Changes in the Amount of Forest on the GreatPlainsAt the end of the last ice age, some 8,000 to 10,000 years ago, the climate was cool anddamp, and a dense coniferous (evergreen) forest occupied the Great Plains, the vastregion stretching from Alberta, Saskatchewan, and Manitoba in Canada south throughTexas. A dark mantle of spruce trees extended from what are now the Canadian prairiessouth through the Dakotas into the central states of the United States, while pinewoodsappear to have flourish on the southern plains of the United States. But as the chill of theglaciation gradually lifted, the climate eased into a drier and warmer phase, marked bymore frequent droughts, and the forest was forced to retreat to the north. Within aremarkably short time, the forests of the Great Plains either surrendered directly tograsses or else gave way first to deciduous trees (trees that lose their leaves seasonally)and then to prairie grasses.1、The word “dense” in the passage is closest in meaning tolargenewdarkthick2、According to paragraph 1. What was true of the region stretching from thepresent Canadian prairies south through the southern plains of the UnitedStates 8,000 to 10,000 years ago?A.It was largely covered with grasses.B.It was largely covered with glaciers.C.It was covered with coniferous forests.D.Its forests contained a mixture of deciduous trees.By the time the transformation was over, coniferous forests could be found in the centralUnited States only on the crowns of the tallest breaks and ridges. 00 High enough to catchthe rain and snow, and cooler than the grasslands below, these uplands created amicroclimate in which the trees could retain a toehold. However, favorable moisture andtemperature levels were not the only factors affecting the survival of conifers at theselocations. 00 The thin mineral soils of the ridges – more suitable for conifers than forgrasses or other plants – probably also gave the trees an advantage. 00 The factor thatmade the biggest difference to the scarp forests (forests on a line of cliffs), however, wastheir high, isolated location. 00 Historically speaking, the greatest threat to prairiewoodlands, apart from prolonged drought, was the fierce heat of grass fires. Where betterto find refuge than atop a natural firebreak? The present distribution of scarp woodlandstherefore probably represents the limits of past wildfires.Paragraph 2 supports which of the following explanations of why scarp forestsare less likely to experience damage fire outbreaks?A.The frequent precipitation on ridges prevents fires from burning forlong.B.The mineral soils of ridges make fires less likely.C.Fires do not burn as easily in the cooler climate where scarp forestsgrow.D.The scarp forests are not in direct contact with grasslands and thusdo not burn.Look at the four squares[▇]that indicate where the followi...
