Why do you want to learn?

Grassland refers to vegetation region, which is dominated by almost continuous grasses. Grassland is beneficial to this kind of vegetation but not to the environment where tall plants (especially trees and shrubs) grow. The factors that hinder the growth of these tall woody plants are different.

Grassland is the most widely distributed vegetation type in the world. However, this is because human use of land has greatly changed the natural vegetation, resulting in artificial grasslands such as grain and pasture, and these areas need some form of unnatural repeated intrusion, such as continuous farming, intensive grazing, burning or mowing. However, the focus of discussion here is natural grassland and near-natural grassland.

[Edit this paragraph] 1, concept classification

The meaning of grassland can be divided into broad sense and narrow sense: broad sense includes vegetation dominated by herbs formed in relatively arid environment, mainly including tropical grassland (savanna) and temperate grassland. Grassland in a narrow sense only includes temperate grassland. Because there are many trees on the savanna.

According to biological and ecological characteristics, it can be divided into four types:

① Meadow grassland;

② Flat grassland (typical grassland);

③ Desert grassland;

④ Alpine grassland. There are many excellent pastures growing on the grassland, which is an important animal husbandry base. In addition, there are many medicinal plants in grassland vegetation, which can be harvested and utilized.

Paragraph 2 of Article 2 of the Grassland Law stipulates that grasslands mentioned in this Law refer to natural grasslands and artificial grasslands. Natural grassland refers to a land type, which is a multifunctional natural complex composed of herbs and woody forage plants and the land they planted. Artificial grassland refers to the grassland planted or improved by selecting suitable grass species and artificial measures.

[Edit this paragraph] 2. origin

The widest grassland can be regarded as the middle of the environmental gradient, with forests and deserts at both ends. Forests occupy the most favorable environment, where there is enough water for tall and dense vegetation, mainly trees, to grow and survive. Deserts exist in places where water vapor is scarce and sustainable vegetation cannot be maintained. Grassland is between these two extremes.

Grass originated in the dry and cold period of global climate (appeared in Cenozoic), similar to the wilderness, desert and shrub land where they often blend. In fact, Gramineae itself (Gramineae and Gramineae) only evolved in the early Cenozoic. The earliest date of grassland appearance varies from place to place. In several areas, a series of vegetation types can be found in Cenozoic fossils when the climate changes gradually. For example, in the past 50 million years, the tropical rain forest in central Australia has been replaced by wilderness, grassland and finally desert. In some places, the expansion of grassland to modern scale only appeared in the extremely dry and cold period 2 million years ago, which is called the "ice age" of the temperate zone in the north.

There is usually a dynamic balance between grassland and related vegetation types. Sometimes, drought, fire or intensive grazing are beneficial to grassland formation, while at other times, rainy season and no major interference are beneficial to woody vegetation growth. The change of frequency and severity of these factors will lead to the overall change of vegetation types.

Other grassland types appear in places that are too cold for trees to grow, that is, above the tree line in mountainous areas or highlands. The typical grassland in the wet and cold region of the southern hemisphere is a tufted grassland, which is dominated by tufted or tufted grasses. These grasses grow intertwined roots and mats, giving plants a rough appearance. Tufted grasslands appear at different latitudes. In the tropics, overgrown grasslands appear above the tree line of some high mountains, such as New Guinea and East Africa. In the high latitudes of the Antarctic Sea, the overgrown grassland forms the vegetation of the sub-Antarctic Islands. Tufted grassland is also a typical vegetation in the cold region of New Zealand and the southernmost part of South America.

However, not all natural grasslands originated from the climate-related environment. For other reasons, woody plants may not grow in some areas, and grasses will spread wildly. One of the reasons is seasonal floods or flooding, which makes some seasons obvious, while other subtropical areas with smaller areas produce and maintain large grasslands. One of the best examples of seasonal floods in subtropical grasslands is Pantanal, Mato Grosso, Brazil. In an area of 65,438+040,000 square kilometers (54,000 square miles), grasslands expand in half of the year, shallow wetlands expand in the other half, and small forests are limited to low hills that will not be submerged in the rainy season. In many other places where the climate is suitable for forest growth, poor or shallow soil will make trees unable to grow and lead to grassland development.

The natural grassland area caused by climate drought is the largest, which can be divided into tropical grassland and temperate grassland. Tropical grassland is usually located between desert and tropical forest, and temperate grassland is usually located between desert and temperate forest. Tropical grassland and savanna appear in the same area, and the difference between these two vegetation types depends on the number of trees. Similarly, there may be some shrubs or trees scattered in temperate grasslands, and when they appear near shrubs or temperate forests, the boundaries may become blurred.

Tropical grasslands are mainly distributed in the Sahel region of sub-Saharan Africa in East Africa and Australia. Temperate grasslands mainly appear in North America, Argentina and vast areas from Ukraine to China, but in these areas, grasslands have been greatly improved by agricultural activities.

Many grasslands that were originally thought to be natural are now recognized as forests that used to grow in the arid climate of the border. They were transformed by early human interference. For example, it is believed that almost the whole large-scale lowland grassland in the eastern part of New Zealand's South Island was burned by Polynesians (the earliest colonists in New Zealand) 800 years before the European reclamation in the18th century.

Semi-natural grassland may appear in places where woody vegetation was cleared for farming but later abandoned, and the original vegetation cannot be restored due to repeated burning or grazing. In humid tropical areas, this type of grassland may be very dense, such as the grassland dominated by elephant grass in East Africa or the grassland dominated by five-node awn in New Guinea, where the grass can grow to 3 meters (9.8 feet) high.

The area and characteristics of grasslands in different places may be partly determined by the long history of communication between grasslands and human beings, especially through the medium of fire.

[Edit this paragraph] 3. environment

Grassland climate varies, but all prairie areas are usually hot (at least in summer) and dry, but not as dry as deserts. Usually, the average annual rainfall in the savanna is 500? 1，500 km (20？ 60 inches), the temperature is about every season 15? 35℃(59? 95℉)。 The dry season can last for 8 months, and only in the wet season will the rainfall be greater than the evaporation, which will cause the river to stop flowing for a short time. The savanna climate and savanna climate widely overlap. As mentioned earlier, these vegetation types are very different from each other, and savanna is only a grassland with sparse trees. Small changes in management and utilization can change both.

Temperate grasslands are drier and colder than tropical grasslands, at least for part of the year. The seasonal temperature change in tropical grassland may be small, but the temperature change in temperate grassland area can reach 40℃(72℉). The average annual rainfall in North American grasslands is 300? 600 kilometers. The monthly average temperature in the north is 65438 0.8℃ (0 ℉), in the south it is 65438 0℃ (50 ℉), and in July it is 65438 0.8℃ (64 ℉) and 28℃(82℉) respectively. The average annual temperature in the northernmost part of the North American grassland is below 0℃(32℉).

Grassland appears in various climatic and geological environments and is also related to many different soil types. Grassland ecosystem itself affects soil formation, which leads to grassland soil being different from other soils. Grassland litter layer and its decomposition type usually lead to the development of soil rich in organic matter (up to 300 mm below the surface). Desert soil does not have this layer, and it is also different from the typical rotten surface layer of forest soil. Its structure is loose and rich in plant nutrition. The lower soil layer is typical white with yellow, especially the soil layer about 2 meters deep.

[Edit this paragraph] 4. Animals and plants

In North America before European colonization, grasslands spread all over the land, from the Los Angeles Mountains in the west to deciduous forests in the east. In this vast area, only some small fragments remain in an environment slightly similar to the original state. The largest central area is composed of mixed grasslands, mainly composed of several grasses of Stipa, Agropyron, Bouteloua and Koeleria. The mixed grassland in the north is replaced by Festuca arundinacea and Festuca arundinacea, the short grassland in the west is Festuca tenuifolia and Festuca hooves, and the long grassland in the east is Leymus elongata and Leymus chinensis. There are usually no trees and shrubs, but many different herbs appear with grass.

The largest herbivorous mammals on the North American grassland include bison and forked sheep, and their typical predators are gray wolves. Rabbits, hares and tapirs are common, as are many small burrowing rodents. Among invertebrates, grasshoppers have always been particularly important. Generally speaking, the total biomass of grassland invertebrates exceeds that of larger and more conspicuous vertebrates, except in areas with a large number of livestock.