Sewage and runoff from agricultural fields into a stream can supply an excess of nutrients, creating problems for aquatic wildlife. Streamside plants can improve water quality by absorbing these nutrients. In times of flooding, vegetation slows the flood-borne materials, minimizing damage. Shading the stream helps keep water temperatures in the range fish and other aquatic species require. The Greenway is unusual in that the wetlands are being preserved, not destroyed.
White alder has a quick growth and a relatively short life span, as do most riparian trees.
Alder roots have nodules that fix nitrogen, making this nutrient available to other plants. Local residents still follow the Native American practice of using alder wood to cook and smoke salmon. In the winter, look for the small brown cones hanging from its bare branches. Because of the availablility of water along the creek, the cottonwood produces a vast network of surface roots. As you travel this trail, look for the roots of the cottonwood tree breaking through the asphalt.