Natural Ecological Communities of Northern Virginia

Why this Website?

This website is about making better plant selections for ecological restoration purposes in Northern Virginia, but is also be applicable to Washington D.C., and close-in parts of Maryland. In addition, the methodology is usable for ecological restoration throughout the United States, albeit with different data sources. The website was born from a love of nature, profound respect for the people and institutions who are trying to restore natural areas, and a great dislike for wasted effort in that work to restore natural areas.

In natural settings, plants do not live in random patterns in the landscape. Rather they tend to group into communities. Those “Natural Communities” have patterns and those patterns have been researched for decades by botanists and ecologists. This website attempts to translate that descriptive research into practical guidance.

The intended audience is people engaged in ecological restoration efforts, professional and experienced volunteers. But it can also be used by landscape professionals, county planners, and others who are interested in helping nature thrive. Individual gardeners, interested in contributing to the biodiversity of their neighborhoods, should also find this material of interest.

Natural Community data can and should serve as the basis for establishing the target of ecological restoration—the “end state” that restoration efforts are shooting for. Too many times, restoration efforts lack that target and results suffer. Plants that are added do not thrive; efforts are wasted. In an era where every hour spent on ecological restoration needs to be highly effective, leveraging the best science will yield better results.

The definition of "ecological restoration" is taken from the Society for Ecological Restoration (www.ser.org) and is "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed". This is a broad definition-- it does not assume a specific level of degration that has occurred; or the specific processes or resources used in the recovery effort, or the specific outcome desired. (Gann GD, et al. 2019. International principles and standards for the practice of ecological restoration. Second edition. Restoration Ecology S1-S46)

Why is the Information about Natural Communities Important?

Humanity is altering the natural aspects of our planet in ways unimaginable until recent years. In addition to the better-known climate change crisis, we are also in a biodiversity crisis. Natural habitats and the inherent biodiversity that accompanies those are being destroyed at an alarming rate. These natural areas are under attack not only by rampant development, deforestation, and expansion of human habitation, but also through the impact of invasive plants. The resulting loss of birds and butterflies, which get noticed by even casual observers, reflect a deeper loss of native creatures from the tiniest to the largest.

The website is being created to make practical the science of Natural Community research. The data has been difficult to access by non-botanists. This website is dedicated to turning science into prescriptive guidance able to be used in restoration efforts of various types. By doing so, the fight to protect biodiversity can be made more effective.

Individuals can also make a difference in fighting this biodiversity loss. The value of making individual property more friendly to natural diversity is becoming more and more recognized. The recent book by Doug Tallamy entitled Nature's Best Hope: A New Approach to Conservation that Starts in Your Yard is a great manifesto for this new awareness and individual action.

Is It Worth the Effort to Use the Natural Communities Information?

Identifying a Natural Community in the field, particularly in a highly degraded or altered setting, is difficult.

Using more traditional methods of selecting plants may be quicker in the beginning. That approach typically involves starting from defined plant lists which would include assessments of the water, soil, sunlight needs of each species. The process would be to select plants for each place based on the specific needs of that species. Risks of the traditional approach are (at least) twofold:

Type 1: The risk of adding species which appear to fit a Community based on soil, water, and light requirements but which, in fact, are not found in that Community in natural settings.

Type 2: The risk of not adding species common to that Community because the plant list used did not include those species.

At an early stage of this research, an assessment was done to consider the benefits of going to the extra work up front. That research considered the potential for both Type 1 and Type 2 risks.

Using an actual Arlington County Park as a case study, the research found that roughly half of the species from traditional approaches would not be optimal to add (Type 1) and roughly half of the species that should have been considered for the Natural Community would be missed (Type 2). The magnitude of the Type 1 and Type 2 improvements was what has provided ongoing motivation to pursue this research.

What is Included in this Website?

The website has background information about natural communities and how to use that information for ecological restoration purposes -- see "The basics". In this section, the approach used to classify the prevalence of species in the community is described in addition to other topics. The website also has detailed information about definitions, sources, and methodology. -- see "The Details".

The core of the website contains detailed information about natural communities found commonly in the Northern Virginia area -- see "Upland Forests". For each natural community, there is a description and species lists for the Dominant, Common, Sparse, and Restricted Species. In addition, there are two downloadable documents for each community -- a PDF description of the community; and an Excel worksheet that has all of the detailed data. Users are free to download and use the documents as needed.

The website also contains information about species and their prevalence across the Natural Communities. The downloadable Excel spreadsheet is also available on the "Across Communities" dropdown menu. If one is trying to determine for a specific species in which Natural Community it is found and in what abundance, this is the place to go.

Identifying Prevalence of Species in a Natural Community

The work to define Natural Communities is data heavy. Plots have to be identified and described in great detail. Within each plot, each species of plant is identified along with its height, and other statistics, and its relative prevalence in each layer of the forest community. While necessary for the scientific exercise, the numbers and statistics are daunting for practitioners. A key focus of this effort has been to create simple but powerful descriptors that translate the Natural Community data into information that is intuitive and readily usable in the field.

To accomplish this objective, we created a single measure of "Abundance" that grouped species of plants into categories-- Dominant, Common, Sparse, Restricted and Rare. This determination combines how commonly the species is found and how much land area it covers in aggregate. The categories are useful for visualization in the field, but also directly relates to guidance on what to plant in restoration settings.

The summarization is based on but is not identical to research published in 2019 by Avolio et al. (Avolio et al., "Demystifying Dominant Species," New Phytologist 2019).

Identifying Natural Communities in the field

A key challenge to use the Natural Communities research is to identify Natural Communities in the field. This challenge exists even in mature stands of largely intact natural areas. In local parks and natural areas, very few spots have not been farmed, forested, or otherwise altered. In some cases, destruction of the original natural habitat has been so complete that few clues may exist as to what was present originally (this is common when new neighborhoods are constructed).

One of the reasons this website is primarily intended for ecological restoration purposes, instead of for homeowner use, is that the identification of the existing Natural Community is easier in parkland and other open areas. In these cases, it makes sense to make the investment to define the Natural Community—either existing or intended.

The Virginia Natural Community research does not include specific analysis of meadows or edge habitats, both of which are prevalent and troublesome for practitioners to address. It is hoped that research from other groups or individuals can become available to help with these types of habitats, but they are not yet included in this website. If anyone knows where to find such research, please contact windyrunarlington@gmail.com and the material will be added as is appropriate.

In addition, this website does not include descriptions or data regarding various successional forest types. The intention is to create clarity about later stage natural communities. It is suggested that if an area is defined as a successional forest type, restoration activities should first establish the desired end state for that successional community and then work towards that end state.

Fine Filter Views of the Natural Communities in Northern Virginia

Early in the research, local experts pointed out that due to the unique physiography and biogeography of the Northern Virginia area, the statewide data could give an inaccurate picture of the Natural Communities. Unique characteristics of the area include being at the boundary of the Coastal Plain and Piedmont -- an area called the Fall Zone and which extends north and south of the DC region for much of the mid-Atlantic region. The Fall Zone contains complex geology that affects natural communities. In addition, the latitude of Northern Virginia is at the southern end of the range for many northern species, and at the northern end of the range for many southern species. Taken together, these factors made us decide to segment the statewide data and analyze plots local to the area to ensure we were obtaining "fine filter" views of the communities as they exist here.

An effort was made to assess the value of the additional effort to segregate the plots in this fashion. Here, the jury is out regarding the value of the additional work. Commentary regarding the value of the fine filter approach is welcomed. Without the need to segment the data in this fashion, a great amount of work would be eliminated and the same essential data could be used by practitioners all over Virginia.

Sources of the information

The Commonwealth of Virginia, through the DCR Division of Natural Heritage (DCR-DNH), has conducted research on ecological communities for decades. Biologists have documented at least 4,736 plots across the state and determined that they fall within over 300 community types. The natural communities commonly found in Northern Virginia are many fewer than 300. Outside of community types found only in the Potomac Gorge, most natural areas will fall into one of 20-25 Natural Community types; and of those, 8-10 will be predominant.

A great introduction to this research is found at the DCR-DNH website at www.dcr.virginia.gov/natural-heritage/natural-communities in the article:

Fleming, Gary P. and Karen D. Patterson 2017. Natural Communities of Virginia: Ecological Groups and Community Types. Natural Heritage Technical Report 17-07. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond, Virginia. 36 pages.