Time and relative dimensions in space in woodland surveys

I first came across Albrecht Durer’s masterly painting of a piece of turf in the 1970s. Trudy was working on grassland at the time, so it was an obvious print to get and the blockmount is still with us. It shows a mixture of herbs and grasses, but not just any old species chosen for their aesthetic appeal. As others have pointed out, it is an assemblage that can still be found today in neutral grassland. By contrast his woodland species paintings (or those assigned to his workshop) tend to be of individual plants – a columbine for example.

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Our blockmount print of Durer’s painting

This is probably just coincidence, but it does reflect the different scales of local diversity in grassland versus woodland. Species tend to be packed together in grassland, whereas under the shade of the trees there are often large patches of a single plant -bluebells, ramsons, bracken, creeping soft grass, or less large areas of bare litter with a scatter of individual plants, albeit a variety of species.

Local high species diversity at a small scale in grassland, compared to bluebell monoculture.

This has of course long been recognised and is the reason that plant ecologists tend to use different-sized quadrats according the formation being sampled. Grassland ecologists tend to use 1×1, or 2×2 m quadrats whereas for woodland vegetation (excluding the trees) 4×4 m is about the smallest size considered and up to about 15 x 15 m have been used. This phenomenon was reinforced for me in the last few weeks because I have been re-recording permanent plots – not in Wytham Woods for a change – but in the Warburg Reserve at Bix Bottom, just north of Henley. Colyear Dawkins, who set up the Wytham system also set up a similar series of plots across this reserve in 1974, shortly after it had been acquired by (what is now) the Berks, Bucks and Oxon Wildlife Trust.

The main ancient woodland interest lies in the beech on some of the steep slopes, a mixture of old coppice and former wood-pasture areas. However there had also been slopes with orchid-rich chalk grassland. In the late 60’s a change of ownership led to some of this being planted with mixtures of conifers and broadleaves, prompting the Trust to step in, buy it and start to remove the plantations from the former grassland to restore it.

Chalk grassland and beech woodland areas on the reserve

Colyear’s plots are spread systematically across the reserve on a 100 m grid, so some fall in the ancient woodland, some in the restored grassland, some in the scrub margins between the two. The plots are 10×10 m, but the protocol also involves listing the species found in thirteen 0.1m2 sub-plots. This allows for two scales of species richness to be considered. In the grassland areas I am regularly getting 5-10 species in a sub-plot  (0.1m2) and over 40 in the main plot (not that that is particularly rich for calcareous grassland); in the ancien t beechwood many plots had less than five species in the whole main plot!

Two plots less than 150 m apart with very different species-richness, but both valued habitats.

Comparing this recording with the last one in 2009, I would expect (the analysis has not been done yet) that the diversity of plots that were grassland at both times will not have changed much. On the other hand, some of the beech plots might have changed a lot, depending on whether in 2009 they were under a gap that has now closed over, or are now a gap where the shading beech in 2009 has blown over.

Both the chalk grassland and the beech woodland are Annex 1 habitats under the EU Habitats and Species Directive and for other groups the relative patterns of species richness would be reversed – not many deadwood invertebrates live in chalk grassland. Even just considering ground flora diversity, the exercise is a salutary reminder of the importance of scale in both temporal and spatial terms when comparing plant formations.

 

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