Thursday, 13 October 2011

A Brambling and the Problem of Trees

Bird News: Ibsley Water - lapwing 111, yellow-legged gull 3, goosander 1.
Ivy Lake - water rail 2.
Centre - brambling 1, lesser redpoll 4+ over.
What with one thing and another I never really got any pictures today. The volunteer team were working on the morning, clearing small trees and brambles from the lichen heath. Although the heath is not part of the designated wildlife site it is the rarest habitat we have and home to many rare and very rare species. The slow encroachment of trees shades out the lichens and in the end would give us fairly ordinary secondary woodland, not really a "good deal". In addition the bare patches that result from digging out the tree roots provide valuable habitat for many insects that use the heath like solitary bees and wasps.
I also felled a few planted Scots pines to open up the canopy for some of the other trees. A particular problem we have at Blashford is the large amount of tree planting that went on as the gravel extraction finished. In places the species mix includes many aliens and everywhere the aftercare has been poor with tree guards being left on and no thinning resulting in severe overcrowding.
The whole issue of tree planting is a very tricky one for conservationists. An ancient woodland of native trees is a wonderful place, with a range of species found nowhere else. Secondary woodlands that have grown up following an earlier clearance can have quite a few specialist species, if it is old enough and close to ancient woodland. Planted woodlands, sadly tend to have few specialist species and are a very pale imitation of their ancient counterparts. High nutrient levels are had to overcome and the incredibly slow colonisation rate of most ancient woodland specialist species make it hard to see that many planted woods will ever reach the hoped for condition.
Curiously, following the last Ice Age Britain was quite quickly covered with woodland including many woodland plants that today seem unable to colonise at a rate of more than a metre or so a year.
Perhaps the lichen heath offers some sort of a model for what things might have been like after the ice retreated. There would have been almost no soil as we would recognise it, nutrients for growth would have been almost totally absent. Over time lichens and mosses would develop and collect nutrients. The first trees would have been species with wind blown seeds and low nutrient needs, like birch, coincidentally the main tree spreading onto the heath at Blashford. Obviously the climate is somewhat different now, but just possibly if we really wanted to try and develop something like an ancient woodland from scratch we should use sites like the lichen heath, next to woods with ancient character and just leave them to develop. The drawback is that we would loose the lichen heath in the process.
As I arrived in the morning a brambling was calling from the top of a birch tree near the Centre, my first of the autumn. It was a bit of a day for finches with several lesser redpoll flying over as well. At the end of the day I had a rare opportunity to look at the start of the arrival of the gulls to the roost on Ibsley Water. These included one especially thickset lesser black-backed gull with a very heavy pale bill. Although this is a very variable species this particular one was not quite like any I remember seeing before. With a record of slaty-backed gull in the UK last winter another potential species to look for has been added to the ever growing list for gull watchers to consider, so who knows maybe this winter Blashford will come up trumps. Lastly, "Pondcam" really performed today, at various times I saw a common toad, two water stick insects sparring and lastly one of them catch a water beetle.

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