Attacking the Nettles
some major threads of thought on the development of Three Hagges Wood have emerged during our dormant winter months. The first was prompted by a constructively critical review of the last blog, The Burden of Weeds, which included comments regarding the wildlife value of nettles, thistles and brambles.
The second was provoked by an excellent Radio 4 programme on 12th February 2013, Costing the Earth, with Tom Heap, entitled When Nettles Attack. It examined the increasing problem that native invasives present to biodiversity and drew on the work of, amongst others, Dr Lindsay Maskell at the Centre for Ecology and Hydrology. They include, of course, the usual suspects: nettles, thistles and brambles, the big three.
Something of a dichotomy there, it would seem, and trying to make sense of it gave me a third thread ‑ that there is much to explain as to why our ecological-holistic approach to the creation of Three Hagges Wood is so critical.
With regard to the wildlife value of the big three, we have to be aware of a tendency to overestimate the importance of a single plant species to a particular insect and to recognise the single minded focus that can result from our own particular passion, be that butterflies, bees, moths, bats or birds. We need also beware that the appreciation of the beautiful does not cloud our judgement regarding the value of less showy species. Conserving butterflies/bees/bats/birds can’t be done in isolation, or at the expense of more cryptic and unremarkable species.
For example, it is true that some butterflies rely on nettles as a larval food source, and the principle that we must have larval food plants in order to have butterflies is sound. Those that rely on nettles, however, are a relatively small group of some half dozen in the subfamily Nymphalinae, among them the colourful and captivating red admiral, comma, peacock and painted lady. There are, indeed, also three lovely species of butterfly that will use brambles as a larval food source: the green hairstreak, the grizzled skipper and holly blue. But for preference, the last three use a diversity of other plant species on which to lay their eggs, including buckthorn, dogwood, spindle, and half a dozen or more herbaceous natives of meadow and woodland.
It’s also true that adult butterflies in general use brambles and thistles as a nectar source. Most of them, however, will use a far more diverse group of flowers in their search of nectar – if only they are available – and in many instances these nectar sources are woodland edge and grassland plants, such as blackthorn, hawthorn, cherry early in the year, and campion, scabious, knapweeds, and meadowsweet later in the season.
I do not say that nettles, brambles and thistles are not useful, but that we must not overstate their usefulness without balancing it against their potential for reducing diversity. They are among the prime factors that reduce the diversity of larval food and nectar-yielding plants, not all of which are robust, vigorous and competitive. Their extreme competitiveness, their effectiveness at grabbing, nutrients, water and light, excludes the colonisation of more diverse plant communities. This is why one of our foremost management aims is to control them.
Of course we do, inevitably, wish to conserve the beautiful and the glamorous, and because they are (or once were) highly visible, this may make a reduction in their numbers easier to observe. But at the same time as committed conservers of butterflies have been bringing this disaster to our attention, our micro- and macro-moths have also been in calamitous decline. According to a joint report on The State of Britain’s Larger Moths, by Butterfly Conservation and Rothamstead Research, published earlier this year, we have lost 40% of our moths in the past 40 years. As to bumble bees, according to Professor David Goulson at the University of Stirling’s Department of Biological and Environmental Sciences, of 27 native species of bumble bee, 3 are already extinct and 8 are very rare. There is no reason to believe that this rate of decline might not be true of whole swarms of other insects, the ones that lack both allure and visibility, but which are the critical but unsung performers in food webs and ecosystems. Every single one relies on plant diversity to survive.
In the broadest terms (and it’s a worldwide phenomenon) the main cause of decline is loss of habitat and/or damage to ecosystems, which happens for a variety of reasons. In rural areas, the destruction of hedges, a lack of sunlight and plant diversity in neglected or abandoned woodland are prime factors.
In the context of creating our new woodland, this means that we need to attempt to construct an ecosystem that includes something for everybody from ground level up: the most useful grasses and perennials in open glades, through an edge mix of shrubs and small trees, right up to a high canopy of forest trees. Our grassland mixture, for example, which includes a mere 9 grass species, potentially provides a larval food source for some 69 species of butterflies and moths, as well as 164 other insect species. Sheep’s fescue, Festuca ovina, alone is a prospective host to the larvae of 11 butterflies, 22 moths and 19 other insects. (Derived from the British Records Centre database: http://www.brc.ac.uk )
Similarly impressive plant-insect associations pertain for every species we will plant. Each additional native species we persuade to thrive in our woodland planting – be it grass, perennial, shrub and tree – will raise the bar for both beauty and biodiversity. These plants are the very foundation of an ecological pyramid. Every single one could sustain an incredible diversity of insects – not just the jewel-like butterflies, moths and bees, but also the more obscure and undistinguished which together, in their short lives, form a vital food source for birds, bats and other small mammals. They, in turn, are food for hunters higher up the food chain. Individually they may represent a singular interest or passion; together they go some way to becoming a healthy ecosystem.
Here are some of the websites that I have visited in writing this blog, you’ll find them a fascinating source of information:
http://www.ceh.ac.uk The Centre for Ecology and Hydrology