Text editing This section is a dynamic system composed of biological communities (including plants, animals and microorganisms) with trees as the main body and their abiotic environments (light, heat, water, gas, soil, etc.). ). It is a landscape unit for material exchange and energy flow among living things, environment and living things. The term ecosystem was put forward by British botanist A.G. Tansley in 1935. He introduced the concept of system into ecology, and thought that there was an inseparable interdependence between biology and environment, which formed an integrated whole of orderly and coordinated logistics and energy flow. This theory has gradually become an important branch of ecology through enrichment and development. After the 1940s, the ecosystem entered the stage of scientific experiment from the theoretical stage. The concepts, theories and research methods of ecosystem have been applied to various biological communities and biological environments, and gradually formed several marginal branches of ecosystem. Forest ecosystem is one of them, which is called terrestrial ecosystem together with natural ecosystems such as grassland, desert, tundra and swamp. Terrestrial ecosystem, freshwater ecosystem and marine ecosystem are all called earth ecosystem, that is, biosphere.
Characteristics and Classification Forest ecosystem is the largest ecosystem in terrestrial ecosystem, with 4.03 billion hectares, accounting for 32.3% of the total land area of 65.438+0.49 billion hectares. It is also the richest ecological resources and gene bank in the world, accounting for more than 90% of terrestrial vegetation biomass, and there are as many as 3 million to 4 million species in tropical rain forests alone. It has large three-dimensional components, long service life, multi-layers, huge underground space and long period. It is the most complex and stable ecosystem in terrestrial ecosystem, which has great influence on other terrestrial ecosystems. Its light energy utilization rate is high, and the annual fixed total energy is about 13× 10 17 kJ, accounting for 63% of the annual fixed total energy of terrestrial ecosystem. The annual dry matter output per hectare is 6 ~ 8 tons. Forest ecosystem has the most types and the widest distribution, spanning cold zone, warm zone and tropical zone. According to its community characteristics and distribution areas, there are coniferous forest, mixed coniferous and broad-leaved forest, deciduous broad-leaved forest, evergreen broad-leaved forest, tropical rain forest, tropical monsoon forest, mangrove forest, coral island evergreen forest, shrub forest and savanna. It can also be divided into small and medium-sized forest ecosystems according to tree species and habitats, including plantation ecosystems.
Therefore, studying the basic laws of composition structure, movement development, material exchange and energy flow of forest ecosystem is helpful to understand its function and time change, so as to take reasonable measures and give play to its economic, ecological and social benefits.
Forest ecosystem consists of biological system and abiotic environment system.
Abiotic environment system is composed of climate, moisture, soil and other ecological factors, including light, heat, water, gas, minerals and so on. Among them, solar energy is the total energy of the ecosystem, which promotes the material circulation in the system and constantly changes its existing form. According to the evolution of geological history and the rhythm of seasonal and day-night alternation, each ecological factor not only has its own unique change law, but also has certain mutual compensation and restriction, coordinating the minimum, optimal and maximum quantitative and qualitative change range required by organisms, forming a variety of ecological environment; Due to the change of time and space, various niches or niches have emerged, which have adapted to the unique physiological and ecological characteristics of various organisms and provided their unique living environment respectively. The more niches in the ecosystem, the richer the biological species and the more complex the system structure. Because of its huge ecological space and stable continuous cycle, forest ecosystem has more niches and biological species than other terrestrial ecosystems.
Biological systems include trees, shrubs, grasses, mosses, lichens, fungi, bacteria, viruses, insects, reptiles, amphibians, birds and mammals. These organisms form food webs according to different nutritional levels. According to their position, function and role in forest ecosystem, they can be divided into three categories: producers, consumers and decomposers.
(1) producer. Refers to the autotrophic organisms with green plant species as the most basic component in the forest ecosystem. It can transform simple inorganic substances into complex organic substances for its own volume growth, respiratory consumption and quantity proliferation. They produce a lot of organic matter through photosynthesis, which lays a material and energy foundation for the movement of forest ecosystem and is the primary producer of the system. Its output in a certain period is called primary output; Its output per unit area is called primary productivity; Deducting respiratory consumption is called net primary productivity. The net primary productivity of forest ecosystem accounts for 65% of the net primary productivity of land. According to their size and ecological characteristics, green plants are distributed in layers or patches in the corresponding horizontal and vertical spaces in the system (see forest structure).
2 consumers. Refers to all kinds of animals in the forest ecosystem, belonging to different trophic levels. Insects, rodents and ruminants that feed on plants belong to primary consumers. Carnivores that feed on primary consumers belong to secondary consumers. Carnivores that feed on secondary consumers belong to tertiary consumers. Omnivores belong to cross-level consumers. In addition, there are parasitic and saprophytic animals, which are also among consumers. The food chain is a nutritional sequence, which starts from the producer and is fed by consumers at all levels in turn. The intersection of several food chains is called food network. The number, distribution and movement of consumers at all levels in the system mainly depend on their feeding habits and food resources.
3 decomposers. Refers to bacteria and fungi that decompose, reduce and transform animal and plant residues in the ecosystem.
Producers, consumers and decomposers are closely dependent on each other. According to their biological characteristics and the law of life activities, they not only have their own time sequence of growth and development, but also occupy the corresponding spatial position in the system, and are arranged in an orderly nutritional level from big to small according to their nutritional categories, individual numbers and productivity. Green plants are the first trophic level, herbivores are the second trophic level, the first carnivore is the third trophic level, the second carnivore is the fourth trophic level and the decomposer is the fifth trophic level. These nutrient levels and criss-crossing food chain structures form an orderly system of material and energy flow between individuals, populations, organisms and the environment, ensuring the stability of the system structure and the effectiveness of its functions. Forest ecosystem has the highest trophic level and high order, which is the reason why its stability is greater than other terrestrial ecosystems.
Exercise and functional life activities are the basic driving forces of ecosystem movement. Forest ecosystem is an open ecosystem. Material energy is input from abiotic environment, and a series of material energy flows through the life activities of organisms in the system and is input into the environment. This repeated internal and external material energy flow and the accompanying information transmission are the basic functions of ecosystem movement. Green plants are the basic starting point of ecosystem movement. Through photosynthesis, solar energy is transformed into chemical energy (biological energy), inorganic substances in the external environment are transformed into internal organic substances, and one group of organisms is transferred to another group through the order of trophic levels. Some materials and energy stored in this way are converted into heat energy and emitted to the environment; Or from internal organic matter to external inorganic matter. For organisms that have lost their lives, part of the material energy remains in the residue, and part of it is released through microbial decomposition and reduction, and transported to the environment (see figure). The flow of matter and energy is synchronous, the flow of energy is unidirectional, and the logistics can be repeated.
The first trophic level of ecosystem has the highest utilization rate of matter and energy and the largest yield. With the improvement of nutritional grade, the production efficiency of matter and energy decreases accordingly. Generally, it is transmitted step by step at the rate of 10%, which is called the ecological nutrition dynamics 10% rule. Arranged in the shape of a pyramid, called an ecological pyramid, expressed by kilojoule/(m2 year); The biomass pyramid is expressed in grams /(m 2 years); The digital pyramid is represented by the number of creatures. Forest ecosystem is rich in species, with high utilization rate of matter and energy, and its ecological pyramid has many levels.
The ordered arrangement of nutrition levels and food networks in forest ecosystem shows that it is a highly self-organized system with obvious feedback and negative feedback: organisms receive the influence of external environment and form information feedback. Because it has the ability of selection, processing and adjustment, its information transmission is manifested in the negative feedback process of system self-regulation, self-restraint and self-organization, forming an orderly and unified structural whole to adapt to environmental changes, ensuring the normal life activities of organisms and the virtuous circle of material and energy movement of the system. On the other hand, if the ecological environment suddenly changes dramatically or the ecological network is seriously broken, and the information transmission and feedback functions fail, it may lead to chaos or even collapse of the ecosystem.
The flow rate and production effect of matter and energy in forest ecosystem are significantly different due to forest types and regional conditions. Generally, it is tropical rain forest > tropical monsoon forest > subtropical evergreen broad-leaved forest > temperate deciduous broad-leaved forest > coniferous forest in cold region and sub-cold region.
The benefits of ecologically balanced forests, including economic benefits, ecological benefits and social benefits (see forest benefits), can only be brought into full play when the forest ecosystem is in dynamic balance. The signs of ecological balance are: the relative stability of biological population, quantity and structure; Ecological community adapts to abiotic environment; The material-energy flow system has high order; The effect of information feedback and negative feedback is obvious; Productivity and biomass reached the highest level. Protecting forest resources, implementing sustainable management, and limiting the amount of cutting not to be greater than the amount of growth are the fundamental measures to protect the ecological balance and ensure the overall benefits of the forest ecosystem.
Research and Application Since the 1940s, the research on ecosystem has made great progress from local to whole, from scattered to systematic, from static to dynamic, from qualitative to quantitative, from phenomenon to essence. Especially in recent 10 years, with the help of thermodynamics entropy change theory, information concept, system engineering and other disciplines, a series of studies have been carried out around the three basic functions of ecosystem, such as material exchange, energy flow and information transmission, as well as the three major benefits of economy, ecology and society.
The main aspects of current research are: ① the study of productivity. It involves forest bioclimate, forest soil, forest primary and secondary productivity, animals and plants, nutrient cycle and so on. Which belongs to the basic research of forest ecosystem. ② Research on material circulation and energy circulation. It involves the system, structure, process and speed of material and energy flow, as well as the accompanying information feedback and negative feedback mechanism, and belongs to the study of forest ecosystem structure and function. ③ Interest research. On the basis of studying the composition, structure and function of forest ecosystem, this paper studies the direct and indirect benefits it can provide, analyzes and compares its potential value, and maintains and exerts its maximum function. ④ Study on artificial ecosystem. With the decrease of natural forests, the proportion of artificial forests is increasing and becoming more and more important. The purpose is to restore and build forests according to the theories, principles and methods of ecosystem. The research contents include site conditions and their productivity, tree species characteristics, land renewal, stand structure allocation, fertilization and irrigation, tending and protection, and reconstruction and restoration of secondary forests. ⑤ Research on system simulation and system design. In other words, all kinds of processes, internal relations and ecosystem engineering designed according to the different benefit requirements of the ecosystem are expressed and described in an abstract way. Because forest ecosystem is a multi-input, multi-output and time-varying open system, the establishment of its dynamic model should first determine the state variables of the system, including the following data: biological population, the structure of biological population and system, and the evolution of biological community and system (such as diversity index, etc.). ), the influence of abiotic environmental factors on population and structure, the relationship between biological populations, the flow of matter and energy and information transmission.
The above research should choose representative forest types and areas to set up positioning stations. China has successively set up fixed points in Xiaoxing 'anling, Changbai Mountain mixed coniferous and broad-leaved forest, Jianghua Cunninghamia lanceolata forest in Hunan and Xishuangbanna tropical rain forest in Yunnan, and provided necessary data for comprehensive analysis and evaluation through long-term systematic measurement, recording and observation. Because this work involves a wide range of subjects, it requires the joint efforts of natural science and social science to achieve the expected results.