Agricultural and Forest Meteorology 106 (2001) 169–170
Book review
Carbon sequestration in soils: Science Monitoring and Beyond: Conference Proceedings: St. Micheals Workshop, Maryland, December 3–5, 1998, NJ Rosenberg, N.J., Izaurralde, C.R., Malone, E.L., Batelle Press, Columbus, Ohio, USA, ISBN: 1-57477-084-5
Carbon sequestration in soils has become an ac-tive research area of international scope because of concern about human influence on the carbon cycle, pursuit of the ‘missing carbon sink’, and restoration of degraded soils. It is generally acknowledged that con-version of native vegetation to agriculture has resulted in an enormous net transfer of carbon from the soil to the atmosphere. The substantially less-clear, sci-entific, economic, and political issues concerning the implementation of strategies to reverse these losses and offset future fossil fuel emission are the subject of this book.
In the first chapter, carbon sequestration potential (CSP) is estimated for a variety of ecosystems. The aggregate annual global CSP is impressive and is of the same magnitude as the total fossil fuel emissions of 1998. Strategies for enhancing carbon sequestration are evaluated including precision agriculture, use of under utilised land resources and existing biodiversity, and plant and microbial biotechnology. The authors note the logistical, ethical and technical concerns that may limit practical application and the finite nature of this sink that dictates that these strategies only ‘buy time’. The authors point out that historically, genetic engineering and plant breeding have increased pho-toassimilate partitioning to grain, increased shoot/root ratio, and decreased lignin content. All of these factors decrease CSP.
The analysis in this book assumes that degraded soils can be restored to their original soil organic car-bon (SOC) content. This assumption must be critically
evaluated because it is based on host of uncertain-ties. Some long-term monitoring studies show that SOC have increased following adoption of intensive agricultural practices that return significantly more residue to soils. However, other studies have found little change or declines in SOC. Agricultural systems are fundamentally different from natural systems be-cause of differences in assimilate partitioning to roots, residue chemistry, temporal and spatial patterns of residue incorporation, and susceptibility to pests and pathogens. Full recovery also implies that soil degra-dation by erosion, loss of soil fertility, salinization, and compaction has not reduced CSP compared to undisturbed systems.
Result from some free air CO2enrichment (FACE) studies and studies of soils and vegetation growing in the vicinity of naturally elevated CO2are not consis-tent with significant increases in carbon storage that are cited in this book. The authors state that it is now thought that regrowth of forests in northern temper-ate latitudes, especially eastern North America, and the global CO2 fertilization effect account for the so called ‘missing sink’. It should be noted that there remains substantial uncertainty as to both the magni-tude of the global carbon imbalance, or missing sink, as well as the location and magnitude of the potential sink. Recent reports suggest that deposition and burial of eroded soils in alluvium, reservoirs, and wetlands, including rice paddies, can account for a significant portion of the sink.
The second chapter includes a review of soil pro-cesses important to CSP, accounting methods for inventorying SOC at various spatial scales, models to simulate carbon dynamics, and field and laboratory methods. Eddy covariance methods for measure-ment of net ecosystem CO2 exchange are suggested because they provide a scientifically rigorous veri-fication tool that can be applied over a annual time 0168-1923/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.
170 Book review
step. Potential monitoring plans are discussed that include identification of specific monitoring sites within representative sub-regions. Monitoring plans must incorporate historical soil data, remotely sensed land-use/land-cover data, digital elevation models, and erosion deposition models. These data must be integrated within an overall model framework that tracks soil carbon dynamics as a function of climate, vegetation, soil, topography, and land management. There are formidable challenges associated with all of these requirements. Also mentioned is the problem of adequately understanding the historical land use be-cause this is critical in the evaluation of current CSP. One interesting complexity is the problem of verify-ing that the measured change is directly attributable to a specific management treatment rather than the ecosystems’ longer-term momentum responding to historical changes in land use or climate.
Chapter 3 explores CSP on desertified lands, which are defined as arid and sub-arid lands degraded through process of erosion, salinization, overgrazing, and agri-cultural exploitation that has reduced fertility and SOC content. Under the rubric ‘desertification control’, the authors discuss strategies for slowing the rate of deser-tification (like erosion control), restoration and recla-mation to increase SOC, and fossil fuel offsets through biofuel production. Only reclamation and restoration strategies represent true net soil carbon sequestration. The influence of climate change on CSP of deserti-fied lands may be important, but as the authors point out, changes in land use are likely to outweigh climate effects on these soils.
A range of policy and economic issues are discussed in the final chapter including farmer acceptance, soil and cultural impediments, holistic agricultural sector analysis, and property right issues. A more quanti-tative analysis, though understandably complex and
speculative, would have made this book more valu-able because such an analysis would have provided a realistic measure by which to evaluate the wide range of sequestration and monitoring strategies proposed. The issue of equity among nations in the approach to this global problem requires more attention. Given the enormous disparity between industrialized and devel-oping nations in per capita CO2emissions and gross domestic products, it is hard to imagine less afflu-ent countries adopting expensive strategies for carbon sequestration without major subsidies from wealthier countries.
In summary, this book presents a comprehensive case for the view that soil carbon sequestration is a scientifically defensible, verifiable, and economi-cally feasible mitigation strategy. The uncertainties, acknowledged by the authors, are illustrated by com-paring the authors’ estimates of CSP with those of a recent study supported by the Dutch National Re-search Program that estimated an order of magnitude less than that presented in this book. These uncertain-ties attest to the need for substantially more quantita-tive research. This book includes a tremendous amount of information and discussion of complex issues and as such is a very useful reference for those involved in research, teaching, or policy-making related to this subject.
T.G. Hutington
U.S. Geological Survey 26 Ganneston Dr. Augusta ME 04330 USA
E-mail address: thunting@usgs.gov
