Cowling Sharon A, Betts Richard A, Cox Peter M, Ettwein Virginia J, Jones Chris D, Maslin Mark A, Spall Steven A
Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, UK.
Philos Trans R Soc Lond B Biol Sci. 2004 Mar 29;359(1443):539-47. doi: 10.1098/rstb.2003.1427.
Modelling simulations of palaeoclimate and past vegetation form and function can contribute to global change research by constraining predictions of potential earth system responses to future warming, and by providing useful insights into the ecophysiological tolerances and threshold responses of plants to varying degrees of atmospheric change. We contrasted HadCM3LC simulations of Amazonian forest at the last glacial maximum (LGM; 21 kyr ago) and a Younger Dryas-like period (13-12 kyr ago) with predicted responses of future warming to provide estimates of the climatic limits under which the Amazon forest remains relatively stable. Our simulations indicate that despite lower atmospheric CO2 concentrations and increased aridity during the LGM, Amazonia remains mostly forested, and that the cooling climate of the Younger Dryas-like period in fact causes a trend toward increased above-ground carbon balance relative to today. The vegetation feedbacks responsible for maintaining forest integrity in past climates (i.e. decreased evapotranspiration and reduced plant respiration) cannot be maintained into the future. Although elevated atmospheric CO2 contributes to a positive enhancement of plant carbon and water balance, decreased stomatal conductance and increased plant and soil respiration cause a positive feedback that amplifies localized drying and climate warming. We speculate that the Amazonian forest is currently near its critical resiliency threshold, and that even minor climate warming may be sufficient to promote deleterious feedbacks on forest integrity.
古气候以及过去植被形态与功能的模拟能够通过限制对地球系统对未来变暖潜在响应的预测，以及通过提供关于植物对不同程度大气变化的生态生理耐受性和阈值响应的有用见解，来推动全球变化研究。我们将末次盛冰期（LGM；2.1万年前）和类似新仙女木期（1.3 - 1.2万年前）的亚马逊森林的HadCM3LC模拟结果与未来变暖的预测响应进行对比，以估算亚马逊森林保持相对稳定的气候极限。我们的模拟表明，尽管末次盛冰期大气二氧化碳浓度较低且干旱加剧，但亚马逊地区大部分仍为森林覆盖，而且类似新仙女木期的寒冷气候实际上导致相对于现今地上碳平衡有增加的趋势。过去气候中维持森林完整性的植被反馈（即蒸散减少和植物呼吸降低）在未来无法持续。尽管大气二氧化碳浓度升高有助于植物碳和水平衡的正向增强，但气孔导度降低以及植物和土壤呼吸增加会导致正反馈，放大局部干旱和气候变暖。我们推测亚马逊森林目前接近其关键恢复力阈值，即使是轻微的气候变暖可能也足以对森林完整性产生有害反馈。
