Willow bark and the covid virus. The Covid pandemic created great strains on health and business services, and the virus continues to impact society in many ways.  It is not surprising that there is an ongoing search for anti-viral agents. Finnish scientists have found that willow bark may have a role to play. Willow bark has been used as a natural medicinal product over the centuries as an effective agent to treat pain and inflammation.  The anti-inflammatory properties of the bark are generally ascribed to salicin, which was to lead to the development of acetylsalicylic acid, that is aspirin.  The Finnish scientists ground up the willow bark in hot water and then sieved it to create an ‘extract’.   This solution was then added to a number of cell cultures that were exposed to different viruses (enteroviruses, a seasonal coronavirus and SARS CoV2).  They then monitored the viral activity, cell infection and viral replication  The extract had an effect on all of the viruses.  In some cases, the extract affected the envelope of the virus (a structure surrounding the viral genetic material) so the viruses essentially broke down, whereas others were prevented from releasing their genetic material and reproducing.  Specifically, though the Covid-19 virus could enter cells when treated with the extract, it could not reproduce once inside. The research team analysed the extract’s chemical composition and tested some known constituents of bark but concluded the success of the extract probably resulted from the interactions of different biologically active compounds.  Compounds in the extract included many complex chemicals (for example, hydroxycinnamic acids, salicylates, flavonoids, flavan-3-ols, and proanthocyanidins (polyphenols).  Further work will focus on the role / interactions of these various compounds. The Hazel Dormouse in peril. The numbers of the hazel dormouse have fallen dramatically since the turn of the century.  The dormouse has disappeared from Staffordshire, Northumberland and Herefordshire in the last few years.  This loss is attributed to The destruction / fragmentation of their habitats Poor management of woodlands and hedgerows, leading to a loss of diversity / niches Rising deer numbers, feeding on saplings and shrubs Extreme weather patterns may also play a part Captive-bred dormice have been re-introduced to some 25 sites in 13 counties across the country, sadly nine of these reintroductions were not successful.  Dormouse bridges have been created to enable the animals to move between areas dissected by major roads (such as the M1), others are planned.   The dormouse (Muscardinus avellanarius) is a nocturnal animal and lives mainly in deciduous woodland,  it feeds among the branches of trees and shrubs. the dormouse rarely descends to the ground.  It feeds on a wide variety of 'foods' ;  flowers (nectar and pollen), fruits (berries and nuts), certain buds and leaves and some insects, such as aphids and caterpillars. The hazel dormouse is regarded as a ‘flagship species’, that is to say, if the dormice are thriving then it is likely that other species are too from butterflies to birds such as the nightingale.  Dormice are currently assessed as ‘Vulnerable’ to extinction in Britain under IUCN Red List criteria, but recent studies suggest a classification of ‘Endangered’ might be more appropriate.  Certainly, their future is uncertain. Detailed information on the hazel dormouse is available at PTES (note this link opens a PDF).  Their report details the state of hazel dormice in 2023. zsaqwa https://youtu.be/4u-yMkXOuTY Changes in the Boreal Forests. Boreal forests encircle the northern reaches of the Earth, lying just below the treeless under of the Arctic.  These forest cover large areas of Alaska, Canada, Scandinavia and Siberia.  These forests contain billions of trees, most are conifers but birch, poplar and aspen may also be found.  The trees (and soils) contribute significantly to the cycling of carbon in nature, absorbing carbon dioxide in photosynthesis. They are also home to many species of migratory birds, plus predator species such as lynx and brown bears, and wandering herds of moose. Due to the remoteness of these forests, they have remained (until relatively recently) unaffected by human impact.  Now these forests are warming at a rate above the global average.  This has a number of effects:  In the southern parts of the boreal forest. Conditions are becoming too warm for cold adapted trees; their growth is slowed and they may die. With the warming comes increased dryness, which leads to water stress and increased risk of insect attack /  infestation. The dryness also means that forest fires are more likely and occur with increased ferocity.  This year, the fires in Canada have been particularly extensive and damaging.  Some 18.5M hectares went up in flames.   The plumes of smoke spread far and wide. [caption id="attachment_40597" align="aligncenter" width="675"] Canadian forest fire[/caption] Scientists are now using satellites to track changes in the extent of the boreal forests.  If trees are being lost on the southern edge of these forest, then it might be expected that the northern limit for tree growth might change.  Indeed, there is some evidence for this in Alaska where young Spruce are now growing some 25 miles beyond the previous tree line, moving into the ‘treeless tundra’.  It may be the loss on the southern edge is compensated by extension of the most northern parts of the boreal forest, but it is not clear whether tree can ‘move’ at the rate of climate change.  

What do nutmeg, allspice, vanilla, cinnamon, anise, cloves, ginger, and cardamom generally have in common ? Broadly speaking, they are spices that we associate with Christmas. They are much used in cakes, christmas puddings, mince pies, mulled wine, and punch. They add nuance and flavour to eating and drinking at this time of year.  Whilst spices are parts of plants, ‘spices’ is not a strict botanical term, more a culinary one. Spices come from a variety of plant sources, ranging from woody shrubs and trees, to the roots, flowers, seeds and fruits of herbaceous plants.   Spices are generally dried plant products, whereas other flavourings notably herbs are used in their fresh state. Spices and herbs offer sensations such as pungency, hotness, freshness as well as feelings of temperature or even pain (think of a very hot chilli pepper or curry).  Apart from the fact that people across the world enjoy the taste of various spices, various hypotheses have been put forward to explain the use of spices (for example, the Darwinian gastronomy hypothesis). Nowadays, spices are regarded as familiar or commonplace but in the past they were exotic and expensive (as was tea, which was kept under lock and key away from the servants).  Spices ‘unlocked’ fortunes for those who ‘discovered’ and transported them from far flung places (such as the Dutch East Indies, the source of nutmeg, cinnamon and black peppercorns). The original source of Nutmeg was the Banda Islands of Indonesia (sugar cane also originated in this area).  The Portuguese and the Dutch fought for control of the islands.  The Dutch East India Company was established in the early 1600’s and operated from Jayakarta for best the best part of 200 years.  Britain briefly occupied the islands and nutmeg trees were sent to Singapore, Malaysia and Sri Lanka, and then on to Zanzibar, Grenada and the Indian state of Kerala. As the tree’s (Myristica fragrans) homeland is tropical, it cannot tolerate frost but it is now widely grown throughout Indonesia, India and Guatemala.  Between them, these countries produce some 85% of the nutmeg harvest each year.  Nutmeg trees are dioecious, that is, there are separate male and female trees.  Young trees begin to produce fruit when they are a few years old but it not possible to determine which trees are male and which are female until then.  Obviously only female trees will produce nutmegs.  Peak production of the fruit occurs when the trees are about twenty years old and productivity falls after some 60 years. The fruit is termed [botanically] a drupe.  That is a fruit in which an outer fleshy part (the skin and flesh) surrounds a single shell (the pit, stone) with a seed (or kernel) inside.  The fleshy covering of the nutmeg is sweet and in Indonesian culture may be used to make a jam, juice or dessert.  Beneath the flesh / pulp is a crimson tissue. This is peeled away, dried and grated to form the spice - MACE.   The seed is dried in the sun, the flesh extracted and ground to make the commercial form of NUTMEG, though it can be grated.  Whilst mace and nutmeg are similar in flavour, mace is sometimes described as having a more subtle taste and a bright orange colour.  Nutmeg has a warm, slightly sweet taste; it can be used to flavour baked goods, puddings, potatoes, meats, sauces,, and such drinks such as eggnog (though cinnamon may be used as an alternative ingredient), mulled wine and chai tea. Interestingly, too much nutmeg can have neurological  effects (convulsions, delirium, headaches).  Whilst the chemicals in nutmeg (and other spices) add flavour to our foods and drink, they are actually part of the plant’s defence mechanisms.  They deter insects and other animals from eating / attacking the plant, and may have anti-microbial properties.  Nutmeg contains a compound called myristicin - it protects the seed against attack.  However, in the body this can be converted into the chemical MMDA, an amphetamine derivative,   The effect(s) of consuming large amounts of nutmeg can take some hours to develop and may persist for some time. The levels recommended for use in cooking etc are generally quite safe. Most recipes use between 1/4 to 1/2 teaspoon of nutmeg, and these recipes are then often split into several portions, so the actual exposure to nutmeg (and myristicin) is small. Incidentally, nutmeg was once thought of as a treatment for the plague! Nutmeg is one of the ingredients of mixed spice.  This is a blend of different sweet spices. It often contains cinnamon, nutmeg, allspice; sometimes cloves, ginger, coriander (seeds) and caraway may be added.  The term "mixed spice" has referred to this blend of spices in cookbooks dating back to the nineteenth century and possibly much earlier. Allspice is the dried fruit of the plant Pimenta dioica, an evergreen tree / shrub. Early attempts to grow the tree from seed failed until it was found that the seeds needed to pass through the gut of birds - this was the ‘trigger’ for successful germination.  The fruits are traditionally dried in the sun, they then resemble peppercorns.  At one time, the plant was thought to grow only in Jamaica and it is sometimes referred to as the Jamaica Pepper. Now, it is grown in many warm parts of the world.   Whilst allspice is a valued ingredient in Jamaican cooking, e.g. jerk seasoning, it is also used in many other cuisines : middle eastern, Polish, Finnish and Swedish.  It is used to flavour stews, soups and meat dishes, but can also be used in various sweet dishes.  Allspice is also an ingredient in mixed spice (mentioned above) often used in baking, and in the making of Christmas pudding or a Christmas cake. [caption id="attachment_40700" align="aligncenter" width="675"] Cinnamon[/caption] Historically speaking, another valued spice was cinnamon.  It was a suitable gift at the Temple of Apollo (at Miletus).  The source of cinnamon was a secret to traders in the Mediterranean world for centuries,  they controlled the spice trade in order to protect their profits / monopoly.  Cinnamon comes from Cinnamonum trees that belong to the Laurel family.  There are many species (see here for a list) but Cinnamomum verum known as "Ceylon cinnamon" is considered to be "true cinnamon”. However, most commercially available cinnamon comes from :- C. burmanni  - Indonesian cinnamon or Padang cassia),  C. cassia  - Chinese cinnamon or Chinese cassia),  C. loureiroi  -Saigon cinnamon or Vietnamese cassia), and C. citriodorum - Malabar cinnamon The trees are coppiced so that multiple stems are produced and it is from the bark of these stems that the strips of cinnamon are produced.   [caption id="attachment_40703" align="alignleft" width="300"] cinnamon quills / sticks[/caption] Cinnamon has a strong, spicy flavour.  The properties of cinnamon come principally from two chemicals - cinnamaldehyde and eugenol. The cinnamaldehyde is largely responsible for the flavour and aroma of cinnamon.    It is known to stimulate particular receptors in the nerve endings in the mouth - the TRP receptors.   The eugenol has a pleasant, spicy, clove-like scent.  Cinnamon is used in the baking of cinnamon rolls and buns, as it handles baking conditions well.  It is commonly used in Sweden, and such is the ‘importance’ of their cinnamon buns - kanelbullar that the Swedes have an official Cinnamon Bun Day - on October 4th!   Cinnamon is also widely used in Portuguese, Turkish and Persian Cuisine. Cinnamon is also used in fragrant candles.  Thousands of years ago, cinnamon (and pine resin) was used in Egypt as a ‘perfume’ / embalming material in the preparation of dead bodies for mummification.  In recent times, cinnamon-rich materials have been investigated for medical uses, particularly in relation to type 2 diabetes and the control of blood sugar levels. Thanks to pixabay for images of nutmeg .

On the Red List! The capercaillie is threatened.  Its numbers in Scotland have roughly halved (between 2010 and 2020).  It was once widespread, but now it is found in the pine forests of the Highlands - notably the Cairngorms National Park.  It is a red listed species. The decline in numbers is associated with poor breeding success, poor weather in early summer when the chicks are developing, another problem is predation by species such as the pine marten, foxes and crows.  The Game and Wildlife Conservation Centre (GWCT) has identified another issue that these birds face - namely collisions with deer fences.     These fences are created to keep deer out of particular areas.  However, when the capercaillie (and black grouse) impact on these fences, they are injured or killed.  Marking these fences, reduces the number of collisions but does not stop them.  Unmarked fences are still killing adult birds.  Marking of these fences or their removal would help with the survival of the capercaillie, though removal would  mean trees and shrubs would be unprotected from deer. Mosquitoes! There are some 36 different species of mosquitoes to be found in the UK, which  are generally harmless (though they bite).  But that may change.  With longer and warmer summers, the UK may become a venue for other species such as the tiger mosquito.   This insect has been found in ‘traps’ (monitored by the UK Health Security Agency) at ports and rail terminals.  This insect is known to transmit various diseases, such as dengue fever.  The mosquito was found in Italy in 1990 and it is spreading on the continent. A species of Culex has also been found in some areas of the Thames estuary - which can spread the West Nile Virus. This virus can result in flu-like symptoms.  Outbreaks have been been mainly in the warmer areas of the Mediterranean, but with climate change and the potential for very hot summers here - vigilance will be needed. Floral defences. Many flowers release a distinctive scent.  The scent serves to attract pollinators like bees and butterflies, or  it may ward off pests that would feed upon the plant.. Many of the chemicals that contribute to scents are terpenes.  Recent research has investigated how these chemicals can affect the growth and development of butterflies - using painted lady butterflies.  These butterflies feed on a wide range of plants and hence are exposed to a variety of scents / terpenes. For these experiments, the researcher (at the University of Centra Florida) used four common floral terpenes  Limonene :  which has a fresh, citrus like smell Linalool. : has a floral scent, reminiscent of lavender Cineole : has a camphor-like smell, slightly medicinal contributes to eucalyptus oil. β caryophyllene : this has a spicy / woody fragrance. Different amounts of these terpenes were fed to caterpillars of the painted lady butterfly, and the subsequent development of the caterpillars was monitored and the size of the adults recorded.  The experiment was also conducted at different temperatures.  Temperature affects scent release by flowers. Higher levels of terpenes has significant affects on the survival of the caterpillars, especially when combined with the higher temperatures.  The caterpillars took longer to enter into pupation when given high levels of terpenes, though the size of the adults that emerged from pupation was unaffected.  If longer and warmer summers become more common, the combined effects of terpenes and heat could become important determinants of development. `

The woodlands blog has reported on urban forests, the trees in our cities, lining our roads and in our gardens.  This green infra-structure in our towns and cities provides a range of economic, environmental, and social benefits. The importance of green, leafy spaces was emphasised during the early days of the Covid pandemic, helping with mental and physical wellbeing of many people. Urban trees offer  Valuable habitats for wildlife and can provide biological corridors / stepping stones that enable birds and other animals to move through the urban environment. Shade and cooling in streets and parks. They can help reduce the risk of flooding, allowing more water to enter the soil rather than running off hard surfaces of tarmac and concrete.   The capture of pollutants, improving local air quality by capturing fine particles from the air (mainly through deposition on leaf surfaces).  Trees and shrubs seem particularly effective in removing ozone.  Through their photosynthetic capacity, trees can take up carbon dioxide into organic form - carbon sequestration. The amount of carbon taken up by London’s urban forest each year has been estimated at 77,200 tonnes.  However, recent studies suggest that many urban trees are under threat : Trees are subject to heat stress as many cities experience the heat island effect, the ambient urban temperature is significantly above the surrounding countryside. Many struggle to get sufficient water as they are planted in small square of soil and surrounded by tarmac, concrete or paving stones. Soil compaction is often an issue, affecting water permeability. They may experience an ‘excess of nutrients’ - due to dog’s urine, this is a source of urea and other nitrogen compounds. Once planted, young trees may not receive after-care / management.  This point is significant.  Many trees die within the first few years of planting. In Boston (USA), some 40% of trees are dead within seven years of planting.  Similar figures are true for New York. Both rural and urban trees suffer significant mortality when young but whereas the death rate of rural trees tend to decrease after a few years - urban trees are more likely to die as they age.   [caption id="attachment_40541" align="alignleft" width="300"] Young urban tree[/caption] There is a struggle to reach maturity.  Most trees need two or three decades to offset the carbon emissions associated with their planting / maintenance etc, and they then sequester carbon at a significant rate.  Work at Boston University (in Professor Lucy Hutyra’s lab) and Harvard has focused on the problems that urban trees are facing, and another issue (apart from those mentioned above) has been identified - the microbiome of the root [that is the variety of micro-organisms that surround / inhabit the root tissues]. Urban trees seem to have fewer symbiotic fungi in their root systems when compared to rural trees.  Roots often develop mycorrhizal associations with fungi.  Such systems allow the roots to access more water / minerals and in return the tree ‘offers’ the fungal network a supply of carbohydrates.  Jenny Bhatnagar (Harvard) has investigated the soil microbiome in eight different plots, some urban and some rural in Massachusetts.  Interestingly, the investigation found that whilst there were more fungi in urban plots, they ‘seemed more reluctant’ to establish symbiotic associations with the roots of the trees.  This failure could be due to the excess nitrogen / nitrates in the soil (from animal urine / faeces?).  When there is an excess of nitrogen available, trees tend to dispense with their fungal partners. The hotter temperature of urban soils might 'favour' a bacterial population (some bacteria ‘fix’ nitrogen). [caption id="attachment_40526" align="alignright" width="300"] Once, there was a cherry tree ...[/caption] It is not clear as yet why so many urban trees fail.  It could be that the loss of the symbiotic fungi renders the trees more susceptible to certain disease-causing microbes.  The hotter and drier soils at the edges of fragmented forests have more pathogens and not so many symbiotic fungi. A number of simple aftercare / management measures would help young trees to establish : Watering the trees in their early years Preventing soil compaction to allow water to percolate, and oxygen to diffuse to the roots. Mulching around the tree base (helps water availability and slows nutrient input from urine etc.) An interesting article on mycorrhizae and urban trees may be found here. [caption id="attachment_40537" align="alignleft" width="220"] Olive[/caption]   The importance of soil micro-organisms is also indicated by research in Australia, where  shrublands / woodlands have been invaded by African olive trees.  The olives have disrupted the partnerships between the Acacia trees (hickory wattle) and symbiotic soil bacteria (Rhizobia ssp).  This is another symbiotic association, where the partners exchange materials for mutual benefit,  Where the Olives have grown, the Acacia have problems establishing root nodules with the bacteria.  To restore these scrublands, a full understanding of the soil / root microbiome will be important. Full details of this work can be found here.  Postscript : In today’s Guardian (03/11/2023), Helena Horton’s article “Ministers should target tree survival ‘rather than planting’” reinforces the points made in the blog about the early mortality of young trees - urban or rural.  Increasing woodland cover will only occur if young saplings survive.  

Many hedgerows were planted originally to keep livestock, such as sheep, cattle, pigs, chickens in specific areas. Some hedgerows were planted to define boundaries – ‘who owned which bit of land’.  Hedgerows often surround fields.   The word ‘field’ comes from Old English ‘feld’, meaning 'an area of felled trees / open country'.   The establishment of many hedgerows was associated with the process of enclosure; a change in land use from arable to pasture (for sheep). Open fields and common land were enclosed by hedgerows, over many years the landscape of England changed. The C20th witnessed the opposite process, the removal of hedgerows for the creation of larger fields to accommodate larger machinery.  In the decades following the end of the second Word War, it has been estimated that a quarter of a million miles of hedgerow have been ripped out / lost.  Fortunately, there are now policies in place to halt or even reverse the loss of hedgerow.  Hedgerows are recognised as an integral part of our landscape and play an important role in the maintenance of biodiversity.  They provide habitats for a variety of animals and plants. Many species of birds nest in hedgerows, such as song thrush, yellowhammer and tree sparrow. Different species favour different heights within the hedgerow. Some species nest near the ground such as wrens and dunnocks, whereas others nest higher up (eg. Bullfinches).   The greater the variety of plant species in a hedgerow, the better the supply of pollen, nectar, fruits and seeds.  Ivy for example will produce flowers late in the year and offers a source of nectar and pollen.  Hawthorn, blackthorn and holly offer fruits in the winter months for birds and small mammals. Hedgerows and hedges have to be be maintained.  Such management may involve planting of trees or shrubs to fill gaps, coppicing, laying or cutting back. [youtube=http://uk.youtube.com/watch?v=Andv7a0NPEc 425 350] However, the effects of pruning and cutting back during the bird-nesting season can be disastrous. Mechanical flailing of a hedgerow is fast, effective and the regrowth is generally slower, but its effects can be particularly bad on birds. They may abandon their nests and / or  their eggs or chicks may be destroyed. The pruning / flailing may also reduce the insect populations of the hedgerow (or other other food sources) on which the birds depend.  Hedge pruning maintenance is :- ideally undertaken outside of the nesting season. and  only done every second or third year. [caption id="attachment_25527" align="aligncenter" width="600"] A flailed hedge[/caption] Hedgerows also support vital insect pollinators : butterflies, hover flies, moths and bees. These insects help with the pollination of crops such as oilseed rape, legumes and fruit trees. Other insects can help with crop yields by predating upon crop pests, such as green fly and blackfly (these may spread viral diseases on crops such as sugar beet).  Insects may overwinter in the hedgerow and move into the fields come the Spring, as the aphids start to increase in number.  If trees are left in situ, they may achieve veteran status.  Then their rough bark, cracks, holes and dead wood will support a diverse range of species. Owls, kestrels and bats may come to nest. There are also niches that offer opportunities for epiphytes, mosses and lichens.     The dead wood may be home for saproxylic beetles.   Hedgerows also act as corridors linking to other hedgerows, woodlands etc along which animals can pass (for example, hedgehogs and other small mammals). Hedgerows provide important wildlife corridors across agricultural landscapes. They provide food for insects, small mammals and birds (due to the range of plants and their different flowering and fruiting times). They provide nesting and roosting sites for birds and bats, and ‘homes’ for a variety of small mammals.  Many insect species over winter in hedgerows. The trees and woody shrubs help with carbon sequestration. Hedgerows offer a windbreak, reducing wind speed and hence lowering soil erosion, they may also offer shelter to animal stock.  The roots also help stabilise the soil. [caption id="attachment_40483" align="aligncenter" width="675"] Hedge with beech, nettle, dog rose, brambles, hazel and ash - amongst others[/caption]  

Hazels, alders, and hornbeams belong to the Birch family - the Betulaceae.  The white birch, silver birch has the scientific name Betula pendula.   The birch is the national tree of Finland. As trees go, it has a rather slender, delicate form, and may be seen swaying in the wind.  Its silvery / white bark develops blackened fissures with age.  Early in the year it forms flowers, the male flowers in the form of catkins.    The female flowers become a dark red colour after pollination, eventually forming small, wind dispersed, winged seeds. The male catkins release large quantities of pollen (before the leaves emerge).  This pollen is the dominant tree pollen in Northern Europe (in Spring).  It is often implicated in allergic responses such as rhinitis (runny nose / sneezing) and asthma.   Birch is a pioneer species, it can colonise open spaces, and disturbed ground quickly.  It grows fast and once established, it helps ‘protect’ or shelter slower growing species, like Oak.  It has a limited life span, perhaps a maximum circa 70 years and then gives way to longer lived species such as Oak and Beech.  The tree can provide a home or food for many species of insect, woodpeckers may nest in the trunks and other birds may feed on its seeds.   The tree is quite susceptible to the honey fungus, which is the name given to several species of the fungus Armillaria. The fungus attacks and kills the roots of a number of trees and shrubs. One symptom of honey fungus is a white fungal ‘layer’ between the bark and wood, often at ground level. Clumps of honey-coloured mushrooms sometimes appear briefly on infected stumps in Autumn. The birch tree has had many uses over the years, some dating back to the neolithic period.  It has been used to make perfumes, adhesives, and besom brooms. Bundles of birch twigs were used for corporal punishment, and the twigs may be available in saunas to stimulate blood flow in the skin!  The wood of the tree is used in furniture making, creating veneers and in wood turning.  However, it is the bark and sap that have attracted most interest and have many uses.  Slabs of the bark are used as roofing shingles, and strips of it were  / are used to make bast shoes and in handicrafts.  The bark has been used in tanning, and when heated a resin forms which can act as a waterproof glue.  In Spring, large quantities of sap rise up the stem(s) of the tree and this can be tapped. The sap is best collected in early Spring as, if collected later, it tends to have a somewhat bitter flavour.   Birch sap contains sugars, amino acids and minerals (e.g. manganese), it may be drunk fresh or fermented.  Bottled birch water is available online.   In recent times, attention has focused on wood pulp from birch.  It is a rich source of plant sterols and stanols.  Sterols and stanols are naturally occurring substances that have a chemical make up that is similar to cholesterol. They are found naturally in small quantities in vegetable oils, legumes, seeds, nuts, legumes, grains, and vegetables. Back in the 1950’s, they were found to lower cholesterol levels in the body, if eaten in large enough quantities. One called beta β-sitosterol was particularly effective in reducing the absorption of cholesterol from the intestines.  However, there was the problem of finding a rich enough source of these compounds.  This was ‘solved’ when it was found that wood pulp could yield the compounds in quantity.  Now margarine-like spreads, milks and yoghurts are available that contain β-sitosterol or similar stanols in sufficient quantity to effect a lowering of blood cholesterol levels.  β-sitosterol has also been to improve urinary flow in men with prostate enlargement.

Across the world there may be three trillion trees. A mature tree may have 200,000 leaves, so there are a lot of leaves in the world - not counting those on herbaceous plants, grasses and shrubs.  The broad structure of a leaf is outlined here in woodlands.co.uk Tree ID. The leaf is the site of photosynthesis, providing food for the tree, and oxygen for us.  As the leaf is rich in nutrients, it is a source of nutrition for many organisms - other than the tree.  Oak trees are said to support over 2000 species, ranging from mammals, birds, beetles, spiders, fungi - through leaf-based food chains.  Leaves also support many micro-organisms through the detrital food chain (the decomposition of leaves in the litter layer and the soil). We do not eat many tree leaves, though some do make their way into our diet.  For example, the evergreen shrub Camellia sinensis is widely grown in many parts of the world for the production of tea.  The young leaves can be picked in spring and dried to make tea.  Leaves of other plants are used in various herbal infusions or for flavouring such as bay, sage, oregano, thyme etc. The fact that leaves are attractive to so many herbivores means that trees (and other plants) take measures to protect themselves. Some measures are physical - such as spines, thorns, prickles etc.   But when is a thorn a thorn, rather than a spine or a prickle?  These terms are used casually and interchangeably.  Botanically speaking, they are all ‘spinose structures’ that is hard, rigid extensions or modifications of leaves, roots, or stems - all of which have sharp, stiff ends and all have the same role - to deter animals from eating the plant that bears them.  Plants that bear sharp structures that deter herbivory are termed spinescent.  There are differences between these various ‘structures’. thorns are derived from shoots (they may be branched or not, may or may not have leaves). The thorns of Hawthorn (Crataegus monogyna) can bear leaves. spines are derived from leaves (they may be formed from all of the leaf or just part of it and like thorns they have vascular tissue*) prickles are derived from the epidermis (the outer layer of cells of a stem, root or a leaf).   Prickles may be found almost anywhere on a plant and they do not have vascular tissue inside.  Wild lemon and lime trees (Genus: Citrus) have spines, which protect young plants and indeed the fruits. The defences on roses are often described as thorns, but they are prickles, as they do not have vascular tissue (xylem and phloem) inside them. Sometimes, the leaf epidermis forms smaller, ‘simpler’ physical barriers called trichomes.  These are outgrowths of epidermal tissue but generally consist of only a few cells which form a defence against small insects.  Equally, a thick,  waxy cuticle on a leaf may be something of a deterrent to smaller insects. Leaves sometimes form ‘teeth’ on the leaf margins and leaf apices.  A classic example of this is seen in Holly.  Holly leaves that develop at ground level are wavy, with large triangular ‘teeth’, bearing spines.   As the tree grows and holly can reach up to 80 feet,  the leaves become less spiny. The spines offer protection against grazing animals at the lower levels but are no longer needed when the trees reach a certain height. While physical defences such as spines, prickles and trichomes can deter various herbivores,  chemical defences may also be deployed.  Chemical defences can take different ‘forms’, such as  [caption id="attachment_28705" align="alignright" width="300"] Oozing latex - Euphorbia[/caption] tannins and phenolics. These create an bitter taste, they are complex polyphenols built from several phenolic molecules. Tannins are common in leaf tissues - particularly in the cells on the top surface of a leaf.  Scale leaves of buds are often particularly rich in tannins, reducing  the palatability or "tastiness" of the tissue thereby offering protection from herbivores.  Alkaloids are again usually bitter tasting compounds -, many of them derived from amino acids. Glycosides, as the name suggests, contain a sugar that is joined to another chemical, such as cyanide (as seen in bitter almonds (amygdalin). Another possibility is that leaves may emit chemicals (aka VOC’ volatile organic compounds, scents, aromas) that deter insect visitors, or if a leaf is under attack by a insect pest then a leaf may release a VOC to ‘warn’ nearby plants of the attack so that they produce chemicals that make the leaves distasteful. How long a leaf lives is incredibly variable, it may be eaten within days of its formation, it may last till autumn or it may last for years.  Many trees of temperate climes are deciduous, that is they shed their leaves come the shorter days of autumn.  The advantage of this is that the tree offers less resistance to the winds of winter, so is less likely to suffer physical damage (also true of snowfall).  The tree enters a state of dormancy until spring.  If in spring the tree produces flowers before the leaves (like Blackthorn) this  can facilitate wind dispersal of the pollen.  However, losing leaves each year means that their nutrients are either lost or have to be moved out and stored somewhere else.  Having longer lasting leaves means that nutrients are retained, which is a distinct advantage in a nutrient poor, harsh environment.  The longest lived leaves are found in a plant of the Namib Desert : Welwitschia.  This plant has two leaves throughout its life of some two thousand years.  The leaves may reach a length of 4 metres, the ends die or get worn away but the base generates new tissue.   Welwitschia is a type of Gymnosperm. Image (with thanks) by Nhelia from Pixabay  

According to the United Nations, a forest is anywhere that is at least 20% trees.  As 21% of our capital city, London, lies under the canopy of trees - it is an urban forest*. It is estimated that there are some 8 million plus trees - nearly as many trees as people.  London is not alone, Johannesburg is a densely wooded city with some 6 million trees, planted throughout the streets and private properties. Tree Cities of the World is a programme that recognises cities and towns committed to ensuring that their urban forests and trees are properly maintained and  sustainably managed. Urban environments can create difficult conditions for tree growth and development. The trees may be exposed to pollutants, high temperatures (heat island effect), drought and/or flooding, and challenging conditions for growth. . Whilst trees may be planted, their subsequent care / nurturing may be limited due to insufficient resources (money / care etc).  There needs to be long term maintenance to sustain not just healthy trees but also to make sure that the trees do not damage pavements / roads etc (for example, through root penetration).   Trees for Streets is a new national tree sponsorship scheme that some councils have partnered with, which gives local residents the chance to have a tree near them or in a local park.   It is a project run by the charity Trees for Cities which aims to support local communities in revitalising forgotten spaces, planting trees and improving the local environment. [caption id="attachment_39418" align="aligncenter" width="675"] Greenery in SE London. View towards St.Helier's hospital.[/caption] In the past, London was a much smaller city surrounded by countryside and woodland, but there are still areas of ancient woodland within it.  Some of this woodland remains such as the Great North Wood in South London (hence Norwood and Forest Hill). Other place names - Wood Green, Forest Gate, Nine Elms and Burnt Oak bear witness to the wooded landscape that was once prevalent across London. In fact, some 8% of London’s area is still woodland, and some of it is even defined as ancient woodland (e.g. Epping Forest). [caption id="attachment_39421" align="aligncenter" width="675"] Dulwich Park[/caption] There are also the many parks of London - Hyde Park, Regent’s Park, Richmond Park, Dulwich Park etc.  Add to these the trees found in school fields, private gardens, squares (like Berkeley and Portman Squares), plus the trees that line so many streets (estimated at 900,000).  Trees (like sycamore and buddleia) have also colonised areas of the built environment,  like railway lines / cuttings.  The most common London trees are sycamore (7.8%), oaks (7.3%) and birch (6.2%). However, the urban forest has a wide spectrum of species that includes native species, such as  ash,  hawthorn,  hornbeam,  field maple and  holly,  but there is a wide variety of exotics and cultivars in parks, streets and private gardens.  In some parts of the capital, the London Plane is a noticeable presence, due to its resistance to pollution and tolerance of root compaction. It sheds 'large flakes' or sections of its bark exposing new material of a variety of colours (brown, grey, yellow), and is sometimes described as ‘self cleaning’.  The London Plane is thought to be a hybrid of the American sycamore and Oriental plane.  So the urban forest is quite diverse in terms of species when viewed across the capital, but there are parts of the city where species diversity is poor and the age profile of the trees is sometimes limited.  This homogeneity can favour pests and disease.  Diversity generally favours to resilience.  Currently, trees face diseases such as acute oak decline, Chalara ash dieback, horse chestnut leaf miner, Massaria disease of plane and oak processionary moth.   London’s urban forest faces an increasing human population and the challenges of climate change.  The latter may bring substantial warming and changing rainfall patterns. Wetter, milder winters and drier, hotter summers may be more common in the coming decades. Some trees will be better able to cope with these changing conditions.  Future planting will have to follow the maxim of “right tree, right place”. The value of London’s forest is difficult to quantify or to put a figure on. It is a major part of the ‘green infrastructure’ – that is the matrix of green spaces, parks, recreation grounds, lakes, canals, and rivers plus the street trees , green roofs and allotments that provides a range of economic, environmental, and social benefits. The importance of green, leafy spaces came to the fore during the early days of the Covid pandemic, helping with mental and physical wellbeing of Londoners.  [caption id="attachment_27166" align="alignleft" width="300"] Mature oak in park.[/caption] The components of the forest offer valuable habitats for wildlife and also provide biological corridors /  stepping stones that enable birds and various animals to move through the urban environment. The ancient woodlands and veteran trees offer a home to a variety of wildlife such as bats, stag beetles, orchids etc.  In recent heatwaves, people have appreciated that trees also provide shade and cooling in streets and parks. Another aspect of extreme weather is very heavy rainfall, trees and green areas can help reduce the risk of flooding, allowing more water to enter the soil rather than running off hard surfaces of tarmac and concrete.   Trees also help capture pollutants, improving local air quality by capturing fine particles from the air (much of this is through deposition on leaf surfaces).  One source suggest that trees remove some 2241 tonnes of pollutants each year.  Trees and shrubs seem particularly effective in removing ozone, and through its photosynthetic capacity the urban forest can take up carbon dioxide into organic form. The amount of carbon taken up by London’s urban forest each year has been estimated at 77,200 tonnes. To maintain and augment this urban forest, it is important  in the coming years that the threats of pests and diseases are fully assessed and controlled  The threats arising from climate change are recognised / mitigated Woodlands are properly managed (eg. coppicing); this may include the training of personnel. Create opportunities for planting of trees, hedgerows and woodland. [caption id="attachment_39422" align="aligncenter" width="675"] Tree nursery - 'ready for planting'.[/caption] * https://cdn.forestresearch.gov.uk/2022/04/21_0024_Leaflet-CC-factsheet-Urban-forests_wip06_Acc.pdf