Trees and shrubs that grow in temperate regions, where the seasons alternate (warm / cold, dry /wet) create annual rings.  The rings formed in a deciduous tree (like beech, oak, lime) are generally quite noticeable when the tree is felled.  They may be counted to give an indication of the age of the tree.  Annual rings are formed because there is a difference in the creation of ‘wood’ / xylem tissue when growth is fast in the Spring and slow as Autumn progresses.  The thickness of the rings from year to year reflects the changing climate and environment that the tree experiences during its life. Xylem tissue is one component of a tree’s vascular tissue.  The xylem tissue conducts water and minerals around the plant, whereas phloem tissue transports sugars and other organic molecules.  Lying between these two tissues is the cambium.  This is a layer of dividing cells, which becomes active in the Spring forming new cells some of which will form new phloem tissue and others develop into xylem tissue. The cells that will form the xylem tissue undergo a series of dramatic changes.   The walls of the cells that will form the long tubes of the xylem are made of cellulose to begin with, but then they are strengthened with lignin.  Lignin is the ‘stuff of wood’.  It is a complex material - made from polyphenols and other substances such as pectins and hemicelluloses.  It is a waterproofing material that is highly resistance to decay.  It lines the tubes of the xylem so that water can be transported from the roots, up the trunk / stem to the leaves etc.  The xylem vessels that form in the Spring [early wood] have a greater diameter than those formed later in the year [late wood].  It is this size difference in the vessels that results in the visible ‘rings’ when a tree is felled. Careful study of tree rings can reveal information about climate, sometimes extending back through the centuries   using species such as the long lived Bristlecones. It has given rise to the discipline of dendrochronology [link opens / downloads a PDF].  This information can then be ‘combined’ with tree ring data from intact remains in cold, dry (and often high altitude) environments and material from archaeological sites.   Apart from measuring the ‘width’ of the annual rings by creating thin section of the wood that can be examined under microscope, it is also possible to use staining techniques to reveal which xylem tissue has a higher / lower, lignin / cellulose content.  By using a double staining technique with the dyes Safranin and Astra Blue, it is possible to identify which xylem vessels are rich in lignin, and which have more cellulose.  Tree rings which stain largely blue are formed from cells which have not lignified properly.  Lignin stains red.  A recent study of blue rings in Pine trees and Juniper shrubs suggests that blue rings are indicators of cold summers. These two species are typical of the upper tree line in Northern Norway. Furthermore, blue rings have the potential to weaken the pine trees, leaving them more susceptible to mechanical damage and / or disease.  This study has identified blue rings associated with the cold summers of 1877 and 1902, which might have been caused by the eruptions of volcanoes as far away as Ecuador and Martinique. Note : The xylem tissue in conifers is different to that of broad leaved deciduous trees.  It is made up of shorter structures called tracheids, which pass water from one to the next via pits - ‘pores’ in their lignified walls. For more information on Blue rings in Black Pine, click here  

In the southern parts of Britain, beech is a dominant woodland/forest tree, further north, oak is prominent.  Beech trees are often large with smooth, silvery grey bark.  They can grow to a height of 150 feet, with a stout trunk (perhaps 10 feet in diameter) and an impressive canopy. The leaves, certainly on younger trees, may persist throughout winter in a brown and withered state — a phenomenon known as marcescence.  The root system of the beech is shallow but extensive.  The large roots spread out in all directions, and establish mycorrhizal connections, often with fungi such as Russula and Laccaria.  The mycorrhizae help the trees by supplying mineral nutrients (like phosphate) and water.  In return, the trees provide various organic nutrients to the fungus. Despite these associations, beech trees are susceptible to drought.  After the drought of the summer of 1976, many beech trees died. It is not surprising that people are concerned about the ‘health’ of beech trees in light of climate change — higher temperatures, extreme weather,  specifically periods of drought.  It was thought that climate change would reduce growth of trees like beech through the increasing frequency and intensity of summer droughts. Recently, a study conducted by researchers at the University of Liverpool looked at tree growth data (annual growth ring and masting data) accumulated over more than forty  years and found that growth was indeed reduced (by some 28%).   However, the reason was that the trees were investing more energy into reproduction than into growth.  Beech trees are known for their mast years - see previous blog on masting. In a mast year, a tree will produce enormous quantities of seeds (beech nuts✝︎). However, it seems that the changing climate is causing a ‘breakdown’ in the masting process, and whilst the trees now reproduce more more frequently.  Total seed production and seed viability is reduced.   It may be that the diminished reproductive capacity of beech trees as a result of climate change will affect their ability to regenerate woodlands and forests in the UK and indeed across Europe in the coming years.   [caption id="attachment_41997" align="aligncenter" width="675"] Marcescence[/caption] ✝︎ Masting means that so many seeds that even the most voracious squirrels cannot consume all of them * After the summer of 1976, drought damaged trees were still dying some 15 years later.

To see the forests of  The Fens,  you would need to be a time traveller, as they were ‘lost’ some four thousand years ago.  Today, The Fens are a low lying agricultural region that forms part of Norfolk, Lincolnshire and Cambridgeshire.    The Fens contain some of the best agricultural land in the U.K., growing potatoes, sugar beet, and wheat.  A naturally marshy area, it was drained centuries ago and is now maintained through a complex system of drainage canals, dykes and pumping stations.  As a result of the drainage, the level of the land in many places has shrunk.  Indeed, in places, the land level is below sea level.  There are occasional ‘hills’ or islands, which have remained dry even when the surrounding area has been flooded.  The city of Ely and its cathedral was built on such a clay island. Deeper ploughing (e.g. for potatoes) in this area has over the years exposed  ’bog oaks’, large logs between two and eight metres in length.  The trunks were sometimes piled up in so-called clearance  cairns on the edges of a field, or allowed to dry out and later used for fuel.  Recently, ‘oaks’ from a number of farms across the region have been examined by researchers at Cambridge University and many have been identified as the remains of ancient yew trees.  The various logs were often well preserved in the peaty soils of the area, and this allowed detailed analysis of the annual rings (dendrochronology). The rings showed that some of the Yews were 400 years old, when they died.  Tree ring analysis plus examination of the pollen grains* (found in the peat), suggests that the area had dense yew (and oak) woodlands some 4500 years ago.  However, these woods were lost about 4200 years before today, probably due to an abrupt rise in sea level.   The trees would have been unable to tolerate the salt water (nor salt spray) when the area around The Wash was inundated.  Quite what was responsible for the rise in sea level is not clear, though other significant climatic events in different parts of the world have been recorded at this time. the 'wall' of pollen grains  [the exine] is made from a chemical [sporopollenin] that is extremely resistant to decay / degradation, so the grains  retain their shape / markings for thousands of years;  this means that plant species can be identified [palynology].  

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’.

Bees and solar parks As the country tries to move towards carbon zero, so we see more and more solar parks  / farms ‘springing up’.  Whilst they do create clean energy, they also take up a lot of land, and it is important to see if such solar parks can offer other commercial or environmental benefits.  One suggestion is to place honeybee hives on such parks.  The bees could provide a pollinating service to surrounding crops / farmland.  Researchers at Reading and Lancaster Universities have studied detailed land cover maps / crop distribution patterns to estimate the economic value of deploying honeybees in solar parks.  Their investigations suggest that a variety of crops from oil seed rape, soft fruits to apples and pears could benefit from such an arrangement.  The benefits would vary across the UK, with the benefits being greatest in the East and South of the country.  Care would need to be exercised though to ensure the placing of hives did not disturb the foraging of wild pollinators, such as carder bees, hoverflies etc. Are plants sulphur deficient? Much has been written about the importance of plants nutrients, especially NPK; that is to say nitrogen, phosphorus and potassium.   However, little is said about sulphur.  However, researchers in Groningen, Graz and Cologne have been looking at the effects of sulphur deficiency, particularly in relation to the colour and shape of the flowers formed.  The work focused on Brassica rapa, a member of the mustard family.  When it was subject to ‘mild’ sulphur stress (by limiting the sulphate in the growth medium), the flowers that formed were smaller and paler - not the usual bright yellow.  They were also likely to be mis-shapen. Colour and shape are features by which pollinators recognise flowers and then visit them. Pollen production by the flowers was also affected; smaller pollen grains were formed.  This may in turn affect the pollinators who visit the flowers foraging for food. In the relatively recent past, sulphur deficiency may not have been a problem due to acid rain, which would percolate through the soil, forming sulphates.  [In the twentieth century, acid rain formed as a result of the release of sulphur dioxide (and nitrogen oxides) into the air through the burning of fossil fuels.  However, various clean air acts have ensured that there is now much less SO2 in the air.] Annual rings, water availability and earthquakes. Christian Mohr (scientist from the University of Potsdam) was studying the transport of sediments in rivers in Chile in 2010 when a massive earthquake shook coastal areas of the country.  When he was able to return to his studies, he noticed that streams in the valleys were flowing faster.  He reasoned that this was because the earthquake has literally shaken up the soil, so that it was now more permeable and ground water could more easily flow down from the ridges.  As a result of increased water supply, he thought that trees down in the valleys would grow more than those on the ridges. He and colleagues drilled out plugs of wood from valley trees and ridge trees, and back in Potsdam they examined the tree rings under a microscope.  They also looked at the uptake of different isotopes of carbon as a measure of photosynthesis.  They found that trees from the valley floor experienced a small but noticeable growth after the earthquake, and this lasted for weeks or months, whereas the trees of the ridges grew more slowly.   It is possible that analyses like these, when combined with other information, could help identify significant historic disturbances. Rising temperatures. Recent years have seen periods of very hot temperatures, Such extreme weather events have been seen not only in the UK but across the globe (Arizona , Victoria Australia, Indonesia).     Extreme heat (and drought) have been known throughout history, but it would seem that extreme events are now more common.  The first two decades of this century are among the warmest on record; this warming is associated with increasing levels of greenhouse gases (due to human activity). Prolonged heat is not without its effects on us, it leads to sweating, teaches, fatigue, dehydration and heat exhaustion.  The very young and the elderly are most at risk from ‘heat waves’.  A 2003 heatwave across Europe is said to have caused several thousand  'excess' deaths’, mainly of the elderly.  Even gradual but sustained warming of the climate can have its effects.  For example, Silwood Park (Imperial’s research station) has commented that though it is now November, they have not recorded a single frosty night - normally they would expect to have three in a ‘normal’ October.  Snowdrops are appearing earlier, and some migratory species are changing their pattern / timing of migration. Across the world, different species are being affected in different ways.   Thick billed murres (type of guillemot, found in and around the Hudson Bay) have a high metabolism to deal with the cold waters into which they dive - they are cold adapted animals. On warm days (when the temperature is 21cC or above) they are dying whilst sitting on their nests - incubating their eggs.  They struggle to keep cool, if they spend more time in the water then they leave their eggs exposed to predators (like gulls and arctic foxes).  Similarly boreal and arctic bumblebee species are sensitive to heat stress, succumbing to stupor; other work indicates that some European / mediterranean species are now to be found in areas of the arctic circle - as a result of changing climatic ‘norms’.  Wild dogs are adapted to deal with heat, but if the temperature goes beyond a certain point they stop hunting, consequently their pups / offspring are less likely to survive. Warming temperatures not only affect animals but they also contribute to the increasing number of harmful algal blooms (in lakes and off shore regions).  These blooms can be dangerous to many animals (including humans) and when they die back they ‘suck’ oxygen out of the water - creating ‘dead zones’.  One species of alga (Karlodinium veneficum) which is known to produce toxins has been shown to acclimatise to higher temperatures (up to 30cC). As climate change and research continues, we will no doubt see further examples of how animals and plants are being affected by changing temperatures / climate .

One particular concern of continued climate change and global warming is drought.  Not only will drought affect people but also plants. Droughts can inhibit the growth of trees, or kill them.  Over time, they can change the species make up of woodlands and forests.   If woodlands and forests experience drought then this will seriously impact their ability to absorb carbon dioxide from the atmosphere - they act as carbon sinks and help mitigate climate change. Recently Tom Ovenden et al from Stirling University and Forest research at Roslin have focused on the effects of climate on Scots Pine.  Scots Pine is a widely distributed tree across Europe and often planted for its timber.  It is a ‘favourite’ with red squirrels.  The research team examined the trees in a pine forest that was planted (near Inverness) back in 1935.  They examined tree rings from trees from high and low density stands.  A ring forms each year and the width of the ring is a measure of the growth the tree has achieved in a particular year.  Wide rings indicating substantial growth.  The width of the rings was then correlated with climate records.  The rings formed in ‘drought years’ was compared to growth in average (non drought) years, and to the rings formed in ‘post drought’ years. Read more...

Forests and woodlands are important in the global ecosystem; they have taken up some 20 to 30% of the carbon dioxide released from fossil fuels in recent times. It had been assumed that the dense and biodiverse tropical forest ecosystems (close to the equator) were particularly effective in ‘soaking up this carbon dioxide’.   However, there is doubt that this will continue to be the case as forests shrink in size.  Plus, recent work at the University of Birmingham (Dr Tom Pugh) has shown that where forests were re-growing,  they took up large amounts of carbon partly because more carbon dioxide was available,  but also as a result of the younger age of the trees. This ‘youthful’ carbon uptake was not associated with tropical areas, but with regenerating forests of more temperate regions. Read more...

Dendrochronology seeks to gather information from the annual rings of trees, dated to their year of formation.   As trees age, they form new distinctive rings, outward from the centre, and each year a circle of new, dead wood is formed (by the cambium) around the trunk of most trees. The annual rings form because the water conducting xylem vessels or early wood formed in late spring and early summer (when growth is rapid) are wider and lighter than those formed in late summer and early autumn, which are narrower and darker (sometimes called the late wood).  A light and dark ring together constitute one year’s growth.   In winter, there is no growth. Trees and their annual rings are essentially long term recording devices that ‘house’ information about climatic variations, past climates and ecosystems; they can even offer insights into historical events. From an annual ring, it is possible to extract information about precipitation, temperature and other climate data about that year. Read more...