灌丛化对黄土高原草地植物群落结构和地上生物量的影响

中国北方草地普遍出现灌丛化现象,灌丛化改变植物群落结构、植物多样性和生产力,直接影响着草地生态保护与可持续利用。该研究以黄土高原灌丛化草地为研究对象,通过植被调查,分析比较不同坡向的灌丛斑块与禾草斑块植物群落结构(物种组成、优势种及物种多样性)和地上生物量的差异。结果发现:(1)灌丛化草地不同坡向对物种多样性及地上生物量均无显著影响(P 0.1),但不同斑块植物群落结构(P=0.001)及地上生物量(P0.001)存在显著差异。(2)灌丛化草地共出现植物29种,其中禾草斑块有27种,灌丛斑块有18种;灌丛化显著改变了植物群落的物种组成,优势种由长芒草(Stipa bungeana)更替为矮脚锦鸡儿(Caragana brachypoda),且灌丛化降低了草地物种丰富度,增加了群落均匀度。(3)灌丛化显著改变了草地地上生物量,其中灌丛斑块地上生物量较禾草斑块地上生物量增加251.2 g·m~(-2),灌丛斑块中灌木/半灌木地上生物量提高了452.1 g·m~(-2),多年生丛生禾草减少了176.5 g·m~(-2),其余功能群植物的地上生物量减少了24.4 g·m~(-2)。(4)灌丛化过程(从禾草斑块—灌丛斑块)中,植物种丢失对地上生物量减少的影响较小,新增物种和群落优势种更替促进了灌木斑块地上生物量增加;虽然灌丛化导致草地地上生物量增加,但植物物种丰富度降低和优势种更替很有可能改变草地多样性和稳定性维持机制。

Effect of Shrub Encroachment on Grassland Community Structure and Above ground Biomass on the Loess Plateau

Shrub encroachment is widespread in the grasslands of northern China. Shrub encroachment changes the plant community structure, plant diversity and productivity, which directly influence the grassland conservation and its sustainable utilization. This study elucidated the differences of plant community structure and above ground biomass between shrub and grass patches with different slopes which formed after shrub encroachment on the Loess Plateau. We observed species composition, species diversity and above ground biomass in these patches. The result showed that: (1) there are significant differences in plant community structure (P = 0.001) and aboveground biomass (P < 0.001) in shrub patches and grass patches. But there is no significant effect in different slopes (P > 0.1). (2) In shrub encroched grassland, we found 29 species, of which 27 species were found in grass patches and 18 species in shrub patches. Shrub encroachment significantly altered species composition. The dominant species Stipa bungeana was replaced by Caragana brachypoda in shrub patches. The species richness was lower than that of grass patches, but the community evenness was increased. (3) The above ground biomass of shrub patches was higher 251.2 g·m^-2 than that of grass patches. In the shrub patches, the above ground biomass of shrubs and semi shrubs were increased by 452.1 g·m^-2, perennial grasses decreased by 176.5 g·m^-2, and other functional groups decreased by 24.4 g·m^-2. (4) The loss of species has less negative impact on the above ground biomass. However, the newly emerging species and dominant species promoted the above ground biomass. Although shrub encroachment have improved the aboveground biomass, its negative effect of species richness and shift in dominant species may change the maintaining mechanism of palnt diversity and community stability.