Needle Decomposition and Nutrient Release in Ponderosa Pine Ecosystems
Abstract:A 34-month study was conducted in the Arizona ponderosa pine forest to determine the influence of several forest stand conditions on rate of dry matter loss and net nutrient release from a uniform substrate of decomposing pine needles. Forest stand conditions included (1) clearcut, (2) dense 54-year-old saplings and small poles, (3) large poles, (4) thinned large poles, and (5) clearcut strip through thinned poles. Needles declined steadily in mass and without treatment differences for the first 10 months of study. Thereafter, differences among treatments began to increase and after 20 months needles in cleared treatments lost weight more rapidly than those in forested treatments. Decomposition half-times for Treatments 1 to 5 were: 2.4, 4.3, 3.9, 3.2, and 2.4 years, respectively. Treatments differed in effect on nutrient losses and patterns of nutrient loss differed among nutrients. Loss of K, both initially and overall (60 percent), was highest among nutrients. N and S remained static for about 20 months, then declined to 86 percent and 78 percent of initial amounts, respectively. Loss of P averaged 40 percent and was continuous. Losses of Mg and Na averaged 20 percent; Ca increased 200 percent. Only the loss of dry matter and C could be predicted with precision. Low precision for other elements was probably the result of variation in loss rate with time, because of cyclic environmental conditions and within site variations. Forest Sci. 31:647-660.
Document Type: Journal Article
Affiliations: Research Soil Scientist, Rocky Mountain Forest and Range Experiment Station, Flagstaff, AZ 86001
Publication date: September 1, 1985
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