In hot weather, the trees effectively block 90 percent of the light striking them. Millions of needles of the canopy catch droplets from fog and rain. The moisture drips down to moss, duf and fallen trees on the forest floor where it is stored for later use. Drops fall into thick layers of mosses and duf that accumulate on the ancient forest floor. Seed coatings shedded by plants and fungal threads bind the soil, just as steel reinforcing mesh strengthens concrete.
Mass erosion is common for many years after logging.
Soil erosion can damage real estate values, hydroelectric dams, municipal water supplies, freshwater fisheries and biological diversity of ecosystems. Many apparent above-ground species, such as fungi, actually spend most of their lives underground. Roots break down rock by insinuating their way into cracks and fragments, then exuding chemicals that aid in extraction of nutrients. The roots of most forest plants, including all northwestern trees, accociate with fungi in this process. The fungus helps trees grow by providing phosphors and receiving sugar and amino acids.