A Flowing Conversation
On a chilly winter day in January, a group of staff and volunteers from Devon Wildlife Trust visited Fingle Woods for a walk and a talk, to share ideas about how parts of the woodland habitat work are going. In particular, they were interested in how the stream along Halls Cleave is being managed as an important aquatic feature within the woods. As with most wildlife conservation projects, biodiversity is a key aim and areas of standing water and wetland are underrepresented habitats in a site the size of Fingle Woods.
The discussion began by looking at one of Fingle’s few veteran oak trees, standing by the stream. Having been relieved of many of the tightly packed, shading conifers from around it, it is showing more signs of life with new lateral branches developing. The increasing levels of sunlight across Fingle over the last few years are giving nature a better chance to thrive and the watery habitat in and around a stream is no exception. Sunlight is essential to keep the freshwater ecosystem healthy.
Moving upstream, the group stopped to look at a few man-made features including a small weir and the large box culvert that spans the water course. The issue of fish passage is one that is considered carefully as obstacles in the stream may be challenging, or even prevent fish such as trout from moving upstream to find suitable feeding and spawning sites. The design of artificial features must consider the mix of aquatic habitats from deep pools to shallow riffles and gravel beds while, at the same time, allowing fish the chance to reach these places.
At the next stop they looked at the water quality monitoring probes that were installed a few years ago. Regular readings of pH (acidity) and turbidity (cloudiness) have been showing some fluctuating patterns in the quality of the water in the stream and along the river and, in time, will produce a clear picture of this part of the catchment. An understanding of this information can help to guide the woodland management and show how the trees can reduce the peaks of acidity in the water, making it a healthier habitat. It also demonstrates the difference in pH levels between the stream and the river Teign. It shows that a large proportion of acidification in the main river may come from further upstream, possibly the headwaters on the moor, which is why some of the timber from Fingle is being milled into boards, to be made into small dams for the
peatland restoration work on the higher parts of Dartmoor
.
It is important for Fingle, as a demonstration site, to share this sort of information with other conservation partners and to pick up a few tips and new ideas along the way. Causing the greatest interest along this stream are the woody debris structures that were built over a year ago; sometimes referred to as ‘beaver dams’. They are often the focus of many discussions around how they may be increasing biodiversity or reducing flood risk by holding back water and slowing the flow. Having just gone through their second winter, they are beginning to take on a natural look and the changes in the stream flow patterns are becoming apparent. Standing at the side of the pools of water, swirling patterns of sediment can be seen below the surface. These dams are clearly working as silt traps; layers of fine particles are building up as they drop out of the flowing water. As well as protecting against flooding, this will probably be having a good effect on the turbidity of the water downstream and should even be keeping the river gravels clean for the fish to spawn in. Keep an eye out for some new woody debris structures of different designs being constructed here in the coming months.
The final stop on the walk visited some small dams that were built last year by Fingle’s volunteers. After a bit of woodland glade clearance to improve some basking areas for flying insects, the volunteers bundled up several piles of brash to make mini woody debris dams. Even after a few months they are visibly slowing the water flow and reducing the particle load in stream. With the slowing down of the water, the patterns of flow are changing too. The stream appears to be taking on a braided look as it meanders away from the defined channel it was once restricted to. This kind of dynamic ecosystem could provide some varied habitats in the future; a few more sunny glades and a bit more wet woodland will help to secure a growing biodiversity throughout Fingle Woods.by Matt Parkins
