Abstract: Taking three ages Betula platyphylla secondary forests (20a, 36a, 82a) in Xiaoxing’an Mountains, China as test objects, this paper studied their remaining rates and nutrient dynamics from May 2009 to November 2010 by using decomposition bag method. The results of two year decomposition showed that the different ages of B.platyphylla secondary forests had a fast decomposing stage (0-150 d) and a slow decomposing stage (150-540 d). For all test litters, their remaining rate had an exponential relationship with time. The annual decomposition constant (k) ranged from 0.584 to 0.657, and the times for decomposing 50% and 95% were 1.06-1.19 years and 4.56-5.13 years, respectively. The decreasing order of litter decomposition rate of these three ages of the B.platyphylla secondary forests was 82a>36a>20a. During decomposition, the elements carbon and potassium in litter released continuously, and the concentrations of nitrogen and phosphorus increased first and then decreased, N concentration of three different ages forests was in enriched mode and P concentration was in released mode in the later period.

Key words: forest age, Betula platyphlla, litter decomposition, nutrient dynamics