Forest Fragmentation

FOREST FRAGMENTATION

When the European settlers first arrived in the Ohio valley over 200 years ago, most of the land was forested. Ohio itself was over 90% forested.

About 100 years later, land clearing for farming had left very little of Ohio in forest. However, over the past 100 years, much of eastern and southeastern Ohio has reverted back into forests as many farms were abandoned.

Causes of Forest Fragmentation:

Forest fragmentation occurs when large tracts of forests are broken down into smaller isolated forest tracts, patches, islands, fragments, or remnants. Some of the causes of forest fragmentation can be construction of roads or utility lines, logging operations, conversion to agriculture, and urbanization. Forest fires, ice storms, or windstorms can also lead to forest fragmentation. Today, much of Ohio and the eastern U.S. is a mosaic of forests, agricultural fields, and urban areas.

Effects of Forest Fragmentation:

The effects of forest fragmentation depend upon the sizes of these isolated fragments and their degrees of isolation. Isolation is the distance from one fragment to its closest similar fragment or fragments.

Forest fragmentation can cause harmful and irreversible effects upon our native floral and faunal species. Fragmentation makes it difficult or even impossible for a species to disperse or to recolonize. This may lead to loss of genetic diversity and to inbreeding of a species. Many of those species require large forests tracts. Some species may even become extinct within these fragments.

The smaller and the more isolated fragments are more likely to lose species and numbers than the larger and the less isolated fragments. A single large forest will have more species and larger populations than several smaller isolated forests, even if the total land areas of the large forest and all of the smaller forests are equal.

Forest fragmentation alters microclimates. Wind can totally penetrate a small forest but not a larger forest. This can affect temperature and humidity.

Edge Effect:

Much of the effects of forest fragmentation occur along the boundaries of the forests. This is referred to as edge effect. The width and the depth of these edges and their effects depend upon several factors.

The directional orientation of the edge is one factor. A south-facing edge will be wider and deeper than a north-facing edge.

The direction of the prevailing winds is another factor. Because of the drying effect of the wind, especially during the growing season, the edges upon the windward sides will be wider and deeper than the edges upon the leeward sides.

The ratio of forest interior to forest edge varies by size and shape of the fragments. Fragments that are rounded or squared will have more interior forest, with the rounded fragments having even more interior forest. Rectangular fragments will have less interior forest, even if the total area is the same as a square or a circle. Linear fragments may have no interior forest, regardless of its length.

Effects on Animals:

Forest fragmentation harms many of our interior woodland Songbird (Suborder Passreri) species. It decreases their nesting habitat. It makes them vulnerable to nest predation from predatory species like Blue Jays (Cyanocitta cristata L.), American Crows (Corvus brachyrhynchos Brehm), Raccoons (Procyon lotor L.), and Feral Cats (Felis catus L.). It also encourages nest parasitism from Brown-headed Cowbirds (Molothrus ater Boddaert). These predatory and parasitic species are not commonly found in large forest tracts.

Forest fragmentation affects larger bird species. Large Hawks (Family Accipitridae) and Owls (Family Strigidae) need at least 1 square mile (640 acres) of forest.

However, Forest fragmentation can benefit other Bird (Class Aves) and Mammal (Class Mammalia) species. Those species require 2 or more habitats. Some of these species include American Robins (Turdus migratorius L.), Eastern Cottontail Rabbits (Sylvilagus floridanus J.A. Allen), and White-tailed Deer (Odocoileus virginianus Zimmermann).

Forest fragmentation creates barriers to native wildlife movement. Amphibians (Class Amphibia) and Reptiles (Class Reptilia) are especially vulnerable.

Forest fragmentation benefits Mosquitoes (Family Culicidae), which are a nuisance species. Unfortunately, it does not benefit Dragonflies (Suborder Anisoptera), the Mosquitoes’ main predators.

Effects on Plants:

Forest fragmentation affects native plant habitats. Most of the plants found along the boundaries are vines and shrubs. These plants are intolerant of shade but are tolerant of dry conditions.

Forest fragmentation encourages exotic invasive plants species, such as Autumn Olive (Elaeagnus umbellata Thunberg), Amur Honeysuckle (Lonicera maackii [Ruprecht] Maximovich), Morrow’s Honeysuckle (Lonicera morrowii A. Gray), Tatarian Honeysuckle (Lonicera tatarica L.), Japanese Honeysuckle (Lonicera japonica Thunberg), and Multiflora Rose (Rosa multiflora Thunberg). Exotic plants can easily out-compete our native plants. Too many exotic plant species in an area leads to loss of plant biodiversity in that area.

Forest fragmentation affects some of our native plant species as well. It benefits Poison Ivy (Toxicodendron radicans [L.] Kuntze). Although Poison Ivy causes bad skin rashes upon humans, its leaves and berries provide food for our wildlife.

Canopy trees near the edges will be affected. These trees tend to lean outward and their lower branched will extend outward toward the open areas. Canopy trees in the interior of larger forests will be straight and will only branch near the top.

Other Effects:

Forest fragmentation’s effects extend well beyond the forest boundaries. The reduction of forest size affects its ability to clean the air. This leads to more air pollution.

With the increase in numbers of White-tailed Deer, there is an increase in cases of Lyme Disease (Lyme borreliosis). Lyme Disease, which is common in the East and in the upper Midwest, is making its way into Ohio.

Forest fragmentation causes loss of scenic views. It also affects recreational uses of the forest, such as hunting, bird watching, and sightseeing.

REFERENCES

FORESTS FOREVER: THEIR ECOLOGY, RESTORATION, AND PRESERVATION

By John J. Berger

LANDSCAPE ECOLOGY

By Richard T. T. Forman and Michel Godron

EASTERN FORESTS

By John Kricher and Gordon Morrison

en.wikipedia.org/wiki/Forest_fragmentation

en.wikipedia.org/wiki/Edge_effects

www.birds.cornell.edu/bfl/gen_instructions/fragmentation.html

sfp.cas.psu.edu/fragmentation/fragmentation.html

www.ontarionature.org/discover/resources/PDFs/factsheets/fragemtation.pdf