TAILIEUCHUNG - Reading knowledge 10

Tham khảo tài liệu 'reading knowledge 10', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | dominates the Douglas fir. After an alder canopy has closed the Douglas fir suffers a marked decrease in growth often dying within several years. Even more shade-tolerant 10 species of trees such as hemlock may remain badly suppressed beneath aggressive young alders. Companies engaged in intensive timber cropping naturally take a dim view of alders suppressing more valuable evergreen trees. But times are changing a new generation of foresters seems better prepared to include in their management plans consideration 15 of the vital ecological role alders play. Among the alder s valuable ecological contributions is its capacity to fix nitrogen in nitrogen-deficient soils. Alder roots contain clusters of nitrogen-fixing nodules like those found on legumes such as beans. In addition newly developing soils exposed by recent glacier retreat and planted with alders show that these trees are applying the 20 equivalent of ten bags of high-nitrogen fertilizer to each hectare per year. Other chemical changes to soil in which they are growing include a lowering of the base content and rise in soil acidity as well as a substantial addition of carbon and calcium to the soil. Another important role many alders play in the wild particularly in mountainous 25 areas is to check the rush of water during spring melt. In Japan and elsewhere the trees are planted to stabilize soil on steep mountain slopes. Similarly alders have been planted to stabilize and rehabilitate waste material left over from old mines flood deposits and landslide areas in both Europe and Asia. 32. What does this passage mainly discuss A Differences between alder trees and Douglas fir trees B Alder trees as a source of timber C Management plans for using alder trees to improve soil D The relation of alder trees to their forest environments 33. The word dense in line 1 is closest in meaning to A dark B tall C thick D broad 34. Alder trees can suppress the growth of nearby trees by depriving them of A nitrogen B .

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