Photo: David Whitaker
In 1996 a process was started to restore some 1300 ha of this former native pinewood on the south side of Loch Garry in Highland Region, Scotland. The wood had been inter-planted with non-native conifers in the period between 1935 and 1970. These have now largely been clear-felled.
Resulting woodland
The resulting woodland is a matrix of pine and birch, which varies in age structure and stocking density. There are extensive areas of clear fell with few mature native trees present. Regeneration of ground flora and, in some areas, trees, particularly birch, has been remarkable. On open sites, which retained few if any higher plants after felling of pure spruce crops, birch is currently regenerating in pure stands of many thousands to the hectare. Young pine is present in places, being most frequent where the soil has been scarified during harvesting operations.
The areas where birch is regenerating profusely are likely to form dense even-aged stands which will self thin over time but never-the-less will produce an overall lack of diversity within the woodland both in species and structure. The loss of glades, flushes and open riparian margins will mean a loss of potential biodiversity for both vertebrate and invertebrate fauna.
Grazing free ranging cattle to help with loss of potential biodiversity
Grazing of free ranging cattle within the pinewood is an option that may help with this problem. Unlike deer, which have a propensity to browse woody growth, cattle are more likely to eat rough grasses.
Wandering as a herd between preferred feeding areas they maintain a mosaic of glade habitats, increase soil fertility and, by trampling, produce a suitable seedbed for pine.
Their ability to keep water holes open would be an asset to Glengarry with its populations of bog-pool dragonflies, in particular nationally scarce white-faced darter and northern emerald dragonflies.
Baseline monitoring
In spring 2003, baseline monitoring of ground layer vegetation and young trees was carried out across the site. Later that year, two 200 ha enclosures were set up and Highland cattle were introduced at two stocking rates (0.1 ha-1 and 0.2 ha-1). The area outside the enclosures was used as a control. Monitoring was repeated in spring 2004 and spring 2006.
The data are currently being analysed. but initial results indicate that the cattle have not affected the density of young Scots pine or birch trees but have reduced their height growth. Browsing rates of rowan and willow were much higher than those of pine and birch suggesting that, in the long term, browsing by cattle may reduce tree species diversity. The cattle increased the cover of bare ground and reduced the cover of purple moor grass (Molinia caerulea). This may lead to increased seedling densities of all tree species in future years.
For further information
Contact
Dr Helen Armstrong
Centre for Human and Ecological Sciences
Forest Research
Northern Research Station
Roslin
Midlothian EH25 9SY
Tel: +44 (0)131 445 6954
Fax: +44 (0)131 445 7335
Email: helen.armstrong@forestry.gsi.gov.uk
