Blog - pollinators
Woodlands web updates : 27
Tree survival and drought. Researchers at the University of California have been working on a method that helps predict whether forests / woodlands can survive periods of drought. As climate change is altering patterns of snow and rainfall, so periods of drought are likely to become more common. Forests are important in terms of carbon sequestration, that is, they take up carbon dioxide from the air and convert it into sugars, starches etc that are stored in the leaves, branches, stems and roots. However, in order to assimilate and convert carbon dioxide (in photosynthesis), trees (indeed all plants) need a supply of water. When water is limited, trees need to make use of their reserve materials. Just as we make use of body reserves of fat and glycogen when food / diet in inadequate. However, reserves can only sustain a tree for a finite period of time. If drought persists, the tree reaches a ’tipping point’ and it will die. The researchers studied a forest in the Sierra Nevada that experienced a period of drought between 2012 and 2015. During this period, millions of trees died. The team recorded rainfall, soil moisture and temperature in the forest AND the amount of carbon dioxide that the trees absorbed, and their reserve materials. They found that the trees were able to maintain function / health after the onset of the drought but with the passing of time, the trees exhausted their reserves and were unable to use / convert carbon dioxide into food. They had reached the tipping point and died. The methodology of this study was called CARDAMON (carbon data assimilation with a model of carbon assimilation); it is hoped that it can be used to evolve strategies to enhance forest and woodland resilience in the face of climate change. Pollinators. [caption id="attachment_35902" align="aligncenter" width="675"] hoverfly[/caption] University researchers from the UK and Finland have been trying to determine the most effective pollinators of crop plants, like strawberries (and other fruits). Plentiful and effective pollinators are needed to ensure a good harvest of the fruits. The researchers studied the pollinators at three strawberry farms through the (long) growing season for the fruit. They adopted two approaches : They caught the insects that visited the strawberry flowers and analysed the pollen they carried in detail (pollen load and type). They also counted the number of flower visits by the different insects, (a quick way to identify key local pollinators). Many insects were identified, including :- European drone fly : Eristalis arbustorum Honeybee : Apis mellifera Levels drone fly : Eristalis abusivus Buff tailed bumblebee : Bombus terrestris White tailed bumblebee : Bombus lucorum Common drone fly : Eristalis tenax Red tailed bumblebee : Bombus lapidarius Early bumblebee : Bombus pratorum Bent-shinned Morellia : Morellia aenescens Hoverflies are true flies, that is, they belong to the order Diptera or true flies, as they have a pair of wings and a pair of halteres (balancing / orienteering organs used when in flight). Several of the flies in the genus Eristalsis are known as Drone Flies (due to their resemblance to honey bee drones). The larvae of Eristalis species are commonly found in putrid / stagnant water and sometimes referred to as “rat-tailed maggots”. It was noted that pollinators also made use of the wild plants to supplement their diets, as strawberries alone cannot meet the nutritional needs of pollinators. ‘Elsanta’ strawberries have a relatively low sucrose and protein content in both their nectar and pollen. The precise order of importance of pollinators varied between farms. Bee (Apis and Bombus) species and hoverfly (Eristalis) emerged as key pollinators. The European drone fly was the most important pollinator at two of the three farms studied, evidence that hoverflies can be effective pollinators. One farm had commercial hives of the honey bee but they were less significant than the activities of of the hoverflies and bumblebees. The abundance of a particular insect, coupled with its active period were / are important determinants of pollinator importance. Sawdust and plastics - a possible use?. Plastics represent a relatively new, but persistent and major form of pollution (on land, in the sea, indeed everywhere). Whilst many plastic objects are instantly visible in the form of discarded bottles, fast food containers, many plastic pollutants are in the form of very small particles of plastics - nano and microplastics. The concern is that we and other organisms are taking these microscopic particles into our bodies from our food / drinking water. However, it is possible that plant materials may offer some ‘solutions’. Water that contains micro and nano plastics can be filtered through sawdust that has been treated with tannic acid. Tannic acid is large molecule, its molecular formula is C72H52O46 . Tannic Acid is found in certain plant galls (swelling of trees caused by parasitic wasps) and in the twigs of certain trees, such as Chestnut and Oak. The wood sawdust contains fibres of cellulose, combined with hemicelluloses and lignin. Water can flow through this material by capillary action. This plant-based filtration (known as bioCap) of plastic-laden water is capable of dealing with a wide range of nanoplastics (PVC, PET, polyethylene etc), and tests with mice suggest that the filtered water may be sufficiently free of plastic to pose little risk.
Many hedgerows were planted originally to keep livestock, such as sheep, cattle, pigs, chickens in specific areas. Some hedgerows were planted to define boundaries – ‘who owned which bit of land’. Hedgerows often surround fields. The word ‘field’ comes from Old English ‘feld’, meaning 'an area of felled trees / open country'. The establishment of many hedgerows was associated with the process of enclosure; a change in land use from arable to pasture (for sheep). Open fields and common land were enclosed by hedgerows, over many years the landscape of England changed. The C20th witnessed the opposite process, the removal of hedgerows for the creation of larger fields to accommodate larger machinery. In the decades following the end of the second Word War, it has been estimated that a quarter of a million miles of hedgerow have been ripped out / lost. Fortunately, there are now policies in place to halt or even reverse the loss of hedgerow. Hedgerows are recognised as an integral part of our landscape and play an important role in the maintenance of biodiversity. They provide habitats for a variety of animals and plants. Many species of birds nest in hedgerows, such as song thrush, yellowhammer and tree sparrow. Different species favour different heights within the hedgerow. Some species nest near the ground such as wrens and dunnocks, whereas others nest higher up (eg. Bullfinches). The greater the variety of plant species in a hedgerow, the better the supply of pollen, nectar, fruits and seeds. Ivy for example will produce flowers late in the year and offers a source of nectar and pollen. Hawthorn, blackthorn and holly offer fruits in the winter months for birds and small mammals. Hedgerows and hedges have to be be maintained. Such management may involve planting of trees or shrubs to fill gaps, coppicing, laying or cutting back. [youtube=http://uk.youtube.com/watch?v=Andv7a0NPEc 425 350] However, the effects of pruning and cutting back during the bird-nesting season can be disastrous. Mechanical flailing of a hedgerow is fast, effective and the regrowth is generally slower, but its effects can be particularly bad on birds. They may abandon their nests and / or their eggs or chicks may be destroyed. The pruning / flailing may also reduce the insect populations of the hedgerow (or other other food sources) on which the birds depend. Hedge pruning maintenance is :- ideally undertaken outside of the nesting season. and only done every second or third year. [caption id="attachment_25527" align="aligncenter" width="600"] A flailed hedge[/caption] Hedgerows also support vital insect pollinators : butterflies, hover flies, moths and bees. These insects help with the pollination of crops such as oilseed rape, legumes and fruit trees. Other insects can help with crop yields by predating upon crop pests, such as green fly and blackfly (these may spread viral diseases on crops such as sugar beet). Insects may overwinter in the hedgerow and move into the fields come the Spring, as the aphids start to increase in number. If trees are left in situ, they may achieve veteran status. Then their rough bark, cracks, holes and dead wood will support a diverse range of species. Owls, kestrels and bats may come to nest. There are also niches that offer opportunities for epiphytes, mosses and lichens. The dead wood may be home for saproxylic beetles. Hedgerows also act as corridors linking to other hedgerows, woodlands etc along which animals can pass (for example, hedgehogs and other small mammals). Hedgerows provide important wildlife corridors across agricultural landscapes. They provide food for insects, small mammals and birds (due to the range of plants and their different flowering and fruiting times). They provide nesting and roosting sites for birds and bats, and ‘homes’ for a variety of small mammals. Many insect species over winter in hedgerows. The trees and woody shrubs help with carbon sequestration. Hedgerows offer a windbreak, reducing wind speed and hence lowering soil erosion, they may also offer shelter to animal stock. The roots also help stabilise the soil. [caption id="attachment_40483" align="aligncenter" width="675"] Hedge with beech, nettle, dog rose, brambles, hazel and ash - amongst others[/caption]
Bumblebee pollen collecting
Bumblebees (and bees) collect nectar and pollen. Pollen is a vital food, used in the various stages of a bumblebee’s life. In Spring, newly emerged queens feed on pollen, then it is used to feed its their sister workers. The workers, in turn, take over the feeding of the colony (the larvae and future queens). If not enough pollen is collected, then the colony will not thrive, which can have significant long term effects. Bumblebees are already facing many threats (from habitat fragmentation, agrochemicals and disease). The collection of pollen is a demanding process, and bumblebees will forage over a wide area. They start their pollen collecting activities earlier than many insects as they can warm themselves up by ‘shivering’, that is, rapid muscle contractions which generate heat, warming the insects up ready for flight. Bumblebees can fly in colder conditions and at higher elevations than many other insects. However, research at North Carolina State University has shown that the North American bumblebee (Bombus impatiens) can overheat when exposed to high temperatures (circa 42oC plus). So, if a bee is carrying a significant load of pollen and it is a hot day, its muscles have to work harder and the bee is at risk of overheating. A bumblebee loaded with pollen may be 2oC hotter than an unladen bee; it may be reaching its ‘thermal limit’ - a temperature at which its organs are damaged. Climate change means that many parts of the world are now experiencing extreme weather events, when temperatures can reach into the forties. [caption id="attachment_39978" align="aligncenter" width="675"] Bumblee leaving foxglove[/caption] Increasing temperatures could affect the foraging activities of bumblebees in a significant way - affecting how much pollen is collected and how much pollination takes place. If pollen collection is reduced then colony development is affected and so population numbers will be affected. Bumblebees are key pollinators in natural and agricultural systems, and if their numbers decline there will be ecological and agricultural consequences.
Flowering plants and pollinators
Plants have existed for hundreds of millions of year - as algae, mosses, liverworts, ferns but flowering plants only appeared about 140 million years ago. The exact timing of their appearance is a matter of some debate (see article) They have been a massive evolutionary success, there are perhaps 300,000 to 400,000 species world wide. They reproduce using pollen. This is used to fertilise the ovules and produce viable seeds. Most plants rely on insects to transfer this pollen to the ovules, indeed over 80% of flowering plants have relied on insects for this service. To this end, flowering plants (Angiosperms) have evolved a number of inducements to attract insects : colour, scent and nectar. When we think of pollinators, we generally tend to think of bees, bumblebees, hover flies. But when flowering plants first evolved, fossil evidence suggests that many of these flowers were quite small so it is probably that the first pollinators were also quite small, and hence able to access these small flowers. The first pollinators were probably small flies, midges or beetles (more than 77,000 beetle species are estimated to visit flowers). Quite when bees (and their pollen collecting activities) evolved is not known. A recent analysis of the "family tree" of the families of flowering plants indicates when different plant families evolved and when various forms of pollination emerged. Insect pollination is / was clearly the most common method of pollination, and was probably the first means of pollination. This analysis also indicated that other means of pollination (involving small mammals, birds, bats) have evolved several times, as has wind pollination. Wind pollination seems to have evolved more often in open habitats and at higher altitudes , whereas animal pollination is associated with closed canopy tropical forests. The pollen of insect pollinated flowers is significantly different to that of wind pollinated species. Flowers that are insect pollinated tend to produce pollen that is heavy, 'sticky' and protein-rich. Pollen is an important constituent of the diet of many insects. Wind pollinated species by contrast produce large quantities of pollen, the grains being light and small.
Professor Goulson on allotments, gardens and bees.
I recently attended the National Allotment Society AGM, where the keynote speaker was Professor David Goulson. His main academic studies focus on the threats to bees, bumblebees and other insects. He is based at Sussex University. Back in 2006, he founded the Bumblebee Conservation Trust; a charity which has grown to some 12,000 members. In his talk at the meeting, he made the following points : He loves allotments because they capture carbon and are rich in biodiversity. They produce a lot of food. Typically producing some 10 tonnes / hectare whereas farming productivity is about 3 tonnes per hectare. The record on a 1m2 in an allotment is 10 kg, which is the equivalent of 100 tonnes / hectare. Allotments not only produce good food for healthy eating, but people get good exercise through their gardening activities. A study shows the ‘over-60s’ with allotments have longer life expectancies [controlling for other variables]. [caption id="attachment_40124" align="aligncenter" width="675"] A bee at risk of extinction.[/caption] There are over 300,000 allotment plots in the UK and some 90,000 people on waiting lists. More allotments could help counter poor health and cut NHS costs. We should turn our cities, towns and villages into a network of nature reserves - essentially a form of urban rewilding. Gardens are a vital part of this, as there are some 400,000 hectares of them in Britain. Prof Goulson is really keen on less mowing, more ponds and no pesticides. Interestingly, France banned pesticide use in public and urban areas, such as parks, back in 2014 - it is an example that we should follow. Even pet flea treatment is damaging to insect life. The strength of the doses used means that the chemicals can pass into the environment - to grass, rivers, canals and pools. Sadly, now 8% of gardens have some plastic lawns, and plastic hedges (and Wisteria !). Plastic makes him despair.Plant diversity in pavements should be celebrated. Wild flowers / weeds are sources of pollen & nectar for pollinators. Verges should be nature reserves. A Scottish "On the Verge" group stopped councils mowing 8x a year and planted a seed mix to transform verges in their area. Councils should mow less. Some people may object, so people should strengthen their Council’s hands by writing to them and praising them for no-mow-May-type efforts. The Buzz Club - has been set up, this is a citizen science project to see what works best for insects. There are lots of short films on his youtube channel . Bees and other pollinators need help. He suggested lots of ways to help them, for example, drilling holes in logs for bug hotels. You can follow Prof Goulson on Twitter or Facebook. [caption id="attachment_40132" align="aligncenter" width="675"] Bumblebees 'enjoing' a small clump of poppies[/caption] [caption id="attachment_40129" align="aligncenter" width="428"] urban herbicide use[/caption]
woodlands web updates : 25
Earlier flowering times. A survey has shown that plants are flowering earlier in the year. Cambridge University researchers compared the dates of flowering of some four hundred plus species before and after 1986. They found that plants are now flowering roughly one month earlier. More recent decades have been associated with rising air temperatures. This change in flowering time may have profound consequences for the plants. The vast majority of plants are dependent on pollinating insects (bees, bumblebees, hoverflies) to set seed and complete their life cycles. By flowering early their cycle, plants may not match up with the activities of their pollinators. They may flower but their pollinators bee ‘missing’. Their pollinators need to emerge from their overwintering stage earlier. Earlier flowering may not matter for those plants that are visited by several pollinators but for those that are dependent on one or two specific visitors - it may critical. For example, Sainfoin. Sainfoin is host to a particular (solitary) bee Melitta dimidiata (remote image here). It is a monolectic bee; i.e., a bee that collects food (nectar and pollen) from only one species of flower - the sainfoin. If the sainfoin flowers earlier in the year and the bee does not match the shift in flowering, then the bee has a problem. Work on the effects of climate change on pollinators has been somewhat limited to date, but studies in Japan suggest that bees / bumblebees are somewhat behind plants in their response to environmental changes. Bee and bumblebee news. Recent research data provide evidence that (buff tailed) bumblebees are not able to detect or avoid concentrations of pesticides [imidacloprid, thiamethoxam, clothianidin, or sulfoxaflor], as used ‘on the farm’ - from signals sent by their mouthparts. The mouthparts are covered with tiny hairs and these hairs have ‘pores’ in them. Chemicals pass through these ‘pores’ to sensory cells; this is how the bee tastes and smells. It seems likely that the bumblebees are at considerable risk of consuming pesticides in their search for nectar when visiting pesticide-treated crops. [caption id="attachment_19675" align="alignleft" width="300"] Bumbles foraging in artichoke[/caption] Another agrochemical, Roundup, has been found to affect the learning and memory of bumblebees. Roundup, which contains glyphosate, affects their ability to learn and memorise connections between colour and taste. Impaired colour vision is likely to affect the foraging and nesting success of the bees. The research was conducted in Finland by researchers at the University of Turku. In yet another concerning study, researchers at the University of Maryland have found that the life span of laboratory-raised honey bees has reduced considerably. Five decades ago, the lifespan for a worker honeybee (Apis mellifera) under controlled laboratory conditions was about 34 days. Now it is some 17/ 18 days - according the report in Nature. The study also reviewed the scientific literature [from the 1970s to now] and noted a trend in the life span of bees. Shortened worker bee lifespan has implications for colony health and survivorship. The work at the University of Maryland is ongoing. Methane release. Ghost forests are found in coastal areas. As a consequence of climate change, sea water has ‘invaded’ low laying areas and trees have died. The dead trees are sometimes referred to as ‘snags. A number of woodland / forest communities along the eastern coast of the United States have been affected. Recent work by North Carolina State University has shown that these ghost forests release methane. The methane is generated by bacteria in the soil but then ‘escapes’ by means of the ‘snags’. As it passes through the wood of the ‘snags’, microbes may consume and alter the methane. As methane is a potent greenhouse gas, understanding the nature and extent of these methane emissions from ‘ghost forests’ is important. Tree rings The study of tree rings has been invaluable in dating many historic objects ./ archaeological sites. Now, it seems that they could play a role in estimating the amount of carbon that trees are actually absorbing (carbon sequestration), if woodland / forest inventories are coupled with core samples of the trees. The measurement of the annual rings from such cores could create a record of ‘tree growth across space and time’, yielding a more accurate estimate of the amount of carbon being taken up by woodland and forests. Forests, soils and oceans are major ‘carbon sinks’.
Some years back, the Woodlands blog posted various articles about hedgerows, noting the loss of many - due to the increased mechanisation of farming in the mid C20th. Now, there is greater recognition of the importance of hedgerows, and there are initiatives to promote the maintenance and expansion of hedgerows. But what is a hedgerow? Natural England offers a definition as follows : A hedgerow is defined as any boundary line of trees or shrubs over 20m long and less than 5m wide, and where any gaps between the trees or shrub species are less that 20m wide (Bickmore, 2002). Any bank, wall, ditch or tree within 2m of the centre of the hedgerow is considered to be part of the hedgerow habitat, as is the herbaceous vegetation within 2m of the centre of the hedgerow. This differs from the definition in the Biodiversity Action Plan, which included references to ancient hedges / species-rich hedges. The definition now includes all hedgerows consisting of at least one native woody species of tree or shrub (mainly), but it does exclude bramble and honeysuckle as ‘woody species’. According to one source, there are some 550,000km of hedgerow in England, with over 400,000 km being actively managed. Hedgerows are an important semi-natural habitat in what is otherwise a managed agricultural landscape. They are found across the country but there are more in lowland regions. Hedgerows in the south east are associated with large fields and fewer trees, the proportion of trees in hedgerows increases as one goes north and west. The nature of hedgerows varies across the country but all are important as : They provide a habitat, shelter (micro-climate provision) and resources for many different species (from plants to insects, birds and mammals). Hedgerows are particularly important as nesting sites for birds. They support animals that have key roles within the broader ecosystem, for example pollinators and predators of pests. They offer an important source of nectar that helps support wild bees - adjacent farmland can be a poor source of nectar Hedgerows are known to support threatened (red listed) species Hedgerows capture and store carbon (above and below ground) Hedgerows offer ecosystem services eg. mitigation of water flux and availability, landscape connectivity, soil conservation / stabilisation. A number of studies indicate that increasing the number of hedgerows would help with landscape connectivity (for example, for hedgehogs) and that planting of blackthorn and hawthorn in association with later flowering species would help support a number of wild bee species. Expanding the number of hedgerows could have some negative effects as they might offer a home to invasive species and / or pathogens; but one study has indicated that ash trees in hedgerows suffer less impact from ash dieback than trees in forests. To date there does not appear to be any detailed research on whether increasing hedgerow coverage would have any impact on tree disease / pathogen spread. Hedgerows, like woodlands themselves, face a number of challenges due to climate change. Warmer winters may mean that the ‘winter chill’ requirements of some shrubs / trees will not be met; this may mean flowers and fruits fail to form properly which in turn means less food for birds, small mammals etc. Drier summers may stress some species, trees like Beech are susceptible to drought. Extreme weather events (like Storm Arwen) can inflict damage on hedgerow trees. If a hedgerow is next to farmland, then it may experience drift from pesticide and / or herbicide spraying nutrient enrichment (eutrophication) due to the use of fertilisers. Hedgerows with a diverse structure, with plants, shrubs and trees of varying ages and heights provide the widest range of niches / microhabitats for wildlife. The inclusion of dead / decaying wood offers opportunities for various fungi, saproxylic beetles, woodlice etc. Some hedgerows are managed / reduced with a mechanical flail (see above !!!). If this is done annually, it can result in a loss of biodiversity. Trimming should be done on a 2 or 3 year cycle; and some sections of the hedge might be left for longer " see (https://www.hedgelink.org.uk/cms/cms_content/files/76_ne_hedgecutting.pdf). Thousands of tree and hedgerow plants are being planted to create a flood defence project at Castlehill, East Hull. The plan is to create some seven hectares of woodland and over five kilometres of new hedgerow, as part of a flood defence project (to store floodwater east of the city). Trees such as field maple, downy birch, English oak, and black alder are being planted along with species of willow, dog rose, guelder rose and blackthorn and hawthorn to create hedgerows and scrubland. Other species will be allowed to naturally develop in the area and the habitat is expected to reach ‘maturity in some fifteen to twenty years. There is a citizen science project that involves surveying hedgerows. It is organised by the People’s Trust for Endangered Species [PTES]. The Great British Hedgerow Survey guidelines can be found here : https://hedgerowsurvey.ptes.org/survey-guidelines Some times hedges offer a home to other things
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.