Effects of climate and nomadic activities on the development of grassland vegetation in Mongolia

蒙古草原一直受到传统游牧活动的强烈影响。研究了气候和游牧活动对草地植被结构和功能的影响。1999年6月，我们建立了面积为100x100米的围栏，以排除梅西奇(游击队)、典型(图门索格特)和干旱(巴扬-昂朱尔)草原地区牲畜的放牧影响。在围栏内外，每个研究地点都设置了10个永久性样本。我们描述了永久样地的植被种类结构，并于1999年至2002年夏季(7-8月)在围栏内外采集了4个0.5x0.5m的样方的植物样本。1999年，在1m^2的面积内出现的物种数量在游击队为45种，在图门索格特为46种，在巴彦昂珠尔为18种。1999年，围栏内外的物种组成和地上植物生物量没有显著差异。物种面积曲线表明，图门索格特和巴彦昂珠尔的物种数在2m^2处接近饱和，而游击队的物种数仍在增加，反映了其较高的物种多样性。虽然2002年的物种组成与1999年没有差异，但围栏内的地上生物量和叶面积指数都高于围栏外的牧区。由于凋落物积累和禁止放牧，土壤蒸发量减少，这可能是围栏内地上生长较高的原因。物种组成随气候变化而变化。随着降雨量的减少，禾本科植物在地上生物量中所占比例增加，物种多样性总体下降。生物量和物种组成存在年际差异，可能是由于夏季降水不同所致。

Mongolian grasslands have been under strong influence of the traditional nomadic activities. We studied how the structure and function of grassland vegetation are influenced by the climate and nomadic activities. In June 1999 we established exclosures with a dimension of100 x 100 m to exclude grazing effects of livestock in mesic (Partizan), typical(Tumentsogt) and dry(Bayan-Unjuul) steppe zone. Inside and outside of the exclosure, ten permanent quadrats were set at each study site. We described species structure of vegetation in the permanent quadrats and harvested plant samples from four 0.5 x 0.5 m quadrates inside and outside of the exclosure in summer (July - August) of 1 999 through 2002. The number of species appeared in an area of 1 m^2 in 1999 was 45 at Partizan, 46 at Tumentsogt and 18 at Bayan-Unjuul. There was no significant difference in the species composition and aboveground plant biomass between inside and outside of the exclosure in 1999. Species-Area curves indicated that species number nearly saturated at 2 m^2 both at Tumentsogt and Bayan-Unjuul, while it was still increasing at Partizan reflecting its higher species diversity. Although the species composition in 2002 was not different from that in 1999, aboveground biomass and the leaf area index were higher in the exclosure than the outside grazing zone. Reduction in soil evaporation due to litter accumulation as well as exclusion of livestock grazing were probably responsible for the higher aboveground growth in the exclosure. Species composition changed with climate. Proportion of gramineae in the aboveground biomass increased and overall species diversity decreased with Bowing of precipitation. There were year-to-year variations in biomass and species composition probably owing to different summer precipitation.