Abstract:

Aims Vegetation is the fundamental measure to control erosion in the Loess Plateau. It is believed that forests use more water than grasslands and hence reduce average annual streamflow; however, the spatial distribution of vegetation restoration and its impacts on annual streamflow, especially on the regional scale, are poorly known. Our objectives were to map the vegetation suitability in the Hekou-Longmen (Short with He-Long) region of the middle reaches of Yellow River and assess the impact of afforestation on streamflow based on two plantation scenarios.
Methods We assumed 1) the combined effects of bio-climatic zones on regional scale and local landform determined vegetation suitability, 2) higher precipitation is more suitable for plantations and 3) the extent of soil moisture availability defined by three local factors (slope, aspect and slope profile) depends on precipitation. We defined high, moderate and low vegetation suitability classes and developed a vegetation suitability map for the region using 100 m Digital Elevation Model (DEM) and the above assumptions. Plantation scenario 1 was developed using only the highly suitable area, and scenario 2 comprised both the highly and moderately suitable areas. The locally calibrated average annual water balance model of Zhang et al. (2001) was used to assess the impacts of afforestation on annual streamflow in the study area.
Important findings The highly suitable area for plantation covers 6.6×10³km², and the moderately suitable area covers 4.9×10³km², representing 5.8% and 4.3% of the total area, respectively. The plantation area made up 0-45% of individual catchments. The area suitable for plantation became increasingly patchy and sparse from south to north. Under current land cover status, average annual streamflow in the region was estimated to be 3.81×10⁹m³ or 33.8 mm. Under scenario 1, average annual streamflow would be reduced by 2.12×10⁹m³ or 1.9 mm (5.5%). Under scenario 2, the modeled streamflow reduction is 3.49×10⁹m³ or 3.1 mm (9.2%). Corresponding to the spatial distribution of plantation, the reduction in streamflow is spatially variable. The rate of streamflow reduction varies from 0 to 36%. Minimum reduction occurred in the northwestern part of the region, where there is little area suitable for plantation development. Maximum reduction of 36% occurred in the southeastern part of the region where precipitation is highest.

Key words: plantation, mapping, DEM, modelling, annual streamflow, the middle reaches of Yellow River