Effect of stand densities on stand dynamics in white fir (Abies concolor) forests in northeast California, USA

Six white fir trials were established during the last half-century to develop guidelines for managing the existing natural stands across northeastern California. We analyzed data collected from these trials at about 5-year intervals since their installation. Because these trials were independent of each other, the design and treatments varied among the sites. Targeted density treatments were selected based on 40, 55, and 70% of normal basal area from early yield tables at three of the sites. More density treatments were included at the remaining three sites. We found a significant response in growth to different stand densities regardless of site qualities, ages, and stand histories. Periodic annual increment for basal area and volume varied significantly by periods for all sites except the basal area at one site. Regardless of site quality, thinning from below leaving about 64% of the original measure of basal area did not significantly reduce productivity. If performed early in the life of the stand, such a thinning will reduce the accumulation of flammable materials due to natural self-thinning. A logistic function of periodic annual increment for basal area to relative stand density fits the data well and can be a useful tool for forest manager.