Natural regeneration potential of the black saxaul shrub-forests in semi-deserts of Central Asia - the Ili River delta area, SE Kazakhstan

摘要

Two saxaul species black saxaul (Haloxylon aphyllum Minkw.) and white saxaul (Haloxylon persicum Bunge) constitute the principal arboreal cover of the cold continental deserts of Central Asia. While the latter is a rain-fed shrub distributed on sand dunes, the former is a ground-water phreatophyte mainly found on alluvial terraces. Saxaul has played an important role as a fodder plant also used as firewood by local herders. Due to over-grazing and over-exploitation for fuel during the past fifty years, the once dominant saxaul vegetation has considerably degraded. Important growth characteristics at the present plantations (such as height, and basal trunk and crown diameters) show a direct quantitative relationship between the plants' age up to the 25-year lifetime and the total tree biomass reduced by natural degradation. Annual productivity largely depends on the overall vegetation density that reflects specific environmental conditions at particular locations. The recommended harvest rate, balancing the calculated natural regeneration capacity, should not exceed 0.82 t/ha at the density of up to 900 shrubs/ha, 1.78 t/ha at the density of 900-1500 shrubs/ha and 2.63 t/ha at the density of 1500-2000 shrubs/ha. The results from the field monitoring sites provide new insights on the natural reproductive potential of black saxaul shrub-forests in undisturbed versus anthropogenically affected and exploited semi desert and parkland settings of Central Asia.