Comparison of a recent elm decline with the mid-Holocene Elm Decline.

The threat of devastating pathogens on a range of tree species has increased recently, which justifies the investigation of the temporal dynamics of tree declines caused by disease. The mid-Holocene Elm Decline was a widespread and synchronous event recorded in pollen diagrams across northwest Europe. The probable drivers of this event have been debated for over 80 years but the role of disease has gathered greatest support in recent decades. Here we report pollen data at sub-decadal resolution from a closely sampled sediment core from eastern Ireland covering the last 160 years. This provides data on the structure and dynamics of the surrounding woodland before, during and after the outbreak of Dutch elm disease in the 1970s. A decline in elm was also recorded in the 1940s associated with an earlier, less virulent, outbreak of elm disease. The elm population recovered from the 1940s outbreak after 20 years but did not recover from the 1970s pandemic. The pollen data also facilitate the comparison of this disease-mediated decline with the mid-Holocene Elm Decline; the impact of human disturbance and disease resulted in different woodland compositions and the adjustment of the woodland in response to these factors was rapid. The impact of Dutch elm disease on this elm 1970s population was very similar to that recorded in the mid-Holocene Elm Decline in Britain and Ireland. [ABSTRACT FROM AUTHOR]