Double-Cropping of Pinus sylvestris L. Containerized Seedlings under Short Growing Season Conditions at High Latitudes

The quality of forest crops significantly depends on the characteristics of the planting stock. To obtain high-quality conifer seedlings, the process of container cultivation is used and optimized and a double-cropping mode is introduced. The aim of this study has been to conduct a comparative analysis of one-year-old containerized seedlings of Pinus sylvestris L. according to morphometric parameters under a double-cropping regime under short growing season conditions at high latitudes. The experiment has been carried out in a forest nursery in southern Karelia, Russia. The duration of the first rotation (1rot) has been 146 days, the second one (2rot) – 91 days, the control one (0rot) – 132 days. The following parameters of seedlings have been determined: seedling height (SH, cm), root length (cm), bud length (mm), root collar diameter (RCD, mm), tree dry mass (TDM, g), shoot dry mass (SDM, g), root dry mass (RDM, g) and needle dry mass. The integral quality indices have been assessed, such as: shoot : root dry mass ratio (SRR) = SDM/RDM, sturdiness quotient (SQ) = SH(cm)/RCD(mm) and Dickson Quality Index (DQI) = TDM/(SH + SRR). The lowest values of seedling dry mass have been revealed in the 2rot variant. For all variants, the difference between the mean SQ and DQI values has been statistically significant at the p < 0.05 level. SRR was the lowest in the 1rot seedlings. The high correlation coefficients between the TDM and RCD for all variants confirm the high significance of the latter index. The results indicate the need to adjust the time regime and use additional agricultural practices to obtain high-quality planting stock.