What makes Piles such an ecologically valuable place?
Piles Copse is mainly situated on a steep and rocky hillside on the left bank of the Erme. It has a westerly aspect. Soils on the hillside are derived from the granite that forms their parent material, giving them a loamy texture and relatively free drainage. They are well developed soils, but the acidic regolith and high rainfall, and lack of artificial liming, have led to a degree of podzolisation in most areas, making them podzolised brown earths. This means that there is a well-developed topsoil, relatively rich in organic matter, and a deep, iron-rich subsoil. In some of the higher areas there are quite peaty topsoil horizons, but the effect of the big top wall in draining the land of Higher Piles has had a profound effect on the soil quality. In the southern half of the area, there was also extensive drainage installed at some stage, to improve the grazing quality of the farm. Also, although mostly formed in situ, there are also colluvial elements to the soils on steeper areas. In some places, particularly in the middle of the wood, the ground is excessively stony. While many of these boulders are clitter, there also appear to be a few outcrops of bedrock, effectively forming small, lower valley slope tors. Clitter represents large rock debris in slow transport down the slope, and to a large extent is a relict feature from the ice ages.
As glacial conditions receded, much of Dartmoor was covered by an ericaceous heath, and later by forest; as the climate became warmer, this pine-birch-willow (Pinus-Betula-Salix) forest declined and hazel (Corylus avellana) colonised bare areas of heath. Oak then followed, and hazel declined. Pollen analyses show that oak was the dominant species of the original Dartmoor forest (the implication being that it had reached a post-glacial climax stage) before it was cleared, probably by human activities, starting from about 5,000 years before the present (BP); but sub-fossilised Quercus pollens are impossible to distinguish and so there is a large degree of hypothesis in the suggestion (first made by Simmons in the 1960s) that Q. robur was the prevalent species at that time. More recent suppositions, based on limited climatic evidence during post-glacial colonisation, suggest that by about 9500 BP the forest in south-western England is more likely to have been of sessile oak (Q. petraea). So it is generally supposed that although oak dominated the post-glacial forests that developed on Dartmoor before clearance by man, it was the other native species – sessile oak – which is the oak found all around the edge of the moor and in other upland locations in Britain.
We may never know for certain what was the natural vegetation, but the copse is now composed predominantly of English, common or pedunculate oak (Quercus robur). This tree is a native throughout southern Britain, but it is a lowland species and its occurrence up to this height on Dartmoor is relatively high for this latitude. Certainly it is more commonly associated with basic loams and clays than with acid upland soils.
Development of Piles Copse
It is most likely that Piles Copse is not natural but was planted at some stage. There was a general shortage of small oak (coppice and underwood) in south-west England by about the sixteenth century, mainly as a result of heavy charcoal use in tin smelting. With extensive tin streaming in the Erme valley, this could certainly have been a particular local problem. Oak may therefore have been planted at Piles, either to provide for this purpose or for pannage (feeding pigs) by the farmers. As the historical assessment shows, Higher Piles was an enclosed farm that must have been occupied and worked at least in the middle ages and possibly later, so the copse may have been partly for agricultural use. In any event, English oak was the favoured species for planting at that time. But soon after that, tin streaming diminished and so it is less likely that an oak plantation would have been established here for charcoal later than the 18th century.
Ultimately, the question of Piles Copse’s existence when the rest of the forest disappeared, and the dominance of the single species (unlike in woods on the margins of the moor) cannot be explained satisfactorily. But while the origin of the copse remains uncertain, it is clear that the general biophysical conditions have given rise to moist oak woodland with luxuriant growth of epiphytes (non-parasitic plants that grow on the stems and branches of other plants) and bryophytes (mosses and liverworts), that is thought to be unique in southern England.
A comparison can be made of the three main ancient oak copses on Dartmoor: Black Tor Copse on the West Okement, Wistman’s Wood on the West Dart, and Piles Copse. Of the three, Piles is the largest, most sheltered and has the best-formed trees, with deformation only occurring along the upper edge, although very few trees have the good form of lowland oaks with timber value.