Put together the plant lists from the 164 permanent plots in Wytham Woods for the five occasions that the plots have been recorded since 1974 and there are 235 species. However just 12 of them provided 47% of all the species occurrences, they make up 82% of the recorded vegetation cover and 87% of the modelled biomass of the ground flora. This dominating dozen consist of bramble, dog’s mercury, nettles, bracken, rough-stalked meadow-grass, wood false-brome, tufted hair-grass, enchanter’s nightshade, ground-ivy, bluebell, wood-avens, and goosegrass.
The first four have previously been described as the ‘thugs’ of British woodland (Marrs et al., 2010) because one or other of them tends to dominate the ground flora in most semi-natural woodland, except on very acid or very wet soils. The one ‘thug’ not mentioned above is ivy, but that has started to spread in Wytham in the last twenty years, since the deer population has been reduced.
The common pattern in most of the plots is for a few species (usually from the above list) to be widespread with about a dozen others (the average number of species in a plot is about 15) present as just a few plants each. Moreover, over time, even in patches of the wood where nothing much seems to be happening, there is quite a high turnover amongst the species present only as a few plants. Some of this is crypto-turnover, where a species really is there but is not recorded because it is overlooked. However there were regularly plots where 5 to 10 species were lost or gained between recordings which surely can’t all be cryto-turnover – we are not that bad a set of surveyors!
The dominant dozen are inevitably going to control most of the contribution of the ground flora to the ecosystem processes in the Wood, simply because of their cover and mass. So are the other, less common species at all important, given that many of them seem to be coming and going in the plots where they occur? They certainly add to the interest of the wood as they include a lot of the prettier and more interesting species – cuckoo-pint, nettle-leaved bellflower, herb paris, the St John’s-worts. They will also be supporting (generally) small populations of associated invertebrates and fungi.
Some are limited by localised environmental requirements – pendulous sedge can be locally abundant but only in the damper hollows; the recently recorded soft shield-fern is only on damp shaded banks. A few may be accidents of history – the yellow birds-nest and white helleborine are found in just one or two places and seem likely to have been brought in with the beech planting of the early nineteenth century. Most could occur quite widely across the woods but are limited by competition from the dominant dozen.
Some may be destined to be the wood-wide dominants of the future: wild garlic has become abundant mainly on the north of Wytham Hill in the last few decades and there are colonising patches scattered elsewhere. My impression is that hedge-garlic (no relation) is also on the up, probably in response to higher levels of nitrogen in the soils from atmospheric deposition. Then there are the recent introductions of non-native species such as the small balsam, Himalayan balsam and Sicilian honey garlic which hardly feature in the plot lists at all at the moment, but have the potential to spread at least locally in the Woods.
At times it has been fashionable to compare the conservation of species to keeping all the rivets on a plane, because you might be able to lose one or two, but if too many pop-out the engine stops or the plane falls apart. It is a nice analogy, but we should admit that while some species really are holding the whole system together, others may be just part of the drinks trolley (hang-on, that really is an essential part of the flight!).
MARRS, R., LE DUC, M., SMART, S., KIRBY, K., BUNCE, R. & CORNEY, P. 2010. Aliens or natives: who are the ‘thugs’ in British woods? Kew Bulletin, 65, 583-594.