Emerging tree diseases are accumulating rapidly in the native and non-native ranges of Holarctic trees

Emerging infectious diseases threaten natural and managed trees worldwide – causing reduced vigour, increased mortality and, occasionally, extirpation – yet we have little understanding of how emerging diseases have accumulated over time and how accumulation has varied by host species, host nativity and in different global regions. To address this challenge, I assembled over 900 new disease reports on 284 tree species in 88 countries and quantified how emerging infectious diseases have accumulated geographically and on different hosts. I show disease accumulation is increasing rapidly globally, with numerous recent years having nearly twice the number of new records as the twenty-year average and the number of new reports doubling every ~ 11 years. Of the tree genera assessed, Pinus had by far the most new diseases reported over the last several decades, likely reflecting both its large native range in the Northern Hemisphere and its wide use in forestry globally. Most hosts tend to accumulate more diseases in their native ranges than their non-native ranges, consistent with pathogen introductions causing most new diseases. Europe and Central Asia had the most accumulated emerging diseases, but accumulation is also increasing rapidly in East Asia. This work suggests that the impacts of emergent tree diseases are likely to continue to compound in the future and threaten native and planted forests worldwide.