GI at Douglas Point, Swallow Falls, and Deal Island

What is green infrastructure?


Maryland has been called "America in miniature". From east to west, Maryland varies from ocean, to barrier island and beaches, to tidal marshes and estuaries, to fertile low-lying farmland, to pastoral rolling hills, to mountains, valleys and plateaus. North and South also meet in Maryland: historically, culturally, and ecologically. Ecologically, Maryland is the northernmost limit of many southern species, and the southernmost limit of many northern species. Like America, the state contains both big cities and small towns, and regions varying from forested to agricultural to urban. In short, Maryland is extraordinarily diverse for a state its size, and reflects conditions found in the nation as a whole.

Like America as a whole, Maryland's diversity and vitality depend on the composition of its landscape: its geology, climate, water, soils, flora, and fauna. These characteristics have shaped the history of the region, and still affect the state today. Maryland's most important natural lands comprise its "green infrastructure," and provide the bulk of the state's natural support system. Ecosystem services, such as cleaning the air, filtering and cooling water, storing and cycling nutrients, conserving and generating soils, pollinating crops and other plants, regulating climate, sequestering carbon, protecting areas against storm and flood damage, and maintaining aquifers and streams, are all provided by the existing expanses of forests, wetlands, and other natural lands. These ecologically valuable lands also provide marketable goods and services, like forest products, fish and wildlife, and recreation. They serve as vital habitat for resident and migratory species, maintain a vast genetic library, provide scenery, and contribute in many ways to the health and quality of life for Maryland residents.

Lake with trees surrounding bird on a branch Plants in the forest

When wetlands and forest are developed into human-centered uses, there are costs incurred that are typically not accounted for in the marketplace. The losses in ecosystem services are hidden costs to society. These services, such as cleansing the air and filtering water, are fundamental needs for humans and other species, but in the past, the lands providing them have been so plentiful and resilient, that they have been largely taken for granted. In the face of a tremendous rise in both population and rate of land use conversion, many people now realize that these natural or ecosystem services must be afforded greater consideration. The breakdown in ecosystem functions causes damages that are difficult and costly to repair, as well as taking a toll on the health of plant, animal, and human populations.


Where is green infrastructure found in Maryland?


a photo of islands on the eastern shore Maryland's green infrastructure was mapped using satellite imagery, road and stream locations, biological data, and other information, with the results reviewed by scientists, local government officials, and conservation groups. Although even backyards and street trees provide some benefits, like shading and air purification, the state's most important natural lands are those that are large and intact enough to provide a full range of environmental functions.

The first step in the assessment of the State's green infrastructure identified the heart of the green infrastructure, called "hubs." These are typically unfragmented areas hundreds or thousands of acres in size, and are vital to maintaining the state's ecological health. They provide habitat for native plants and animals, protect water quality and soils, regulate climate, and perform other critical functions.

The second step connected hubs with "corridors" - linear remnants of natural land such as stream valleys and mountain ridges that allow animals, seeds, and pollen to move from one area to another. They also protect the health of streams and wetlands by maintaining adjacent vegetation. Preserving linkages between the remaining blocks of habitat will ensure the long-term survival and continued diversity of Maryland's plants, wildlife, and environment.

Examples of Maryland's green infrastructure are found throughout the state:


What is the status of Maryland's green infrastructure?


construction in western Maryland It has been estimated that before colonization by Europeans, Maryland was 95% forested, the other 5% being tidal marsh. By 1993, both forest and wetlands had decreased by half. The area converted to development is increasing even more rapidly now, as suburbs expand outward and large-lot houses are built in formerly rural areas. The scattered pattern of modern development consumes an excessive amount of land and fragments the landscape.

As forests are divided and isolated by roads, houses, and shopping malls, wildlife habitat and migration corridors are lost, and normal ecosystem functions such as absorption of nutrients, recharging of water supplies, and replenishment of soil are disturbed or destroyed. Water quality has been degraded in numerous streams and rivers, as well as in the Chesapeake Bay itself. Many of Maryland's remaining wetlands have been drained, filled, polluted, or otherwise degraded. Habitat loss and fragmentation have contributed greatly to a continuing loss of biodiversity in Maryland. At least 180 plant and 35 animal species have been extirpated from Maryland. Another 310 plant and 165 animal species are rare, threatened, or endangered.

Today, Maryland has only two million acres of ecologically significant land that has not been consumed by some kind of human development. Of these two million acres of green infrastructure, nearly 70% are unprotected. Billions of dollars are spent each year to construct or maintain the state's built infrastructure of roads, bridges and utilities that we depend on for modern life. By contrast, the state's green infrastructure, which exists naturally, is under tremendous pressure from development, yet receives little support in public policy. Left unprotected, the remaining green infrastructure is vulnerable and will be further reduced and fragmented.

Focusing conservation efforts on green infrastructure will help protect the ecological health found in each region of the state, including forests, streams, and wetlands, preserving and enhancing this heritage for future generations. By acting now, Maryland can ensure cleaner air and water for its citizens, safeguard habitat needed to spare native animals and plants from extinction, and preserve outdoor recreational opportunities that a large and increasing number of people enjoy.


What are the benefits of green infrastructure?


a kayaker Green infrastructure benefits all Maryland citizens. For some people, like watermen, those who harvest and process timber, and those who cater to outdoor recreation, it provides their livelihood. For farmers, it provides insect control by birds. For city dwellers, it provides clean drinking water. For those living or farming near shorelines, streams, or steep hillsides, it protects their land from erosion. The green infrastructure provides places for hobbies, recreational activities, and learning opportunities. Children and teachers can, together, learn the wonders of nature by using the green infrastructure as a living classroom. Nature lovers can enjoy hiking, camping, observing, and photographing an impressive diversity of plants and wildlife.

Studies have shown that if the values of ecological services are considered, natural lands show a net gain in cost-benefit analyses. While residential areas require public services, natural areas need little, other than protection. Further, they make public construction of many engineered facilities unnecessary.

In addition to their ecological and economic contributions, these lands provide a sense of place and a unique identity. Natural landscapes make communities more comfortable and appealing; they link current generations to their heritage and cultural past. For everyone who lives in or visits Maryland, protecting green infrastructure helps to preserve our rich quality of life and safeguard, for future generations, Maryland's Chesapeake Bay and the legacy of Maryland's special natural landscapes, including the picturesque mountains of Western Maryland; the forests and wetlands of Southern Maryland; the expansive tidal marshes of the Eastern Shore; and the stream valleys of the Western Shore and Piedmont region.

Ninety percent of respondents in a 1999 national poll agreed that "open spaces make our communities more livable", and 85% said that "parks and open spaces contribute to the property values and economic stability of neighborhoods." In Maryland, polling surveys in 1995 and 2001 revealed that the vast majority of the state's citizens support public land conservation programs.


Can green infrastructure be protected?


Middle Fork - brook trout stream. Land protection is often first on the chopping block when budget cuts are considered. Yet, protection of natural land is a vital investment. Preserving open space stimulates spending by local residents, increases property values, increases tourism, attracts businesses, and reduces public costs. Biodiversity is responsible for at least $1.9 billion in economic and environmental services in Maryland. In fact, if the values of ecological services are considered, the benefits from conserving natural land gives a return on investment of at least 100 to 1!

Because much of the state's key natural resource land has been lost, Maryland needs to protect as much as possible of what remains. A focus on permanent protection of green infrastructure provides multiple benefits:

Over the past several decades, the State of Maryland has enacted several effective land conservation programs. These include Program Open Space and Rural Legacy, a variety of agricultural preservation efforts, private conservation easement agreements, and regulations that help preserve wetlands and shorelines. As a result, Maryland is known nationally as a leader in land conservation and natural resource protection. While these initiatives proved effective in addressing specific needs related to wetlands, endangered species, recreation, or farmland, they were not designed to protect a comprehensive network of ecologically sensitive lands. Despite our successes, only 30% of the identified green infrastructure was protected as of 2004.

Focusing on protection of green infrastructure builds upon existing conservation programs by:

Developers, private landowners, and others benefit from having a clear understanding of where the most ecologically valuable lands are located, and where targeted conservation activities will be directed. Citizens interested in increased stewardship activities will know where their efforts are most needed. Land planners and developers can use the green infrastructure maps as a reference in the development of site plans and management objectives.

Using green infrastructure maps and data, local governments can enhance their efforts to provide open space, recreation lands, and natural areas that retain the unique character of their communities and rural landscapes. This can complement their efforts to direct growth to specified areas.

Private land trusts can also benefit. Conservation groups, and their members, will find that focusing on green infrastructure will give them a greater overall impact. It not only identifies large blocks of habitat and linkages, it gives a sense of how each given place fits into the larger landscape.

The approach to protecting green infrastructure involves four steps:

The first three parts of this approach are known as the Green Infrastructure Assessment. Maps and other data from this assessment are distributed by the Maryland Department of Natural Resources to parties interested in land stewardship, as well as the general public. The fourth and most important part, actual land protection and management, is performed by various state programs, county governments, land trusts, and other entities.

In a sense, we are in a race against time. Once an area is developed, it will remain so indefinitely. And development is proceeding at a rapid rate, all across the state. Action is needed now to ensure that our children, our grandchildren, and generations to come, have the same opportunities to enjoy Maryland's outstanding natural resources and high quality of life that we do today.


Landscape assessment procedures


Green Infrastructure GIS model To identify and prioritize Maryland's green infrastructure, we developed a tool called the Green Infrastructure Assessment (GIA). The GIA was based on principles of landscape ecology and conservation biology, and provides a consistent approach to evaluating land conservation and restoration efforts in Maryland. It specifically attempts to recognize:

The GIA identified two types of important resource lands - "hubs" and "corridors." Hubs are typically large contiguous areas, separated by major roads and/or human land uses, that contain one or more of the following:

In the GIA model, the above features were identified from Geographic Information Systems (GIS) spatial data that covered the entire state. Developed areas and major roads were excluded, areas less than 100 contiguous acres were dropped, adjacent forest and wetland were added to the remaining hubs, and the edges were smoothed. The average size of all hubs in the state is approximately 2200 acres.

Corridors are linear features connecting hubs together to help animals and plant propagules to move between hubs. Corridors were identified using many sets of data, including land cover, roads, streams, slope, flood plains, aquatic resource data, and fish blockages. Generally speaking, corridors connect hubs of similar type (hubs containing forests are connected to one another; while those consisting primarily of wetlands are connected to others containing wetlands). Corridors generally follow the best ecological or "most natural" routes between hubs. Typically these are streams with wide riparian buffers and healthy fish communities. Other good wildlife corridors include ridge lines or forested valleys. Developed areas, major roads, and other unsuitable features were avoided.

The GIA also provides an approach for ranking or prioritizing land protection efforts. Hubs and corridors were assessed for a variety of ecological parameters, and then ranked within their physiographic region. Physiographic regions have a characteristic geology and climate, which shapes the ecosystems and communities within them. We wanted to protect the best examples of each of these regions, ensuring ecosystems adapted to different climates and substrates were represented in the top ranking hubs. The hubs were also grouped by physiographic region because natural conditions and communities vary greatly between the Coastal Plain and the Appalachian mountains. For example, tidal marsh is not found outside the Coastal Plain, and high gradient streams are not found inside it.

The GIA can also help evaluate specific local areas. Individual "grid cells" were pixels determined by the resolution of the satellite imagery we used. The cells were squares corresponding to an area of 0.314 acre. Each cell in Maryland was given an ecological score based on both its local significance and its landscape context. Part of the cell ecological score was the rank of the landscape feature in the Green infrastructure network (i.e., whether it fell within a hub or corridor, and the relative ecological importance of that component), and part of the cell rank was based on local features (e.g., proximity to streams or rare species habitat). The cell-based evaluation permits more detailed site comparisons and prioritizations.

Green infrastructure hubs and corridors were also examined for their level of protection, management status, and risk of development. The vast majority (70%) of the Green infrastructure is unprotected. And only 13% of hubs, and less than 1% of corridors, were in areas managed primarily for natural values. Some of the factors used to estimate relative development risk included land ownership, regulatory restrictions, zoning, water and sewer service, population trends, parcelization, commuting distances, land value, proximity to roads, presence of waterfronts, and proximity to parks or other preserved open space. A hub or corridor's risk of development can be combined with its ecological score to help prioritize conservation efforts. Individual cells were also examined for their development risk.

Gaps are developed, agricultural, mined, or cleared lands within the Green infrastructure network that could be targeted for restoration. These were evaluated for their potential restoration to forest, wetland, or riparian buffers, by considering watershed condition, landscape position, local features, ownership, and programmatic considerations. Gaps with hydric soils were probably once wetlands, and could be restored as such. Reforestation of gaps along streams would not only benefit wildlife, but improve water quality and stream stability. Dredged, filled, or drained wetlands can also be restored. Roads in the Green infrastructure can be modified to mitigate some of their negative impacts. Structures such as underpasses or bridges can be designed to assist wildlife movement where roads and railways form barriers across corridors and hubs. Similarly, stream blockages can be examined for fish ladders, bypasses, or other structures that allow fish passage.

The results of the GIA were reviewed by field ecologists and county planners, and compared to other inventories of important natural resources in Maryland. Hub and corridor locations identified by the model were largely consistent with existing natural areas, although some small features, like some streams and isolated wetlands, were missed. Although only about a third of the land in the state were identified as being in the Green infrastructure network, most of Maryland's important natural resources were captured.


Setting priorities for parcel acquisition


parcel ratings for Catoctin area In 2003, Governor Ehrlich helped institutionalize the Green Infrastructure into State Land Conservation Planning by expanding the criteria used to evaluate the State’s land preservation purchases to include a comprehensive set of ecological indicators.

Through this initiative, State land conservation programs such as Rural Legacy and Program Open Space will prioritize their conservation activities on areas identified as Green Infrastructure. A copy of the Governor's Land Conservation Plan can be accessed by clicking HERE

The following protocol was developed to help select and prioritize parcels for acquisition by State land conservation programs using elements of the green infrastructure. This is a three tier process:

Tier 1:

Identification of candidate properties for acquisition, either proactively in focus areas (hubs and corridors that are highly significant ecologically, and under significant threat from development); or opportunistically from existing pools of willing sellers and other sources. The parcel boundaries are then digitized from tax maps.

Tier 2:

Evaluation of the property to determine:

  • if the project contains green infrastructure as delineated in the Green Infrastructure Assessment model,
  • the amount, percentage, and ecological significance of green infrastructure present,
  • proximity to existing protected lands and contribution to further protection of the green infrastructure hub or corridor the property lies in,
  • an overall ecological score for the project, and
  • the presence of other conservation features on the property.

Tier 3:

For those properties rating highly in Tier 2, a cursory or "drive-by" field visit to areas easily accessible by roads or trails, to:

  • verify the Green Infrastructure Assessment model,
  • identify potential restoration needs, and
  • estimate the threat of development the property faces if fee or easement acquisition is not pursued.
This step was performed by helicopter for areas on the Eastern shore and southern Maryland.


The Green Infrastructure Assessment methodologies, along with relevant background material, are described in http://www.dnr.state.md.us/greenways/gi/gidoc/gidoc.html. The finer details are found in the Appendices.

Further information can be obtained by contacting the Maryland Department of Natural Resources, Watershed Services Center.


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