Objective This paper aims to explore the effects of different aspects on the growth and biomass allocation of Quercus mongolica saplings in the mountain area of northern Hebei Province of northern China, so as to provide scientific basis for the afforestation of Quercus mongolica in the area.

Method The 9-year-old Quercus mongolica saplings on the east, southeast and west aspects of the mountain area of northern Hebei Province were selected. The basal diameter, plant height, crown width and organ biomass were measured in different aspects. One-way analysis ( ANOVA ) was used to test whether there were significant differences in basal diameter, plant height, crown width and biomass among the aspects. The method of standardized main axis estimation was used to test the allometric relationship between the organ biomass of Quercus mongolica saplings in different aspects.

Result (1) The basal diameter and plant height of the east aspect were significantly larger than those of the southeast aspect, with a difference of 0.29 cm in ground diameter and 11.81 cm in plant height. And there was no significant difference in crown width between the east aspect and the southeast aspect. The basal diameter, plant height and crown width of the west slope were significantly smaller than those of the east slope and the southeast slope. The slope of diameter-height curve was highest on the southeast slope (0.458), centered on the east slope (0.377), and lowest on the west slope (0.349). (2) There was no significant difference in total biomass accumulation between the east slope aspect (1 144.50 g/tree) and the southeast aspect (961.58 g/tree), and the west aspect (365.33 g/tree) was significantly smaller than the east aspect and the southeast aspect. There was no significant difference in biomass accumulation of leaves, trunks, and roots between the east aspect and the southeast aspect. The biomass accumulation of stems on the east slope (217.59 g/tree) was significantly higher than that on the southeast slope (159.17 g/tree). The biomass accumulation of all organs on the west aspect was significantly lower than that on the other two slopes. (3) The biomass allocation ratio of stems (13.32%) and trunks (24.10%) on the west aspect was significantly lower than that on the other two aspects, while the root biomass allocation ratio on the west aspect (44.79%) was significantly higher than that on the other two slopes (east aspect 34.28%; southeast aspect 32.67%). The stem biomass allocation ratio on the east aspect was significantly higher than that on the southeast aspect, while the leaf allocation ratio on the eastern aspect was significantly lower than that on the southeast aspect. And the trunk and root allocation ratio had no significant difference between the east aspect and the southeast aspect. (4) The biomass of paired organs in each slope direction showed an isokinetic growth relationship, but it showed different organ allocation trends.

Conclusion Quercus mongolica saplings show different growth patterns in the three slope directions, and the east aspect is the optimal aspect for it.