It may be that a dead hedge is just that, your once carefully manicured box hedge which has now been ravished by the box moth.  However, in terms of managing your woodland, a dead hedge may have a different meaning. Here, a dead hedge may be a barrier to an area of new planting, it may be a way to ‘persuade’ people to keep to a footpath, or keep away from a pond / stream.   The dead hedge will be made from the bits and pieces that have be culled in clearing and thinning operations within the wood, material that foresters sometimes refer to as ‘lop and top’ and tree surgeons call ‘arisings. It can also include material cut from brambles and climbers such as ivy, honeysuckle and Old Man’s Beard (Clematis). Using natural materials to create barriers (and indeed) a habitat in a woodland is a way of using ‘waste’ in an ecologically sound way.  It saves having to remove trimmings from the site and offers opportunities to ‘top up’ the hedge if desired.  Obviously diseased materials should not be used.   Creating a dead hedge from clippings and trimmings is a way of using natural materials, rather than plastic & other materials that do not readily decompose.  A dead hedge will be an effective barrier for a period of time but it will break down sooner or later as bacteria and fungi break down the woody remains (lignin and cellulose).  The disappearance of the hedge will take time as the branches twigs etc are largely off the ground, so relatively dry and decomposition is facilitated by warmth and wetness. After its initial ‘construction’, the hedge will become part of the woodland, it will be colonised by some plants and it will offer shelter, nesting sites for birds and small mammals, and a ‘home’ to many different invertebrates, such as woodlice, beetles, even certain species of bumblebees.  As the hedge deteriorates, that is, decomposes, so the soil will gain in humus and fertility as the nutrients from the decaying wood etc are released through the detrital food chains.   Another way of using / recycling bits from pruning, clearing etc is by Hugelkultur.   Hugel beds are basically raised beds with a difference - they are filled with rotting wood and other biomass.  They are packed with organic material, nutrients and air pockets. Such beds can be an effective way of creating a productive area for growing fruits and vegetables in your woodland.  There is a woodlands blog about hugelkultur here. Large chunks of wood e.g. sawn up tree trunks can be stacked up in small piles and will over time make an excellent home for many invertebrates but especially xylophagous (wood eating) insects, for example,  saproxylic beetles.  These are beetles that live / eat in dead wood.  In the UK, some 600+ beetle species (from 53 different) families are associated with deadwood. Some feed on the deadwood itself (often with the aid of symbiotic bacteria in their gut), others feed on the fungi that are gradually ‘dissolving’ the wood.  Ants and wasps sometimes make their nests in dead wood.   Using wood to increase the organic content of the soil is good in terms of  carbon sequestration,  improving soil fertility,  water conservation and  productivity.  

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.

It would seem that pollinators have ‘favourite plants’.  Research centred on the National Botanic Garden of Wales has looked in some detail at the foraging habits of bees, bumblebees, hover flies and solitary bees - our most important pollinators. Dr Abigail Lowe identified the plants that the insects were visiting by analysing the DNA from pollen grains on their bodies (a process known as DNA barcoding). It is clear that the ‘preferences’ of the insects change with the seasons and indeed the availability of particular flowers.  In Spring, nearly all the pollinators frequent buttercups, lesser celandines and dandelions (all brightly coloured yellow flowers).  Come the summer, honey bees and bumblebees tend to favour thistles, knapweeds and brambles, whilst hover flies may be seen on hogweeds and angelica plus thistles and knapweeds.  In autumn, the bumblebees can be see visiting asters (Daisy family flowers) and brambles. Full details of her work can be found here : https://botanicgarden.wales/press/plants-for-pollinators-new-dna-research-reveals-fascinating-insights-into-the-plants-used-by-bees-and-hoverflies/ There are also suggestions on how to help pollinators in your garden, such as encourage buttercups and dandelions by reducing mowing (in the Spring) plant late flowering daisy type flowers encourage some bramble (you might get some blackberries, in return) reduce the use of chemicals (especially pesticides and herbicides) hoverflies can be encouraged by damp, wet areas and rotting wood and these suggestions would also work in a woodland.   [caption id="attachment_38320" align="aligncenter" width="700"] Marmalade hover fly[/caption]

In recent decades, signs of Spring have occurred earlier and earlier, indeed the early flowering of crocuses and daffodils in our gardens is one such sign. Now a detailed analysis of such ‘signs’ has been undertaken by using the information held in Nature’s Calendar.  This is an enormous database * of records of seasonal changes; it has records of some 400+ species of plants, from trees, to shrubs and herbs. Nature’s Calendar includes records from organisations like the Royal Meteorological Society, plus those of scientists, naturalists and gardeners. Recording when things happen (such as when horse chestnut and ash trees come into leaf, or when the first swifts or bumblebees are seen) is known as phenology. These timings vary from year to year.  Phenology is not a new discipline. One of the first phenologists was Robert Marsham, who recorded ‘indications of spring’ starting back in 1736. He catalogued some 27 different natural events on his family’s estate in Norfolk.  In 1875,  the Royal Meteorological Society set up a national recorder network.  Nature’s Calendar includes thousands of these historical observations and enables scientists to look for trends and see if they correlate with changes in temperature, rainfall, weather phenomena. The research team from Cambridge University looked at FFDs - first flowering dates and temperature records. They found a difference in flowering dates from the 1750s and the most recent years of almost a month.  Professor Ulf Büntgen has said that rising global temperature has brought Spring forward by several weeks.   This raises concerns. For example, if a plant grows and comes into flower earlier in the year what happens to insects that are dependent upon it? For example, some bees collect from only one species of plant.  Or to put it another way, suppose the plant flowers earlier but its pollinating agent (an insect such as a hover fly) is not about, has not emerged from its over-wintering stage? What if there is a ‘late’ frost?   * Nature’s Calendar : The Woodland Trust joined forces with the Centre for Ecology & Hydrology to collate phenology records into Nature’s Calendar; this has some 3.5 million records- some going back to eighteenth century.  

Reports on pollinators. Research by workers at the University of Reading and the Centre for Ecology and Hydrology has shown that various ground level pollutants (nitrogen oxides and ozone) have significant effects on the pollinating activities of bees, moths, butterflies and hoverflies.  The number of flower visits by these insects declined, as did the level of pollination and seed production. The University of Göttinggen has published a study that bumblebees need a diverse pollen diet, collected over a variety of habitats.  A varied pollen diet contributes to better colony growth, more offspring (particularly young queens).  It also helps offset the effects of infestation with wax moth larvae.  Wax moth caterpillars feed on nest debris, but as they grow they switch to feeding on the food stores and even grubs / larvae, effectively destroying the nest. Recent work by an Irish postgraduate student on insect pollinators in Dublin suggests that a “less is more’ approach  might be effective when it comes to natural green areas in cities.   Emma King looked at the pollinators present in Areas of planted meadows or sown with wild flower mixes. Areas with reduced mowing that were allowed regenerate naturally. She found that though insects like bumblebees and hoverflies were more frequently recorded in planted meadows, statistically there was no significant difference in the numbers; and the community of pollinators was similar in both types of green areas.  The advantage of allowing green areas to develop naturally is that it reduces labour and material (seeds) costs.  They may take a bit longer to establish a diverse flora but they will offer resources to pollinators. Such green spaces promote habitat connectivity within the urban environment. Sunflower update Work by staff at the University of British Columbia has revealed that sunflowers (like many other flowers) helps bees to visit by invisible (to us) ultra-violet patterns - usually in the form of a ‘bulls-eye’.   They observed that sunflowers growing in drier conditions had flowers with larger UV ‘guides’.  Furthermore, it was found that a particular gene was responsible for the nature of the bulls-eye pattern, and this gene was also associated with the production of flavonol compounds.   Quite how the gene and the production of flavonols is related to the capacity of sunflowers to retain water is not known. [Full details of the work of Dr M Tedesco et al here].

Reports in the papers and electronic media have made us aware that many forms of wildlife are under threat.  This threat is wide ranging - from the destruction of tropical rain forests, coral reefs, the loss of species-rich meadows, the insect apocalypse - indeed where does this loss of plant and animal species end? One small positive observation amidst the doom and gloom is the findings of The Biodiversity in Urban Gardens project [BUGS] at the University of Sheffield.  The original study focused solely on Sheffield and finished in 2002, but  it was then extended to five cities across the U.K.    Professor K Gaston who led the study is now working at the University of Exeter.  The original study was important in that it revealed within Sheffield city, there was 33 km2 of wildlife habit was available within the city 360000 trees in the city limits 45000 nest boxes 25000 ponds and  50000 compost heaps Furthermore, there were in excess of a thousand plant species (flowering plants, ferns and conifers) and a diverse collection of invertebrates (bumblebees, hoverflies, beetles and spiders).  Whilst the diversity was in no way comparable to that of an ancient woodland (with veteran oak trees etc) or indeed of wetlands, it is significantly better than that found on farmland - particularly in those areas where the farming is intensive and characterised by monocultures (e.g. oil seed rape extending to the horizon).  Farmland now occupies some 70% of the landscape. Gardens, parks and urban areas are therefore an important resource for wildlife.  It is important as house building proceeds, on both brown and green field sites, that the associated gardens continue to provide ‘sanctuaries’ for wildlife, for example, by avoiding large areas of hard standing for cars (which also encourage  rain / water run off - which can overwhelm the drainage systems).  Professor Gaston has emphasised the importance of ‘dimensional complexity’ in gardens; that is a variety of trees, shrubs and plants of different shapes and sizes.  This provides a range of different niches / habitats for wildlife.  Of course,  in gardening to promote wildlife, there are the additional benefits (for householders) of physical and mental well-being.   Remember later this month, there is the Big Garden Birdwatch, organised by the RSPB. For further information, click on the image below:- [caption id="attachment_36525" align="aligncenter" width="670"] Ladybird 'stalking' aphids[/caption]

Climate change is affecting all parts of the world, from the melting of the ice caps in Antarctica, to droughts in Australia and California.  On a more local level, we may see changes in our rainfall pattern.  Certainly for many parts of the UK, it has been a very dry start to the Spring, coupled with some very cold nights. Cold and dry weather affects plant growth in significant ways.  Warmth is needed for a plant’s enzymes (catalysts) to work, speeding up reactions and allowing growth.  Similarly, if water is in short supply, growth is stunted; plants do not realise their full ‘potential’. They are smaller overall as is the number and size of flowers that they produce.  Flowers attract visitors by colour, size and scent; or combinations thereof.   Smaller and fewer flowers, in turn, have ‘knock-on effects’ for their pollinators - bees, bumble bees, hoverflies etc. The effects of drought on pollination has been recently investigated by researchers at Ulm University in Germany.  They studied the effect of drought on field mustard (aka Charlock) : Sinapsis arvensis.  This is an annual plant that is to be found in fields, waysides and field margins across Europe.  It has bright yellow flowers, with four petals.  It is visited by many different pollinators (it cannot self-pollinate).   The researchers compared the number of visits by bumblebees (Bombus terrestris) to drought-stressed plants to well-watered ones.  The data showed that as the number and size of the flowers decreased so did the number of pollinator visits.  [caption id="attachment_21589" align="aligncenter" width="600"] Bumblebees also favour the teasels[/caption] The ‘attractiveness’ of the plants / flowers to pollinators was reduced, and it is possible that the smaller flowers were more difficult for relatively large pollinators (like the bumblebees) to ‘deal with’.  If pollen movement is reduced, then fewer fruits / seeds will be set and (insect pollinated) plant populations could decline.  The effects of reduced rainfall and water stress need to be considered alongside the declining number of pollinators.  The reduction in pollen movement has lead some to speculate that it might lead to a selective pressure for self-pollination / self-fertilisation, with plants dispensing with the need for visiting insects.  Other Woodlands blogs have reported on the falling numbers of insects / pollinators. Featured image : garlic mustard.

Bees and solar parks As the country tries to move towards carbon zero, so we see more and more solar parks  / farms ‘springing up’.  Whilst they do create clean energy, they also take up a lot of land, and it is important to see if such solar parks can offer other commercial or environmental benefits.  One suggestion is to place honeybee hives on such parks.  The bees could provide a pollinating service to surrounding crops / farmland.  Researchers at Reading and Lancaster Universities have studied detailed land cover maps / crop distribution patterns to estimate the economic value of deploying honeybees in solar parks.  Their investigations suggest that a variety of crops from oil seed rape, soft fruits to apples and pears could benefit from such an arrangement.  The benefits would vary across the UK, with the benefits being greatest in the East and South of the country.  Care would need to be exercised though to ensure the placing of hives did not disturb the foraging of wild pollinators, such as carder bees, hoverflies etc. Are plants sulphur deficient? Much has been written about the importance of plants nutrients, especially NPK; that is to say nitrogen, phosphorus and potassium.   However, little is said about sulphur.  However, researchers in Groningen, Graz and Cologne have been looking at the effects of sulphur deficiency, particularly in relation to the colour and shape of the flowers formed.  The work focused on Brassica rapa, a member of the mustard family.  When it was subject to ‘mild’ sulphur stress (by limiting the sulphate in the growth medium), the flowers that formed were smaller and paler - not the usual bright yellow.  They were also likely to be mis-shapen. Colour and shape are features by which pollinators recognise flowers and then visit them. Pollen production by the flowers was also affected; smaller pollen grains were formed.  This may in turn affect the pollinators who visit the flowers foraging for food. In the relatively recent past, sulphur deficiency may not have been a problem due to acid rain, which would percolate through the soil, forming sulphates.  [In the twentieth century, acid rain formed as a result of the release of sulphur dioxide (and nitrogen oxides) into the air through the burning of fossil fuels.  However, various clean air acts have ensured that there is now much less SO2 in the air.] Annual rings, water availability and earthquakes. Christian Mohr (scientist from the University of Potsdam) was studying the transport of sediments in rivers in Chile in 2010 when a massive earthquake shook coastal areas of the country.  When he was able to return to his studies, he noticed that streams in the valleys were flowing faster.  He reasoned that this was because the earthquake has literally shaken up the soil, so that it was now more permeable and ground water could more easily flow down from the ridges.  As a result of increased water supply, he thought that trees down in the valleys would grow more than those on the ridges. He and colleagues drilled out plugs of wood from valley trees and ridge trees, and back in Potsdam they examined the tree rings under a microscope.  They also looked at the uptake of different isotopes of carbon as a measure of photosynthesis.  They found that trees from the valley floor experienced a small but noticeable growth after the earthquake, and this lasted for weeks or months, whereas the trees of the ridges grew more slowly.   It is possible that analyses like these, when combined with other information, could help identify significant historic disturbances. Rising temperatures. Recent years have seen periods of very hot temperatures, Such extreme weather events have been seen not only in the UK but across the globe (Arizona , Victoria Australia, Indonesia).     Extreme heat (and drought) have been known throughout history, but it would seem that extreme events are now more common.  The first two decades of this century are among the warmest on record; this warming is associated with increasing levels of greenhouse gases (due to human activity). Prolonged heat is not without its effects on us, it leads to sweating, teaches, fatigue, dehydration and heat exhaustion.  The very young and the elderly are most at risk from ‘heat waves’.  A 2003 heatwave across Europe is said to have caused several thousand  'excess' deaths’, mainly of the elderly.  Even gradual but sustained warming of the climate can have its effects.  For example, Silwood Park (Imperial’s research station) has commented that though it is now November, they have not recorded a single frosty night - normally they would expect to have three in a ‘normal’ October.  Snowdrops are appearing earlier, and some migratory species are changing their pattern / timing of migration. Across the world, different species are being affected in different ways.   Thick billed murres (type of guillemot, found in and around the Hudson Bay) have a high metabolism to deal with the cold waters into which they dive - they are cold adapted animals. On warm days (when the temperature is 21cC or above) they are dying whilst sitting on their nests - incubating their eggs.  They struggle to keep cool, if they spend more time in the water then they leave their eggs exposed to predators (like gulls and arctic foxes).  Similarly boreal and arctic bumblebee species are sensitive to heat stress, succumbing to stupor; other work indicates that some European / mediterranean species are now to be found in areas of the arctic circle - as a result of changing climatic ‘norms’.  Wild dogs are adapted to deal with heat, but if the temperature goes beyond a certain point they stop hunting, consequently their pups / offspring are less likely to survive. Warming temperatures not only affect animals but they also contribute to the increasing number of harmful algal blooms (in lakes and off shore regions).  These blooms can be dangerous to many animals (including humans) and when they die back they ‘suck’ oxygen out of the water - creating ‘dead zones’.  One species of alga (Karlodinium veneficum) which is known to produce toxins has been shown to acclimatise to higher temperatures (up to 30cC). As climate change and research continues, we will no doubt see further examples of how animals and plants are being affected by changing temperatures / climate .