Effects of Different Litter Treatments on Seed Germination and Seedling Growth of Pinus densata in Southeast Tibet, China

The aim of this study is to explore the effects of the litter cover thickness and cleaning methods on seed germination and seedling growth of Pinus densata. The overall goals are to provide a reference for the cultivation of seeds and seedlings of P. densata in Tibet and to establish a theoretical basis for the sustainable development and utilization of P. densata. Five typical P. densata forest plots have been set up in Nyingchi City, Tibet, and their litter and cones have been collected in the plots. Experiment 1 has set 0, 1, 2, 3, and 4 cm as different litter cover thickness treatments. Each thickness level has been used three times, and the seed germination and seedling growth have been recorded for each. Experiment 2 has been site preparation treatments in the sample plots: no removal of shrubs and litter, removal of herbs and litter, removal of shrubs and litter, removal of shrubs and herbs, and removal of shrubs, herbs, and litter. Each treatment has been repeated three times, and the survival rate of the seeds and the growth of the seedlings have been recorded in each case. The results have shown the following. Litter cover thickness and the interaction between the cover and the seeds have had significant effects on the survival rate and germination potential of P. densata seedlings. The lesser the litter cover, the higher the seedling survival rate has been, meaning there is a negative correlation. The root length and stem length of P. densata seedlings has first increased and then decreased with the increase of litter coating thickness. The needle length of P. densata seedlings has been relatively stable, and basically has not varied with changes in litter thickness. On the other hand, root, stem, and leaf biomass and total biomass of P. densata seedlings have varied significantly with changes in litter cover thickness. The biomass has first increased and then decreased with the increase of litter thickness. There have been significant differences in the survival rate of P. densata seeds under different cleaning methods, and the survival rate of P. densata seeds has been the lowest under the A treatment. The preserved shrubs have had the greatest impact on the survival rate of P. densata seeds and had a strong promoting effect. The root length of P. densata seedlings has reached its longest under the B treatment, and the values range has been the largest. The basal diameter of seedlings has shown a gradual downward trend moving from the A treatment to the E treatment. Significant differences in root, stem, leaf, and total biomass of P. densata seedlings have occurred under different cleaning methods.