Forests, savannas, and grasslands: bridging the knowledge gap between ecology and Dynamic Global Vegetation Models

[摘要] The forest, savanna, and grassland biomes, and the transitions between them,are expected to undergo major changes in the future due to global climatechange. Dynamic global vegetation models (DGVMs) are very useful forunderstanding vegetation dynamics under the present climate, and forpredicting its changes under future conditions. However, several DGVMsdisplay high uncertainty in predicting vegetation in tropical areas. Here weperform a comparative analysis of three different DGVMs (JSBACH,LPJ-GUESS-SPITFIRE and aDGVM) with regard to their representation of theecological mechanisms and feedbacks that determine the forest, savanna, andgrassland biomes, in an attempt to bridge the knowledge gap between ecologyand global modeling. The outcomes of the models, which include differentmechanisms, are compared to observed tree cover along a mean annualprecipitation gradient in Africa. By drawing on the large number of recentstudies that have delivered new insights into the ecology of tropicalecosystems in general, and of savannas in particular, we identify two mainmechanisms that need improved representation in the examined DGVMs. The firstmechanism includes water limitation to tree growth, and tree–grasscompetition for water, which are key factors in determining savanna presencein arid and semi-arid areas. The second is a grass–fire feedback, whichmaintains both forest and savanna presence in mesic areas. Grasses constitutethe majority of the fuel load, and at the same time benefit from the opennessof the landscape after fires, since they recover faster than trees.Additionally, these two mechanisms are better represented when the modelsalso include tree life stages (adults and seedlings), and distinguish betweenfire-prone and shade-tolerant forest trees, and fire-resistant andshade-intolerant savanna trees. Including these basic elements could improvethe predictive ability of the DGVMs, not only under current climateconditions but also and especially under future scenarios.

[学科分类] 地球化学与岩石