The Old Man of Wytham

Most people, if asked to picture a woodland ground flora will probably think of bluebells or primroses, or perhaps a mixture of heather and bilberry under Scots pine. These are the sorts of images that appear in woodland paintings from the late 19^th, early 20^th century. One such print hung on our kitchen wall and inspired my childhood interest in forests.

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Ecologists might refer to the variety of plants recorded in the different woodland communities of the National Vegetation Classification (Rodwell, 1991) which remains the standard breakdown of woodland vegetation. We should though remember that the tables of species in this book represent the overall community composition based on tens of samples that went into defining a community or sub-community – not what was found in any one woo. Moreover, the field work was done 40 yrs ago – and many woods have changed since.

However, there is another issue, in that, on the whole, the sampling for the National Vegetation Classification woodland section focused on long-established woods. The majority of the woodland cover in GB – conifer plantations, young broadleaved woods on farms, scrubby belts along railways or road verges – was largely excluded. For most purposes it does not matter that we don’t have a formal classification for the sparse flora of upland spruce forests, or the bramble-nettle vegetation found in lowland farm woods. However perhaps if we had, it would give us more structured approach to looking at the question of what we might expect in these sorts of site as they develop.

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I tend to group drivers of variation in the ground flora in existing woods under four broad headings (history, management, soils and climate) and these can also be useful for thinking about the flora of new woods. George Peterken has described the influence of history in driving the flora differences  between ancient and recently-developed woods (Peterken and Game, 1984). The longer a wood has existed, the more specialist woodland plant species it is likely to have. So to use a term favoured by Martin Hermy (Hermy, 2015), new woods have a colonisation credit – that is there is a long list of species that might be able to grow in them if they could reach them.

In the past our woods were often quite open because they were regularly cut-over as part of the coppice cycle or were open to allow for grazing in wood-pastures. Woodland plants do tend to be more shade-tolerant than non-woodland species but very few species can grow in deep shade. Existing broadleaved woodland has tended to become more shady through abandonment of past management in recent decades with a decline in the abundance of many typical woodland species.  In a similar way new woods are usually full of young trees that form a dense shade which has the advantage of reducing the vigour and cover of the open ground vegetation (often dense grasses and competitive generalist species), but this also restricts the growth of the woodland flora.

Our woodland flora has proportionately more species associated with moderately rich soils and fewer on acid soils or the most nutrient-rich places, compared to non-woodland plants. However most new woods have been created on acid soils such as former heathland or moor, or more recently on improved grassland and arable which tends to have higher levels of nutrients than in soils under ancient woodland. So again the specialist flora is disadvantaged by the types of places we choose for woodland creation.

Finally, if we look at climate factors, there are more woodland species with a southerly bias to their distribution in Britain than with a northerly bias. This should mean that, with climate change there is the potential to expand the range northward of some species through new woodland creation, provided the soils are suitable and the species can reach these new sites.

Taking all these factors together it is not surprising then that new woods are not botanically very rich. So, what do we want to do about it? We could just ‘leave it to nature’, to see which species end up being favoured by future soils, climates and landscape patterns: but it will almost certainly take many decades for distinctive and interesting plant communities to develop as the evidence from the past century suggests.

Or we could intervene more by sowing seeds, moving plants, inoculating new sites with woodland soil and its associated microbes. We will also have to look at how our management then favours (or doesn’t!) these introductions. It may feel like gardening, but we live in a cultural landscape where human interventions are unavoidable. Conservation then becomes trying to reduce those interventions to the minimum that will deliver the conditions and species we desire and in the most cost-effective way. We are already intervening in a big way by planting new woods or encouraging their development by natural colonisation: introducing ground flora is only a further small step. Provided we are clear what we have done, our successors may thank us more for woods with enhanced richness in woodland plants, including assisted migration to help species adapt to climate change, than solid stands of bramble or Yorkshire fog.

HERMY, M. 2015. Evolution and changes in the understorey of deciduous forests. . In: KIRBY, K. J. & WATKINS, C. (eds.) Europe’s changing woods and forests: from wildwood to managed landscapes. Wallingford, UK: CABI.

PETERKEN, G. & GAME, M. 1984. Historical factors affecting the number and distribution of vascular plant species in the woodlands of central Lincolnshire. The Journal of Ecology, 72, 155-182.

RODWELL, J. S. 1991. British plant communities: 1 woodlands and scrub, Cambridge, Cambridge University Press.