science 52:37-44.
  6. Schlarbaum S, Hebard F, Spaine P, Kamalay J. 1997. Three American tragedies: chestnut blight, butternut canker, and Dutch elm disease. In: Britton, Kerry O., ed. Proceedings, exotic pests of Eastern forests; 1997 April 8-10; Nashville, TN. Tennessee Exotic Pest Plant Council: 45-54
  7. US Department of Agriculture Forest Service. 1995. Pest Alert: Butternut Canker.
  8. US Department of Agriculture Forest Service. 2009. Major forest insect and disease conditions in the United States 2007.
  9. Mielke ME, Daughtrey ML. 2001. How to identify and control dogwood anthracnose.
  10. US Department of Agriculture Forest Service. 1998. How to identify and manage Dutch elm disease.
  11. Conley G. 2003. European elm bark beetle and Dutch elm disease in Seattle. Accessed 2015
  12. US Department of Agriculture Forest Service. 1998. How to identify and manage Dutch elm disease.
  13. Parsons J. 2008. Plant Answers.
  14. US Department of Agriculture Forest Service. 2017. Major Forest Insect and Disease Conditions in the United States: 2015.
  15. University of Maryland Extension. 2008. Beech Bark Disease. Accessed 2018
  16. Pennsylvania Department of Conservation and Natural Resources. 2008. Forest Health Fact Sheet: Beech Bark Disease .
  17. Pennsylvania Department of Conservation and Natural Resources. 2008. Forest Health Fact Sheet: Beech Bark Disease .
  18. California Oak Mortality Task Force. 2008. Sudden oak death.
  19. California Oak Mortality Task Force. 2008. Sudden oak death.
  20. USDA Animal and Plant Health Inspection Service. 2008. Sudden oak death.
  21. USDA Animal and Plant Health Inspection Service. 2008. Sudden oak death.

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Population Dynamics

Sudden, sharp increases in individual populations of native animals or plants can have serious consequences to the natural communities they and others depend on.

Explore this section:

White-Tailed Deer

White-tailed deer populations have skyrocketed in the eastern United States since the late 1900s due to several factors: suburbanization (which increases favorable edge habitats for deer and concentrates their breeding populations), a decline in hunting, and the lack of non-human predators.

Forests are resilient in providing the living requirements of many animals. But over-browsing by hungry white-tailed deer has multiple effects.

First, over-browsing severely reduces the number and diversity of native plants growing on the forest floor. This diminishes the quality of the natural communities as habitat for creatures that depend on the native groundcover for nesting, foraging, and protection—small mammals, eastern box turtles, and ground-nesting birds, for instance. Many sensitive species of songbirds cannot be found in areas where the understory has been removed by grazing.1

Perhaps even more importantly, as dense populations of deer consume too many woody tree seedlings and saplings, tree regeneration is threatened.2 Deer taste-preferences for certain tree seedlings can actually influence what a forest will look like in the future. Deer seem not to like American beech seedlings, while white oak seedlings seem to be a favorite, with many other oaks a close second. (Chestnut oak seedlings seem to be an exception: deer seem to snub them unless particularly hungry.) Putting them at a second disadvantage, oaks are very slow-growing compared to other tree species, leaving their tender leaves vulnerable to deer browse for several years; thus, many oaks won’t survive to maturity. Of course, many more oak seedlings take root than could ever be sustained in the forest canopy, so it is a natural process for animal browse and other pressures to limit the number of seedlings that make it to maturity. However, too many deer can leave too few young oaks to renew a forest as it ages.

A transition away from oak in a forest that has long been dominated by oak would not only change how the forest looks, it would also impact the animal communities that depend on the acorns they produce, the insects they host, and a myriad of other factors.

Stewardship

How to deal with severe increases or drops in populations of native animals or plants is a challenge to resource managers. Why is it occurring? What is being impacted? What might happen if humans intervene? What might happen if they don't?

Everything in nature is interdependent, so the consequences of taking (or not taking) action must be carefully weighed. Often it takes months or years of study and sometimes public comment before a park embarks on a "preferred" course of action to intervene. Even then, staff has to be prepared to respond to results that no one could foresee.

Rock Creek Park in Washington, D.C. is taking seriously the importance of thoughtful stewardship of the white-tailed deer population, following an alarming population growth trend around the turn of the 21st century. After many years of study and public input, they embarked in 2013 on a Deer Management Plan for Rock Creek Park, with hopes of more sustainable forests and deer population within several years.3 4

Citations

  1. Carruthers T, Carter S, Florkowski N, Runde J, Dennison B. 2009. Rock Creek Park Natural Resource Condition Assessment.
  2. Rossell Jr. CR, Patch S, Salmons S. 2007. Effects of deer browsing on native and non-native vegetation in a Mixed Oak - Beech Forest on the Atlantic Coastal Plain. Northeastern Naturalist. 14(1):61-72
  3. National Park Service. 2013. Frequently Asked Questions About Rock Creek Park's Deer Management Plan.
  4. National Park Service. 2017. White-Tailed Deer Management in Rock Creek Park.

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Assessing Vulnerability of Species

The National Park Service and other agencies protect and monitor plant and animal species whose populations are rare or in danger of being eliminated in particular regions. How do they—or anyone else—know if a species is vulnerable?

Organizations like NatureServe help develop international standards (a "common language" of sorts) that people from different agencies and countries can use to understand which plant and animal species may be of conservation concern locally or globally. NatureServe and their member programs and partners around North America do extensive field work ("surveys") to find out which species are common in particular places, and which are not. Out of the data they gather from these surveys and others, they develop Conservation Status Ranks.

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Last updated: July 26, 2024