A comparative analysis of forest cover and catchment water yield relationships in northern China
During the past few decades, China has implemented several large-scale forestation programs that have increased forest cover from 16.0% in the 1980s to 20.4% in 2009. In northern China, water is the most sensitive and limiting ecological factor. Understanding the dynamic interactions between forest ecosystems and water in different regions is essential for maximizing forest ecosystem services. We examined forest cover and runoff relationships in northern China using published data from a variety of sources. In the Loess Plateau region, forest cover is not correlated with annual precipitation (r = 0.08, p > 0.05) at micro (<50 km2) and meso scales (50–1000 km2), while they are positively correlated at macro (>1000 km2) scale (r = 0.77, p < 0.05). Moreover, forest cover is negatively correlated with the runoff coefficient (r = -0.64, p < 0.05). In Northwest China, natural forest distribution is highly correlated with annual precipitation (r = 0.48, p < 0.05) but not with the runoff coefficient (r = -0.09, p > 0.05). In Northeast China, we found a positive relationship between forest cover and the runoff coefficient (r = 0.77, p < 0.05), but the correlation between forest cover and precipitation was not significant (r = 0.28, p > 0.05). The multiple stepwise regression analysis indicated that runoff was influenced by altitude, annual precipitation, forest cover, and PET (potential evapotranspiration) in Northeast China. We concluded that geographic differences could mask the true role of forests in the partitioning of rainfall into runoff and evapotranspiration (ET) in a catchment. In determining the forest–water relationship, one must consider climatic controls on ET in addition to forest cover. Forests could potentially enhance the complementary relationship between ET and PET. Therefore, a greater amount of ET in forested areas may decrease the PET on a regional scale.