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.    

There are eleven thousand trees in Kew Gardens.  Each year, a few trees are lost due to natural causes, old age, disease etc.   In 2002, a drought resulted in the loss of  some 400 trees.  Such a prolonged dry spell is  likely to occur again and again as global temperatures rise, and climate change takes a hold. Modelling of future climate scenarios by Kew scientists suggests that towards the end of this century between a third and a half of Kew’s trees could be lost.  Trees like the English oak, beech, birch and holly could be vulnerable to warmer temperatures and extended dry spells.  There is a plan at Kew to replace gradually trees with species currently found in warmer areas, such the Mediterranean, Asia and Central America. Examples might include species such as the iberian alder, cherry hackberry and Montezuma’s pine.  Many of the plants in the gardens will survive, [including Kew’s ‘Old Lions’] as they were collected from in and around the Mediterranean; some of these date back to the victorian era or earlier. The ‘old lions’ of Kew are trees from the original grounds / garden that still survive. Examples include : Japanese pagoda tree (Styphnolobium japonica) Maidenhair tree (Ginkgo biloba) Oriental plane (Platanus orientalis) Caucasian elm (Zelkova carpinifolia) Black locust (Robinia pseudoacacia) The Caucasian elm dates from 1762, when an arboretum was planted.  It is thought that it might have been in a batch of plants from the Caucasus, planted in what is now the herbarium paddock.  In 1905, the height of the tree was recorded as 60 feet (18M), though they can grow to 100 feet.  A larger caucasian elm can be seen at  Tortworth. One species of oak that is common at Kew is the holly or holm oak (Quercus ilex).  This is a common, naturalised oak that was probably introduced into the country in the sixteenth century.  It is a hardy, slow growing tree and many new holm oaks were planted in 2008 to redefine the Syon Vista.  The wood of the tree is strong and, in the past, it was used in carts and farming equipment. Its acorns start off green in colour but turn a reddish brown; they are a tasty treat for pigs. The threat to Kew's trees is not unique, parks and urban spaces across the country need to plan for the future, to ensure that their trees can offer some resilience to changing weather patterns. Full details of Kew's planning here.  

Forests, woodlands, trees are vital to life.  They absorb carbon dioxide, they release oxygen, they offer food and shelter to countless species (including us).  The global forests (equatorial to boreal) play an important role in mitigating climate change due to fossil fuel emissions.  However, many forests and their particular tree species are being  threatened by the world’s warming climate.  Recent years have seen catastrophic fires in many parts of the world, from Canada, Siberia, Sweden to Australia. In 2019/20, intense fires caused extensive damage to the Eucalypt forests in Australia.  Eucalypt rich woodland / forest is likely candidate for fire because the leaves of Eucalypts produce volatile and highly combustible oils.  The litter underneath such trees is rich in organic compounds such as phenols, which slow down the microbial breakdown of the dead leaves.   Consequently,  a layer of dry, eminently burnable material builds up. In Eastern Australia, some 40+% of the native eucalypt forests suffered severe canopy damage.   Trees on the west coast of America have also been subject to intense fires.  Their susceptibility to fire has been accentuated by drought across the region.  Analysis of the growth rings of trees, such as the Red Cedar (in areas such as Oregon) show that trees suffered reduced growth in the years prior to their death.  Drought stress increases the probability of attack by bark beetles and pathogens.  In California, many native species such as white fir, red fir and ponderosa pine have died and provided material for the fires that were to follow.  Fires in 2020/21 swept across the region, destroying vast swathes of forest.  The fires were of such an intensity that even Giant Sequoias were killed.   [caption id="attachment_40596" align="aligncenter" width="675"] Forest Fire in Canada[/caption] Sequoias had been thought ‘indestructible’ as they have a thick bark, which protects the inner living tissue, plus their canopy is usually well above the flames on the forest floor.  In the past, the fires burned litter on the ground, removing competitors, and releasing nutrients.  The heat would also open up the cones of the Sequoias releasing their seeds, so young trees could establish. Some of the Sequoias that died in these recent fires had stood for centuries and survived many wildfires.   In the past, the amount of litter / dead material was limited.  Indigenous people managed these forests (reducing the fuel load) to create forage for game animals, so that wildfires were of mild to moderate intensity.  Now, the fires are different - they are intense. There is more material to burn - including the trees that have already died from drought and disease. The fires can now reach into the canopies of the Sequoias. One of the Sequoias that died was the King Arthur tree - the 8th largest giant redwood in the world; it died in the Castle Fire of 2020. The drought driven deaths of many tree species is probably the start of a longer lasting shift in the growing range of the affected trees.  Temperature and water availability are two of the major determinants of the range of a given species.  It is possible that trees may ‘move’ northward and upward (grow at higher elevations).  Trees will begin to ‘die off’ at the edge of their range / lower elevations as drought / warming increases.  Die offs may also affect commercial plantations of species such as Douglas fir.

A lot of research work now focuses on the resilience of woodlands and forests in the light of climate change, that is their ability to cope with conditions like drier, hotter summers and/or  warmer/wetter winters. It has generally been assumed that trees at the limit of their range in dry regions would be most affected by climate change (with rising temperatures and less water).  However, a major study of some six million tree annual ring samples, (involving 120+ species) coupled with analysis of historical climate data has shown that trees in drier regions show a certain resilience to drought.  Trees seemingly become less sensitive to drought as they approach the edge of their range.  Trees in wetter climates are less resilient when they experience drier conditions or drought.  It seems probable that many species in wetter woodland and forest ecosystems will face significant challenges if the climate does move to a drier and warmer state. Assisted migration may be needed.  One idea is to ‘exploit’ the genetic diversity found at the edge of a species range.  The slow natural migration of trees may not be able to keep pace with the speed of climate change. Full details of this study by the University of California can be found here : Drought sensitivity in mesic forests heightens their vulnerability to climate change The effects of climate change have become very clear in recent times.  This last year witnessed:- Record breaking wild fires in Canada, with the smoke extending across to the East coast of the States. [caption id="attachment_40597" align="aligncenter" width="675"] Canadian forest fire[/caption] Heat waves in parts of America , for example, Phoenix (Arizona) suffers the best part of a month with temperatures of 43oC. Parts of the North Atlantic Ocean saw unprecedented temperatures The global temperature in July was 1.5oC above the pre-industrial average, September saw temperatures 1.8oC above the pre-industrial average. Parts of Chile and Argentina saw a ‘heatwave’ in the middle of their winter. It is clear that ‘unchartered waters’ lie ahead.

Tree survival and drought. Researchers at the University of California have been working on a method that helps predict whether forests / woodlands can survive periods of drought.  As climate change is altering patterns of snow and rainfall, so periods of drought are likely to become more common. Forests are important in terms of carbon sequestration, that is, they take up carbon dioxide from the air and convert it into sugars, starches etc that are stored in the leaves, branches, stems and roots.  However, in order to assimilate and convert carbon dioxide (in photosynthesis), trees (indeed all plants) need a supply of water.  When water is limited, trees need to make use of their reserve materials.  Just as we make use of body reserves of fat and glycogen when food / diet in inadequate. However, reserves can only sustain a tree for a finite period of time.  If drought persists, the tree reaches a ’tipping point’ and it will die.  The researchers studied a forest in the Sierra Nevada that experienced a period of drought between 2012 and 2015.   During this period, millions of trees died.  The team recorded rainfall, soil moisture and temperature in the forest AND the amount of carbon dioxide that the trees absorbed, and their reserve materials.  They found that the trees were able to maintain function / health after the onset of the drought but with the passing of time, the trees exhausted their reserves and were unable to use / convert carbon dioxide into food.  They had reached the tipping point and died.   The methodology of this study was called CARDAMON (carbon data assimilation with a model of carbon assimilation); it is hoped that it can be used to evolve strategies to enhance forest and woodland resilience in the face of climate change. Pollinators. [caption id="attachment_35902" align="aligncenter" width="675"] hoverfly[/caption] University researchers from the UK and Finland have been trying to determine the most effective pollinators of crop plants, like strawberries (and other fruits).  Plentiful and effective pollinators are needed to ensure a good harvest of the fruits. The researchers studied the pollinators at three strawberry farms through the (long) growing season for the fruit.  They adopted two approaches : They caught the insects that visited the strawberry flowers and analysed the pollen they carried in detail (pollen load and type). They also counted the number of flower visits by the different insects, (a quick way to identify key local pollinators). Many insects were identified, including :-  European drone fly :           Eristalis arbustorum Honeybee :                               Apis mellifera Levels drone fly :                   Eristalis abusivus Buff tailed bumblebee :     Bombus terrestris White tailed bumblebee :  Bombus lucorum Common drone fly :             Eristalis tenax Red tailed bumblebee :      Bombus lapidarius Early bumblebee :                Bombus pratorum Bent-shinned Morellia :   Morellia aenescens Hoverflies are true flies, that is, they belong to the order Diptera or true flies, as they have a pair of wings and a pair of halteres (balancing  / orienteering organs used when in flight). Several of the flies in the genus Eristalsis are known as Drone Flies (due to their resemblance to honey bee drones).  The larvae of Eristalis  species are commonly found in putrid / stagnant water and sometimes referred to as “rat-tailed maggots”. It was noted that pollinators also made use of the wild plants to supplement their diets, as strawberries alone cannot meet the nutritional needs of pollinators.  ‘Elsanta’ strawberries have a relatively low sucrose and protein content in both their nectar and pollen. The precise  order of importance of pollinators varied between farms.  Bee (Apis and Bombus) species  and hoverfly (Eristalis) emerged as key pollinators. The European drone fly was the most important pollinator at two of the three farms studied, evidence that hoverflies can be effective pollinators.  One farm had commercial hives of the honey bee but they were less significant than the activities of of the hoverflies and bumblebees. The abundance of a particular insect, coupled with its active period were /  are important determinants of pollinator importance.  Sawdust and plastics - a possible use?. Plastics represent a relatively new, but persistent and major form of pollution (on land, in the sea, indeed everywhere).  Whilst many plastic objects are instantly visible in the form of discarded bottles, fast food containers, many plastic pollutants are in the form of very small particles of plastics  - nano and microplastics.  The concern is that we and other organisms are taking these microscopic particles into our bodies from our food / drinking water. However, it is possible that plant materials may offer some ‘solutions’.  Water that contains micro and nano plastics can be filtered through sawdust that has been treated with tannic acid.   Tannic acid is large molecule, its molecular formula is C72H52O46 .  Tannic Acid is found in certain plant galls (swelling of trees caused by parasitic wasps) and in the twigs of certain trees, such as Chestnut and Oak.  The wood sawdust contains fibres of cellulose, combined with hemicelluloses and lignin.  Water can flow through this material by capillary action.  This plant-based filtration (known as bioCap) of plastic-laden water is capable of dealing with a wide range of nanoplastics (PVC, PET, polyethylene etc), and tests with mice suggest that the filtered water may be sufficiently free of plastic to pose little risk.  

During a drought, the trees in a woodland or forest become 'stressed' and may die.  The  reason for their death is not immediately obvious (beyond lack of water), and  it is not possible to ‘transplant’ a mature tree and its complete root system to a lab for detailed investigations.  However, recently, researchers at the University of Innsbruck have taken ‘the lab’ to a set of mature pine and pine trees. The trees were fitted with rugged and waterproof ultra-sound detectors.  Some of the trees had their canopies covered by a ‘roof’ so that the summer rain was denied to the trees, and they essentially experienced a ‘drought’.   Drought stressed trees produce ultrasound ‘clicks’ (faint acoustic waves that bounce off of air bubbles) that can be picked up by the detectors.  Air bubbles or emboli form in the vascular system of the trees when they are struggling for water.  Water is drawn up the xylem vessels by the evaporation of water (via the stomata) from the leaves, there is a continuous column of water.  When the column of water breaks, bubbles form with the xylem vessels and the transport of water to the leaves is reduced.  If the flow of water is substantially reduced the tree will die. The sound detectors found that the spruces produced more clicks than the beeches when water stressed, suggesting more emboli were formed within their xylem tissues.  It may be that the beeches were able to access the deeper reserves of water in the soil, whereas the spruces had a shallower root system. Trees can, of course, reduce water loss from their leaves by closing down their stomates.  But when their stomates are closed, they cannot take in carbon dioxide for photosynthesis and make the sugars / starch that they need for their metabolism.  At the end of the experiment, the trees that experienced ‘drought’ were drenched with water and most recovered well, and their rates of photosynthesis caught up with the ‘control’ groups of trees (those with summer rain).  However, the spruces’ water reserves were somewhat depleted; this was determined by measuring the resistance the tissues offered to an electrical current. The ability to withstand / recover from drought could over time affect the make up of woodlands and forests,  particularly if the trend for hotter and drier summers continues. Interestingly, some work in the United States (at University of Wisconsin–Madison) suggests that young tree saplings that have experienced drought or heat are more likely to survive when transplanted into more challenging areas.  It seems that the soil microbes that young saplings experience can help young trees establish themselves.  Saplings grown in soil (and microbes) that have experienced drought / cold / heat are more likely to survive when later transplanted and faced with similar conditions.  Trees with ‘cold-adapted’ microbes survived better when experiencing Wisconsin’s winter temperatures. The work was conducted with different species of tree in a variety of locations in Wisconsin and Illinois. The transplant locations varied in temperature and rainfall.  It may be that fungi that inhabit the roots of the saplings are involved in these ‘responses’, though the microbial population of the soil is diverse. For more details of this work, follow the link here.

Across the world forests and woodlands are under threat,  suffering  fragmentation and shrinkage.  This is not good news for the plants and animals that rely on these habitats for their survival.   In a large forest or woodland, animals can move around over considerable distances in search of food / partners - without having to leave the area that supports them.  Similarly, plant seeds when dispersed are more likely to find the micro-climate that they need for germination and subsequent growth (humidity, shade, soil type etc).  Some species have very ‘exacting’ requirements that can only be met in the heart of a forest or woodland.  For example, there is a frog that is restricted to undisturbed mountainous forests in Borneo. Sadly, recent surveys suggest that many forests continue to suffer from fragmentation / loss of area.  The two main reasons for this loss are : clearance for agriculture (palm oil plantations etc) - this has mainly affected tropical and sub tropical area.  Sometimes fires are used as a deliberate ‘tool’ to clear an area of forest so that the area can then be used for agriculture. wild fires - these have affected the Boreal Forests but also regions of the Amazon Basin.  In areas like Siberia and Canada, drought and high temperatures have lead to extensive fires. (Zombie fires are underground peat fires that smoulder in the winter months but reignite when the ground dries in the Spring or Summer.) Recent times have seen extensive fires across Siberia, Canada, parts of the West Coast of America and Australia. Woodlands have experienced fragmentation due to the expansion of agriculture, the building of motorways & roads, and the expansion of housing.  Wild flower meadows have suffered even more dramatically - with some 90+% lost in relatively recent times. Obviously fires are devastating locally, killing vast numbers of animals and plants. Fire also destroys the organic content of the soil and its complex microbial population.  The plumes of smoke released by fires (such as those seen in Canada and Australia) spread extensively.  The Canadian fires (883 fires raging at one point) left mile after mile of blackened forest, and forced hundreds of people from their homes.  The smoke spread far beyond Canada’s borders, as far away as parts of Europe.  New York City was ‘bathed’ in an ‘orange haze’ and experienced a hazardous level of air pollution. The plumes from such fires are rich in black carbon soot.  The soot particles absorbs solar radiation, keeping heat in the atmosphere. Recent analysis of smoke plumes indicates that there is also ‘dark brown carbon’.  This consists of a previously unknown type of particle and whilst these particles absorb less light per particle than black carbon, they are approximately four times as many brown carbon particles in wildfire smoke (compared to black soot particles).  There is also the suggestion that these brown particles retain capacity to absorb solar radiation for longer.  

In 1820, John Keats famous poem “To Autumn’ was published.  Its opening line often serves to describe autumn as ‘The season of mists and mellow fruitfulness’.  Indeed, Autumn has arrived here.  Woodlands have been transformed into a 'tableau' of red, yellows, and oranges as the leaves are shed and the woodland floor has become a veritable fungal jungle, (as Jasper has described).  Hawthorn and other bushes are laden with berries, conkers and acorns are generously strewn across woodland floors, squirrels are eating hazelnuts (and hiding them as a winter food store).  But this cornucopia of fruits and seeds may be in response to the long, hot and very dry summer we have experienced.  Trees and shrubs have been stressed by the heat and drought. Some have responded by mobilising their reserves / efforts into producing more fruits and seeds, to ensure that they pass on their genes to the next generation.   Different trees are responding in other ways. Some are ‘holding on’ to their leaves for longer, whilst others (like some birches and rowans) have already shed theirs - in order to limit the damage from wilting and water loss during the intense heat and drought of summer.  [caption id="attachment_39130" align="aligncenter" width="675"] Autumnal colour[/caption] Blackberries appeared early this Summer and few are to be seen this Autumn, some animals (like the dormouse) will search in vain. [caption id="attachment_39026" align="aligncenter" width="675"] Black Bryony berries (photo by Art Symons)[/caption] Will this Autumn be long and mild? It may extend into the traditional winter months. There is also the threat of extreme weather events (like Storm Arwen that brought severe winds across the UK last November).  Whilst we might welcome mild weather (with the high price of gas and electricity), it could be mean an increase in bacterial and fungal infections, not only of plants but also affecting overwintering insects - tucked up in cocoons and pupal cases. Prolonged cold periods, coupled with frosts limit the spread of such infections.  The cold of winter is also the traditional signal for animals like hedgehogs to hibernate.  If they are still active in winter when food is scarce, then they will lose condition and possibly starve to death.  Milder weather in Autumn and Winter also affects the migratory behaviour of birds, some birds may choose to overwinter here.  Some seeds need to experience cold temperatures before they will germinate in the following Spring. Climate change and severe weather events are here to stay until there is a coordinated and concerted effort to reduce greenhouse emissions on a global scale.  On a local scale, our gardens (which represent some 400,000 hectares of land) can make a contribution by encouraging wildlife / pollinators and promoting biodiversity.  Gardens can also help to some extent with extreme rainfall.  During heavy rain, water runs off hard surfaces and into the drains, these may also deal with sewage.  When the drains are overwhelmed by storm water, sewage is discharged into our rivers (and the sea).   Gardens can help by  reducing hard landscaping, so that rain can soak into the soil instead of running off into the drains making use of water butts.  They capture water, so it does not enter the drainage system.  It is also there to use when the garden needs water (and there is a hose pipe ban) mulching the soil with a layer of plant material. It is an effective method of conserving water in the soil and it reduces surface runoff, increasing the infiltration / penetration of water into the soil.  It helps keep the soil moist in times of drought, and helps reduce run off during heavy rainfall.  Particularly important when planting young trees / shrubs. [caption id="attachment_38957" align="aligncenter" width="675"] a light mulch (in Art's garden)[/caption]