Measurement of light transmission in young conifer plantations: a new technique for assessing herbicide efficacy
1992
Jobidon, R.
A rapid and accurate technique, sing a simple measure of light intensity, for assessing the efficacy of herbicide treatment is proposed. Herbicide treatment efficacy was independently measured 1, 2, and 3 years after a single application of glyphosate on three adjacent plantations of black spruce reinvaded by red raspberry and fireweed in eastern Quebec. Each plantation represents a given time, 1, 2 or 3 years, after herbicide application. Light intensity, expressed as percent of full sunlight in the PAR spectral region (400-700 nm) reaching the upper one-half of the tree seedlings, significantly discriminates released and unreleased tree seedlings. Spruce seedlings receiving 60 to 100% of full sunlight grew, significantly better in height and basal stem diameter and had significantly fewer stems and less height growth of competing vegetation than seedlings receiving less than 60% of full sunlight. This indicates that measuring the intensity of light reaching the tree seedlings is an easy and effective way to assess efficacy of herbicide treatment and also competition between spruce seedlings and surrounding vegetation. It is suggested that light reaching tree seedlings be measured instead of quantifying the competition variables. The proposed technique eliminates all potential bias from subjective standard procedures which in turn makes possible quantitative comparisons between evaluations of herbicide treatment efficacy.
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