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.

Deer are eating out the bottom of our woodlands and wildlife is suffering.  Although the size of the national deer population is not known for sure it is probably at its highest for a thousand years. There may be as many as two million deer in the UK’s countryside. There are several types, such as the two native species, being the Red deer (Cervus elaphus) and the Roe deer (Capreolus capreolus) - which is the most populous of the larger deer being, perhaps, 500,000 animals. Then there are the ones the Normans introduced, the Fallow deer (Dama dama) with a population of at least 150,000. On top of that there are three species of deer which have been introduced from the Far East including the Sika deer (Cervus nippon).  The other two from China are very different - there are relatively small numbers of the Chinese Water deer (Hydropotes inermis), whereas there are probably hundreds of thousands of the small and mostly nocturnal Muntjac (Muntiacus reevesi). They are all hungry and they all love woodlands. Most people believe the deer population needs to be controlled, or even reduced in number, but the range of species makes that harder to do. If you reduce the population of one type of deer the others will expand their numbers. Culling, or shooting, is certainly helping but stalkers are usually only interested in the larger species with enough meat to make it worthwhile and this leaves the muntjac space to thrive. Here is a film we made of a Scottish deer stalker explaining her job and how her stalking helps with environmental management: [embed]https://www.youtube.com/watch?v=ISh2sN-Ljy8&ab_channel=WoodlandsTV[/embed] Megan: “99% of stalking is looking through the binoculars.” Other ways of controlling the deer population are fencing them out but that is expensive and unlikely to work in the large open areas of the British countryside such as the moors and the uplands. Another potential method of control is introducing predators such as lynx or other larger hunting species. This meets some resistance from the public and the unintended consequences are that the predators might well go after different species altogether and occasionally humans. Most work is going on with contraceptive solutions so that the birth rate is reduced and less killing or culling is needed. This is also being researched for controlling populations of wild boars and grey squirrels to keep their numbers in check. It means getting the drugs to the target species and usually to the females which is often done through their foodstuffs, using food hoppers which are designed to be only accessible to that species. Other approaches include sterilization through injections and the Deer Initiative partnership has done a lot of work on examining different methods of biological control of deer numbers: https://www.thedeerinitiative.co.uk/pdf/contraception-and-wild-deer-control.pdf It’s not easy.  Even if one of these methods works, it will require an enormous effort to cut deer populations particularly of the smaller and more evasive species such as the muntjac. What do you think should be done? Meanwhile , deer are dangerous to motor cars.  The British Deer society estimates that annually there are between 40,000 and 70,000 accidents involving deer and this leads to about 700 human injuries, and far more deer fatalities!. So, in short, an overpopulation of deer is a large and growing problem: they damage the flora in woodlands, they eat young saplings, they compete with other mammals for space, they eat farmers’ crops, they carry ticks and they cause road accidents. The challenge of controlling the deer population is very real.

Many trees emit a scent or fragrance.  They form volatile organic compounds (VOC’s), often oils.  Pine trees, for example, release pinenes. Such VOC’s contribute to the smell that you may experience as you walk through a woodland.  The VOCs contribute to the formation of aerosols.  An aerosol is a ‘mixture’ of very small particles (solid or liquid) in air; other examples of aerosols include mist, cigarette smoke, or even car exhaust fumes!  Recent research by the University of East Finland has showed that aerosols formed from VOCs can reduce the amount of solar radiation that reaches the earth’ surface, by scattering some of the radiation back into space.  [caption id="attachment_40200" align="aligncenter" width="532"] Felling in progress[/caption] Pine trees are often grown in vast numbers and periodically felled for timber and paper making.  One by-product of paper-making (by the Kraft process) is turpentine - formed by the condensation and collection of the volatile oils in the wood). The pinenes (α and β) are major constituents of turpentine.  ‘Turps’ is used as a solvent to thin oil-based paints, for producing varnishes and as a ‘raw material’ in the chemical industry.  α-Pinene was used to make toxaphene (an insecticide, now banned).  Pinene can also treated with acetic acid to make a perfume with a pine needle smell. Recently a team of scientists at the University of Bath have found a new use for the by-products of paper production.  Using pinene from turpentine, they have been able to make a number of pharmaceutical compounds that can then be made into the painkillers - paracetamol and ibuprofen.  They have also successfully made other chemicals from the plant based turpentine, including compounds that may be used to synthesise `beta-blockers (heart tablets) and salbutamol (used for asthma).   At present, many pharmaceuticals and other chemicals are ultimately derived from crude oil.  Hopefully, this research will ultimately lead to a more sustainable and ‘green’ approach to drug / pharmaceutical manufacture. Biochar is the black residue, consisting of carbon and ashes that remain when plant biomass is subject to pyrolysis - that is, very high temperatures with very little  or no oxygen present oxygen. The material that remains is largely elemental carbon.  The benefits of converting plant biomass into biochar is that the carbon is ‘locked up’, rather than being released by decay and decomposition into the atmosphere as carbon dioxide.  Its advocates claim that when added to soil, it improves soil structure and function, as well as being a form of carbon sequestration.. [caption id="attachment_40215" align="alignleft" width="300"] cocoa fruit[/caption] Various forms of biomass (woody debris, corn stalks) have been used to produce biochar, however, a novel method makes use of ‘discarded’ cocoa bean shells.  These are heated to a temperature in excess of 600oC, with no oxygen present.  This particular form of biochar is being produced in in Hamburg. The plant, which is one of the largest in Europe, receives a supply of used cocoa shells viably a network of grey pipes from a neighbouring chocolate factory.  Apart from its use as a fertiliser, it is possible that it might be used as an ingredient to create a ‘green’ (or more environmentally friendly) form of concrete. The sequestration of carbon is vital if we are to avoid the worst effects of climate change.  Global warming has triggered an increase in heatwaves, floods, droughts, and forest fires in recent years; June temperature data confirms it was the planet's hottest on record. Cocoa fruit : courtesy of Pixabay.

As society and industry have become increasingly aware of environmental damage, so there has been a growth in the search for sustainable practices, for example, switching from oil / coal based power generation to wind and solar power.  Now various industrial processes are looking to use natural and sustainable materials that cause less environmental damage, by making use of ‘green chemistry’. The leather industry (worldwide) make extensive use of chromium salts in the tanning process.  The object of the tanning process is to change animal hide into a leather that is resistant to microbial attack.  Chromium (III) sulphate is an effective and efficient tanning agent, forming compounds that interact with a protein (collagen) in the animal hide.  However, certain chromium (VI) compounds are hazardous if released into the environment.    Whilst chrome tanning is faster than vegetable tanning and produces a stretchable leather suitable for handbags and garments, research and thought are now being given to the greater use of vegetable tannins, using plant waste material.  Tannins are produced by many higher plants, indeed the bark of many trees, such as Oak, Chestnut, Acacia and Eucalyptus are rich sources of tannin. Tannins bind to the collagen in the hide so it becomes more resistant to bacterial attack. In a living tree, tannins serve to defend the tree against microbial attack and to dissuade herbivores (from insects to mammals) from eating the plant material - because of their bitter taste. Recent work has shown that waste material (bark) from Acacia nilotica (the Gum Arabic tree) and Eucalyptus globulus (Blue Gum tree) is rich in tannins and can be used commercially for tanning in the leather industry, and is a relatively eco-friendly process.  The process of reusing, recycling or composting waste materials and converting them into more useful products (materials, chemicals, fuels or sources of energy) is sometimes referred to as waste valorization. “Waste-to-energy” scenarios are becoming important as resources are depleted, and waste production and disposal  are increasingly problematic Eucalyptus image(above left) by sandid from Pixabay

The Gloucestershire Wildlife Trust has spearheaded an initiative to introduce Pine Martens to the Forest of Dean. Some 35 Pine Martens have been released into the forest, between 2019 and 2021.  They have produced litters each year, and there is now thought to a population of some 60 animals.  Pine Martens have two or three ‘kits’ (young) a year.   At one time, Pine Martens were common across the U.K. but the loss of their natural habitat (forest and woodlands) combined with hunting has reduced their presence to remote areas in the North and West. Now, they are a protected species; it is illegal to kill, disturb, sell or possess a pine marten.  Scotland’s population is estimated at 3700 adults.  In the Galloway Forest, the numbers of adults and young are being monitored with thermal imaging cameras.   Pine Martens enjoy a broad diet, ranging from small mammals, insects, eggs and wild fruits - eating that which is most abundant.  They will prey on grey squirrels, and there is the possibility that this may help red squirrels re-establish themselves in more southerly areas.  Forestry and Land (Scotland) have placed artificial pine marten dens in areas where there are red squirrels.  The boxes (with wood shavings to encourage nesting) are placed some 4 to 5 metres off the ground.  The Yorkshire Arboretum has just constructed a special enclosure and introduced a small population of red squirrels.  The enclosure is designed to keep Red Squirrels in and Grey Squirrels out. Two of the females have just produced four kits (young). The Gloucestershire Wildlife Trust is also involved in the Severn Treescapes project.  This is a scheme that involves significant tree planting to link the Wye Valley with the Wye Forest - to create a significant corridor of woodlands, hedgerows, orchards etc across the counties of Gloucestershire, Herefordshire and Worcestershire.   Woodlands TV has a video about the Pine Marten : [embed]https://youtu.be/20RS1M-U008[/embed]

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  

An obvious answer to this question would be - caterpillars.  But when did butterflies first appear?  There are now some 160,000 species of moths and butterflies -worldwide.  Seemingly, they appeared some 100 million years ago  - in North America.  They evolved from nocturnal moths in the period when flowering plants were undergoing a major expansion (in the Cretaceous period).  Butterflies may have become diurnal to avoid predation by bats, or it may have been to take advantage of nectar production and availability [using the proboscis]. The butterflies and their caterpillars were able exploit the diverse range of food resources that these ‘new’ plants offered.  Butterflies moved out from North America to South America and then on to other parts of the world, though they probably did not arrive in Europe until some 17 million years ago. The evolutionary expansion of the butterflies has been investigated by researchers at the University of Florida; they analysed the genetic makeup of many species (from 90 countries).  They were able to build up a picture of the relationships between the various groups of butterflies and also determined their evolutionary point of origin.  They also catalogued the plants eaten by the caterpillars and it was found that some two thirds of butterfly caterpillars feed on plants from the legume family (the Fabaceae - peas and beans).  It is probable that the first butterfly caterpillars also fed on these plants. Research at the Georgetown University in Washington DC suggests that larger species of butterfly are ‘coping’ better with higher temperatures, associated with global warming.  Bigger wings seem to offer a greater range of movement and the opportunity to find new and suitable habitats.  Smaller butterflies are not faring so well.  The study involved an analysis of the range of some 90 North American species between 1970 and 2010, during which period the monthly minimum temperature increased by 1.5oF. Others have analysed the butterfly collections at the Natural History Museum, using digital technology.   The Natural History Museum’s British and Irish butterfly (and moth) collection is probably the oldest, largest, and most diverse of its kind in the world; some of the specimens date back over a hundred years The measurements of the various specimens were paired with the temperature that the species would have experienced in its caterpillar stage. It was found that for several species that the adult butterfly size increased as the temperature increased (during late larval stage). So, it may be that we will see a gradual increase in butterfly size as temperatures increase with global warming. Join the Big Butterfly Count ? Between Friday 14th July and Sunday 6th August , the big butterfly count will take place.   For full details visit : https://bigbutterflycount.butterfly-conservation.org/about Thanks to Angus for images.

Bumblebees (and bees) collect nectar and pollen.  Pollen is a vital food, used in the various stages of a bumblebee’s life. In Spring, newly emerged queens feed on pollen, then it is used to feed its their sister workers. The workers, in turn, take over the feeding of the colony (the larvae and future queens). If not enough pollen is collected, then the colony will not thrive, which can have significant long term effects.  Bumblebees are already facing many threats (from habitat fragmentation, agrochemicals and disease). The collection of pollen is a demanding process, and bumblebees will forage over a wide area.  They start their pollen collecting activities earlier than many insects as they can warm themselves up by ‘shivering’, that is, rapid muscle contractions which generate heat, warming the insects up ready for flight.  Bumblebees can fly in colder conditions and at higher elevations than many other insects. However, research at North Carolina State University has shown that the North American bumblebee (Bombus impatiens) can overheat when exposed to high temperatures (circa 42oC plus).  So,  if a bee is carrying a significant load of pollen and it is a hot day, its muscles have to work harder and the bee is at risk of overheating. A bumblebee loaded with pollen may be 2oC hotter than an unladen bee; it may be reaching its ‘thermal limit’ - a temperature at which its organs are damaged.  Climate change means that many parts of the world are now experiencing extreme weather events, when temperatures can reach into the forties. [caption id="attachment_39978" align="aligncenter" width="675"] Bumblee leaving foxglove[/caption] Increasing temperatures could affect the foraging activities of bumblebees in a significant way - affecting how much pollen is collected and how much pollination takes place.  If pollen collection is reduced then colony development is affected and so population numbers will be affected.  Bumblebees are key pollinators in natural and agricultural systems, and if their numbers decline there will be ecological and agricultural consequences.