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Vegetation cover in a warmer world simulated using a dynamic global vegetation model for the mid Pliocene.

A growing number of studies have demonstrated the importance of climate-vegetation interaction in understanding climate sensitivity and climate change. Initial vegetation modelling efforts concentrated on coupling the outputs from global climate models to empirical models of vegetation. However, the complexity of vegetation models quickly increased to allow for the representation of numerous physiological processes such as photosynthesis, respiration, transpiration, and soil water uptake. Whereas initially output from global climate models were simply used offline to the vegetation model itself, many of the vegetation models are now asynchronously or dynamically coupled to global climate models.

Haywood et al. (2002) used a mechanistically based biome model (BIOME 4), offline to an atmospheric general circulation model (AGCM), to predict biome distributions for the last interval of geological time in which global temperatures were warmer than any interglacial of the Quaternary — the Pliocene. This study was useful in that they helped to quantify Pliocene climate-vegetation feedbacks and aided in the identification of Pliocene vegetation patterns that are in equilibrium with different ice-sheets and insolation scenarios. However, to better understand Pliocene climate-vegetation feedbacks the land-cover needed to be treated as an interactive element (i.e., actively growing vegetation) by incorporating a dynamic global vegetation model (DGVM). In this study a DGVM (TRIFFID) and the HadAM3 GCM (Hadley Centre Atmospheric General Circulation Model version 3) were dynamically coupled to investigate vegetation distributions during the Pliocene.

Major outcomes:

  • TRIFFID simulates a significant increase in forest cover during the Pliocene, composed of needle leaf trees in the higher latitudes of the Northern Hemisphere and broad leaf trees in other regions.
  • Needle leaf trees extend from the northern mid latitudes to the Arctic coast and replacing tundra vegetation that is dominant today.
  • On Antarctica temperatures warm sufficiently to allow shrubs to grow, a result which concurs with Nothofagus fossil material found in the Sirius Group formation of the Transantarctic Mountains.
  • The fractional coverage of bare soil (arid deserts) declines in North Africa, the Arabian Peninsula, Australia and southern South America, a trend consistent with geological data.
  • The predicted expansion in broad leaf trees in Africa is difficult to reconcile with the savannah hypothesis for the evolution of hominid bipedalism. Rather the results lend credence to an alternative hypothesis which suggests that bipedalism evolved in wooded to forested ecosystems and was, for several million years, linked to arborealism.

Find link to the full paper in the NERC Open Research Archive

Authors

Haywood, A.M. & Valdes, P.J. 2006. Palaeogeography, Palaeoclimatology, Palaeoecology

Publication

Palaeography, Palaeoclimatolgy, Palaeoecology 237 (2006) 412-427