Planet Earth Online

English woodlands are losing their character

22 July 2009, by Sara Coelho

The hawthorn is now more widespread than it was in the past.

Back in the 1930s, botanist Roland Good cycled around the English county of Dorset to list all plant species at more than 7000 locations. PhD student Sally Keith from the University of Bournemouth recently re-enacted part of the 'Good survey' to find out how British woodlands have changed since then.

Keith identified about 600 patches of woodland surveyed in the 1930s that have not been replanted or developed. Of these, she picked 86 random locations for detailed inspection.

Keith visited each site on a day and month as close as possible to the date listed on the 1930s survey and spent approximately two hours in each woodland patch, compiling a list of all plant species she observed. 'The idea was to copy the method used by Professor Good,' she explains, 'so that we could directly compare our results with the old survey.'

The round trip across Dorset's woodlands took about three months to complete and the results were published online today in the Proceedings of the Royal Society B.

Dorset woodlands, old and new

Keith found that today's Dorset woodlands lost 117 species to local extinctions and gained 47 species. Overall species not native to Britain have had little impact and 'the average number of species within a site remained more or less the same, around 55,' she says.

However, the new survey revealed that today's woodlands look more similar today than in the 1930s: one patch has now more items in common with other patches. Species including holly, wild garlic and the common nettle were reported in many more woodlands today than 70 years ago. The increase in species similarity is called taxonomic homogenisation. Keith's work is the first time the trend has been reported in the UK.

'This is an important observation,' says Keith, 'because this kind of biodiversity loss is not obvious from visits to a single woodland.'

So why are Dorset woodlands losing their distinctiveness? The plants are responding to changes in the environment and for once climate change is not to blame. The woodlands are looking more similar due to higher levels of nitrogen in the soil and the overgrowth that reduces the sunlight reaching the ground.

'Higher levels of nitrogen are a consequence of increased use of fertilisers in agriculture,' says Keith. 'And the light is decreasing because we're not managing woodlands the way we used to.'

In the past, it was common for woodland owners and farmers to remove stems of trees for use as fuel and building and then let them grow again. This sustainable management allowed sunlight to beam down on the small bushes and seedlings at ground level. Now, overgrown woodlands are shadier and less welcoming to some species of plants.

The species detected in Keith's survey that were less common in the 1930s are plants well adapted to low light exposure and high nitrogen levels in the soil.

If left unchecked, the trend may leave all woodlands looking very similar. To stop the process 'we need to bring back traditional woodland management and control the use of fertilisers,' suggests Keith.

Keith's research was a collaborative effort with Natural England and the Centre for Ecology and Hydrology.

Species that became more widespread in Dorset's woodlands

• Ramsons (wild garlic)
• Lords-and-ladies
• Hawthorn
• Foxglove
• Herb Robert
• Ivy
• Holly
• Common nettle

Species that were lost from the sites

(Although possibly present elsewhere in Dorset)

• Red bartsia
• Devil's-bit scabious
• Wood millet
• Lesser skullcap
• Wych elm
• Yellow iris

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