Study area and species descriptions
The present study was conducted in the plantations of Institute of Sand Land Control and Utilization of Liaoning Province in NE China (42°42′ N, 122°29′ E; 226.5 m a.s.l.). This site is located in the southeastern part of the Horqin Sandy Land, i.e. the largest desertified land in China with a total area of over 500, 000 km2. The study site has a temperate continental climate with mean annual temperature of 7.8 °C, maximum and minimum mean monthly temperature of 26.2 °C and -18.4 °C, respectively. The precipitation is strongly seasonal that on average 382 mm out of 501 mm occurs during the growing season (June to September). In this semi-arid region, vast areas of tree plantations mainly composed ofPinus sylvestris var. mongocica Litv. (Mongolian pine) trees have been created as shelter forests. However, severe decline and mortality of Mongolian pine plantations have occurred since the 1990s (Zhu et al., 2003), which may become even worse under the influence of the significant warming-drying trend caused by climate change (Fig. 1). To look for optimal afforestation species in this area, different pine species have been tested and they showed large variations in performances in terms of growth and survival. In the present investigation, we compared tree radial growth patterns and physiological traits of seven pine species growing in a common environment of tree plantations (Table 1). Sample trees for all the studied species were growing in pure stands with stand density ranging between 750 and 800 stems ha-1.