Controlled restoration of forest ecosystems on sandy technogenic substrates in the far northern taiga of the Russian European Northeast

Abstract

Effective methods for restoring damaged areas are required now due to the recent intensification of natural resource extraction in the north of the taiga zone of the European northeast of Russia. However, approaches of forest recultivation for this region are still under development. The aim of our research was to justify planting of trees simultaneously with creation of an artificial herb cover from perennial grasses. We started an experiment including trials with planting of Pinus sylvestris L. (seedlings and large wide trees), without tree planting and with simultaneous planting of perennial herbs and application of organic and mineral fertilizers. Care of artificial communities included addition of plantings. In trials with herbs, it included addition of mineral fertilizers (See Table 1). The experimental plot was laid at a dry sandy quarry in the far northern taiga (66°1643'N, 57°16'41''E). We studied the dynamics of biometric parameters and phytopathological state annually during eight years in tree plantings. We also estimated the projective cover and mean tree height. The aboveground phytomass was assessed by hay cutting, and the underground phytomass was by a monolith approach. It soil samples, we determined potentiometric water pH, organic carbon and nitrogen by gas chromathography; labile potassium and phosphorus by Kirsanov's approach and exchangeable Ca2+ and Mg2+ by the displacement by NH4Cl followed by atomic absorption analysis. Population of soil microorganisms was studied by diluting soil suspension followed by inoculation in standard media. In order to estimate the significance of differences in the trials, we used single-factor analysis of variance and a two-sample t-test with different variances. Creation of pine cultures by local large wide trees with ground lump accelerated the formation of a tree layer in comparison with the use of seedlings (See Tables 2-6). In the trials without agricultural approaches, there was no vegetation cover and changes in the sandy substrate (See Tables 7 and 8). In the trials including tree and perennial herb planting with mineralization, a constant increase in the projective cover and phytomass was detected for the artificial herb layer, but this herb layer degraded quickly when these additions were stopped (See Fig. 1 and 2a). Due to this addition, by the 8th year of controlled succession, over 780 g/m2 of plant matter had been accumulated at the plot, the sandy substrate had been consolidated and its water-chemical and agrochemical properties had improved (See Table 7), biogeneity had increased (See Table 8), vascular plants had been implanted more actively and the moss layer formed by pioneer species had covered up to 70 % of the surface. In the trial with the average developed herb layer (phytomass about 170 g/m2), by the 8th year of the experiment, the medium height and livability of pine cultures had been higher (p=0.05) than in other trials with seedlings. The livability and growth rate of seedlings in the trials with a well-developed herb layer (phytomass about 300 g/m2) did not differ from the trial with seedlings without fertilizers. Therefore, in order to consolidate the sandy technogenic substrate and to accumulate organic matter, on the one hand, and to reach a suitable pine growth rate, on the other hand, it is good to create a herb layer with phytomass about 150-200 g/m2