In the eighteenth and nineteenth century, many explorers / adventurers brought ‘exotic’ plants back to the United Kingdom. These ‘exotics’ were planted in arboreta, botanic gardens, and some in gardens.  One bush that was introduced was Rhododendron ponticum. The plant is native to the eastern and western Mediterranean, and the Pontic Mountains, hence its name). It was introduced into Britain in the late eighteenth century, by Conrad Loddiges.  It was planted in Victorian hunting estates, also on heathland areas to provide shelter for game species. Its rootstock has been used for grafting of less hardy, more colourful types.  Many Rhododendron species are a delight and an adornment to our parks and gardens, indeed many hundreds of species of Rhododendron are known (many in China and the Himalayas)*.   Rhododendron ponticum has proved to be invasive.  It is a threat to key parts of our woodland ecosystems, such as Atlantic Oak Woodland.  Atlantic oak woodland is sometimes referred to as Celtic Rainforest.  It is characterised by lichen covered trees, growing amongst a rich moss and liverwort flora.  This woodland environment is damp and humid, to which streams and waterfalls contribute. These woodlands have evolved under the influence of the Gulf Stream,  which helps keeps warm and wet the area.  In some parts of the country, the woodlands have remained in their 'ancient state', since the last ice age.  However, these woodlands were more extensive but now exist as much smaller ‘pockets’ - damaged by grazing, pollution, and ‘exotics or aliens’ like R. ponticum. When this shrub ‘invades’, it 'takes over' and the woodland floor becomes a dark and barren place. A deep shade results from the thickets of the Rhododendron.  This results in the loss of much of the ground flora so that only some shade tolerant mosses and liverworts remain.  They form a ‘mat’ of dense vegetation that is a barrier to seed germination.  Even when the Rhododendron thicket is removed, the re-establishment of the original flora is compromised.  There is also evidence that as it grows this shrub produces chemicals which inhibit the growth of other species;  this is known as allelopathy. R.ponticum has spread in many areas, mainly to the West of the country. Each flower can produce several thousand seeds, so that a large bush can produce several million seeds in year. These seeds are tiny and wind dispersed; and though not all the seeds will germinate and grow, many will and colonise an area. Even when bushes have been removed from an area and the litter layer cleared, the seeds may persist in the seed bank of the soil - allowing the species to recolonise. In consequence, follow up over a five year period is really important. Recent figures suggests that some 37,000 hectares are affected in the UK.  Though the government does make a grant available for the removal of Rhododendron, progress with its removal has been slow. In Wales, there is a project called the Celtic Rainforests Project  (YouTube video link here) that focuses on invasive species and their attempted eradication in Atlantic Oak Woodlands in Wales.  With the agreement of the landowner, the project will organise surveys to identify the scale of the problem, and then contractors to carry out the work over the period of a management agreement, at no cost to the landowner [woodlands.co.uk has groups of buyers who have agreed for their various woods to be covered by such management agreements]. Clearing an area of this plant is difficult and expensive. An  effective first treatment to eliminate R. ponticum is to drill the stems, and inject herbicide directly into the plant.  This uses a lot less herbicide than spraying, and is a selective approach.  Mabberley’s Plant-book notes that the cost of eradicating the plant from Snowdonia was £30 M and that was in 1988.  Further information about the work in the welsh oak woodlands here. The plant is also a problem in Ireland. Indeed, referring to the Killarney National Park a politician has said “nothing short of calling in the army is going to put it right.” [caption id="attachment_39688" align="aligncenter" width="675"] Rhododendron ponticum growing near to the River Tay.[/caption] Forest Research has a number of publications about the management and control of R. ponticum. * Details of the genus may be found in Mabberley's Plant-Book. With thanks to Chris Colley

A besom is a bunch of twigs tied to a handle to make a broom. In fiction and children’s stories, a witch is often depicted as flying on such a broom. However, a witch’s broom* can also refer an abnormal growth of twigs in a tree. A number of trees and shrubs (evergreen or deciduous) can develop these ‘abnormal growths’, but in the UK they are more likely to be seen on Birch.  When high up in the canopy, they may be mistaken for a bird’s nest or a ball of mistletoe.  Mistletoe is a different organism, a partial parasite, growing on the tree, whereas a witch’s broom is part and parcel of the tree itself. Normally, the buds of a tree develop in a predetermined sequence that is governed / controlled by plant hormones.  On a twig or stem, the apical bud is dominant and the lateral buds are ‘held back’.  This is under the control of the growth regulator - auxin (indole acetic acid).  Auxin slows or inhibits the growth of the lateral buds so that the apical bud is favoured.  If auxin production is impaired the regulated development of the twigs is upset so that many buds open and develop, and a multitude of closely packed twigs is formed.   Many things can interfere with auxin production, for example, physical damage to a tree, which may allow the entry of micro-organisms - for example, infection with the fungus Taphrina betulina. This fungus can affect dwarf birch, silver birch and downy birch.  Different species of Taphrina can infect hornbeam and cherry resulting in witches brooms on these trees.  Sometimes, a witch’s broom can form as a result of a mutation occurring in a growing region (meristem).  Such brooms are more often seen in certain conifers, sometimes cuttings of these are propagated to make attractive dwarf or colourful new cultivars (for example Picea abies 'Clanbrassiliana Stricta’). * or hexenbesen in German. Thanks to Torquil and Helen for images.

Whilst browsing the web looking for reports, information that might interest readers of the blog, we came across a very useful site "Discover the Wild".  Discover the Wild offers a number of very useful identification sheets that can be downloaded in PDF form and are easily printed. Some of the sheets / PDFs available are :- Tree buds in winter (very useful) Garden Moths Wasps Spring in the garden (a variety of moths, butterflies, other insects and some plants) Autumn fungi Common tree leaves Seashore shells (not 'woodlandy' but might be good if you are having a day at the beach with children / grandchildren ) DISCOVER THE WILD IS DEFINITELY WORTH A VISIT. https://www.facebook.com/DiscovertheWild [email protected]    

The terms veteran tree or ancient tree are often used. But what is a veteran? A veteran tree may be defined by a combination of factors: its age its size; its condition; its history; its position. Read more...

Many plants have a distinctive scent, think of sweet peas, jasmine or honeysuckle, or stand next to a pine tree on a warm, summer’s day.  The scent is due to the release of volatile organic compounds (VOC’s, often oils), produced by specific tissues or glands.  Often it is the nectaries within flowers that produce the scent, apart from their ‘job’ of producing the sugary nectar.  The nectaries may be found on almost any structure within a flower - petals, sepals, stamens, ovary*. The location of nectaries varies from species to species.  There are other structures that can produce scent, for example, trichomes, and osmophores. Osmophores are clusters of cells specialising in scent production.  Any part of a plant can release scent, for example, the leaves of eucalyptus, lavender or myrtle. The scent of a plant may include a variety of VOC’s, indeed there may be dozens of different organic compounds contributing to a particular scent.  Many of these compounds are terpenoids (isoprenoids).  They contribute to the scent of eucalyptus oil, lavender oil and the flavours of cinnamon and ginger. Scent may have a number of functions.  It may be released to attract specific pollinators - moths, butterflies, bees, hoverflies etc. (who have learned to recognise the scent).  The production of VOCs can be modulated, for example,  scent production may be turned off when a flower is pollinated.  A scent may also unfortunately be a signal to herbivorous insects to ‘come and feed’. So, scent have positive or negative effects. A scent may be produced to deter herbivory by certain insects.  Sometimes, plants have a different approach. For example,  when pollen beetles feed on oil seed rape, the rapeseed releases VOCs which attract the attention of other insects.  Specifically, those that will lay their eggs in the larvae of the pollen beetles. These insects are usually from the same family as bees, wasps and ants - the Hymenoptera (insects with membranous wings and a ‘narrow waist’).   The pollen beetle larvae are then ‘eaten’ from the inside by the developing parasitoid larva.  The release of VOC’s is affected by a number of factors temperature, light, circadian rhythms, physical damage and drought.  As the temperature increases so the amount of VOCs released increases (usually). This may be experienced in coniferous woodland.  Conifers give off a variety of volatile oils (i.e. biogenic VOC’s) that contribute to a unique aroma and the formation of aerosols found in the air in and around such woodlands and forests; it is most noticeable in warm weather.  [An aerosol is a ‘mixture’ of very small particles (solid or liquid) in air; other examples of aerosols include mist, cigarette smoke, or car exhaust fumes]. In snapdragons, the most scent is emitted at noon which tends to coincide with pollinator activity, in contrast tobacco plants scent release is in the evening / night when hawkmoth are active.  Drought reduces the ability of plants (like rosemary and thyme) to produce / release VOC’s, this in turn, has been observed to affect which pollinators visit their flowers.  Nectaries located within the flowers of a plant are sometimes referred to as nuptial nectaries, whereas those found in other parts are termed extra-nuptial.  

The (European) hedgehog population is in decline.  In Britain, the population has roughly halved in recent times and is considered to be vulnerable to extinction.  The Danish Hedgehog project, a citizen science project, headed up by Dr Sophie Lund Rasmussen* (also known as ‘Dr Hedgehog’ : link to YouTube videos) has been investigating the life span of hedgehogs.    This has been done by analysing the jaw bones of dead hedgehogs collected by volunteers all over Denmark.   The jawbone shows a line of reduced growth when the animal goes into hibernation, the number of lines equates to the age of the animal in years.  The oldest hedgehog found to date was 16 years old.  Sadly this hedgehog died after being attacked by a dog, which is not an uncommon cause of death for hedgehogs.   The study has revealed the average life span of a hedgehog to be roughly two years only, with males faring slightly better than females.  The study also found that the most common cause of ‘hedgehog death’ was crossing a road. Another finding was that the hedgehog population is quite inbred.  This may be due to the reduced population size and the difficulty hedgehogs face in finding a mate due to habitat fragmentation (garden fences, roads, railway lines which divide up the environment).  Inbreeding leads to loss of genetic diversity, which in turn reduces the overall fitness of the individual and the population. Hedgehog populations can be helped by Creating hedgehog friendly gardens by removing barriers to movement between gardens. Ensuring there is plenty of greenery /  plant life in the garden so there are earthworms, insects, snails etc. for hedgehogs to feed on. Avoiding the use of pesticides and slug pellets in the garden.  Also be careful with the use of netting, keep it above ground level.  Providing a shallow dish of fresh water and food (such as meaty cat or dog food), particularly during long dry spells. NB : ponds with steep sides can be a problem for a hedgehog if it falls in.  More information on hedgehogs can be found here : https://www.britishhedgehogs.org.uk/ Thanks to Nigel Palmer for his excellent hedgehog pictures, visit his hedgehog post here * https://www.biology.ox.ac.uk/people/dr-sophie-lund-rasmussen#tab-3324091  

The blog tends to write about trees in the context of woodlands and forests, but the trees to be found in hedgerows, parks, streets and gardens are important in many ways.  London is sometimes referred to as an urban forest, as it has some eight million trees within its boundaries.  Though their individual contributions of any given tree may be small, collectively the trees help with : Carbon storage  Carbon sequestration Air pollution removal Removal of pollutants (e.g nitrogen and sulphur oxides) Capture / removal  of particulates Reducing runoff, helping with flood mitigation  Noise réduction temperature regulation. The role of trees in temperature regulation has received some attention recently.   With climate change, many parts of the world have experienced periods of extreme hot weather / heatwaves.  Whilst it is true that extreme cold weather is associated with more deaths than hot, heat waves and the associated deaths are a significant problem.  Heatwaves, such as that experienced in 2015, have been associated with cardiorespiratory problems and premature deaths.   Cities, in particular, record higher temperatures than the surrounding countryside or the suburbs. the so-called urban heat island effect.  The lack of vegetation, the use of air conditioning systems, coupled with the dark asphalt of roads means that heat is retained / trapped; giving rise to the urban heat island effect.  On a summer’s day, some city centres may be some 10oC hotter than the surrounding countryside.  Europe saw its hottest summer last year, and its second warmest year.  Cities in southern and eastern Europe were particularly affected by recent heat waves. They tended to have significant urban heat island effects and low tree coverage.   In contrast, 27% of Gothenburg is covered by trees.  Studies / modelling by the Barcelona Institute for Global Health have indicated that increasing tree cover to 30% of the urban space could decrease the deaths associated with heatwaves / extremes of hot weather (perhaps by a third).  A number of cities, like Barcelona and Seattle have committed to increasing tree cover.  Indeed, Barcelona’s Trees for Life Master Plan is making progress towards its goal of covering 30% of the city with trees,  Barcelona is also encouraging green roofs.  Studies have also shown that ‘green spaces’ can have other benefits from reducing cardiovascular disease, poor mental health, and helping to improve cognitive functioning of children and the elderly.

Poplars belong to the same family as the willows. Like willows, they have a 'preference' for wet soil. There are a number of poplar species – white, grey and black poplar and the western balsam poplar,   A poplar that is common is the Lombardy Poplar, it is a variant of the Black Poplar and probably the most recognizable poplar,  as its branches grow almost parallel to the main stem.   It is a tall, thin tree. The leaves of black poplar (Populus nigra) are arranged along the stems in an alternate fashion. The leaf has a long, slender leaf stalk – which is slightly flattened. The leaf is sometimes described as ‘triangular’ or ‘diamond shaped’. When first formed, the leaves may have a bronze tinge and the young shoots, leaves and stalks have fine, tiny hairs.   The upper leaf surface is a dark green, whereas the lower surface is not such a deep green. In Autumn, the leaves may turn a vibrant 'banana' yellow. The bark of the Black Poplar is grey / brown and deeply fissured with age. The tree may grow to a height of 100 feet, but is usually smaller than this.  The species is dioecious, that is, there are separate male and female trees. In some parts of the country, like Cheshire, the number of Black Poplars is falling, due to changes in land management, a reduced need for particular timbers and an ageing population of trees.  The natural regeneration of black poplars is limited because : male and female trees need to be near each other the fertilised seeds are only viable for a short period  and the seeds need to fall on damp ground   Added to this, there is the risk of hybridisation with other forms of Poplar. So, The Canal and River Trust in conjunction with Chester Zoo have initiated a program to plant black poplar trees in Cheshire’s Weaver Valley.  They have taken cuttings from native Cheshire trees and raised over 1,000 new trees, which have been planted in sites across Cheshire since 1995. For example, male and female trees have been planted by the River Weaver (Hartford) to encourage future natural propagation. Such black poplars can help promote biodiversity, providing homes for moths, bees, birds and butterflies.   Should you have a portion of woodland that has damp soil, and are considering planting some black poplar, there is company that seems to specialise in Poplars : http://www.poplartree.co.uk/poplartree/.  It lists some of the uses / benefits of poplars.