Red alder is a common component of low elevation CWH zone forests in South-western BC and often grows intimately with young conifer stands on highly productive sites. It is a strong competitor in young conifer stands and rapidly overtops juvenile conifers, often making it challenging to meet free growing obligations under current standards. Presently, many forest managers err on the side of caution and expend resources to control red alder to meet free growing requirements. Unfortunately, we are unable to determine whether these expenditures are warranted due to a lack of scientific data. This project provides preliminary best available information to assist in improving policies and practices around free-growing. This project utilises mixed alder-conifer experiments that were designed to study the competitive effects of red alder on conifers. The experimental sites are now old enough to assess the 11-yr free growing window. During the first year of this project (2004/2005) standard GY measurements and state-of-the-art light measurement techniques were used. A variety of competition indices that use measures of the number, size, proximity and location of broadleaf trees within a small plot centred on the subject tree were tested to estimate the intensity of broadleaf competition. In this study densities of red alder ranged between 0 and 400 stems/ha and basal area ranged up to 9m2/ha, resulting in light levels ranging between 100% and 37% of full sunlight. These densities and light levels had only weak competitive effects on Douglas-fir and western redcedar on certain sites. We found consistent relationships between the basal area of red alder and light levels at the height of mid-crown for both western redcedar and Douglas-fir at the four study sites. However, on some sites conifer growth was positively related to red alder density. As expected due to its greater shade tolerance, western redcedar showed less sensitivity to the presence of red alder than Douglas-fir. On the Coast, current standards for free growing in BC do not accept alder within a 1m radius of conifers. While one alder within a 1m radius may be indicative of densities approaching 10,000 alder/ha, however, our results suggest that densities of up to 400 red alder/ha, may be acceptable and possibly desirable on some sites. An alder density of 400 trees/ha corresponds to one alder in a 2.82m radius plot (25m2), two alder in a 3.99 m radius (50m2) plot, and four alder in a 5.64 m radius (100m2) plot. We found that for the red alder densities in this study the radius of assessment plots should be at least 4m. These findings suggest the use of larger radius plots may be a consideration for evaluating red alder competition and free-growing in coastal conifer plantations. These are only preliminary findings and we will need to re-assess these plantations at the end of the free growing window (15 years) to evaluate the impacts of alder densities on conifer growth and determine whether larger radius assessment plots are warranted.
Thomas, Keith, Harper, George J.; Comeau, Phillip G.; Fielder, Peter P.; Cortini, Francesco; Hill, Susan. 2005. Management of complex coastal mixedwoods in BC for productivity and free-growing. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report