Planting Resilient Woodlands
I have been planting woodlands in eastern England for over 30 years and have been following the debate on planting resilient woodlands with great interest. In 2008 I planted a small woodland next to my tree nursery. It was intended as a demonstration woodland that I could show to potential customers of my business. In 2017 Nursery Wood was given the Gold Award for Excellence in Forestry in the small and farm woods section by the Royal Forestry Society. My experience with Nursery Wood and other new woodlands is that planting a greater variety of trees and a greater range of genetic material is essential if we are to create resilient woodlands. But equally important for resilience is how we design these woodlands of the future.
I recently attended a Royal Forestry Society field meeting. We visited a 30 year old plantation consisting of 2 rows Oak, 2 rows Scots Pine, 2 rows Ash, 2 rows Scots Pine, 2 rows Oak etc. The rows of pine had been removed some years ago and the ash were suffering from Chalara disease. The plantation was a mess, but provoked some lively discussion. If only the wood had been planted as an intimate mixture and a selective thinning regime established, we could have been looking at a fully stocked oak plantation with a plentiful supply of ash firewood.
Such line planting is rarely seen nowadays but block planting is still widely practised (even by conservation bodies) and the result is often the same. A typical 20 year old broadleaved wood planted with a woodland creation grant has a block of unthinned, unpruned oak, next to a block of ash with Chalara. A block of cankered cherry from an unsuitable provenance is next to a block of rowan which looks totally out of place next to a block of field maple that should have formed the understorey throughout the wood.
Block planting ensures that the species composition of the wood remains exactly the same for the next 50 years. Where is the resilience in that?
Intimate mixed planting allows the species composition of the wood to change over the years either through environmental pressures (pests, diseases, climate change, soil conditions) or through management (thinning to promote timber trees or other species, as previously unrecognised markets develop). Allowing natural selection combined with management will make ensure woodland resilience.
The current advice for new woodland planting is "right tree in the right place", which sounds sensible but what is the right tree for your woodland. Trees that you plant now may be expected to live for 100 years. How do you know which species of tree will cope with future pests and diseases if you don't know what pests and diseases will occur in the future?
Conifers were planted in Britain in the 1920s and 1930s to provide pit props for the coal mines, but the market had largely disappeared before the trees had grown. In the lowlands, poplars were grown in the 1950s for making into matchsticks, but lighters then took over in popularity.
Tree seed collected from native sources has a wide genetic base. Trees in a natural oak wood come into leaf at different times. Some of the oak trees produce a reliable crop of acorns most years while others barely produce acorns at all. There is no need to collect acorns from oak trees 300 miles to the South so that the trees can cope with future climate change. The genes are already in our native oaks and other trees, waiting for natural selection to bring them to the fore.
If we combine the wide pool of genetic material in our native trees with a wide variety of tree species that are able to exploit all the ecological niches of a natural woodland, then we can grow resilient woodlands.
Pests and diseases generally attack individual trees. Very rarely do they wipe out an entire species. They are never a threat to a mixed biodiverse woodland.