Abstract: [Objective] This study was designed for analyzing the difference of soil thickness among seven micro-topographies, the responses of quantitative characteristics of plant community to soil thickness, and determining the threshold values of soil thickness response to quantitative characteristics of plant community, with the aim of supplying reference for the revegetation in the gneiss mountainous area.[Method] Based on the data of soil thickness and characteristics of plant community in gneiss mountainous area in Pingshan County of Hebei Province, this paper adopted the canonical correlation analysis to analyze the main factor which influenced the characteristics of plant community, and analyzed the differences of soil thickness on seven micro-topographies. Change-point analysis 2.3 was performed to determine the thresholds values of soil thickness response to quantitative characteristics of plant community.[Result] According to the canonical correlation analysis, the soil thickness, micro-topography influenced the change of quantitative characteristics of plant community and diversity, among which soil thickness was the main factor. And the soil thickness of gneiss mountainous area was very thin, just about 15 cm. The soil thickness on most of the micro-topographies were deeper than the undisturbed slope. U-gully, collapse, stone shadow contained significant higher soil thickness (23.1, 21.3 and 21.8 cm) than other micro-topographies and the undisturbed slope (P<0.05), and the lowest on slope crest and scarp (4.2 and 7.9 cm). According to change-point analysis on the soil thickness, the biomass, height and coverage of the plant community were increasing gradually along with soil thickness. When soil thickness reached 12.5 cm, the biomass transited from 201 g·m^-2 to 275 g·m^-2, and we called this point as the threshold. It meant that the biomass increased slowly when the soil thickness was less than 12.5 cm, but increased fast when the soil thickness was greater than 12.5 cm; Similarly, when the height transited from 30 cm to 40 cm, the threshold of soil thickness was 9.4 cm; When the coverage transited from 38% to 51%, the threshold of soil thickness was 10.5 cm.[Conclusion] The quantitative characteristics of plant community varied significantly with the soil thickness (P<0.05), indicating that soil thickness was the main factor which influenced the quantitative characteristics of plant. It's meaningful to grasp the spatial variability and thresholds of soil thickness for the revegetation in gneiss mountainous area. If revegetation was carried out first in areas with soil thickness greater than 10.5cm, the vegetation reconstruction in the whole gneiss mountain area would finally achieved by the way of from point spreading to surface.

Key words: gneiss mountainous area, micro-topography, quantitative characteristics of plant community, soil thickness, spatial variability, analysis of abrupt change, thresholds