Abstract

ISSN 1948‐6596 news and update tions, and underline the value of their outputs in long‐term field studies. These might restore them to their rightful place in the ecological pantheon, places where students can learn to appreciate the insights they offer, and hence maintain them. Francis Gilbert School of Biology, University of Nottingham, UK. e‐mail: Francis.Gilbert@nottingham.ac.uk; http://ecology.nottingham.ac.uk/~plzfg/ Edited by Markus Eichhorn book review Macro‐ecology of the world’s savannas Ecosystem function in savannas: measurement and modelling at landscape to global scales, by Michael J. Hill and Niall P. Hanan (eds.) CRC Press, 2010, 623 pp. ISBN: 978‐1‐4398047‐0‐4 Price: US$159.95 (Hardback) http://www.crcpress.com/ A quarter of a century has passed since the ‘legacy work’ of Tucker and collaborators (e.g. Tucker et al. 1985) characterizing the spatio‐temporal dy‐ namics of vegetation using temporal series of NDVI data from the NOAA AVHRR sensor, notably over the Sahel region. In the meantime, thanks to advances in Earth Observation (EO), an impressive array of technologies and methods has emerged, multiplying the number of biological and physical variables that can be measured, mapped and monitored over broader spatial and temporal scales than ever before. Progress comes from the development of new sensors, but also thanks to numerous initiatives aiming at facilitating data accessibility, the most recent of which is the launch of the Google Earth Engine© platform. Therefore, although a number of books ex‐ ist on savanna ecology, the time is definitely ripe for a general survey of where we are, after these crucial developments, in our understanding and monitoring capacity of savanna ecosystems. This is what Hill and Hanan, along with an impressive team of renowned contributors, have achieved in this volume, notably by bringing together differ‐ ent communities working respectively on field measurement, remote sensing assessment and modelling of savanna structure, dynamics and bio‐ geochemical fluxes at landscape to global scales. A central question, which continues to stimulate the scientific community, concerns the determinants of tree–grass coexistence in savan‐ nas. Mainstream hypotheses are reviewed (chapters 2 and 13), such as bottleneck models, in which perturbation by fire, herbivory or drought tend to reduce tree density, as opposed to the so‐ called Walter niche‐separation hypothesis, ac‐ cording to which trees are maintained by access to deeper soil resources. Of course, real mecha‐ nisms are a great deal more complex, and a num‐ ber of feedbacks and interactions between plants (facilitation and competition), and with grazers or browsers, are detailed. We could further argue that the question itself of ‘tree–grass coexistence’ might be stated in over‐simplified terms, because not all tree and shrub species, for instance, show the same dynamics and strategies with regard to fires and herbivory (see e.g. Beckage et al. 2009). Given the number of variables interacting in different soil and climate contexts (well presented in chapter one), and the spatial and temporal scales involved, it is clear that empirical/ experimental approaches are difficult to imple‐ ment. The combination of ‘natural experiment’ approaches with modelling studies is therefore a good way forward. In the former, one investigates multiple correlations and interactions between biological variables and potential physical drivers, through space and time, using EO data; in the lat‐ ter, these correlations can be tested in ‘controlled‘ conditions in silico. This brings us back to the technological de‐ velopments of remote sensors. In a synthetic table (table 27.2), the authors list a range of biophysical variables that can be estimated at different reso‐ © 2011 the authors; journal compilation © 2011 The International Biogeography Society — frontiers of biogeography 3.1, 2011

Highlights

  • ISSN 1948‐6596 tions, and underline the value of their outputs in long‐term field studies. These might restore them to their rightful place in the ecological pantheon, places where students can learn to appreciate the insights they offer, and maintain them

  • A number of books ex‐ ist on savanna ecology, the time is definitely ripe for a general survey of where we are, after these crucial developments, in our understanding and monitoring capacity of savanna ecosystems

  • We could further argue that the question itself of ‘tree–grass coexistence’ might be stated in over‐simplified terms, because not all tree and shrub species, for instance, show the same dynamics and strategies with regard to fires and herbivory

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ISSN 1948‐6596 tions, and underline the value of their outputs in long‐term field studies. Ecosystem function in savannas: measurement and modelling at landscape to global scales, by Michael J.

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