Plants make use of sunlight in order to photosynthesise and grow.  However, not all wavelengths of light are useful to plants.  The red and blue wavelengths of light are absorbed by chlorophyll and used in photosynthesis.  Green light is reflected, hence we see green leaves etc.  Another component of sunlight is ultra-violet light.  Whilst UV light can help our skin manufacture vitamin D, it can also do considerable damage to the skin and cause premature ageing and skin cancers.  As this is the case, we are advised to apply sun screen to exposed skin as it helps prevent sunburn, skin cancer and premature ageing.  But what of plants?  Do they also protect themselves from UV irradiation / damage?  Some new research suggests that the plant cuticle has a role. The cuticle is usually a thin layer made up of fatty/waxy material that covers the outside (the epidermis) of the plant.  Its ‘primary’ function is a barrier to the evaporation of water from the underlying tissues.  It also prevents tissues becoming waterlogged as its ‘repels’ rain / water (see headline image) and it also resists the entry of pathogens / micro-organisms.  In most flowering plants, the cuticle tends to be thicker on the top of the leaf (aka the adaxial surface) which is exposed directly to incoming light. Though the cuticle is usually a thin layer, in plants living in arid environments, it can be quite thick to limit water loss. Since the waxy cuticle repels water (i.e. is hydrophobic), the adhesion of water to the cuticular surface is minimised so globules form.  Some plant leaves (eg. Nasturtiums and the Lotus) exhibit ultrahydrophobicity, so that they essentially become self-cleaning surfaces. Now, the rôle of the cuticle in protecting plants from UV damage is unravelling.  Research at the University of Malaga has shown the cuticle can quench UV light.  It does this though the phenolic compounds present in the cuticle.  Phenolics are rings of carbon atoms, with hydroxyl (OH) groups attached.  Examples are the cinnamic acids [e.g. p-coumaric acid]. When these molecules absorb UV light, they change shape momentarily.  On changing back to the original state, the absorbed energy is released but at a longer wavelength, which is far less damaging than UV light. As these molecules do not react this way to red and blue light, the red and blue wavelengths can pass into the leaf to be used in photosynthesis. [caption id="attachment_38494" align="aligncenter" width="700"] The leaves of some plants have quite amazing surfaces, some are hairy whilst others have protective spines.,[/caption]

Even if a tree looks healthy the trunk may be rotten to the core.  One day it will be vertical the next day suddenly horizontal and in falling it can kill people, crush cars and damage buildings.  So, knowing what's under the bark is really important.  Suspicion of rot might have been raised from a fungus, or a die-back of branches, or a hollow sound when the trunk is trapped.  In any event, it's one thing to suspect rot and another to know the exact extent of it and where it is, which is the problem that can be solved by a Sonic Tomograph, which is an ultrasound scan. The tree surveyor puts a series of nails into the tree in a ring around the outside - often about 40-90 cm above the ground - and he/she wires these up to the ultrasound.  The kit illustrated here is a PiCUS (named after the Latin for Woodpecker) made in Germany which can be carried in a small bag the size of a briefcase. For a horse-chestnut tree like this one with a diameter of about 2.5 metres the arboricultural surveyor needed ten nails.  Once these have been banged in through the bark, and the PiCUS wires attached to each one the surveyor then taps each one lightly with a special hammer and this sends sound waves through the trunk to each of the sensors attached to the other nails.  The PiCUS device will measure whether these sound waves are going through good timber, rotten timber or voids.  This then allows the computer to create a detailed and colourful picture of the trunk showing how much rot there is and where it's located in the cross-section. In our case the horse-chestnut tree, which looks fairly healthy, turns out to have rot covering 41% of the cross section.  Anything above 30% suggests the tree is unsafe and in this particular case the tree is overhanging a busy road and pavement so the whole tree will almost certainly need to be dismantled and replaced. Many of the sonic Tomograph surveys are done for local authorities and institutions to protect the public by reducing the risk of falling trees. A single tree only takes about 20 minutes to survey so there is good economy in doing several on each visit.  One official I spoke to said, "one reason we do these PiCUS surveys is so that neighbours and local people can see why we are cutting down trees that they love." The contractor here is Kim Gifford who is based in South East England and is on 07831 488456.  He's a very experienced surveyor and also spotted another rotten tree on his visit - a Tulip tree - which he surveyed and showed that it too needs to be cut down, sadly.  An alternative, in some circumstances is to take off the whole branch structure and turn the tree into a monolith, though in most circumstances it's better to eliminate the tree and start again with planting a new tree.

Mites and bees. Varroa destructor also known as the Varroa mite is a small, external parasite of the honey bee : Apis mellifera. It is a mite. Mites are small members of the arachnids (8 legged arthropods).  The mite(s) attaches to the body of the bee and feeds upon its fat bodies; this weakens the bee. The mite also feeds on bee larvae. Not only that but the mite can act as a vector (‘distributor’) for five different viruses that also weaken the bees.  The varroa mite originally was to be found in Asia, and was parasitic on the Asian honeybee, Apis cerana.  Sadly, it has now spread to many countries and is responsible for significant infestations of European honeybee hives.  Over time, the mites have become increasingly resistant to chemical treatments. Now a program / study by the Universities of Exeter and Louisiana has been selectively breeding bees that identify and remove mites from their colonies [ie. showing hygienic behaviours].  They do this by removing infected larvae from the colony.  This is sometimes referred to as varroa sensitive hygiene.  Such colonies showed significant reduction in mite numbers and were more than twice as likely to survive winter as compared the ‘standard’ honey bees. The colonies also had reduced levels of three honey bee viruses The study looked at bee colonies across three American states, including California.  In the States, beekeepers move thousands of bee colonies to provide pollination services for many different fruit crops (e.g. almonds) in the Spring, thus winter survival of the colonies is vital. Historic rainfall records. was launched in March 2020 (during the 'first stay at home' / lockdown).  Members of the public were asked to help record digitally the information on pre-1960 weather sheets.  The Met Office archives had some 65000 sheets that contained the ‘scribbled records’ of thousands of weather stations/ weather recorders across the country.    Many of these sheets were the records of amateurs dating back decades, many before the foundation of the Met Office in 1854. One such 'recorder' was Lady Bayning of Norfolk, she was an early rainfall observer who took readings from 1835 to 1887.  Deciphering the idiosyncratic handwriting could not be done by character recognition software. However, the volunteers rose to the challenge and the task was completed in some 16 days. As a result, now the Met office has: Rainfall readings stretching back to 1836 Data from an increased number of rain guages  Identified the driest year on record - 1855 Identified the driest month on record February 1932 Identified the wettest month on record October 1903 Note : [The Met Office was founded by Robert Fitzroy, the captain of HMS Beagle, that carried Charles Darwin on his epic voyage around the globe. Fitzroy essentially established the science of weather forecasting] Trees on the move ? We know that trees can ‘move’.   They did so at the end of the last Ice Age (some 12,000 years ago).  As the glaciers retreated so trees started to return to the newly exposed soils as the temperature warmed.  The discovery of the remains of acorns in archaeological digs, and analyses of fossil pollen records indicates that even oaks colonised areas of the UK at the rate of nearly a kilometre a year.   Similarly, Norwegian Spruce colonised areas around the Baltic Sea and the boreal forests grew and expanded - long before humans arrived there.   Now we have warming temperatures as we have moved into the Anthropocene.  In order to survive changes conditions, plants, like us, have to move. So, like after the ice Age, plants and trees are on the move.  Scientists in California have calculated that as a result of global temperature changes, plants need to move northwards (or upwards) at the rate of 400+ metres a year.  In the eastern parts of the United States, it has been estimated that trees were shifted north and westward at a rate of 10 / 15 km per decade.  The conifers going north. Whilst oaks and birches going west.  In Scandinavia, which has experienced significant aspects of global warming, birch saplings are now found higher up mountains, gaining 500 metres in elevation within two decades.  Pines, spruces and willows are also growing at higher altitudes than previously.  Similar colonisations of  hillsides and ‘bare valleys” are seen in Alaska of alder, willow and dwarf birch. Further information here [caption id="attachment_38737" align="aligncenter" width="700"] Busy bee[/caption]

How many trees are there in the world? When Thomas Crowther and Henry Glick used geospatial data in 2015 to estimate the number of trees in the whole world there was good news and bad news. Good news that there were several times as many trees as anyone had previously realised (total is about 3 trillion) and bad news that the number was declining faster than expected.  The calculation was done partly to establish a baseline so that tree-planting efforts could be put into perspective - the UN's Billion Tree Campaign managed to plant about 15 billion trees over 10 years in virtually all countries across the world (193).  But whilst these numbers sound large this has only added 0.5% of trees so much more needs to be done if we want to reduce the damage humans have done to tree numbers - before humans emerged there were about twice as many trees as there are now.  Perhaps that's why the Trillion Tree Campaign was launched in 2018 in Monaco - a principality covering only two square kilometres and almost bereft of trees. More locally, the UK has a tree count of about 3 billion trees - about 45 trees per person - calculated by analysing aerial photos and estimating tree numbers as was done under the UN's Plant for the Planet project.  There is some flexibility on the definition of what counts as a tree - and this assumes you don't count all the self-sown seedlings or bushes, which some might consider as trees.  This number is dominated by a few species - of the commercially grown plantations in Scotland, for example, 60% of the trees are Sitka Spruce so they don't add as much to biodiversity as a wider species mix would do.  And those 45 trees per person is a bit misleading in that there may be nearer to  400 trees per person in Scotland  - it is more sparsely populated with less than a tenth of the UK's population but almost half the trees. The UK's tree-planting is put into perspective by comparing the relative numbers - the UK's 3 billion trees amounts to one thousandth of the global total whereas nearer to 1% of the world's population is British - so by comparison with the world's average, on a per-person-basis a Briton has a tenth as many trees as the average citizen of the world.  The most densely tree-ed parts of the world are the tropics where 43% of the world's trees are growing. At a recent general election (2019) the political parties were competing to promise how many new trees they would ensure were planted - the Liberals and SNP each promised 60 million a year, whereas Labour said they would do 100 million every year.  A more realistic Conservative party promised 30 million trees every year which would equate to about 15,000 hectares (or 6,000 acres).  Despite this lower manifesto promise, the government is really struggling to achieve even that amount - but if they did reach that target every year for 10 years it would add 10% to the UK's tree cover. There is ample scope for more trees with the UK having only 13% tree cover, but are there are other ways to increase the numbers beyond tree planting? Trees will naturally establish themselves if they are not cut or grazed - perhaps one thing the government could do would be to reduce the number of wild grazers - mostly deer and sheep.  

Occasionally, there is a blog about Mistletoe, it tends to be around December and Christmas. It is a plant associated with that time of year.However, mistletoe* is botanically  interesting as it is a hemi-parasite.  It grows on other plants - notably apple, blackthorn, lime, willow and poplar.  It has evergreen, smooth-edged, oval leaves so it can photosynthesise, making sugars and other complex organic compounds.  However, it relies on its host plant for water and mineral salts.  It ‘hijacks’ water and minerals by forming ‘clamp-like’ connections (known as haustoria) with the xylem (water conducting tissue) of the host. Mistletoe produces its characteristic white berries (known as drupes) during the winter months. Within the flesh of the  berries are the seeds.  The berries are often taken by birds and as the tissue around the seeds is sticky, the bird will often try to scrape off a seed sticking to its beak by ‘wiping’ the beak against the bark of a tree. The stickiness of this material probably helps stick the seed to a host.  The sticky material is fibrous and is known as viscin (the scientific name for mistletoe is Viscum album).  [caption id="attachment_38403" align="aligncenter" width="600"] slightly dehydrated Christmas mistletoe berries[/caption] Now viscin is being investigated in depth for its adhesive properties.  Each berry can produce some two metres of the sticky viscin fibres, and when wet these can be processed to form thin films.  It may be that it can be used as a wound sealant or skin covering.  Seemingly viscin can stick to almost anything, not only natural materials from wood, skin and feathers but also plastic, glass and metal alloys.   [caption id="attachment_38404" align="aligncenter" width="560"] 'Balls' of mistletoe[/caption] Research into viscin has been initiated at McGill University and the Max Planck Institute of Colloids and Interfaces.  It may be that it will offer a new type of adhesive that is biodegradable and biorenewable. Mistletoe is a member of the Santalaceae, which includes the sandalwoods,

Every year humans release 40 billion tons of greenhouse gases (like methane) and carbon dioxide (CO2) into the atmosphere, something that needs to change if we’re going to stop the effects of climate change from worsening. As we all learned in science class, trees remove carbon from the atmosphere during photosynthesis, making planting them an excellent way to offset our carbon emissions. The carbon offset of one tree (at maturity) can be up to 22lbs per year during its first 20 years of growth, meaning a hectare of trees removes between 5 and 45 tons of carbon in the same timespan.  In England, the government plan to plant 180,000 hectares of trees by the end of 2042 as a means of reaching their goal to become carbon neutral by 2050. The question is, where should these trees be planted and how can the public help to reach this target by planting trees themselves? Right tree in the right place In the coming years it might be tempting to encourage, on an individual and national level, as much tree planting as possible in order to backtrack the effects of climate change, but tree planting needs some consideration in order to offset carbon emissions, taking into account which species, or combination of species, can store the most carbon and which areas are the best for planting. There are certain places where trees shouldn’t be planted, not just because they might interfere with our homes and infrastructure, but because planting trees in these areas could actually have a negative carbon impact. One example of this is Scotland’s peatlands, which hold 20 times more carbon than the UK’s forests; planting trees in these areas would necessitate their draining, and result in more carbon being released than the forest planted would be able to absorb.  [caption id="attachment_34388" align="aligncenter" width="650"] Stream flowing through peat moorland[/caption] Instead, trees should be planted in areas where they will benefit the surrounding area and be able to store the most carbon. Luckily there are lots of low-risk areas available for planting trees to offset carbon in the UK, such as low-quality agricultural land, marginal land or existing forests that are under managed. Around 1/3 of carbon sequestration needed for the country to become carbon neutral by 2050 could come from improving the management of existing forests by encouraging carbon storage and resilience in existing trees and helping younger and better trees to thrive.  Planting trees on agricultural or ex-agricultural land can have similar benefits. [caption id="attachment_38247" align="aligncenter" width="675"] Carbon impact of tree planting[/caption] Urban tree planting There are also potential benefits to afforestation and tree restoration in urban areas. Global warming has come with the rise of urbanisation, causing tree coverage to become sparser in urban areas. As trees have a cooling effect, cities have become hotter, developing ‘heat islands’ where roofs and dark construction materials absorb solar energy and radiate it back. Planting trees in areas with asphalt can reduce this warming, and provide more shade and water. Afforestation to reduce air pollution is an effective strategy in urban areas, as trees absorb pollutants.   Be aware that certain species, such as Eucalyptus and Pines, emit high volumes of volatile organic compounds (VOCs) in particular environments, such as when combined with high temperatures and high nitrogen oxide concentrations (i.e. urban centres), so can contribute to the formation of ozone and carbon monoxide.  Tree planning in urban areas should prioritise increasing the number of low-VOC emitting trees and those with long life spans that require minimal maintenance.  Which species to plant? No matter where you’re planting trees, planting native species is often encouraged; those which have been a part of the UK ecosystem for thousands of years.  In the UK broadleaf species are native, and some species, such as oak and beech, have huge carbon storing potentials as they grow slowly, locking in significant volumes of carbon over time. Though some tree planting schemes have favoured faster growing trees like Sitka Spruces (as these will offset carbon more quickly), they may not yield such long term benefits over a longer timeframe.  An important factor is not how fast a tree grows, but how much carbon it’s able to store when it reaches maturity.  It is also important to grow a diverse range of tree species in order for a forest to be efficient at offsetting carbon. Biodiverse forests store twice the amount of carbon as monocultural forests, so growing a combination of species such as broadleaves and Sitka Spruce will allow for more carbon to be fixed; with each tree species introduced to an area, there is an increase in 6% of its total carbon stocks. Different species grow at different heights and speeds, so this will provide more tree coverage and have short and long term carbon offset benefits, as well as providing habitats for a larger range of animals and improving the soil and climate conditions.  [caption id="attachment_38248" align="aligncenter" width="675"] Carbon impact of tree planting[/caption] Get planting! As you can see, planting trees has great potential to offset carbon emissions, but where we plant trees and what types of trees we plant defines just how effective trees can be at storing carbon. Whether you’re planting trees in your back garden or buying land to plant trees, it’s worth considering which species of tree you’re planting and whether the land is suitable for planting, ensuring the project has the best chance possible of removing carbon from the atmosphere!

The pollen forecast across much of SE England this week is very high, according to the Met Office.  Pollen is the ‘powdery material’ produced by higher plants (angiosperms and gymnosperms). It is made up of individual pollen grains, which are produced in the anthers⚘.  When these anthers split open, the pollen grains are released and move by means of the wind or insects to the female reproductive structures (style and stigma in flowering plants, or the female cones in conifers etc).  If a pollen grain lands on a compatible stigma or female cone*, it germinates - producing a pollen tube that transfers the male gamete to an ovule within the ovary. Individual pollen grains are small enough to require magnification to see any detail.  A pollen grain has two layers : The outer layer of the pollen grain is called the exine and is made of a material called sporopollenin. This is a polymer (long chain molecule) made up of various organic molecules; it does not degrade easily. In fact, it can exist in the soil and sediments for hundreds if not thousands of years. The persistence of this outer wall of pollen grains enables scientists to identify species that were present in various sediments formed thousands of years ago. Under the electron microscope the exine has a sculptured, almost ‘sci fi’ appearance - with ridges, groves, spikes, and distinctive patterns across its surface - which are unique to each species.  The inner layer of the pollen grain is the intine. It is made from  pectin and cellulose; it has a role in the germination of the pollen tube. Wind dispersal of pollen is referred to as anemomophily.  Anemophilous plants, like the grasses, generally produce large quantities of lightweight pollen. This is because wind dispersal is random and the likelihood of any one pollen grain landing on another compatible flower is remote, but the probability is increased by there being large amounts of pollen. The individual flowers of anemophilous plants are often small, inconspicuous but may collected together into significant structures (think pampas grass).  The pollen of insect pollinated flowers is relatively heavy and sticky (often protein-rich). The hind limbs of bees and bumblebees are modified for the collection of pollen - the pollen baskets or corbiculae.  Each corbicula is a cavity surrounded by a fringe of hairs into which the bee places the pollen.  Apart from this collection of pollen, pollen may be seen sticking to the hairs / the surface of a visiting insect. [caption id="attachment_24330" align="aligncenter" width="600"] Bumblebee dusted with pollen[/caption] [caption id="attachment_38370" align="alignleft" width="300"] Grass inflorescence - with protruding stamens[/caption]   Whilst pollen is generally harmless, there are some pollens which really ‘get up your nose’ - specifically Tree pollen, from trees such as Birch and Lime Grass pollen, from ryegrass and timothy “Weed’ pollen, from ragweed, mugwort, plantain, fat hen These various pollens can cause allergic reactions when inhaled and the body’s defences are alerted.  The defence reactions may include, sneezing, a runny nose, watery / inflamed eyes.  Tree pollen tends to peak earlier in the year than grass pollen.  Grass pollen is probably the worst offender when it comes to ‘hay fever’ / allergic rhinitis.  The pollen calendar (courtesy of Kleenex) gives a seasonal guide to pollen by month and by area.   ⚘ Anthers are the pollen producing tubes / sacs at the end of the filaments.  Anther plus filament = stamen. * Conifer pollen grains often have air ‘bladders’ which help with the ‘bouyancy’ of the grains so they are easily dispersed in the wind.]  [caption id="attachment_38360" align="aligncenter" width="700"] stamens that have released their pollen[/caption]   Pollen grain image, thanks to Open ClipArt on Pixabay.

The UK has 58 resident species of butterflies, according to Butterfly Conservation.  Sadly, approximately half are now under threat - being on the Red List of endangered butterflies.  The Red List has seven levels of conservation: least concern,  near threatened,  vulnerable,  endangered,  critically endangered,  extinct in the wild, and  extinct.  Butterflies and moths generally need : A source of food for their caterpillars. Sometimes, this is a single plant species but most species are not quite so ‘fussy’. Adults usually need a source of nectar - in the form of nectar; the sugar-rich liquid formed in the nectaries of flowers.  Again, some species have very specific requirements and will only visit certain plants.  Conversely, some adult moths do not feed at all !  For butterflies and certain day-flying moths, they need a place to warm up and fly, to bask in sunlight.  Caterpillars may need warmth in order to develop to maturity.  All invertebrates are ‘cold blooded (poikilothermic), taking their temperature from the surroundings. Eggs, larvae or adults need a place to spend the winter in ‘safety’, where they are not so vulnerable to predators or extremes of weather.  This often takes the form of taller vegetation, sometimes evergreen, like ivy.  Structurally diverse woodlands can also provide warm micro-habitats, shelter and breeding spots. There is some good news amongst the bad. Two species, the large blue and the high brown fritillary, have been subject to targeted conservation interventions and have now moved from away from critically endangered. The large blue, in fact,  was declared extinct in 1979 but was re-introduced with specimens from Sweden and is now to be found in Somerset and the Cotswolds on restored wildflower grasslands.  The high brown fritillary has also benefitted from conservation efforts e.g. creation of clearings and rides so whilst still vulnerable, its status has improved. Another positive is that the large tortoiseshell has reappeared (since 2019) in several locations in Southern England.  Its decline / loss has been associated with the loss of millions of elms (through dutch elm disease) on which caterpillars feed.  They can, however, be found on Aspen, Poplars and Willows. There are still concerns for some species with the loss of specific habitats, such as flower-rich chalk grassland (favoured by the chalk hill blue and silver spotted skipper).  It is thought that nitrogen pollution (from fertilisers and vehicles) may be a factor.  More nitrogen encourages more vigorous grasses which outcompete certain species of wildflowers (critical to caterpillar survival). On the moth front, recent weeks have seen the arrival of the striped hawkmoth.   This is a migratory species but it cannot survive our winters. Specimens of the painted ladies have also arrived on the prevailing winds.   These have travelled from sub-saharan Africa (by means of several generations) always moving in search of food.  The painted ladies can breed here during the summer months, making use of thistles, nettles, and mallows.  At trend of the summer, the painted ladies return to warmer climes, but they fly at such high altitudes that they are not normally seen.  Their migration was spotted by the use of radar, which can detect insects at heights of a kilometre or more.  It recorded painted ladies flying at a height of some 500 metres as they left the UK going south, again making use of favourable winds.