The Earth has experienced many glacial and interglacial periods over hundreds of thousands of years.  Since the last ice age, the Earth has warmed (the average global temperature has rising by some 4 to 5oC) but the temperature rise was about 0.1oC per century.  Today's warmer climate took 5,000–8,000 years to ‘evolve’, during which time the average global temperature rose at a rate of around 0.1oC every century.   This gradual change allowed trees to adapt to the changing climate.  In the last century, ‘we’ have driven a 1.3oC rise just in the last century - this is some ten times faster than the change post ice age.  [caption id="attachment_35526" align="alignleft" width="300"] drought[/caption] Not only has the climate warmed, it has become increasingly unpredictable with heat waves, drought and torrential rain.  These can have dramatic effects on our trees and heathlands.  For example, the heatwave in 2022 resulted in Kew Gardens losing some 460 of its trees.  This last summer saw 4 periods of heatwave conditions.   So, it is not surprising that some of our most familiar trees are struggling with these changed conditions.  They are stressed, and it would seem that the climate is not likely to moderate in the immediate future.  In recognition of the changing climate, Forestry England has produced a 'species for the future' list.  The trees in the list are those which might thrive in a warmer climate. Whilst it includes familiar species like oak, birch, and alder, other species such as the coast redwood and Corsican pine are included,  which hopefully will create more resilient woodlands.  The trees are listed below Aspen (Populus tremula) Beech (Fagus sylvatica) Coast redwood (Sequoia sempervirens) Common alder (Alnus glutinosa) Corsican pine (Pinus nigra subsp. laricio) Douglas fir (Pseudotsuga menziesii) Downy birch (Betula pubescens) European silver fir (Abies alba) Field maple (Acer campestre) Grand fir (Abies grandis) Grey alder (Alnus incana) Hornbeam (Carpinus betulus) Japanese red cedar (Cryptomeria japonica) Lodgepole pine (Pinus contorta var. latifolia) Macedonian pine (Pinus peuce) Maritime pine (Pinus pinaster) Norway spruce (Picea abies) Pedunculate oak (Quercus robur) Red oak (Quercus rubra) Rowan (Sorbus aucuparia) Scots pine (Pinus sylvestris) Sessile oak (Quercus petraea) Silver birch (Betula pendula) Sitka spruce (Picea sitchensis) Sweet chestnut (Castanea sativa) Sycamore (Acer pseudoplatanus) Western hemlock (Tsuga heterophylla) Western red cedar (Thuja plicata) Wild cherry (Prunus avium) Wild service tree (Sorbus torminalis) The list contains both native and non-native species, the aim is to create through planting stronger and more biodiverse woodlands that can tolerate our changing climate over the coming decades.  The rate of climate change is the main issue. Whilst some of the trees already grow here, others come come from warmer / drier areas, such as the Mediterranean or  North America.  There are already many redwoods in the UK.  They were introduced in victorian times, when they were planted on the estates of the wealthy and landed gentry. There are now probably more redwoods in the UK than in their native Pacific Coast range,  there intense heat and dry weather has exposed them to intense forest fires. Another possibility to promote resilience is to use seed produced by trees such as Oak that has been ‘produced’ by trees growing in warmer regions. The inclusion of trees that might be suited to our changing climate is often referred to as assisted migration.  However, the introduction of non-native species is not without its problems, for example the introduced species could become of invasive or add to the burden of pathogens that our trees are exposed too.

‘Trees for Life’ and ‘Woodland Trust Scotland’ are trying to revive lost pinewoods, that once formed part of the Caledonian Forest.  This forest supported a rich and diverse flora and fauna, including serrated wintergreen, distinctive lichens, crossbills, capercaillie, wild cats and red squirrels.   After the last Ice Age, plant and animal species moved across the 'land bridge' that connected us with continental Europe.   Pines (Scots Pine aka Pinus sylvestris) were ‘quick’ to move into Scotland and the land vacated by the glaciers.  Now less than 2% of this once great forest survives. To find pockets of ancient and ‘lost’ pine trees, these two organisations have adopted a number of approaches. Making use of old maps and texts, for example, those produced by the Reverend Timothy Pont (a Scottish minister and cartographer) in the 1500s. He was the first to produce a detailed map of Scotland.  These can point to areas that were formerly populated by “fir trees”, ie pine. Examining Gaelic place names, which might reference woodland or pine trees. Using the original ordnance survey maps (which often had fir tree symbols) to produce digital copies, which can be overlain on modern maps - hopefully to reveal former woodland sites. Using ecological evidence.  For example, wild pine often grows with old birch trees, whereas planted pine is usually found with larch and other ‘commercial conifers’. Old pine trees often have a distorted shape, with thick, gnarled and twisted trunks; they survive in remote gorges and crags.  Areas that previously supported wild pine, often have old stumps still present and / or certain distinctive lichens / plants - remnants of once diverse ecosystem. Using these various techniques, dozens of lost pine woodland areas have been identified and located.  Much of the original Caledonian Forest was lost through felling (for timber and / or fuel) over the centuries.   Later came sheep farming and this was followed in Victorian times by deer and grouse shooting.  In the last century, commercial forestry resulted in the further loss of ancient woodland. However, restoration is possible.  Where some old trees have survived, there is often a seed bank in the soil and these seeds can germinate if the dense canopy of commercial conifers is removed.  Many pine seeds that do germinate are lost as seedlings due to grazing due to deer or sheep - who seem to prefer them to Sitka etc.  Hopefully as areas with pine grow on, so other species such as rowan, birch and hazel will develop and in time a ‘full’ woodland will develop.

Several thousand years ago, Scotland was extensively forested.  As the Ice Age came to an end, so the glaciers retreated and Scots Pine, birch, rowan, aspen and juniper populated the land, forming the Caledonian* Forest.  Pollen records indicate that Scots Pine was present in southern England some 9000 years ago, it then moved into Scotland.  Scots Pine is one of the UK’s three native conifers; the other two being Yew and Juniper. As the climate warmed, Scots Pine was lost from most of England.  The pine woodland that formed in Scotland was the westernmost part of the boreal forest that extended across most of Northern Europe.  At its peak, (about seven thousand years ago), the forest covered some 1.5 million hectares in Scotland.  It was a ‘home’ to beavers, wild boar, brown bears, elk and wolves.  These have since been ‘lost’, though in recent times, the European Beaver has been re-introduced. However, with the arrival and establishment of neolithic farmers, areas of heath and woodland were burned to encourage fresh growth of heather for their cattle and goats. Some time later (about 3000 years ago), there was period of cold and wet weather, peat bogs spread and the tree line was lowered. In places, broad leaved trees replaced Scots pine.  Throughout historical times, the felling of trees for timber and fuel continued, as did the grazing of livestock.  Later came extensive sheep farming and this was followed in Victorian times by deer and grouse shooting.  All of these limited woodland regeneration.  So what was once an extensive forest was reduced to a fraction of its former size. Remnants of this once great forest can still be found and even today these woodlands offer a rich habitat that supports a diverse flora and fauna, where pine marten, capercaillie, red squirrel, Scottish crossbill and wildcat can be found.  Glenmore is a National Nature Reserve with many mature Scots Pine, Glen Tanar is another area of Caledonian* pine forest, set within the Cairngorms National Park.  The woodland floor provides a habitat for many plant species typical of the Caledonian Forest - twinflower, creeping lady's-tresses.    Rare and unusual insects are also to be found such as the bumblebee robber fly. According to a recent study by “Trees for life” many of the the remnants of the ancient pine forest are on a ‘knife edge’. Large numbers of deer have and are damaging the woodlands.  The deer eat pine saplings and damage bark. This can result in birch replacing pine. Whilst there have been efforts to exclude deer in some areas by putting fencing in place, the fenced areas were often not big enough or over time the deer were able to breach the fencing and continue to forage.  Pine trees need time to establish themselves free from the impact of grazing. Some areas of pinewood suffered from the planting (in the 1950s) on non-native conifers, such as Sitka Spruce.  As these grow they can crowd out Scots Pine.  Many others areas are small and ‘isolated’. This leads to a reduction in biodiversity, so it is more difficult for natural regeneration to occur.  It also means that resilience is lost in the face of threats like climate change.   * the roman name for the area now Scotland was Caledonia.   Scots Pine is sometimes described as an ‘honorary hardwood', as it grows slower than certain conifers and produces better quality timber. The loss of forest across the Earth is a cause for concern - see https://theconversation.com/how-forest-loss-has-changed-biodiversity-across-the-globe-over-the-last-150-years-140968    

Sadly, the number and range of various species in the U.K. is decreasing, biodiversity is falling. Our wildlife-rich areas are actually separated and fragmented, by tracts of intensively-farmed land, by motorways and roads,  and the ever increasing spread of urban areas. The dispersion and isolation of wildlife areas makes it difficult for both plant and animal species to move.  The ability to move around is ever more important as a result of climate change.   Rainfall patterns and average temperatures in different regions are changing, extreme weather events are more common.  For a species to stay in its  ‘comfort zone’, it may need to move ‘northwards’ as climate change continues.    According to a report released by Rewilding Britain, the speed at which species need to migrate in order to stay in their ‘comfort zone’ is approximately some 5km / year Read more...

During the last Ice Age, much of the UK was covered with a layer of ice up to kilometre deep, or by enormous glacial lakes. Certainly in northern parts, there was no vegetation as glaciers scraped their way across the landscape.  So much water was locked up in the glaciers that sea levels dropped dramatically; we were connected to Europe by areas such as Doggerland.  Details of the glaciation and its effect can be found on the BRITICE site.  When the ice age came to an end some eleven thousand years ago, plants, animals and humans migrated back to the previously frozen and inhospitable land.  Over time, large forests and woodland areas developed.  In the North, boreal forest grew up - represented today by the remaining Caledonian Forest.  Further south, there was the wildwood (as described by Rackham and others). The wildwood was probably a complex and tangled mixture of different trees, with many of the trees either dead or dying through the effects of wind, fire (lightning strikes) and flooding. It would have offered a vast variety of habitats and niches for plants, insects and mammals. Read more...

Checking through my emails, I came across a link sent by a friend to one of the winter talks in the program offered by the Botanical Society of Scotland - specifically “The Scottish Uplands: how to revive a degraded landscape” by Dr Helen Armstrong.  The talk was live-streamed but was also recorded and is available here.   Dr Armstrong spent 24 years at the Nature Conservancy Council, the Macaulay Land Use Research Institute, Scottish Natural Heritage and Forest Research carrying out research and advisory work. The following is an attempt to summarise some of the key features of her informative and enlightening talk. Read more...

In terms of a ‘head count’ of tree species, Europe does not do well when compared to Asia or North America.  There are approximately five hundred tree species scattered across Europe, whereas Asia and North America are home to some thousand species each.  There is fossil evidence that tree species such as Liquadambar (Sweet Gums) and Liriodendron (Tulip tree) once lived here. So one might ask why did they disappear? The answer may be due a combination of glaciation and topography.  During the late Pliocene period, the  global climate cooled and massive glaciers began to extend across the Earth’s surface. Glacial and interglacial periods  followed in the Pleistocene or Quaternary Period; sometimes referred to as the Ice Age. As the glaciers moved relentlessly south, so plants (and animals) had to move Read more...

Atlantic oak woodland is often referred to as the Celtic Rainforest.  It is characterised by lichen covered trees, together with a rich moss and liverwort flora.  The environment is damp and humid, with streams and waterfalls contributing to this. These woodlands have evolved under the influence of the Gulf Stream,  which helps keeps the area warm (and wet). The difficult access and rugged terrain (in some areas) has helped to preserve these woodlands, plus they have not proved suitable for agriculture or ‘industrial forestry’.  Consequently, in many areas,  they have remained in their 'ancient state', going back to the last ice age.  Their sessile oaks are very important for wildlife but as they are not always productive of good timber, they have often been left to grow to maturity.  By the same token, Birch trees have relatively low timber value - which has been their salvation.  Woodlands like this were more extensive in the past covering the Atlantic fringe of Western Europe from North West Scotland down to the South of Portugal.  This type of woodland is rich in terms of biodiversity (primroses, violets, wild garlic, ferns and grasses) and some species are only to be found here and nowhere else in the world. Read more...