The latest report from Michael Walter:
The mean monthly temperature has been above average in every month so far this year in the UK, and November looks set to add an eleventh record. Three days ago (13th November), on a walk over the North Downs, I saw two peacock butterflies and a brimstone, which is fairly exceptional, though not unheard of, for this time of year. Both these butterflies hibernate as adults, whereas most other species pass the cold months as eggs, caterpillars or pupae. Consequently, when we enjoy unseasonably warm conditions, there is scope for brimstones and peacocks to be roused from their slumbers and to venture out into the unwonted sunshine. Whether this is such a good move is a moot point: the butterflies will be using up their stores of energy on flying, yet there will be few opportunities to refuel on nectar, so they risk depleting food reserves that are needed to tide them over the winter. I haven’t been in the wood so much recently, so don’t know if there have been similar records of late-flying butterflies there.
Recently I was fortunate in being able to take a local historian around the north-western part of the wood. We were particularly interested to investigate a series of parallel ditches that showed up on a Lidar survey conducted some years ago. Lidar is an acronym for Light Detection And Ranging, and is a cunning technology developed in recent years to measure minor irregularities in the surface of the ground. Rapid laser pulses are beamed down to earth from an overflying aircraft, and the time taken for their reflections to return to the aircraft can be measured. It is so accurate that if the surface is just a few inches lower (a ditch) or higher (a bank) than expected it will record the anomaly and so be able to build up a map of these features. While working best in open landscapes, it is still capable of penetrating through the tree canopy, and so the system was able to produce a map of ditches and banks across the whole of Blean Woods. In many areas of the wood the drainage network is fairly sparse and erratic, the ditches snaking irregularly across the terrain, indicative of natural waterways or medieval digging. But in other areas there are much straighter ditches, which are almost invariably associated with drainage operations within the last couple of hundred years or so. One particularly interesting network that had teased my imagination was an oblong block about 500 metres by 200 metres. One long edge was defined by a stream marking the edge of the wood, and the other by an arrow-straight ditch. That wasn’t so remarkable, but linking the two sides was a series of 19 straight, parallel ditches, mostly about 20 metres apart. This area of woodland had in fact been recognised by the Blean Research Group as being the “Grub’d ground wood” of a 1611 report deposited at Lambeth Palace, and in The Blean – the woodlands of a cathedral city, published by the research group in 2002, it was surmised that the area, which had been cleared because so wet and unproductive, had subsequently been planted up with hornbeam during the period 1760-1800, the logwood possibly destined for the manufacture of gunpowder at the Faversham works, or to be bundled up into faggots and firewood, for which it was greatly prized on account of the intense heat it gave out. Unfortunately, the research group didn’t have the benefit of the Lidar maps, which were produced some years later, and it is no wonder that its members didn’t stumble upon the parallel ditches, as they have been infilled with leaf litter over the centuries, and are now barely perceptible, even with the benefit of the Lidar map. The close spacing of the parallel ditches strongly suggests that the land was managed intensively and at considerable expense to create better conditions for a replanting venture.