Statically speaking, forest distribution is a comprehensive response of forest flora to specific regional environmental conditions, and it is the result of long-term adaptation of the two. In other words, the types of forests or vegetation in a certain area are closely related to the environment, mainly to the climate. Climatic conditions have a direct impact on vegetation and an indirect impact through soil. The relationship between soil and vegetation is quite close, which can be regarded as a unity. Their properties depend on the influence of climate and parent rock on soil, while flora acts on vegetation.
The evolution and succession of forest communities are two completely different concepts. "Evolution" refers to the historical evolution process of forest plant communities. All the existing forest plant community types are the products of the long-term historical evolution and development of nature, and are gradually formed in the long-term evolution process. Forest distribution is the result of geographical and historical changes and the evolution of forest plant communities.
The evolution of forest plant community is generally realized by absorption evolution and differentiation evolution. The so-called evolutionary path of absorption is actually the process of forming a new community type at the contact point of each participant. In this process, the forest plant species and their complexes obtained from the new community have expanded their adaptability to the changed ecological environment when forming the new community, thus gaining new impetus for further evolution. The contact of several different forest plant communities often leads to the emergence of evolutionarily young communities. The evolutionary path of differentiation is opposite to the evolutionary path of absorption, and the evolutionary path of absorption is a process in which a community type is differentiated into several derivative community types. Usually, it is a very complex large cluster containing many dominant tree species, which is divided into several clusters dominated by one or several tree species.
These two evolutionary processes are usually combined. The original vegetation types and their differentiation products of multi-dominant species are influenced by the surrounding vegetation types, and the latter all play the role of entrants to some extent.
The driving forces of forest plant community evolution mainly come from geological changes and climate changes.
The ancestors of modern forests are Greek communities, which first appeared in the Carboniferous period about 345 million years ago, and were mainly composed of gymnosperms and ancient pteridophytes. At the end of Permian, the seabed expanded, the primitive ancient continent began to separate, the ancient Mediterranean formed on the southern edge of Eurasia, and a huge orogeny took place, and the climate changed dramatically from warm to cold. The ancient pteridophytes were extinct, leaving only gymnosperms, and a large area of ancient coniferous forest was formed in Triassic about 225 million years ago. Since then, from Jurassic to Cretaceous, the earth's surface climate has been warming continuously, and angiosperms have developed rapidly, forming a forest plant community with complex vertical differentiation and multi-layer structure with its high plasticity and diverse life forms. They are the main components of modern forest plant communities.
From Cretaceous to Cenozoic Tertiary, large-scale orogeny appeared again on the earth, and the largest modern mountain system was formed during this period. The climate on the earth has also undergone further changes, which is manifested in the continuous expansion of tropical and subtropical climate ranges. The vegetation belt has also changed accordingly. There are two vegetation belts with different appearances on the earth: one is an evergreen forest belt in a warm and humid climate, and the other is a deciduous forest belt in a climate with moderate rainfall and alternating seasons.
About 2 million to 3 million years ago, the Quaternary glacial movement began. Glaciers advance and retreat. The climate gets cold at first and warm at the end. The tree species composition of warm-loving forest was obviously affected, and a large number of coniferous and broad-leaved trees appeared, which formed a cold temperate coniferous forest during this period. Typical broad-leaved tree species retreat to the south, forming a forest grassland on the southern edge of the forest belt. Influenced by the Quaternary glacial movement, the typical forest tree species formed in the Early Tertiary disappeared from the European continent, and remained as a relic tree species in a few areas less affected by glaciers, which made the forest plant communities in these areas, including the southwestern mountainous areas of China, Japan, Southeast Asia, northern Mexico and parts of the southeastern and southwestern United States, have the characteristics of temperate, tropical and subtropical transition.