Forest soil ecosystem services
Following on from his blog on Six Things to Know about Forest Soils, Andy Moffat has picked up on the theme of forest soil ecosystem services.
In forest ecosystems, it is almost artificial to distinguish between trees and the soil beneath – there are so many linkages between them. Of course, the soil promotes tree growth, of particular interest in commercial forestry. But in turn, the litter (leaves, needles, twigs etc) from the trees help in soil formation. The trees ‘feed’ from the nutrients in the soil, but in turn the soil is ‘fed’ from nutrients, notably nitrogen but other too, that are captured by the tree’s foliage and transported to the soil by canopy drip and flow down the tree stem. The soil obviously supplies water to support transpiration, photosynthesis and other biochemical processes in the tree. But it also helps to moderate the way that excess rainfall is transmitted into the surface and groundwater systems, ultimately helping in flood regulation. These examples of forest soil function are nowadays called ‘ecosystem goods and services’, but the definition of Sustainable Forest Management, now nearly 27 years old, included them in its concept of multifunctionality, still included in the latest version of the UK Forestry Standard (2017).
As well as the examples above, we should include others such as carbon sequestration and archaeological protection. Did you know that a recent survey of forest carbon in British forests identified that 74% resides in the soil! And given the importance of keeping carbon out of the atmosphere to prevent global warming, you can see that forest managers have an important role to play here. There are even financial incentives to do so: the Forestry Commission Woodland Carbon Code allows for soil carbon accumulation to be claimed for projects on mineral soils where the previous land-use was arable or rotational grass and the woodland will be managed as minimum intervention.
Forest managers also need to be aware of archaeological evidence in their forests: for example, Forestry Commission Scotland estimate that over 25,000 archaeological features lie in or around Scotland’s woodlands – many of these will be rooted in the forest soil. Such evidence can be preserved – or destroyed – depending on decisions about forest operations which affect the soil.
Above: Know the difference, Left, brown soils and right, podzols. Pictures FC/Crown copyright
So, management of trees, woodlands and forests should take the range of forest soil ecosystem services into account. Not all will be relevant or well expressed at every site or forest compartment, and it won’t be possible to manage the land such that all are optimized. Nevertheless, an appreciation of the nature of forest soils, their functions and the services they can offer will help in decision-making. Often there are synergies between these services such that management to support timber production will also support others: at its most simple, this is achieved through preservation and retention of soil and its functions rather than degradation or loss through erosion. In other cases, changes to existing operational practice may be warranted, such as moving to minimum cultivation to enhance soil carbon storage or leaving deadwood on a site to support soil biodiversity. But different soil types will provide a different ‘mixture’ of soil ecosystem services – so it is important to know how to identify them.
A previous blog on the subject (http://www.rfs.org.uk/news/blog-spot/woodland-management/six-things-to-know-about-forest-soils/) made the point that in the UK, forest soils are very variable. You can’t manage what you don’t know, and you won’t know until you look! In many ways, foresters should be as aware of the main differences between ‘podzols’ and ‘brown earths’ as they are between Sitka spruce and oak. And it’s not difficult to do so once you get your eye in!
Andy Moffat is both a Fellow of the British Society of Soil Science and a Member of the Institute of Chartered Foresters, and holds a degree in Geography and Soil Science. He started his career as a Soil Surveyor for the Soil Survey of England and Wales before taking up a position as Soil Scientist at the Forestry Commission Alice Holt Research Station.