NSF 今日图说 | 玫红同心圆（双语）
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近二十年来，科学家们注意到北极的苔原栖息地发生了巨大的变化。脚踝那么高的草和树篱已经腾出地儿，让位给了长到腰或脖子那么高的大片灌木丛。苔原变灌木，对像北美驯鹿这样的动物提出了挑战，后者一般只适应较低高度的北美植被。和低纬度地区的树木一样，每个生长季节里，冻原上的灌木会在它们的茎周围形成同心环。一个研究小组利用了这些像年轮一样的同心环的特点，收集了不同土壤条件下的数百株灌木茎。研究小组发现，无论土壤是否肥沃，或降雨量如何变化，迄今为止决定一年内灌木生长情况的最大因素是六月的气温。六月气温越高，则灌木生长越旺盛。
Rings around the rosy
For nearly two decades, scientists have noted dramatic changes in Arctic tundra habitat. Ankle-high grasses and sedges have given way to a sea of woody shrubs growing to waist- or neck-deep heights. This shrubification of the tundra challenges animals like caribou that are adapted to low-stature arctic vegetation. Like trees at lower latitudes, shrubs in the tundra form concentric rings around their stems each growing season. A research team used these annual rings to their advantage, collecting hundreds of shrub stems across a range of soil conditions. The team's research found that regardless of soil fertility or rainfall amounts, the single variable that was by far the strongest determinant of how much a shrub grew in a given year was the temperature in June. A warmer June means faster shrub growth.
Image credit: Daniel Ackerman
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