Site preparation techniques for the establishment of mixed pine-hardwood stands: 22-Year results

Abstract

Four site preparation techniques were evaluated after 6 and 22 growing seasons to determine effectiveness in establishing pine-hardwood mixtures after hardwood regeneration harvests in Tennessee, USA. Pinus taeda L. and Pinus strobus L. were planted at 20- × 20-ft spacings after the harvest, allowing natural hardwood regeneration in the gaps. A randomized complete block with a split-plot treatment design divided 20 plots into 5 blocks. The four treatments were (1) commercial clearcut harvest, (2) silvicultural clearcut harvest, (3) fell-and-burn after a commercial clearcut, and (4) brown (herbicide)-and-burn after a commercial clearcut. At 6 and 22 growing seasons, survival and diameter growth of each pine species in the burn treatments were significantly greater than in the nonburn treatments. Loblolly pine performed better than white pine at both time intervals and with each treatment. The silvicultural and commercial clearcuts resulted in stands composed of 90% hardwoods by basal area with 10% pine. The two burn treatments had a greater proportion of planted pine by basal area (30 and 44% for the fell-and-burn and brown-and-burn treatments, respectively). Burning as a part of site preparation hindered natural hardwood regeneration, initially benefiting establishment and growth of planted pine seedlings in the development of mixed pine-hardwood stands.