The effect of prolonged stratification and shading on the emergence of Pseudotsuga menziesii (Mirb.) Franco seedlings

Abstract

The Douglas fir has been cultivated in Europe since the mid-19th century, but its artificial regeneration leads to a low yield of seedlings. It could be improved by prolonged pre-sowing treatment (cold stratification of seeds) or the early shading of sowings, so that their effect on five Douglas fir seed lots and their emergence and growth of seedlings were analysed. One lot came from the USA; four lots came from the Czech Republic. The germination capacity and germination rate were analysed for seed without pre-sowing treatment and seed after 21-day and 49-day stratification. The emergence rate was tested for variants of the 21-day and the 49-day stratification (shaded and unshaded treatment) and for autumn sowing (unshaded treatment). The results show that the maximal germination capacity of full seeds is achieved after the 21-day stratification. The prolonged 49-day stratification increases the germination rate, especially in seed lots with lower vitality. The biggest seedlings, in terms of length and biomass of the above-ground part and the biomass of the root system, emerged from seeds sown in autumn. The combination of the 49-day stratification of seeds and the 3-week shading after spring sowing can accelerate seedling emergence and increase the emergence rate of seedlings; seedlings achieve more biomass and length of the above-ground part, the root system compared to unshaded seedlings or seedlings emerged from 21-day stratified seeds. Comparable or better results were achieved from autumn sowing.