Early pruning affects 15-year growth of cottonwood planted at 40- by 40-foot spacing
We compared the growth of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) trees planted at 40- by 40-foot spacing and subjected to four pruning treatments from the 2nd through the 8th year of growth. Treatments were (1) no pruning, (2) prune to one-third of total height annually, (3) prune to one-half of total height annually, and (4) prune to 17 feet when diameter at breast height (d.b.h.) exceeded 8.5 inches, which occurred in the 4th year. Diameter and height measurements were taken annually for 15 years. By age 15, average diameters differed significantly among all four treatments and ranged from 16.8 inches (half-height pruning) to 19.8 inches (no pruning). Pruning had no effect on total height, which averaged 110 feet across all treatments. Total sawtimber volume differed significantly among treatments and ranged from 3,921 board feet (Doyle) per acre (half-height pruning) to 6,919 board feet (Doyle) per acre (no pruning). In widely spaced cottonwood plantations, pruning is not recommended if pulpwood production is the sole objective of management, but is necessary if quality sawtimber production is the primary objective of management. The mean d.b.h. of unpruned trees planted at 40- by 40-foot spacing represents the maximum potential diameter achievable for cottonwood and can serve as a benchmark for comparison to diameters observed at narrower spacings.