Research By W.L. Mason, F. MacDonald, M. Parratt and J.P. McLean What alternative tree species can we grow in western Britain? 85 years of evidence from the Kilmun Forest Garden Summary use in diversifying spruce dominated Nearly 300 tree species have been planted forests in western Britain. planted at Kilmun Forest Garden in Argyll since 1930, mostly in small plots Introduction allowing the collective performance of Recent years have seen increasing an individual species to be evaluated. awareness of the potential impacts of Results from the mid-1990s showed that both projected climate change and a about 60 species had formed productive range of pests and diseases upon the closed canopy stands, with a number of long-term sustainability of British forests conifers all showing health and potential (Read et al, 2009). One concern is the productivity equivalent to that of Sitka low numbers of species in our forests, spruce, the major species grown in the for example in 2005 around 55% of UK forests of western Britain. Since 2000, forests were single species stands (Forest there has been increased interest in the Europe, 2011). In addition, the British collection at Kilmun, partly because timber industry is dependent on very few it allows the comparison of long-term species with Sitka and Norway spruce growth of a wide range of species at accounting for over 55% of softwood a time when species diversification is timber production in 2012, a figure being encouraged as a means of adapting projected to increase to nearly 70% forests to climate change. Accordingly, by 2030 (Forestry Commission, 2014). existing plots have been remeasured, Single species stands can be vulnerable to some have been sampled for their the impact of biotic and abiotic hazards, timber properties and a number of new a recent example in Britain being the plots have been established. There are extensive mortality of Japanese larch now around 200 different species in (Larix kaempferi) and other larch species the collection, of which 145 are in good caused by the pathogen Phytophthora health. Growth measurements show the ramorum (Webber et al, 2010). continuing good performance of about Awareness of a lack of species diversity 18 conifer and broadleaved species at has resulted in renewed interest in between 45 and 85 years of age: these other tree species that could be used species would be prime candidates for to diversify British forests, either as THE AUTHORS Enterprise Scotland, based at the Glenbranter office of Cowal and Trossachs Forest District. He has been involved with Kilmun for W.L. Mason*, F. MacDonald, M. Parratt and J.P. McLean over 15 years and has been responsible for operational work there *Corresponding author. Email: [email protected]. for the last 7-8 years. Forest Research, Northern Research Station, Roslin, Midlothian, Matt Parratt is a silviculturist based at FR’s Northern Research Scotland. EH25 9SY. Station with a special interest in tree species and their Bill Mason is a Research Fellow of Forest Research (FR) based at identification. the Northern Research Station near Edinburgh. He has been Paul McLean is a research scientist based at FR’s Northern responsible for the FR involvement with Kilmun for 20 years. Research Station where he leads the Tree and Wood Properties Fraser MacDonald is a Forest Management forester in Forest research programme. 24 | SCOTTISH FORESTRY Left: General view of Forest Garden in 1962. A forest garden differs from an arboretum in that the focus is on evaluating the collective growth of trees in a stand rather than on the development of individual specimens. Amongst the forest gardens that still survive in Britain are those at Bedgebury (Kent), Brechfa and Vivod (Wales), Crarae, Kilmun, Kirroughtree and Lael (Scotland). Of these sites, Kilmun on the Cowal peninsula near Dunoon in Argyll probably has the largest collection of tree species plots (as opposed to individual specimen trees) in the British Isles. At the beginning of this century, about 50% of the conifers planted at Kilmun were classed as ‘Rare’ or ‘Very Rare’ elsewhere in Britain, while 30% of the conifers were ‘Threatened’ in the wild (pers. comm. Dr Richard Jinks, Forest Research). Kilmun Forest Garden was established “A forest garden differs from an arboretum in that the focus is on evaluating the collective growth of trees in a stand rather than on the development of individual specimens” in 1930 to test and demonstrate the performance of tree species in the west of Scotland. In 1950 the overall objective Figure 1: A view of part of the Kilmun Forest for the forest garden was defined as: Garden taken from across the Holy Loch in “[the growing of ] stands of timber trees autumn 2017. The area within the Forest (of a wide range of species) under forest Garden stretches from just behind the houses along the coast road up to the upper boundary conditions in a high rainfall area of formed by solid blocks of forest above open western Scotland”. bracken areas showing brown autumn colour. A previous report (Mason et al, 1999) described results from the first 65 years of the collection, based on plots that were alternative production species or to and little knowledge of their timber established either in the 1930s or between increase the resilience of single species properties and potential markets. In 1950 and 1971. This had involved planting stands to pests and diseases. Examples such circumstances, comparison of 482 plots of 260 species from 50 different of this interest include recent articles candidate species in long-term trials can genera; a survey in 1995 found that 110 describing a range of alternative conifers provide valuable information. Such long- different conifers and 52 broadleaves still and broadleaves that might be grown in term trials include the ‘forest gardens’ survived. Particular features included different parts of Britain (e.g. Wilson, established in the early decades of the successful plots of a wide range of Abies 2007; Bladon and Evans, 2015; Savill, last century, defined as sites where a species, the healthy state of a wide range 2015; Wilson et al, 2016). However, wide range of species are trialled in small of species from north-west America owners and managers are often reluctant plots prior to large-scale operational and eastern Asia, and the large size to plant lesser known species for which testing of a few, selected species attained by surviving trees of a number of there is limited silvicultural guidance (MacDonald et al, 1957). Eucalyptus species (Mason et al, op.cit.). Volume 72 No. 1 Spring/Summer 2018 | 25 Research Since 2000, there has been renewed • To provide a year-round destination New plot establishment investment in Kilmun with new plots for visitors to the Loch Lomond and Most species have been raised in established and older plots remeasured: Trossachs National Park, linked to containers (normally in 175-300 cm3 Kilmun has also served as a ‘safe site’ the Royal Botanic Gardens Edinburgh cells) in the glasshouses at FR’s Northern for ex situ plantings of endangered (RBGE) at Benmore. Research Station and are supplied to conifers collected by the International Kilmun as two to three year-old plants Conifer Conservation Programme These objectives are implemented depending on growth rate. Sometimes (ICCP) (Gardner, 2014). This paper through a strategy based on planting plants are potted into one-litre pots to summarises recent developments and and management of small plots (i.e. improve size and vitality. Occasionally relates the results to the current interest 50-200 plants = ‘mini-forests’) of species species have been obtained from other in diversifying the species composition likely to be adapted to the current and bodies such as the RBGE or from of Scottish forests as a means of future climate of western Scotland. commercial nurseries. In the late increasing their resilience against This is guided by an accessions list of summer or autumn, potential areas abiotic and biotic hazards. around 140 species (approximately 55% for planting are identified and cleared. conifers) suitable for future planting at Planting normally takes place in the Site details Kilmun. The list concentrates on species following March or April and all plots Kilmun Forest Garden covers about 50ha threatened in the wild, of particular are protected against browsing using on steep slopes overlooking the Holy landscape or cultural value, which a temporary deer fence. Plots may be Loch in Argyll where elevation ranges might be adapted to a future climate, hand weeded for two-three years after from about 20m on the lower slopes to and which have the potential to produce planting and failures are beaten-up about 300m asl at the top of the site. utilisable timber. with plants of the same species if these Several streams and steep-sided gorges are available. run though the site, which combined Management with the steep terrain, have influenced Since the early 1990s, management Assessments both plot layout and access. Soils are of the collection has been guided by Forest Research staff carried out a mainly upland brown earths although a partnership between staff from the quinquennial inspection of all plots gleys and wet flushes occur wherever local Forest District of Forest Enterprise (and other specimen trees) within the the ground flattens out. This gives a soil Scotland and from Forest Research (FR). collection in 2004, 2010 and 2015. Plots moisture regime of ‘fresh-moist’ and a The former have overall responsibility are scored visually on a simple 1-4 system ‘poor-medium’ soil nutrient regime in for the site including establishing new where 1 indicates all trees in a plot are the Ecological Site Classification (ESC) plots and maintaining old ones while the healthy, 2 indicates that most trees are terminology (Pyatt et al, 2001).