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A wildlife corridor, habitat corridor, or green corridor
The main goal of implementing habitat corridors is to increase biodiversity. When areas of land are broken up by human interference, population numbers become unstable and many animal and plant species become endangered. By re-connecting the fragments, the population fluctuations can decrease dramatically. Corridors can contribute to three factors that stabilize a population:
- Colonization—animals are able to move and occupy new areas when food sources or other natural resources are lacking in their core habitat.
- Migration—species that relocate seasonally can do so more safely and effectively when it does not interfere with human development barriers.
- Interbreeding—animals can find new mates in neighbouring regions, increasing genetic diversity.
Rosenberg et al. (1995)
Although corridors had originally been implemented with the assumption that they would increase biodiversity, not enough research had been done to come to a solid conclusion. The case for corridors had been built more on intuition rather than
A habitat corridor could be considered as a possible solution in an area where the destruction of a natural area has greatly affected its
Corridors can be made in two distinct areas—either water or land. Water corridors are called riparian ribbons and usually come in the form of rivers and streams. Land corridors come on a scale as large as wooded strips connecting larger woodland areas. However, they can also be as simple as a line of shrubs along a sidewalk (Fleury & Brown 1997). Such areas can facilitate the movement of small animals, especially birds, from tree to tree, until they find a safe habitat to rest in. Not only do minimal corridors aid in the movement of animals, they are also aesthetically pleasing, which can sometimes encourage the community to accept and support them.
Species can be categorized in one of two groups; passage users and corridor dwellers.
Passage users occupy corridors for brief periods. These animals use corridors for such events as
Corridor dwellers can occupy the passage anywhere from several days to several years. Species such as
Habitat corridors can be categorized according to their width. Typically the wider the corridor, the more use it will get from species.
- Regional – (>500 metres (1,600 ft) wide); connect major ecological gradients such as migratory pathways.
- Sub-regional – (>300 metres (980 ft) wide); connect larger vegetated landscape features such as ridgelines and valley floors.
- Local – (some <50 metres (160 ft)); connect remnant patches of gullies, wetlands, ridgelines, etc.
Habitat corridors can also be divided according to their continuity. Continuous corridors are strips that are not broken up, while “stepping stone” corridors are small patches of suitable habitat. When stepping stones are arranged in a line, they form a strip of land connecting two areas, just like a continuous corridor.
Some kinds provide linkages between protected core areas and stimulate or allow species to migrate.
Corridors can also be miniature in the form of
Corridors can be expensive to plan out and put into action. For example, Daniel Simberloff et al. state that “a bridge that would maintain a riparian corridor costs about 13 times as much per lane-mile as would a road that would sever the corridor.” He also states that maintenance of a corridor would be much more costly than refuges for endangered species. It would simply be easier to move animals between refuges than to buy land, install a corridor, and maintain it. However, where the goal is not just to preserve a few large animal species but to protect biodiversity among all plants and animals, then habitat corridors may be the only option. Corridors are going to be expensive to implement no matter what, but it does depend on the type, location, and size, which can all vary to a great degree. With the lack of field data on the effectiveness; many organisations, government's, are not willing to consider putting their capital and efforts in green corridors.
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Researchers must pay attention to the population changes in animals after a corridor has been implemented to ensure that there are no harmful effects. Researchers can use both mark-recapture techniques and evaluate genetic flow to observe how much a corridor is being used. Marking and recapturing animals is more useful when keeping a close eye on individual movement. However, tagging animals and watching them does not give any data on whether the migrating individuals are successfully mating with other populations in connected areas of land.
Genetic techniques can be more effective in evaluating migration and mating patterns. One of the most important goals of developing a corridor is to increase migration in certain animal species. By looking at a population's gene flow, researchers can understand the genetic consequences of corridors via information about the migration patterns of an entire population instead of the movements of a few individuals. From these techniques, researchers can better understand whether or not habitat corridors are increasing biodiversity.
Stephen Mech and James Hallett introduce an additional reason genetic techniques are more useful; they “measure average migration rates over time, which reveals the effects of fragmentation of several generations and is not as sensitive to current population sizes as mark-recapture studies are.” For example, when a population is extremely small, mark-recapture is almost impossible.
According to new research, wildlife corridors are best built with a certain degree of randomness or asymmetry, rather than built symmetrically. The research was conducted at the University of California, Davis.
Wildlife corridors are susceptible to
Both the safety of animals and humans can be achieved through the creation of corridors. In Alberta, Canada, an overpass was constructed to keep animals off the busy highway which crosses a national park. The top of the bridge is covered in the native grass of the area. fences were also put on either side of the overpass to help guide animals in the right direction.
In Southern California, 15 underpasses and drainage culverts were observed to see how many animals used them as corridors. They proved to be especially effective on wide-ranging species such as carnivores, mule deer, small mammals, and reptiles, even though the corridors were not intended specifically for animals. Researchers also learned that factors such as surrounding habitat, underpass dimensions, and human activity also played a role in how much use they got. From this experiment, much was learned about what would constitute a successful habitat corridor.
In South Carolina, five remnant areas of land were monitored; one was put in the center and four were surrounding it. Then, a corridor was put between one of the remnants and the center. Butterflies that were placed in the center habitat were two to four times more likely to move to the connected remnant rather than the disconnected ones. Furthermore, male holly plants were placed in the center region, and female holly plants in the connected region increased by 70 percent in seed production compared to those plants in the disconnected region. The most impressive dispersal into the connected region, though, was through bird droppings. Far more plant seeds were dispersed through bird droppings in the corridor-connected patch of land.
There have also been positive effects on the rates of transfer and interbreeding in vole populations. A control population in which voles were confined to their core habitat with no corridor was compared to a treatment population in their core habitat with passages that they could use to move to other regions. Females typically stayed and mated within their founder population, but the rate of transfer through corridors in the males was very high. Researchers are not sure why the females did not move about as much, but it is apparent that the corridor effectively transferred at least some of the species to another location for breeding.
In 2001, a wolf corridor was restored through a golf course in
Elephant corridors are narrow strips of land that allow elephants to move from one habitat patch to another. There are 88 identified elephant corridors in India.
In Africa, Botswana houses the largest number of free-roaming elephant herds. Elephants Without Borders (EWB) studies the movement of elephants is working to gain community support of local community corridors, so that elephants and humans can co-exist.
Major wildlife corridors
- The Paséo Pantera (also known as the MesoAmerican Biological corridor or Paséo del Jaguar)
- The Eastern Himalayan Corridor
- China-Russia Tiger Corridor
- Tandai Tiger Corridor
- The European Green Belt
- The Siju-Rewak Corridor, located in the Garo Hills of India, protects an important population of elephants (thought to be approximately 20% of all the elephants that survive in the country). This corridor project links together the Siju Wildlife Sanctuary and the Rewak Reserve Forest in Meghalaya State, close to the India-Bangladesh border. This area lies within the meeting place of the Himalayan Mountain Range and the Indian Peninsula and contains at least 139 other species of mammal, including tiger, clouded leopard and the Himalayan black bear.
- The Ecologische Hoofdstructuur is a network of corridors and habitats created for wildlife in the Netherlands
- The 16 kilometres (9.9 mi) long Kanha-Pench elevated corridor on NH 44.
- Two elephant passes and two minor bridges on NH 54 in Assam’s Lumding Reserve Forest.
- Three elephant underpasses, each with 6 metres (20 ft) of vertical clearance on NH 72 and NH 58 in Uttarakhand, India.
- Terai Arc Landscapes, Lower Himalayan Region.
This section needs additional citations for verification. (April 2019))
Some animal species are much more apt to use habitat corridors than others depending on what their migration and mating patterns are like. For example, many cases of birds and butterflies successfully using corridors have been observed. Less successful stories have come out of mammals such as deer. How effective a corridor is may simply rely on what species it is directed towards. Corridors created with birds in mind may be more successful because they are highly migratory, to begin with.
Human interference is almost inevitable with the quickly increasing population. The goal behind habitat corridors shows the most hope for solving habitat fragmentation and restoring biodiversity as much as possible. Although there are many positives and negatives, there may be enough positives to continue studying and improving corridors. It is truly difficult to say whether corridors are the solution to increasing biodiversity, because each one must be judged on its own. Each corridor has its own set of standards and goals that may set it apart from another one.
A major downfall to habitat corridors is that not much information has been gathered about their success. Due to the lack of positive data, many agencies will not allow corridors to be established because they are unsure of their effectiveness. Another problem with corridors is that they are not as useful as simply preserving land so that it cannot be fragmented. However, it is becoming very difficult to set aside land for nature reserves when road-building, industry, and urban sprawl are all competing for space.
Even if corridors are sought as a solution, it does not necessarily mean that animals will use them. Especially in the case of overpasses, research shows that animals do not like to use them to get to another remnant area of land. Usually overpasses are built over busy highways, and many species are too timid to expose themselves in front of all of the traffic. As more roads and buildings arise, there becomes less space to try to preserve.
Habitat corridors need to be species-specific (not every kind of animal will use every kind of corridor) and corridors can be barriers to some species. For instance plants may use road verges as corridors however some mammals will not cross roads to reach a suitable habitat.
When a corridor is implemented, many times development is so close by, that it becomes difficult to build a wide enough passage. There is usually a very limited amount of space available for corridors, so buffers are not usually added in. Without a buffer zone, corridors become susceptible to harmful outside factors from city streets, suburb development, rural homes, forestry, cropland, and feedlots.
Unfortunately, another limiting factor to the implementation of corridors is money. With such inconclusive data about the effectiveness of connecting land, it is difficult to get the proper funding. Those who would be in charge of the corridor design and construction would ask such questions as, “What if the corridors affect species negatively?” and “What if they actually aid in the spread of disease and catastrophic events?” Furthermore, there is a possibility that corridors could not only aid in the dispersal of native organisms, but invasive ones, as well. If invasive species take over an area they could potentially threaten another species, even to the point of extinction.
Although wildlife corridors have been proposed as solutions to habitat and wildlife population fragmentation, there is little evidence that they are broadly useful as a conservation strategy for all biodiversity in non-developed or less-developed areas, compared to protecting connectivity as the relevant ecological attribute. In other words, corridors may be a useful meme for conservation planning/ers, but the concept has less meaning to wildlife species themselves. Very few wildlife follow easily identified "corridors" or "linkages" (e.g., using computer modeling), instead most species meander and opportunistically move through landscapes during daily, seasonal, and dispersal movement behavior. Wildlife corridors may be useful in highly developed landscapes where they are easily identified as the last remaining and available habitat.
Habitat corridors may be defenseless against a number of outside influences, but they are still an efficient way of increasing biodiversity. Strips of land aid in the movement of various animal species and pollen and seed dispersal, which is an added benefit to the intended one. For example, when insects carrying pollen or birds carrying seeds travel to another area, plant species effectively get transported, as well.
Another positive aspect of corridors is that they allow both animals and humans to occupy virtually the same areas of land, and thus co-exist where without the corridor this would not be possible. Large animals such as bears can be attracted to residential areas in search of food due to lack of natural resources because of habitat fragmentation. A corridor would provide a passage for the bears to forage in other locations, so that they would not pose as much of a threat to humans.
- Aquatic organism passage
- Biolink zones
- Emerald network
- Habitat conservation
- Habitat destruction
- Landscape connectivity
- Marine Protected Area
- Natura 2000
- The Pollinator Pathway
- Gary Tabor, wildlife corridor conservationist
- Wildlife crossing
- Yellowstone to Yukon Conservation Initiative
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- Defragmentation in Belgium (Flanders) - Connecting nature, connecting people. Accessed: 22 January 2009
- Wildlife Corridors Project Regeneration
- Wildlife passages - De-Fragmentation in the Netherlands - How to evaluate their effectiveness? Accessed: 22 January 2009
- CorridorDesign.org - GIS tools for designing wildlife corridors Accessed: 9 March 2010
- ConservationCorridor.org - information, tools and links to connect the science of landscape corridors to conservation in practice. Accessed: 14 September 2012