Member Contribution #1

Do Fish Grow on Trees?

by Steven Singer

The answer is an emphatic YES! Both living and dead trees are essential to the survival of steelhead and coho salmon in the Santa Cruz Mountains. If we are to maintain healthy stream ecosystems we must understand the ecological role of trees. Trees support fish in many ways.

Here's how.

Tree roots stabilize banks and create stable undercut banks that provide escape cover for fish. Leaf and needle drop from trees covers the surrounding slopes with a natural mulch layer that controls surface erosion. The result is less sediment entering the channel and more silt-free gravels that are necessary for spawning.

The foliage in tree crowns forms a dense canopy that shades the stream. This shade is crucial to keeping water temperatures below 68 degrees (F), which is near the upper limit for coho salmon. Needle and leaf fall into the water are energy sources that provide part of the basis for the aquatic food chain. Fallen leaves feed insects that in turn provide food for fish. Foliage-feeding insects that fall into the stream from the canopy are also an important source of fish food.

Trees form forests that catch fog and convert it to a water source called fog drip. Water supplied by fog drip reduces water use by trees and helps fish by boosting summer stream flow levels.

Dead trees that have fallen into the stream channel are also valuable. Some, like alders, are relatively short-lived, but large redwoods or Douglas-firs, can persist for hundreds of years. They provide a type of stream environment and particular aquatic habitats that our anadromous salmonids have adapted to through thousands of years of evolution. Large logs are crucial to maintaining stream hydraulics that are "fish friendly". Well-anchored logs and small logjams produce a stair-stepped longitudinal stream profile that dissipates excessive energy, reduces sediment movement, and stabilizes the stream bed. Plunge and scour pools formed by instream logs and logjams provide essential summer rearing habitat and winter refuge areas for the young fish. These important habitat features are typically in short supply in our coastal streams.

Knowing the value of our riparian forests, it is disappointing to see how few farmers, ranchers, foresters, and public works/flood control department officials take those values into consideration. That they don't is clearly evident by the many farm fields plowed to the edge of the stream, the many stream banks degraded by cattle, the many redwood stumps left by logging operations that cut right up to the water's edge, the gaping gullies below many road culverts, and the channels lacking instream logs and leaning trees following misguided flood control efforts. These sights are all too common throughout the Santa Cruz Mountains Bioregion.

To effectively attack these problems and to assist state and federal fisheries agencies in protecting our streams and fish, we need to create no-disturbance buffer strips along all of our streams. No logging, farming, grazing, or road building would be allowed within 100 - 300 feet of a stream. Such a protected riparian strip would make for cleaner water, keep water temperatures cool enough for fish through increased shading, provide large logs that could naturally fall into the stream thereby maintaining rearing pools for young fish, and yes, in a very real sense, allow our trees to grow fish.

-- February 2002