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Friday, 5 June 2015

BushScience: Why woodland isn't just woodland (NVC Classifications)

Geoff wrote a month or so ago about ancient woodland indicator plants, and the usefulness of plant identification (an essential Bushcraft skill) in other areas, including ecology and conservation. He specifically mentioned the National Vegetation Classification (NVC) as a means of describing woodland habitats more specifically, and asked me to write a bit about how they are used in ‘real world’ settings.

NVC was first proposed in the 1980’s and formalised in the early 1990's as a more detailed way of describing particular types of habitat based on the species of vegetation found there. For any sort of meaningful management or monitoring to take place a more specific description than just ‘woodland’ or ‘grassland’ is essential. Comparing lists of plant species and soil data between sites was too long winded so a method was needed to describing common, and rare, types of habitat. What emerged was the NVC, essentially a list of different habitat codes, each describing a slightly different community of plant species which could be assigned to an area to give ecologists or other site managers an idea of what could be found there and the most appropriate way to manage and conserve, or in some circumstances change, those conditions. These species compositions are affected by environmental variables such as geographical location, topography, moisture levels, soil type, stage of succession, historical management influences and  climatic variables, but the codes are assigned purely on the observed species. This is known as a ‘phytosociological’ classification, i.e. the observed ‘plant society’.

In this picture from Riddy Wood we can see at least
3 species of tree (Oak, Elm & Ash) and a wide variety
of ground flora including at least Bluebell, Greater
Stitchwort, Dogs Mercury and others. This is just
one example of a woodland plant community.
The NVC works by splitting each broad habitat type (e.g. woodland) into distinct communities and sub-communities, with each having a alpha-numeric code and a name (usually consisting of the scientific names of the dominant species in that community). So for example W8 (Woodland type 8) describes Fraxinus excelsior - Acer campestre - Mercurialis perennis woodland (Ash - Field Maple - Dogs Mercury), but there are 7 sub-communities which are described as W8a, W8b etc. down to W8g.

In total there are 12 broad habitat types, divided into 286 total communities, some of which are further split into sub-communities. So it takes a bit of getting used to! For further information on the in’s and out’s of the NVC see this page from the Joint Nature Conservation Council (JNCC).

It is not a perfect system, in the real world nature doesn’t compartmentalise itself or stick to rigid boundaries, not very often anyway, so these communities will often grade into each other with no clear boundary. Not do plants familiarize themselves with the other species they are ‘supposed’ to associate with. It is this limitation which prevents the NVC being as widely used as you might suspect. Nevertheless it remains a very useful and widely used descriptive tool for habitat management.

In scientific research, an area where they may seem very useful, these classifications are not widely used: this is largely due to the need for very specific data to allow comparative statistical analysis to be meaningful. While these classifications offer a far more specific description than broad habitat types, there is still variation within classifications which for a scientific approach is too general for reliable and meaningful comparison.

They are widely used by ecologists working in development and planning. In-depth habitat surveys, sometimes referred to as Extended Phase 1 Habitat surveys are commonly conducted when an area of land is to be disturbed or affected in some way by building or other development work - these are normally carried out by ecological consultants who advise companies on planning applications. An in depth knowledge of what is present is required for decisions to be made - the decision may be that the area is of sufficient value or conservation concern that the development is not allowed to go ahead, or can only do so with alterations to leave the highest value areas undisturbed. A ‘lesser quality’ or more common habitat may be allowed to be developed, but a mitigation, or biodiversity offsetting, plan be required which dictates a habitat has to be replaced or created elsewhere. In these cases knowing precisely what was destroyed or damaged is essential if you are to try and recreate it elsewhere. There are also of course situations where an area is deemed sufficiently unimportant biologically that no conditions are placed on its development. This is probably the most common use of NVC classifications in real world industry.

In conservation they are sometimes used as a target - a goal to be reached in the restoration or recreation of habitats. A hypothetical example may be a newly acquired nature reserve which was formerly heathland but had been intensively managed as pastoral farmland. The years of management, including planting different grass species, the application of fertiliser and other agricultural chemicals will have fundamentally altered not only the species composition but also the soil conditions which hosted the plant community. A target may be set to return the area to a more typical heathland plant community e.g. H1 Calluna vulgaris - Festuca ovina (Heather - Sheeps Fescue) heath, a type of lowland dry heath. The management actions which would be written into the habitat management plan would then all work together to do whatever it took to restore that community which could include actions such as soil profile inversion or soil stripping, efforts to reduce soil nutrient levels and sowing seed mixes to restore the correct species. If you think that sounds like a long winded process, your right, but there are rarely effective short-cuts in landscape scale habitat management! 

An area of lowland dry heathland in Suffolk where I conducted some
research on Beetles last summer. The Heather is of course a dominant
and iconic heathland plant but I noticed that another one, Common Gorse,
was missing. When I spoke to the site manager (from Suffolk Wildlife
Trust) he confirmed that there is a lot less than they would expect, that it
found in much higher densities nearby, and that they are not sure why
exactly it isn't so common on this site. They have even tried to increase
the quantities by sowing seed but with very limited success. Goes to
show nature can't always be fitted neatly into a box! 

We’ll be conducting some more in depth vegetation surveys as part of The Riddy Wood Project this summer and will likely be using the NVC as a starting point for describing what we have got to work with. Catch up with us on the new Riddy Wood website to see how those surveys are progressing and follow us on Twitter @Riddywood to get instant info on some of the new species we discover as the work goes forward.

Hope this has been useful or interesting, or even both!


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