Topic 30: Environments

Vegetables are parts of (1) __________ that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, (2) __________ the flowers, fruits, stems, leaves, roots, and seeds. Originally, vegetables were collected from the wild by hunter-gatherers and entered cultivation in several parts of the world, probably during the period 10,000 BC to 7,000 BC, when a new agricultural way of life developed. At first, plants which grew locally would have been cultivated, but as time went on, trade brought exotic crops from (3)__________ to add to domestic types. Nowadays, most vegetables are grown all over the world as climate permits.

Crops may be cultivated in protected environments in less suitable locations, and global trade in (4) __________ products allows consumers to purchase vegetables grown in faraway countries. The scale of production varies from subsistence farmers supplying the needs of their family for food, to agribusinesses with vast areas of single-product crops. Depending on the type of vegetable concerned, harvesting the crop is followed by grading, storing, processing, and marketing. Vegetables can be eaten (5) __________ raw or cooked and play an important role in human nutrition, being mostly low in fat and carbohydrates, but high in vitamins, minerals and dietary fiber. Many nutritionists encourage people to consume plenty of fruit and vegetables, five or more portions a day often being recommended.

The “balance of nature” is not an empty phrase. Nature provides a population to occupy a suitable environment and cuts down surplus on population to fit the available food supply. One means of reducing surplus population is predators; others are parasites and diseases. Also, population density produces nervous disorders and even drivers animals to mass migrations, like the lemmings of Norway who plunge into the sea.

That predator populations increase to control other animals has long been known. Many years ago, the Hudsons Bay Company records revealed that the fox population went up and down about a year after the rabbit population had gone up and down.

Sometimes a situation occurs in which the predator population is reduced to a level below that which nature can readily replace. On Valcour Island in Lake Champlain (New York), a costly campaign resulted in the elimination of predatory animals only to have birds and small animals (including grouse and hares, popular game) increase for four years afterward. Then, lacking predator control, nature resorted to disease to cut down on these populations.

Jamaica had an example of natures persistence in providing animals for existing habits. Sugar planters, about 75 years ago, imported mongooses to control rats. The mongooses killed off the rats and, with plentiful food, multiplied. Rats became scarce and the mongooses ate lambs, puppies, and wildlife. Eventually, food became scarce and the mongooses’ population declined.

Trees are useful to man in three very important ways: they provide him with wood and other products; they give him shade; and they help to prevent droughts and floods.

Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important. In his eagerness to draw quick profit from the trees, he has cut them down in large numbers.

Two thousand years ago, a rich and powerful country cut down its trees to build warships, with which to gain itself an empire. It gained the empire but, without its trees, its soil became bare and poor. When the empire fell to pieces, the country found itself faced by floods and starvation.

Even though government realizes the importance of a plentiful supply of trees, it is difficult sometimes to make the people realize this. They cut down the trees but are too careless to plant and look after new trees. So, unless the government has a good system of control, or can educate the people, the forests will slowly disappear.

This does not only mean that there will be fewer trees. The results are even more serious: for where there are trees, their roots break the soil up, allowing the rain to sink in, and also bind the soil. This prevents the soil from being washed away. But where there are no trees, the rain falls on hard ground and flows away on the surface, and this causes floods and the rain carries away the rich topsoil in which crops grow. When all the topsoil is gone, nothing remains but worthless desert.

(Source: www.cmr.com.cn/teach/tongkao/tksV200505_dxyyb_st.doc)

Scientists have uncovered a new threat to the world’s endangered coral reefs. They have found that most are incapable of growing quickly enough to compensate for rising sea levels triggered by global warming. The study suggests that reefs – which are already suffering serious degradation because the world’s seas are warming and becoming more acidic – could also become overwhelmed by rising oceans.

The research – led by scientists at Exeter University and published in Nature this week – involved studying growth rates for more than 200 tropical western Atlantic and Indian Ocean reefs. It was found only 9% of these reefs had the ability to keep up with even the most optimistic rates of sea-level rises forecast by the Intergovernmental Panel on Climate Change. “For many reefs across the Caribbean and Indian Ocean regions, where the study focused, rates of growth are slowing due to coral reef degradation,” said Professor Chris Perry, of Exeter University. “Meanwhile, rates of sea-level rise are increasing – and our results suggest reefs will be unable to keep up. As a result, water depths above most reefs will increase rapidly through this century.”

Sea levels rose by several inches over the past century and measurements indicate the speed of this increase is now rising significantly. Two key factors are involved: climate change is making ocean water warmer and so it expands. And as ice sheets and glaciers melt, they increase amounts of water in the oceans.

At the same time, reefs are being weakened by ocean warming and also by ocean acidification, triggered as the seas absorb more and more carbon dioxide. These effects lead to bleaching events that kill off vast stretches of coral and limits their ability to grow.

“Our predictions, even under the best case scenarios, suggest that by 2100, the inundation of reefs will expose coastal communities to significant threats of shoreline change,” said co-author Prof Peter Mumby of Queensland University. This point was backed by US marine scientist Ilsa Kuffner writing in a separate comment piece for Nature. “The implications of the study are dire. Many island nations and territories are set to quickly lose crucial natural resources.”

(Source: https://www.theguardian.com/)