At present, our forests and many across much of Europe have a medley of different species, and this has been the case for many hundreds of years.  They have survived minor fluctuations in climate and weather.  However, now climate and weather are changing in significant ways.  There are more extreme weather events, ranging from unprecedented rainfall to drought and periods of very high temperatures.  Winters seem to be be warmer and wetter, summers hotter and drier. Consequently, there is concern that many tree species being planted today will not be able to survive in the conditions that they are likely to experience in 50 or a 100 years time.  Species like the European Beech (Fagus sylvatica) are likely to struggle (like many did in the heat wave of 1976).  The root system of the beech is shallow, and though it has large roots spreading out in many directions, it cannot access water that may be present at deeper levels in the soil.   Though it is not known how native trees might adapt or be able to respond to a changing climate, it is possible that the number of tree species per km2 able to survive through to the next century may well fall by a third to a half in a warmer climate (depending on how quickly the warming occurs). Examination of some 60 plus European trees species at University of Vienna by Johannes Wessely et al suggested that the English or Pedunculate Oak (Quercus robur) may be a species that could cope with changing climatic conditions. It seems that native UK Oaks are genetically diverse, and this gives rise to variation and the potential to adapt to changing conditions.  Oak is wind pollinated and its light pollen can be dispersed over long distances, which promotes outbreeding and genetic diversity. Whilst the oak has always been valuable as a species for :- Timber production : it is used in furniture making and in the past thousands of oaks were used in the building of ships such as the Mary Rose. Carbon sequestration / storage - it is long lived and has a large above ground biomass Biodiversity : it provides a ‘home’ for many species of animals, plants and fungi. It offers food and shelter for many invertebrate species, numerous insects and spiders); its leaves often show the ‘scars’ of their feeding activities. Its bark is an ideal substrate for many lichen and bryophyte species (epiphytes). The roots of the trees establish mycorrhizal associations with various fungi. Now, the Oak may prove to be valuable in a warmer world as a species for timber production and reforestation projects.  The Oak’s ability to support other plant, animal and fungal species would also be important in terms of biodiversity and resilience..   Forests with a smaller number of tree species are thought to be less resilient to climate change and less biodiverse.   [caption id="attachment_41217" align="aligncenter" width="675"] A solitary oak[/caption]

Large trees are important in terms of carbon storage - with large quantities of above ground biomass, lots of carbon is locked away for years. Trees like Sequoiadendron giganteum, the giant redwoods, are truly large trees;. They are, by volume, amongst the largest trees in the world and incredibly long lived.  Some are thought to be over 3000 years old. Seeds of Sequoiadendron giganteum only arrived in the UK in the 1850’s, brought in by Patrick Matthew and William Lobb.  Lobb was employed by the Veitch Nurseries, based in Exeter.  He travelled extensively in both North and South America (including Argentina and Chile), and brought back not only seeds of the giant redwood but also some 3000 seeds of the monkey puzzle tree (Araucaria araucana).  He made a second trip to South America and brought back many different species of flower, including the chilean bellflower, the flame nasturtium, species of myrtle, and Escallonia macrantha. Exotic trees and shrubs were much prized by wealthy Victorians, and redwoods were planted in the estates and at the entrances of many grand country properties.  They also make appearances in many public parks and gardens, see for example the redwoods at the Lower Pond at Whinfell Quarry Garden in Sheffield. Forestry England estimates that there are half a million Sequoias (giganteum & sempervirens) in the country, and nearly 5000 giganteum trees are recorded by location by redwoodworld.co.uk, the woodland trust ancient tree index and the Forestry Commission.   Though it is only some 170 years since their introduction to the UK, some of these trees are amongst the largest trees in the country. This despite the fact that the climate here is not the same as that on the West Coast of America, their 'natural home'.  Due to their growth rate and carbon sequestration potential, there has been some discussion as to whether they might be included in commercial planting initiatives as they seem resilient to changes in climate, rainfall, soil moisture etc.  Disease resistance in another consideration.  The growth and biomass of some 97 Sequoias at three different sites (Lakehurst, Havering and Benmore) has recently been investigated (using laser scanning)*.  The growth of the trees at Havering was less than that at the other sites, possibly due to lower rainfall (and increased competition) in the East.  However, the growth rates of the trees studied were in the region of 150kg above ground biomass per year (this equates to 81kg of carbon per year).   Such growth is broadly similar to that of their American counterparts of a similar age.  It would seem that Sequoias might be a good choice for planting in terms of carbon uptake.   *Full details of this work here : https://royalsocietypublishing.org/doi/10.1098/rsos.230603    

The woodlands blog has reported on urban forests, the trees in our cities, lining our roads and in our gardens.  This green infra-structure in our towns and cities provides a range of economic, environmental, and social benefits. The importance of green, leafy spaces was emphasised during the early days of the Covid pandemic, helping with mental and physical wellbeing of many people. Urban trees offer  Valuable habitats for wildlife and can provide biological corridors / stepping stones that enable birds and other animals to move through the urban environment. Shade and cooling in streets and parks. They can help reduce the risk of flooding, allowing more water to enter the soil rather than running off hard surfaces of tarmac and concrete.   The capture of pollutants, improving local air quality by capturing fine particles from the air (mainly through deposition on leaf surfaces).  Trees and shrubs seem particularly effective in removing ozone.  Through their photosynthetic capacity, trees can take up carbon dioxide into organic form - carbon sequestration. The amount of carbon taken up by London’s urban forest each year has been estimated at 77,200 tonnes.  However, recent studies suggest that many urban trees are under threat : Trees are subject to heat stress as many cities experience the heat island effect, the ambient urban temperature is significantly above the surrounding countryside. Many struggle to get sufficient water as they are planted in small square of soil and surrounded by tarmac, concrete or paving stones. Soil compaction is often an issue, affecting water permeability. They may experience an ‘excess of nutrients’ - due to dog’s urine, this is a source of urea and other nitrogen compounds. Once planted, young trees may not receive after-care / management.  This point is significant.  Many trees die within the first few years of planting. In Boston (USA), some 40% of trees are dead within seven years of planting.  Similar figures are true for New York. Both rural and urban trees suffer significant mortality when young but whereas the death rate of rural trees tend to decrease after a few years - urban trees are more likely to die as they age.   [caption id="attachment_40541" align="alignleft" width="300"] Young urban tree[/caption] There is a struggle to reach maturity.  Most trees need two or three decades to offset the carbon emissions associated with their planting / maintenance etc, and they then sequester carbon at a significant rate.  Work at Boston University (in Professor Lucy Hutyra’s lab) and Harvard has focused on the problems that urban trees are facing, and another issue (apart from those mentioned above) has been identified - the microbiome of the root [that is the variety of micro-organisms that surround / inhabit the root tissues]. Urban trees seem to have fewer symbiotic fungi in their root systems when compared to rural trees.  Roots often develop mycorrhizal associations with fungi.  Such systems allow the roots to access more water / minerals and in return the tree ‘offers’ the fungal network a supply of carbohydrates.  Jenny Bhatnagar (Harvard) has investigated the soil microbiome in eight different plots, some urban and some rural in Massachusetts.  Interestingly, the investigation found that whilst there were more fungi in urban plots, they ‘seemed more reluctant’ to establish symbiotic associations with the roots of the trees.  This failure could be due to the excess nitrogen / nitrates in the soil (from animal urine / faeces?).  When there is an excess of nitrogen available, trees tend to dispense with their fungal partners. The hotter temperature of urban soils might 'favour' a bacterial population (some bacteria ‘fix’ nitrogen). [caption id="attachment_40526" align="alignright" width="300"] Once, there was a cherry tree ...[/caption] It is not clear as yet why so many urban trees fail.  It could be that the loss of the symbiotic fungi renders the trees more susceptible to certain disease-causing microbes.  The hotter and drier soils at the edges of fragmented forests have more pathogens and not so many symbiotic fungi. A number of simple aftercare / management measures would help young trees to establish : Watering the trees in their early years Preventing soil compaction to allow water to percolate, and oxygen to diffuse to the roots. Mulching around the tree base (helps water availability and slows nutrient input from urine etc.) An interesting article on mycorrhizae and urban trees may be found here. [caption id="attachment_40537" align="alignleft" width="220"] Olive[/caption]   The importance of soil micro-organisms is also indicated by research in Australia, where  shrublands / woodlands have been invaded by African olive trees.  The olives have disrupted the partnerships between the Acacia trees (hickory wattle) and symbiotic soil bacteria (Rhizobia ssp).  This is another symbiotic association, where the partners exchange materials for mutual benefit,  Where the Olives have grown, the Acacia have problems establishing root nodules with the bacteria.  To restore these scrublands, a full understanding of the soil / root microbiome will be important. Full details of this work can be found here.  Postscript : In today’s Guardian (03/11/2023), Helena Horton’s article “Ministers should target tree survival ‘rather than planting’” reinforces the points made in the blog about the early mortality of young trees - urban or rural.  Increasing woodland cover will only occur if young saplings survive.  

Many trees emit a scent or fragrance.  They form volatile organic compounds (VOC’s), often oils.  Pine trees, for example, release pinenes. Such VOC’s contribute to the smell that you may experience as you walk through a woodland.  The VOCs contribute to the formation of aerosols.  An aerosol is a ‘mixture’ of very small particles (solid or liquid) in air; other examples of aerosols include mist, cigarette smoke, or even car exhaust fumes!  Recent research by the University of East Finland has showed that aerosols formed from VOCs can reduce the amount of solar radiation that reaches the earth’ surface, by scattering some of the radiation back into space.  [caption id="attachment_40200" align="aligncenter" width="532"] Felling in progress[/caption] Pine trees are often grown in vast numbers and periodically felled for timber and paper making.  One by-product of paper-making (by the Kraft process) is turpentine - formed by the condensation and collection of the volatile oils in the wood). The pinenes (α and β) are major constituents of turpentine.  ‘Turps’ is used as a solvent to thin oil-based paints, for producing varnishes and as a ‘raw material’ in the chemical industry.  α-Pinene was used to make toxaphene (an insecticide, now banned).  Pinene can also treated with acetic acid to make a perfume with a pine needle smell. Recently a team of scientists at the University of Bath have found a new use for the by-products of paper production.  Using pinene from turpentine, they have been able to make a number of pharmaceutical compounds that can then be made into the painkillers - paracetamol and ibuprofen.  They have also successfully made other chemicals from the plant based turpentine, including compounds that may be used to synthesise `beta-blockers (heart tablets) and salbutamol (used for asthma).   At present, many pharmaceuticals and other chemicals are ultimately derived from crude oil.  Hopefully, this research will ultimately lead to a more sustainable and ‘green’ approach to drug / pharmaceutical manufacture. Biochar is the black residue, consisting of carbon and ashes that remain when plant biomass is subject to pyrolysis - that is, very high temperatures with very little  or no oxygen present oxygen. The material that remains is largely elemental carbon.  The benefits of converting plant biomass into biochar is that the carbon is ‘locked up’, rather than being released by decay and decomposition into the atmosphere as carbon dioxide.  Its advocates claim that when added to soil, it improves soil structure and function, as well as being a form of carbon sequestration.. [caption id="attachment_40215" align="alignleft" width="300"] cocoa fruit[/caption] Various forms of biomass (woody debris, corn stalks) have been used to produce biochar, however, a novel method makes use of ‘discarded’ cocoa bean shells.  These are heated to a temperature in excess of 600oC, with no oxygen present.  This particular form of biochar is being produced in in Hamburg. The plant, which is one of the largest in Europe, receives a supply of used cocoa shells viably a network of grey pipes from a neighbouring chocolate factory.  Apart from its use as a fertiliser, it is possible that it might be used as an ingredient to create a ‘green’ (or more environmentally friendly) form of concrete. The sequestration of carbon is vital if we are to avoid the worst effects of climate change.  Global warming has triggered an increase in heatwaves, floods, droughts, and forest fires in recent years; June temperature data confirms it was the planet's hottest on record. Cocoa fruit : courtesy of Pixabay.

Back to one’s roots? Some of the effects of agriculture are very obvious, such as the vast areas of land now covered by monocultures of wheat or oil seed rape.  The expansion of mechanised agriculture has resulted in significant reductions in biodiversity, for example, through the loss of hedgerows and ponds (see the post on ghost ponds in Norfolk).  However, agriculture has others effects that are not quite so obvious.   Soils are ‘filled’ with roots, and roots help engineer landscapes.  They help: break up bedrock, improve permeability of the soil to water  stabilise the soil,  store carbon transport water and minerals to the plants.   They have been doing this for millions of years since the colonisation of land by plants. Now, research by scientists in the United States, has shown that the roots of agricultural crops are significantly less deep than those of  the  natural vegetation in an area.  Indeed, the root depth may be shallower by some 60 cm, compared to the natural root systems of an area.  If the soil is less root material then there is  decreased carbon storage,  reduced nutrient recycling and  possibly reduced soil stability.   Whilst there are some areas where “woody encroachment” is occurring (for example, shrubland taking over in some grasslands and forest advance into regions of tundra so root depth is increasing) -  the onward march of agriculture is dominant. Full details of this analysis / research : https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF002897 Shrinking in winter Recent research has shown that some small mammals (like moles and shrews) shrink in size during periods of cold temperature.   This shrinking is thought to be a response to cold temperature rather than lack of resources.   This change in form has been known for some 70 years and is referred to as Dehnel’s phenomenon.  Professor Dehnel observed this change in form in shrews [in Poland in 1949].  However, shrews have a short lifespan so an extended studied of this phenomenon with these animals was not / is not possible.   Recent studies by German researchers have focused on moles, who can survive harsh winters by becoming  smaller.  It is thought that this reduction in size enables energy savings.  According to Dr Dina Dechmann this reduction in size comes at a cost, as the animals’ cognitive behaviour is affected. Further information here : https://royalsocietypublishing.org/doi/10.1098/rsos.220652 Farming and sustainability With the expansion of farming, less and less of the land is available for our native plants and animals,  Hedgerows and ponds have been lost / removed, natural habitats have been reduced. The government has produced new guidance on environmental land management schemes (ELMs).  That is subsidies that will be paid to farmers if they help promote and protect nature and improve the environment (e.g. using less insecticide and reducing pollution). There would be payment /subsidies for some 280 measures, for example : Creating fenland from lowland peat Maintaining sphagnum moss Creating land that could produce organic fruit Establishing a skylark plot Adding organic matter to the soil Creating green cover over winter (on 70% of the land) Welcome as these measures might be, there is criticism that they favour big arable farmers and do not really help those working on more marginal land (such as upland and moorland regions). Further information available here. Trees - From Root to Leaf For those who like their trees, here is a new book about them.  Written by Paul Smith -who was head of the Millennium Seed Bank of the Royal Botanic Garden, Kew.  Not read or seen a copy but the Sunday Times comment "'Stunningly illustrated and detailed ... a celebration of all things arboreal, from the seeds, leaves, flowers and fruit to the diversity of trees and how they have influenced art, culture and science' suggests that it might interest.  See "https://press.uchicago.edu/ucp/books/book/chicago/T/bo186012850.html"  

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.  

It is depressing to pick up a paper or turn on the news to be met with a catalogue of distressing and difficult stories.  There is also the overarching problem of global warning and climate change.  Only recently, there have been reports of flooding in Sydney after torrential rain, fires are springing up again in Colorado and other States, and India experienced a heat wave (combined with a drought), with some cities experiencing temperatures of 40o+C.  This has resulted in the deaths of individuals, and as the heat wave occurred in the final weeks of the wheat growing season it has killed many crops before harvest.  In Balochistan, the peach and apple harvest has been severely impacted. Here in the UK, there are a number of problems, indeed we have been described as “one of the most nature-depleted countries in the world”.  We have lost plant and animal species, such losses could lead us into an ‘ecological recession’. This occurs when ecosystems systems lack the diversity needed to function well. Much of the damage to (or loss of) our ecosystems is associated with the industrial revolution followed by the  intensification of mechanised farming. The 1950’s and 1960’s witnessed the loss of vast tracts of hedges and the removal of small copses to increase the area for farming / food production, and allow the use of heavy duty mechanised machinery.  There was also the extension of road networks - motorways etc. and urban sprawl /development.  Though woodlands and forests were being eroded long before the industrial revolution; woodland, forest and pasture covered much more of the land than now. There were areas of ‘wilderness’ that were home to animals and plants that have long since gone or are now very rare - ranging from wolves, bears, to beavers and red squirrels. Whilst woodlands were and are havens for many plant and animal species, meadows and pastures have suffered too.  The PlantLife charity has suggested that the UK has lost some 97% of its wildflower meadows during the course of the last century and what remains could be under threat. Lowland meadows are rich sources of biodiversity, both plant and animal, they also store carbon in the soil and ‘knit’ the soil together, so that it is not subject to erosion. [caption id="attachment_38489" align="aligncenter" width="700"] A meadow, partly mown and partly 'wild'.[/caption] Many species are dependent on these habitats, but with the expansion of agriculture and construction of motorways - the landscape has become fragmented and many species cannot across the formidable barriers.  The Scottish primrose is now only to be found on the north coast of Scotland and Orkney, and some orchids are described ‘as just hanging on’.  Species like the common blue butterfly is reliant of bird’s foot trefoil, Greater Bird’s-foot-trefoil, Black Medick and white clover for food for its caterpillars.  The great yellow bumblebee is sadly now one of the rarest British bumblebees. It is limited to flower-rich areas in the Orkneys, Caithness and Sutherland. It is particularly associated with red clover. It is a large species, and was once widespread across the U.K. Creating space and opportunities for wild flowers has been PlantLife's foremost objective from “No mow May”, “Save nature on our roadside” (see the woodland blog here and here) ’Fight for sites” all of which aim to increase the number of sites for wild flowers and their pollinators to flourish.  The Scottish Government has been helping establish wildflower meadows at some of its national nature reserves - notably St Cyrus, Flanders Moss and Forvie, and they are working with PlantLife to create an action plan for Scotland’s grassland.  It is keen for farmers to be involved, offering areas of wild flowers on their farms.  By increasing the areas in which wild flowers (and their associated insects) can flourish, the connectivity can be restored (at least in part).  The creation of biological corridors allows plants and animals to move, which is particularly important in these times of climate change.  

Certain upland areas of the UK , such as Dartmoor, have experienced long term grazing.  This has lead to soil compaction, which in turn means that water run-off is greater. Instead of percolating into the soil, rain water runs over the surface and into rivers. This can lead to flooding during extreme weather events.   Dartmoor (National Park) is a large upland area, which historically was dominated by oak woodland.  Oak woodland now covers a very small area.   The region is now dominated by blanket bog, heathland and acid grassland.  The number of grazing animals (sheep, cattle and ponies - deer) increased significantly between the 1950s and 2000, resulting in soil compaction. Researchers at the University of Plymouth have investigated areas of upland pasture on Dartmoor, and the potential for the establishment of native oak saplings. Working with test sites, they were able to show that significant improvements in soil properties could be observed with 15 years of sapling establishment.   The most effective location (in terms of flood prevention) for sapling / tree planting was on steep hillside on the edge of upland areas.   Their initial work on the planting of woodland has since been expanded to determine the factors that affect the establishment of the tree (oak) saplings.  Their most recent paper notes that the presence of livestock meant that fewer oak saplings survived and those that did were smaller.  However, the effects of cattle and ponies was not always negative in that their trampling could reduce the growth of bracken - allowing more light to reach young tree saplings. [caption id="attachment_34391" align="aligncenter" width="650"] A southern upload moorland - Exmoor[/caption] The research team formulated a number of recommendations relating to the creation / establishment of woodlands in such upland pastures. Livestock should be excluded in areas where there are seedlings and young saplings (1 - 3 years). This exclusion should last for some 12 years. Larger oak (4 - 7 yrs) saplings can be planted into areas of dense vegetation, as this protects the saplings from livestock. Livestock could be allowed to graze in the vicinity of mature oak trees as this would reduce dense, competitive vegetation, allowing seedlings to grow / develop.  Strategic planting and management should be considered  / encouraged for upland slopes where drainage is poor - to allow for soil recovery and development of ecosystem services (flood mitigation). Whilst natural tree colonisation is a low-cost and environmentally sensitive mechanism to promote woodland expansion (working towards government targets on climate mitigation, carbon sequestration etc.), it is likely that the expansion of oak woodland into upland pasture systems will require strategic planting and informed livestock management. [caption id="attachment_37920" align="aligncenter" width="650"] Exmoor Ponies.[/caption] Full details of their paper can be found here : https://besjournals.onlinelibrary.wiley.com/doi/10.1002/2688-8319.12126  (Thanks to Art for images of exmoor and ponies).