Tree density and growth of Mytilaria laosensis stands with natural seed regeneration on clearcut land

To explore the effect of density on growth of young Mytilaria laosensis stands with natural seed regeneration on clearcut land, a single factor randomized block design experiment with natural spacing (ck treatment, three replications) and spaced seedling(TA, TB and TC treatments, three replications) stands was established, and variance analysis of the stands were analysed with Least Significant Difference methods in Data Processing System(14.5), to test diameter at breast height (DBH), tree height, and single volume. Results showed that:(1) between ck and spaced seedling stands, during 3.5 years after spacing, stand density significantly decreased (P 0.05). Spaced treatments(finished in 1.5 years old of seedling, remain density in hectare:TA 1 650, TB 2 800, and TC 2 500)significantly improved (P < 0.01) the average growth of the stands and reduced differentiation of diameter grades in the stands. (2) The higher stand density(ck), the earlier intersection time of the average growth curve and the annual growth curve for average DBH or tree height of the stand was appeared. Also, the peak value of annual growth for average DBH of ck stands occurred in the second year, and the peak value of spaced stands was during the second and 4th year. Before the 5th year, it was fast growth period for the stands with natural seed regeneration, so spacing was very important with radial growth of the stands. (3) The time of intersection for curves of average growth and annual growth of tree height in the ck stands was between the second and third year, but with the spaced stands did not intersect before the 5th year. Growth for tree height of dominant trees in all stands before the 5th year was fast(the annul increment of top height in each treatment was more than 1.49 m in each year). (4) Different types of stands had different diameter distributions; the ck stand had an inverted J distribution, but the spaced stands had an approximately normal distribution. (5) In the spaced stands, after 3.5 years, the average growth for DBH, tree height, and volume of less dense forest stands(TA treatment stands) was better than those with higher density treatments(TC or TB stands). Thus, understanding of the mature period for seeds, the seed falling-stage, and natural regeneration characteristics of Mytilaria laosensis could enhance the scientific cutting time, cutting methods, clean ways for removing residues, shrubs, and herbaceous plants, and methods for spacing seedlings to enable effective natural regeneration on cutover land thereby promoting forest growth.