The adhesion of water droplets to leaves is important in controlling rainfall interception, and affects a variety of hydrological processes. Leaf water drop adhesion (hereinafter, adhesion) depends not only on droplet formulation and parameters but also on the physical (leaf roughness) and physico-chemical (surface free energy, its components, and work-of-adhesion) properties of the leaf surface. We selected 60 plant species from Shaanxi Province, NW China, as experimental materials with the goal of gaining insight into leaf physical and physico-chemical properties in relation to the adhesion of water droplets on leaves. Adhesion covered a wide range of area, from 4.09 to 88.87 g/m2 on adaxial surfaces and 0.72 to 93.35 g/m2 on abaxial surfaces. Distinct patterns of adhesion were observed among species, between adaxial and abaxial surfaces, and between leaves with wax films and wax crystals. Adhesion decreased as leaf roughness increased (r =  −0.615, p = 0.000), but there were some outliers, such as Salix psammophila and Populus simonii with low roughness and low adhesion, and the abaxial surface of Hyoscyamus pusillus and the adaxial surface of Vitex negundo with high roughness and high adhesion. Meanwhile, adhesion was positively correlated with surface free energy (r = 0.535, p = 0.000), its dispersive component (r = 0.526, p = 0.000), and work of adhesion for water (r = 0.698, p = 0.000). However, a significant power correlation was observed between adhesion and the polar component of surface free energy (p = 0.000). These results indicated that leaf roughness, surface free energy, its components, and work-of-adhesion for water played important roles in hydrological characteristics, especially work-of-adhesion for water.

China leads the world in afforestation, and is one of the few countries whose forested area is increasing. However, this massive "greening" effort has been less effective than expected; afforestation has sometimes produced unintended environmental, ecological, and socioeconomic consequences, and has failed to achieve the desired ecological benefits. Where afforestation has succeeded, the approach was tailored to local environmental conditions. Using the right plant species or species composition for the site and considering alternatives such as grassland restoration have been important success factors. To expand this success, government policy should shift from a forest-based approach to a results-based approach. In addition, long-term monitoring must be implemented to provide the data needed to develop a cost-effective, scientifically informed restoration policy.

Large-scale forestation has been undertaken over decades principally to control the serious soil erosion in the Loess Plateau of China. A quantitative assessment of the hydrological effects of forestation, especially on basin water yield, is critical for the sustainable forestry development within this dry region. In this study, we constructed the multi-annual water balances to estimate the respective grand average of annual evapotranspiration (ET) and runoff for forestlands and non-forestlands of 57 basins. The overall annual runoff and corresponding runoff/precipitation ratio were low, with a mean of 33 mm (7%) ranging from 10 (2%) to 56 mm (15%). Taking the grand average of annual precipitation of 463 mm for all basins, the corresponding grand averages of annual ET and runoff were 447 and 16 mm for forestlands, 424 and 39 mm for non-forestlands, respectively. Thus, the corresponding ratios of annual ET and runoff to precipitation were 91Ð7 and 8Ð3% for non-forestlands, 96Ð6 and 3Ð4% for forestlands, respectively. Although the absolute difference in grand average of annual runoff was only 23 mm, it represents a large difference in relative terms, as it equates up to 58% of annual runoff from non-forestlands. We argue that the large-scale forestation may have serious consequences for water management and sustainable development in the dry region of NW China because of a runoff reduction. This study highlights the importance of quantifying the ET of forests and other land uses and to examine how land cover change may affect the water balances in an arid environment.