Natural plant communities made easy (relatively!)
Plants in nature grow in communities - repeating patterns of plants that vary depending on soils, moisture, sunlight, etc. The natural communities support the diversity of insects and other critters that depend on them. Anyone restoring a natural area needs to know what natural community is (or should be) growing there and choose plants accordingly. This is less important in our yards, where just planting locally native plants that are appropriate for the current conditions will benefit the birds and butterflies tremendously. There are many native plants that are not picky about their conditions and that are found across our region in many different plant communities. An easy way for gardeners to add ecological value is to plant a diversity of these generalist species, lists of which can be found on Earth Sangha’s Compendium.
But if you want to provide even more benefit, and especially if you live near a natural area, you could take it a step further by incorporating plants into your landscape that normally grow in a particular plant community, one that is appropriate for your location.
One way to think about this is to consider where you are in relation to the nearest creek or river. With that information, you can take a pretty good if rough guess about which plant community is appropriate, even if you don’t know how to identify the plants you see in the remnant natural areas nearby.
Plants that live together in Small Stream Floodplain Forest communities are the obvious choice for any relatively flat areas next to streams at the bottom of a slope.* There the soil is deepest and most fertile, but because it is sometimes saturated with water, it is prone to low oxygen conditions that most upland plants cannot tolerate. In much of Northern Virginia, those floodplain areas have disappeared as the streambanks deepened from erosion.
Just uphill from the streams will be either a Mesic Mixed Hardwood Forest or a Basic Mesic Hardwood Forest. These areas have rich soils that have washed down from above and tend to have diverse mixtures of ground layer plants. The soils tend to hold moisture but are not saturated.
Between there and the hilltops is found the Acidic Oak-Hickory Forest, where the soil is more dry but still fertile. West of the immediate DC area, the Hardpan Basic Oak-Hickory Forest can be found, in an area called the Triassic basin where the soils are thin but rich, with underlying bedrock near the surface.**
At the top of the hill, the soils are thin, dry and less fertile as gravity pulls water, clay and organic matter downhill. Gravel or stone cobbles are found on the surface many times. The most common communities there are the Mixed Oak-Heath Forest and Chestnut Oak Forest, and in southern Fairfax County, the Oak-Beech Heath Forest. These communities tend to have sparse understories with plants that can tolerate dry and infertile conditions.
These rules of thumb are just approximations, though. There are plenty of exceptions to this layered scheme, not to mention many other (but much less common) types of plant communities besides the ones named above. If nothing else, having some idea about the intricacies of nature may enhance your enjoyment as you walk through the woods.
* Wetlands are our most precious ecosystems. Many jurisdictions require you to get a permit before removing any vegetation or disturbing the soil within 100 feet. The process is not difficult. Basically, you need to show that you know what you are doing.
Lowbush Blueberry is in the Heath family and prefers acidic soil
Small Stream Floodplain Forests are often rich with ferns
Which natural community makes sense in a yard?
Matt Bright of Earth Sangha has these recommendations.
Small Stream Floodplain Forest - “In the garden, you could use this list to create forest buffer edges [for streams] (depending on how close and far down the nearest stream is – as you get upslope you will see a transition to other plant communities). These species could be used in a more targeted fashion to address modest runoff from storm water in shady areas of your yard.”
Mesic Mixed Hardwood Forest - “In a garden context, think about this list as a good place to start for recreating a buffer at the edge of your property in medium-moisture settings, or replanting under existing tuliptree canopy. Perhaps you want to enjoy a nice evergreen Christmas Fern glade – in which case integrating some of these other canopy, understory, and herbaceous plants would help you towards a more natural arrangement.”
Acidic Oak-Hickory Forest - “In a garden context, think about these species as good options for buffering dry forest edges, or reestablishing a more natural context around an existing specimen white or red oak, or hickory in a well-drained space.”
Acidic Seepage Swamp A seepage swamp is a wet forest where the water comes from underground. “This plant community is badly threatened locally by development and changes to hydrology from increased impervious surface and other human interference. In the garden context, it’s unlikely that you will have remnant examples of this plant community. But, plants from this list are good options for creating ersatz seepage swamps in wet swales or slow-draining raingardens where persistently wet soils may provide a reasonable analogue for the natural hydrology.”
Stay tuned! More will be added soon.
** Soil types
The acidity and fertility of soil in nature is determined by the underlying bedrock. Detailed maps of those rock types are available for all of Northern Virginia. If you live in the part of the Piedmont known as the Triassic Basin - western Fairfax County (including Herndon) and Prince William County (including Manassas) and eastern Loudoun County (including Leesburg) - you are more likely to run into a Hardpan Basic Oak-Hickory Forest near the top of hills and Basic Mesic Hardwood Forest at the mid level of the slopes. (“Basic” in this case does not refer to alkaline but rather to base-rich, meaning full of minerals.) Roughly speaking, the soils tend to be more fertile in the Triassic Basin because of those minerals.
The term “Heath” refers to a family of shrubs that are usually found in acidic, infertile soil and that include blueberries, huckleberries and rhododendrons. (Azaleas are a type of rhododendron.) Other than that, most of our native species tend not to be too pH sensitive. We don’t recommend that you try to alter the soil acidity. Besides confusing the plants, if you have been putting lime on your lawn, the pH will temporarily rise, but in time it will revert to its natural condition.
Unfortunately, most homeowners are not going to be dealing with soils found anywhere in nature. Between topsoil removal, subsoil mixing and compaction, the actual soils in our yards may bear little resemblance to the original. So the natural communities are only a first approximation about what will thrive in your yard.
Click to enlarge
This is just a drawing, not a real map. :)
This is just a drawing, not a real map. :)
Will plants grow well outside their natural communities?
Often yes. For example, floodplain trees do not necessarily prefer those saturated conditions. It’s just that they can tolerate the low oxygen levels that would kill upland trees, and therefore they have a competitive advantage down by the creeks. If you plant them in your yard where there is no competition, they are likely to thrive. They may do even better than upland trees in areas of compacted soil that is too low in oxygen for the species that would normally be living at that altitude. Mimicking natural plant communities is a great idea where practical, but the first consideration in a built landscape needs to be to choose plants that tolerate any human-created stressors such as soil compaction, road salt, and pollution.
This River Birch is a long way from any river!
What about meadows?
Natural meadows in Northern Virginia tend to be transient and on their way to forest succession. Allowing your property to reforest is the most natural thing to do and also the easiest for gardeners, as less weeding is required in shade than in sun. But grasslands are also important ecologically and even more endangered than our woods. If you would like to freeze your plant communities into a meadow-like state, see Earth Sangha’s lists for dry/moist and moist/wet conditions in full sun areas and our page on meadows for advice on creating them.
Meadow garden at Wolf Trap Natonal Park
for the Performing Arts
Who to ask for help
If, like most of us, all that sounds way too technical to try to apply to your yard, then at least it demonstrates that if your property includes natural areas, you should avoid mucking them up by attempting to “improve” them by adding random species. Consider consulting an expert if you are trying to restore a disrupted ecosystem.
Audubon-at-Home - Volunteers will walk your property to help you strategize about creating habitat. Their experience with plant communities varies, so if restoration is your intention, let the organizers know ahead of time.
Earth Sangha - Experts can do site visits for publicly held restoration sites.
Urban foresters - Your local forester may be able to help you create a management plan for your woods.
Professional companies - Several companies do ecological restorations.