Specifications include, but are not limited to:. The Contractor will hand thin trees in units. The Contractor will progress at a rate that indicates all required work be accomplished within the performance period. The average stem spacing should vary so that the best trees are retained. Two or more sides of the crown of the leave tree should have a minimum of 4 feet of open-air space between itself and the tips of other tree crowns. Western white pine trees lethally infected with blister rust will not be thinned or counted in plots. Tree Quality Selection Criteria: The best trees of each species will be retained as leave trees in all units. Indicators of desirable trees are: straight stems, small branch diameter, good crown coloration, good crown form, good crown ratios (> 45%), freedom from insects, diseases, and physical and mechanical damages, vigorous annual growth as indicated by long terminal leader. These indicators of undesirable trees shall determine the trees to be cut; slight defects may be acceptable for leave tree if it is the best selection within a competitive group. Indicators of undesirable trees are: multiple tops, poor crown ratios (< 45%), poor crown form and coloration, crook or sweep in boles, dead or broken tops, large branch diameter, presence of insects, diseases, or physical or mechanical damages, suppression, poor annual growth as indicated by short terminal leader Felling Requirements Cut trees shall be completely severed from the stump. No hang-up "straps" will be permitted. All felled trees shall be severed below the lowest live limb. The maximum stump height shall be 6 inches above ground level, as measured on the uphill side of the tree. Cut trees shall be felled parallel to each other and not criss-crossed or jack-strawed. Cut trees shall be felled away from unit boundaries into the units, roads, maintained trails, wildlife trails, fence lines, established land corners, and streams. Any trees felled on such areas shall be removed. Old roads that are closed can have cut trees fell across them. This will be on a case by case basis. Dead standing trees shall not be cut. Bearing, section-line, or trail-blazed trees shall not be cut. Unit boundary trees with unit flagging can be cut if determined to be excess.