GRASSLAND DESERTIFICATION AND MICRO METEOROLOGICAL CHANGES IN NAIMAN

摘要/Abstract

摘要： Overgrazing is one of primary causes for desertif ication in semiarid zone of China. Since 1992 a graz ing experiment was being conducted in Naiman (42° 55' N, 120° 42' E, 405 m above sea level), Inner Mongolia, China to elucidate desertif ication mechanism, especially initiation of desertif ication of grassland resulted f rom overgraz ing. The experiment f ield includes four plots in which grazing sheep number diff ers with 0, 3, 6, and 9 respectively. Micrometeorological data are analyzed using Bowen ratio energy balance method and aerodynamic gradient method. The results show that:① Ground surface ref lectivity (albedo) increases with graz ing intensity, i. e., albedo of the overgraz ing plot has increased f rom 0.20 at the beginnig of the experiment in 1992 to 0. 28 in 1994. The overgrazing plot has been desertif ied. Thus, albedo becomes an important indicator of grassland desertif ication. If albedo exceeds a critical value then desertif ication will occur. ② Partitioning of net radiation exhibits distinct patterns among the four plots, which is the results of interplays of albedo and in situ vegetation. The net radiation and contribution of latent heat f lux tend to decrease due to increasingly grazing intensity. Heavy trampling by sheep also aff ects heat budget over the ground surf ace. ③ Wind profiles above the ground of each plot have dif ferent structures. Much larger wind shear on the overgraz ing surf ace is a signif icant driving f orce resulting in intense sand f low activity on which desertification processes are based. ④ Optimum graz ing capacity of the studied grassland is proposed, such as 3~4 sheep per hm2, according to the experiment and plant community dynamics.

关键词: Grassland, Grazing intensity, Micrometeorology, Desertification

Abstract: Overgrazing is one of primary causes for desertif ication in semiarid zone of China. Since 1992 a graz ing experiment was being conducted in Naiman (42° 55' N, 120° 42' E, 405 m above sea level), Inner Mongolia, China to elucidate desertif ication mechanism, especially initiation of desertif ication of grassland resulted f rom overgraz ing. The experiment f ield includes four plots in which grazing sheep number diff ers with 0, 3, 6, and 9 respectively. Micrometeorological data are analyzed using Bowen ratio energy balance method and aerodynamic gradient method. The results show that:① Ground surface ref lectivity (albedo) increases with graz ing intensity, i. e., albedo of the overgraz ing plot has increased f rom 0.20 at the beginnig of the experiment in 1992 to 0. 28 in 1994. The overgrazing plot has been desertif ied. Thus, albedo becomes an important indicator of grassland desertif ication. If albedo exceeds a critical value then desertif ication will occur. ② Partitioning of net radiation exhibits distinct patterns among the four plots, which is the results of interplays of albedo and in situ vegetation. The net radiation and contribution of latent heat f lux tend to decrease due to increasingly grazing intensity. Heavy trampling by sheep also aff ects heat budget over the ground surf ace. ③ Wind profiles above the ground of each plot have dif ferent structures. Much larger wind shear on the overgraz ing surf ace is a signif icant driving f orce resulting in intense sand f low activity on which desertification processes are based. ④ Optimum graz ing capacity of the studied grassland is proposed, such as 3~4 sheep per hm2, according to the experiment and plant community dynamics.

Key words: Grassland, Grazing intensity, Micrometeorology, Desertification

中图分类号:

S812.6

LI Sheng gong, ZHAO Ha lin, HE Zong ying, CHANG Xue li, Yoshinobu HAROZONO. GRASSLAND DESERTIFICATION AND MICRO METEOROLOGICAL CHANGES IN NAIMAN[J]. 中国沙漠, 1998, 18(4): 359-365.

LI Sheng gong, ZHAO Ha lin, HE Zong ying, CHANG Xue li, Yoshinobu HAROZONO. GRASSLAND DESERTIFICATION AND MICRO METEOROLOGICAL CHANGES IN NAIMAN[J]. JOURNAL OF DESERT RESEARCH, 1998, 18(4): 359-365.