Second, forests have natural epidemic prevention functions. Trees can secrete fungicides with strong lethality, kill germs and microorganisms in the air, and have a certain health care effect on human body. Some people have measured the content of bacteria in the air in different environments: 65,438+0,000 in parks where people walk, 30,000-40,000 in urban streets, and only 55 in forest areas. In addition, the bactericidal dose secreted by trees is also considerable. For example, a hectare of cypress forest can secrete 30 kilograms of bactericide every day, which can kill diphtheria, tuberculosis, dysentery and other germs.
Third, the forest is a natural oxygen factory. Oxygen is the basic condition for human life. The human body is breathing oxygen and expelling carbon dioxide all the time. It is common sense that healthy people will not die if they don't eat or drink for three or two days, but will die if they lack oxygen for a few minutes. According to the literature, a person needs to inhale 0.8 kg of oxygen and expel 0.9 kg of carbon dioxide every day to survive. Forests absorb a lot of carbon dioxide and release oxygen during their growth. According to research, for every 44 grams of carbon dioxide absorbed by trees, 32 grams of oxygen can be released; Leaves produce one gram of glucose through photosynthesis, which can consume all the carbon dioxide contained in 2500 liters of air. According to theoretical calculation, every cubic meter of wood grown in the forest can absorb about 850 kilograms of carbon dioxide in the atmosphere. At the peak of tree growth, one hectare of broad-leaved forest can absorb one ton of carbon dioxide every day and produce 750 kilograms of oxygen. The data show that 10 square meter of forest or 25 square meters of grassland can absorb all the carbon dioxide that a person breathes and supply the required oxygen. It is true that trees also absorb oxygen and expel carbon dioxide at night, but the amount of carbon dioxide inhaled during the day is very large, almost 20 times that at night, compared with the side effects at night. On a global scale, forest green space can treat nearly 1000 billion tons of carbon dioxide for human beings every year, provide 60% clean oxygen for the air, and absorb suspended particles in the atmosphere, which has great ability to improve air quality; And can reduce greenhouse gases and thermal effects.
Fourth, the forest is a natural muffler. With the development of transportation, especially in cities and towns, noise is more and more harmful to human beings. According to the research results, the noise is below 50 decibels, which has no effect on people; When the noise reaches 70 decibels, it will cause obvious harm to people; If the noise exceeds 90 decibels, people can't work for a long time. As a natural muffler, forest has a good anti-noise effect. Experiments show that parks or woodlands can reduce noise by 5-40 decibels, which is 5-25 decibels more than the natural attenuation effect of open spaces at the same distance from the sound source. The car tweeter can reduce the noise 10-20 decibels when it passes through the multi-level forest belt composed of lawns, shrubs and trees with a width of 40 meters, which is 4-8 decibels more than the natural attenuation effect in the open area. Planting trees on urban streets can also reduce noise by 7- 10 decibels. In order to have a good effect of noise reduction, there must be at least one forest belt with a width of 6 meters (crown) and a height of 15 meters in the city. The forest belt should not be too far away from the sound source, and it is generally between 6- 15 meters.
5. Forests can regulate climate. The dense forest canopy can absorb, scatter and reflect part of solar radiation energy in summer, thus reducing ground warming. Although most forest leaves wither in winter, dense branches can still reduce the wind speed blowing across the ground, reduce air flow, and play a role in heat preservation and moisture preservation. According to the measurement, the temperature of forest in summer is 2-4℃ lower than that of urban open space, and the relative humidity is high 15-25%, which is lower than that of asphalt concrete cement pavement 10-20℃. Because the roots of trees go deep into the ground, they constantly absorb the water in the deep soil for trees to transpiration, which makes the forest form fog normally and increases precipitation. Through analysis and comparison, the annual precipitation in forest areas is more than that in non-forest areas 10-30%. According to foreign reports, in order to protect the natural environment, the green coverage rate of forests should account for more than 25% of the total area.
Six, the forest changes the low-level airflow, which has the functions of preventing sandstorms and reducing disasters, conserving water sources and conserving water and soil. Due to the blocking and friction consumption of forest trunks, branches and leaves, the wind speed entering the forest area will be obviously weakened. According to the data, dense canopy can reduce the wind speed by as much as 50% in summer. The wind is 200 meters before entering the forest, and the wind speed changes little; After crossing the forest, it takes about 500- 1000 meters to restore the speed before crossing the forest. Humans use this function of forests to plant trees and control desertification.
The rotten layer of forest surface litter is increasing, forming a thick humus layer, just like a huge sponge that absorbs rainwater, which has powerful functions of absorbing water, delaying runoff and weakening flood peak. In addition, the canopy can intercept rainwater, reduce the impact of rainwater on the ground, and maintain soil and water. According to the calculation, the canopy can block 10-20% of the precipitation, most of which evaporates into the atmosphere, and the rest falls to the ground or seeps into the soil along the trunk to become groundwater, so a forest is a reservoir. The roots of forest vegetation can firmly fix the soil, prevent the land from being washed by rain, prevent soil erosion and prevent land desertification.
Seven, the forest has the function of dust removal and sewage filtration. Smoke, dust and waste gas emitted by industrial development seriously pollute the air and threaten human health. The folds and fluff on the leaves of tall trees, as well as the viscous oil and juice secreted by stomata, can intercept a lot of dust and have obvious blocking, filtering and adsorption effects. According to the data, spruce can absorb 8 8. 14 grams of dust per square meter every day, 9.86 grams of pine forest and 3.39 grams of elm forest. Generally speaking, the air dust concentration in forest areas is lower than that in non-forest areas 10-25%. In addition, the forest has a strong ability to purify sewage. According to foreign research, the bacterial content of sewage can be reduced by half when it passes through the forest land of about 40 meters, and then with the increase of the distance through the forest land, the number of bacteria in sewage can be reduced to more than 90% at most.
8. Forest is the habitat of many kinds of animals, the growth place of many kinds of plants, and the most active area of biological reproduction on the earth. Therefore, forests protect biodiversity resources; Moreover, whether around the city or in the outer suburbs, forests are extremely valuable natural landscape resources.
Because people consume a lot of forest wood resources, the forest area on the earth is decreasing year by year, which has caused many environmental problems, such as drought, lack of rain, climate warming, reduction of animal and plant resources, soil erosion, sandstorm and increased air pollution. Therefore, the value of forest to environment and ecology is much higher than the value of wood it provides.
Therefore, planting trees, expanding forest area and increasing forest resources are important events related to economic, social, environmental and human survival.