What Good Is a Tree?(2/2)
树有何益?
By Lowell Ponte

Odd Alliances. Trees have always been green machines, producing substances that humans learned to use. The ancient Greeks, for example, treated pain with a tea made by boiling willow leaves and bark, a tea modern scientists now know contains salicin, a precursor of acetylsalicylic acid—aspirin. For centuries, the Chinese have derived medicines from the ginkgo tree. More recently, researchers isolated and synthesized the chemical ginkgolide from the tree for use in treating asthma, toxic shock and other ills.
奇怪的联合。一株株树木就成了一部部绿色的机器，生产出各种物质来，让人类学会使用。例如，古希腊人用柳叶和柳树皮煮成的茶水来止痛。现代科学家已经了解到，这种茶里面含有水杨苷成分，就是乙酰水杨酸——阿司匹林的前身。几个世纪以来，中国人一直在银杏树上提取药材。最近，研究人员从这种树上分离并合成了化学药物银杏苦内脂，用来治疗哮喘、中毒性休克等疾病。
As scientists unlock the secrets of trees, they uncover surprising facts. In the early 1980s David Rhoades, a chemical ecologist at the University of Washington, Seattle, discovered that trees send unseen signals to each other. When willows are attacked by webworms and tent caterpillars, they give off a chemical that alerts nearby willows. The neighboring trees respond by pumping more tannin into their leaves, making them more difficult for the insects to digest.
科学家揭开各种树木秘密的同时，也就揭开了令人吃惊的事实。在20世纪80年代早期，西雅图市华盛顿大学的化学生物学家戴维•罗德斯发现，树木之间能互相传递我们看不见的信号。当柳树遭到结网毛虫或梅毛虫袭击时，它们就会发出一种化学物质，以警告附近的柳树。邻近的柳树就会在它们的叶片内注入更多的单宁酸，使叶子难以被这些虫子所消化。
Researchers have found similar responses in sugar maples, birches and other trees. To their surprise, the scientists found evidence that trees respond differently to different attackers—trees will not react if leaves are nipped with sterilized scissors, for example, but do release tannin if the attacker is an insect.
研究人员在糖槭树、桦树等其他一些树木上也发现了类似的反应。令科学家们感到吃惊的是，他们发现，树木对不同的侵犯者会产生不同的反应——例如，用灭菌的剪刀剪断树叶时，树木没有反应；而如果害虫前来入侵，它们就会释放出单宁酸。
It has long been known that trees enhance rainfall by cooling the land, slowing wind evaporation and erosion, and transpiring water into the sky from their leaves. An acre of large healthy maples, for instance, puts 20, 000 gallons of water into the air each day. Without trees our entire world would be a much drier place.
长久以来人们就知道树木能提高降雨量，原理就是，树木使大地变得更凉爽，同时减慢风力蒸发和侵蚀，并使叶子上的水汽蒸发到空气中去。例如，一亩茂盛的枫树林每天就会使20,000加仑的水蒸发到空气中去。没有了树木，我们整个世界都将会是一片非常干燥的大地。
Now scientists have found that trees may cause rain in more peculiar ways, too. Many species are inhabited by the bacterium. Pseudomonas syringae. When wafted into the air, the microscopic bugs are believed to act as ice nuclei, thus increasing the likelihood of rain or snow. In this symbiotic arrangement, trees provide a home for the bacteria and the bacteria help wring water from the sky for the trees.
如今，科学家还发现有些树木以更为独特的方式来促使降雨的发生。许多树种上都有细菌寄生，如丁香假单孢菌。这些微生物被微风吹到空气中时，会起到冰核的作用，因而就提高了降雨或降雪的可能性。这这种共生模式中，树木为细菌提供了住所，而细菌则帮助树木从空中“榨出”水份。
Trees have made an alliance with another amazing microscopic symbiont, mycorrhizal fungi. Beneath the typical tree, roots generally reach half as deep and twice as wide as the tree we see above ground. When the roots of two trees touch, a battle for dominance usually ensues—unless the mycorrhizal fungi are on the scene. Forest scientist David Perry of Oregon State University has found that these fungi not only reduce competition between the trees but also link together roots from trees of the same or even different species. In one experiment, Perry grew seedlings and watched their roots join through the mycorrhizal. Then the scientist cast shade over one of the seedling. The shaded tree began to draw nutrients from the sunlit tree through the fungal linkage between them.
树木还有另外一种令人惊异的共生微生物——菌根真菌。一些典型的树种地下的根系深度是树高的一半，而根系的横向范围和我们看到的地上的树木范围一样宽。如果两棵树的根系相遇了，一场争取支配地位的战争通常难以避免——除非菌根真菌登场。俄勒冈州立大学的森林科学家戴维•佩里发现，这些真菌不仅减少树木之间的竞争，而且还会让同种树木，或者甚至是异种树木的根系联系在一起。在一次试验中，佩里种了一些树种，然后观察它们的根通过菌根真菌而连接的情形。没有受到光照的树通过真菌的联系而从光照充足的树上汲取养分。
“Thanks to these fungi,” says Perry, “it could be that a whole forest is linked together like a community. If one tree has access to water, another to nutrients, a third to sunlight, the trees apparently can share with one another.”
“多亏了这些真菌，”佩里说，“它使得整个森林像一个社会一样被联系起来。如果一棵树得到了水分，另外一棵得到了养分，第三棵得到了阳光照射，那么树木之间显然可以共同分享这些资源。
Agro-forestry. Of course, humans live in symbiosis with trees too: trees take in the carbon dioxide people and their machines make and turn it into needed oxygen. And we plant and care for trees in return for the many benefits they confer on us. Unfortunately, it often takes the loss of trees to remind us just how much we depend on them.
农林业。当然，人类与树木也是共生的。树木吸收人类生活及其机器生产所产生出来的二氧化碳气体，并且把转化成必需的氧气。我们植树护林，能从树木给予我们的许多回报中受益多多。然而不幸的是，经常只有失去树木的时候才使我们想起，我们是多么离不开它们啊。
A leafy canopy shades about 30 percent of the average American city. But in many cities only one tree is replaced for every four that die.
树木的绿色枝叶搭成的天蓬大约遮盖了平均30%的美国城市。但是在许多城市，平均每死掉4棵树，补种的只有1棵。
As settlers came to Los Angeles, they found it hot and dry. They brought in water and planted groves of orange trees across the L.A. Basin. “That cooled the climate by several degrees,” says Art Rosenfeld, a physics professor at the University of California at Berkeley.
当外来移民刚刚来到洛杉矶的时候，他们发现这里气候炎热而干燥。于是他们就运来水，沿着洛杉矶盆地种下一片片橘林。“这使得气温降低好几度，”伯克利市的加利福尼亚大学的物理学阿特•罗森费尔德教授说。
In recent decades the orange groves have been cleared for buildings and blacktop, and the climate is now six degrees hotter. says Rosenfeld: “Residents each year use up two gigawatts of electricity to compensate for the extra heat, at all added cost of $ 2 billion.”
在最近几十年里，为了盖楼筑路，这些橘林不断遭到砍伐，而这里的气温比过去上升6度。罗森费尔德教授说：“居民们每年要用去10亿瓦的电量用来降低这些升高的热量，总计耗费20亿美元。”
In warm weather, those living in homes near trees save directly on their utility bills. Lee Laechelt of the Alabama Forestry Commission calculates that shade from trees could save up to $175 a year in air-conditioning.
天气暖热的时候，那些依树傍绿的家庭就节省了电费开支。阿拉巴马州林业署的李•雷彻尔特算了一笔账，树荫一年可以为家中节省175美元的空调用电开支。
The need for trees is even greater elsewhere in the world. In some countries, researchers are now experimenting with agro-forestry—the planting of crops between rows of special trees. Gliricidia Sepium, for example, is a Central American tree that grows well even in poor, dry soil. It produces leaves that farmers can feed to cattle, and it has roots that enrich the soil with nitrogen. The trees protect crops from wind and prevent soil erosion. When cut for firewood, they will sprout new growth from the remaining stump.
世界上其他一些地方甚至对树木的需求更为强烈。有些国家的研究人员正在开展一项农林相结合的实验——在一排排特殊的树木间种植庄稼。例如，毒鼠豆树生长在中美洲，它甚至在贫瘠干旱的土壤中也能茁壮成长。它长出的叶子可以让农民用来喂牛，其树根中的氮可以增强土壤肥力。若砍树作柴，则砍后的树桩还会生出新芽来。
In Israel, the Jewish National Fund has planted over 200, 000 genetic “super trees” developed and donated by Georgia-Pacific Corp. If this tree-planting experiment works in the Negev Desert, forests might be able to grow in many barren parts of the world that are too dry for most trees.
在以色列，犹太国家基金已经出资种植了20万株基因技术培养的“超级树木”，这些树木是乔治亚—太平洋公司捐资培养的。如果这项植树计划在内盖夫沙漠试验成功的话，或许在世界上许多因干燥而使植物难以生长的不毛之地，都可以植树造林的。
Back home, tree planting is becoming a national pastime. Global ReLeaf, sponsored by the American Forestry Association, is working to get 100 million new trees planted in cities and towns across the United States by 1992. The National Arbor Day Foundation in Nebraska City, Neb., has challenged cities to earn its green-and-white “Tree City U.S.A” flag by planting and protecting more trees. In hundreds of cities, citizens have organized to re-green their communities: San Francisco Friends of the Urban Forest, New York City Street Tree Consortium, Green Shore in Baltimore, the Open Lands Project in Chicago.
回到国内，植树活动正逐渐成为一项全民性的业余活动。美国林业协会发起的“全面绿化”行动，截止到1992年，已经在全美的城市和乡镇栽下了一亿株树苗。在内布拉斯加城的国家植树节基金会向许多城市挑战，它们通过栽种和保护更多的树木而赢得了那面白绿条格相间的“美国树城”的旗帜。在数百个城市中，市民自发组织起来开展绿化社区运动，有旧金山的“森林之友”，有纽约的“街道树木联盟”，有巴尔的摩的“绿色海岸”，还有芝加哥的“土地开发计划”。
For a few dollars you can purchase a tree that will give you decades of fruits or nuts, flowers and shade, a quieter and more beautiful home. And you can take pleasure in knowing that, according to the U.S. Forest Service, trees call boost the market value of your home by an average six or seven percent.
只花几美元，你就能买上一棵树，它能使你享受几十年的鲜花、果实和树荫，以及一个更为安静而美丽的家园。而且，根据美国林业服务部门的说法，树木能使你房产的市场价值提升平均六到七个百分点，你一定很高兴了解到这一点。
A hint to the beginning home forester: check with your local library, agricultural service or nursery about best kinds of trees for your area and how to care for them.
顺便提醒一下要着手绿化的家庭：到当地的图书馆去查阅一下，或者到农业服务部门或育种所咨询一下，看那些树种适合您的区域，以及如何养护这些树木。
Plant your tree where it will not uproot sidewalks or grow into power lines. On the south side of your home, you might select a deciduous tree that gives shade in the summer but loses leaves in winter and lets the sunshine through.
请不要将树木栽种在会给人行道或者电线造成安全隐患的地方。在房屋的南侧，你或许可以选择栽种一株落叶树，它在夏季给你送上荫凉，到了冬季叶子会纷纷落下，以便阳光可以照射入屋内。
Trees have great practical value, but they also partake of the eternal. They are a link to the past and a bridge to the future. Trees touch something deep in the soul that naturalist John Muir recognized when he wrote, “The clearest way to the universe is through a forest wilderness.”
树木的实用价值巨大，但是它们还纵览人世变迁。它们是联系过去的纽带，又是通向未来的桥梁。树木能触到人类灵魂深处的某种东西，自然主义者约翰默尔认识到了这一点，他写道：“通往万物的最明晰的路径，就是那莽莽森林。”