Spacing and Shrub Competition Influence 20-Year Development of Planted Ponderosa Pine

Growth and stand development of ponderosa pine (Pinus ponderosa) were monitored for 20 years after planting at five different square spacings (6, 9, 12, 15, and 18 ft) in the presence or absence of competing shrubs on the westside Sierra Nevada. Mean tree size was positively correlated and stand values negatively correlated with spacing in the absence of competing shrubs. Trees growing with competing shrubs attained 76% of the diameter, 80% of the height, and 58% of the cubic volume of trees free of shrub competition when all spacings were combined. This study suggests that the major effect of shrub competition in ponderosa pine plantations on good sites is to lengthen the rotation. West. J. Appl. For. 5(3):79-82, July 1990.