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Predicting the time of green up in temperate and boreal biomes

机译：预测温带和寒带生物群落绿色的时间

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Direct observations as well as Normalized Difference Vegetation Index (NDVI) data from satellites have shown earlier leaf appearance in the northern hemisphere, which is believed to result from climate warming. The advance of leaf out to earlier times in the year could be limited or even reversed, however, as temperate and boreal trees require a certain amount of chilling in winter for rapid leaf out in spring. If this chilling requirement is not fulfilled, an increasing amount of warming is required. Implications of these chilling requirements at the biome level are not clear. One approach to estimate their importance is to generalize the exponential relationships between chilling and warming established for single species. Previous work using NDVI data suggests that this is indeed feasible but much has been limited to specific biomes or a very few years of data for the modelling. We find chilling requirements for northern temperate and boreal biomes by fitting various phenology models to green-up dates determined from NDVI using various methods and 12 years of data. The models predict that in northern middle and high latitudes the advance of green-up will be limited to a total of 4 to 5 days on average (but up to 15 days regionally) over the time period 2000-2060 as estimated using two contrasting climate simulations. This results from the exponentially increasing warming requirements for leaf out when winter chilling falls below a threshold as shown by a comparison with models that consider only spring warming. The model evaluation suggests an element of regional adaptation of the warming required for leaf out in large biomes.
机译：来自卫星的直接观测以及归一化植被指数（NDVI）数据显示，北半球的叶片出现较早，这被认为是气候变暖的结果。到今年早些时候出苗的时间可能会受到限制甚至逆转，但是，由于温带和北方树木在冬季需要一定程度的寒冷才能在春季迅速出苗。如果不满足该冷却要求，则需要增加加热量。这些对生物群落水平的冷却要求的含义尚不清楚。一种估计其重要性的方法是概括为单个物种建立的冷暖之间的指数关系。以前使用NDVI数据进行的工作表明这确实可行，但是很多都局限于特定的生物群系或很少的建模数据。通过使用各种方法和12年的数据，根据NDVI确定的绿化日期拟合各种物候模型，我们找到了北部温带和北方生物群落的低温需求。这些模型预测，在2000-2060年期间，使用两种不同的气候估计，北部中高纬度地区的绿化进展平均将被限制为平均总共4至5天（但区域上最多15天）模拟。这是由于当冬季寒冷降至阈值以下时，对叶子的升温需求呈指数增长，这与仅考虑春季变暖的模型的比较显示。模型评估表明，对大型生物群落中的叶片变暖所需的区域适应性进行了区域调整。

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