Title Page: Journal of Agricultural Science, Cambridge accepted on 30 March 2000

Global change and the challenges for agriculture and forestry

C. S. AWMACK¹, P. SMITH^2*AND P. J. PINTER, JR.³

* Corresponding author

¹ Department of Entomology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA,

² Department of Soil Science, IACR-Rothamsted, Harpenden, Herts, AL5 2JQ, UK,

³ USDA, ARS, U.S. Water Conservation Laboratory, 4331 E Broadway Rd, Phoenix, AZ 85040, USA.

Running title: Global change: challenges for agriculture and forestry

Address for correspondence:

Corresponding author: Dr Pete Smith

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Global change and the challenges for agriculture and forestry

C. S. AWMACK¹, P. SMITH² AND P. J. PINTER, JR.³

¹Department of Entomology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA, ²Department of Soil Science, IACR-Rothamsted, Harpenden, Herts, AL5 2JQ, UK, ³USDA, ARS, U.S. Water Conservation Laboratory, 4331 E Broadway Rd, Phoenix, AZ 85040, USA.

A key need of the global change research community is to be able to synthesise the data collected by scientists from a wide range of disciplines and use it to make predictions about our future environment. In an agricultural and forestry context, this will allow predictions of yields under elevated atmospheric CO₂ levels and/or changed climate using data from studies of both the direct effects of global change on plant growth and physiology and indirect effects on soil fertility, water resources, pests and diseases.

A conference held at the University of Reading, UK in September 1999, and organised under the auspices of Focus 3 (Global Change Impact on Agriculture, Forestry and Soils; http://mwnta.nmw.ac.uk/GCTEFocus3) of the IGBP Core Project "Global Change and Terrestrial Ecosystems" addressed many of these issues. The overall aim of the conference was to present and discuss latest findings to assist the development of predictive tools designed to help policy makers make informed decisions about the sustainable management of Earth's resources. Selected publications arising from the meeting will appear in special issues of Agriculture, Ecosystems and Environment. The conference included several themes covering plant physiology, soil science and fertility, global carbon budgets and climate predictions, the effects of air pollutants on pests and diseases and the effects of anthropogenic influences on the stability and function of our forest and agricultural ecosystems. The majority of the oral and poster presentations also considered the human impact on ecosystems through land use and management. Just over a quarter of the presentations addressed global climate change while about a third specifically dealt with increased atmospheric CO₂ concentrations. Other important components of climate change such as increasing temperature and rising concentrations of pollutants such as ozone and nitrous and sulphur oxides received less attention. About half the presentations on soils considered soil organic matter while slightly fewer dealt with erosion, compaction or some other aspect of degradation, while about a quarter of the presentations examined water resources or quality. The majority of the vegetation studies focused on agricultural monocultures but many considered multi-species mixes or rotations. Nearly half of all presentations contained a modelling component, whereas only one third reported experimental data. An important problem identified in many presentations was the difficulty of scaling up data collected from small-scale experimental plots to provide information that is relevant to policymakers interested in larger scales.

Modelling the direct effect of environmental change on the productivity of crops and pastures received considerable attention. Simulation models are considered integral to understanding the possible effects of global change on agriculture, forests and soils and hence are a key component of GCTE Focus 3 research. Over the past five years, significant advances have been made in incorporating elevated CO₂, temperature, and nutrient and water availability into crop simulations. Bruce Kimball (USDA, ARS, Arizona), Pete Jamieson (New Zealand Institute for Crop & Food Research Ltd, Christchurch) and others from the GCTE Wheat Modelling Network showed that models now reliably predict crop responses to elevated CO₂, water and nitrogen stress in regions where (i) there is a strong weather signal that drives plant growth and development and (ii) there is also some knowledge of cultivar response to local conditions. Models are still challenged by differences in soil processes, pests, and new technologies as these can override the weather signal. Continued progress is however being made in integrating these factors into single crop models.

Scaling and integration issues remain problematic for modellers and policy makers faced with uncertainties of global change and thus will receive more attention by GCTE Focus 3 in the future. How, for instance, does one extrapolate results from intensively-managed monocultures to patchy, family-managed farms in the developing world, or to more complex natural grasslands and forests? Although several ecosystem models can deal with this level of complexity, the integration of data and the assessment of the impacts of increased variability in Earth's climate system on production is still an area which remains poorly understood. Uncertainty analysis and risk assessment were featured in less than 10% of presentations; yet these are surely areas to which more attention also needs to be paid in the future. Nearly two thirds of the presentations were relevant to the more developed countries, but encouragingly, the modellers are now also involving local farmers from different parts of the world. Agricultural decision support systems are also beginning to link crop simulations with climate forecasts, stochastic weather generators, risk aversion factors, and economics to guide crop management and production at the local level (Jim Jones, University of Florida). These approaches should increase profitability, improve resource use efficiency, and promote food security.

The environmental consequences of increasing food production, such as increases in N₂O and CH₄ emissions (Keith Smith, University of Edinburgh), were considered at several scales. Ram Babu Singh (University of Delhi) highlighted an urgent need to maintain high farm productivity in rural Indian communities in the face of rising soil salinity and nutrient deficiency problems as well as enormous population pressures. Pedro Sanchez (ICRAF, Nairobi) presented inspiring case studies of poor East African communities where low-tech, cheap management strategies were used to augment the fertility of the soil producing three-fold yield increases. He and several others pointed out that political instability and poverty frequently outweigh biophysical constraints to productivity and often determine changes in land use. Land ownership is a critical factor affecting sustainable production because there is little incentive for good environmental stewardship when the land is not owned by the people that derive their sustenance from it. Several speakers (particularly Andrew Bennett, DFID, London) stressed that the underlying issue of population growth dwarfs many of the problems that might be caused by climate change. The dramatic increase in crop yields seen over the last 40 years (the "green revolution") must be maintained at the same rate for at least the next 50-100 years to support the Earth's increasing population if further new land areas are not to be cleared (extensification). Mitigation and adaptation strategies will help to ameliorate the effects of some of these problems and are likely to be fertile areas for Focus 3 research for many years to come.

Population increases and hence dwindling supplies of fresh water per capita were major factors in Jim Wallace's (Institute of Hydrology, Wallingford) eloquently argued presentation. Based on a minimum water requirement of 1000 m³ year^-1 person^-1 for direct and indirect consumption, he calculates that by the year 2050, 70% of the Earth's population will be living with insufficient or marginal supplies of fresh water. This problem will be most severe in developing countries where faster rates of population increase will further reduce the per capita water availability. In areas where irrigation is used for crop production, only 10-30% of the water supplied is actually used by the plant, so rather small improvements in water conservation and delivery efficiencies may translate into much larger increases in agricultural productivity than could be achieved by trying to breed or bioengineer improved plant water use efficiency. Large-scale hydrology is of key importance to soils, plant production and indirectly to pest and disease epidemiology. It appears that water resources may well be a critical proximate global change driver in the future.

Both Richard Baker (Central Science Laboratory, York) and Bob Sutherst (CSIRO Entomology, Australia) presented data from climate studies which considered the direct effects of increases in temperature on pest distribution. The effects of changes in temperature and the frequency of extreme temperature events on the available land areas for agriculture were also considered. Stephen Nandwa (Kenya Agricultural Research Institute) noted that even slight deviations from average temperatures could have a disproportionate effect on crop yield: for example, a 3.5°C increase in temperature at critical stages in crop development can lead to a decrease in maize yield of up to 70% because of increased transpiration.

Economic, political, and regional policy issues (e.g. world market prices, land ownership, and deforestation) may have a far more threatening and imminent effect on the sustainability of the Earth's resources than actual changes in temperature, precipitation, or greenhouse gas emissions brought about by global change. Nevertheless global change factors will further complicate what is already a demanding challenge and scientists have a responsibility to communicate relevant research findings more clearly to the people who make the policy decisions and to those directly affected. There is also a pressing need to be able to project experimental data upwards to the regional, country, or continental scales so that research findings can be used effectively by all who work in the global change community. In his concluding remarks, Will Steffen (IGBP Secretariat, Sweden) observed that methods used to produce food and fibre are having increasingly greater impacts on the functioning of the Earth. This is, in part, due to the large land areas involved and, in part, to major increases in resource use and human impacts on soil, water and the composition of the atmosphere. The challenge for GCTE is to deliver appropriate science to help make informed decisions for natural resource management and production systems in a changing world.