Study On The Impacts Of Forest Cutting And Fire Behvior On Generation And Species Group Structure Of Dahurian Larch

By investigating the situations of dahurian larch forest in the Daxing抋n Mountain areas, six problems as the following: the impacts of forest cutting on species group structure, the relations of crowns disturbance and natural generation, forest cutting methods and generation measures of dominant forest style, ecological skidding modes, the impacts of fire behavior on species group structure of dahurian larch and the mixed forest of birch and larch, are studied in this paper. The experiment sites distributed in Huzhong Forestry Bureau, Huzhong National Nature Protection District, Tahe Forestry Bureau, Amuer Forestry Bureau and Jiagedaqi Forestry Bureau in Daxing抋n Mountain areas. According to the middle disturbance and climax community theories, combined the investigation of temporary sites with the test in position sites and data analyzed by using the SAS software, the results show as the following: (1 )crown disturbance. By investigating the forest styles of dahurian larch with alder, birch, brushes and ledum, the average diameter of dying trees in these forests is 19.1cm, the average diameter of blow-down trees in these areas is 30.4cm and the average diameter of wind broken trees is 24.8cm. The proportion of middle timbers in wind broken trees is respectively: 87.3% in larch-birch forests, 67% in larch-alder forests, 59% in larch forests with ledum and 75% in larch forests with brushes. The proportion of large timbers in blow-down trees is separately: 69% in larch-alder forests, 60% in larch forests with ledum, 71% in larch forests with brushes and 45% larch-birch forests. The generation effects in Daxing抋n Mountain areas are better. The quantity of seedlings is 9000 per hectare. From the age scope and total amount, the species group of seedlings under forest crowns has stability. (2)ecological skidding modes: According to the characteristics of forest resources scattered in Huzhong Forestry Bureau, a new style skidding method was presented. The new technology changed the settled frame loading to mobile hydraulic crane loading and changed the settled loading depot to mobile loading point. The loading method can lessen the skidding distances, increase the economic benefits and decrease the disadvantage impacts of skidding on forest ecological environment. (3)the technical points of improving quality of natural generation: Generally, to improve quality of the natural generation must content with the following conditions: over 30 seeds per square meter in the effective period of holes, having 0.3~0.5 vegetable shades, below 150 of slope facing the sunlight, below 200 of slope against sunlight, not planting seeds on the areas with low wateriness and exposed stones, planting seeds in August and September. Because of the periodicity of seeding of dahurian larch, thoroughly plowing must be used to last the effective period of holes and to accumulate the falling seeds to increase the survival ratios of seeds. The experiment shows the way of thoroughly plowing is feasible and practical. (4)clear cutting method: To improve the generation quality after cutting, the clear cutting areas are less to 5 hectare and the intensity is 40?0% of forest stand volumes. If the conditions in cutting sites are better, the areas of clear cutting may be 15 hectare. (5)rules and trends of forest succession in Daxing抋n Mountain areas: succession of dahurian larch keep the original succession and form the stable forest community without the exotic disturbances. The unreasonable forest cutting will change the rules of forest succession if the positive actions are no...