Have you ever wondered why some trees keep their leaves in winter when all about them other trees are losing theirs?
When selecting trees for the garden there is generally a choice of deciduous or evergreen though in reality there are many that fall into the category of semi-evergreen, trees and shrubs that in certain circumstances with lose some or all of their leaf cover. In the temperate climate of Ireland the majority of trees are deciduous; as a form of protection they lose all of their leaves for the winter. They also tend to be the most popular choice due to their greater range of tree shape, leaf shape, flowers, berries and spectacular autumn colour. Some of the common deciduous trees include large ones like oaks, beech and maples, or smaller varieties such as cherries, crab apples and rowans.
Evergreens do lose their leaves, just not in one great dollop as the autumn arrives and the temperatures drop, so they retain a cloak of green all year round. This makes them very popular to add drama to winter landscapes where they make beautiful backdrops amid a light dusting of frost or snow or as a sprig of greenery for the home; they include well known shrubs like holly and conifers such as pine, yew and juniper though some conifers, such as larch, which still have needle-like leaves but will lose them each autumn.
Evergreens are not immune to dropping foliage since most needles or leaves die after a few years anyway, in fact, most needles only live between four and seven years. For some trees, this is a continuous process with a few leaves dropping almost weekly throughout the year. Although the older foliage eventually turns brown and dies, this normally takes place in the interior of the tree, so the process goes unnoticed until the detritus covering the ground at the base of the tree provides the evidence.
Evergreen trees have evolved a different set of protective adaptations that serve the same function as deciduous ones; protecting the tree from dehydration during the winter. The leaves on evergreen plants are covered with a thick waxy coating (cuticle) that prevents water loss and they also have fewer stomata on the surface of the leaf which helps to lessen the water evaporation.
Evergreens evolved in the colder places of the planet and are really good at living there, in areas where there aren’t a lot of nutrients in the soil or available water. Evergreens take up and store up all those nutrients inside their leaves and needles and can use them through the winter months; storing water in their foliage too which helps them to stay green.
.The trees have worked hard to take up those nutrients and water so need to hang on them as long as possible, and by retaining leaf cover. enables them to do so. Leaves are designed to carry out photosynthesis, a metabolic process by which light from the sun is converted into usable chemical energy in the form of sugar. Because their leaves are so numerous and have a constant cover, evergreens are able to capture sunlight even in shady areas where the risk of evaporation from their leaves is low.
The term "evergreen" has come to refer to something that perpetually renews itself, or otherwise remains steady and constant. It is why in folklore the festive season would not be the same without evergreens, holly leaves and red-berried twigs, ivy and pine boughs used for decorating homes all across the country. A sign that was used to celebrate the winter solstice; to ward off evil spirits and to mark the approach of new growth in spring.
Holly; a native species which forms the shrub layer in some of our oldest woodlands, slow growing and very dense, it is only female hollies that bears berries and along with ivy were traditionally used for midwinter decorations, as a sign of green life to come.
Ivy - A contentious evergreen, the self-supporting climber known to clothe trees, fences and buildings but is one of the top 5 wildlife plants. Ivy produces pale yellow flowers in winter, food for the few winter-flying insects, and its berries ripen in spring when they are an important food for blackbirds and thrushes. One of the two seasonal evergreen used in wreaths and garlands to symbolise that even in the depths of winter, life persists.
It is around this time of year that I am asked the most questions about wasps. A much maligned creature with a general belief that wasps serve no purpose, that they are just a more angry version of bee but I try to show that wasps are actually invaluable to the ecosystem and many stories about them just aren’t true.
,One of the biggest myths about wasps is that they are naturally aggressive and will sting without provocation but despite their occasional aberrant attack, they only sting under certain circumstances; they sting to defend themselves and they sting to defend their nests.
Social wasps - Vespula vulgaris, the common wasp, are found in various habitats including urban areas, which in the Irish context means they are fairly ubiquitous and can be found almost anywhere on the island. When a fertilised Queen wasp emerges from hibernation she will begin to form a new colony. Wasps. make nests, like bees and these hard-working insects actually make their own building materials by turning raw wood into paper pulp. They chew wood fibers (they love my front door and the boards on the shed) into a soft pulp. This pulp plus the wasp's saliva forms the basis of the nest, which is a network of tiny hexagonal cells arranged together in a honeycomb shape, enclosed in a protective layer that covers the whole nest. Although made out of paper, the nests are sturdier than you might expect, nevertheless, they will decompose naturally over the course of the winter, due to weather and other factors and a new nest will be built each year.
Many wasp species swarm primarily to protect their nest, swarming to fend off the perceived attacker whether that is animals or people if their nest is disturbed. Although most social wasps build their nests in the eaves of houses, in sheds and outbuildings and in trees, some wasps build their nests in shrubs or climbers but also in the ground where they can be disturbed much more easily and unintentionally, causing a swarm reaction.
After building a very small nest the queen will lay the eggs that become the first workers of the colony. In the early part of the year, the nest stays quite small and growth is slow until a certain point when new workers then emerge in larger and larger numbers.
During the early summer months, when people rarely notice wasps, they seek out aphids, spiders and flies, small caterpillars. mosquitos and other insects which they bring back to the larvae in the nest. Most people are stung in late summer because this is when the fertilised queen is preparing to hibernate. In this period, a lot of the wasps die off and the workers left behind are hungry because there is less food around and they are stessed and confused because of their nestmates are dying. They are on the lookout for sugar and outdoor dining in the form of picnics and barbeques are a source of rich pickings. Then, they more likely to sting when people try and swat them; only when they think you are trying to kill them do they usually become hostile.
As well as being voracious and ecologically important predators, wasps are increasingly recognised as valuable pollinators, transferring pollen as they visit flowers to drink nectar. Many people thought that wasps were not pollinators like bees as they have a smooth body. However, they most certainly are. The hairs on the black and yellow striped abdomen of many wasps is so fine, it renders it almost invisible to the naked eye. Only on close examination fine but dense hairs were found on the abdomen and thorax of even the common wasp. The presence of hairs coupled with the fact that they visit flowers for nectar persuaded researchers that wasps were indeed plant pollinators.
In fact, researchers have found that wasps are the exclusive pollinators of some species of orchid and fig. Indeed, if wasps didn’t exist, picnics would be less fraught but, without wasps, many of the ingredients might not exist at all. Research into by a team in Florence have found that the guts of wasps provide a safe winter refuge for yeast – specifically Saccharomyces accharomyces cerevisiae, the fungus we use to make wine, beer and bread.
Sadly, wasps are facing a similar decline to bees and many other of our wild pollinating insects and that is something the world can't afford. Both bees and wasps pollinate flowers and crops - but wasps also destroy pests and insects that carry human diseases.
Our dislike of wasps is largely shaped by a small number of social stinging species, these represent a small percentage as the vast majority of wasps, more than 75,000 species are solitary ones. Global concern about the decline of pollinators has resulted in a phenomenal level of public interest in, and support of, bees (though this attention seems to be concentrated on honeybees rather than wild bees in general). The much loved bee is seen as more helpful to people and the environment than the wasp; if this global concern could be mirrored for wasps it would need a complete cultural shift in attitudes towards them..
Driving along the roads, boreens and trackways of Ireland this month you can almost watch as the hedgerows besides them unfold into glorious flower.
Hedges in all countries are generally planted to provide stock-proof barriers and to denote land boundaries, often but not always on raised banks of soil (this soil bank was normally the result of the excavation of associated roadside ditches (dykes) to provide drainage from the fields and roads.
Hedgerows should be considered as complete ecosystems, as green or wildlife corridors (though you would be hard pressed to look at some hedgecutting and wonder if the land owner wants a boundary at all, stock proof or otherwise). Good native hedges allow free movement from one habitat to another for the birds and animals that would also be used a nesting sites, song posts, roosting and feeding sites and especially as protective cover from predators on both four legs or wing.
The more species of trees and shrubs within the hedgerow, the more wildlife it will support. Some trees, like whitethorn (Crataegus monogyna) and the mighty, common oak (Quercus robur) support a wide variety of insect and bird species and willows (Salix sp.) are particularly valuable in supporting different species early in the year. As Ireland has so little native woodland cover, hedges are important substitutes as habitats - not only the trimmed or untrimmed hedge but the large trees allowed to grow within them.
A varied composition of plants provides a continuity of food for insects, birds and small mammals, with leaves, flowers, seeds, fruit and berries opening and ripening at different times. As well as trees, shrubs too have found their way into hedgerows and the more that you see, the more they provide a richer provision for wildlife. In an old whitethorn hedge you would also hope to see some elder (Sambucus nigra), Guelder rose (Viburnum lantana), dog rose (Rosa canina), wild cherry (Prunus avium), crab apple (Malus sylvestris), holly (Ilex aquifoium) and hazel (Corylus avellana). In some areas shrubs such as spindle, wild damson and buckthorn have crept in slowly from nearby and increase the diversity. Brambles and honeysuckle that scramble through the branches add another layer of pollen and nectar for bees and butterflies in summer, leaves for moth and butterfly catterpillars and berries for the birds and small mammals in the autumn
Small birds, like robins and wrens prefer hedges that are thick at the base, providing dense foliage cover when they are scratching around for insects, particularly in winter when the open ground may be frozen. The rich source of food at the bottom of the hedgerows with its carpet of dead leaves also attracts small rodents; kestrel and barn owl hunt along the grass verges and bases of hedgerows strangely enough, because they hunt small rodents.
Young trees and saplings that grow one or two metres above the main body of the hedgerow are used regularly as song posts and robin, blackbird and thrushes will often be seen reminding others of their territory with their song. Much taller trees and dead wood standing within the hedgeline can be used by birds of prey on the lookout for their own food sources.
Today, it is estimated, that Ireland has only a native hedgerow length of 300,000km, many are now at the end of their natural lifespan, more still have been left to grow wild and are more of a tree line than a hedgerow. In fact a lot of hedges no longer fulfil their basic function as barriers, having become gappy or bare at the base. This is often due to the way they are cut, or not cut at all and left to grow stumpy instead of thick and stockproof.
The most significant changes to hedgerows in recent times has been, firstly, the widescle clearance associated with the development of land for building, including new and widened roads and with more intensive agricultural, the removal of hedges enclosing very small fields to larger ones.
The second has been hedgerow maintenance and management with the majority of country hedgerows now being cut with flail mowers with the resultant damage and disease it can cause. Flails are designed to cut young growth on a regular basis but you only need to drive on some of the roads to see the appalling sight of decimated stems and branches (too large for this type of machinery) being stripped and shattered leaving uneven stumps, mangled bark and torn and twisted remains.
It is these factors that have led to a reduction in diversity both through physical removal and through disturbance and fragmentation of the remaining hedgerow habitats, not only of wildlife but of the plants that die out because the cutting regime does not suit all type of hedgerow shrubs.
The current generation of Irish farmers have planted around 10,000km of new hedges - the most significant planting in almost 200 years and the revival of the ancient art of hedgelaying has also returned to Ireland, especially in light of grants available through certain schemes. This is a hedge management method that takes advantage of the ability of broadleaved trees to make new growth after being cut back hard; effectively rejuvenating the hedge and extending the lifespan of most hedgerow species indefinitely.
As new hedgerows are planted, with well chosen plants and good management, field hedges could once again be fit for purpose, to provide stock proof boundaries as well as those vital corridoors for all the wildlife that are facing so many difficulties in the countryside today.
Large or small, bats have a bit of an image problem.
The origins of bats
Bats are one of the most prolific groups of mammals today, but the fear they generate often overshadows the fascinating fact that bats are the only mammals to have evolved powered flight, that they have been doing so for 50 million years or more, yet, their early evolutionary history is virtually unknown. The earliest known bat fossil is Icaronycteris from Wyoming, a fossil that is 51 million years old but since it looks very similar to modern bats, it doesn’t help science to figure out how bats evolved their unique bodies or the ability to fly. The anatomical characteristics of the fossil indicate it is likely Icaronycteris could already echolocate, so the origin of that trait too, is also unknown.
Many of the earliest bats may have lived predominantly in forested environments, which are known to have poor preservation potential, even the fossil record of modern bats that live in forests and jungles is largely incomplete, probably for the same reason. Icaronycteris lived around lakes that were much better for preservation; the fine sediment and oxygen-depleted water on the lake bottoms allowed the bones to be covered quickly in an environment that scavengers and other decomposers couldn’t reach.
With over 1400 species currently recorded, bats are actually one of the world's largest groups of mammals (just behind rodents) and make up a fifth of all known mammal species. They range in size from the 25mm Kitti’s hog-nosed bat (Craseonycteris thonglongyai) weighing 2g to the enormous, 1.3kg Giant golden-crowned flying fox (Acerodon jubatus) with a wingspan of 1.7m. Their diets are as diverse as their size, feeding on anything from fruit and nectar to insects and blood.
Bats are very rarely at the top the favourite animals list, but perhaps to some degree, they should be.
Why bats are important
Bats get a pretty bad rap due to countless myths and common misconceptions, in reality, they play an extremely important role in the environment, from pollinating plants, spreading seeds and managing insect populations. The pollination of plants by bats is called Chiropterophily and globally over 500 plant species rely on bats to pollinate their flowers and whilst these plants rely on bats, the bats rely on the fruit and flowers these plants provide for their own survival.
Like birds, some bats play a critical role as re-foresters, spreading the seeds of trees and other plants as they travel from place to place. Fruit is a plant’s way of enticing animals to eat and disperse their seeds and many plants choose to attract bats. The fruit bats then carry seeds inside them as they digest the fruit and excrete the seeds far away from the parent tree with even their own ready-made fertiliser. The seed dispersal has been known to play a role in helping natural regrowth after forest clearances in tropical and sub tropical areas.
Nearly 70% of bat species are insectivorous, including here; Irish bats only eat insects. In a single night, a pipistrelle bat can eat as many as three thousand small insects including midges, moths, mosquitoes and tiny beetles. Insect-eating bats are great for keeping bug numbers down and a study in the US found that the natural pesticide services from bats were likely to be worth over $3bn a year. When bats are around to eat the insects, there is less damage to crops, and because bats eat so many insects in some regions, they can also reduce the need for chemical pesticides.
Long live bats!!
The aging pattern for mammals is that larger species are generally longer-lived than smaller ones, however, bats are a major exception to this. For decades, biologists have noticed that bats live much longer than they should according to their body size. If you think of a mouse, which is a comparable size, their average lifespan is less than 3 years. A male Brandt’s bat (Myotis brandtii), however, weighing just 7g, has recently been recaptured in the wild 41 years after its original ringing, making it the world’s longevity champion for small mammals. Bizarrely, all of the oldest bats are male; it is not clear why all long-lived individuals are male, but the same pattern has been reported in another exceptionally long-lived bat species, the little brown bat (Myotis lucifugus), recorded at 35 years.
Researchers aren’t exactly sure why this is, but a recent genome sequencing study on Brandt’s bat shows one of its genes, one thought to be linked with body size and aging, is unique when compared to other mammals. Scientists also believe the answer may lies in bat DNA, specifically telomeres, the caps on the ends of chromosomes. Basically, the length of telomeres determines lifespan length. Myotis bats — also known as mouse-eared bats — do not experience wear and tear on their telomeres, that typically in other species, deteriorate over time. Researchers say that studying mouse-eared bats could provide essential information on engineering anti-aging drugs for people.
Many people associate bats with carriers of disease, especially viruses and yes, bats have been strongly linked to Covid-19 though yet to be definitively proven, but they are also known to rarely get sick themselves. Over the last decade improved techniques for disease detection have implicated bats as likely reservoirs and vectors for a growing list of pathogens that can affect humans and domestic animals.
Recent research has identified molecular and genetic mechanisms that allow bats to stay healthy while hosting viruses that have the potential to kill other animals, including people. The research has suggested that stresses on bats, such as confinement and habitat loss disrupts the virus balance of their immune system and allows the virus to multiply, providing a latent reservoir that may spill over into other species.
The study tried to understand bat’s immune systems by attempting to trigger an immune response. The test bats displayed none of the most common signs of illness; they had no fever and no increased white blood cell count; for reasons not well understood, bats seem unharmed. They have a sort of super immunity, the bat cells adapt by maintaining a natural antiviral response, a function which shuts down in other species, including humans rather than producing inflammation-causing proteins that are the hallmarks of sickness.
Operating together, these adaptations result in the virus remaining long-term in the bat but being rendered harmless to the bats and others until something, such as disease or other stressors, upsets this delicate equilibrium.
Threats to bats
Sensational headlines at the beginning of the pandemic last year, mainly from the tabloid press and entreaties such as ...' with the terrifying death toll bats have been blamed for around the world, why are we protecting them?', negates in peoples minds the great benefits that bats provide for the natural world and, in turn, ourselves. They are facing more and more direct threats from people who assume all bats carry covid-19 (and, none of them do) and are destroying colonies that may be protecting their future crops from infestations of insects or even worse pollinating the crops which supply the food they grow..
The loss of natural habitats remains the most widespread threat for bats worldwide indeed forest habitats are disappearing at an alarming rate — the result of timber harvesting, mining operations, cattle pastures and tillage and continual urbanisation. The danger is even more significant for tropical rain forests, home to the richest diversity of bat species, and intensive agriculture with the increasing use of pesticides may mean that bats go hungry from the lack of insect prey.
In Ireland, the destruction of hedgerows and woods in farmland is also concerning, as bats rely on these features for roosting but also for navigating their way around and for hunting. Bats also remain vulnerable to threats such as water pollution, increased artificial lighting at night and pesticides.
Though we may not think of them as lovable creatures, they are an essential part of a natural, well functioning ecosystem. It is when, through our incursion and destruction, these ecosystems break down, that we then release, often deadly, diseases into the world.
A haven of quiet countryside highlighting issues affecting the natural world.