Changes of farming-pastoral ecotone

The evolution of agro-pastoral ecotone in China can be seen from two aspects.

I. Climate change

In this paper, four historical examples, namely, the relocation of Beiping City to the capital, the migration of Lingbei area in the middle Yuan Dynasty, the evolution of Horqin sandy land in the early 65438+2002 century, and the relocation of Wuliangha Sanwei to the south in the early Ming Dynasty, are used to discuss the changes in the transition zone between agriculture and animal husbandry and the corresponding social changes when the climate becomes cold and dry. The impact of climate change on the transition zone between agriculture and animal husbandry in history is certain to exist. At the same time, the impact of climate change on the transition zone of agriculture and animal husbandry plays a role through the human social system. Different social conditions and combinations will produce different realities and corresponding social problems in the transitional zone between agriculture and animal husbandry. When farmers and herdsmen confront each other near the transition zone between agriculture and animal husbandry, the change of climate to the cold direction often becomes the fuse of social unrest, which will have very serious consequences in extreme cases.

Most of the heat energy obtained by the earth is solar energy (sunlight), and the causes of climate change are natural phenomena such as solar activity and volcanic eruption, and global warming, acid rain and the destruction of the ozone layer caused by the discharge of a large number of synthetic compounds also have direct or indirect effects.

In addition, due to desertification, abandoned ground will further promote the vicious cycle of climate drought. The exposed ground due to desertification leads to the increase of sunlight reflectivity; Due to the reduction of sunlight absorption, the temperature drops; The downward flow is strengthened, so there is less rain. In fact, desertification does have a negative impact on the climate and environment in this area.

Second, human factors.

The original transition zone refers to the transition zone between agriculture and animal husbandry during and after the construction of the Great Wall. The "possible change zone" refers to the boundary between semi-arid and semi-humid, grassland and forest, agriculture and animal husbandry that changed here later (nearly 300 years) because of war, unreasonable economic activities and frequent replacement of agriculture and animal husbandry.

There are three points to be clear:

1, under the action of northwest wind, the desert belt pushes southeast; (mentioned earlier)

2. Reason: unreasonable economic activities of human activities;

3. Distribution of severe areas (typical areas): Horqin Sandy Land and Mu Us Sandy Land.

By 193 1, the scale of agricultural reclamation in Inner Mongolia is basically the same as it is now. A vast transitional zone between agriculture and animal husbandry has been formed in the southeast of Inner Mongolia, which will form a long-term dividing line between agriculture and animal husbandry from Qin and Han Dynasties to Ming Dynasty.

Due to the intensification of human activities, farming is often carried out in areas where grazing should be carried out, which will expand the scope of farming, thus making the farming-pastoral ecotone move to the arid and semi-arid areas in the west or north, leading to the contradiction between man and land. Newly reclaimed farmland will be desertified due to the change of surface vegetation and the decrease of precipitation.

(1) Animal husbandry (nomadic, grazing)

When the amount of plants consumed by livestock exceeds the limit of plant growth, that is, overgrazing will exceed the damage to vegetation and accelerate the exposure of the surface, which will become the cause of wind erosion or rain erosion. When there is abundant rainfall and lush vegetation, the number of livestock increases rapidly, but if there is drought in the later period and the vegetation decreases, the number of livestock will be adjusted. But in fact, this adaptation is quite difficult, and in most cases it will lead to desertification. Moreover, in recent years, the nomadic settlement policy has been implemented everywhere, but grazing in a limited area leads to the concentration of livestock, and cutting down surrounding trees as fuel has brought bad results to vegetation management in many cases.

Because grazing livestock requires a large area of grassland, overgrazing accounts for the largest proportion in various reasons for the formation of desertification areas, so while determining the number of livestock in balance with vegetation, we are seeking to improve grazing methods.

2) Dry farming (rain-dependent agriculture)

With the agricultural practice of relying only on natural rainfall, the rainfall in many areas is 250 ~ 500 mm in winter and 400 ~ 600 mm in summer, and a large number of grains such as wheat and sorghum are planted.

In order to make use of the poor water in the soil, it is necessary to stop planting fallow 1 ~ 2 years at least, and then use the accumulated water in the land for farming. Therefore, when fallow, wind erosion is easy to occur in dry season and water erosion is easy to occur in rainy season. In particular, due to dry years and insufficient food, land exposure has to be shortened, leading to soil erosion. In addition, the cultivation of cash crops has also caused excessive use of land and excessive expansion of cultivated land. At the same time, grazing on cultivated land and burning wasteland are also important reasons for soil erosion.

(3) Irrigation agriculture (oasis agriculture)

The proportion of irrigated agriculture in arid areas is higher than other agricultural practices, and its development will be further accelerated in the future because of its stable output. However, it is the final result of irrigated agriculture that causes the exhaustion of water resources and the salinization of soil (salt accumulation).

As the groundwater level rises due to continuous irrigation, the inorganic salts in the soil dissolve in the water and move upward through capillary action, so the salt concentration in the near-surface soil will increase. Moreover, due to the evaporation of water, only salt residue accumulates on the ground, which is called soil salinization. This will hinder the growth and development of plants and make them die.