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The Green Links project was started in 1996 by the Douglas College Institute of Urban Ecology in British Columbia. The project utilizes strategic planning to improve the connectivity of green spaces and natural areas within the Greater Vancouver region. This is accomplished through various activities such as planting native vegetation in wildlife corridors, parks, playgrounds, and backyards. Green Links is working on corridors in several sites, including riparian corridors along streams in Coquitlam and Fraser River drainage basins, and hedgerows through agricultural areas in Delta.

Biodiversity threats
Urbanization results in habitat fragmentation and decreased ecosystem value. Fragmentation caused by urban development is considered one of the biggest threats to biodiversity. Habitat fragmentation decreases populations of native species, increases extinction rates, hinders colonization, and increases the risk of habitat loss to invasive species. Loss of biodiversity can result in mass extinctions, which can take the Earth several millions of years to recover from. Green Links aims to increase the value of fragmented habitat by connecting smaller habitats to each other, allowing them to function as one larger habitat which would better preserve biodiversity in the area. These "metapopulations" depend on migration between patches.

Research and solutions
Leaving an unlogged corridor of forest between stands is one solution to habitat fragmentation in wilderness areas. For highly disturbed areas, links may need to be created or included in city plans. In order to establish green links in these developed areas, the project focuses on planting native vegetation and involving the community as a whole in the process. Volunteer organizations, youth groups, NGOs, and local governments are the primary sources for labor and community outreach in the Green Links project. Green Links director Valentin Schaefer outlined three approaches that Green Links will use to improve and maintain natural areas in the Greater Vancouver area:

1.    Research into the impact of urban biodiversity on regional ecosystem health.

2.    Education through workshops, conferences, contests and lectures to increase awareness of environmental concerns and community involvement in the project.

3.    Stewardship of public and private lands by the creation of corridors, greenways, backyard habitats, hedgerows, playgrounds and parks.

Methods
The Green Links project focuses on one zone at a time. A zone is a large tract of land bordered by major physical barriers such as highways, mountains, and rivers. Within each zone are multiple green spaces, called “nodes.” The largest nodes in the zone are called “mother nodes” and the surrounding patches that rely on colonization by individuals from the mother node are known as “satellite nodes.” Immigration rates depend on the amount of connectivity between nodes, which is a function of the size and abundance of nodes, the size and abundance of links among nodes, and the total number of networks in the zone. An ideal corridor contains a diverse range of plant species that form a layered habitat with few or no invasive species.

The minimum area requirement chosen for the study was 0.5 hectares because it is the minimum habitat size required by most species that live in urban areas. To measure distances between green spaces, Green Links chose to use minimum distances, "as the crow flies," rather than centroid distances which would measure the distance from the center of one green space to the center of another. Minimum distances provide a more accurate estimation of the distance that animals must travel to move between green spaces.

Biodiversity is measured in two ways. The Simpson's index uses the average biodiversity for birds in the area to judge overall diversity. Green Links aims to increase the index by 30% over the course of a 10-year project. The second method involves further use of indicator species, under the pretense that if a habitat is made suitable for a species with more sensitive requirements then the habitat will also be suitable for species with less specific needs. The indicator species chosen often varies by the type of habitat and level in the canopy that the species occupies.

Analyses
Green Links uses the gravity model to measure the degree of interaction between nodes. This analysis compares the characteristics of each node in the study area with the minimum habitat requirement. Na = [x(ha)/s(ha)] X 10 Where Nais the relative weight of the node, x is the area (in hectares), and s is the minimum habitat size required by the indicator species. It is multiplied by 10 to normalize the results and prevent a green space from having a nodal weight less than 1. The gravity model can then be used to measure the connectivity between areas. As a general rule of thumb, areas that are large and near to each other interact more often than small, distant areas.

Gab = (Na X Nb)/Dab2

Where Gab is the level of interaction between nodes a and b. Na and Nb are the nodal weights of nodes a and b, respectively, as described by the gravity model. Dab is the distance between the two nodes.

Networks
Green Links used MATLAB to analyze data and produce a set of potential networks that could be used to connect as many nodes as possible with the greatest efficiency of use. The simplest and cheapest network model for the builder is the branching network. The Paul Revere model connects all nodes in a linear fashion, without completing a loop. On the other hand, circuit networks are usually more complex but easier to use. Examples of this are the Traveling Salesman and the Least Cost to User. The Traveling Salesman network is similar to the Paul Revere model, except that it completes the loop and all nodes are connected to two other nodes. In the Least Cost to User model, all nodes are connected to each other, making it the most expensive to produce but the most efficient to use.

The networks that MATLAB generates are evaluated using three types of indices:

The Gamma ratio ranges from 0 to 1 and represents the connectivity of the network. It is calculated by dividing the number of links in the network by the total possible number of links in the study area.

The Beta index represents the complexity of the network and is calculated by dividing the number of links by the number of nodes within the network. A Beta value of less than 1 indicates that the network is open or branching; a value equal to 1 means that the network is a single circuit; and a value of more than 1 indicates a greater network complexity.

The Cost Ratio index compares the costs to user (wildlife) and the costs to builder (the city). It can be calculated by multiplying the number of links in the network by the total distance of the links and subtracting 1 from the product. A Cost Ratio value near 1 implies a high cost to builder and low cost to user.

Success
As mentioned above, the success of a Green Links project can be measured by the Simpson's Index and/or the presence of indicator species. Green Links, however, is not only interested in improving biodiversity in an area but also in improving community support for restoration projects. Overall, Green Links managed to:

1. Restore roughly 30 sites in the Greater Vancouver Regional District

2. Plant over 50,000 native trees, shrubs, and perennials

3. Involve more than 5000 community volunteers

4. Attract 12,000 citizens to their educational workshops

5. Appeal to 2500 lecture and symposium participants

6. Have over 150 articles and news reports publicizing the Green Links project

The Coquitlam Corridor
The project's first site was the Coquitlam corridor along the BC Hydro/BC Gas right-of-way. The site was chosen for the study because the Institute of Urban Ecology already has a corridor linking the mother node, Mundy Park, to several satellite nodes and provides an opportunity to identify more potential links. The success of the Coquitlam Corridor was measured using Simpson's Index. Over the course of the project, Green Links improved the biodiversity of birds in the area from roughly 10 species to 13 and successfully connected five ecosystem fragments:

1. Colony Farm, consisting of field and marsh habitats along the Coquitlam River 2. Riverview Lands, which is maintained by the Riverview Horticultural Society and includes an arboretumthat contains every tree species that grows in British Columbia

3. Mundy Park, which combines forest, lake, and bog habitat

4. Pinnacle Creek ravine, which runs between the river and Port Moody, forming part of the Chine Heights escarpment

5. Scott Creek ravine, a salmon stream and part of the Westwood Plateau

Related Projects
Louisiana's Plan Baton Rouge, a project started by the Downtown Development District (DDD), hopes to create green space in downtown Baton Rouge and effectively connect various parks and neighborhoods with walking and bike trails.

Alabama's Operation Green Team, a volunteer organization sponsored by the city of Huntsville that is dedicated to improving aesthetic green spaces and reaching out to school children to teach environmental responsibility.