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

蒙古草原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，我们在中度（Partizan）、典型（Tumentsogt）和干燥（Bayan-Unjuul）草原区建立了100 × 100米的围篱，以排除牲畜的放牧影响。在封闭的内外，每个研究地点设置了10个永久样方。在1999 - 2002年夏季（7 - 8月），我们描述了永久样方的植被种类结构，并采集了圈闭内外4个0.5 x 0.5 m样方的植物样本。1999年在1 m^2的面积上出现的物种数为：Partizan 45种，Tumentsogt 46种，Bayan-Unjuul 18种。1999年封地内外物种组成和地上植物生物量均无显著差异。物种-面积曲线显示，图们江和巴彦-云珠尔的物种数量在2 m^2时接近饱和，而游击队的物种数量仍在增加，反映出较高的物种多样性。虽然2002年的物种组成与1999年没有差异，但封育区地上生物量和叶面积指数均高于放牧区外。由于凋落物堆积导致的土壤蒸发减少以及不放牧牲畜可能是封育区地上生长较高的原因。物种组成随气候变化而变化。随着降水的减少，禾本科在地上生物量中的比例增加，总体物种多样性降低。生物量和物种组成的年际变化可能与夏季降水不同有关。

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.