Age-Related Dynamics of Above-Ground Phytomass Structure of Scots Pine Plantations Aged up to 25 in the Western Khentii Mountains of Northern Mongolia

Abstract

The evaluation of forest productivity has been one of the main objectives of forest science for the last 170 years. Forest science in recent decades has highlighted the priority and significance of research aimed at identifying the most significant parameter of forest stands productivity - the mass of stem wood. Scots pine (Pinus sylvestris L.) is the main tree species, which is generally used for artificial reforestation in coniferous boreal forests of Mongolia. The research purpose was to study the age-related dynamics of above-ground phytomass structure of Scots pine plantations growing in the western Khentii Mountains of northern Mongolia. The study involved differently aged monocultures ranging from 9 to 25 years, artificially established by filling-up Scots pine seedlings. Model trees were selected from temporary sample plots (10 from each). The phytomass of each sampled tree was separated into the following fractions: dry and live branches, needles, bark and stem wood. We have found a gradual growth in tree volume with increasing plantation age, and at the age of 25 the total tree volume reached 21.8 m(3) ha(-1). A regular growth of relative proportion for stem wood phytomass fraction is observed in total above-ground phytomass with age. The relative proportion of stem wood in above-ground phytomass increased from 23.1 % (9-year old) to 47.8 % (25-year old) in the studied plantations. There is an inverse correlation for the needles phytomass fraction. Percentage of needles in the above-ground phytomass decreases from 57.7 % in 9-year-old plantations to 15.0 % in 25-year-old ones. The obtained results can be used in estimation of tree phytomass in forest plantations of northern Mongolia. Therefore, the findings of this study might be useful to develop a forest management plan aimed at improvement of forest productivity, and quality of forest conservation measures against pests and fires.