Sunday, 3 March 2013

How ash die back shows the importance of protecting species diversity

David North, Head of People and Wildlife
One of the basic tenets of nature conservation is that habitats rich in species diversity matter and that losing species is pretty much always a bad thing. As a naturalist I tend to take this as a given, without thinking about it too much. I like living on a planet that oozes biodiversity wherever you look and I hate the idea of losing such a wonderful tree as the ash, the third commonest native tree in England, from our Norfolk woodlands. There is still hope, of course, that here in England the genetic diversity of our trees will mean that at least some of our ash trees prove resistant to this fungus attack. 

NWT Foxley Wood, photo by John Waller
However thinking about ash die back does make you realise how important maintaining species diversity in ecosystems can be.  Our ancient woodlands here in Norfolk tend to be mixed species woodlands, supporting a range of tree species including oak, ash, hawthorn, blackthorn, willow, alder, sycamore ( yes I know it’s probably not native but many ancient woodlands now have them), and depending where you are beech, hornbeam, aspen, Scots pine, lime, plus several species of small shrubs. Ancient woods with a mix of species will come through this hopefully temporary loss of a single species, ash, and other species will soon fill any gaps in the woodland canopy keeping the woodland ecosystem intact and functioning, though somewhat changed.  This is the process that nature uses to make ecosystems resilient to change, and if  some individual ash trees prove resilient in time they may spread and reclaim our woodlands. For an ancient woodland a century may be a mere ‘blink of an eye’ and our human time scales largely irrelevant. A new disease would be catastrophic for a woodland, or any ecosystem, composed of a single species, but fortunately that’s not the way nature usually works.

Protecting species diversity, biodiversity as we now call it, helps provide the resilience to change that ecosystems need. And given all the things humanity is doing to the planet that bring about change -climate change, pollution, fragmentation of habitats, introduced non-native species, to name just a few – then we need ecosystems to be as resilient as possible if they are going to continue to provide us with our survival systems, the ecosystem services, that we depend on.

So if you needed an argument for protecting biodiversity then maintaining our planet’s resilience to change is a good one. There are plenty of others too. Though like me you may simply believe a planet blessed with the astonishing biodiversity we have is richer, more beautiful and should simply be protected in its own right. If you do then why not join NWT and be part of protecting some of the astonishing biodiversity we have on our doorstep. Wildlife certainly needs your support and I for one don’t think leaving it up to Government,  or cash strapped agencies of Government, seems like a good idea just now!          


  1. Is the die-back of ash caused by the rampant spread of a fungus through a monoculture? I get the impression that ash trees have been propagated from one strain leading to no diversity within the ash population.

    1. Hi John, Reply from David North:

      As I understand it the ash trees in our UK ancient native woodlands are thought to be genetically quite diverse and as the new disease of ash trees is now affecting ancient woodlands including our NWT Lower Wood, Ashwellthorpe then I don't think we can say its just spreading through a monculture. The infection was first discovered outside of imported ash plantations at NWT Ashwellthorpe but this was much more to do with the alertness and vigulance of our wardening staff than this being acutually the fist wood affected. Indeed now its been detected in many natural woods across much of the country.

      However you do have a valid point that the import of propogated trees especially if grown through cuttings (which creates genetically uniform clones) could make plantations very vulnerable to future diseases. However the sites like our nature reserves at Foxley Wood, Honeypot Wood, Wayland Wood and Ashwellthorpe are incredibly diverse ecosystems, about as far from monocultures as you can imagine and yet Ash Die Back will affect ash trees on these very varied sites.

      I hope you enjoyed the post and found it interesting - I'm not an expert on Ash Die Back so these are just my thoughts. There is more detailed information on Ash Die back on the Forestry Commission's web site - it a complex disease and still not fully understood.

    2. Reply from our Senior Woods and Heath officer, Steve Collin:

      Planting with clones is a concern, even clones that have a resistance to Chalara is risky. It's quite possible that in the future a new strain of the disease will come along and attack so called 'resistant forms'. Indeed it was a second strain of Dutch elm disease that did all the damage to British elms. It's important not to put all your genetic eggs in one basket. Unfortunately British Ash are not as genetically diverse as other tree species, due to there very late arrival after the last ice age, but ancient woodlands must surely be the best gene bank that we've got, after all, the oldest tree specimens in Britain are said to be coppiced Ash stools.