广西森林植被的地理分布规律

The Geographic Distribution Laws of Forest Vegetation in Guangxi

广西地处北纬21°36′—26°21′,东经104°28′—112°5′,地貌是一个由西北向东南倾斜的盆地,盆地周围群山环绕,最高峰海拔2000米以上;盆地内,酸性基岩地貌和岩溶地貌交错发育,形成特殊的生态地貌景观。南部沿海还有各种海岸地貌发育,构成复杂的地质地貌条件,造成局部环境的明显差异,加深了森林植被类型的分化和地理分布的复杂性。由于广西气候条件、特别是热量条件具有较明显的带状分异,森林的分布在地区范围内,呈现一定的规律性。

There are two important developing phases of palaeophytes in the forests. One is the luxuriant phase of gymnospermae from Late Trias to early and middle phases of Late Cretaceous Epoch, the other is the rapidly developing phase of angiospermae from late phase of Late Cretaceous Epoch to Tertiary. With the change of floral elements of forests, the forests change correspondingly. Because some palaeophytes may be the ancestrys of modern forest plants in the development of forest plants of Guangxi, Guangxi is not only one of the key regions of the origin and evolution of forest plants, but also has many old aboriginal types of forest vegetation. The forest vegetation in Guangxi is mainly composed of the tropical- subtropical distribution pattern plants, which are mainly dominated by Pinaceae and Fagaceae. Because the landform is mainly the mountain (60%) and hill (25%) in Guiangxi, the forest has a characteristic of the mountain type, The forests of Pinaceae and Fagaceae are the main and the one of represen- tative types in Guangxi. The forests in Guangxi have outstanding regional differentiation and distribute regularly. Because of the difference of parent rock, the forests are divided into forests on acidic soil and forests on calcareous soil, which can develop into the zonal ones respectively under the same climatic condition. With the increase of latitude, the major zonal vegetation changes as follows: seasonal rain forest in the Northern Tropical Zone→monsoon evergreen broad-leaved forest in the Southern Subtropical Zone→typical evergreen broad-leaved forest in the Central Subtropical Zone, and the forest at each longitude has a characteristic of different constructive species. The vertical distribution of mountain vegetation is different because of the difference of geographical situation, geomorphy and general circulation of mountains, and other reasons. The vertical zonal spectrams of forests on acidic soil mountain and limestone moutain result from the vertical distribution of quantity of heat and of soil water content respectively. The major vertical zonal vegetation changes as follows: evergreen forest→mountain mixed evergreen and deciduous broad-leaved forest or theropencedrymion→elfin forest, but there are not mountain mixed evergreen and deciduous broad-leaved forest and thropencedrymion in the Northern Tropical Zone for its abscence of high mountain. In general, the forest in the northern part of Guangxi distributes more widely than that in the southern part of Guangxi, and also at the edge of the basin than in the inner part. The Rongjiang River Valley, the southern coast of the Hongshuihe River and the Xunjiang River Valley are the main distribution regions of the forests.