History has demonstrated that massive crop losses can occur when climatic conditions are particularly conducive to disease development. Interest in the consequences of climate change on pathogen population dynamics in agricultural systems is understandable. Furthermore, while some environmental changes, such as increasing temperature and changing precipitation, are linked directly to changes in pathogen incidence and severity, others, such as increases in CO 2 levels, have more indirect effects by changing biomass production, the density of crop stands, and hence humidity within the canopies. However, the disease triangle of any plant–pathogen interaction may shift in response to climate change, favoring different climatic preferences and niche breadths in the future. Such studies make a range of epidemiological assumptions based on observations of current disease triangles (host–pathogen–environment) and predictions of climate change. Much has been written about the likely impact of climate change on disease incidence and severity, epidemic frequency, and its spatial distribution in agriculture. Essentially, none of these interventions are practically feasible or environmentally acceptable in natural plant communities.įeatures of the changing patterns in agriculture and forestry Humans have at least some control over the size and impact of pathogen populations in agriculture through breeding, agronomy, nutrient and moisture manipulation, and the use of chemical controls. Our ability to mitigate such changes is far more limited in natural systems than in agricultural systems. For natural ecosystems and communities, the implications are perhaps less well understood but are arguably even more concerning, given the potential to precipitate a cascade of effects: changes in the fate of an individual pathogen species-an increase or a decrease leading to local extinction-may be surpassed by consequent increases or decreases in host fitness, generating “knock-on” effects in the structure of whole plant communities. From an agricultural point of view, these changes have major implications for the geographic distribution of crops and their associated pathogens and the extent and reliability of production. Many plant and animal communities are now experiencing rapid and significant changes in temperature, rainfall, evaporation patterns, and a dramatic increase in the occurrence of extreme events. Climate change is the most challenging environmental issue facing humankind today.