To elucidate wind environment characteristics of forest stands and directional flow field variations near stands in complex mountainous terrains, providing theoretical support for forest fire prevention and control.

This study examined birch forests on the northern slope of the main peak of Baishi mountain in Laiyuan County, Baoding City, Hebei Province. Through field investigations and wind environment simulation experiments, we conducted an in-depth analysis of the wind environment. Porous media models for birch forests at different slope positions were constructed, and a preliminary mountain terrain model of the main peak was established, laying the foundation for revealing the intrinsic mechanisms underlying wind environment characteristics and fire prevention efficacy in birch forests.

1) Wind velocity flow fields: distinct fluctuating zones formed on the windward side of forest stands across all slope positions. As initial wind speed increased, the low-velocity area at upper slope positions gradually shifted eastward, while those at middle and lower slope positions exhibited relatively smaller spatial extents; 2) Wind direction flow fields: near stands across all slope positions, airflow remained relatively stable in the upper boundary layer. The transition layer exhibited significant airflow disturbances with irregular fluctuations due to the wind-blocking effect of stands. Notably, irregular airflow perturbations above stands were substantially weaker than in non-forested areas. In the lower boundary layer, high trunk porosity minimized wind-blocking effects, resulting in frequent directional changes of airflow; 3) Airflow disturbances near forest stands altered local wind directions, thereby influencing fire spread trajectories. Concurrently, terrain morphology and stand structure synergistically accelerated localized wind speeds, increasing fire propagation rates. Wind environment simulations demonstrated significantly higher fire prevention complexity at upper slope positions than at other slope positions.

All forest stands attenuated airflow velocity, yet wind velocity and direction flow fields responded heterogeneously under varying initial wind speeds. The combined effects of slope positions and initial wind speeds modulated fire behavior (direction and intensity), amplifying fire prevention challenges.

In order to quantitatively analyze the effects of different grazing intensities on the understory soil physical properties of natural Quercus mongolica forest and explore the evaluation system of forest soil physical properties under grazing disturbance in mountain areas of northern Hebei province.

Soil of 0-20 cm in natural Q. mongolica forest under heavy grazing (HG), moderate grazing (MG), and light grazing (LG) were collected as the research object, and the same site conditions and long-term closed treatment were taken as the control group (CK). One-way analysis of variance (ANOVA) and grey correlative degree analysis were conducted to reveal the effects of different grazing intensity on soil physical properties of natural Q. mongolica forest. Principal component analysis method, multidimensional coordinate-synthetic-evaluation method and entropy weight TOPSIS method were used to evaluate the soil physical quality under grazing disturbance.

1) The contents of coarse silt, sand grain and clay in soil increased with the increase of grazing intensity, while the contents of medium silt and fine silt decreased with the increase of grazing intensity. The effect of grazing intensity on soil fractal dimension was not significant. 2) The soil bulk density increased with the grazing intensity, and other physical factors decreased as the grazing intensity increased. There were significant differences in each soil physical factor between the heavy grazing group and other grazing groups. 3) All the three evaluation methods showed consistent ranking results: CK > LG > MG > HG.

In view of the impact of grazing on the physical properties of understory soil, it is concluded that light grazing can promote the decomposition of understory litters and improve the physical quality of understory soil, while overgrazing may cause adverse effects on understory soil. The effects of grazing on the understory soil are multi-level, so it is necessary to strengthen the long-term monitoring and in-depth study.