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Native Plant Synoptic Garden
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Site Preparation
In order to implement the proposed design, there will be a need to utilize heavy
machinery during construction. When heavy machinery such as backhoes, excavators, and dump-
trucks are used during construction, there is certainly a high probability for them to alter the site
in ways that are not optimal for plant growth and sustainability. For example, the weight of the
machinery often causes soil compaction. The effects of compaction can be amplified when soils
levels are wet or near the point of saturation. The site analysis for the proposed project area has
already shown soil bulk densities around the site to be excellent for plant growth. In order to
preserve these optimal bulk densities, and not alter soil structure, careful planning of pathways for
equipment use will need to be determined. By limiting the access of equipment to designated
paths or areas, soil compaction over the site will be minimized. The soil under these designated
pathways should be over-laid with a thick layer of wood chips (6+ inches) in order to minimize
compaction directly under paths (Matheny and Clark, 1998). Once the project is finished, the
wood chips may either be utilized elsewhere as mulch, or left in place to decompose.
Another consideration will be the need to control erosion on site. Erosion of surface soils
poses two immediate concerns. First, sediment runoff into the adjacent wetland areas could
impact delicate wildlife and vegetation. Second, surface runoff tends to modify the texture of
soils by carrying away finer soil particles and then depositing them in mass elsewhere. This
would result in soil compositions that may be less that optimal for plant growth; such as very high
concentrations of clay or silt particles. Soil textures that are dominated by silt and clay generally
have higher moisture retention, lower gas exchange rates, and may become compacted over time
to degrees that restrict root growth (Brady et la., 2004). The problem of erosion would be of
particular concern where slopes are greatest, such as the forested ridge area. Possible forms of
protection could be a light mulch layer, temporary erosion control fabrics, or a combination of
these two methods. These protective measures would mediate the infiltration of water into the
soil; especially when precipitation occurs in amounts greater than the ability for quick soil
percolation.
Plant Specifications
The Native Plant Synoptic Garden will be constructed on a site that is already occupied
by plants, trees, and shrubs accessioned into the collection of the Washington Park Arboretum.