BIOSPHERE MODELING FOR CLIMATE STUDIES

The role of the biosphere in the global climate system is briefly outlined, and their interaction is investigated through two specific modeling exercises. First, since vegetation is sensitive and slowly adjusting to climate fluctuations, its composition and diversity reflect the interplay of the laws of succession under the constraints of climatic and environmental stress. This interaction can be studied with the help of dynamic gap forest models. A particular instance of this class of models is used to investigate whether the forest affects ecological succession through a modification of its own microclimate. It is found that such feedbacks are not strong enough in the wet climate of Minnesota, and this implies that the pollen record truly represents the overall climatic conditions of the region. This paper also proposes a new approach to the exploitation of trees as a climate archive. Dendroclimatology has traditionally resorted to empirical correlations between tree-ring characteristics and climate in the recent past, and extrapolated such relations beyond the period of instrumental records. An explicit modeling approach provides a powerful and flexible tool, but its application requires the technique of model inversion. A simple tree-ring model is constructed, and it is shown that this method retrieves the climatic information of a particular year from an analysis of the variability of rings between different trees subject to the same climate, rather than from the ring-to-ring variations in the same tree.