Study On The Law Of Growth And Development Of Natural Betula L. Stand

Natural Betula L. stand is the main part of the forest in Hebei province, and it is also one of the natural stands which are protected.. In the past national economic construction, Natural Betula L stands once played an important part. At present, Natural Betula L still acts an important role in social benefit and ecological benefit.The origin of some natural Betula L. stand is seedling. Some are sprout forest. They are widely distributed over temperate zone and frigidly temperate zone which cover the area with high elevation in the north because they like light and have cold resistance. Natural Betula L. formed as disturbed by nature and people. So they have obvious characters of natural stand:(1) They grow fast in the early period. Young stand (l-20a) grows about 0.5m on average. The index k which shows growth power of height is the largest in the early period by tuersiji formula. This shows the exuberant growth of Betula L. is in the young period. (2) They often make up mixed forest with Quercus L. - Populus, Acer mono etc, and with less Picea asperata ^ larcrK Pinustabulaeformis etc. The features of the forest appear tier upon tier. (3) Most of Betula L. natural stands are young^ middle and nearly mature stand. The result of research suggests the age structure is different in the different growth periods. But stand age almost concentrates on around average age .It forms a curve in which average stand age is the apex and the left and the right is symmetrical, so it was a shape of mountain curve with a single apex. This shows natural Betula L. in Hebei province basically belongs to the relative even-aged stand. (4) Based on stand density and competition theory, this article proposed a new stand density measurerown volume Index. (5).The diameter distribution of natural Betula L. obviously differently in different growth period. When they are young, the diameters have no much change. The average number of diameter class is 3 or 4, and most tree are concentrate in small diameter class, The diameter distribution shaped a extremely leftbias truncated normal distribution curve. When they are in middle period, their diameters change a lot. The average number of diameter class is about 8. The diameter distribution shaped a left bias nearly normal distribution curve. When they are in matured period, their diameters are completely divided. The average numbers of diameter class is up to about 10, and some up to 14. The diameter distribution shaped a gentlely (kurtosis is right) left bias normal distribution curve. This article shows law of diameter structure of natural Betula L. stand in different growth period by weibull distribution function. (6) Height and diameter of a tree are two factors to show growth in upright and cross. When they are young, the ratio of height and diameter is more than 1. It shows the fact that natural stand, especially natural sprout forest grows fast in early period. Later, with the age increasing, the ratio of height and diameter gradually reduces. In nearly mature stand and mature stand, increment of diameter is over increment of height.