Abstract:

The stand net productivity and biological cycle of nutrient elements in the 29-year-old plantations of Chinese fir on different rotations were studied.The results indicated that along with the increasing continuous plantations of Chinese fir, biomass of tree stratum from the second and the third planting decreased by 27.39% and 44.17%, their gross biomass of stand decreased by 26.43% and 41.78%, and their net productivity decreased by 21.20% and 24.41% separately, comparing with those of the first planting.The proportion of tree stratum making up the stand net productivity declined from 77.52%(the first planting) to 49.82%(the third planting).The nutrients accumulated in the undergrowth of the second and the third Chinese fir were higher than those in their tree stratum, but the first planting was an exception.Supposing that the nutrient uptake, retention, and return in the first planted Chinese fir stand were 100% separately, nutrients uptake by the second and the third plantings were 109% and 156%, nutrient attention 103% and 162%, nutrient return 117% and 149%, respectively.The order of the nutrient cycling rate were the second planting (0.493)> the first planting (0.460)>the third planting (0.439).

Key words: Chinese fir, Continuous plantations, Net productivity, Nutrient elements, Biological cycling