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 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 equivalent of ten bags of high-nitrogen fertilizer to each hectare per year. Other chemical changes to soil i
n 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 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.
31. What does the 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
32. The word "dense" in line I is closest in meaning to
(A) dark
(B) tall
(C) thick
(D) broad
33. Alder trees can suppress the growth of nearby trees by depriving them of
(A) nitrogen
(B) sunlight
(C) soil nutrients
(D) water
34. Thc passage suggests that Douglas fir trees are
(A)a type of alder
(B)a type of evergreen
(C)similar to sword ferns
(D)fast-growing trees
35. It can be inferred from paragraph I that hemlock trees
(A) are similar in size to alder trees.
(B) interfere with the growth of Douglas fir trees
(C) reduce the number of alder trees In the forest
(D) need less sunlight than do Douglas fir trees
36. It can be inferred from paragraph 2 that previous generations of foresters
(A) did not study the effects of alders on forests
(B) did not want alders In forests
(C) harvested alders for lumber
(D) used alders to control the growth of evergreens
37. The word "they" in line 21 refers to
(A) newly developing soils
(B) alders
(C) bags
(D) chemical changes
38. According to the passage that alders are used in mountainous areas to
(A) nitrogen
(B) calcium
(C) carbon
(D) oxygen
39. It can be Inferred from the passage that alders are used in mountainous areas to
(A) prevent water from carrying away soil
(B) hold the snow
(C) protect mines
(D) provide material for housing
40. What is the author's main purpose in the passage?
(A) To argue that alder trees are useful in forest management
(B) To explain the life cycle of alder trees
(C) To criticize the way alders |
