Kilmun Forest Garden: Diversifying tree species in commercial forests to improve resilience to climate change
Diversification of the tree species grown in commercial forests is an important way to improve forest resilience in the face of climate change. In particular, climate change may decrease the suitability of growing conditions for Sitka spruce – the most widely used commercial species – in certain parts of the UK.
The suitability of alternate species can be assessed in forest gardens like Kilmun – which is one of the largest forest gardens in Britain, and the largest in Scotland. Forest gardens are important because they allow species to be assessed based on their performance when grown in a stand rather than as specimens (in arboreta).
Kilmun Forest Garden was established in 1930 on land managed by the Forestry Commission at Kilmun near Dunoon in Argyll. In total, more than 260 tree species have been planted, mainly during the 1930s, between 1950 and 1970, and since 2005.
The site itself is a discrete block of 50 ha situated in the Cowal Peninsula. Prior to planting the whole area was open hillside grazed primarily by sheep. It has a south-westerly aspect, overlooking the Holy Loch. The altitude ranges from 20 to 300 metres a.s.l. The climate is favourable to tree growth with a mean annual rainfall of 2100 mm and accumulated temperature is greater than 1375 oC. The plots lie within the “warm moist” climate zone defined by the Ecological Site Classification. The underlying lithology comprises Dalradian quartzose mica-schists and in general the soils are freely-draining brown earths. The windthrow hazard class ranges from two on the lower slopes to three at the top of the area. Open ground is rapidly colonised by bracken which limits floristic diversity.
Recent figures suggest around 65% of the species have survived, with survival being higher in the conifers. The genera adapted to moist oceanic climates, for instance Abies,have proved particularly successful. Pines and species more suited to drier climates have done less well. Similarly, broadleaf species have survived less well but a number of species have still grown well including those from the genera Acer, Alnus and Nothofagus.
Growth rates have generally been high with a number of species (Abies amabalis, Abies grandis, Abies procera, Cryptomeria japonica, Cupressocyparis leylandii, Sequoia sempervirens, Sequoiadendron giganteum) having achieved a General Yield Class estimated in excess of 20 m2 ha yr-1.
Although none of these species show sufficient promise to be considered a replacement for Sitka spruce, they do provide a range of alternative species which could have a role in the diversification of Scottish forests. Diversification may prove increasingly important in the face of possible climate change causing a decrease in the suitability of growing conditions for Sitka spruce.
For an in depth look at Kilmun Forest Garden please see Mason et al. (1999).
Mason, W.L., Cairns, P. & Tracy, D.R. (1999) Kilmun Forest Garden – A review. Scottish Forestry, 53 (4) pp 247-258