Best replacement tree species to mitigate the loss of ash in Britain

As the spread of ash dieback across Britain becomes more noticeable, there is a peak in interest about the consequences of ash dieback, with landowners and conservationists seeking good advice about what tree species is best to plant to help nature recover.

The following information is a summary of the findings of a research paper I co-authored, published in 2019. As with many research papers, unless the researchers pay the publishers, then the paper is hidden behind a paywall for readers. After all, someone has to pay for the costs of publication. In this case, the paper was featured in the journal’s blog, along with a supplementary guide for landowners. I am therefore pleased to be able to provide the following information without falling foul of copyright. If you are interested in accessing the full paper in the Journal of Applied Ecology, here are the details:

Hill, L, G Hemery, A Hector, and N Brown. 2019. “Maintaining Ecosystem Properties after Loss of Ash in Great Britain.” Journal of Applied Ecology 56 (2): 282–93. https://doi.org/10.1111/1365-2664.13255

Our approach used the distributions and functional traits of tree species to map the changes in traits that may occur across Britain. Functional traits are the characteristics of organisms that can influence ecosystem functioning (such as height or fruit type), and where there are large changes in the functional traits present in an ecosystem there are likely to also be changes to other important aspects of ecosystems. For instance, the provision of ecosystem services and the suitability of an ecosystem for habitation by other species are both closely linked to the functional traits of the ecosystem.

Three Key Actions for Landowners

1. Replace ash in vulnerable ecosystems with recommended tree species mixes, by planting or encouraging regeneration:

In many cases planting will be important to supplement natural regeneration. Older trees have higher ecological value, so planting should start as soon as possible after ash loss, especially in locations with very high densities of ash. This is particularly important in highly vulnerable areas and woodland types. See below for recommendations of species mixtures in different locations and woodland types.

2. Replace lost ash trees outside of woodlands with suitable mixtures of trees:

Replant ash trees as they are lost from hedgerows etc. If you are in a vulnerable region, consider using recommended species (see tables below). Ash trees outside of woodlands have a critical role in connecting patches of fragmented woodland across the countryside. Maintaining this connectivity after loss of many ash trees should be a key aim of management.

3. Encourage compensatory growth and regeneration of other tree species:

Enhance natural regeneration and resilience of woodlands by managing pressures (such as herbivore damage, abandonment, pollution, invasive species and diseases). Management prescriptions will depend on specific threats to individual woodlands and might include thinning, herbivore control, action on invasive species, and promoting diversity within stands. More information and advice can be found in the UK Forestry Standard (UKFS)


Selecting replacements to ash in Britain’s most vulnerable regions

These are the most highly recommended tree species for the replacement of ash in regions of Britain most vulnerable to ash loss. Recommended species are those that would compensate best for the lost functional traits of ash in each area, and are listed in order of priority. Ideally all species listed would be included where possible.

Most Vulnerable RegionsRecommendations for Replacement Species
Yorkshire WoldsPopulus tremula; Alnus glutinosa; Tilia cordata; Quercus petraea
Cannock ChasePopulus tremula; Alnus glutinosa; Acer campestre
FenlandPopulus tremula; Alnus glutinosa; Acer campestre; Quercus petraea
Northern Norfolk BroadsPrunus avium; Tilia cordata; Acer pseudoplatanus; Castanea sativa
AngleseyPopulus tremula; Alnus glutinosa; Acer campestre; Quercus petraea
Western WigtownshirePopulus tremula; Alnus glutinosa; Quercus petraea
West AyrshirePopulus tremula; Alnus glutinosa; Quercus petraea
South PembrokeshirePopulus tremula; Alnus glutinosa; Castanea sativa
HerefordshireAlnus glutinosa; Acer campestre; Quercus petraea

Selecting replacements to ash in different NVC communities

The following NVC woodland community types [*see reference below] contain constant or frequent ash. The recommended species are those that would compensate best for the lost functional traits of ash in each community type, and are listed in order of priority. Ideally all species listed would be included where possible.

*Hall, J.E., Kirby, K.J., Whitbread, A.M. (2004). National vegetation classification field guide to woodland. Download publication.

NVC woodland sub-communities
W5aSorbus aucuparia; Rhamnus cathartica; Quercus robur; Betula pubescens
W5bSorbus aucuparia; Rhamnus cathartica; Alnus glutinosa; Quercus robur
W7aSorbus aucuparia; Betula pubescens; Acer pseudoplatanus; Quercus robur
W7cBetula pubescens; Acer pseudoplatanus; Sorbus aucuparia
W8aPopulus tremula; Acer campestre; Sorbus aucuparia
W8bPopulus tremula; Sorbus aucuparia; Acer campestre
W8cAlnus glutinosa; Populus tremula; Quercus petraea
W8dPopulus tremula; Acer campestre, Quercus petraea
W8eBetula pubescens; Acer campestre; Quercus petraea
W8fAcer pseudoplatanus; Acer campestre; Quercus petraea
W8gSorbus aucuparia; Prunus padus; Quercus petraea
W9aAlnus glutinosa; Betula pubescens; Prunus padus
W9bPrunus padus; Sorbus aucuparia; Populus tremula
W10eBetula pubescens; Alnus glutinosa; Quercus petraea
W12aAcer pseudoplatanus; Acer campestre; Quercus robur

Read more about ash dieback

Editor’s Choice 56:2 – A trait-based approach for forest ecosystem management

The £15 billion cost of ash dieback in Britain

A trait-based approach for forest ecosystem management

6 thoughts on “Best replacement tree species to mitigate the loss of ash in Britain

  1. Thank you for this article. Leicestershire is facing widespread ash die back, with the ash being the predominant tree in hedges across much of the county. We have a large, and growing, network of voluntary (amateur) tree wardens and I, for one, am keen to encourage landowners to plant ecologically-selected hedgerow trees whilst we have time and whilst the ash are still declining rather than already gone. Some suggest sycamore as hedgerow trees.Would you recommend any particular species mix for Leics?
    In addition, like so many other parts of rural Britain, substantial housing developments are appearing within our villages. I wish to persuade our village developers to plant trees with an ecological function alongside amenity value, both within developments and to screen the new village edge. To my mind, Aspen would be an attractive type as part of the mix, with crab apple and Midland hawthorn with sorbus and rowan. Would you be able to suggest a better mix? Especially with the suckering habit of aspen possible presenting issues to ground management companies.

  2. I am concerned about the widespread use of Populus tremula in certain locations, for instance where woodland shares a boundary with herb rich meadow, where the preservation of grassland is important. Populus tremula suckers prolifically and if not controlled can turn grassland into woodland within a matter of years, which could be great if that is intended, but a major management headache if that was not the intention. Suckers are no respecters of boundaries and a single aspen can send suckers out tens of metres from the parent plant, creating hundreds of offspring. The suckers are much more resilient in grassland than seeds say from ash trees, where grass suppression would limit the regeneration, suckers don’t seem to be troubled by this. Do others have thoughts on this?

    1. Thanks John. This is a helpful promotion of the ESC (Ecological Site Classification) tools. However, the paper that I summarise here is more specific than choosing the right species to suit a particular site with environmental change in mind, it is about which species can best fulfil the ecological niche provided by ash. In reality, we report that it takes a number of species together to even come close to supporting the whole range of species with ash.

  3. Excellent article, although I would council against being too prescriptive. The impact of Ash dieback in Holland and the Netherlands is so crushing because this was used as a replacement following the loss of Elm due to DED. A wide planting palate of exotics is being trialled here on the Norbury Park Estate where we are tenants. This was to look at the impact of climate change but perhaps the use of exotics particularly in urban environments would provide a greater resilients to disease than relying on the native selection which with climate change may turn out to be more transitory than we use to think anyway.

    1. Thanks Rob. Remember please that this was not prescriptive in terms of the needs of landowners or wider society, this paper was focussed on the needs of the natural world in terms of loss of habitat and ecological niche. Any landowner should apply their own motivations alongside these suggestions, and hopefully arrive at a number of compromises. Gabriel

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