Ma Quanlin

Spatial and temporal dynamics of Tamarix forest in the peripheral areas of the Minqin Oasis

Species in genus Tamarix are widely used for wind breaks and desertification control. Tamarix spp. have played an important role in protection and improvement of desert environments of the Minqin Oasis. However, during past five decades, the succession of Tamarix forests in the peripheral areas of Minqin desert showed a direction towards more and more arid communities, due to the effect of successive drought. The succession process in the targeted area was summarized as follows: Tamarix spp. + Kalidium spp. (or Karelinia caspica) or Tamarix spp. + Elaeagnus spp., Populus euphratica or P. simonii rarr Tamarix spp. + Reamuria soongorica rarrTamarix spp. + Nitraria spp. or Tamarix spp. + Nitraria spp. + Haloxylon ammodentron (artificial)rarrNitraria spp. or Nitraria spp. + Haloxylon ammodentron(artificial). In general, community species changed from mesophytes to xerophytes and further to super-xerophytes as climax, which implied a process of land degradation. With the development of the succession, the number of xerophytes and super-xerophytes increased, the Tamarix forest belt became narrower, height of the Tamarix spp. became lower, the community shrank and its coverage decreased. Consequently, the function of sand stabilization and wind breaks of the forests largely reduced. All of the Tamarix forests around the three major cropping areas of the Minqin Oasis showed degradation. The forests at Baqu (at upper reaches) most seriously degraded, with remaining width of 30-75 meters of the forest belt. This belt survived depending on the extravasating water from irrigation. This belt was in its final stage of the succession of Tamarix community in Minqin desert. The Tamarix forests in Huqu (lacustrine area) degraded least among the three types. The width of the remaining forest belts reached 200-1,000 meters. The degradation of the forest belt in Quanshan area was in between.

The succession and spatial structure of vegetation on desertified land in arid area

It is well known that man-assisted revegetation is one of the most effective methods to stabilize sand dunes, promote biodiversity, reduce the damages of desertification and hence reverse the course of desertification. The objectives of this study were to monitor the succession and changes in spatial structure of the vegetation after establishment of revegetation on windward sand dunes in arid area of Northwestern China, where the average annual rainfall is 160 mm. Field observations revealed that during the past 20 years, the main vegetation community has undergone a series of changes from herbages to herbages + Hedysarum scoparium to herbages + H. scoparium + Artemisia ordosica to Artemisia ordosica + herbages. In the diluvium and alluvium based sandy areas where the Nitraria tangutorum was the dominant species, the vegetation have had the succession from Nitraria tangutorum + herbages to Nitraria tangutorum + herbages + Artemisia ordosica to Artemisia ordosica + herbages + Nitraria tangutorum to Asterothamnus centrali + Stipa gobica + Artemisia ordosica. It is clear that, with the degradation of the man-assisted revegetation, e.g. H. scoparium, the natural species, such as Artemisia ordosica and herbages have dominated the communities. With the succession of the dominant species, the spatial structure of the plants has tended to concentrate to the height of 20-60 cm. Results revealed that the feasibility of sand dune fixation not only relates to the coverage of vegetation, but also to the spatial structure of the plants.