Can we replant our way back from ash dieback?

There’s no getting away from it, the loss of up to 98% of all of our ash trees is going to have a massive impact on the landscape, on woodlands, on roadsides and around our farms. Ash is thought to be the most commonly occurring tree in the whole of Kent in terms of the area taken up by ash. They are, quite simply, everywhere. According to the Forestry Commission, 9% of all of the woodland in South East England is made up of ash and although that figure varies from woodland to woodland, it is rare to find a wood that doesn’t contain ash. Some of the largest and most majestic trees in our landscape are ash trees and we will undoubtedly lose the vast majority of these.

So what can we do? The seemingly unstoppable march of ash dieback across the country is going to change the face of the countryside in a similar way to Dutch elm disease and there appears to be no cure. Can replanting with other species make up for this loss? Put quite simply, no it can’t. A four hundred year old ash tree can’t be replaced, the unique suite of other species that are supported by ash can’t be supported by any other tree species and the beauty, form, smell and feel of an ash tree is matchless. Couple these reasons with the fact that after the great storm in 1987 tree planting projects in woodlands were largely ineffective and natural regeneration (just allowing nature to take its course) was generally considered more effective. So to start not a great case for replanting so that’s the end of this article…or is it?

Whilst the ash tree is undeniably irreplaceable, that doesn’t necessarily mean that planting new trees can’t play a part in an attempt to mitigate for the losses that ash dieback will cause. To understand what part planting can play we need to look at what might happen if we don’t do anything.

Nature abhors a vacuum, and that truth holds for trees as well. In a wood, when there is a gap in the canopy, something will soon rise to the challenge and fill that space. It is thought that where less than 10% of the canopy of a woodland is made up of ash that the existing trees will just expand to fill in the gap left by ash trees when they die. As the number of trees lost increases the gaps in the canopy will become large enough for new trees to take the place of ash. In South East England over 30% of woods have more than 20% ash in their canopies so this natural regeneration will make up for the loss of ash trees. Equally, in copses of trees and other collections of trees in the landscape, so long as the land where ash trees die is not grazed or mown, shrubs and then trees will take the place of ash. So far so good. However, what species will replace ash. Studies suggest that sycamore will be the most likely species to make the most of these opportunities. At this point we’re not going to get into a debate about the merits or otherwise of sycamore, that’s a whole other blog article, but it is worth noting that there will be many places where natural regeneration won’t improve the levels of tree species diversity. It is here that replanting just might serve a purpose.

When it comes to specimen trees the case is even clearer. Without planting and adequate protection for the newly planted tree there will be no replacement for these in field trees that are perhaps some of the most spectacular trees within the landscape. The same can be said for filling gaps in hedgerows where ash dies, especially in order to allow hedgerow trees to become a part of a hedge line.

So there is a case for planting in certain circumstances, but if we do replant then what should we be trying to achieve. Purely from a biodiversity point of view a case can be made for replanting. A JNCC (Joint Nature Conservation Committee) report on The Potential Ecological Impact of Ash Dieback made a study of 1058 plants and animals that live on or around ash. These range from mammals through invertebrates to lichens, fungi and bryophytes. The report showed that whilst 44 of these species are obligate to ash (only found on ash trees) and their fate will be inextricably connected to that of ash trees, selective planting can mitigate for a large part of the ecological impact of losing ash trees. The study, led by Ruth Mitchell, suggested that by planting a combination of 11 different tree species, 798 out of the 1058 species supported by ash could be provided with alternative hosts. That provides a fairly good case for planting schemes that simply give natural regeneration a helping hand and add a diversity of tree species to the mix of trees that take the place of ash naturally.

So what are these 11 trees and should we be planting them all over Kent. There are one or two surprises in the list but actually nothing particularly revelatory. The species are field maple, birch, hawthorn, aspen, oak, small leaved lime, sycamore, hazel, beech, cherry and goat willow. So can we simply plant these trees in areas that have been impacted by ash where they don’t naturally regenerate? Unfortunately it isn’t quite that simple. We don’t want to be creating woodlands, hedgerows and trees with high landscape value that are identical right across the county. The unique character of our countryside is formed from a complex combination of factors including soil type, cultural heritage, industry and, to some extent, coincidence. What we should be trying to achieve is to create planting plans that reflect or at very least complement the existing treescape. This can partly be achieved by promoting trees that suit the soils of particular areas (for example encouraging rowan planting on sandy soils and whitebeam on chalk soils) but also looking at what else is common in the locality of the planting scheme.

Before we sign off there is one more thing to throw into the mix. The current landscape and the trees found within it is markedly different from historic landscapes from before woodlands have been manipulated by humans. By examining pollen records it is possible to see that forestry techniques over hundreds and thousands of years have favoured some species and led other once common species to become very rare within woodlands. Examples of these kinds of trees in Kent include both small and large leaved lime, alder buckthorn and wild service tree. Because of their rarity, trees like these are unlikely to take advantage of the opportunities for natural regeneration and replanting schemes can give them a helping hand by replanting once common species.

Whilst replanting of trees will not answer all of the problems caused by the loss of ash trees, nothing will, carefully thought out selective planting can help to limit the impact on biodiveristy, help restore ancient habitats and prevent dramatic tree loss within the landscape.

To assist with this process The Ash Project will be teaming up with the Woodland Trust to offer packs of trees to landowners over this and next winter. Sign up to the mailing list for more information.

 

Mike Phillips has been working with and around trees in Kent since 2000.  As the training officer at BTCV (now The Conservation Volunteers) he first started teaching people about trees and how to identify them alongside co-ordinating the Kent Tree Warden Scheme.  Kent Tree Wardens look after the trees in their locality and are still operating today as an independent group.  His work has also included writing management plans for both community and commercial woodlands and working with people to enhance the biodiversity of their woodlands.