Estimating changes in terrestrial vegetation and carbon storage: Using palaeoecological data and models
Résumé
Climatic changes that accompanied the transition from the last glacial to the present interglacial conditions over the past 18,000 (14)C years impacted both terrestrial ecosystem structure (vegetation distribution) and function (carbon dynamics), which in turn influenced the climate through biogeophysical mechanisms. Palaeoecological records provide not only past records of vegetation patterns at various spatial and temporal scales, but also a means of evaluating the associated change in past terrestrial carbon storage. After a brief review of the role of palaeoecological data and biosphere models in evaluating the potential impacts of past climate change on terrestrial ecosystems, we synthesize the methods for reconstructing the vegetation patterns from palaeoecological data and the way to integrate it with biosphere models to reconstruct the long-term terrestrial carbon dynamics since the Last Glacial Maximum (LGM). The main results obtained at both the global and regional scales suggest that colder, more arid and low atmospheric CO(2) climatic conditions at the LGM may have favored the extensions of steppe and grassland dominated by C4 plants, to the detriment of forested ecosystems. However, the warmer and wetter climatic conditions during the Holocene favored extensions of temperate deciduous forests in mid-latitudes and reduced the tundra and taiga forests at high latitudes. Carbon storage in terrestrial vegetation was relatively low during the full-glacial time and increased considerably to a maximum during the mid-Holocene. Most of the recent estimates converge to an increase of about 30% global carbon storage from the LGM to the present. There still is a significant gap in our understanding of ice-age terrestrial carbon budget. The difference between the marine and terrestrial estimations is about 150-430 Pg C (1 Pg = 10(15) g). It results from the uncertainties in reconstruction of terrestrial vegetation and carbon storage as well as the uncertainties in the interpretation of marine Delta partial derivative(13)C changes. Further progress in understanding the dynamic processes of global vegetation and carbon cycle will require both the development of global palaeoecological database and the development of biosphere models. (C) 1998 Elsevier Science Ltd. All rights reserved.