Long-term ecosystem effects of sand-binding vegetation in the Tengger Desert, northern China

Summary

Establishment of sand-binding vegetation is one of the main techniques used in ecological restoration in sandy arid zones. This method has been widely used in arid desert regions as a way to combat desertification. The planting of sand-binding vegetation in the Shapotou region at the southeastern edge of the Tengger Desert, northern China, began in 1956 to insure unhindered operation of the Baotou–Lanzhou railway. This case study describes the ecological changes that occurred over 46 years as a consequnce of this dune stabilization mangement.

Study area:  A 'vegetation protection system'  to stabalise sand dunes was established along 16 km of the railway line in 1956 at Shapotou (1,339 m), Ningxia Hui Autonomous Region. This steppe desert zone has natural vegetation dominated by slenderbranch sweetvetch Hedysarum scoparius and squarrose agriophyllum Agriophyllum squarrosum (approx. 1% cover) and is characterized by high barchan dunes. The substrate is loose, impoverished, moving sand.

Initial sand stabilization and  planting: Protective belts were established along the line; on the north side 500 m wide and to the south 200 m wide. The first stage involved installation of ‘sand barriers’ made of woven willow Salix branches or bamboo to act as a windbreak. Behind this barrier, straw checkerboards (1 × 1 m) were inserted to a depth of 15–20 cm above the dune surface. This windbreak remained intact for 4–5 years, and allowed xerophytic plants to establish. A number of native shrubs were planted inside the checkerboards e.g. Korshinsk peashrub Caragana korshinskii, Ordos wormwood Artemisia ordosica and H.scoparium.

Plant monitoring: Monitoring was undertaken at five different-aged sites planted with sand binding vegetation (1956, 1964, 1973, 1982, and 1992) and at a control site (moving sand dune, no planting). To record plants, 10 quadrats were established in each of the five planted sites along the 500 m wide area north of the line. Species, height and cover, thickness of microbiotic crusts, topsoil and litter fall was recorded. To measure algal and cyanobacteria species, 10, 0.25 m² plots were established in the five areas in a hollow between stabilized sand dunes and compared with the control. For mosses, an adjacent naturally fixed sand dune was chosen as a control plot.

Insects sampling: Insect diversity was assessed by netting and manual catch, and night lamp catch methods. Five replicate samples were conducted in moving dune plots before the establishment of sand-binding vegetation in the summer of 1956, and in the vegetated areas in the summer of 1982 and 2001.

Bird surveys: Line transects were used to survey birds and provide density estimates. Surveys were carried between May and July. Birds were recorded in a 200 strip along each 10 km in vegetated areas. The adjacent steppe desert was surveyed in 2001 for comparison.

Soils sampling: Soil water content, soil water variation, soil bulk density, soil particle size, pH, soil organic matter, soluble salts; total nitrogen, phosphorus and potassium were measured using standard methods.

Wind: Wind speed was measured at 20 cm above the surface using an anemometer in spring (10 days between March and April in 2001).

Vascular vegetation: Vegetation gradually increased over time. After 40 years of revegetation, species composition tended toward a relatively balanced state (species number varied between 12 and 14). Among those that established were Artemisia ordosica, and annuals e.g. little lovegrass Eragrostis poaeoides, divaricate bassia Bassia dasyphylla, tickseed Corispermum sp. Russian thistle Salsola rutherica and three-awn-grass Aristida adscensions.

Cryptogam diversity: Within 4–5 years of establishment of sand-binding vegetation, the physical surface structure of the dunes stabilized and microbiotic soil crusts formed, comprising cryptogams such as desert algae and mosses. In the 46 years since establishing sand-binding vegetation, some 24 algal species have been recorded in the crusts. Four years after revegetation two diatoms, Pinularia microstaucon and Hantzchia amphioxys var. capitata and three cyanobacteria, Lyngbya martensiana, Hydrocoleus violacens and Phormidium amblgum occurred in the surface layer of fixed dunes. Twenty years later 14 algae were identified, and 46 years later 24 algal species were found. Algal diversity in microbiotic crust steadily increased with time, but by 38 years the increase in algae slowed and reached its peak, algal cover reaching up to 50–55%.

Like the algae, replanted vegetation promoted the colonization of mosses in the area, but compared with algae, moss species showed little change in diversity overtime. Four years after revegetation, Byum argenteum occurred in crusts in places such as interdune depressions. However, after 46 years of succession, only five moss species occurred in crusts, this less than 50% of the moss species in naturally fixed sand dunes.

Insect diversity: Only 10 common insect species were found in the control site, including the most drought-resistant, heat-resistant and hunger-resistant species, Sternoplax sp. and Anatolica potauivi, owing to the sparse vegetation in the moving sands. As vegetation succession progressed, insect species increased (34 species found in the 20 year old vegetation and 50 in the 46 year old vegetation).

Bird diversity: Eleven bird species were found in the 30 year old vegetation-fixed dune areas in summer, with a density of 21.6 birds/km². The commonest were: red-tailed shrike Lanius cristatus speculigerus and saxaul sparrow Passer ammodendri. In the 42-year-old vegetation, there were 33 bird species, with a density of 18.6 birds/km², including three granivores: rufous turtle dove Streptopelia orientalis, hill pigeon Columba rupestris and collared dove Streptopelia decaocto; commonest species were again saxual sparrow and red-tailed shrikes. In the 46-year-old sand-binding vegetation area, there were 28 species, with a density of 18.9 birds/km². Additional species included oriental greenfinch Carduelis sinica and Pallas' sandgrouse Syrrhaptes paradoxus.

Soil and wind:  Near-surface wind velocity in the 46-year-old vegetation area was reduced by 54% compared with that in the moving dunes; soil organic matter increased from 0.06% in moving dunes to 1.34% in the 46-year-old vegetation area; the main soil nutrients (N, P, K etc.) increased; soil physiochemical properties improved; and soil-forming processes occurred in the dune surface layer.

Conclusions: Planting and establishment of sand-binding vegetation promoted the improvement and restoration of a steppe desert ecosystem.

The restoration initiated successional processes with according increase and changes in cryptogam, vascular plant, insect and bird species diversity. This restoration effort shows the potential over the short-term to influence environmental variables through increasing plant cover via vegetation planting and establishment.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/journal.asp?ref=1061-2971