Terrestrial Global Productivity
J. Roy, B. Saugier and H. A. Mooney (eds.). Academic Press, San Diego, 2001, xx + 573 pages. Price AUD$234. ISBN 0 12 505290 1.
Primary productivity is the rate at which plants convert energy into biomass, and is a key process that links the biosphere with the climate system through the global cycling of carbon, water and nutrients. Terrestrial Global Productivity embraces this global perspective and seeks to summarize the current state of knowledge regarding the primary productivity of the Earth's terrestrial ecosystems.
The book comprises 23 chapters, separated into three sections. The first section, ‘Component processes’, provides a summary of the various processes that together determine the rate at which plant canopies fix atmospheric carbon, and the rate at which it is eventually released back into the atmosphere via decomposition and disturbance. The section begins with a discussion of the two fundamental processes of photosynthesis and autotrophic respiration. The next two chapters trace the flow of carbon through terrestrial ecosystems by considering, in turn, photosynthate allocation, phenology and growth, litter production, and decomposition. Additional chapters include a discussion of the potential importance of herbivory on productivity estimates, and a discussion of the effects of water availability, nitrogen and rising atmospheric CO2 concentrations on plant productivity. Two opposing themes emerge. The first highlights the excellent progress that has been made over recent years in many areas of research, such as the development of the eddy-covariance methodology, and the increasing use of remotely-sensed technology for the estimation of vegetation growth and standing biomass. The second theme highlights the significant gaps that still remain in our knowledge of the terrestrial carbon cycle, most notably in the areas of litter production, soil carbon accumulation and decomposition processes. In addition to providing a comprehensive summary of the current state-of-play regarding the measurement of stand-level primary production, a major strength of this first section is the emphasis that is placed on identifying the limitations in current knowledge and methodologies, and the identification of priority areas for future research.
The second section, ‘Ecosystem productive performance’, is quite different from the first in both tone and content. There are nine chapters, each devoted to a single globally important vegetation type or ‘biome’. The biome classification comprises arctic ecosystems, boreal forests, deciduous temperate forests, temperate grasslands, agricultural ecosystems, Mediterranean ecosystems, deserts, savannas and tropical rainforests. Each chapter begins with a biome definition and description, and is followed by a summary of the latest estimates of productivity and standing biomass. Most chapters also include a discussion of the impact that humans have had on the functioning of these ecosystems, and a discussion of the potential impacts of global change.
On an individual basis the chapters are well written and illustrated, and anyone seeking the latest productivity and biomass summaries for individual biomes is likely to be well serviced by the information contained in these chapters. However, it is extremely difficult to compare results across chapters because of the inconsistent use of units and terminology. For example, in the arctic ecosystems chapter, productivity is reported in units g C m−2 year−1, in the savanna ecosystems chapter the units are g dry matter m−2 year−1, and in the tropical rainforests chapter t C ha−1 year−1. There are also many cases where the units are ambiguous, in that it is unclear whether the reported values refer to dry matter or carbon. There are similar inconsistencies in the use of terminology. For example, the majority of chapters use the abbreviation ‘ANPP’ for ‘above-ground net primary productivity’. The exception is the Mediterranean ecosystems chapter, where it used to denote ‘annual net primary productivity’.
For the novice or unwary reader these inconsistencies could easily result in confusion and misinterpretation of the results. For those more familiar with the literature, having to continually make the appropriate conversions to facilitate comparison quickly becomes both tedious and distracting. All of this could have been avoided with a little more editorial control. To find such inconsistencies was particularly disappointing given the overall high quality of the individual contributions, and given that the introductory chapter of the book deals specifically with issues of units and terminology.
The final section, ‘Global productivity’, comprises six chapters with the underlying theme of quantifying ecosystem production at the global scale. The opening chapter summarizes existing databases of productivity measurements, and the methods that are used to extrapolate these measurements to the global scale. This theme continues in the subsequent chapter, where the range of different modelling approaches that are used for estimating global productivity is reviewed. Taken together, these two chapters provide an excellent introduction to this vast and often complicated literature. Other chapters include the historical reconstruction of productivity from palaeodata, a review of global terrestrial productivity from 1850 to the present, and a chapter showcasing the use of models for developing forward projections of global terrestrial productivity. A common theme running through this section is the very large impact that land-clearing and other anthropogenic disturbances have had, and will continue to have, on the productive capacity of the earth's ecological systems. The chapter on land use and global productivity by Richard Houghton makes for particularly sobering reading.
The final chapter provides the book's main summary, and includes tables combining the biome-specific information on productivity, standing biomass and a range of other biophysical and ecophysiological parameters such as canopy height, albedo, boundary-layer conductance and radiation-use efficiency. These tables will undoubtedly prove to be a valuable resource for those seeking estimates of these quantities for the Earth's major biomes. One minor complaint is that no indication of the variability around the ‘mean’ biome productivity and biomass values is given in the summary tables, even though these variation estimates were often given within the individual biome chapters.
Overall, this book is a timely contribution, given the recent confirmation by the Intergovernmental Panel on Climate Change that climate change is both real and measurable, is almost certainly driven by anthropogenic influences, and that terrestrial ecosystems and their management play an important role in determining these trends (Intergovernmental Panel on Climate Change 2001). In the final analysis, this book succeeds as a synthesis of current methods and results of terrestrial productivity research, and I recommend it to any researcher actively working within this broad area of research. This book will also be of interest to those readers who are less interested in the technicalities of researching productivity at canopy-to-global scales, but who are simply seeking the latest information on the productivity, biomass and overall functioning of the earth's major biomes. Stephen Roxburgh CRC for Greenhouse Accounting Research School of Biological Sciences Australian National University Canberra, Australia
