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.