Litter decomposition under snow cover in a balsam fir forest

Abstract

In a subalpine balsam fir forest in Quebec, Canada, mass losses, respiration rates, and nitrogen and sulphur dynamics were measured on fir needles, birch leaves, lichens (mixed species), and small twigs decomposing under deep (> 1.5 m) winter snow for 6 months. Mass losses ranged from <6% (twigs) to 70% (lichens) and relative decomposition rates of needles and leaves were reversed from those expected at higher temperatures. Isolation of fir needles from direct contact with the snow did not affect decay rate, nor was decay accelerated by spring snowmelt. In situ respiration rates increased from about 1 mg CO2/(g∙day)) in February to 3–5 mg CO2/(g∙day)) in May, mostly because of rising temperatures. Summer respiration rates were much higher (> 6 mg CO2/(g∙day)). Nitrogen and suphur concentrations increased in all nonwoody litter over winter, but only birch leaves and some fir needles appeared to assimilate nutrients from the environment. Melting snow could easily have provided all of the nitrogen and sulphur taken up by decomposing litter. Decomposing lichens released 40 and 60%, respectively, of their initial nitrogen and sulphur contents. A literature review indicates mass losses from leaf litter decomposing under deep snow vary according to the proportion of labile material in the litter and usually constitute 40–60% of total first-year mass losses. Key words: decomposition, winter, balsam fir, snow.