气候变化背景下冻土环境对地上植物群落的影响备受关注。鉴于此,选择了大兴安岭北坡作为研究区,应用双向指示种分析(TWINSPAN)和典范对应分析法(CCA)对大兴安岭北坡不同冻土融深的30个样地进行了群落分类,分析了物种多样性对冻土融深的响应。结果表明,1)研究区30个沟谷冻土样地植物群落可划分为3个群丛组,TWINSPAN的分类结果很好的反映了群丛组的分布与冻土融深的关系,即随着冻土融深由浅变深,群落由柴桦(Betula fruticosa)+狭叶杜香(Ledum palustrevar.angustum)-苔草(Carex subpediformis)群丛组逐渐过渡到柴桦(Betula fruticosa)-苔草(Carex subpediformis)群丛组和柴桦(Betula fruticosa)+细叶沼柳(Salix rosmarinifolia)-苔草(Carex subpediformis)群丛组,并在CCA二维排序图上得到了验证;2)地上植物群落的物种多样性指数随着冻土融深的增加表现出先上升后下降的单峰变化趋势;在50cm

This study analyzes mid-21st century projections of daily surface air minimum (T-min) and maximum (T-max) temperatures, by season and elevation, over the southern range of the Colorado Rocky Mountains. The projections are from four regional climate models (RCMs) that are part of the North American Regional Climate Change Assessment Program (NARCCAP). All four RCMs project 2A degrees C or higher increases in T-min and T-max for all seasons. However, there are much greater (> 3A degrees C) increases in T-max during summer at higher elevations and in T-min during winter at lower elevations. T-max increases during summer are associated with drying conditions. The models simulate large reductions in latent heat fluxes and increases in sensible heat fluxes that are, in part, caused by decreases in precipitation and soil moisture. T-min increases during winter are found to be associated with decreases in surface snow cover, and increases in soil moisture and atmospheric water vapor. The increased moistening of the soil and atmosphere facilitates a greater diurnal retention of the daytime solar energy in the land surface and amplifies the longwave heating of the land surface at night. We hypothesize that the presence of significant surface moisture fluxes can modify the effects of snow-albedo feedback and results in greater wintertime warming at night than during the day.

A quantification of coastal erosion processes on a clay cliff in a cold temperate region was conducted. This study was based on a network of markers that were measured on a monthly basis from 1998 to 2003. During that period, the average retreat rate of the cliff was 1.5 m/y. Our results demonstrate that weathering is a more significant cliff retreat factor than hydrodynamic processes on fine sediment shorelines. This statement opposes conventional understanding. In fact, 65% of the annual cliff retreat took place through the winter season when the waves could not reach the foot of the cliff because of an ice foot. This erosion is caused by cryogenic processes in winter, particularly through freeze-thaw cycles, whereas desiccation and wave undercutting contributed respectively for 20% and 15% of the total annual retreat. The field measurements conducted before and after major storms, especially on October 29, 2000, illustrated that wave undercutting was negligible for the clay cliff. These results do not corroborate with previous studies showing that cliff erosion is mostly controlled by wave undercutting with negligible winter erosion. In a context of global warming, the intensity of cryogenic processes can become more important due to milder winters, an increase in the number of freeze-thaw cycles, and the reduction of the ice foot and snow cover (especially on south-facing cliffs directly exposed to solar radiation). This study demonstrates that the evaluation of sensitivity of coastal systems to climatic change should not be done just for sea-level rise and increased storminess, but also for other climatic parameters. Future research should also take into account approaches combining the studies of marine and terrestrial erosion processes.