Nutrient Exports Under Different Harvesting Regimes in Two Types of Larch Plantation with Different Age in Northeastern China

It has been confirmed in studies conducted in different regions and forest types that the harvesting regime has a significant impact on the export of nutrients from a plantation. Through establishing allometric growth equations and studying nutrient distribution patterns, the amounts of nutrients exported from larch (Larix spp.) plantations with different stand ages under different harvesting regimes (removal of stem wood, branches and bark (Rsbb), removal of stem wood and bark (Rsb), and removal of stem wood (Rs)) were determined in the present study. The results showed the following: 1) the organs of 20-year-old and 40-year-old larch trees exhibited basically the same nutrient distribution pattern. However, due to the difference in biomass partitioning in trees of these ages, they showed a significant difference in the cumulative amounts of nutrients in their organs. Specifically, the cumulative amounts of nutrient elements in the leaves and old branches of 20-year-old larch trees were significantly higher than in 40-year-old larch trees. However, the cumulative amounts of various nutrients in the xylem of the trunks of 20-year-old larch trees were significantly lower than in 40-year-old larch trees. 2) Compared with the Rsbb20, Rsbb40 or Rsb20 could result in significant decreases in the annual mean amounts of nutrients exported, the ratio of the annual mean total amount of nutrients exported to the annual net cumulative total amount of nutrients and the proportion of soil nutrients in the 0-30 cm soil layer. Changing the Rsbb20 to an Rsb40 or an Rs40 could further reduce the annual mean amounts of nutrients exported, the ratio of the annual mean total amount of nutrients exported to the annual net cumulative total amount of nutrients and the proportion of soil nutrients in the 0-30 cm soil layer. 3) Among the examined harvesting regimes, the Rs20 resulted in the lowest annual mean amounts of nutrients being exported. However, there was no significant difference in the annual mean amounts of nutrients exported between the Rs20 and the Rs40. The amounts of N, Ca and Mg exported under the Rs20 were slightly higher than under the Rs40, whereas the amounts of P and K exported under the Rs20 were slightly lower than under the Rs40. Hence, the harvesting regime is an important factor that results in the export of system nutrients and a decline in soil fertility. Therefore, prolonging the harvesting cycle and adopting Rs are two options for reducing the nutrients export.