伊金霍洛旗近15年来植被覆盖度的动态变化

Dynamics of the vegetation coverage in recent 15 years in Yijinhuoluo County,Inner Mongolia,China

植被状况是评价荒漠化地区荒漠化程度的重要指标,其中植被盖度是最为重要的植被表征。本文选择地处我国北方农牧交错区的内蒙古伊金霍洛旗,利用Landsat卫星遥感数据,基于植被指数,反演了这一地区1989年9月11日、1998年8月19日、1999年8月13日、2002年8月6日、2004年7月2日的植被盖度变化情况。通过分级比较发现,1989-1998年研究区植被覆盖度明显增加,1998-1999年植被覆盖度显著减少,1999-2002年植被覆盖度又明显增加,而2002-2004年植被覆盖度又有所减少。这种起伏变化表明:导致研究地区荒漠化发生和扩展的各种自然和人为因素并未根本消除,在局部地区荒漠化仍有恶化趋势。影响植被覆盖度变化的因素主要有三个方面:气候因素、土地利用政策和农业经济结构的优化调整。

The status of vegetation is a very important indicator in the desertification evaluation for the sand regions, in which the vegetation coverage is a popular factor. In the past, the vegetation coverage was obtained by the means of field investigation. Desertification is a macro-scale changing process, so the field vegetation investigation is not satisfied with the vegetation change monitoring. Now, with the development of RS, GIS and GPS technology, especially the satellite remote sensing, we can analyze the vegetation change. In this article, the Yijinhuoluo County, Inner Mongolia was taken as an example. With the landsat images of 1989, 1998, 1999, 2002 and 2004, we calculated vegetation coverage fc in the study region based on the NDVI index. In order to analyze the vegetation coverage expediently, the vegetation coverage was divided into three levels： low（0≤fc 〈 15% ）, middle（ 15% ≤fc 〈40% ） and high（fc ≥40% ）. The result showed that vegetation coverage was presented with waving characteristics. During 1989 -1998, the vegetation coverage was increased, while the value of 1998 -1999 decreased, it of 1999 -2002 increased again, however, it of 2002 -2004 decreased again. These changes showed that all kinds of natural and social elements were still existed which could lead to the desertification in the study region. In some places, the desertification appeared more seriously. In general, there are three factors affecting vegetation coverage, which are climatic variation, land-use policy as well as the optimization and adjustment of the agriculture economic structure. During the period of 1959 - 2000, the changes of precipitation in Yijinhuoluo County was in evidence, and the decreasing velocity reached 5.15 mm/a. Different from the precipitation, the annual average temperature showed a inverse trends, whose increasing velocity reached 0.08 ℃/a. The warm - dry climatic pattern is disadvantageous to the vegetation growing. Since 1970s, many large scale regional eco＇projects were brought into effect, which included the construction of shelter system in the ＂north-east, north and north-west of China＂, natural forest conservation project and mandatory conversion of marginal farmlands to forest lands. By the implement of these projects, the forestry land was increased from 3.98 × 10^4 hm^2 in 1973 and to 19.24 × 10^4 hm^2 in 2005. By the end of 2005, the preserve area of artificial forestry and grass land were 22.7 × 10^4 hm^2 and 7 ×10^4 hm^2 respectively. By tradition, the main economic income was from agriculture and stockbreeding. From 1949 to 2005, the economic construction showed that the crop planning was reduced continuously and the forestry and stockbreeding was increased. In 2000, the ratio among first, second and third industry was 10：40：50. However, it was 5：38：57 in 2004. The labor force＇ s transferring from the first industry to the second and third industry for the optimization of economic construction. As a result, the population pressure on the vegetation was extenuated in large scale. So the grassland building was promoted and the statue of vegetation coverage was improved significantly.