Field sites and experimental design

This study was carried out in two different sites in Hunan province, China. One area is located in the Botanical Garden in Changsha (28°06′N, 113°02′E). The annual rainfall on this site is 1422 mm and the mean annual temperature is 17.2 °C, belonging to typical subtropical monsoon climate. The altitude ranges from 50 to 100 m. The soil type is Alliti-Udic Ferrosols with well-drained clay-loam red soil developed from slate parent rock, and total N concentrations ranging from 0.57 to 1.56 g kg⁻¹ in top 30 cm depth of the soil profile [26]. Single species and two species mixed patches, consisting of 24- and 45-year old P. massoniana were selected. In monocultures and mixed stand, few Pinus elliotii were also admixed here. Considering the similarity of growth characteristics and the difficulty of root separation between P. massoniana or P. elliotii, we treated them one group (thereafter called “Pinus”). Three plots of size 20 m × 20 m were established in mixed Pinus–Cinnamomum stands at age of 24 and 45 years old and corresponding pure species stands (Pinus and Cinnamomum) at each age, amounting to 18 plots. The another site is located in Taolin forestry station (28°55′N, 113°03′E) in Miluo county, approximate 100 km from the main site with similar climate and parent soil type. The mean annual precipitation is about 1353.6 and mean annual temperature is 16.9 °C. Here, only the smaller patches of mixed and pure species stands with 10 years old Pinus and Cinnamomum were found. Therein three plots of 12 m × 12 m in mixed forests stands and corresponding pure stands were set up as conducted above. Thereby our study consisted of 27 plots of mixed Pinus–Cinnamomum plantations and corresponding monocultures at age of 10, 24 and 45 years old. All the stems were recorded and selected site characteristics are presented in Table 1. More detailed information about the experimental site and soil condition referred to Wen et al. [26].

Stand characteristics in pure species Pinus stands, pure Cinnamomum stands and mixed Pinus–Cinnamomum stands at the age 10, 24 and 45 years old (mean ± standard deviation)