Introduction Directory UMM :Data Elmu:jurnal:A:Agricultural & Forest Meterology:Vol102Issue2-3May2000:

Agricultural and Forest Meteorology 102 2000 125–137 Grassland desertification by grazing and the resulting micrometeorological changes in Inner Mongolia Sheng Gong Li a,∗ , Yoshinobu Harazono b,1 , Takehisa Oikawa a,2 , Ha Lin Zhao c,3 , Zong Ying He c,3 , Xue Li Chang c,3 a Institute of Biological Sciences, University of Tsukuba, Tsukuba 305-8572, Ibaraki, Japan b National Institute of Agro-Environmental Sciences, Tsukuba 305-8604, Ibaraki, Japan c Institute of Desert Research, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China Received 9 June 1999; accepted 11 January 2000 Abstract Overgrazing is one of the most primary causes of desertification in semi-arid zones of China. From 1992 to 1994 we conducted a grazing experiment in Naiman lat. 42 ◦ 58 ′ N, long. 120 ◦ 43 ′ E, 345 m asl, Inner Mongolia, China to elucidate desertification mechanisms. Our experimental field, which was covered with some short grasses, legumes and forbs, included four plots where grazing sheep numbers differed 0, 3, 6, or 9 individuals. Micrometeorological measurement data were analyzed using the Bowen ratio energy balance method. Ground surface reflectivity albedo increased with grazing intensity. The overgrazed plot had been desertified after 3 year’s grazing experiment. Albedo can be regarded as an important indicator of potential grassland desertification. When desertification occurs, then albedo will exceed a critical value. Partitioning of net radiation exhibited distinct patterns among the four plots as a result of the interplay between albedo and in situ vegetation. Ratios of the net radiation or net available radiation to solar radiation tended to decrease with increasing grazing intensity. But this pattern of changes was largely affected by soil moisture regime and vegetation status during the measurements. Grazing also remarkably affected wind regimes over the grazing experimental plots through altering surface roughness. Especially, sustained overgrazing decreased surface roughness length so substantially that wind could act directly on sandy grassland surface to initiate desertification. A permissible grazing capacity of the studied temperate semi-arid grassland was also proposed for future grassland management. © 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Grassland; Grazing intensity; Micrometeorology; Desertification; Albedo ∗ Corresponding author. Fax: +81-298-53-2530. E-mail addresses: shengonerc2.suiri.tsukuba.ac.jp S. Gong Li, yoshi4niaes.affrc.go.jp Y. Harazono, oikawaoak.biol.tsukuba.ac.jp T. Oikawa, resdivns.lzb.ac.cn H.L. Zhao 1 Fax: +81-298-38-8211. 2 Fax: +81-298-53-6661. 3 Fax: +86-931-8847524.

1. Introduction

Desertification is the process of deterioration in ecosystems of arid and semi-arid areas resulting from interplays of climatic variations and human activ- ities Dregne, 1985; UNEP, 1992. Desertification and its influence on regional environmental change have become the research focus of many scholars in the past few decades. Charney 1975 and Charney et al. 1975, 1977 suggested that the drought and 0168-192300 – see front matter © 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 9 2 3 0 0 0 0 1 0 1 - 5 126 S.G. Li et al. Agricultural and Forest Meteorology 102 2000 125–137 dynamics of deserts in the Sahara be controlled by a biogeophysical feedback mechanism. Biological feedbacks play an important role in desertification worldwide Schlesinger et al., 1990. Deforestation and resulting hydrological changes of land surface affect regional and even global climates e.g. Shukla and Mintz, 1982; Shukla et al., 1990; Nobre et al., 1991; Wright et al., 1992. Some GCMs suggest that future global warming will likely exacerbate the degradation of semi-arid grasslands on a large scale in North America and Asia Manabe and Wetherald, 1986. It is also true in the arid and semi-arid zones of Northern China that deforestation and afforestation affect the regional pattern of precipitation and tem- perature regime Chen et al., 1992; Lin et al., 1993. For example, in the Horqin Steppe, the desertified grassland area is still expanding due to inappropriate anthropogenic activities such as prolonged overgraz- ing, poor farmland management and over-lumbering Zhu and Wang, 1992. Vegetation plays very impor- tant roles in mass and heat exchange between land surfaces and the atmosphere Grace et al., 1981. Removal or deterioration of vegetation cover affects water and heat budget of the surfaces. Therefore, in the desertification-prone areas such as the Horqin Steppe, it is requisite to conduct research on the re- lationship between desertification mainly caused by degradation of vegetation and micrometeorological changes. The primary objectives of this paper are: 1 to describe impacts of different levels of grazing intensity on the micrometeorological characteristics of grassland; and 2 to assess initiation of grassland desertification under increasing overgrazing.

2. Materials and methods