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Forest Ecosystems in Urban and Suburban Midatlantic North American

Introduction

Before the arrival of Europeans, forests covered the eastern United States. It was said that a squirrel could travel from the Atlantic shore to the Mississippi River without ever touching the ground. Forested land has now been reduced to tiny fragments.
The majority of our native plants and animals are adapted to life in forested ecosystems, Our forests vary from back dune holly forests along the sea shore, to moist coastal-plain forests on rich, deep soil; to dry, rocky upland oak woods.
Our forests perform vital services for us. These services include carbon dioxide (CO2) uptake, oxygen (O2) production, uptake of pollutant gases, cooling through transpiration of water, soil formation, waste treatment, noise abatement, wind speed control, erosion control, storm water storage, filtration, and runoff control (i.e. flood control), nutrient cycling, habitat for plants and wildlife, and genetic resources.
Forests provide habitat for plant pollinators and seed dispersers, and they are the major home for most of our native plants, animals, fungi, and soil invertebrates. They are major resources for recreation, and cultural services. People derive psychological, spiritual and aesthetic values from forests. These quality of life resources are particularly critical in urban and suburban areas where residents need refuge from crowding, noise, and the hardness of the built environment.

Forest Structure

Soil is the base upon which all plant and animal communities stand. Native forest soils have developed over the thousands of years since the last glaciers retreated from North Eastern North America. They vary greatly in composition and support a wide variety of native plants. Native soils are becoming increasingly scarce as land is filled, paved over, or soil is removed for developments. Preservation of intact, native soils is of the utmost importance to any conservation program.

A forest ecosystem begins below the soil surface with the deep mineral layers including gravel, sand, silt and clays of the subsoil. Above that, the topsoil mixes mineral soil with organic materials and chemicals derived from plants and animals. The top most layer of forest soil is called humus. It is the black, crumbly, rich “compost” in which much of the soil life is concentrated. Healthy forest soil has a complex ecology of its own, upon which the life of the forest depends. It contains hundreds or thousands of types of bacteria fungi, microscopic invertebrate animals, and larger soil animals from insects to moles.
One of the most important living components of the humus and top-soil are mycorrhizae. These are associations between fungi and plant roots. They increase the uptake of water and nutrients in dry, acidic soils.
Above the humus layer is the litter layer, which becomes humus as it slowly decays. Litter consists of dead leaves, sticks, animal droppings and other decaying organic material. It helps insulate the soil, traps rainwater and provides habitat for many small animals. Soil fungi, bacteria and invertebrates break this down into humus, and release the stored nutrients (mostly nitrogen and phosphorus) that are taken back up by growing plants to complete the cycle of use.
However, in previously glaciated areas, it does not naturally contain earthworms. These invertebrates prevent humus formation by mixing leaf litter into the topsoil.

Above and below the soil level, life is supported by the energy of sunlight. Chlorophyll, the chemical that makes plants green, uses sunlight to convert water and carbon dioxide into sugars. Oxygen is produced as a waste product. This process is called photosynthesis. From these simple sugars, with the addition of nitrogen, phosphorous and some trace minerals, plants create carbohydrates, proteins, nucleic acids and all the chemicals needed by living things.

The plants that create the structure of the forest above the soil are arranged, roughly, in layers. These are the herb, shrub, sub-canopy and canopy layers. However, they tend to blend one into another, especially in dense, moist forests.
The first layer of plants growing above the soil consists of herbs and the seedlings of trees and shrubs. They are vital for holding soil in place, providing food and shelter for small forest animals and slowing the flow of rainwater so that it sinks into the soil, rather than running off. Herbs include spring and fall wildflowers, grasses, and sedges. This layer of plants is the first to suffer when people use the forest in destructive ways such as biking or hiking off-trail. When the herb layer is gone, the soil begins to wash off with every rainstorm, losing its structure and taking nutrients out of the system. This eroded soil often finds its way into streams where it buries stream-dwelling animals, clouds water and clogs the gills of fish, suffocating them.
The next layer of plants, above the herbs, is the shrub layer. It contains not only shrubs but tree saplings. These are the next generation of forest trees. Most tree saplings grow very slowly due to low light levels. A sapling less than eight or ten feet tall can be several decades old. They only get a chance to grow up into the canopy if the old trees above them fall in a wind or ice storm. Forest shrubs are adapted to low light levels and can grow and flower as long as they get flecks and patches of sunlight that filter through the forest canopy during the course of a day.
The forest sub-canopy is made up of trees that normally do not grow very tall, such as flowering dogwood (Cornus florida) and Ironwood (Carpinus caroliniana). It also contains immature canopy trees. In an eastern forest, there is usually not a sharp difference between sub-canopy and canopy.
The canopy of the forest is the layer of mature trees forming an irregular “ceiling” at the top of the forest. It can range from very dense and dark, such as that of young red maples in a swamp forest, to open and sparse in a mature oak forest on dry, sandy soil.
The natural cycle of renewal of forest in this region involves formation of larger or smaller gaps in the forest canopy by windstorm blow-downs and ice storm breakage. The increased light in forest gaps allows establishment of trees requiring high light levels and increased growth of suppressed tree saplings. These seedlings and saplings eventually re-form a closed canopy.

Our Forests in Trouble

The forests of this region are very different from those that were here four hundred years ago. When Europeans came to North America they found great expanses of unbroken forested land. They began to clear this land for timber and agriculture. Today’s remnant forests in urban and suburban Northeastern North America have regrown many times over, having been cleared, logged, burned, farmed, grazed, built over and abandoned. As a result, the original forest communities have drastically changed. They now consist of small remnant patches with a very high ratio of open edge to closed canopy interior. They have lost many native species, from the American chestnut to most species of orchids. A recent study found that Staten Island New York has lost 40% of its native flora and that a third of its plants are non-natives. What is left is subject to the continued assaults of air pollution, fires, dumping, heavy recreational use, bike traffic and motorized vehicles.

In addition to clearing forests Europeans also brought with them seeds of numerous plants that were never before found in the New World. These exotic species are plants that have originated in parts of Europe and Asia with climates similar to ours. Some were introduced accidentally in crop seeds. Many others have been imported as horticultural plants. These imports have continued and most landscaped areas contain more introduced plants than indigenous ones.
Some of these exotic plants escape from cultivation and invade natural areas, displacing native plants. These invasions are made easier because of the large amount of open “edge” habitat that surrounds each forest remnant. Indeed, the strips of woodland along highway margins and small patches of woodland in urban and suburban parks are virtually all edge.
Invasive plants decrease biodiversity by overwhelming native (indigenous) species in natural areas. A healthy forest has a very diverse community of trees, shrubs and herbs. Invasive plants destroy this diversity by crowding out, covering and shading out native herbs, wildflowers, tree seedlings, saplings and shrubs. Instead of dozens of species, a forest degraded by fragmentation and invasive plants may have only six or seven. Most often these include a ground layer consisting only of two or three weedy herbs, (usually garlic mustard and wild garlic), a dense layer of Japanese honeysuckle, and an exotic shrub or two such as Tatarian honeysuckle and multiflora rose.
There are a number of exotic, woody vines that are having profoundly detrimental affects on Northeastern forests and woodlands. Most of these vines have fleshy fruit that is eaten by birds, which then disperse the seeds into surrounding areas. The vines add tremendous amounts of weight to branches and tree trunks, causing breakage during ice and snowstorms in the winter. Woody vines twine around the stems and branches of small trees distorting their growth, strangling them and preventing them from reaching upward to form a canopy. Major infestations of vines can prevent reforestation of open areas or prevent maturation of replacement trees in older forest stands. The result is a “vineland”, a more or less permanent, matted, impenetrable mass of vines replacing woodlands. In some places it seems likely that that replacement of native forest communities has been permanently disrupted.

Eastern white-tailed deer, while native, have also become a large problem in forest regeneration. Without natural predators, and with restricted hunting of does, deer populations have become far greater than can be sustained by the landscape. In addition, deer are adapted to eating native plants and will eat native tree and shrub seedlings in preference to non-native plants. Many forested areas are failing to regenerate due to intensive browsing by white-tailed deer.

There is a growing awareness of the problems facing our forest fragments. An increasing number of people work as volunteers helping to restore their local forested parklands. With more participation and more funding for restoration and management we may be able to save some of what remains.

Definitions
Carbohydrates: Organic chemicals made of carbon, oxygen and hydrogen (sugars, starches, cellulose), with the general formula C6H12O6.
Chlorophyll: The molecule that keeps the world alive. A chemical that absorbs the energy from red light (and reflects green light) to transform carbon dioxide and water into sugar and oxygen (see photosynthesis).
Ecosystem: A community of plants and animals and their physical environment and their interactions.
Nucleic acids: The chemical building blocks of genes and chromosomes containing both nitrogen and phosphorus, as well as carbon, oxygen and hydrogen.
Photosynthesis: Use of energy from sunlight to produce sugar from carbon dioxide and water:
6CO2 + 6H2O —sunlight + chlorophyll? C6H12O6 + 6O2
Pollinator: An insect or bird that picks up pollen (the sperm container of plants) from one plant and transports it to the female organs of another plant of the same species.
Proteins: Chemicals that make up enzymes, muscle and connective tissue and other vital components of living things. Made of strings of amino acids, which contain nitrogen as well as carbon, oxygen and hydrogen.
Seed dispersers: Animals that transport seeds away from the parent plants. Birds and mammals eat fruit and deposit seeds in feces.
Transpiration: Loss of water from plant leaf pores. Water is pulled into plant roots, travels up tube-like cells and enters leaves where it is used for photosynthesis, some also evaporates from leaf pores.

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