Threats to Sustainability in Intensified Agricultural Systems: Analysis and Implications for Management

Abstract

Although agricultural production normally rises as a consequence of intensification, this increase is often accompanied by damage to the natural resource base - either to other agricultural or non-agricultural systems within or outside the area, or to the future agricultural potential of the area itself, so that the increased production is not sustainable. This paper considers 3 case studies of the latter type, examining their respective responses to spatial, temporal and technological aspects of intensification. The first case study (of spatial intensification) is of eucalypt [Eucalyptus sp.] dieback in New South Wales, Australia, where forest decline has been precipitated by the clearing of eucalypt trees to provide extra pasture for sheep production. Tree death is apparently caused by heavy feeding (leading to defoliation) by increasing populations of scarab and other beetles, which have been favoured by the improved pastures. A simple mathematical model [Trenbath, B.R.; Smith, A.D.M. Basic concepts for a systems analysis of eucalypt dieback in New England. In Eucalypt dieback in forests and woodlands, edited by Old, K.M.; Kile, G.A.; Ohmart, C.P. Australia; CSIRO, 1981] of the system is described, used to demonstrate its dynamic behaviour, and to suggest management options for controlling the dieback. The second case study (of temporal intensification) presents a simple mathematical model of shifting cultivation, whose parameter values are mainly based on SE Asian data. The implications of the model (which may be of doubtful validity) are discussed. The third case study (of technological intensification) considers pesticide use on a plot of cropland surrounded by plots of similar crops grown without pesticides, using a model of Comins, H.N. [J. Theor. Biol. (1977) 64, 177-197. The development of insecticide resistance in the presence of migration] to predict the likely implications for buildup of resistance among the insect pests of the crop. The model seems able to provide strategic guidelines for pesticide usage. A major implication of its results is that for sufficiently recessive genes, any strategy that increases effective migration rate and effective size of the untreated population is to be recommended. The conclusion to the paper demonstrates that there are striking similarities between the 3 case studies and discusses the gradual decrease in recuperative power of a system after human intervention in terms of a loss of system resilience.