Temporal-spatial Variation In Climatic Variables And Ecological Implications In The Longitudinal Range-gorge Region, Southwest China

One of the most significant intellectual challenges to ecologists and biogeographers is to understand spatial patterns in biodiversity. Identifying the potential effects of climate change on plant species richness has become the focus of ecological research. Five mountains in LRGR were selected. Xishuangbanna belongs to the tropical area. Ailao mountains, Wuliang mountains, Gaoligong mountains and Baima snow mountains are subtropical mountains. The elevation patterns of species richness, area and climatic variables are analyzed. This study has explained the variation in species richness patterns along the elevation gradients by climatic variables and explored the potential effects of climate change on plant species richness along elevation gradients. The results have shown that:Annual variation of air temperature and soil surface temperature of mountains at different latitude in LRGR decrease monotonically with increasing elevation, and have positive relations with latitude. Annual variation of soil surface temperature is larger than annual variation of air temperature at the same station. Average relative humidity is larger than seventy-five percent in the rainy season and larger than sixty percent in the dry season. The patterns of annual variation of precipitation are unimodal. A major feature in the LRGR region is the clear-cut changes between the two seasons: the dry season (November-April) and the rainy season (May-October). Precipitation of the rainy season makes more than seventy percent of the whole year. In general, air temperature, soil surface temperature and relative humidity are higher from May to October, and are lower from November to April. The main climate condition in the LRGR region is that more energy and precipitation present to the same period. With the parallel elevation, the east slope receives more energy inputs than west slope, and water condition of west slope is better than the east. Lapse rates of air temperature are between 0.54℃/100m and 0.78℃/100m. Lapse rates of soil surface temperature fall into the range between 0.62℃/100m and 0.66℃/100m. Lapse rate of air temperature has a positive relationship with latitude and is larger on the east slope than that on the west slope. Lapse rate of air temperature and soil temperature are very different in monthly and seasonal scale and it is bigger in the rainy season and hottest month than it in the dry season and coldest month. Precipitation has a positive relationship with increasing elevation, maximum precipitation-elevation is not observed. Except for Gaoligong Mt., precipitation tends to decrease with increasing latitude. Lapse rates of precipitation also show the same pattern and it's larger on the east slope than it on the west. Except for Xishuangbanna, relative humidity increase with increasing elevation and the lapse rates are larger on the east slope.The field station on the mountaintop is experiencing remarkable temperature increase. Air temperature increases significantly at all the stations owing to the increase in the dry season and the incremental rate is biggest in the dry season, moderate for the whole year and the least in the rainy season. The incremental rate in the hottest month is faster than that in the coldest month and the difference of air temperature in annual scale shows a downward trend. There is also a remarkable increase in the∑t≥0℃accumulative temperature and∑t≥10℃accumulative temperature. The lapse rate of air temperature shows a statistical significant upward trend on the windward slope (west) and it has a slight increase on the leeward slope (east). Precipitation tended more or less to increase owing to the increase in the rainy season. Comparing to the west valley, the east valley is experiencing a much hotter period, then it comes to the mountaintop.Based on sample data, the patterns of plant diversity of trees and shrubs along elevation gradients are hump-shaped, the maximum values of height, DBH and biodiversity index present to the transition between mid-mountain humid evergreen broad-leaved forests, monsoon evergreen broad-leaved forests and semi-humid evergreen broad-leaved forests. Plant diversity of herbs tend to decrease with increasing elevation. Maximum total Shannon-Wiener index and species richness (including herbs, shrubs and trees) are observed at 2000m. With the parallel elevation, biodiversity index is higher on the west slope than it on the east slope and biodiversity index of monsoon evergreen broad-leaved forests is higher than that of semi-humid evergreen broad-leaved forests, the minimum biodiversity index is observed in dry and hot valley vegetation. There are two obvious transition of similarity index along elevation gradients, one is between monsoon evergreen broad-leaved forests, semi-humid evergreen broad-leaved forests and mid-mountain humid evergreen broad-leaved forests, the other is between dry and hot valley vegetation and semi-humid evergreen broad-leaved forests.The patterns of species richness along elevation gradients can be divided to two types in LRGR. Species richness is higher in the lowlands and then decreases monotonically with increasing elevation in the tropical mountains and has unimodal relationships with elevation in the subtropical mountains. The elevation peaks in family richness, genus richness and species richness of seed plants emerge at higher elevation in the mountains with the increasing latitude. The patterns of fern species along elevation gradients are hump-shaped in Xishuangbanna, Ailao Mt. and Baima Snow Mt.. Elevation peaks of fern species are higher than that of seed plants. The patterns of species richness based on elevation mid-point show good agreement with the results from those based on interpolation. Elevation ranges of species are narrower at both the tops of mountains and the bottom of the gradients, wider elevation ranges are observed at the middle of the gradients.As the patterns of area and species richness along elevation gradients are not the same in Xishuangbanna and species richness does not peak at the elevation where the area is largest for all the five mountains. After adjusted of its area, the patterns of species density are the same as that in species richness along elevation gradients. So the effect of area on the patterns of species richness along elevation gradients is not remarkably. Among the climate variables, actual evapotranspiration (AET) as a measurement of water-energy balance has strong relationships with species richness. The decline in species richness is due to the higher temperature and less precipitation in the lowlands of the subtropical mountains. Species richness decreases significantly with increasing MI as the reinforcements of the arid climate conditions in the lowlands of the subtropical mountains.Water-energy balance should be an exclusive elucidative climatic variable for the distributive ranges of vegetation type. Air temperature increased significantly at all the locations of the mountains and the valleys are experiencing a much more severe dry and hot period especially in the dry season. Climate change would be expected to affect species distribution along the whole elevation gradient as the reinforcement of the"inferior"climatic conditions (temperature increase and drought development), but the intensity would not be uniform among different locations in the mountains. As a result of climate change, plant species may be pushed upwards along elevation gradient and may be eliminated if already at mountains'summit. Based on the"Species-Energy Theory", species richness may decrease in the lower part of the mountains. Some species with narrow elevation ranges currently found in the valleys may be extinct.