突破瓶頸，掃清生僻學科：熱帶雨林

來自專欄李文勍

【BEAT托福】原創

公眾號：李文勍

作者：李杼鵬

未經作者授權 禁止轉載

在托福考試當中，閱讀和聽力部分曾多次考查過關於熱帶雨林 Rain Forest的文章。

例如：

閱讀TPO 17-2 Animal Signals in the Rain Forest，

TPO 41-2 Latitude and Biodiversity，

TPO 53-2 Rain Forest Soils等。

熱帶雨林作為托福考試中最高頻的考點之一也意味著我們要對其背景知識做到充分了解。做過充分準備的同學，對於再次遇到相關考試內容，一定會更加得心應手。

大家想看哪一方面的乾貨，可以在文末暢所欲言

作者：李杼鵬

熱帶雨林是地球上一種常見於赤道附近熱帶地區的森林生態系統，主要分布於東南亞Southeast Asia、南美洲、中美洲和眾多太平洋島嶼等。

熱帶雨林是地球上抵抗力穩定性resistance stability最高的生物群落biome，常年氣候炎熱，雨量充沛，季節差異極不明顯，生物群落演替succession速度極快，是世界上大於一半的動植物物種的棲息地。

熱帶雨林是人類最為寶貴的資源之一。由於眾多雨林植物的光合作用凈化地球空氣的能力尤為強大，其中僅亞馬遜熱帶雨林產生的氧氣就佔全球氧氣總量的13，故有「地球之肺」的美譽。

熱帶雨林主要的作用是調節氣候，防止水土流失，凈化空氣，保證地球生物圈的物質循環有序進行。

Rainforests are forests characterized by high rainfall, with annual rainfall in the case of tropical rainforests between 250 and 450 centimeters (98 and 177 in), and definitions varying by region for temperate rainforests. The monsoon trough, alternatively known as the intertropical convergence zone, plays a significant role in creating the climatic conditions necessary for the Earths tropical rainforests.

Rainforests are responsible for 28% of the worlds oxygen turnover, sometimes misnamed oxygen production, processing it through photosynthesis from carbon dioxide and consuming it through respiration.（節選自Wikipedia）

1) 氣候特徵

熱帶雨林分布的地區，年降雨量很高，通常高於1800毫米，有些地方達3500毫米。全年雨量分配均勻，常年濕潤，空氣相對濕度95%以上。平均降水量超過每年的蒸發量。無明顯的季節變化，白天溫度一般在30℃左右，夜間約20℃。

2) 地理位置

熱帶雨林主要分布在南美、亞洲和非洲的叢林地區，大多數熱帶雨林都位於北緯23.5度和南緯23.5度之間（即南回歸線和北回歸線之間的地區）。在熱帶雨林中，通常有三到五層的植被，上面還有高達150-180英尺的樹木像帳篷一樣支蓋著。下面幾層植被的密度取決於陽光穿透上層樹木的程度，照進來的陽光越多，密度就越大。

In a mature floodplain tropical forest in the Amazon River basin, the canopy (the uppermost layers of a forest, formed by the crowns of trees) takes on a stratified structure. There are three clear peaks in leaf cover at heights of approximately 3, 6, and 30 meters above the ground; and the very highest layer, at 50 meters, corresponds to the very tall trees that stand free of the main canopy and form an open layer of their own. So, such a forest contains essentially four layers of canopy. （節選自TPO 41-2 Latitude and Biodiversity）

3) 地形地貌

雨林地區的地形複雜多樣，地貌造就了形態萬千的雨林景觀。在熱帶雨林中，靜靜的池水、奔騰的小溪、飛瀉的瀑布；參天的大樹、纏繞的藤蘿、繁茂的花草皆囊括其中。

在觀賞熱帶雨林鬱鬱蔥蔥的植物生長時，多數人會誤認為它下面的土壤營養豐富。但是，充分的降雨容易將礦物質營養物質從土壤中沖刷出併流入溪流。這個過程被稱為浸出leaching。由於雨水浸出，大多數熱帶雨林土壤的礦物質含量都很低。

On viewing the lush plant growth of a tropical rain forest, most people would conclude that the soil beneath it is rich in nutrients. In many contexts—grasslands and most other types of forest, for example—that inference would be correct. However, although rain forest soils are highly variable, they have in common the fact that abundant rainfall washes mineral nutrients out of them and into streams. This process is known as leaching. Because of rain leaching, most tropical rainforest soils have low to very low mineral nutrient content. （節選自TPO 53-2 Rain Forest Soils）

熱帶雨林的高濕度和高溫度加速了分解有機化合物的土壤微生物的生長，因此熱帶雨林土壤的有機物化合物的含量通常比其他森林或草地土壤低得多。由於有機化合物有助於鬆散粘土土壤，保持水分，結合礦物質營養，土壤中有機物質的缺乏對植物十分有害。

High moisture and temperatures speed the growth of soil microbes that decompose organic compounds, so tropical soils typically contain far lower amounts of organic materials (humus) than do other forest or grassland soils. Because organic compounds help loosen compact clay soils, hold water, and bind mineral nutrients, the relative lack of organic materials in tropical soils is deleterious to plants. （節選自TPO 53-2 Rain Forest Soils）

鑒於土壤如此貧瘠，繁茂的熱帶森林如何存在？答案是，森林的礦物質被保存在其生物的體內——樹木、其他植物和動物身體中。死葉、樹枝等植物部分，以及熱帶雨林動物的廢物和屍體，幾乎還沒有到達森林的地面，就被大量的細菌和微生物迅速分解。腐爛釋放出來的礦物很快被眾多淺而細的植物根系吸收並儲存在植物組織中。因此，熱帶雨林通常具有所謂的封閉營養系統，其中礦物質從一個生物體轉移到另一個生物體，幾乎沒有滲漏到土壤中。當礦物質營養素在土壤中消耗的時間不多時，它們不會被浸出進入溪流。

Given such poor soils, how can lush tropical forests exist? The answer is that the forests minerals are held in its living biomass—the trees and other plants and the animals. Dead leaves, branches, and other plant parts, as well as the wastes and bodies of rainforest animals, barely reach the forest floor before they are rapidly decayed by abundant decomposers—bacterial and fungal. Minerals released by decay are quickly absorbed by multitudinous shallow, fine tree feeder roots and stored in plant tissues. Consequently, tropical rainforests typically have what are known as closed nutrient systems, in which minerals are handed off from one organism to another with little leaking through to the soil. When mineral nutrients do not spend much time in the soil, they cannot be leached into streams. （節選自TPO 53-2 Rain Forest Soils）

在多樣和不斷變化的森林光照環境下，熱帶雨林中的動物需要發送視覺信號給自己的同類，同時避免被捕食者發現。很多兩棲動物amphibians（青蛙和蟾蜍）和爬行動物reptiles（蜥蜴和蛇）都可以通過改變顏色圖案來偽裝自己或發出信號。變色龍chameleon lizard在這方面有著最驚人的能力。

In the varied and constantly changing light environment of the forest, an animal must be able to send visual signals to members of its own species and at the same time avoid being detected by predators. An animal can hide from predators by choosing the light environment in which its pattern is least visible. Many species of amphibians (frogs and toads) and reptiles (lizards and snakes) are able to change their color patterns to camouflage themselves. Some also signal by changing color. The chameleon lizard has the most striking ability to do this. （節選自TPO 17-2 Animal Signals in the Rain Forest）

不能進行變色的物種則在光照對它們有利的時候才會利用光照，來進行視覺上的自我展現。例如雄性極樂鳥會置身於匯聚的光線之下，在最佳的場景中展現自己繽紛絢爛的羽翼，以吸引雌鳥的注意。某些蝴蝶則飛到穿透森林的太陽光點處，在明亮的光點中扇動著帶有美麗圖案的翅膀來展現自己。

Other species take into account the changing conditions of light by performing their visual displays only when the light is favorable. A male bird of paradise may put himself in the limelight by displaying his spectacular plumage in the best stage setting to attract a female. Certain butterflies move into spots of sunlight that have penetrated to the forest floor and display by opening and closing their beautifully patterned wings in the bright spotlights. （節選自TPO 17-2 Animal Signals in the Rain Forest）

對於生活在熱帶雨林中的色彩不夠鮮艷動物來說，它們則傾向於發出其他形式的信號，如聲音信號。東南亞雨林中有能發出尖銳叫聲的犀鳥和叫聲清厲的長臂猿。雄性極樂鳥在求愛期則同時運用了視覺和聲音這兩種信號傳送。它張開翅膀時發出的聲響能夠極好地傳送到遠距離之外，鋪天蓋地地宣傳著它的儀錶風采。而當雌鳥吸引而來時，儀式化的視覺展現就得以近距離地進行交流。

Less colorful birds and animals that inhabit the rain forest tend to rely on forms of signaling other than the visual, particularly over long distances. The piercing cries of the rhinoceros hornbill characterize the Southeast Asian rain forest, as do the unmistakable calls of the gibbons. In densely wooded environments, sound is the best means of communication over distance because in comparison with light, it travels with little impediment from trees and other vegetation. （節選自TPO 17-2 Animal Signals in the Rain Forest）

通過今天的介紹，希望同學們對熱帶雨林能有更多了解。雖然在考試當中，或許會出現只依靠背景知識就能解答的題目，但是同學們必須要依靠文章給出的閱讀和聽力獲取相應信息進行答題。相關背景知識能為同學們在學習過程當中提供更多的幫助，但是切勿只依靠背景進行作答。