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 growth and development of red fir (Abies magnifica A. Murr.) stands, we established an experiment in a 60-year-old stand using a 2 × 3 factorial design with nitrogen-fertilized and nonfertilized treatments and three stocking levels. Plots were established in 1976 and were measured every 5 years for 26 years. The periodic annual increment in basal area was 97%, 51%, 38%, and 33% greater in fertilized trees than in nonfertilized trees during the first, second, third, and fourth 5-year periods, respectively. After 20 years, annual basal area increment was greater in nonfertilized trees. The response of annual volume increment to fertilization was not statistically significant until the fourth period. Yet, volume increases of the fertilized plots were 25%-92% greater than those of the nonfertilized plots from 1976 to 1996. Similarly, basal area increment was greater in lightly thinned plots than in unthinned plots from the second period on, until heavy mortality during 1996-2002. Basal area increment was greater in the heavily thinned plots from the fourth period on. Results indicate that red fir can respond to fertilization and thinning quickly and that 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. Résumé :Pour déterminer l'impact de la fertilisation et de l'éclaircie sur la croissance et le développement de peuplements de sapin rouge (Abies magnifica A. Murr.), nous avons établi, dans un peuplement de 60 ans, un dispositif expé-rimental de type factoriel 2 × 3 avec présence et absence de fertilisation et trois niveaux de densité. Les placettes ont été établies en 1976, puis mesurées à tous les 5 ans pendant 26 ans. Les arbres fertilisés ont eu un accroissement annuel périodique en surface terrière de 97, 51, 38 et 33 % supérieur à celui des arbres non fertilisés après les première, deuxième, troisième et quatrième périodes de 5 ans, respectivement. Après la quatrième période de 5 ans, les arbres non fertilisés ont eu une meilleure croissance annuelle en surface terrière. La réaction de l'accroissement annuel en volume à la fertilisation n'a pas été statistiquement significative avant la quatrième période de 5 ans. Malgré tout, les placettes fertilisées ont eu un accroissement en volume de 25 à 92 % supérieur à celui des placettes non fertilisées entre 1976 et 1996. De la même façon, les placettes légèrement éclaircies ont eu un accroissement en surface terrière supé-rieur à celui des placettes non éclaircies à partir de la deuxième période de 5 ans jusqu'à un épisode de mortalité intense survenu entre 1996 et 2002. Les placettes fortement éclaircies ont montré un accroissement en surface terrière supérieur à partir de la quatrième période de cinq ans. Les résultats indiquent que la réaction du sapin rouge à la fertilisation et à l'éclaircie est rapide...

Response of Boreal Jack Pine (Pinus banksiana Lamb.) Stands to a Gradient of Commercial Thinning Intensities, with and without N Fertilization

“…This pattern could result from reduced intraspecific competition for soil resources and generally better tree vigour. However, this result disagrees with studies by Yang [18] and Zhang et al [42] which reported that nitrogen loadings increased tree mortality.…”

“…We expected that by increasing tree growth, fertilization would also increase self-thinning mortality due to higher intraspecific competition [42]. Contrary to our hypothesis, fertilization did not increase tree mortality in controls or low intensity thinned plots.…”

“…This is particularly evident in unfertilized stands and consistent with previous thinning experiments in which cumulative volumes were usually greater in controls than in thinned stands [19]. However, low thinning intensities combined with short thinning cycles could result in cumulative stand volumes higher than that of controls [42]. Finally, in fertilized stands, improved tree growth and, more importantly, reduced tree mortality compensated for the loss of harvested trees.…”

“…Trees in all social classes should benefit from fertilization. While it was expected that thinning from below would reduce stand mortality over the study period, we anticipated that, by increasing tree growth, fertilization would increase competition and tree mortality in controls and low-intensity thinned stands [42]. Volume increment over the 14 year period of residual trees in thinned stands was not expected to compensate for the volume harvested.…”

Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon

“…A pulsed fertilization 1995 1996 1997 1995 1996 1997 1995 1996 1997 1995 1996 1997 Ring width (mm) The dashed lines show the ring widths (adjusted for covariates age and DBH) for the entire data set for the 2 sites. Solid horizontal line: median; box: 25th to 75th percentiles; whiskers: 10th to 90th percentiles; dots: data points beyond the whiskers experiment on red fir Abies magnifica in California produced 20 to 50% annual increases in volume growth during the first 10 yr after fertilizer was added at 30 g N m -2 (Zhang et al 2005). Nemani et al (2003) reported an average increase of net primary production of 6.6% yr -1 for the period from 1983 to 1999 for the boreal zone.…”