Litter decomposition in a cool temperate deciduous forest

Abstract

Amounts of autumn tree leaf litter fall, understory litter input, tree leaf litter nutrient input, and rates of dry weight loss in decomposing leaf litter were estimated in an aspen woodland (Populus tremuloides Michx. – P. balsamifera L.) site in the Rocky Mountains in southwestern Alberta. Tree leaf litter input amounted to 250 g m−2 and comprised 3.7% of the total organic matter in the ecosystem (1.92 × 105 kg ha−1). The ratio of the weight of aspen leaf fall to balsam leaf fall was about 6:1. The tree leaf litter input and the total litter input figures were similar to those for other Northern Hemisphere aspen forests. The understory litter input in the study plots was measured as 99 g m−2. The importance by weight of some of the nutrients returned to the soil via tree leaf litter fall was Ca > N > K > Mg > P > Zn > Fe > Mn > Na > Cu. The total weight of these nutrients returned to the soil was 116 kg ha−1, with N, Ca, and K comprising 89% and Mg and P comprising 9.8% of the total.The dry weight loss of decomposing aspen and balsam leaves was measured at 1-, 5-, 8-, 12-, 18-, 24-, and 30-month intervals by using 3-mm-mesh litter bags, and at 12-, 24-, 36-, 48-, and 60-month intervals by using 10-mm-mesh bags. Litter-bag mesh size was of little consequence to the rate of dry weight loss for the first 12 months, but subsequent dry weight loss was greater in the 3-mm-mesh bags, which maintained higher, more representative, moisture conditions than did the 10-mm-mesh bags. However, tethered leaves lost 1.7 times more weight over the first 12 months of decomposition than did confined litter. The decay rate decline with time and with the depth of the litter bag in the litter layers, with maximum dry weight loss occurring over the period encompassing the fall freeze, winter, and the spring thaw and runoff. Leaf litter placed on north-facing slopes was characterized by significantly slower decay rates than that on south-facing slopes.The dry weight loss for aspen leaf litter was 26.2 ± 2.0% after 12 months. 40.0 ± 1.6% after 30 months, and 58.7% after 60 months (by regression): for balsam litter it was 21.2 ± 1.9% after 12 months, 37.4 ± 1.7% after 30 months, and 47.9% after 60 months (by regression). The highly leachable component of leaf litter was estimated at 23.1% for aspen and 21.4% for balsam. The time required for 99% decomposition was calculated as about 24 years for aspen and about 27 years for balsam, which gives average annual decay rates of 3.2% for aspen and 2.9% for balsam. The decay rate for Populus leaf litter was lower than that for aspen in Alaska and appeared to fit the range for deciduous leaf litter from some forested IBP Tundra Biome sites.