Lessons to learn for better safeguarding of genetic resources during tree pandemics: the case of ash dieback in Europe

TL;DR

This paper reviews conservation strategies for ash trees affected by dieback in Europe, emphasizing the need for systematic frameworks to preserve genetic diversity amid ongoing threats and knowledge gaps.

Contribution

It analyzes 47 studies to identify key dimensions and challenges in conserving ash genetic resources during pandemics, highlighting gaps and urgent needs.

Findings

Limited integration of genetic safety in conservation plans

Most studies focus on local-scale solutions

Rapid decline of ash populations observed in recent years

Abstract

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.