Wooded sites require special design consideration in order to preserve and enhance existing trees. A number of design guidelines should be considered to accomplish this.
Minimize Lawn The typical suburban lawn should be minimized or even eliminated on a wooded site. There are several reasons for this recommendation. As already identified, a wooded area has noticeably little sunshine and relatively dry soil conditions during the summer season. A lawn frequently struggles under these circumstances, even if it is a variety that will tolerate some shade. A wooded environment is simply not conducive to lawn. In addition, the installation of lawn generally requires that understory plants be removed and that the ground surface be regraded. The loss of understory plants is apt to reduce the overall health of a wooded ecology while also eliminating the ability of the wooded area to regenerate itself. Regrading is apt to harm tree roots and change drainage patterns, both of which can injure or even kill trees.
If a lawn area is deemed necessary, it should be minimized in size and located in an area that receives some sunshine during the course of a summer day. It might be located adjacent to the street where sun probably shines through because of the open street corridor, or the lawn might form a space near the house where it can provide some separation between the house and preserved woods (Figure 13—13). The rest of the site should be allowed to remain in its naturalized state with native ground covers and understory trees.
Design Around Trees Every effort should be made to design outdoor spaces and functions around existing trees. This requires extra effort because the exact locations of trees must first be mapped. Then, spaces must be carefully woven among tree trunks so that few, if any, trees are removed to accommodate exterior functions. This is especially necessary for structured outdoor spaces such as sitting, entertaining, or eating spaces that have paved or wood deck ground planes. Existing trees may need to be allowed to extend up through these surfaces and will probably result in spaces that are more divided and complex than if the trees were not present (Figure 13—14). This approach is also likely to require field adjustment during construction.
Maintain Existing Grade There should be minimal grading or alteration of the existing ground elevation on a wooded site in order to minimize disturbance of tree roots. If the site is a newly built house, it is likely that the ground will have been altered most around the house. Beyond this construction zone, every effort should be made to retain the existing ground level. Again, this is most significant in locating
paved walks, structured outdoor spaces, walls, or even lawn areas if they are part of the design. These uses should, as much as possible, be molded to the existing ground while also maintaining proper standards of construction. If significant regrading is necessary, then retaining walls or tree wells should be used to maintain the existing grade around the base of existing trees. At a minimum, the existing grade should be preserved within the entire drip line of a tree or grove of trees. Never place fill (soil that is added to the existing ground surface) below the drip line of a tree because this will change the ability of existing tree roots to obtain air and moisture from the soil.
Minimize Soil Compaction The existing soil on a wooded site should not be compacted because this too reduces the amount of both air and water in the soil. Compacted soil is also more difficult for roots to grow through. Soil compaction results from the constant use or movement, including foot traffic, across the ground. Although occasional walking through a wooded area will probably do little harm, repeated movement over the same ground will compact and damage the underlying soil. One way to avoid soil compaction is to elevate walks and outdoor use areas on decks above the existing ground level (Figure 13—15). The initial installation of posts to support a deck system will cause some disturbance, but in the long term the ground soil will be preserved. This concept also minimizes regrading and allows precipitation to still reach the ground.
Use Shade-Tolerant Plants Plant materials introduced to a wooded site should be carefully selected for shade tolerance. Some zones on wooded sites may receive no direct sunlight during the course of a summer day, whereas other areas may receive sun during only a portion of the day. Plants must be chosen to fit each of these conditions. Thus, the palette of plants should be different from that used on a more typical residential site. One approach to planting in a wooded site is to use native plants that are already found on or near the site. Native wooded plants not only tolerate the special wooded conditions, but also look as if they belong to the wooded environment.