你也许知道城里老鼠和乡下老鼠的区别，但你知道城里的树和乡下的树有什么不同吗？研究发现，城里的树生长速度比乡下的树高出四倍，但死亡率是后者的两倍多。这是为什么呢？
Trees in cities 'live fast but die young' compared to rural forests, warns a new study.
一项新研究警告说，相比乡间树林里的树，城里的树“长得快但死得早”。
Researchers found that trees in urban areas die faster than ones in the countryside as higher levels of carbon dioxide make it harder for the plant to survive.
研究人员发现，城区树木的寿命比乡间树木短，因为城市二氧化碳浓度更高，让树更难存活。
City-dwelling trees suffer a net loss of carbon storage which means trees produce less energy from the air.
生长在城里的树碳储量是净亏损的，这意味着树用空气转化成的能量更低。
Now researchers say more must be done to tackle the environmental impacts of urbanisation.
研究人员表示，必须做更多工作来应对城市化对环境的影响。
Ian Smith, a PhD student of Boston University in the United States, said: 'Cities are at the forefront of implementing climate mitigation policies including urban greening, to combat rising temperatures and atmospheric CO2 concentrations.
美国波士顿大学的博士生伊恩·史密斯说：“为了对抗气温升高和大气中二氧化碳浓度变高，在推行城市绿化等减缓气候变化的政策时，城市是处于最前线的。”
'We find that tree planting initiatives alone may not be sufficient to maintain urban canopies in older cities like Boston.
“我们发现光是种树也许不足以在波斯顿等老城市保持树冠覆盖率。”
'Due to the age and size structure of the existing canopy, efforts to aid in the establishment and preservation of tree health are imperative for increasing urban tree cover and maximising the wide range of ecosystem services provided by the urban canopy.'
“由于现有绿树的年龄和大小结构，想要增加城市里的绿树覆盖面积，让城市树冠提供的生态系统服务范围最大化，就必须努力增进和保护绿树健康。”
The research team used a model to forecast short-term changes among street trees for several planting and management scenarios.
研究团队用了一个模型，通过多种植树和管理方案来预测街道树木的短期变化。
Researchers applied the model to estimated tree growth, mortality and planting rates both among trees in Boston city and forests in rural Massachusetts.
研究人员用这个模型来预估马萨诸塞州波斯顿市和乡间森林的树木的生长情况、死亡率和种植成活率。
It was discovered that rates of carbon cycling and mean diameter growth rates among urban trees were nearly four times faster in the city than the countryside.
研究发现，城市树木的碳循环率和平均直径增长速度比乡间树木高出近四倍。
mean[min]: adj. 平均的
But the positive findings were outweighed by net loss of carbon storage and high mortality losses - which are more than double than trees in rural forests.
但是这一积极的研究发现被净损失的碳储量和高死亡率抵消了——城市树木的死亡率是乡间树木的两倍多。
The study, published in the journal PLOS ONE, has prompted scientists to urge communities to do more to establish and preserve trees which are essential to increasing street-tree canopy cover and carbon storage in vegetation.
发表在《科学公共图书馆·综合》期刊上的这项研究促使科学家敦促社区更努力地去种植和保护树木，这对于增加街道树冠覆盖率和植被的碳储量至关重要。
Researchers say strategic combinations of planting and maintenance will be needed to secure urban sustainability but more needs to be done to develop understanding of urban trees and their ecosystems - which may differ from rural forests.
研究人员表示，为了保证城市可持续发展，需要在战略上把种树和保护绿树结合起来，但还需要增进对城市树木及其生态系统的了解，这一点可能有别于乡间森林。
