As climate changes, the effects of forest diseases on forest ecosystems will change. We review knowledge of relationships between climate variables and several forest diseases, as well as current evidence of how climate, host and pathogen interactions are responding or might respond to climate change. Many forests can be managed to both adapt to climate change and minimize the undesirable effects of expected increases in tree mortality. We discuss four types of forest and disease management tactics -monitoring, forecasting, planning and mitigation -and provide case studies of yellow-cedar decline and sudden aspen decline to illustrate how forest diseases might be managed in the face of climate change. The uncertainties inherent to climate change effects can be diminished by conducting research, assessing risks, and linking results to forest policy, planning and decision making.

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Dothistroma needle blight (DNB) is one of the most important diseases of pine. Although its notoriety stems from Southern Hemisphere epidemics in Pinus radiata plantations, the disease has increased in prevalence and severity in areas of the Northern Hemisphere, including Europe, during the last two decades. This increase has largely been attributed to expanded planting of susceptible hosts, anthropogenic dispersal of the causative pathogens and changes in climate conducive to disease development. The last comprehensive review of DNB was published in 2004, with updates on geographic distribution and host species in 2009. Importantly, the recognition that two species, Dothistroma septosporum and D. pini, cause DNB emerged only relatively recently in 2004. These two species are morphologically very similar, and DNA-based techniques are needed to distinguish between them. Consequently, many records of host species affected or geographic location of DNB prior to 2004 are inconclusive or even misleading. The objectives of this review were (i) to provide a new database in which detailed records of DNB from 62 countries are collated; (ii) to chart the current global distribution of D. septosporum and D. pini; (iii) to list all known host species and to consider their susceptibility globally; (iv) to collate Drenkhan et al. 410 |

Summary Dothistroma needle blight (DNB) caused by Dothistroma septosporum and Dothistroma pini is a damaging disease of pine in many countries. The disease led to the abandonment of planting susceptible Pinus species in parts of Africa, Asia, Australasia, Europe and North America. Although the disease can be effectively controlled using copper fungicides, this chemical is only routinely applied in forests in New Zealand and Australia. Other management tactics aimed at making conditions less favourable for disease development, such as thinning or pruning, may be effective on some, but not all, sites. Disease avoidance, by planting non‐susceptible species, is the most common form of management in Europe, along with deployment of hosts with strong disease resistance. Although D. septosporum is present almost everywhere Pinus is grown, it is important that an effort is maintained to exclude introductions of new haplotypes that could increase virulence or enable host resistance to be overcome. A global strategy to exclude new introductions of Dothistroma and other damaging forest pathogens, facilitated by collaborative programmes and legislation, is needed.

SummaryDothistroma needle blight (DNB), caused by the two fungi Dothistroma septosporum and D. pini, is a major disease of pines with a worldwide distribution. Increases in the incidence and severity of disease in areas where the disease has long been established and notable range expansions have both recently been observed. The aim of this review was to assess the relationship between DNB, weather factors and climate to better understand possible underlying causes of this recent intensification in disease. A substantial body of literature shows that the life cycles of the fungi are closely related to weather factors such as precipitation and temperature. Given the rapid response of DNB to favourable weather conditions, it seems plausible that changes in disease behaviour could be due to changes in climate. The recurrent El Niño-Southern oscillation (ENSO) phenomenon influences patterns of temperature and precipitation in many regions of the world, often resulting in warmer and wetter conditions than normal. We found that since the 1950s, four of the past five strong El Niño events appear to have coincided with reports of increased DNB activity on an intercontinental scale. The lack of long-term standardized data records limits our ability to fully interpret this relationship, but the projected future climatic conditions in the Northern Hemisphere appear to be increasingly favourable for the disease. Still, other areas of the world may become less favourable, and further research is required to be able to accurately predict DNB outbreaks and their impact on pine forests in the future.