Arctic and boreal ecosystems of western North America as components of the climate system
Arctic and boreal ecosystems of western North America as components of the climate system
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DOI：
10.1046/j.1365-2486.2000.06022.x
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发表时间：
2000-12-01
影响因子：
11.6
通讯作者：
Running, SW
中科院分区：
文献类型：
--
作者：
Chapin, FS;McGuire, AD;Running, SW
综合几个北极和北方研究方案的结果，可以证明高纬度生态系统在气候系统中的重要作用。在北美西部、北极和北方森林地区，世纪的平均地表气温每十年上升0.3摄氏度。降水量也有所增加，但土壤湿度的变化不确定。北方森林的干扰率有所增加;例如，在过去20年中，北美被烧毁的面积翻了一番。冻土带的扰动机制可能没有改变。苔原有3-6倍高的冬季植被比北方森林，但夏季植被和能量分配之间的差异更强烈的生态系统内苔原或北方森林比这两个生物群落之间。这表明，需要提高我们的了解植被动态内，以及之间，生物群落。如果区域表面变暖继续下去，由于雪的提前融化和长期的树线向北移动，降雨量和能量吸收的变化可能会对区域变暖起到积极的反馈作用。地表干燥和优势植物从苔藓到维管植物的变化也会增强冻土带的感热通量和区域变暖。在北美西部的北方森林中，落叶林在冬季和夏季的蒸腾量都是针叶林的两倍，蒸散量高出50-80%，因此夏季的显热通量只有针叶林的30-50%。因此，变暖引起的火灾频率增加，增加了景观中的落叶林的比例，将作为一个负反馈区域warming.Changes的热岩溶和空中的湿地，湖泊和池塘的范围将改变高纬度甲烷通量。目前对高纬度生态系统和大气之间CO2通量的大小和方向的估计存在很大差异。这些差异与外推方法和假设的关系比与基础数据的不一致性的关系更大。大气CO2浓度的逆模型表明，高纬度地区是大气CO2的中性或净汇，而实地测量表明，高纬度地区是中性或净CO2源。这两种方法都依赖于难以验证的假设。现有数据的最简约的解释是，干燥苔原和干扰北方森林增强CO2排放。然而，由于气候的区域变化和地形决定的土壤湿度的局部变化，冻原和北方森林的许多地区仍然是净汇。为了更好地了解高纬度生态系统在气候系统中的作用，需要开展协调一致的研究工作，重点关注控制陆地-大气交换、物种组成和生态系统结构的过程中的地理变化。未来的研究必须在足够长的时间内进行，以检测和量化生态系统的反馈。
Synthesis of results from several Arctic and boreal research programmes provides evidence for the strong role of high-latitude ecosystems in the climate system. Average surface air temperature has increased 0.3 degreesC per decade during the twentieth century in the western North American Arctic and boreal forest zones. Precipitation has also increased, but changes in soil moisture are uncertain. Disturbance rates have increased in the boreal forest; for example, there has been a doubling of the area burned in North America in the past 20 years. The disturbance regime in tundra may not have changed. Tundra has a 3-6-fold higher winter albedo than boreal forest, but summer albedo and energy partitioning differ more strongly among ecosystems within either tundra or boreal forest than between these two biomes. This indicates a need to improve our understanding of vegetation dynamics within, as well as between, biomes. If regional surface warming were to continue, changes in albedo and energy absorption would likely act as a positive feedback to regional warming due to earlier melting of snow and, over the long term, the northward movement of treeline. Surface drying and a change in dominance from mosses to vascular plants would also enhance sensible heat flux and regional warming in tundra. In the boreal forest of western North America, deciduous forests have twice the albedo of conifer forests in both winter and summer, 50-80% higher evapotranspiration, and therefore only 30-50% of the sensible heat flux of conifers in summer. Therefore, a warming-induced increase in fire frequency that increased the proportion of deciduous forests in the landscape, would act as a negative feedback to regional warming.Changes in thermokarst and the aerial extent of wetlands, lakes, and ponds would alter high-latitude methane flux. There is currently a wide discrepancy among estimates of the size and direction of CO2 flux between high-latitude ecosystems and the atmosphere. These discrepancies relate more strongly to the approach and assumptions for extrapolation than to inconsistencies in the underlying data. Inverse modelling from atmospheric CO2 concentrations suggests that high latitudes are neutral or net sinks for atmospheric CO2, whereas field measurements suggest that high latitudes are neutral or a net CO2 source. Both approaches rely on assumptions that are difficult to verify. The most parsimonious explanation of the available data is that drying in tundra and disturbance in boreal forest enhance CO2 efflux. Nevertheless, many areas of both tundra and boreal forests remain net sinks due to regional variation in climate and local variation in topographically determined soil moisture. Improved understanding of the role of high-latitude ecosystems in the climate system requires a concerted research effort that focuses on geographical variation in the processes controlling land-atmosphere exchange, species composition, and ecosystem structure. Future studies must be conducted over a long enough time-period to detect and quantify ecosystem feedbacks.