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

Acer pseudoplatanus is known as the sycamore in the U.K, or the sycamore maple in the United States. It was first described in botanical terms by the Swedish naturalist Carl von Linné in 1753.  It is thought that the sycamore is an introduced species, as its native range is central Europe and Western Asia.  It probably arrived in this country in the Tudor period (circa 1500 CE).  That it has no old native names is perhaps indicative of its absence before Tudor times, (Some say it has been here longer and have suggested that it persisted in Scotland).  It was recorded in the wild in Kent in 1632.  The sycamore is probably best regarded as a neophyte.  A neophyte is a plant that is not native to a particular area / region and has been introduced in recent history. Whatever its background, the sycamore is now to be found spread across the country. Its spread is due in no small part to the capacity of a single tree to produce many hundreds, indeed thousands of seeds.  The seeds are ‘winged’.  The wing of each seed develops from an extension of the ovary wall.  Two seeds are joined together to form a structure termed a double samara - a 'helicopter-like' device.  The wings catch the wind and the fruit rotates as it falls from the tree. This slows the descent and enables seed dispersal over a greater distance.  The sycamore has been deliberately introduced in a number of countries as it is tolerant of air pollution, salt spray and wind and it readily invades disturbed ground (abandoned farmland, brownfield sites, roadsides etc).  It is now regarded as an invasive species in, for example, New Zealand.  The leaves of the sycamore are simple but large. Each leaf has five distinct lobes and five veins radiate from the base of the leaf into the lobes. The edge of the leaf is somewhat ‘ragged’ with rounded 'teeth'. The lower surface may bear some hairs. The leaves are arranged in opposite pairs around the twigs / stem. In Autumn,  heavy leaf fall can mean that the ground under a sycamore tree can be smothered with a significant layer of the leaves, consequently the diversity of the ground flora underneath the tree may suffer. In spring and summer, the leaves can support large populations of aphids. Evidence of aphids on the leaves may be seen in the form of honeydew; this is the sugary waste of their feeding.   It may fall onto lower leaves (and cars); it provides food for flies and other insects.  The aphids themselves are a food source for ladybirds.  Sometimes the leaves are covered with small, red 'blobs' / projections - these are galls caused by a mite (a small spider-like creature).  The female mite lays eggs in these structures. Sycamores can be coppiced, that is, cut down to a stump which will rapidly produce new growth - for poles etc.  The timber of the sycamore is close grained, white to cream in colour that turns ‘golden’ with age.  It can be used in making musical instruments (violins), furniture, wood flooring There are many other species in the genus Acer, for example, Acer platanoides - the Norway Maple, Acer campestre - the Field Maple, Acer palmatum - Japanese Maple, and Acer saccharum - the Sugar Maple.  All of these have a (diploid) chromosome number of 26. Interestingly, the sycamore has a chromosome number of 52 - the number of chromosomes per cell has doubled.  The sycamore is a polyploid. A couple of interesting historical points about sycamore ;  The Tolpuddle Martyrs' Tree is a very old sycamore. The tree was used as a meeting point (in 1833) for six local agricultural labourers to discuss low wages and their poor living / working conditions.  They are associated with the birth of the trade unionist movement.  The 'Tolpuddle Martyrs' (as they came to be known) were sentenced to seven years of penal labour in Australia and were transported to Botany Bay. Dule trees were used as gallows for public hangings and also used as gibbets for the display of the corpse after such hangings.  One such dule tree lies within the grounds of Leith Hall, near Huntly, Aberdeenshire. This tree is a sycamore. The strong timber of sycamore made it a favoured tree for this purpose. [caption id="attachment_36329" align="aligncenter" width="645"] emerging leaves[/caption]  

What do the seeds of ash, sycamore and maple trees have in common?  They all are enclosed in a wing-like structure that helps them disperse - away from the parent plant and indeed each other.  Wind dispersal is also known as anemochory.  Effective fruit / seed dispersal provides a tree's offspring with the chance to colonise a new area, and reduces competition for resources with their parent and siblings; it also reduces the likelihood of infection with pests and pathogens.  A single Ash tree (Fraxinus excelsior) can produce thousands of fruits (also  known as keys) in large clusters attached to the tips of its branches. Read more...

Street lighting may make our roads and homes safer places, but it also contributes to light pollution.  The bright lights of towns and cities make it difficult for us to see the stars and constellations in the night skies.  In places, the ‘warm yellow’ glow of street lights is being replaced with the white light of LEDs,  the benefits of LED lights include energy savings plus an increased life time as compared to conventional lights. However, when compared to older street lamps they emit more  blue light increases.   Some think that this blue light can suppress the production of melatonin ; this is involved in the regulation of our circadian rhythms - particularly our sleep patterns. Read more...

You may well have heard that bees are in trouble. Domestic honeybee hives seem to die more often than they used to, and some of our wild bees have disappeared altogether; for example, three of the UK’s twenty seven bumblebee species have gone extinct. The big, long-term driver of declines has been farming intensification; where once we had plentiful hay-meadows and chalk downland, rich with flowers, we now have flower-free monocultures of wheat or silage grass. Pesticide use is also contributing to the problem, particularly new generations of systemic, persistent insecticides called neonicotinoids that get into nectar and pollen of both flowering crops and wildflowers. Read more...

The grey squirrel (Sciurus carolinensis) is found throughout England, Wales and parts of Scotland. It was introduced between 1876 and 1930 from the States/Canada, probably on a number of occasions. In many parts of the UK they have displaced the native Red Squirrel. Grey squirrels eat an amazing variety of food – bark, buds, flowers, nuts, berries, seeds and fruit from many different species of shrubs and trees (and therein lies the problem). Read more...

Dead and decaying wood forms an important part of any tree or woodland. In the past, dead branches and trees in woodland might have been taken for a sign of neglect or a poorly managed wood; it was regarded as a possible source of disease or ‘rubbish’ that needed to be tidied away. However, dead wood, whether it is part of a living tree or lying on the woodland floor, should be regarded as a resource that contributes to the diversity of the flora and fauna. As wood decays, it offers a series of different microhabitats. It has been estimated that dead and decaying wood can offer a home to some 1800 species. Read more...