Long-term effects of thinning and fertilization on growth of red fir in northeastern California

Abstract

To determine the impact of fertilization and thinning on red fir (Abies magnifica) stand growth and development, we established an experiment in a 60-year-old stand using a 2x3 factorial design with nitrogen fertilized and non-fertilized treatments and three stocking levels. Plots were established in 1976 and were measured every 5 years for 26 years. Fertilized trees grew 97%, 51%, 38%, and 33% more PAI basal area than non-fertilized trees during the first, second, third, and fourth 5-year periods, respectively. After that, non-fertilized trees grew more basal area per year. Annual volume increment response to fertilizer was not statistically significant until the fourth period. Yet, the fertilized plots grew 25-92% more volume than did the non-fertilized plots from 1976 to 1996. Similarly, lightly thinned plots grew more basal area than unthinned plots from the second period on until heavy mortality during 1996-2002. The heavily thinned plots grew more basal area from the fourth period on. Results indicate that red fir can respond to fertilization and thinning quickly and both treatments speed stand development. In addition, fertilization increases the stand’s carrying capacity. Therefore, forest managers can use these silvicultural practices to improve stand growth, to reduce fire fuels, and to accelerate stand development.

Citation

Zhang, Jianwei; Oliver, William W.; Powers, Robert F. 2005. Long-term effects of thinning and fertilization on growth of red fir in northeastern California. Canadian Journal of Forest Research 35:1285-1293.