  Ash dieback (ADB) is threatening populations of European ash (Fraxinus
excelsior & F. angustifolia) for more than three decades. Although much
knowledge has been gathered in the recent past, practical conservation measures
have been mostly implemented at local scale. Since range contraction in both
ash species will be exacerbated in the near future by westward expansion of the
emerald ash borer and climate change, systematic conservation frameworks need
to be developed to avoid long-term population-genetic consequences and
depletion of genomic diversity. In this article, we address the advantages and
obstacles of conservation approaches aiming to conserve genetic diversity
in-situ or ex-situ during tree pandemics. We are reviewing 47 studies which
were published on ash dieback to unravel three important dimensions of ongoing
conservation approaches or perceived conservation problems: i) conservation
philosophy (i.e. natural selection, resistance breeding or genetic
conservation), ii) the spatial scale (ecosystem, country, continent), and iii)
the integration of genetic safety margins in conservation planning. Although
nearly equal proportions of the reviewed studies mention breeding or active
conservation as possible long-term solutions, only 17% consider that additional
threats exist which may further reduce genetic diversity in both ash species.
We also identify and discuss several knowledge gaps and limitations which may
have limited the initiation of conservation projects at national and
international level so far. Finally, we demonstrate that there is not much time
left for filling these gaps, because European-wide forest health monitoring
data indicates a significant decline of ash populations in the last 5 years.
