Stinging nettles grow in a wide range of natural habitats, river banks, swamps, meadows, wastelands, floodplains, disturbed areas and gardens. They are are particularly effective colonisers of disturbed, bare or ‘waste’ ground. They flourish in nitrogen-rich soils.  Their seeds can lie dormant in the soil for some five years (and can even survive soaking in salty water), plus they spread using their underground rhizomes. Nettles may not be the most friendly plants to us, as their leaves and stems are ‘armed’ with special ‘hairs’. The hair-like structures are termed trichomes and each trichome has a hollow tube-like structure. At the bottom of the tube is a swollen base, which is filled with a number of chemicals, (including histamine, serotonin, formic acid and acetylcholine). The tip of the tube is easily broken, leaving a sharp point that can penetrate the skin and deliver the ‘biochemical cocktail’. [caption id="attachment_7154" align="aligncenter" width="600"] Trichomes - loaded with their chemical 'cocktail'[/caption] [NB: there is a video on YouTube that shows this mechanism here.] This collection of chemicals gives the characteristic rash/inflammation of a nettle sting.  Nettles may be found near to dock leaves which, if crushed and rubbed where you have been stung by the nettle, may take away some of the pain. More detailed information on the chemistry of the 'chemicals' in the nettles can be found here.  The hairs / trichomes probably evolved as a defence mechanism to limit grazing by sheep, deer or rabbits. Despite their ‘weaponised hairs’, nettles are in fact very good for wildlife, particularly in urban / sub-urban areas.   This is also true in areas under intensive farming practices.  The spread of farming, urban sprawl, habitat fragmentation and pollution have all contributed to the loss of natural habitats (for plants and animals), and that’s without mentioning climate change. Stinging nettles are the food plant for the caterpillars of comma, painted lady, peacock, red admiral and small tortoiseshell butterflies. The presence of nettles in our gardens and urban areas has allowed these butterflies in. And it’s not just butterflies that rely on nettles. For example,  ladybirds often lay eggs on nettle leaves. This insect might be termed a “gardener’s friend” as it has a voracious appetite for aphids - greenflies and blackflies that suck the sap from plants, ravage the vegetables in our gardens / allotments, Some aphids spread plant viruses, for example, virus yellows on sugar beet. Having nettles in our gardens and near farms give ladybirds and other insects somewhere to shelter, ready to feast when the aphid population rises. Aphid populations can rise very quickly as females give birth to live young, without fertilisation. Nettles can be used to make tea, soup, flavour beer, wrap cheese (Cornish yarg) or make cloth.  Using nettle fibres to make fabric / clothing is a very old practice, dating back to the Bronze Age.  Nettles can also be used to dye fabric [caption id="attachment_34107" align="aligncenter" width="650"] stinging nettle[/caption]

Ragworts are a group of daisy-like flowers.  The flowers are actually composites, that is, they are made up of many smaller flowers held together in a structure called a capitulum.  The family of daisy-like flowers is known as the Asteraceae (previously called the Compositae).  There are several different species of ragworts, for example : Common Ragwort (Jacobaea vulgaris, previously Senecio jacobaea) Oxford Ragwort (Senecio squalidus)  Hoary Ragwort (Senecio erucifolis) Marsh Ragwort (Senecio aquaticus) Silver Ragwort (Senecio cineraria) Perhaps, the Common Ragwort and the Oxford Ragwort have attracted the most attention in recent times.  The story of the Oxford Ragwort is interesting. The plant is actually native to Sicily, growing on volcanic ash and scree.  It was grown in the Oxford Botanic garden around 1690.   After some years, it ‘escaped’ and could be seen growing around Oxford.  Later, with the advent of the railways, it was able to spread along the railway tracks and then across the country. The genetics of this plant and related species have been the subject of various research projects in recent years, and has resulted in the ‘reclassification’ of some ragwort species. However, it is the Common Ragwort (Jacobaea vulgaris, previously Senecio jacobaea) that has been the focus of much attention.  This is a native, biennial plant, but can be perennial. Its seeds are spread by wind and a single plant can produce thousands. Consequently, it can become a problem on waste land or other uncultivated areas. Ragwort may be seen in coppiced woodland,  particularly in the years immediately after cutting the coppice when there is lots of light and the ground flora 'comes alive'. The plant is a good food source for a wide range of insects and it is much 'loved' by pollinators.  Over a hundred insect species feed on its nectar  (bees, flies, moths and butterflies).  Not only is it a good source of nectar, it also provides a home and / or a food source for many invertebrate species.  Some insects feed on the ragwort exclusively.  [caption id="attachment_40185" align="alignleft" width="300"] Cinnabar moth caterpillar[/caption] One species that is particularly associated with this plant is the cinnabar moth, whose status is described as ‘common and widespread, but rapidly declining”.  The caterpillars are distinctive with yellow and black stripes. They feed on the ragwort absorbing its alkaloids, which make the caterpillars distasteful to predators.   Alkaloids are organic compounds produced by plants and many of them have potent medical uses - such as quinine (for malaria) or morphine (pain relief).  Most alkaloids have a bitter taste.  Many alkaloids are toxic (for example, atropine from the nightshade family of plants).  The alkaloids present in ragwort can make it a problem when present in fields / areas grazed by horses or cattle, though it is not usually a problem in gardens.  Horses do not normally eat ragwort due to its bitter tasting alkaloids but if consumed in any quantity then the alkaloids can cause liver damage (a form of cirrhosis). [caption id="attachment_40489" align="alignleft" width="300"] Tweet from Prof Goulson[/caption] Ragwort poisoning is relatively uncommon and may arise through feeding with hay that contains dried ragwort.  In U.K., the common ragwort is classed as an injurious weed under the provisions of the Weeds Act 1959, and there is the Ragwort Control Act 2003.  The latter provides for a code of practice relating to ragwort.  Removing common ragwort from an area is not without its problems.  Sometimes, other species are ‘identified’ as ragwort and sprayed with weedkiller.       Friends of the Earth have produced a ‘briefing’, which notes that Ragwort has been blamed for animal deaths which are unproven Scare stories have been based on poor or irrelevant statistics, and biased surveys Ragwort has been falsely labelled as a threat to human health / the countryside As a result, unnecessary measures have been used to control ragwort (in nature reserves or areas like the New Forest, and indeed roadside verges). The briefing, entitled  “Ragwort: problem plant or scapegoat?” which can be accessed here offers a number of solutions to the ‘ragwort problem’  

The honey bee, Apis mellifera, stores food in the form of bee bread. Bee bread is formed through the fermentation of a mixture of pollen, nectar and bee saliva.   It is 'inoculated' with a range of bacteria and yeasts that ferment the material after storage in the comb cells of a hive.  Bee bread is the chief protein resource for bees, particularly for the feeding of larvae [and adults].  As it is a nutrient-rich material, it ‘supports’ various microorganisms, despite its acidic nature and low water content. Bee bread is also coated with propolis.  Propolis (sometimes called ‘bee glue’) is a resinous substance collected by bees from tree bark and leaf buds. This resin is ‘chewed’, mixed with salivary enzymes and the partially digested material is mixed with beeswax.  It is an antimicrobial substance.  It is used by bees to seal holes in their honeycombs and help in the construction of the hive. The very nature of bee bread and the coating of propolis create a ‘challenging environment’ for microbes to grow and survive.   However, despite the ‘unwelcoming’ nature of bee bread, several species of fungi and bacteria form a microbiome within a hive, and are thought to play an rôle in the life of the bees. Recent studies have revealed that the fungus Aspergillus flavus is well adapted to survive in bee colonies.  A strain extracted from a hive was found not only tolerate low pH (which other strains of the fungus could not cope with) but could also deal with the low water content of bee bread, and with the propolis - which is thought to have anti-fungal properties.  Further work demonstrated that this strain of the fungus had mutations that allowed it to develop within the ‘bee bread environment’.  That this fungus can live with the bees suggests that there might be some form of mutual benefit to both fungus and bee, but the relationship (if there is one) is not as yet understood. Full details of this study can be found here  

Woodland covers some 1,000 hectares of the Ashdown Forest, that is roughly 40% of its area. Much of the woodland is relatively young. However, the forest’s capacity for regeneration / renewal is being damaged by overgrazing.  Local deer populations have grown and now represent a problem. Deer browse / graze on vegetation, shoots, flower buds and foliage are stripped off plants.  Young saplings are damaged and bark is eaten, especially when food is scarce.  Consequently, tree and shrub regeneration is limited.  Other species are affected by the feeding of the deer, either through loss of niches or food.  Among those at risk are small mammals and certain butterfly species. [caption id="attachment_34368" align="aligncenter" width="650"] deer damage[/caption] Damage is found in woodlands in many parts of the country, as deer populations have increased in recent times. In the 1970s, the deer population was estimated to be around 450,000 as compared to today’s estimates of over 2 million.  The National Forest Inventory highlighted that "40 percent of British forests have ‘unfavourable’ levels herbivore damage, which limits the survival of young trees and threatens biodiversity".  Apart from deer damage, there is damage by the grey squirrel populations. Deer browsing can : Prevent natural regeneration Affect biodiversity Affect woodland resilience Reduce food availability to the herd which can lead to starvation / loss of condition Deer are also hosts to ticks.  The ticks may be infected with Borrelia burgdorferi  bacteria and transmit them to humans, resulting in Lyme disease. Deer  also contribute to collisions with motor vehicles; more than 450 deer were hit by vehicles on Hampshire roads last year .  In Scotland,  government agency figures indicate that deer vehicle collisions  [DVCs] have almost doubled between 2008 and 2020.   Sadly, people are injured or killed in DVCs, and the repair cost to vehicles runs into millions. The solution to the ‘problem’ is not clear cut. Culling [the selective killing of animals] to control deer populations is one way in which numbers can be reduced, and the damage to woodland mitigated.  However, this approach has been met with opposition by many, including animal rights organisations.  There is the argument that whilst a reduction in deer numbers might fix some problems in the short term, the subsequent increase in plant growth and food availability might lead to increased breeding by the remaining deer and numbers would then increase again.  Also, unsuccessful or inaccurate shooting leads to animal suffering, mutilation and / or a lingering death.   Some might advocate rewilding and the introduction of apex predators (such as the wolf, lynx, wild cats*) as a means of reducing numbers but that might raise other problems! Deer have been 'part and parcel' of woodlands since mediaeval times, when the forests were used for hunting. In the Ashdown Forest, the number of red deer declined during the C17th,  and poaching was a factor in their decline. Fallow deer numbers also declined. [Fallow deer were introduced to England by the Normans around 1100 AD.]  The deer population roaming the forest has increased significantly in the recent decades, and now there are the relatively recently introduced species, muntjac and sika deer.   There are six species of deer in UK woodlands – the two native species, the red deer and roe deer and fallow, muntjac, sika and chinese water deer make up the four non-native species. The problem of over grazing is not unique to the Ashdown forest. For example, deer numbers in Scotland have doubled in recent years to almost a million since 1990.   Finding sustainable (and humane) solutions to the large numbers of deer is difficult. * Wildcats were once widespread in Britain, but by the end of the 18th century, they were to be found only in the northern regions. [caption id="attachment_34415" align="aligncenter" width="700"] Remnants of birch woodland near Loch Muick are subject to browsing by red deer (especially in the winter), so temporary fences have been put in place to allow for regeneration.[/caption]

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

The soil in many arid ecosystems (for example, savanna, deserts, & shrublands) is often covered by a thin layer of organisms, a community of lichens, mosses, liverworts, fungi, cyanobacteria and other microbes. They form a biocrust in the very top layer of the soil.  These organisms produce a variety of chemicals that glues together the soil particles.  Most biocrusts start of with a single type of organism (often a lichen or cyanobacteria, they are hardy). As these grow, they change the immediate environment so that others can then colonise the area so slowly the community grows.. The resulting biocrusts are important in helping reducing soil erosion and dust production.  Whilst dust can hold nutrients that will benefit plants as and when it is deposited, it can also have negative effects. Dust reduces water and air quality.  Dust storms can be truly massive and terrifying, for example, the 2009 Australian Dust storm. Occasionally, in this country we experience saharan dust that his been carried hundreds of miles on the wind.  If wind-blown dust lands on glaciers, snow or ice sheets then it affects the albedo.  The albedo is a measure of a surface’s ability to absorb and retain energy, or putting it the other way round, the ability to reflect heat / light energy.  Dark coloured objects tend to absorb more light energy than light coloured surfaces.  So if snow or ice becomes coated with dust, it will absorb more heat and may melt.   Biocrusts prevent many millions of tonnes of dusts entering the atmosphere each year.  It is thought that they may cover some 12% of the earth’s land surface.  Soil with a biocrust needs a far stronger wind before it starts to erode.  Sadly, like many other things, biocrusts are under threat due to climate change and shifting patterns of land use. [caption id="attachment_41261" align="aligncenter" width="675"] Church wall being colonised by Lichens[/caption] Biocrusts can also form on walls and buildings, for example, lichens and mosses colonise gravestones.  Whilst biocrusts have positive effects when they form on soils, it is thought that they can have deleterious effects on stone / brick surfaces due to the various organic acids and other chemicals that the colonising organisms can produce.  The production of these chemicals can degrade (weather) structures and lose their integrity / aesthetic appeal.   The Great Wall of China, which once stretched for some 8000+ kilometres, is protected by biocrusts in parts.  Construction of the wall started about. 200 BCE and continued (on and off) till the 1600’s CE.  Much of the wall has now been lost.  Some parts of the wall were made from stone and bricks (held together by sticky rice mortar). Other sections were constructed from ‘rammed earth’, made by compressing natural materials (eg. chalk, gravel, lime) with soil.  Some have regarded these sections of the wall as ‘weak points’.  Recent work by Bo Xiang and colleagues found that the ‘rammed earth’ sections were often covered by a biocrust, (of lichens, mosses and cyanobacteria).  This biocrust actually helps maintain the integrity of the wall by protecting it from wind and water erosion.  It reduces temperature extremes and the porosity of the wall, reducing infiltration and its water holding capacity.  All of these help maintain the integrity of these sections of the wall. If biocrusts are lost, through fire, climate change or human intervention then recovery can be problematic.  Organisms like cyanobacteria may recolonise a site quite quickly by organisms blowing in from nearby and undisturbed areas.  Full recovery of the crust and composition generally occurs more rapidly where the soil is fine  textured and moist. When the soil is coarse and dry then re-establishment of a biocrust may take hundreds or thousands of years. Thanks to Art for lichen image on church wall.  

‘Trees for Life’ and ‘Woodland Trust Scotland’ are trying to revive lost pinewoods, that once formed part of the Caledonian Forest.  This forest supported a rich and diverse flora and fauna, including serrated wintergreen, distinctive lichens, crossbills, capercaillie, wild cats and red squirrels.   After the last Ice Age, plant and animal species moved across the 'land bridge' that connected us with continental Europe.   Pines (Scots Pine aka Pinus sylvestris) were ‘quick’ to move into Scotland and the land vacated by the glaciers.  Now less than 2% of this once great forest survives. To find pockets of ancient and ‘lost’ pine trees, these two organisations have adopted a number of approaches. Making use of old maps and texts, for example, those produced by the Reverend Timothy Pont (a Scottish minister and cartographer) in the 1500s. He was the first to produce a detailed map of Scotland.  These can point to areas that were formerly populated by “fir trees”, ie pine. Examining Gaelic place names, which might reference woodland or pine trees. Using the original ordnance survey maps (which often had fir tree symbols) to produce digital copies, which can be overlain on modern maps - hopefully to reveal former woodland sites. Using ecological evidence.  For example, wild pine often grows with old birch trees, whereas planted pine is usually found with larch and other ‘commercial conifers’. Old pine trees often have a distorted shape, with thick, gnarled and twisted trunks; they survive in remote gorges and crags.  Areas that previously supported wild pine, often have old stumps still present and / or certain distinctive lichens / plants - remnants of once diverse ecosystem. Using these various techniques, dozens of lost pine woodland areas have been identified and located.  Much of the original Caledonian Forest was lost through felling (for timber and / or fuel) over the centuries.   Later came sheep farming and this was followed in Victorian times by deer and grouse shooting.  In the last century, commercial forestry resulted in the further loss of ancient woodland. However, restoration is possible.  Where some old trees have survived, there is often a seed bank in the soil and these seeds can germinate if the dense canopy of commercial conifers is removed.  Many pine seeds that do germinate are lost as seedlings due to grazing due to deer or sheep - who seem to prefer them to Sitka etc.  Hopefully as areas with pine grow on, so other species such as rowan, birch and hazel will develop and in time a ‘full’ woodland will develop.

Last week's woodlands’ blog talked about the fall in insect numbers across the UK.  This is not just a UK problem, it is far more widespread.  Insects,  bees and bumblebees as pollinators aside,  are important in ecosystems;  there are armies of other insects that are providing ‘services’ for us. When a tree dies in a woodland, bacteria and fungi are important agents in the decay of the tree and the recycling of elements, but they are assisted by beetles. If the dead tree was a veteran, during its lifetime it will have provided  a variety of micro-habitats.  Holes and crevices would have been used by bats,  birds,  insects etc.  Now, the the decaying wood will be support different organisms, from microbes to larger fungi, such as bracket fungi that can erupt from surface of the dead tree.   As the wood decays,  the material may become a ‘home’ for saproxylic beetles. For example, Stag beetle larvae feed on decaying wood (building up fat reserves, which the adults later rely on. it adds humus and fertility to the soil as its nutrients are released. Though bees and bumblebees (members of the order Hymenoptera) are important as pollinators (of many fruit and crop plants, so are the hoverflies key to  the pollination of many wild flowers.  Hoverflies belong to a different group of insects - the Diptera. There are several thousand hoverfly species spread across the world. They are found on every continent with the exception of Antarctica.  Work by Dr. Wotton and his team at Exeter University suggests they are situations where hoverflies may be more effective pollinators than bees and bumblebees, and the role of hoverflies in crop pollination may have been under-estimated.  Hoverflies can carry pollen over considerable distances, and may  visit isolated plants.  The common drone fly (Eristalis tenax) has been known to travel some 100km and carry the pollen of eight plant species.  Hoverflies (or Syrphidae) are also known to migrate over considerable distances.  The female marmalade hoverfly can migrate from Scandinavia to Spain and North Africa, migrating in the autumn to lay their eggs.  In the following Spring, succeeding generations migrate north again.  Some American hoverflies are known to migrate from Canada to the southern states. Insects are not just important in terms of facilitating decay or aiding pollination, some are involved in seed dispersal.  Scientists at Kobe University studied the dispersal of seeds from the fruit of the silver dragon plant.  Using  time lapse photography techniques, they watched to see which animals feed on the plant’s fruit at night. Whilst crickets (order : Orthoptera) ate much of the fruit, earwigs (order : Dermaptera) and woodlice (not insects, but terrestrial crustaceans) also consumed significant amounts of the tiny seeds of the fruit.  Further work demonstrated that many of the seeds survived the passage through the gut of these animals.  So apart from being seed predators, small invertebrates may also help their dispersal, depositing them away from the parent plant. Woodlice are interesting land based crustaceans that generally feed on dead and decaying plant material, helping in the recycling of nutrients. Further examples of the importance of insects in nature can be seen in fig production.  The fig wasp 'gives its life' in the process of pollinating the fig, in return the fig provides a safe ‘nursery’ for the young on the wasp, seed the woodland blog on the fig.  There are many types of fig and each has its own wasp, to ensure successful pollination.  Full details of the life cycle of fig wasps can be followed here.  The association between the wasps and figs is an example of mutualism. This co-dependence probably had its origin some seventy million years ago, and the wasps and figs have co-evolved since then. .