Many of us want to plant native trees for their beauty and the benefits they offer for humans, wildlife, and the ecosystem. But how do we know which native trees are best suited to our site? The key is understanding what conditions our native trees are adapted to in the wild, and choosing native trees that match the conditions of our site. Its also important to create a wholistic habitat and ecosystem for the newly planted tree that will best support it. In their natural environment, native trees grow in layers, thrive in their natural habitat, and exist as part of natural plant communities. Let's explore each of these concepts in turn.
Native Trees Grow in Layers
In their natural state, native trees typically grow in plant clusters that include canopy trees on top, and understory trees, shrubs, perennials, and ground covers below. See the picture below illustrating the natural layers of Scotts Run Nature Preserve. What is missing is the ubiquitous turf that exists in most suburban neighborhoods. In their natural state, trees grow on natural ground with leaf litter and a bevy of understory and ground layers. It's possible to mimic this natural condition in areas or edges of traditional suburban yards. Remove an area of turf and plant a variety of layered native trees, shrubs, perennials, and groundcovers in its place. Leave the leaves in the fall. Trees will be happier if planted in this setting, one that mimics their natural environment.
Native Trees Thrive in their Natural Habitat
Native trees thrive in their natural habitat, where they have evolved and grown over time on their own. In such an environment, native trees exist as part of a larger ecosystem. A native tree that is planted alone by itself has a tougher time thriving than those knitted together in this natural motif.
Native Trees Belong to Natural Plant Communities
Native trees are part of natural plant communities when they grow in the wild. What is a natural plant community? Think about natural plant communities as social groupings of plants that thrive together in similar types of settings. Have you seen certain native plants growing together in the woods, such as Oak and Tulip Poplar trees, ferns, and Mayapple as in the picture below? All of these plants are part of a unique, shady, forested, natural plant community. A native tree that is planted alone by itself (particularly one planted in turf) has a tougher time thriving than one that exists in its natural plant community.
Defining Natural Plant Communities
A good definition of natural plant community is from a book written by Frank Waugh and published in 1917: "The Natural Style in Landscape Gardening.” In it, Waugh wrote: “Practically every [plant species] is associated habitually with certain other species. Thus they form set clubs or societies. And these friendly associations, based upon similarity of tastes and complementary habits of growth, should not be broken up. If we as landscape gardeners desire to preserve the whole aspect of nature, with all its forms intact, we will keep all plants in their proper social groupings.” The natural plant community defines the spirit of the place, and the environmental conditions in that community define the community of plants that coexist together. Different communities with different environmental conditions support different sets, or communities, of plants.
McLean's Natural Plant Communities
Much of McLean is developed, so it is not easy to determine what natural plant communities were once there. But McLean is blessed with numerous relatively untouched stream valleys, and in these often forested valleys, one can observe vestiges of its original natural plant community. Four primary natural plant communities can be observed in McLean's stream valley parks: 1) the Basic Mixed Hardwood Forest, 2) the Oak-Beech-Heath Forest, 3) the Small Stream Floodplain Forest, and the 4) Wetland Swamp Forest. And it follows that McLean's native trees are associated with at least one of these plant communities.
THE MESIC MIXED HARDWOOD FOREST
The Mesic Mixed Hardwood Forest is the dense and lush forest that surrounds many of McLean's stream valleys. It is a rich forest with dense canopy and understory tree and shrub layers, and a lush herbaceous and fern ground layer. Many McLean neighborhoods back to these forests that reside just above the stream valleys. If you would like to plant a tree in a location that is shady, such as a woodland edge, the trees mentioned below that tend to dominate these woody natural areas would be excellent choices. While these trees may adapt to more exposed, sunnier locations, some may not do as well. The native canopy trees that tend to dominate McLean’s Mixed Mesic Hardwood Forests are American Beech, White Oak, Red Oak, and Tulip Poplar The native canopy trees that tend to dominate McLean’s Mixed Mesic Hardwood Forests are American Beech, White Oak, Red Oak, and Tulip Poplar
THE OAK BEECH HEATH FOREST
The Oak Beech Heath Forest is a drier site typically located on steeper ravine slopes, often north facing, with acidic soil. It features many canopy trees, some understory trees and shrubs, and a relatively sparse ground layer. If your location shares these characteristics, the trees shown below would be good choices. The native canopy trees that tend to dominate McLean’s Oak Beech Heath Forests are, again, American Beech, Chestnut Oak, White Oak, and Black Oaks. Lots of Oaks! The dominant understory trees in this forest community are Sassafras, Red Maple, Black Gum, Dogwood, and Serviceberry. Typical but less common in this natural plant community is the understory tree Witch Hazel.
THE SMALL STREAM FLOODPLAIN FOREST
The Small Stream Floodplain Forest is the low elevation area surrounding our local streams. It too features acidic soil and is often subject to flooded conditions. The trees common to these sites can tolerate occasional flooding and drought conditions. This is a special set of trees that are suitable for residential sites that experience stormwater challenges and occasional ponding or flooding. The Small Stream Floodplain Forest and the one that follows feature wet conditions. Native trees that do well in wetter environments are adapted to these forest conditions and are also best for addressing stormwater concerns more generally. Native canopy trees that dominate McLean’s Small Stream Floodplain Forest are Tulip Polar, Sweetgum, Sycamore, Red Maple, and various Oak species. The dominant understory trees in this community are American Holly, River Birch, Hornbeam, and Dogwood.
THE WETLAND SWAMP FOREST
And the more rare Wetland Swamp Forest is an area that is constantly wet with many seeps and standing pools of water and small streams. Trees that are suited to this type of environment would do well in areas that tend to collect runoff. The native canopy trees that dominate McLean’s Wetland Swamp Forests are Red Maple, Black Gum, and Tulip Poplar, and Sycamore. The dominant understory trees in this forest community are Sweetbay Magnolia and American Holly, and, to a lesser extent, Fringe Tree.
So, select your native trees carefully based on your site conditions and how they relate to the native tree's natural habitat and natural plant community. Avoid planting native trees in turf. Instead, try to mimic the native tree's natural, layered, ecosystem to create a natural habitat and help it thrive. Finally, don't forget to support the native trees that provide maximum benefits to wildlife . These are called keystone species because they host lots of caterpillars. Among canopy trees, the keystone standouts are the oaks, which host more caterpillars than any other native tree species. White and Red Oak, which host over 557 caterpillar species, are the most widely available, but other Oak species are just as beneficial if you can find them.
Now, go plant a native tree!
Frank A. Waugh, "The Natural Style in Landscape Gardening," Cornell University Press,1917.