Objective This paper aims to study the water balance law and supply-demand relationship of Larix principis-rupprechtii plantations in the northern Hebei Province region of northern China, and accurately calculate the proper management density of L. principis-rupprechtii plantations under different precipitation conditions in the region.

Method The calculation parameters were determined through long-term location observation of sap flow, understory evapotranspiration, water redistribution characteristics of L. principis-rupprechtii plantations in Xiaowutai Mountain Nature Reserve, and the construction of relationship model between DBH and xylem perimeter, and the carrying density of each diameter class of L. principis-rupprechti plantation under different precipitation conditions was calculated.

Result (1) The growth season of Larix principis-rupprechtii in the Xiaowutai area was 6 months, with an average diurnal transpiration time of 15 h during the growth season. The average sap flow velocity of L. principis-rupprechtii during the growth season was 0.012 kg/(h·cm). Except for lower values in April and June, it reached above 0.011 kg/(h·cm) in all other months, with the highest value reaching 0.021 kg/(h·cm) in August. (2) The average evapotranspiration rate under L. principis-rupprechtii forest during the growth season was 1.448 kg/(m²·d), and the annual average rate was 0.833 kg/(m²·d). The evapotranspiration rate increased rapidly from April to June, slowly increased from June to September, and reached its peak in September, rapidly decreased in October, and remained at a relatively low value from November to February of the followed year. (3) The canopy interception of L. principis-rupprechtii forest accounted for 21.22% of the precipitation, the penetrating precipitation accounted for 78.10%, the trunk runoff accounted for 0.68%, the slope runoff accounted for 1.50%, and the soil infiltration accounted for 77.28%. (4) There was a linear correlation between DBH and xylem perimeter of L. principis-rupprechtii, R² was 0.958.

Conclusion Based on the principle of water balance, the bearing density of different DBH of L. principis-rupprechtii forests under varied precipitation conditions in the Xiaowutai area is calculated, which has important guiding significance for the scientific management of existing forests in the northern Hebei region of northern China.