. Venti anni di crescita della Ponderosa Pine alberelli assottigliati fino a cinque intervalli nella zona centrale di Oregon. Ponderosa Pine Oregon; foresta assottigliamento Oregon. La figura 1-coppia ponderosa pine stand con una fitta, soppresso 40- e 70-anno-vecchio alberello sottobosco prima di assottigliamento di varie densità. Esperimenti nella gestione di giovani, sup- premuto si erge nel nord-ovest del Pacifico hanno cambiato negli ultimi quarant'anni. I primi esperimenti di solito coinvolti due tenute, uno assottigliato per una conserva- tivo spaziatura di 6 o 9 metri, l'altro a sinistra non diluita (Mowat 1953). Più tardi, di- zioni in colture di assottigliamento della struttura sono state stabilite (Barr

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. Twenty-year growth of ponderosa pine saplings thinned to five spacings in central Oregon. Ponderosa pine Oregon; Forest thinning Oregon. Figure 1—Mature ponderosa pine stand with a dense, suppressed 40- to 70-year-old sapling understory before thinning to various densities. Experiments in managing young, sup- pressed stands in the Pacific Northwest have changed over the past 40 years. The first experiments usually involved two plots, one thinned to a conserva- tive spacing of 6 or 9 feet, the other left unthinned (Mowat 1953). Later, experi- ments in crop-tree thinning were established (Barrett 1969). All studies showed that suppressed, understory trees are capable of substantial response to thinning. The full potential for diameter growth of second-growth ponderosa pine was not visualized until a study of free- growing trees was reported by Dahms and Silen in 1956.' They observed young trees free from competition growing at the rate of 6 to 7 inches per decade. They also found that heavy competition from brush reduced the growth rate to about 3 inches per decade. Thus, a tentative rate for maximum diameter growth was sug- gested and the importance of brushy understory competition was estab- lished. This work by Dahms and Silen suggested that the next thinning study should sample a wide range of spac- ings and should attempt to quantify the effect of brush competition on tree growth. The Methow study, established about 4 years later, tested spacings of 9.3, 13.2, 18.7, and 26.4 feet as well as growth in unthinned plots (Barrett 1981). It showed that dense, sup- pressed ponderosa pine responded to increased space with more diameter and height growth. This study also showed that wider spacings produced large diameter trees in 20 years after thinning but that very wide spacings (26.4 feet) where the understory is predominantly pine grass can sacrifice substantial yields of wood fiber during the early part of a rotation. This paper presents 20-year results from a sp

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