Blog - Climate Change
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.
According to the United Nations, a forest is anywhere that is at least 20% trees. As 21% of our capital city, London, lies under the canopy of trees - it is an urban forest*. It is estimated that there are some 8 million plus trees - nearly as many trees as people. London is not alone, Johannesburg is a densely wooded city with some 6 million trees, planted throughout the streets and private properties. Tree Cities of the World is a programme that recognises cities and towns committed to ensuring that their urban forests and trees are properly maintained and sustainably managed. Urban environments can create difficult conditions for tree growth and development. The trees may be exposed to pollutants, high temperatures (heat island effect), drought and/or flooding, and challenging conditions for growth. . Whilst trees may be planted, their subsequent care / nurturing may be limited due to insufficient resources (money / care etc). There needs to be long term maintenance to sustain not just healthy trees but also to make sure that the trees do not damage pavements / roads etc (for example, through root penetration). Trees for Streets is a new national tree sponsorship scheme that some councils have partnered with, which gives local residents the chance to have a tree near them or in a local park. It is a project run by the charity Trees for Cities which aims to support local communities in revitalising forgotten spaces, planting trees and improving the local environment. [caption id="attachment_39418" align="aligncenter" width="675"] Greenery in SE London. View towards St.Helier's hospital.[/caption] In the past, London was a much smaller city surrounded by countryside and woodland, but there are still areas of ancient woodland within it. Some of this woodland remains such as the Great North Wood in South London (hence Norwood and Forest Hill). Other place names - Wood Green, Forest Gate, Nine Elms and Burnt Oak bear witness to the wooded landscape that was once prevalent across London. In fact, some 8% of London’s area is still woodland, and some of it is even defined as ancient woodland (e.g. Epping Forest). [caption id="attachment_39421" align="aligncenter" width="675"] Dulwich Park[/caption] There are also the many parks of London - Hyde Park, Regent’s Park, Richmond Park, Dulwich Park etc. Add to these the trees found in school fields, private gardens, squares (like Berkeley and Portman Squares), plus the trees that line so many streets (estimated at 900,000). Trees (like sycamore and buddleia) have also colonised areas of the built environment, like railway lines / cuttings. The most common London trees are sycamore (7.8%), oaks (7.3%) and birch (6.2%). However, the urban forest has a wide spectrum of species that includes native species, such as ash, hawthorn, hornbeam, field maple and holly, but there is a wide variety of exotics and cultivars in parks, streets and private gardens. In some parts of the capital, the London Plane is a noticeable presence, due to its resistance to pollution and tolerance of root compaction. It sheds 'large flakes' or sections of its bark exposing new material of a variety of colours (brown, grey, yellow), and is sometimes described as ‘self cleaning’. The London Plane is thought to be a hybrid of the American sycamore and Oriental plane. So the urban forest is quite diverse in terms of species when viewed across the capital, but there are parts of the city where species diversity is poor and the age profile of the trees is sometimes limited. This homogeneity can favour pests and disease. Diversity generally favours to resilience. Currently, trees face diseases such as acute oak decline, Chalara ash dieback, horse chestnut leaf miner, Massaria disease of plane and oak processionary moth. London’s urban forest faces an increasing human population and the challenges of climate change. The latter may bring substantial warming and changing rainfall patterns. Wetter, milder winters and drier, hotter summers may be more common in the coming decades. Some trees will be better able to cope with these changing conditions. Future planting will have to follow the maxim of “right tree, right place”. The value of London’s forest is difficult to quantify or to put a figure on. It is a major part of the ‘green infrastructure’ – that is the matrix of green spaces, parks, recreation grounds, lakes, canals, and rivers plus the street trees , green roofs and allotments that provides a range of economic, environmental, and social benefits. The importance of green, leafy spaces came to the fore during the early days of the Covid pandemic, helping with mental and physical wellbeing of Londoners. [caption id="attachment_27166" align="alignleft" width="300"] Mature oak in park.[/caption] The components of the forest offer valuable habitats for wildlife and also provide biological corridors / stepping stones that enable birds and various animals to move through the urban environment. The ancient woodlands and veteran trees offer a home to a variety of wildlife such as bats, stag beetles, orchids etc. In recent heatwaves, people have appreciated that trees also provide shade and cooling in streets and parks. Another aspect of extreme weather is very heavy rainfall, trees and green areas can help reduce the risk of flooding, allowing more water to enter the soil rather than running off hard surfaces of tarmac and concrete. Trees also help capture pollutants, improving local air quality by capturing fine particles from the air (much of this is through deposition on leaf surfaces). One source suggest that trees remove some 2241 tonnes of pollutants each year. Trees and shrubs seem particularly effective in removing ozone, and through its photosynthetic capacity the urban forest can take up carbon dioxide into organic form. The amount of carbon taken up by London’s urban forest each year has been estimated at 77,200 tonnes. To maintain and augment this urban forest, it is important in the coming years that the threats of pests and diseases are fully assessed and controlled The threats arising from climate change are recognised / mitigated Woodlands are properly managed (eg. coppicing); this may include the training of personnel. Create opportunities for planting of trees, hedgerows and woodland. [caption id="attachment_39422" align="aligncenter" width="675"] Tree nursery - 'ready for planting'.[/caption] * https://cdn.forestresearch.gov.uk/2022/04/21_0024_Leaflet-CC-factsheet-Urban-forests_wip06_Acc.pdf
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
A Changing World
The world is warming and many scientists are concerned that the earlier springtime flowering of many plants will disrupt the ‘normal interactions between the plants and their pollinators, be they bees, butterflies, bats. Other subtle changes have been observed. The flower ‘morning glory - Ipomoea is a weedy, vine-like plant in the States . Between 2003 and 2012, the size of its flowers has increased (from a diameter of 4.5 cm to 4.8 cm). The study also revealed that flowering occurred 4 days earlier and the flowers have increased their ‘floral rewards’. That is they devote more resources in the production of pollen and nectar to attract the bees, flies and wasps that visit the flowers. The changes were more noticeable in northern populations of the Morning Glory. Extra Growing time ? In the late nineteenth century, an Ohio farmer (Thomas Mikesell) kept detailed records on local trees*, noting their growth, daily temperatures, rainfall, dates of frosts, snows & thunderstorms. With the death of Thomas Mikesell [July 18, 1917], the world lost an dedicated student of nature and a remarkable phenological record came to an end. It forms the only detailed record of plant and tree growth in North America during the late C19th / early C20th. Since that time, significant global warming has occurred. Now researchers at Ohio State University have compared Mikesell’s observations with growth data of present day trees - from time of bud burst to peak (autumnal) leaf coloration (for seven tree species). They concluded that trees now experience a longer growing season. Leaves stay on the trees for approximately one month longer than they did a hundred years ago. Quite how this longer growing ‘season’ affects the trees is not known, there may be a positive through increased carbon assimilation. On the other hand, higher temperatures may stress the trees in ways which are not yet understood. *A Calendar Of The Leafing, Flowering And Seeding Of The Common Trees Of The Eastern United States.
Trees in towns and cities.
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.
In recent times, peatlands and areas of blanket bog have been recognised as important parts of our landscape. Blanket bog is mostly found in wetter and more northern regions - in parts of Ireland and Scotland; in England a lot is to be found in Yorkshire. Peatlands and bogs play an important part in controlling the run off of water from hillsides, plus they also represent an enormous store of ‘sequestered carbon’. The remains of plants (and animals) have been buried in wetlands but have not decomposed fully (usually due to the acidic conditions). Sometimes large chunks of trees are found in peat bogs, and occasionally even human remains (for example Tollund man) have been found. Some of the peat deposits are incredibly thick and the material stored in them may be many thousands of years old. Moorland ‘management’ techniques have been implicated in the severe erosion of certain areas, and the peat (that has accumulated over thousands of years) is being washed away. [caption id="attachment_32147" align="aligncenter" width="650"] Water logged conditions are ideal for peat formation[/caption] The UK has lost many areas of wetland habitat in recent times. A research team lead by Dr Swindles (Leeds University) examined many peatlands and looked at the changes that have occurred over the last two millennia. They found that the majority of peatlands have become drier. This drying out changes the role of a peatland from carbon sink to carbon source; i.e. releasing carbon into the atmosphere - contributing to global warming and climate change. The streams and rivers that permeate these areas often turn a deep, rich brown as this organic material is washed out. [caption id="attachment_34388" align="aligncenter" width="650"] Stream flowing through peat moorland[/caption] Various efforts are being made to help stabilise these valuable ecosystems and a number of techniques to have been tried. At Fleet Moss, a North Yorkshire moor between Wharfedale and Wensleydale, the Yorkshire Peat Partnership project has been working to restore areas of degraded peatland by creating dams and reintroducing wildlife. The conservationists have been using grass seed to try and stabilise the peat, hoping that as it grows and extends its roots, it will stop the peat from being washed away while allowing bog plants and sphagnum to flourish. Sphagnum moss can hold 26 times its weight in water. Their work is already bearing fruit,. Originally, the land was largely acres of heather, with little variety in terms of the animals and plants that had made a home there. But over time, owls, frogs, foxes and weasels have appeared. With time, the grass should stabilise the peat and allow bog plants to establish themselves. However, it has not been an easy process. Whilst the scattering of grass seed has worked in some areas, this does not always work everywhere, particularly on exposed sites; seeds can be battered by rain and wind. Even at the height of summer, the weather on some of England’s highest terrain can be fierce, and scattering grass seeds on areas that are battered by wind and rain has proved to be problematic. So now in some areas a hydroseeder is being used where grass colonisation has failed. This is where green sludge and the bioengineering company TerrAffix come in. TerrAffix uses a hydroseeder to spray the mix of brash (chopped heather), grass seeds, fertiliser and a special adhesive (or tackifier), to areas facing particular challenges. This equipment has been used to reseed prairies in the States, and can also be used on the steep slopes of motorways, It will be some time before it is known whether this technique is successful in boggy and peatland areas. If it does show signs of success then plugs of plants such as bog asphodel and sphagnum will be added, in the hope of recreating a more natural and diverse flora for the areas. Further information on the restoration of peatlands can be found on Dr. Emma Shuttleworth's web pages and in articles such as this. Featured image is a 'book' made from bog oak.
Felling trees, planting trees.
In recent times, we have heard much about various initiatives to plant more trees, such as The Queen’s Green Canopy tree planting project to mark the platinum jubilee. Tree planting is part of the government’s plan to mitigate certain aspects of climate change as the trees will absorb carbon dioxide from the atmosphere, which is one of the principal greenhouse gases. Once absorbed and used in photosynthesis, much of this carbon is then locked away for many years in the form of complex compounds, such as cellulose and lignin. The peak of carbon dioxide uptake by UK woodlands and forests was estimated to be just under 20 million tonnes in 2009. However, since that time the amount has actually declined. Many of the conifer plantations that were planted back in the 1970’s and 1980’s have now been felled / harvested, so they no longer contribute to the uptake of carbon dioxide. It is important that these clear felled areas are replanted and tree cover restored; indeed, in places increased. Planting rates have risen in Scotland but the performance by the rest of the UK is somewhat limited. Even with new planting, it takes time for such new forests / woodlands to reach the CO2 absorption levels seen in the 2000’s. Continuous cover forestry (CCF) is a different approach to woodland forest management; it seeks to avoid clear felling and promotes a mosaic of trees by age and species. There are a number of factors that influence new planting, such as the availability of land. Using high grade agricultural land for tree planting would affect targets for increased agricultural productivity and domestic food supply. Also, with climate change and the increasing number of extreme weather events (storms, flooding, drought etc) greater thought needs to be given to risks such as forest fires. Recent months have demonstrated the ferocity of forest fires in France, California and Portugal. We cannot assume that the UK will be exempt from such events. Similarly, we have witnessed powerful storms (such as Storm Arwen) which felled many thousands of trees (and impacted on public services such as electricity and train travel). The warming climate is also associated with ‘new’ diseases and parasites in our woodlands and forests. New planting needs resilience ‘built in’ to the plan. The Environment, Food and Rural Affairs Committee in its recent report (2021/2) has made a number of important comments in relation to tree planting in the UK, notably : It noted that the Forestry Commission had said that nurseries in the UK will struggle to expand production to deliver the number of young trees required for the Government to achieve its planting ambitions. There is a lack of a sufficiently skilled and large workforce to achieve England’s tree planting ambitions. To meet the Government’s tree planting goals, the UK will need to import seeds and young trees (until domestic capacity increases); and this carries the risk of the introduction of pests and diseases.
In 1820, John Keats famous poem “To Autumn’ was published. Its opening line often serves to describe autumn as ‘The season of mists and mellow fruitfulness’. Indeed, Autumn has arrived here. Woodlands have been transformed into a 'tableau' of red, yellows, and oranges as the leaves are shed and the woodland floor has become a veritable fungal jungle, (as Jasper has described). Hawthorn and other bushes are laden with berries, conkers and acorns are generously strewn across woodland floors, squirrels are eating hazelnuts (and hiding them as a winter food store). But this cornucopia of fruits and seeds may be in response to the long, hot and very dry summer we have experienced. Trees and shrubs have been stressed by the heat and drought. Some have responded by mobilising their reserves / efforts into producing more fruits and seeds, to ensure that they pass on their genes to the next generation. Different trees are responding in other ways. Some are ‘holding on’ to their leaves for longer, whilst others (like some birches and rowans) have already shed theirs - in order to limit the damage from wilting and water loss during the intense heat and drought of summer. [caption id="attachment_39130" align="aligncenter" width="675"] Autumnal colour[/caption] Blackberries appeared early this Summer and few are to be seen this Autumn, some animals (like the dormouse) will search in vain. [caption id="attachment_39026" align="aligncenter" width="675"] Black Bryony berries (photo by Art Symons)[/caption] Will this Autumn be long and mild? It may extend into the traditional winter months. There is also the threat of extreme weather events (like Storm Arwen that brought severe winds across the UK last November). Whilst we might welcome mild weather (with the high price of gas and electricity), it could be mean an increase in bacterial and fungal infections, not only of plants but also affecting overwintering insects - tucked up in cocoons and pupal cases. Prolonged cold periods, coupled with frosts limit the spread of such infections. The cold of winter is also the traditional signal for animals like hedgehogs to hibernate. If they are still active in winter when food is scarce, then they will lose condition and possibly starve to death. Milder weather in Autumn and Winter also affects the migratory behaviour of birds, some birds may choose to overwinter here. Some seeds need to experience cold temperatures before they will germinate in the following Spring. Climate change and severe weather events are here to stay until there is a coordinated and concerted effort to reduce greenhouse emissions on a global scale. On a local scale, our gardens (which represent some 400,000 hectares of land) can make a contribution by encouraging wildlife / pollinators and promoting biodiversity. Gardens can also help to some extent with extreme rainfall. During heavy rain, water runs off hard surfaces and into the drains, these may also deal with sewage. When the drains are overwhelmed by storm water, sewage is discharged into our rivers (and the sea). Gardens can help by reducing hard landscaping, so that rain can soak into the soil instead of running off into the drains making use of water butts. They capture water, so it does not enter the drainage system. It is also there to use when the garden needs water (and there is a hose pipe ban) mulching the soil with a layer of plant material. It is an effective method of conserving water in the soil and it reduces surface runoff, increasing the infiltration / penetration of water into the soil. It helps keep the soil moist in times of drought, and helps reduce run off during heavy rainfall. Particularly important when planting young trees / shrubs. [caption id="attachment_38957" align="aligncenter" width="675"] a light mulch (in Art's garden)[/caption]