In Conservation our goal is primarily about conserving the widest range of genetic diversity within each species in a given area. If each area conserves their local genetic diversity of a native species then we will end up with the most diverse/robust option across the country, given our current starting point. We need to conserve that breadth of genetic variation and then create an abundance of that breadth to put us in the most resilient position possible to face a future of climate change and the new pests/diseases that may appear in a given area in the UK.
The best-practice way to achieve that with trees is through natural regeneration of locally native trees i.e. the trees naturally produce seed and that seed germinates nearby and grows to produce new trees. In many places the site where trees are wanted can be too far away from a seed source to be reached under current conditions and so the best option here is to hand-collect seed from the nearest ecologically similar source of locally native trees and hand sow it in the appropriate place on the new site. Not all genotypes within a tree species produce enough seed to collect in any given year and so ideally collection (and sowing) should be over several years so as to maximize the genetic variation possible in the new area of trees. Collecting seeds from an established habitat over a few years helps build local knowledge, particularly expertise in identification and local species location. As trees have such a long life-span, investing time in creating new woodlands or groups of trees makes sense, as does encouraging and developing local knowledge and expertise.
Sowing in this way gives genetic diversity, but also structural diversity (some trees may be grazed as seedlings making them multi-trunked in future, others may have branches that sweep down to the ground), building a more varied habitat than trees closely planted with tree guard protection and made to have neat single straight trunks.
In the future we will need to make the UK economy more resilient to changes in world politics and increasing timber production for home use is one of the ways in which we can do that. It can also have the benefit of carbon capture, and if planned correctly, slow the speed at which water runs off the land into streams and rivers.
When growing timber as a crop it is important to look for certain characteristics, for e.g. quick growth, rot resistant wood, a straight easily-harvestable trunk, and so it is logical to select a species that has the desirable characteristics and then to select the most appropriate ecotypes from that species to grow your timber…much in the same way a farmer would select a particular variety of wheat to grow on their farm. It need not be native species and there is a viewpoint that planting native species with genetics not from the local area could be harmful (see later). As the timber can be a high-value crop it makes economic sense to sow the high-value seeds in a nursery, grow them on, plant them out with rabbit/grazing protection and generally give them sufficient TLC so that they grow in the desired way producing a crop as quickly and efficiently as possible.
The latest report on “Genetic considerations for provenance choice of native trees under climate change in England” was published this year https://www.forestresearch.gov.uk/documents/7110/FCRP030.pdf and it makes for uncomfortable reading with regard to what we don’t know about our native trees. “no investigations into provenance variation among British populations of alder, aspen, elm, hazel, yew, willows, bird and wild cherry, juniper, limes or hornbeam, have been conducted.” And the ones on “silver birch, ash, Scots pine and oak,” are primarily related to how well they survive when planted in a different area and how quickly they grow…nothing about effect on the web of native insect/fungi species etc. that might rely on the trees as a habitat.
The Forest Research report discusses a way of preparing for a climate change scenario in England of an increase in 4 deg C by the 2050s by using tree genetic material from further south that already grows in a warmer climate…but there are drawbacks – one hard frost and the southern material is knocked back…and then it’s possible that there is sufficient adaptability within existing local populations to cope with the change, they don’t know. In summary; it’s complicated and we haven’t carried out enough research, and the research that has been carried out relates mainly to timber production.
There are also possible disadvantages to creating large areas of native species of non-local provenance within an area as this report points out https://staffprofiles.bournemouth.ac.uk/display/report/11496 (it’s the only one I can find that assesses the issue although it is about wildflower/grasses). Using trees of non-local provenance can swamp areas with non-local genes and so affect smaller local populations – how adverse the effect is we don’t know. According to Defra, there are no scientific studies commissioned by government into the effect of the widespread planting of trees of native species of non-native genetic origin has had/could have on genetic variation within our native tree species (I asked in an FOI). If anyone knows of any do let me know please.
There is also no requirement to record where seed comes from for trees planted and Defra have not done so (the same FOI). And whilst the Forestry Commission may keep some records of the genetic source of plantings (the Forest Research report calls for more of this, which rather suggests it doesn’t happen much – see page 35) I very much doubt private individuals, local authorities, charities, or the Department for Transport who have all planted vast amounts of trees keep such records.
Many nurseries in the recent past used seed from the continent as it was cheaper and some didn’t even use native species hence the random assortment of Italian alder and suckering grey alder and that can be found amongst plantings of “mixed native species” trees from the 80s and 90s. And we know that pests and diseases have been imported this way (Ash Dieback) and on importation of larger trees for amenity planting (ref. Hartlepool, Oak Processionary Moth https://www.hartlepool.gov.uk/news/article/1643/caterpillar-infested_oak_trees_removed ).
Using tree saplings sourced from large national nurseries for conservation purposes can mean that the trees planted throughout the country come from the same narrow genetic base – inevitably any tree nursery supplying the whole country cannot supply as genetically diverse a tree as could collecting seed locally.
Planting trees goes against what the government’s 25-year environment plan asks Conservationists to do, i.e. conserve the genetic range within each species.
You can of course throw your hands up in the air and say it’s all a big mess and too complicated and so it doesn’t really matter what we do, as long as we plant trees and as quickly as possible. Against that position is the example Ash Dieback sets us…we don’t know what is coming our way in the future; planting any old thing may just cause future problems if we narrow the genetic base of our native tree species too much. And if the fifth (or are we sixth now?) largest economy in the world can’t research and conserve its own native trees properly, what chance has the rest of the world got?