Conifers for the chop
How is change in rural land use transforming UK forests?
The Forestry Commission announced this week that it intends to replace tens of millions of spruce, fir and pine woodland with native deciduous species such as oak, ash, beech and hazel (The Guardian, November 22, 2003).
Forest land coverage reached an all-time low of 3% in the UK in 1919 but has been rising steadily ever since and currently stands at 11%. However, a large proportion of this consists of coniferous plantations established by the Forestry Commission during the 20th Century.
The Forestry Commission was established in 1919, following the end of the Great War, to increase timber supplies through a policy of land use changes. Marginal areas of plagioclimax grassland, heather and moorland (where deciduous trees had once stood) underwent a further transition to become coniferous forest, particularly in areas of Highland Scotland. This radically altered the hydrology of many drainage basins and the characteristics of local ecosystems (including levels of net primary productivity, biomass, the functioning of nutrient cycles and local food web structures).
Strategic and economic needs clearly favoured such fast-growing conifers at the outset. In 1919, there was still a great demand for wood supplies for such diverse uses as ship deck-building, pit props for coal-mining and house construction. Many of these uses have subsequently declined while Scandinavia can provide us with ample supplies of pine wood where demand remains (for furniture and construction). There is thus little justification for the continued use of large areas of the countryside to support conifers. Instead, the concepts of biodiversity and rural stewardship are beginning to take centre stage, supplanting purely economic concerns.
Conifer plantations have environmental costs associated with their growth. The needle leaf litter they produce can acidify soils and the trees, often planted very close together, do not encourage much under-canopy growth. As a result, they provide very few niches for native animal and bird species. The hope is that biodiversity will grow where native deciduous species are allowed back into areas that are currently used exclusively for coniferous forest.
Managing the changes
The hydrological risks of felling large areas of coniferous woodland are considerable, given the important role that vegetation plays within the drainage basin water cycle as an interception store. Water is caught on leaves and branches, delaying the speed at which it reaches streams and rivers. As a consequence, surface run-off is very rare in forested areas. Instead, water is far more likely to infiltrate into well-aerated forest soils and to be transmitted as throughflow. Forested river catchments rarely generate flashy hydrographs.
Forest clearance radically alters the flows and stores of the drainage basin hydrological cycle. For instance, in 1998 there was widespread flooding in the Scottish village of Lamlash in Arran, following the harvesting of a large spruce plantation. A Combination of heavy rain, steep slopes and bare earth that had been compacted by forest-clearing machinery generated high levels of overland flow, flooding many properties that bordered the affected area.
The Forestry Commission is therefore intent on making the changes to existing woodland gradual, aiming instead to thin the existing plantations, allowing light levels on the forest floor to increase. Nature should then take its course as a process known as secondary succession will occur. Seeds carried by animals, wind or run-off from neighbouring areas of deciduous woodland should naturally re-colonise the cleared areas. The first area targeted for this policy is the one million coniferous trees covering Cranborne Chase in Dorest. A fifty-year plan has been devised and by 2053 the area should look much as it did in the 19th Century, with its original plant and animal community restored.
British forests: a long history of change
When normal climatic conditions were re-established at the end of the Pleistocene ice age (around 10,000 years ago), most of the land area of the UK developed to form a zone of deciduous woodland (with oak often as the dominant species) underlain by brown earth soils. However, this forest was progressively removed by pre-Roman, Roman and Anglo-Saxon populations until only about 15% of the natural woodland remained by 1066.
However, throughout the following centuries, a sustainable 'working woodland' economy developed in the absence of any real population pressure. The remnants of the ancient deciduous woodland became a busy and vital society and economy where the sustainable practise of 'coppicing' was widely followed (where wood is harvested without killing the tree). As the Robin Hood myths remind us, the Normans policed and preserved 'the greenwood', with severe penalties for trespassers (the word forest actually derives from 'foris', meaning outside of the common law).
It was during the later Middle Ages and early modern period, that forest use changed to become unsustainable:
- The dissolution of the monasteries freed forested land to entrepreneurial bidding
- There was a rising demand for timber for shipyards as the British Empire began to grow
- Demand for house-beams rose as an era of unprecedented population growth began after 1750
- More farmland was required for this growing population
By 1919 only 3% of the ancient forest was left. Windsor Forest is an example of one of the small surviving areas of the ancient woodland that survived into the modern era. Once a vast medieval Royal hunting forest, the 3,100 hectares of woodland holds more than 900 oak and beech trees over 500 years old. Over 2,000 species of invertebrate and 1,000 species of fungi have been found here, testament to the rich biodiversity of the native deciduous forest. English Nature now manages Windsor Forest in a way that meets a range of objectives. Some geographers use the term 'post-industrial forest' to describe such woodland, associated as it is with recreation and conservation, rather than timber production.