By Alister Wynn, Head of Woodlands and Impact

Species choice for new woodland planting is one of the most common questions we get asked. Part of our remit as a woodland creation charity is to create resilient new habitats in the face of a changing climate.

As well as the threat from climate change our wooded landscape has to deal with the ever increasing risk from pests and diseases. So species choice is not quite as simple as maybe it once was. Fortunately there are many organisations and clever people putting their collective minds to the task of trying to understand and predict what the next century and beyond might look like for our trees. However before we look at what others are doing around climate change it’s worth pointing out that species choice is primarily dictated by both your own objectives for each site, its environment (present and future) and soils but also an influencing factor is where you or your organisation sit on the human intervention spectrum.

Letting nature guide you

Many conservation led organisations lean towards the natural world deciding for us what species will thrive, evolve and naturally select over time. This lends itself to approaches such as natural regeneration and allowing woodland to expand by itself through removing grazing and deer pressure or by looking at what is in the landscape already and then replicating this so that local ecology has more of the local habitat it is adapted to. There is good logic and sense in this approach. For example many of the species that are native to the U.K. are also native to areas in central and southern europe. This would suggest that, given time, our native populations of the same species will adapt to the warmer continental heat we are predicted to be getting over the next century. Time is the key unknown here and our climate is changing at a rate not seen for millions of years, so it is yet unclear as to how our natural world will adapt and how quickly it can do this. Many believe it can and will adapt.

Humans will decide

On the other end of the spectrum is a more human centric approach whereby we try and predict future climate scenarios and come up with a species mix that suits that climate. There is also good logic and sense in this approach. This is particularly true when growth of timber is a key driver for species choice and the yield it will give you over it’s lifetime. This is important when trees are grown for financial benefit, like that of productive forestry, where a small difference in yield over the entirety of a stand can mean profit or not in 40 or 100 years time. However you run the risk of the climate not changing as predicted and possibly creating new woodlands that aren’t adapted to current conditions and the local ecology. There are widely used tools within the forestry industry which use modelling and predictions to guide decision making around species choice. The Industry standard is Forest Research’s Ecological Site Classification (ESC) tool. This approach can mean a higher likelhood of selecting non native species when looking at climate scenarios for 2080 and beyond, something which many in the conservation world are against.

Both approaches have there benefits and drawbacks and evidence base to suggest they might be right.

A blended approach

There is a case for not putting all of your eggs in one basket. Resilience should be baked into not only the breadth of the species you are selecting but also the approach you are taking. Our current process for species selection is to adopt both natural regeneration where it is likely to succeed fairly rapidly and a slightly more interventionist approach where planting is more appropriate.  Where we plant trees we have the opportunity to tinker with what the local wooded landscape is telling us (if we feel this is necessary). Bear in mind that many of the trees in our landscape are here by design, as we have been shaping the landscape for millenia and deciding what trees best suit our needs. So inheriting the historic decisions of our ancestors in the face of new challenges on the horizon might not be the best approach if applied on mass (reference points above).

Our starting point for deciding on the planted species mix is to look at the soils and geology of the site, this should always be done through soil sampling and not a desk based exercise. Certain species will thrive in certain soils and it’s key to understand what soil type you are working with and how this might be affected by more extreme climatic events, flooding, drought etc. Once this is known then you have a pallette of trees to work with, some of which according to tools like ESC, perform well now but might not look so rosey in a 100 years time. Beech is a classic example of this and it is suggested that due to Beech’s intolerance to drought, then it might not do so well in the South of England as we move forwards. This is not to say that you shouldn’t plant Beech and it is certainly an important tree in many landscapes. A potential good substitute for Beech on certain soils is Hornbeam, which although is not as valued as Beech for it’s timber and thus not as commonly planted, is a fairly resilient tree that is lessy fussy and ‘could’ prove its worth in the near future.

Widening our choice

As our species choice gets narrower due to pests like Ash Dieback then we need to make a concerted effort to widen our species selection to build in the resilience we need moving forwards. Some species are hard to get hold of and are considered rare in our landscapes. Two native trees that could do with more of presence in our planting schemes are Wild Service Tree and Small Leaved Lime. These species have been managed out of our of the landscape over the millenia and are sometimes considered Ancient Woodland indicators. Identifying existing mature specimens of these trees and collecting their seed is a good start to bringing them back into the mix.

Three key takeaways when deciding on species mix in a changing world are…
1. Understand your soils
2. Make your planted schemes ‘species rich’
3. Design to objectives