Loss of nitrogen fixing species. Some plants can ‘fix’ atmospheric nitrogen.  That is they can take nitrogen from the air and use it to make complex nitrogen-containing organic compounds (such as amino acids / proteins).  This fixation of nitrogen is due to the presence of symbiotic bacteria in root nodules.  Gardeners often make use of ‘nitrogen fixers’, such clover, peas and beans to augment soil fertility. A recent study has investigated the changes in the makeup of the flora in European forests (over several decades) from 1940 to 2019.  What they found was that the proportion of nitrogen fixing plants has declined.  The changes did not seem correspond to any changes in temperature  or aridity / rainfall during the time period, but to nitrogen accumulation in the environment.  When nitrogen levels are low, nitrogen fixing plants have an advantage, but when nitrogen levels increase their advantage over other plants is lost. Nitrogen compounds in the soil can result from the intensive use of fertilisers on nearby agricultural land or atmospheric deposition of various pollutants.  Nitrogen levels have increased tenfold since the start date of the surveys.  This loss of nitrogen fixing plants might, in the long term, result in a loss of ecosystem resilience. For further info - visit https://www.science.org/doi/full/10.1126/sciadv.adp7953 The great green wall project. There are a number of large scale tree planting projects, many associated with offsetting global warming.  The great green wall aims to grow a belt of trees some 8000 km in length, and 15 km wide in the Sahara.  The planned route supported trees in the past.  The aim is to ‘stabilise’ the desert, limiting further expansion into the Sahel, as the tree roots help to stabilise the soil, limiting erosion.  Desertification is associated with drought and overgrazing.  The idea of such a barrier was taken up and approved by countries south of the Sahara in 2002, during a special summit.  The trees selected are drought resistant species, that also serve to fertilise the soil and contribute fruits, fodder and fuel wood for local communities. Though millions of trees have been planted, the project needs more funding if it is to succeed. Further details about the great green wall can be found here and here. Dealing with drought ? [caption id="attachment_35526" align="alignleft" width="300"] drought[/caption] Drought is a problem not only for woodlands but also for crops, resulting in substantial food loss across the globe.  The damage to crops is likely to increase as fresh water availability declines.  During drought, the availability of water in the topsoil decreases, leaving water only accessible in the  deeper subsoil.  Plants seek water through their roots and whilst roots generally grow downwards, they also tend to spread outwards to form a network. So, if the roots are mainly located in the upper layer of the soil, they may not be able to absorb water as the soil dries.   Now, research at the University of Nottingham has found that the plant growth regulator abscisic acid plays a critical role in a plant’s response to drought.  The abscisic acid  promotes the production of another growth regulator - auxin.  The two enhance the plant’s geotropic response* - so that the roots permeate deeper into the soil in search of water. Full details in the research paper here : https://www.sciencedirect.com/science/article/abs/pii/S0960982224016439?dgcid=coauthor * Geotropism is a plant’s response to gravity.

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

In a previous woodlands.co.uk blog, Professor  Dave Goulson (University of Sussex) has written about the problems that bees and bumblebees face.  Recently, he joined with Clipper teas (who produce organic tea products) to again emphasise the problems that bees and other pollinators face, and to explain how our lives would be affected if they were to be lost.  Bee, bumblebee and other pollinator populations are at risk or in decline.  Professor Goulson estimates that there are some 6,000 different species of pollinating insects in the U.K alone, but they face risks as a result of Habitat loss Pollution Climate change Use of pesticides (insecticides, herbicides, fungicides) [caption id="attachment_36158" align="aligncenter" width="650"] Hoverfly foraging[/caption] Whilst it is true that insecticides such as neonicotinoids are directly toxic to bees and bumblebees, many other compounds used as herbicides and fungicides are also harmful to these insects.  Obviously herbicides get rid of weeds, but weeds or wild flowers are a food source for these pollinators.  Pesticides can have what are termed  ‘sub-lethal effects’, so that the learning ability of the insects is reduced.  Bees and bumblebees can learn which flowers are best as food sources, they can navigate to and from their nests / hives through open countryside.  Also these compounds can affect their resistance to disease, and their fertility / reproduction. It is a concern that that bees’ honey stores may contain a cocktail of several pesticides that the bees have encountered during their foraging.  In collecting pollen and nectar, a single bee may visit / pollinate four thousands flowers in a day. Not only are many thousands of  wild flowers species dependent on bees for pollination but some three quarters of our food crops also need bees and other insects.  Without them, the range and availability fo fruit and vegetables in our supermarkets would be substantially reduced. Whilst going organic and reducing reliance on the many forms of pesticide agriculturally is great help to pollinators, there is also good news in that small growers and even domestic gardeners can have a positive impact on the numbers of bees and others pollinators, such as : Planting a range bee-friendly plants in their gardens Creating a wild flower area in the garden or Allowing the lawn to grow up to form a small meadow like area Reducing the use of all pesticides - insecticides, herbicides, fungicides etc.

Beavers Two decades after were first returned to the UK, in Scotland, and 400 years after the species was hunted to extinction in Britain, counties across England and Wales will also become home to new beaver families.   Beavers were hunted to extinction in the UK some 4000 years ago.  A number have been reintroduced in Scotland and the South West, but this year should seen more re-introduction in Wales, the Isle of Wight,  Derbyshire and Nottinghamshire.  It is hoped the beavers’ activities will help restore/create wetland habitats, boosting biodiversity and reducing flood risks. Further details of these reintroductions can be found here. Peatlands As the woodlands blog has reported, peatlands are often under threat, for example, by fire.  The Wildlife Trusts has called on the Government to do more to protect and restore our carbon rich habitats.  The peatlands of the UK are estimated to store 3.2 billion tonnes of sequestered carbon - more than UK woodlands. Greening cities. London is to introduce a green space system in the coming months -  termed the Urban Greening Factor (UGF).  The Green Space Factor is an innovation of the City of Berlin in 1994,  The plan calls for the various boroughs to implement urban greening practices.  Ideas behind the plan have also come from the Swedish city of Malmö.  Here, the Western Harbour (20-minutes from Malmö’s centre), was essentially 175 acres of contaminated soil and deserted docklands, subsequent to decline of the city’s shipbuilding industry. But now, it has been redeveloped with new apartment blocks - each of which is complemented by a green space area.  There are parks, social courtyards and meeting spaces which offers beds planted with a native herbs and wildflowers.  There are also stormwater drains and ponds that offer opportunities for wildlife. The impact of the road network. Our road network is extensive.  There are nearly 700,000 km of road across the UK, which cover some 0.8% of the land.  Roads permeate nearly every part of the country.  Roadless areas are in short supply; they are mainly upland regions (peat bogs, moors, heathland and grasslands).  Pollution from roads can take many forms Light pollution, Noise pollution, Heavy metals,  Nitrogen oxides Particulates (PM2.5 & PM10) Whilst high levels of pollution are localised and associated with the busiest roads, a recent study (by researchers at Exeter University and the CEH) suggest that low levels of pollution from road networks are pervasive, and may extend over 70% of the land area of the UK. As the woodlands blog has reported, hedges can help block pollution to some degree and this has been substantiated by work done by Dr Tijana Blanusa et al at the Royal Horticultural Society.  They investigated the effectiveness of hedges in ‘soaking up’ pollution, comparing different types of shrubs/trees - such as  hawthorn and western red cedar.  They found that on roads with heavy traffic that a species of Cotoneaster (franchetti) was 20% more effective than other species; though shrubs with ‘hairy’ leaves were generally effective in ‘trapping’ particulates.

In winter, woods can seem a bit ‘naked’ and empty. Trees and shrubs have entered into a dormant state in order to survive the rigours of the winter months. Their buds await the signals that herald Spring. Many birds will have migrated to warmer climes, some animals will be hibernating. Many insects will be spending the winter as eggs or pupae, whilst herbaceous plants will over-winter as seeds, corms or bulbs.  But on the bark of many trees and on the surfaces of fences and walls, there will be lichens – they are there in summer, winter, spring and autumn.  Lichens are rather unusual in that they are an amalgam of two (or occasionally three) organisms : a fungus and algae. They are symbiotic systems, where two partners work together for mutual benefit (occasionally there are more than two partners). The fungus makes up the bulk of the lichen’s structure (known as the thallus), but the algae (green algae or cyanobacteria) are essential as they can photosynthesise and provide the organism with carbohydrates.  The nature of the biochemistry and physiology of the lichen symbiosis is largely due to the pioneering work of Dr David Smith at the University of Oxford in the 1960's and 70's. Read more...

Plastic mulch - white (though sometimes black) polyethylene strips, each about a meter wide, can occasionally be seen stretching across fields.  Crops grow through the slits or holes in the thin plastic sheeting. The sheets are used because they help to conserve water,  suppress weeds,  reduce soil compaction boost soil temperatures reduce waste - by keeping ripening fruit off the soil Read more...

For some years now, the United Nations has promoted an ‘international day of forests’.  Essentially, the day is a celebration of forests and woodlands; it seeks to raise awareness and importance of all types of woodland (large or small).  Woodlands and forests offer a wide range of ‘ecological services’ : Read more...

We are seeing increasing interest in the forestry industry in ‘Natural Capital’ – defined in simple terms as the wide range of benefits derived from nature. What is it? ‘Natural Capital’ refers to the value forestry and woodlands offer above and beyond commercial timber value. This includes the benefits and services that a woodland may offer such as cleaner air, flood defence, climate regulation, pollination or recreation and health benefits. This is not a new concept to owners of small woods who have long considered the value of their woodlands to be so much more than value of the trees themselves. Read more...