IELTS Academic Reading – Practice Passage 1

Reading Passage

AFor as long as people have built cities, they have also planted trees along their streets and in their squares. What was once valued mainly for shade and beauty is now being re-examined for a more urgent reason. Dense concrete, asphalt and glass absorb the sun’s heat during the day and release it slowly at night, so that a large city can be several degrees warmer than the countryside around it – an effect known as the urban heat island. As summers grow hotter, planners who once thought of trees as decoration are turning to them as a practical tool for keeping cities liveable.

BTrees cool their surroundings through two distinct natural processes. The first is straightforward: a broad canopy intercepts sunlight before it can reach and heat the ground, so shaded pavements and walls stay markedly cooler. The second is less obvious. Through a process called evapotranspiration, a tree draws water up from the soil and releases it as vapour through tiny pores in its leaves. Converting liquid water into vapour absorbs heat from the surrounding air, cooling it in much the same way that sweating cools human skin. A single mature tree can move hundreds of litres of water in this way on a hot day.

CQuantifying these effects has become a busy field of research. Using sensors mounted on vehicles and satellites, scientists can now map temperature street by street. In one study of a mid-sized European city, streets shaded by mature trees were found to be up to 6°C cooler at midday than nearby streets with no tree cover at all. The difference is not uniform: it depends on the size of the canopy, the width of the street and the local climate. Even so, the pattern is consistent enough that some researchers describe well-placed trees as one of the most cost-effective cooling technologies available to a city.

DThe advantages of urban trees, however, reach well beyond temperature. Their leaves filter airborne pollutants, so leafy districts often enjoy cleaner air. Their roots and the soil around them absorb stormwater after heavy rain, easing the burden on drains and lowering the risk of flooding. Streets lined with trees tend to command higher property values, and a growing body of evidence links access to greenery with better mental health and faster recovery among hospital patients. For a single intervention, the range of returns is unusually wide.

ENone of this means that planting trees is without difficulty. In dry regions, trees may compete for scarce water that a city can ill afford, and irrigation adds to the expense. Some species release large amounts of pollen that trouble allergy sufferers, while others drop fruit or lift pavements with their roots, creating hazards and repair bills. A tree planted in the wrong place – beneath power lines, or in a pit too small for its roots – may die young or cause damage that outweighs its benefits. Cooling a city with trees, in short, demands far more than simply putting saplings in the ground.

FChoosing the right species is therefore central to success. The ideal street tree tolerates poor soil, drought and pollution, casts dense shade, and grows to a size suited to the space available. Native species are often preferred because they support local wildlife and are adapted to the regional climate, but in some hot cities carefully selected non-native trees survive better on baking streets. Increasingly, planners aim for variety, since a street planted with a single species can be wiped out by a single disease. Getting these decisions right requires long-term planning, because the benefits of a tree appear only as it matures over decades.

GPerhaps the greatest challenge is not botanical but social. Studies in many countries have found that wealthier neighbourhoods typically enjoy far more tree cover than poorer ones, so the cooling and health benefits of the urban forest are shared unequally. As cities set ambitious targets for expanding their canopies, campaigners argue that new planting should be directed first to the districts that have least, and that residents should have a say in what is planted near their homes. Deciding where the next tree goes, it turns out, is as much a question of fairness as of science.