Official 29 Set 2

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Pedodiversity

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What does the professor mainly discuss?
  • A. Causes of soil diversity in old-growth forests

  • B. The results of a recent research study in a Michigan forest

  • C. The impact of pedodiversity on forest growth

  • D. How forest management affects soil diversity

显示答案 正确答案: A

我的笔记 编辑笔记

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    NARRATOR:Listen to part of a lecture in a plant ecology class.

    FEMALE PROFESSOR:So far we've covered biodiversity in the hardwood forests here in the Upper Peninsula of Michigan from a number of angles.We've looked at everything from how biodiversity relates to species stability, to competition for forest resources, and more.But now I want to discuss what's called pedodiversity.

    Pedodiversity is basically soil diversity.When we analyze pedodiversity within an area, we're measuring how much variability there is in soil properties- and how many different types of soil there are in a particular area.So, we look at soil chemistry- for example, how much nitrogen or magnesium there is in the soil in one spot- and we compare it with the chemistry of the soil a short distance away.

    Until recently there hasn't been a whole lot of attention paid to pedodiversity. But that's changing rapidly. More and more studies are being done in this field.There's a link between biodiversity and pedodiversity... an obvious relationship between soils and flora and fauna.Which is why pedodiversity really should be considered in forest management.

    A high degree of soil variability in a small area is common, particularly within forests.If you compare soils from a forest with soils that don't come from a forest, the amount of variability will most likely be greater in the forest soil.It generally has more diversity.

    Um, OK, there are three main causes of pedodiversity within old-growth forests here in our region of Michigan.

    One is tree species. Different species have different influences on soil formation and soil properties.For example, pine trees drop pine needles, and those needles add a lot of acid to the soil.The organic litter of another tree species might add less acid but more of something else.A lot of different types of trees in an area might mean more pedodiversity.

    Another cause? Gaps created when trees fall. You see, where there are gaps-open areas-in the forest, the soil there changes.Um, for instance... without a tree to absorb radiation from the Sun, to offer shade, the full intensity of that radiation reaches the ground. The soil where the tree used to be heats up.And without a tree to soak up moisture from the ground, the soil remains wetter than in the surrounding forest.With a higher temperature and more moist conditions, the process of organic matter decomposition speeds up.In other words, organic matter gets broken down and added into the soil more quickly in these gaps than in the surrounding forest.

    OK, and the third cause: trees being uprooted.When a tree is uprooted, it might fall into some other trees on its way down, thus falling only part way over, or it might crash all the way down to the forest floor.Either way, if its roots are pulled up from out of the ground as the tree topples over, then there's usually a big hole- a pit-left in the ground where the roots used to be.And there's still a lot of soil attached to the roots... clinging to the roots.As that soil is eventually shed from the roots by rain and wind and the movement of squirrels climbing around, things like that, um, as the soil is shed, it drops down and forms a little hill of dirt-a mound.

    Pits and mounds have significantly different soil properties than other areas in the forest.You get a redistribution and mixing of soil as deep roots are ripped up from the ground.Rock fragments can be pulled up too, if they've gotten entangled with the roots over the years.So rock fragments from the subsoil can end up concentrated on the surface.

    There are forest-management implications I want to point out.Forest management impacts soil quality.And when we better understand pedodiversity, we will be better able to predict the impact of forest management on soil.But in general, for positive impact, forest-management practices should mimic natural forest processes.And the goal should be to promote pedodiversity, and through this, biodiversity in general.

    I have a handout-an article on pedodiversity in a section of forest near here.I want you to read it because it makes a point that I've only touched on.From what I've been saying about the causes of pedodiversity, you might assume that the relationship between forest dynamics-what happens to the trees- and pedodiversity is a one-way street.As the article explains, forest dynamics affects pedodiversity, but pedodiversity also affects forest dynamics.It's worth bearing in mind.

  • 旁白:听一段植物生态学课程。

    教授:目前为止,我们已经从多个角度讲了密歇根上部半岛阔叶林中的生物多样性。我们已经讲完全部内容了,从生物多样性与物种稳定性之间的关系,到竞争森林资源等。今天我想讲讲土壤多样性。

    土壤多样性即土壤的多样性。我们分析某个地区的土壤多样性时,我们会测量土壤属性的变化量及在某个地区内有多少种不同的土壤类型。所以,我们看土壤的化学性质,比如说,在某个地方的土壤里有多少氮和镁,然后我们将其与附近土壤的化学性质作比较。

    直到最近,人们才开始关注土壤多样性。但情况迅速改变。越来越多人在此领域做研究。生物多样性和土壤多样性之间是有联系的,土壤与动植物之间有明显关系。这就是为什么在森林管理中,土壤多样性也需要考虑在内。

    小范围地区内的土壤变化程度很高是很常见的,特别是在森林中。如果你比较森林土壤和非森林土壤,前者的变化程度很可能更高。一般森林土壤更多样。

    嗯,好的。在我们所处的密歇根区域的老龄森林中,造成土壤多样性的原因主要有三。

    一是树种。不同的树种对土壤成分和土壤性质有不同的影响。比如说,松树会掉落松针,这些松针给土壤增加了不少酸性。另一种树产生的有机废物可能不会给土壤增加这么多酸性,但会增加别的东西。若在某个区域有很多种不同的树,很有可能意味着这儿的土壤多样性程度很高。

    另一个原因?空地,当树木倒下后就会产生空地。在森林中有空地(开放区域)时,那儿的土壤就会发生改变。举个例子吧,(如果)没有树来吸收太阳辐射,没有树遮阴,太阳辐射以最大强度到达地面。树木曾经所在地的土壤就会升温。而且没有了树来吸收地里的水分,这儿的土壤就会比周围森林(的土壤)更湿润。有了更高的温度和更湿润的条件,有机物分解过程就加快了。换句话说,这些空地上的有机物分解并进入土壤的速度比周围的森林更快。

    第三个原因——树被连根拔起。当一棵树被连根拔起,它很可能会在向下倒时倒在其它树上了, 变成半倒不倒的样子,或者它也可能在倒向森林地面的途中把别的树都撞倒了。哪种都好,如果树木在倒下时把树根从地里拔起来,地面通常会有个大洞,在原来树根所在地留下一个坑。在树根上还有很多附着的泥土。由于下雨和刮风,还有松鼠爬来爬去等,最终这些泥土会从树根上掉落。像这样的,最终这些泥土会从树根上掉落。泥土脱落后会往下掉,形成小土堆。

    比起森林其它地区,土坑和土堆的土壤性质有着显著不同。土地深处的树根被拔起时,土壤会重新分布,或混在一起。岩石碎片也可以被拉上来,如果它们在过去被树根缠住了。所以地下土层的石块可能最后会在地表聚集。

    这些都是我想指出的森林管理可能的影响。森林管理会影响土壤质量。(如果)我们对土壤多样性更了解,我们就能更好地预测森林管理对土壤的影响了。但总体来说,若想产生积极影响,森林管理实践应模仿自然森林过程。其目标应是提升土壤多样性,从而总体提升生物多样性。

    我有一份材料,是一篇讲附近森林的土壤多样性的文章。我希望你们能看完这篇文章,因为这里面所提到的观点,我才仅仅涉及了表面。从我所提到的土壤多样性的原因,你们可能会觉得森林动态(树木都发生了什么)和土壤多样性之间的关系是单向的。正如文章所阐释的,森林动态会影响土壤多样性,但土壤多样性也会影响森林动态。这值得我们注意。

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    题型分析:主旨题

    原文定位

    Professor: But now I want to discuss what’s called pedodiversity …. There are three main causes of pedodiversity within old-growth forests here in our region of Michigan.

    选项分析

    文章先对bio -diversity 展开讨论,然后引出新论点pedodiversity 并进行了定义,接下来讲到了两者的Link以及the cause of pedodiversity。

    A选项即为对话核心的原文定位,是对全文主旨最准确的概括。

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