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Stream Protection Zone (SPZ)

Benefits of SPZ's

The SPZ acts as an effective filter and absorptive zone for sediment.

1. The SPZ with its thick plant growth creates a mat of decomposing material on top of the soil. It is often damp because the water table is at or near the soil surface. The sponge-like qualities of the SPZ control the quantity of water flowing into the streams. Soils in this area absorb water during the wet seasons and slowly release moisture into the stream. This minimizes the effects of peak runoff and keeps streams from drying out sooner than usual.

2. The SPZ provides filtering of surface runoff. This filter acts as a trap, blocking sediment and other debris from entering the stream, lake, or reservoir. It catches and holds sediment in the mat of plants and duff. When this last line of defense isn't working, sediment ends up in the stream, causing water quality problems.

Since logging activity occurs in many of Idaho's watersheds, water quality must be protected by a healthy SPZ. Healthy SPZ's control the amount of water coming from a watershed. And we all depend on sediment-free water for household use, irrigation, and healthy fisheries.

The SPZ maintains shade; conserves aquatic and terrestrial riparian habitats; protects the stream channel and banks; and promotes flood plain stability.

An adequate SPZ protects the absorptive and filtering action of the riparian area. The absorbent mat of forest humus, litter, and duff helps to trap sediment before it reaches the stream, ensuring good water quality.

What's wrong with sediment in streams?

Trout and other fish reproduce by burying their eggs in stream-bottom gravel. The eggs develop in the gravel and hatch into "sac fry." When the yolk is absorbed, the young fish emerge from the gravel.
Sac fry and young fish can be choked by sediment. When too much sediment falls to the stream bottom, it fills the gaps between the gravel and suffocates the fish. The streambed becomes cemented over. This tomb of sediment traps the young fish without clean water, oxygen, or food. For those fish that survive, the sediment has an abrasive effect on their sensitive gill tissue.

Sediment also kills aquatic insects and algae, fills in resting pools, and interferes with recreation.
Sport fishing is enjoyed by thousands of Idahoans, and generates substantial revenues for the state. Fish losses due to forestry activities can be minimized with healthy SPZ's.

Equipment Operation Waste

The Idaho Forest Practices Act doesn't allow waste from logging operations; such as crankcase oil, filters, or grease and oil containers, inside Class I or Class 11 stream protection zones.

Responsible operators also dispose of worn-out chokers, cable, replaced parts, welding and other machinery repair debris, paper or plastic packaging, lunch garbage, beverage cans, and other refuse away from forest operations.

Other SPZ Benefits:

SPZ's and stream shade

Maintaining water temperatures helps fish pawning. Without trees and overhanging shrubs, stream temperatures would be higher in the summer and colder in he winter. Some fish species and aquatic organisms would then be unable to live in the streams. In the summer, cold water from shaded streams eventually flows into larger rivers and helps maintain their fish and aquatic life by keeping these waters cool all the way downstream.

SPZ's and food

Leaves and insects drop into streams from overhanging trees and shrubs. In fact, 90 percent of the food in forested streams comes from bordering vegetation. Even in large rivers, over 50 percent of the food consumed by fish is from streamside trees and other vegetation.

SPZ's protect streambanks

Many streambanks are stabilized by streambank trees. They anchor banks and prevent erosion during periods of high water. Removing trees and shrubs and substituting shallowrooted grasses can lead to streambank collapse and stream sediment.

Healthy SPZ's stabilize floodplains. During times of high water, SPZ's reduce the velocity of floodwaters. Their dense vegetation and deep humus slow down racing waters. Forest floodplains suffer less damage when SPZ's are protected during logging activities.

Bank tree roots also supply important cover for fish

Bank overhang is created by stream flows undercutting the stream bank and tree roots. Fish can rest, hide from predators, and feed in these protected areas.
In the northern Rockies, 59 percent of the land birds use SPZ's for breeding. Of those birds, 39 percent can breed only in SPZ's. Others hunt in healthy SPZ's where food and cover are abundant. The reason is that SPZ's supply a great variety of plants needed by birds and other wildlife. Grasses, shrubs, vines, and trees all grow well in moist, fertile soil. Turtles, beaver, muskrats, and water snakes thrive in SPZ's. Deer, wood duck, and bear feed and see cover in the thick vegetation. Eagles, owls, and songbirds occupy the trees. Pools supply breeding sites for frogs, toads, and insects. SPZ's are also well-traveled wildlife corridors, connecting one area with another.

SPZ's and humans

We like SPZ's too, for a lot of reasons. The recreational activities that we enjoy in and around streams are many. The financial value of healthy SPZ's to the people of Idaho is large enough for all of us to be careful when we do anything in and around them.

SPZ's and timber production

For those who grow and harvest trees, the fact is that trees often grow best in riparian areas. Trees respond to those deep, fertile, and moist soils. SPZ's are not timber harvest "keep out" zones. But they are locations where timber-harvesting activities must be modified to protect the many benefits mentioned above.

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Idaho Forest Products Commission
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