托福official29听力lecture1 Pedodiversity Plant原文解析+翻译音频

[00:00.00]NARRATOR: Listen to part of a lecture in a plant ecology class.[00:07.48]FEMALE PROFESSOR: So far we have covered biodiversity in the hard wood forest here in the upper peninsula of Michigan from a number of angles.[00:14.67]We've looked at everything from how biodiversity relates to species stability, to competition for forests resources and more.
[00:21.88]But now I want to discuss what's called pedodiversity. [00:27.94]Pedodiversity is basically soil diversity. [00:31.16]When we analyze pedodiversity within an area, we are measuring how much variability there is in soil properties and how many different types of soil there are in a particular area.
[00:41.72]So we look at soil chemistry.[00:44.54] For example, how much nitrogen or magnesium there's in the soil in one spot.[00:49.30]And we compare it with the chemistry of the soil a short distance away.[00:55.64]Until recently, there hasn't been a whole lot of attention paid to pedodiversity. [01:00.11]But that's changing rapidly.[01:02.08] More and more studies are being done in these fields. [01:04.76]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.[01:17.04]A high degree of soil variability in a small area is common, particularly within forests.[01:23.41]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's soil. [01:32.13]It generally has more diversity.[01:34.38]Um, OK. There are three main causes of pedodiversity within old-growth forest here in our region of Michigan.[01:43.55]One is tree species. [01:45.35]Different species have different influences on soil formation and soil properties. [01:50.89]For example, pine trees drop pine needles.[01:54.31] And those needles add a lot of acid to the soil. [01:57.47]The organic litter of another tree species might add less acid but more of something else. [02:03.59]A lot of different types of trees in an area might mean more pedodiversity.[02:08.76]Another cause? Gaps created when trees fall. [02:12.99]You see, where there are gaps—open areas—in the forest, the soil there changes.[02:18.79]Um, for instance, without a tree to absorb radiation from the Sun, to offer shade, the full intensity of that radiation reaches the ground. [02:29.03]The soil where the tree used to be heats up. [02:32.16]And without a tree to soak up moisture from the ground, the soil remains wetter than in the surrounding forest.[02:38.56]With a higher temperature and more moist conditions, the process of organic matter decomposition speeds up.[02:45.25]In other words, organic matter gets broken down and added into the soil more quickly in these gaps than in the surrounding forest.[02:53.19]OK. And the third cause: trees being uprooted. [02:57.73]When a tree is uprooted, it might fall into some other trees on its way down, thus falling only partway over. [03:05.11]Or it might crash all the way down to the forest floor. [03:08.36]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.
[03:19.18]And there's still a lot of soil attached to the roots, clinging to the roots. [03:23.81]As that soil is eventually shed from the roots by rain and wind and the movement of squirrels climbing around, things like that. [03:31.52]Um... as the soil is shed, it drops down and forms a little hill of dirt— a mound.[03:37.84]Pits and mounds have significantly different soil properties than other areas in the forest. [03:44.13]You get a redistribution and mixing of soil as deep roots are ripped up from the ground.[03:49.12]Rock fragments can be pulled up too, if they've gotten entangled with the roots over the years. [03:54.24]So rock fragments from the subsoil can end up concentrated on the surface.[03:59.10]There are forests management implications I want to point out. [04:03.04]Forests management impacts soil quality. [04:05.94]And when we better understand pedodiversity, we will be better able to predict the impact of forest management on soil. [04:13.26]But in general, for positive impact, forest management practices should mimic natural forest processes. [04:20.18]And the goal should be to promote pedodiversity, and through this, biodiversity in general.[04:26.32]I have a handout, an article on pedodiversity in a section of forests near here. [04:31.77]I want you to read it, because it makes a point that I've only touched on.[04:35.25]From what I have 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. [04:46.33]As the article explains, forest dynamics affects pedodiversity. [04:51.42]But pedodiversity also affects forest dynamics.[04:55.26] It's worth bearing in mind.