过牧及封育对红砂荒漠植被演替的影响

红砂灌丛植被是我国西北荒漠地区的主要放牧地,并在生态保护中具重要作用。本试验以内蒙古阿拉善盟不同过牧强度下的退化(轻度、中度和重度)红砂(Reaumuria soongorica)+无芒隐子草(Cleistogenes songorica)荒漠草地为对象。首次研究报道了不同过牧梯度和围栏封育对红砂植被演替的影响。经过6a过牧(平均1.8只羊·hm^-2),植被总盖度已由12%降至8%,平均每年盖度绝对值下降0.7%。随草地过牧加重红砂灌丛在逐渐消亡,在中度和重度退化样地的盖度已分别较轻度样地(7.5%)下降了74%和84% (P<0.05);质量差或产量低的草本在增加;无芒隐子草和匍根骆驼蓬(Peganum nigellastrum)的增加可分别作为该类草地中度和重度过牧演替的指示种。短期封育效果十分显著,封育一年的各样地平均较放牧样地比,植被盖度绝对值提高了1.7%,产草量增加2188%,红砂种子产量是放牧样地的371倍。然而,优势种红砂的产草量和盖度在封育期的相对恢复速率皆随样地退化加重而显著降低(P<0.05),重度退化区盖度封育当年的恢复速率为0。所以,封育是保护和恢复我国红砂荒漠植被的有效措施,但封育宜尽早开始,否则,红砂将恢复缓慢或难以复存。

Affects of Over Grazing and Enclosure on Desert Vegetation Succession of Reaumuria soongrica

Desert shrub land with Reaumuria soongrica as the dominant or edificator species is one of the main grassland types in the northwest of China. It plays an important role in environmental protection. Affects of different over grazing intensities and enclosure on vegetation succession of Reaumuria soongrica Cliestogenes songorica grassland at Alxa region, Inner Mongolia, were reported in this study. The total vegetation coverage had reduced to 8% from 12% during the last 6 years. As grassland degraded (light, medium and heavy degradation), the R. soongrica shrubs were gradually decreased, it s coverage at medium and heavy degraded regions were 74% and 84% of that in the light degraded region respectively, where the cover was 7.5% (P<0.05). Accordingly, the herbs with lower yield or poorer feeding value were increased. The increasing of C. songorica and Peganum nigellastrum could be the indicators for the medium and heavy degradation grasslands, respectively. Significant effects of vegetation restoration were obtained from short time fencing without grazing. One growing season after fencing, the average vegetation cover increased by 1.7% and forage yield increased by 218.8%, compared to that of open grazed, and seed yield of R. soongrica was 371 times of grazed paddock. However, during the fenced period the relative restoration rates of the dominant species R. soongrica were increasingly reduced (P<0.05) both in coverage and yield as the grassland degradation become heavier. And restoration rate was zero at the heavy degraded paddock. Therefore, the fenced non-grazing technique is an effective approach to restore and protect the R. soongrica desert grassland, however, the fencing work need start as early as possible, otherwise, the restoration of R. soongrica vegetation will be either very slow or impossible.