Analysis of wind environment for Betula platyphylla forests in different slope positions along the northern foothills of the Taihang mountains

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.