Study On The Solar Radiation Environment In The Forest Of The North Part Of Ailao Mountains, Yunnan Province

Based on the observation data of solar radiation at Ailaoshan station for forest ecosystem studies from February 2005 to January 2006, and the observation data of solar radiation in and out a forest at 8 observation sites of east and west slopes of Ailao mountains in periods of September to October 2005 and March to April 2006, the observation data of solar radiation in and out the montane evergreen broad-leaved forest, the characteristics of solar radiation between in and out the montane evergreen broad-leaved forest and the influence of solar radiation by the difference of forest-type in the northern part of Ailao mountains were analyzed. The results indicated that:1. Total annual global radiation is 5247.2MJ/m~2·a. The global radiation in dry season (2802.7MJ/m~2) accounted for 53.4% of total annual global radiation and in rainy season (2444.4MJ/m~2) accounted for 46.6% of it, with 39.7%, 23.7% and 36.6% of global radiation partitioned into net radiation, reflective radiation and effective radiation respectively. It indicated that because of the influence of Southwest monsoon, the characteristics of seasonal variation of solar radiation in montane evergreen broad-leaved forest region in Ailao mountains was distinct different from it in subtropical evergreen broad-leaved forest in eastern of China; we could reckon that the higher solar radiation in dry season (low temperature) is helpful to the existence and development of montane evergreen broad-leaved forest. 2. On the whole year, the variation range of distributing ratio of net radiation is the highest, effective radiation lower and the reflective radiation is the lowest; on the daily variation, the distributing ratio of reflective radiation and effective radiation is higher in the early morning and dusk, lower in the daytimes, but the distributing ratio of net radiation is higher in the daytime, lower in the early morning and dusk. In different seasons, the distributing ratio of solar radiation components is different: effective radiation>net radiation>reflective radiation in the dry season and net radiation>effective radiation>reflective radiation in rainy season. The results show that because of the joint influences of the atmospheric circulation (southwest monsoon), the location (low latitude and high altitude) and the local climate (the distinct difference between dry season and rainy season), the montane evergreen broad-leaved forest region in Ailao mountains has special characteristics of solar radiation.3. The transmission trough the canopy of montane evergreen broad-leaved forest is 3.7%, and it's higher in dry season lower in rainy season. The ratio of total daily value of net radiation in the forest to the value out the forest is 4.3%, for the reflective radiation it's 4.3%, and 1.9% for the effective radiation in dry season; in rainy season the value of these ratios is 2.3%, 4.0%, and 3.8% respectively. These indicated that the canopy of mid mountain evergreen broad-leaved forest has notable reduced action to the solar radiation, the existence of the forest not only greatly reduce solar-radiation which reaching the forest floor, but also changed the distributing ratios of solar radiation components, and had a definite impact to the local climatic conditions.4. The variation disciplines of the difference of the percentage of solar radiation components between in and out the different forest-type in Ailao mountains were, the transmission through the canopy: Pinus kesiya var.langbianensis stands>Hot-dry vale Vegetation stands>Semi-humid evergreen broad-leaved forest>Dwarfing mossy forest > montane evergreen broad-leaved forest; the influence on the total daytime values of solar radiation components: montane evergreen broad-leaved forest and Dwarfing mossy forest> Semi-humid evergreen broad-leaved forest> Hot-dry vale Vegetation stands and Pinus kesiya var.langbianensis stands; the difference of the percentage of net radiation between in and out the forest of difference forest-types: the dwarfing mossy forest is the highest(38.80%), then the montane evergreen broad-leaved forest and Hot-dry vale Vegetation stands, the Semi-humid evergreen broad-leaved forest and Pinus kesiya var.langbianensis stands is the lowest; the difference of the percentage of reflective radiation and effective radiation between in and out the forest of difference forest-types is similar with net radiation...