退化梭梭林禁牧封育周期的研究

对阿拉善荒漠地区不同时间（2005年、2002年、1999年和1980年）禁牧围封梭梭生态特征进行了对比研究。生态特征分析表明7年封育梭梭恢复效果最好，梭梭盖度达到了22．6％，密度增加到每公顷594株，生物量提高到每公顷12．01吨。而25年围封梭梭林密度、盖度和生物量均低于7年封育。年龄结构分析表明1年、4年和7年禁牧封育梭梭均发展趋势，而25年禁牧封育梭梭呈现衰退趋势。动态模拟分析表明通过禁牧封育，干旱区退化梭梭林恢复最佳周期14年，生物量达15．3吨／公顷，盖度28％，密度高达770彬公顷。

Timing The Recovery High - Point of Degenerted Haloxalon Ammodendron Woods by Enclosure and Grazing Prohinbition

Aims Natural restoration by enclosure and grazing prohibition is an effective way to recover the degenerative vegetation of Haloxylon ammodendron. It, however, remains unknown of the speed and time of restoration to the best status of Haloxylon ammodendron vegetation. The enclosure of Haloxylon ammodendron vegetation in Lamajing, Alax of Inner Mongolia, was singled out to investigate the time for best restoration of Haloxylon ammodendron vegetation by an analysis of ecological features of Haloxylon ammodendron vegetation in differ- ent duration of enclosure. This study can provide scientific bases for the project of restoration of Haloxylon ammodendron vegetation and return grazing to grasses. Methods According to duration of enclosure time, sample plots were divided into four sample plots, viz. 1980, 1999, 2002, and 2005 sample plots. Four samplesquares are designed in the four sample plots under relatively consistent conditions of soil and topographic shape, area for each sample - square is 40m × 40m. Biomass, density, height, and coverage of Haloxylon ammodendron vegetation of the four sample plots were measured. The duration for best restoration of degenerated Haloxylon ammodendron vegetation was calculated using regression analysis based on data collected. Important Findings A numerical analysis indicates that the Haloxylon ammodendron veg- etation recovered best by 7 years of enclosure and grazing prohibition, the coverage of Haloxylon ammodendron is up to 22.6% , the density is up to 594 individuals per hectare, the biomass is up to 12.01 kg. The density, coverage, and biomass of Haloxylon ammodendron vegetation by 25 years of enclosure and grazing prohibition are inferior to those by 7 years. An analysis on age structure indicates that the Haloxylon ammodendron vegetation shows a developing tendency within 1, or 4, or 7 years of enclosure and grazing prohibition while the vegetation shew a degenerating tendency in 25 years Of enclosure and grazing prohibition. A dynamic modeling suggests that the time fo