The Right Tree in the Right Place? – by Dr Richard Birch CEcol MCIEEM

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The right tree in the right place? This is something of a Natural Resources Wales mantra derived from a Beth Chatto aphorism… but what if the right tree isn’t ‘native’ such as a sturdy English oak (Quercus robur), a noble sycamore (Acer pseudoplatanus), or an elegant Scots pine (Pinus slvestris)? All of which have been recommended to override my esoteric choices of a moderate percentage of holm oak (Quercus ilex), maritime pine (Pinus pinaster) and a seaward buffer of French tamarix (Tamarix gallica). This was an Atlantic-Mediterranean selection I was considering to future-proof a tree planting scheme for a Welsh coastal location that looked more like the backdrop for a spaghetti western in summer! Astute dendrologists will have already noted that sycamore isn’t native, and Scots pine dubiously so in Wales, on the strength of pollen being found in peat samples[1].

Of course, the choice for that location also included a much greater proportion of natives, including the native, much-vaunted sessile oak (Quercus petraea), which does grow nearby, albeit looking decidedly unhappy in the exposed conditions. Back in the days of my apprenticeship (the 1980s) I recall being told by a Species Officer for English Nature that oak was ‘functionally extinct’ in East Anglia because the seedlings require about three years to establish a root system strong enough to withstand summer drought. Even back then, the climate was not fulfilling that requirement. We’re not yet there in Wales, but I fear we may not have long to wait.

It is, though, getting rather hard to find a British tree that can be used in a native tree planting scheme! Oak? Suffers from ‘sudden oak death’ (Phytophthora ramorum – which also affects larch). Elm? Dutch elm disease (Ophiostoma novo-ulmi). Ash? ‘Ash dieback’ (Hymenoscyphus fraxineus). We’re left with the pioneering early colonisers: birches, willows and cherries, and an eclectic mix of trees like hornbeam, beech and aspen – a strange woodland indeed for North Wales.

So far, my design choices for incorporating a proportion of trees from the Atlantic seaboard of Southern Europe have been totally negated by those responsible for authorisation, with the following arguments:

  1. ‘Not native to the area’ – but then neither is that thing the Romans did for us when they introduced sycamore, yet all have been put forward as alternatives.
  2. ‘Not good for biodiversity’ – I would dispute that for holm oak compared to sycamore, particularly regarding its mycorrhizal associations.
  3. ‘They contain species regarded as invasive’ – particularly holm oak, featured in the Field Guide to Invasive Plants and Animals in Britain (Booy et al. 2015) where specifically its colonisation of limestone pavement is emphasised.
  4. ‘Culturally inappropriate’ – an argument which follows the logic ‘we’ve been wrecking the environment for years – its part of our culture’.

The Woodland Trust has an ambiguous stand on this matter. In their Woodland Creation Guide, they point out that “native trees and shrubs co-evolved for many thousands of years with native wildlife to form characteristic ecologically rich and diverse communities, well-adapted to their local geology, soils and conditions”. If you take a stroll through a European woodland, much of what you will see will also occur in Britain (where it is probably less common). There will be a considerable percentage of species that are unfamiliar because they didn’t colonise the UK during one of the interglacial periods, or it was formerly outside their climatic range, or because they are highly localised. This percentage will shift depending on where in Europe the woodland is, and the percentage will be greater the further away from Britain you travel (although the rule still applies as far away as in Eastern Canada[2]). The British flora is actually quite depauperate. When a non-native tree is introduced to the UK, some of its associated species (including its pathogens) may come with it, but not its entire ecocosm – that will take longer, because there is a lag in the rate that different species colonise. Of course, its associated pests may jump to native species with alacrity and find them ill-defended against novel pathogens – mobile and adaptable organisms are good at that – but in time many will reach us anyway. That is a climate change certainty, despite the moat that separates us from Europe. We are already receiving the more mobile species, but generally it is the scary ones that make headlines[3].

Conversely, the Woodland Trust emphasise the wide range of genetic diversity in British trees, almost as if this was a unique trait to our trees. It is also a generalisation: English elm, that statuesque epitome of the pre-1960s countryside of my childhood, is now reduced to a mere shrub by the ravages of Dutch elm disease. It is also almost entirely clonal[4]. The effect of this bias is to create the impression that anything other than native trees is bad (although to credit them, the Woodland Trust do not state this). In extreme cases, the trend reduces further to regional or even local provenance: a sort of ‘botanical eugenics’. I produced a species list of non-native ornamental plants of known biodiversity value for BREEAM in 2011[5]. It was adopted for awhile, but you won’t find it now. It’s as if all the geese, thrushes and finches that come here from Europe every year never bring any foreign seeds in their gut…

Cultural diversity is the anthropocentric equivalent of biodiversity: it is important that different languages and ways of life should persist, but they should not be marinated in aspic, especially if they conflict with the science. As ecologists, we appear to have a very small voice in this argument[6]. But hey! We should be used to that by now. As our trees are pushed out by climate change, there will inevitably be a colonisation hiatus if we don’t pre-empt the species that would ordinarily fill the gaps. As the world changes, some things will have to change with it – even if the very idea is an affront to our perceptions. Climate, you see, just doesn’t care.

Richard is a Principle Ecologist and member of CIEEM’s Wales Policy Group.

[1] See Godwin, H. (1940). Pollen analysis and forest history of England and Wales. The New Phytologist, 39(4), pp.370-400. and Sassoon, D., Fletcher, W.J., Hotchkiss, A., Owen, F. and Feng, L. (2021). Scots pine (Pinus sylvestris) dynamics in the Welsh Marches during the mid to late-Holocene. The Holocene, 31(6), pp.1033-1046.

[2] see Scott, J. S. & Black, D. (2006). Wildflowers of Newfoundland and Labrador

[3] https://www.mirror.co.uk/news/uk-news/invasion-giant-hornets-huge-european-5813471

[4] Gil, L., Fuentes-Utrilla, P., Soto, Á., Cervera, M.T. and Collada, C. (2004). English elm is a 2,000-year-old Roman clone. Nature, 431(7012), pp.1053-1053.

[5] The original document is no longer available but a condensed list of examples can be found here.

[6] George Monbiot breaks down. https://www.youtube.com/watch?v=gJnxj6kiAKU

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