Thursday, 9 January 2014

Offsetting Ancient Woodland

Looking at the pronouncements on possible ratios of replacement trees to original trees, I wonder if the Government has seriously considered the areas of land required to offset loss of ancient woodland? Using some basic calculations, it seems to me that they are going to have to require some major areas of the countryside to be allocated to tree planting if they are serious about a 100:1 replacement ratio.

I have just done some 'back of a fag packet calculations (thankfully I gave up 10 years ago, so I have to use scrap paper but I doubt that makes much difference to the science!) and the following figures come up:

1. In traditional coppice with standards, tree density is likely to be anywhere between 30 and 100 crowns per hectare. That, I suspect refers solely to the 'standards' and thus the question must be whether additional provision needs to be made for the coppice stools?

2. Working on a density of 65 crowns per hectare as a median, that suggests that the Government is proposing a compensation ratio of 6.5 ha for every 1 lost to development. This is a ratio that far exceeds any so far for displacing migratory waterfowl.

3. If the pastiche is to replicate ancient woodland, then there also needs to be management to create the mix of coppice stools and standards. What needs to be borne in mind from an ecological perspective is that the coppice stools form a substantial part of the ecological value. This is largely underground and comprises the decaying timber that supports many fungi and the animals whose larvae feed on the fungi and bacterial soup that results.

4. It follows that the offset will require intensive management, unless of course we are simply looking at replacing an ancient woodland with a poor quality plantation. If so, there is even more to go on in terms of ecological loss because the relative importance of plantations and semi-natural habitats ought to be relatively easily demonstrated.

There is plenty of sound ecology to challenge the proposals, but perhaps the more important issue is economics? Is it really worth trashing an ancient woodland if the developer has the cost of buying anything between 3 and 10 ha to replace each hectare lost, and then has to pay for intensive management for sufficient time to create anything approaching pastiche? Someone better than me can do the economics, but it seems to me that the likely cost of creating the offset will at least mirror the cost of the ancient woodland and may indeed greatly outstrip it because woodland is relatively cheap and even low grade arable is phenomenally expensive, without adding on the cost of long-term silviculture.

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