Airflow Field Around Hippophae rhamnoides in Alpine Semi-Arid Desert

Abstract

The research on wind regimes and the wind protection mechanism of sand-fixing plants has mainly relied on wind tunnel experiments; few observations have been made in the field. At the same time, airflow around individual standing vegetation elements and communities is relatively lacking in alpine semi-arid deserts. Therefore, this paper selected 10-year-old Hippophae rhamnoides (sea buckthorn) on sandy land on the eastern shore of Qinghai Lake as the study object. Based on spatial and temporal changes of wind regime in the afforestation forest, a structural simulation of airflow near the plant and at different layers above the ground, and the annual changes in wind protection, we studied the wind protection mechanisms of H. rhamnoides as single elements or communities. The results were as follows: the effective protection length of the sublayer of H. rhamnoides was 1.0 to 1.8 m. The higher the layer, the smaller the decrease in wind velocity behind elements, and the smaller the effective protection length. Wind velocity downwind of H. rhamnoides increased, with height increasing where the airflow decreases rate (R) decreased in the sublayer, and increasing in the middle layer as plant height increased. Meanwhile, the airflow decreases rate (R) was negative in the upper layer because it decreased as the plant height increased. The airflow movement between elements had various directions because the upper layer was prone to fluctuations due to the swinging of the crown and branches, and turbulence was seen at the sublayers owing to the mechanical resistance of the elements. When the wind speed at the standard point was 8.5 m/s and the wind direction was east (E), the increase of airflow velocity at the side and center in the upper layer was more significant, and there was a strong wind zone in the azimuth of NW‒N‒NE‒E‒SE, while the S‒SW‒W azimuth zone was weaker. The sand-fixing shrub H. rhamnoides had a significant windproof function, and the 1.5 m square interval density of H. rhamnoides was suitable for alpine desert control projects.

Vegetation–soil dynamics in an alpine desert ecosystem of the Qinghai Lake watershed, northeastern Qinghai–Tibet Plateau

“…Before artificial measures were taken, sand movements were extremely strong on mobile dunes because of forceful winds in winter and spring. Once plantations were established on dunes, wind-related hazards decreased considerably (Tian et al, 2020).…”

“…The WPSER is a low-wind energy environment whose aeolian activity is strongest from late autumn to early spring, being controlled by the north-west wind direction. The threshold wind velocity for sand movement on a mobile dune is 6.5 m s −1 , but it is greater than 8 m s −1 on afforestation dunes (Tian et al, 2020). The natural shrub species distributed in natural fixed dunes are mainly Artemisia ordosica and Caragana jubata, while natural herbs are Carex qinghaiensis and Achnatherum splendens.…”

“…The study was conducted at the eastern shore of Qinghai Lake, which belongs to the Ketu Wind Prevention and Sandfixation Experimental Range (hereafter, WPSER; 36 °46.9′ N, 100 °46.8′ E; 3,224 m; for more details about WPSER, refer to Tian et al (2019) and Tian et al (2020)). Mega-dunes and continuous mobile dunes are distributed across the WPSER.…”

“…Recent studies in this area have mainly focused on desert formation, dynamic changes of desertification, desertification control measures, soil particle composition, soil moisture dynamics, effective control and evaluation of straw checkerboards, and individuals' effects on reducing winddriven sand erosion (Tian et al, 2015;Tian et al, 2019;Tian et al, 2020), in addition to water use sources of afforestation species (Wu et al, 2016;Wang et al, 2022). Work by Wu H et al (2019) has analyzed species characteristics (richness and traits) and other afforestation community features over several years.…”

Determine the Optimal Vegetation Type for Soil Wind Erosion Prevention and Control in the Alpine Sandy Land of the Gonghe Basin on the Qinghai Tibet Plateau

“…Tian et al [28] found that Hippophae rhamnoides has a significant windproof function in the Qinghai-Tibet Plateau, with a suitable Hippophae rhamnoides spacing density of 1.5 m for alpine desert control projects. Li et al [29] demonstrated that the artificial forests of Populus cathayana in the northeastern part of the Qinghai-Tibet Plateau contribute to the stability and ecological restoration of the Mugetan Desert, where a 30-year-old artificial forest can form a moss crust on the surface of the sand dunes, thereby stabilizing them.…”