Growth response of pitch X loblolly pine hybrids following crown touching release

摘要

The 13 yr growth response of pitch x loblolly pine hybrids following a crown touching release conducted at age 7 in the Virginia Piedmont was evaluated. Growth of crop trees was related to the degree of crown release as measured by the free-to-grow (FTG) rating that ranged,from 0 (no release) to 4 (complete release on all sides). Diameter growth of the released crop trees (FTG greater than or equal to 3) was 63% greater than diameter growth in nonreleased trees (FTG < 3), while height growth was 9% greater. At age 20, the average dbh of the crop trees was 10.3 in., while the average dbh of the nonreleased trees was 7.8 in. The live crown ratio in the crop trees was significantly greater than in the nonreleased trees (47% vs. 38%), which contributed to the growth response. However, stem quality of the crop trees was poorer than in the nonreleased trees, due to the persistence of branches on the lower bole. These results suggest that sawtimber size pitch x loblolly hybrid pines can be grown in a short rotation if adequate growing space is provided.