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.

Forests across Europe occupy some 40% of the land area, and until recently they were regarded as not only a source of timber but also an important ’sink’ of carbon.  That is to say, they took in more carbon dioxide in photosynthesis (and stored it away in complex organic compounds) than they released in respiration. However, in recent times, these important biomes have turned from carbon sink to carbon source.  This year, the Finnish forests changed from sink to source.  Forests in the Czech Republic and Germany also released more carbon than they absorbed.  Though French forests are still a sink, their absorption of carbon dioxide has roughly halved in recent years (from 74 million tonnes of CO2 to 37.8 million tonnes in 2022).   Norway has seen a similar reduction in carbon dioxide storage from 32 million tonnes to 18 million tonnes. Seemingly, forests across the continent are losing the ability to act as carbon sinks, but why?  One reason seems to be the increased harvesting of timber,  many forests are privately owned and run on a commercial basis.  The Russian invasion of Ukraine has been a factor as sanctions against Russian timber has lead to more ‘domestic’ culling, for example in Finland.  However, climate change is an important factor in this downturn.  In recent times, droughts (in 2018 and 2022) have had a significant effect of forests, trees are stressed and the effects of drought have been greater than anticipated.  Drought can also be coupled with other extreme weather events (such as storm damage) and outbreaks of bark beetle (which have particularly affected spruce woodlands).  The Czech Republic has reported several outbreaks of bark beetle in recent times. What can be done to mitigate this loss of carbon sinks? Clearly reducing the harvesting of trees for timber and the banning of clear felling would help.  After a clear cut in a boreal or temperate region, it can take a forest 10 to 15 years to become a sink again, and even longer for the original emissions associated with the clear cut to be compensated for. Increasing the diversity and resilience of trees used in forestry is another approach to increasing CO2 absorption, however, it would take some time to determine which trees would be most effective in creating a carbon sink in the face of climate change.  Sadly, it is also the case that many tropical forests are in decline in terms of carbon storage due to deforestation,  expansion of agriculture and fires. Further reading : https://forest.eea.europa.eu/topics/forest-and-climate/carbon-sinks-and-sources  

Climate change is a fact, though not one always accepted by certain politicians.   Greenhouse gas emissions have been growing since the C18th, and particularly in the period 1970 - 2004.   The warming of the world climate system is certain; air and ocean temperatures have increased.   Though we cannot say how climate will change in any specific area with certainty, we can be sure that extreme weather events will become more common - droughts, heat waves, heavy rainfall, high winds and cyclones. Read more...