Recovery Plan for the Northern Spotted Owl - DRAFT

acre, 4 to 12 inches in diameter), and c) 10 percent of the trees 12 to 26inches in diameter.* Space created by tree removal was regenerated at a density of about 200trees per acre by planting or releasing advanced regeneration.* By age 120 years, this stand was projected to have a diameter distributionresembling those around owl nest sites (Figure G. 1 1 Stand A). Largesttrees were more than 44 inches dbh. There were more than 150 trees peracre less than 12 inches in diameter in the understory. Estimated understoryheight ranged from 45 feet to more than 120 feet; estimated canopycover is 100 percent.* Snags and logs on the forest floor might not occur naturally with thissystem, and may have to be made by killing live trees.Note that the untreated stand was not projected to have developed multiplelayers or have the desired structure by age 120 years.Example 2: A Douglas-fir, grand fir, bigleaf maple stand, site index 120 feet at50 years, with an initial density of 881 stems per acre. Since stocking wasso high, this stand was simulated to have three thinnings (Figure G. I 1,Stand B). Hardwoods were left to develop a multilayered structure.* At age 40 years, 50 percent of the conifers in the 10- to 16-inch diameterclasses were thinned. There were 362 conifers and 114 hardwoods per acreleft; 100 conifers per acre were planted.* At age 60 years, 50 percent of the trees in the 10- to 22-inch diameter classwere converted to snags, logs on the forest floor, or harvested. There were275 conifers and 70 hardwoods per acre left; 100 conifers per acre wereplanted.* At age 80 years, 60 percent of the conifers 8- to 22-inches in diameter weremade into snags and down logs or harvested. There were 224 conifers and70 hardwoods per acre left.Removing trees or killing them for snags or down logs allowed space for developmentof large trees (42+ inches in diameter) and establishment and growth ofan understory. No trees more than 22 inches in diameter were removed orkilled for snags or down logs. At age 120 years, the treated stand was projectedto have the required structure (Figure G. 1 1, Stand B); simulated understoryheight ranged from 30 feet to 110 feet; canopy cover was 53 percent.Without treatment, the stand would not have a multilayered structure; understorywas projected to be about 22 percent.Example 3: Two young stands were simulated to grow without treatmentuntil age 120 years. Stand A, which had about 230 bigleaf maple stems peracre, developed a second layer as the conifers overtopped the maple (FigureG. 12). However, the understory was not nearly as well developed as the standused for nest sites (or the managed stands in examples 1 and 2), since thesecond layer had fewer, shorter trees than stands used for nesting. Stand B,which had no maple, would not likely form a second story.C. Redwood and Mixed Conifer from NorthwesternCalifornia (Tlornburgh 1991 b)This is a simulation of a redwood and Douglas-fir plantation on a productivesite (site index 200 feet at 100 years). At 15 years, there are 78 redwoodsprout clumps per acre (4 to 12 sprouts per clump). The rest of the stand isplanted to redwood and Douglas-fir and there are natural saplings and seedlingsof grand fir, western hemlock, Sitka spruce, and tanoak (Figure G. 13).Also present are salal, ceanothus, huckleberry, and red alder. The goal is to508