Effects of Red Alder Density on Growth of Douglas-fir and Western Redcedar

• Author / Creator

  Fang, Chengdong

• Red alder (Alnus rubra [Bong.]), is the most common hardwood species along the Pacific Northwest coast and is widely distributed as a component of mixed stands with conifers on highly productive sites. It is also a strong competitor in young conifer stands and rapidly overtops associated juvenile conifers, often making it challenging to meet free-growing obligations under current standards in Southwestern British Columbia (BC). Presently, many forest managers err on the side of caution and expend resources to control red alder to meet free-growing requirements. Due to a lack of scientific data, we are unable to determine whether these expenditures are warranted. The goal of this study was to provide information to assist in improving policies and practices around free-growing relating to alder in coastal conifer stands.
  Data from mixed red alder-conifer plantations established by the BC Ministry of Forests in 1992 and 1994 were used to examine: 1) the effects of differing initial densities of red alder (Alnus rubra [Bong.]) on the growth of Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco) and western redcedar (Thuja plicata Donn.), at both individual tree level and plot level; 2) the competitive effects of red alder on conifers, and the effectiveness of various distance dependent and independent competition indices for predicting conifer growth, including both additive and replacement experiment series; and, 3) the influence of light and nitrogen on conifer growth.

  Current standards for free-growing in B.C. do not accept alder within 1 m radius of conifers. While one alder within a 1 m radius may be indicative of densities approaching 10,000 alder per hectare, our results suggest that densities of up to 400 alder per hectare may be acceptable and possibly desirable on some sites. The growth of Douglas-fir may be enhanced when red alder density is relatively low during the first 25 years after establishment. We found that the competitive effects of red alder were consistently lower than that of conifers, and Douglas-fir height was largest in the highest density treatment (400 tph) from age 7 to age 15, and same for alder height growth. 200 alder per hectare gave the largest Douglas-fir height and diameter at age 20. As also expected due to western redcedar’s greater shade tolerance, it showed less sensitivity to the presence of red alder than Douglas-fir. 100 alder/ha gave the best growth of redcedar. These findings suggest the current free-growing assessment standards may be overestimating red alder competition, that alder density up to 400 stems/ha are not having negative effects on Douglas-fir or western redcedar on mesic sites and the use of larger radius plots should be considered.

• Subjects / Keywords

  • Density effects
  • Light
  • Competition
  • western redcedar
  • Free-growing standards
  • Nitrogen
  • Red alder
  • Douglas-fir

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3FT8F14Z

• License

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