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California has lost half its big trees since the 1930s, according to a study to be published Tuesday and climate change seems to be a major factor （因素）.
The number of trees larger than two feet across has declined by 50 percent on more than 46,000 square miles of California forests, the new study finds. No area was spared or unaffected, from the foggy northern coast to the Sierra Nevada Mountains to the San Gabriels above Los Angeles. In the Sierra high country, the number of big trees has fallen by more than 55 percent; in parts of southern California the decline was nearly 75 percent.
Many factors contributed to the decline, said Patrick McIntyre, an ecologist who was the lead author of the study. Woodcutters targeted big trees. Housing development pushed into the woods. Aggressive wildfire control has left California forests crowded with small trees that compete with big trees for resources （资源）.
But in comparing a study of California forests done in the 1920s and 1930s with another one between 2001 and 2010, McIntyre and his colleagues documented a widespread death of big trees that was evident even in wildlands protected from woodcutting or development.
The loss of big trees was greatest in areas where trees had suffered the greatest water shortage. The researchers figured out water stress with a computer model that calculated how much water trees were getting in comparison with how much they needed, taking into account such things as rainfall, air temperature, dampness of soil, and the timing of snowmelt （融雪）.
Since the 1930s, McIntyre said, the biggest factors driving up water stress in the state have been rising temperatures, which cause trees to lose more water to the air, and earlier snowmelt, which reduces the water supply available to trees during the dry season.
1. What is the second paragraph mainly about?
A. The seriousness of big-tree loss in California.
B. The increasing variety of California big trees.
C. The distribution of big trees in California forests.
D. The influence of farming on big trees in California.
2. Which of the following is well-intentioned but may be bad for big trees?
A. Ecological studies of forests.
B. Banning woodcutting.
C. Limiting housing development.
D. Fire control measures.
3. What is a major cause of the water shortage according to McIntyre?
A. Inadequate snowmelt.
B. A longer dry season.
C. A warmer climate.
D. Dampness of the air.
4. What can be a suitable title for the text?
A. California’s Forests: Where Have All the Big Trees Gone?
B. Cutting of Big Trees to Be Prohibited in California Soon
C. Why Are the Big Trees Important to California Forests?
D. Patrick McIntyre: Grow More Big Trees in California
decline v . 下降
spare v . 使免遭伤害；使幸免
foggy adj . 有雾的；雾气朦胧的
contribute to 促成；有助于
lead author 主要作者
push into 推进，推动
aggressive adj . 咄咄逼人的；强势的
evident adj . 明显的；明白的
shortage n . 不足，短缺
figure out 弄明白；想出
take into account 考虑；顾及
dampness n . 湿度
drive up 使……上升
1. The researchers figured out water stress with a computer model that calculated how much water trees were getting in comparison with how much they needed, taking into account such things as rainfall, air temperature, dampness of soil, and the timing of snowmelt.
本句主句结构简单，修饰成分复杂，主要难点在于with引导的短语，其中包含了修饰model的由that引导的定语从句和由taking引导的现在分词短语。
（参考译文） 研究人员在综合考虑降水量、气温、土壤湿度、融雪时间等因素的基础上，运用计算机模型计算出与树木的需水量相比它们吸收了多少水分，从而揭示了树木缺水的状况和成因。
2. Since the 1930s, McIntyre said, the biggest factors driving up water stress in the state have been rising temperatures, which cause trees to lose more water to the air, and earlier snowmelt, which reduces the water supply available to trees during the dry season.
本句为主系表结构，since引导时间状语，McIntyre said为插入语，driving引导的现在分词短语修饰主语factors，第一个which引导定语从句，修饰表语temperatures，第二个which也引导定语从句，修饰snowmelt。
（参考译文） 麦金太尔称，自20世纪30年代以来，加剧加州树木缺水最主要的原因是气温升高和融雪时间提早，前者导致了树木的水分蒸发加剧，而后者又减少了旱季树木的供水量。