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原植被结构和功能的影响。1999年6月，我们建立了100 x 100 m的围栏，以排除梅西奇（Partizan）、典型（Tumentsogt）和干旱（Bayan-Unjuul）草原区牲畜放牧的影响。围栏内外各设10个永久样方。我们描述了植被的物种结构在永久样方和收获植物样品从4个0.5 × 0.5米的内，外围在夏季（7 - 8月）的1999年至2002年。1999年，在1平方米的面积内出现的物种数量在Partizan为45种，在Tumentsogt为46种，在Bayan-Unjuul为18种。1999年围栏内外植物种类组成和地上生物量差异不显著。物种-面积曲线表明，图门朝格特和巴彦-温朱尔的物种数量在2平方米处接近饱和，而游击队的物种数量仍在增加，反映出其较高的物种多样性。虽然2002年的物种组成与1999年没有什么不同，但围栏内的地上生物量和叶面积指数都高于外放牧区。减少土壤蒸发，由于凋落物的积累，以及排除牲畜放牧可能是负责较高的地上生长在围栏。物种组成随气候变化而变化。随着降水量的增加，禾本科植物在地上生物量中的比例增加，物种多样性总体下降。生物量和物种组成的年际变化可能与夏季降水量的不同有关。

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.