STRATIFICATION OF SOIL ECOLOGICAL PROCESSES - A STUDY OF THE BIRCH FOREST FLOOR IN THE ALASKAN TAIGA

In the forest floor of Alaskan taiga, annual layers of Equisetum (hors etail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during June-September 1993. Forest floor m aterial was separated into each of the three most recent litter cohort s, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age) and over the growing seas on. Nitrogen mineralization potential increased with depth, and fluctu ated over time. Microbial biomass did not vary with depth, but did inc rease greatly in September in conjunction with increased litter moistu re. Litter C:N ratio decreased with time and varied with depth accordi ng to the year-to-year variation in litter chemistry. We present a con ceptual model of the forest floor describing microbial activity on a l itter cohort as controlled primarily by litter chemistry, but modified by the vertical position in the forest floor and seasonal climatic va riation. Litter quality was the main factor associated with changes in microbial activity with season and down the soil profile. Microbial a ctivities occurred within an environment controlled by the climatic bu ffering of the decomposing leaves themselves. As the quality of litter as a substrate decreased with depth, the quality of the environment f or microbial activity increased. Yearly precipitation cycles also play ed a role in controlling soil biomass and activity.