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.

Since its formation, the earth has undergone change.  Life forms have come and gone.  There have been five major extinctions, the last being at the end of the Cretaceous Period; it killed off the dinosaurs and many other species.  This particular extinction event is thought to have been particularly rapid, due to an asteroid impact.  It caused a series of cataclysmic events and a rapid cooling of the Earth’s climate. Other changes, such as intense volcanic activity and tectonic uplift, may have pre-dated the asteroid impact but the event saw the elimination of many, many life forms. We are witnessing significant global change, that is also rapid in geological terms. Changes in the Earth’s climate and species composition usually take place over millennia, indeed over millions of years.  However, recent years have been very warm.  Global temperatures have changed noticeably. The warming that has been recorded “is exceptional relative to any period since before the last ice age, about 125,000 years ago”.  This warming has resulted in extreme and severe weather events in this country and across the world.  This year a record breaking January temperature of 19.9oC was recorded at Achfary, with storms Henk, Isha, and Jocelyn in the same month. The Earth’s warmest year on record (between 1850 to 2023) was 2023.  In early September 2023, the UK experienced a significant heatwave when daily maximum temperatures exceeded 30°C [somewhere in the UK] for seven consecutive days. [caption id="attachment_35526" align="aligncenter" width="675"] Drought![/caption] Such changes are not without effect. Phenology observations indicate that trees are producing their leaves earlier, woodland plants are coming into flower earlier. See the woodlands blog “Spring is on the move”.  A concern with these changing phenologies is that ‘mismatches’ can occur.  When trees come into leaf determines when caterpillars can feed and that, in turn, affects when birds can feed on the caterpillars and raise their young.  If these events do not occur in synchrony then the ‘functioning of the ecosystem’ is disturbed.  [caption id="attachment_25123" align="alignleft" width="300"] Leaf 'unfolding'[/caption] The agricultural and horticultural ecosystems that we have created are also affected by climate change. This year, heavy rainfall has meant that farmers in many parts of the UK have been unable to plant certain crops [such as potatoes, wheat and vegetables] during the key spring months. Some crops have rotted in the soil. In April, there was 111.4mm of rain, [the average for April is 71.9mm]; the sixth wettest April of the last 189 years.  Persistent wet weather also affects lambing, and can mean it is not possible to turn dairy cattle out onto grass / pasture, which in turn affects milk production. Monthly temperatures are more likely to be above average than below as climate change take effect.  This was true for the first three months of the year.  Warmer air holds more moisture and it can evaporate more water from the seas / oceans. A one degree (Celsius) rise in temperature adds 7% more moisture in the air.  Woodlands are affected by heavy rain as soil becomes waterlogged, which affects woodland flowers, and wet winters do no favours for animals that hibernate. The UK is not the only place to be affected by extremes of weather, be it rainfall and flooding, or high temperatures and drought.  India has recently experienced a period of extreme temperature, with temperatures approaching 50oC.  Such temperatures push human physiology to its limits.  Just as extreme rain is a problem for farmers, so is extreme heat and / or drought.  Brazil has been the main exporter of oranges for producing orange juice, but its recent crop has been substantially reduced as a result of flooding and drought; resulting in the worst harvest in decades. Spanish orange production has also been reduced due to drought. Like California, large parts of Florida ‘the Sunshine State’’ has seen its once-famous citrus industry reduced over the past two decades. Two diseases, greening and citrus canker have taken their toll, and then Hurricane Ian in September 2023, hit the citrus industry at the beginning of its growing season.  Large parts of the one famous citrus industry (oranges and grapefruit) have been lost and farmers are turning to the PONGAMIA tree to repurpose fallow land. [caption id="attachment_41381" align="alignleft" width="650"] Pongamia  : image thanks to Sarangib on Pixabay[/caption] This is a climate-resilient tree from India. They do not need fertiliser or pesticides.   It has been grown as a shade tree. As a member of the Fabaceae, it produces small, brown beans.  These are so bitter than not even wild hogs will eat them.  However, the beans are easily harvested by a machine that shakes the tree.  A San Francisco based company has found a way to remove the bitter tasting chemicals and use the beans in food production, as they yield a high quality protein and also an oil.  The bean (a legume) has been used to make a table oil, protein bars and a biofuel.   Orange juice production is not the only drink to be affected by changing climate.  Drought affects coffee plants and damages the quality of the soil, and excessive rainfall ‘favours’ fungal disease [e.g.coffee leaf rust and cherry rot], all of which will impact the yield and quality of the beans harvested.  Similarly, chocolate production is threatened. Cacao trees are impacted by global warming,  they can only grow and thrive within 10 degrees of the Equator, needing stable temperatures, high humidity, and ample rain.  However, temperatures are rising while rainfall has decreased. These changes lower the humidity. The trees are also under attack by a virus - cacao swollen shoot virus disease (CSSVD). Changing temperatures and rainfall patterns will influence what crops can be grown and where, it will also influence their cultivation and the working patterns associated with those crops.  Climate change is thus a factor contributing to food inflation and insecurity across the world.    

With global temperatures rising and many places facing extremes of temperature, cities and urban environments often face the brunt of these climate extremes.  Cities absorb and hold onto the energy of the sun, creating ‘urban heat islands’. Recently, the temperature in New Delhi soared to a record high of 126.1oF (52.3oC), and other areas of India also suffered from the heat wave that claimed lives.  At a personal level, the shade of a tree can offer a place of refuge on a blisteringly hot day but a neighbourhood can benefit from the careful and strategic planting of trees.  Greater tree cover can mean that neighbourhoods are measurably cooler than those with few trees. If a heat wave is prolonged, then the physiological stress that people experience builds, affecting the old and young particularly.  Extreme heat / temperatures can also result in elevated levels of ozone, which affects people with asthma.  High temperatures may also be accompanied by high humidity and if the air has a high level of water vapour this makes it difficult for people to lose heat through sweating.  As water evaporates from the skin, its change of state (liquid to vapour) takes heat from the body. Researchers at UCLA analysed the ‘effects’ of four heat waves that occurred in the early years of the 21st century in Los Angeles, they focused on areas that varied in tree cover and pavements and road cover (essentially impermeable surfaces).  They also gathered information on ‘heat related’ visits to medical facilities.  They found that greater tree cover (and more reflective surfaces) reduced the number of heat-related medical interventions.   Whilst it might be agreed that increasing tree cover in urban settings is a good idea, there are practical problems.   Firstly, which trees to plant?  Ideally, the trees planted should be able to cope with the changing climate.  We don’t know what the climate will be like in 20 or 50 years but ideally the trees planted now should be able to cope with what nature might ‘throw at them’. Secondly, caring for the trees.  After planting, trees are vulnerable.  They need care and protection.  They need water - which is becoming an increasingly scarce resource in some parts of the world. Planting more trees needs to be coupled with increasing ‘green areas’ where water can permeate after rainfall into natural aquifers or water storage systems. Community involvement is also needed so that the trees are not only planted in areas where they will give the greatest benefit, but where people want them and will nurture them.   Los Angeles now has an Urban Forest Management Plan.  It aims to increase tree canopy in particular areas, locating areas to plant trees and collaborating with the residents of the areas.

The blog tends to write about trees in the context of woodlands and forests, but the trees to be found in hedgerows, parks, streets and gardens are important in many ways.  London is sometimes referred to as an urban forest, as it has some eight million trees within its boundaries.  Though their individual contributions of any given tree may be small, collectively the trees help with : Carbon storage  Carbon sequestration Air pollution removal Removal of pollutants (e.g nitrogen and sulphur oxides) Capture / removal  of particulates Reducing runoff, helping with flood mitigation  Noise réduction temperature regulation. The role of trees in temperature regulation has received some attention recently.   With climate change, many parts of the world have experienced periods of extreme hot weather / heatwaves.  Whilst it is true that extreme cold weather is associated with more deaths than hot, heat waves and the associated deaths are a significant problem.  Heatwaves, such as that experienced in 2015, have been associated with cardiorespiratory problems and premature deaths.   Cities, in particular, record higher temperatures than the surrounding countryside or the suburbs. the so-called urban heat island effect.  The lack of vegetation, the use of air conditioning systems, coupled with the dark asphalt of roads means that heat is retained / trapped; giving rise to the urban heat island effect.  On a summer’s day, some city centres may be some 10oC hotter than the surrounding countryside.  Europe saw its hottest summer last year, and its second warmest year.  Cities in southern and eastern Europe were particularly affected by recent heat waves. They tended to have significant urban heat island effects and low tree coverage.   In contrast, 27% of Gothenburg is covered by trees.  Studies / modelling by the Barcelona Institute for Global Health have indicated that increasing tree cover to 30% of the urban space could decrease the deaths associated with heatwaves / extremes of hot weather (perhaps by a third).  A number of cities, like Barcelona and Seattle have committed to increasing tree cover.  Indeed, Barcelona’s Trees for Life Master Plan is making progress towards its goal of covering 30% of the city with trees,  Barcelona is also encouraging green roofs.  Studies have also shown that ‘green spaces’ can have other benefits from reducing cardiovascular disease, poor mental health, and helping to improve cognitive functioning of children and the elderly.

Bees and solar parks As the country tries to move towards carbon zero, so we see more and more solar parks  / farms ‘springing up’.  Whilst they do create clean energy, they also take up a lot of land, and it is important to see if such solar parks can offer other commercial or environmental benefits.  One suggestion is to place honeybee hives on such parks.  The bees could provide a pollinating service to surrounding crops / farmland.  Researchers at Reading and Lancaster Universities have studied detailed land cover maps / crop distribution patterns to estimate the economic value of deploying honeybees in solar parks.  Their investigations suggest that a variety of crops from oil seed rape, soft fruits to apples and pears could benefit from such an arrangement.  The benefits would vary across the UK, with the benefits being greatest in the East and South of the country.  Care would need to be exercised though to ensure the placing of hives did not disturb the foraging of wild pollinators, such as carder bees, hoverflies etc. Are plants sulphur deficient? Much has been written about the importance of plants nutrients, especially NPK; that is to say nitrogen, phosphorus and potassium.   However, little is said about sulphur.  However, researchers in Groningen, Graz and Cologne have been looking at the effects of sulphur deficiency, particularly in relation to the colour and shape of the flowers formed.  The work focused on Brassica rapa, a member of the mustard family.  When it was subject to ‘mild’ sulphur stress (by limiting the sulphate in the growth medium), the flowers that formed were smaller and paler - not the usual bright yellow.  They were also likely to be mis-shapen. Colour and shape are features by which pollinators recognise flowers and then visit them. Pollen production by the flowers was also affected; smaller pollen grains were formed.  This may in turn affect the pollinators who visit the flowers foraging for food. In the relatively recent past, sulphur deficiency may not have been a problem due to acid rain, which would percolate through the soil, forming sulphates.  [In the twentieth century, acid rain formed as a result of the release of sulphur dioxide (and nitrogen oxides) into the air through the burning of fossil fuels.  However, various clean air acts have ensured that there is now much less SO2 in the air.] Annual rings, water availability and earthquakes. Christian Mohr (scientist from the University of Potsdam) was studying the transport of sediments in rivers in Chile in 2010 when a massive earthquake shook coastal areas of the country.  When he was able to return to his studies, he noticed that streams in the valleys were flowing faster.  He reasoned that this was because the earthquake has literally shaken up the soil, so that it was now more permeable and ground water could more easily flow down from the ridges.  As a result of increased water supply, he thought that trees down in the valleys would grow more than those on the ridges. He and colleagues drilled out plugs of wood from valley trees and ridge trees, and back in Potsdam they examined the tree rings under a microscope.  They also looked at the uptake of different isotopes of carbon as a measure of photosynthesis.  They found that trees from the valley floor experienced a small but noticeable growth after the earthquake, and this lasted for weeks or months, whereas the trees of the ridges grew more slowly.   It is possible that analyses like these, when combined with other information, could help identify significant historic disturbances. Rising temperatures. Recent years have seen periods of very hot temperatures, Such extreme weather events have been seen not only in the UK but across the globe (Arizona , Victoria Australia, Indonesia).     Extreme heat (and drought) have been known throughout history, but it would seem that extreme events are now more common.  The first two decades of this century are among the warmest on record; this warming is associated with increasing levels of greenhouse gases (due to human activity). Prolonged heat is not without its effects on us, it leads to sweating, teaches, fatigue, dehydration and heat exhaustion.  The very young and the elderly are most at risk from ‘heat waves’.  A 2003 heatwave across Europe is said to have caused several thousand  'excess' deaths’, mainly of the elderly.  Even gradual but sustained warming of the climate can have its effects.  For example, Silwood Park (Imperial’s research station) has commented that though it is now November, they have not recorded a single frosty night - normally they would expect to have three in a ‘normal’ October.  Snowdrops are appearing earlier, and some migratory species are changing their pattern / timing of migration. Across the world, different species are being affected in different ways.   Thick billed murres (type of guillemot, found in and around the Hudson Bay) have a high metabolism to deal with the cold waters into which they dive - they are cold adapted animals. On warm days (when the temperature is 21cC or above) they are dying whilst sitting on their nests - incubating their eggs.  They struggle to keep cool, if they spend more time in the water then they leave their eggs exposed to predators (like gulls and arctic foxes).  Similarly boreal and arctic bumblebee species are sensitive to heat stress, succumbing to stupor; other work indicates that some European / mediterranean species are now to be found in areas of the arctic circle - as a result of changing climatic ‘norms’.  Wild dogs are adapted to deal with heat, but if the temperature goes beyond a certain point they stop hunting, consequently their pups / offspring are less likely to survive. Warming temperatures not only affect animals but they also contribute to the increasing number of harmful algal blooms (in lakes and off shore regions).  These blooms can be dangerous to many animals (including humans) and when they die back they ‘suck’ oxygen out of the water - creating ‘dead zones’.  One species of alga (Karlodinium veneficum) which is known to produce toxins has been shown to acclimatise to higher temperatures (up to 30cC). As climate change and research continues, we will no doubt see further examples of how animals and plants are being affected by changing temperatures / climate .