The response of the feather moss, Pleurozium schreberi, to 5 years of simulated acid precipitation in the Canadian boreal forest

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Abstract
Permanent plots dominated by the feather moss, Pleurozium schreberi (Brid.) Mitt., were established at a Canadian boreal forest site to study the effects of simulated acid precipitation on percent cover, growth, and photosynthesis of vegetation. For a 5-year period, beginning in 1981, plots of P. schreberi received twice-monthly sprayings of simulated rain, adjusted to pH 5.6, 4.0, 3.5, 3.0, or 2.5 with a 2:1 molar mixture of sulfuric and nitric acids. Unsprayed plots were also monitored. Almost complete elimination of the moss had occurred in the plots sprayed with pH 2.5 by the end of the 2nd year of treatment, and substantial decreases in cover were also recorded at pH 3.0 and 3.5 over the 5 years. Significant reductions of up to 75% in total and living frond height and dry weight were recorded at pH 3.5 and lower. Lateral branches produced in acid-treated plots also were stunted and few in number. This decline in growth and percent cover of P. schreberi may have resulted from the decreased net photosynthetic rates measured in the field and would be accelerated by increased rates of evapotranspiration in the altered moss microhabitat.