All the leaves were down and the sky was grey, we went for a soils walk on a winter’s day… On the East Dartmoor National Nature Reserve we joined soil specialist, Rob Parkinson, to look at what is going on below the leaves – in the soils around Haytor and Yarner Wood. Following the route of a new walking trail, we looked at how soils are formed, and how the soils’ physical and chemical properties can be determined by the local geology, climate, topography and vegetation.
We started below Haytor Rocks, looking at how the high levels of rain and cold temperatures lead to anaerobic conditions that create peat soils, these are made of large amounts of organic matter, containing decaying plant material. We also looked at the relationship between the vegetation found in these areas and the structural and physical properties of the soil – such as the structure and chemistry. We found that as the plants and sphagnum mosses die, they add to the organic matter layer of the soil, known as topsoil, changing the structure; we learnt is that the presence of sphagnum mosses that changes the soil chemistry by increasing the acidity. The group spent a large amount of time discussing the importance of peat within the landscape and how it is a limited soil type, with great importance for water quality, water storage, biodiversity and carbon storage.
After spending time looking at the peat soils we moved into an area that had previously been used for open tin streaming. Here we learnt about how disturbance of the soil, through digging and burning, led to the removal of vegetation and changes in topography. This soil was created in the same climatic conditions and geology as the peat soils, but was freely draining so held less water, leading to increased decomposition of dead plant material. This resulted in a soil profile that was more varied and shallower. This increase in drainage led to a decrease in the acidity of soils, which were still acidic, but also contained iron deposits and other nutrients into the soil layer. However, despite the changes in the structure and the chemical composition, the texture of the soils were still coarse. We learnt that this was because the underlying geology of igneous granite was the same as the first stopping point.
We then walked towards Black Hill, which was once an area that contained large amounts of peat, however, due to human intervention, the soils found here today are very different. We learnt that this is in part due to the steeper topography, leading to increased erosion. This led to a smaller layer of organic matter and an increase in nutrients, and also a neutral soil that’s not acidic. We found that the texture of the soils on the slopes of Black Hill were finer than the first two stopping points. This is because of a change in geology, from the igneous granite, to metamorphic mudstones.
We then walked into the top of Yarner Wood, where there was a range of large broadleaved trees that had dropped their leaves, forming a layer of dead leaves on the woodland floor. We stopped at several points and looked at a range of soil profiles which were different from those we had seen in the other habitats. The soils in the wood were thin, and very acidic, due to the periglacial effects from the last Ice Age. We discovered that the woodland contained subsoils – these were grey to blue in colour, and claylike in texture, unlike those found on the mire and heath. This grey/blue soil is called a gley, and remains wet because of the throughflow of water within the subsoil layer. However, similar to the heathland areas, signs of iron can still be found in some of the soils that are freely draining, the distinctive orange colour can be found around old roots that have decomposed. We learnt that as trees in Yarner Wood suck water up through their roots, they drain the water from the topsoil, creating a dry and loamy texture. We also found out that the dead leaves, from the trees in the wood, create a thin nutrient rich humus layer on top of the acid soil.
At the end of the walk we summed up the key components that influence the chemical and physical properties of soil. We discussed how time plays a large impact on the composition of soils. We learnt that all of these soils have changed over time, due to changes in land management alongside climate, local geology, topography and vegetation.
On this walk we followed the route of the soon to be released Dartmoor Story Soils around Haytor and Yarner leaflet. In the meantime if you would like to enjoy similar walks take a look at the information on the Dartmoor National Park’s Heritage Trails website and the walking routes page on the East Dartmoor Woods blog.
Written by George Koyler, Natural England Conservation Assistant