Forests are essential for providing water to people, agriculture and wildlife throughout California.
More than 60% of California’s drinking water comes from the Sierra Nevada mountains, in the form of rain in fall and winter, and melted snow in spring and summer. Our forests play a vital role in helping to ensure a sustainable year-round supply of life-giving water that flows from the mountains to our central valleys and coasts. Without healthy forests, we would lose the natural mechanism for capturing and storing water for year-round use – essential for our Mediterranean climate. Forests absorb rainfall, refill groundwater reserves, filter contaminants in water, slow storm run-off, reduce flooding, and maintain soil stability and resilience. Trees also transfer large volumes of water from the soil to the atmosphere through “transpiration,” part of the dynamics that form clouds carrying rain. Deforestation decreases the amount of transpiration, resulting in longer dry seasons.
Clearcutting increases erosion, leading to sedimentation, nutrient-loading, and decreased storage capacity.
Studies of logging methods and amount of bare ground suggests that, per unit of ground, the potential for stream channel effects from surface soil erosion is greater on clearcuts. Clearcutting can send heavier loads of sediments and nutrients downriver, harming water quality and fish and decreasing storage capacity (as water volume is displaced by sediments). Shasta Lake, for example, has 60 feet of sediment built up behind the dam, and the resulting decrease in water-storage capacity ends up costing the water agency, which then passes the cost onto consumers.
Clearcutting causes changes in water yields.
Vast swaths of clearcut forests, along with warmer temperatures, are changing the way water is distributed from the Sierra, Cascades and other ranges to the foothills and valleys below, with increased high-flows from storms in the winter, and spring run-off; and decreased low-flows in summer. This means we are losing capacity to capture and store our winter supply of water (in the form of snow) to provide water through the summer and fall. This negatively affects riparian and aquatic habitat for wildlife and fish, and will significantly impact the availability of water supplies for agricultural, industrial and residential needs.
Tree plantations can harm rivers and streams.
Converting natural forests into tree plantations (which usually includes clearcutting for most industrial timber companies) involves a very intensive management regime that includes large-scale logging, site preparation, replanting, and herbicide application intended to suppress competing plants. Studies show that logging and associated road-building during post-fire logging and reforestation operations significantly harm aquatic systems, thereby reducing survival of salmon and other aquatic species.