Blog - Flora & Fauna
Thomas Meehan : American autumnal colours
The changing colours of the leaves in autumn is a phenomenon that affects the vast majority of deciduous trees (and some conifers, eg. Larch). The leaves change from green to various shades of yellow, brown, orange, red and even purple. The nature of these changes has been the topic of a previous blog. What is interesting is that this colour change is particularly marked in the trees of the North Eastern region of the United States. Indeed, bulletins are published listing the best places to see the myriad of colours that the trees display. This difference in the colours of American and European trees was commented upon by Thomas Meehan, back in the nineteenth century. Meehan first worked as a gardener at Kew but later moved to Philadelphia (where he is credited with saving Bartram’s Garden). His botanical studies led to him being the editor of The Gardener’s Monthly, writing articles for various newspapers and authoring 'The Native Flowers and Ferns of the United States'. In 1881, Meehan noted in a paper presented to the Proceedings of the Academy of Natural Sciences of Philadelphia, (Vol 33) that the intensity and variety of autumnal colours was much greater in the States than in Europe. He suggested that the difference might be due to the “American light” and that European trees might (after many generations) adapt to this light and then show similar colours. Recently, Renner and Zohner* have investigated this difference. Their paper(s) offer a number of observations / findings: American trees start to break down their chlorophyll earlier in autumn than European trees, so the period in which the leaves operate as photosynthetic 'factories' is shorter. The earlier onset of senescence means they are at greater risk of light mediated damage in the bright days of early autumn (particularly if coupled with cold nights). Trees growing at a particular latitude in Eastern North America receive significantly more light than trees growing at the same latitude in Europe. North American trees react differently to the shorter days of autumn that European trees - when grown in the same area / garden. A greater percentage of North American trees produce anthocyanins - which give the red and purple colours. Anthocyanins absorb light over a wide range of wavelengths. They act as a sunscreen, protecting the leaves at a time when they are undergoing rapid and complex changes that allow them to export valuable nutrients / resources to other regions. It would seem that Meehan’s comments about the ‘American light’ were remarkably prescient some 140 years ago. Renner and Zohner’s detailed papers are available here : https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.15900 https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/416178/nph.16594.pdf?sequence=3&isAllowed=y [caption id="attachment_36385" align="aligncenter" width="650"] Thanks to Oliver for this photo of autumn colour at Westonbirt[/caption]
Mosses in woodlands
As we move through Autumn, the leaves of deciduous trees have ‘done their job’. Their capacity for photosynthesis dwindles (as does the light and temperature. In fact, the leaves become a ‘liability’ to a tree, in that they would make use of the reserves that have been stored away. Also, the leaves offer resistance to the winds of winter so a tree is likely to sustain damage. If branches are lost from the stem, then bacteria and / or fungi could enter. The leaves are ‘discarded’ as Autumn progresses. The green colour of the chlorophyll is lost and other colours emerge - reds, oranges and yellows. These colours are associated with different pigments, the carotenes, xanthophylls and the anthocyanins. As the leaves are lost so the trunk and branches becomes more apparent, but they are not necessarily ‘naked’ - devoid of cover. Indeed, walking through a woodland at this time of year, one is often struck by the abundance of mosses. Tree trunks are often laden with ‘carpets’ of moss and their branches bear ‘decorations’ of many different mosses. Beneath the tree, there is often a soft, spongey layer of mosses. Mosses are bryophytes. They are ‘simple’, non-vascular plants ; that is to say they do not have sophisticated transporting tissues (of phloem and xylem). Nor do they have true roots, instead they have structures called rhizoids (which may be uni or multicellular). They live in moist places, indeed they are dependent on water for their reproduction. Mosses or rather their ancestors were some of the first plants to colonise land (which was the rather inhospitable rock of the Ordovician period), previously there were only algae in the seas. Mosses develop sex organs, The male organ is called is called an antheridium, it produces male gametes that can move by means of a flagellum. These gametes swim in a film of water towards the female organ (an archegonium). When the male and female gamete fuse, the structure grows to form a sporophyte. This eventually produces a capsule, which releases spores that grow on to form a new generation. Mosses seldom grow to any great height, mainly due to the absence of supporting mechanical tissue but they can form extensive mats in damp, shady places (as can liverworts). These mossy mats can in some situations prevent soil erosion, and in others allow the accumulation of humus and soil enrichment / formation. An extreme example of the accumulation of mossy material I can be seen in the case of the moss Sphagnum. Sphagnum is unusual in that can hold many times its own weight in water; because of this absorbency, Sphagnum was used as a wound dressing in WW1. It grows in acidic, marshy conditions, often forming a sphagnum bog. The low fertility and cool climate result in slow growth of the Sphagnum (and other plants). The decay of dead plant material is even slower (due low oxygen levels). Hence, peat forms and accumulates. Large areas of the land can be covered to a depth of several metres with peat. Peat bogs are a very effective means of carbon sequestration, locking away carbon for hundreds iff not thousands of years. Unfortunately, many have been drained and allowed to dry out and / or the peat cut from them as a form of fuel. When peat areas are drained (channels are cut through the peat), they degrade and dry out. Then, they are then at risk of burning as has been seem in recent years -for example, in the U.K (Saddleworth Moor). 'Mossy ball' and 'autumn leaves 'photos - thanks to Art Symons.
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.
The effect of deer on woodland plant communities.
Images of deer in a woodland clearing may seem charming, but quite how deer and woodlands interact is not fully understood. It is certainly the case that deer affect tree regeneration; they browse on saplings and can cause extensive damage to bark (through territorial behaviour / antler rubbing) to larger trees. The lower levels of the plant communities are also affected by deer. By changing these, deer also can change the animals to be found in this lower layer of a woodland. Research by Dr. Simon Chollet and colleagues showed that deer interaction can influence soil water availability, and soil fertility. Their study looked at the role of Sitka black-tailed deer on the plant communities in forests in parts of western Canada. Chollet et al. examined twenty areas where deer were excluded for some two decades. An exclosure is a limited area from which browsing animals, such as deer, are excluded by fencing or other means. Unsurprisingly, they found that deer did have a significant effect on the plant communities. The exclusion of deer resulted in an increase in vascular plant richness and cover, though bryophyte (mosses etc) cover declined. They also found that with the deer gone, the exclosures started to develop broadly similar plant communities. There was no increase in beta diversity - that is the development small, localised communities of varying character. It was suggested that the dominance of certain species within the exclosures was linked to historic over-browsing. Consequently, those plants that are able to withstand the presence of deer over time are best placed to achieve ‘dominance’ once this grazing pressure is removed. This might explain why the different enclosures developed similar vegetation and plant species. Biotic homogenisation has been seen in the UK woodlands, as was discussed in a previous blog. It can be the result of introduced species, pollution (eutrophication - increased nitrate and phosphate levels), which allows botanical thugs (like nettles) to dominate, or poor woodland management.
October’s Monthly Mushroom – Blackening Brittlegill (Russula nigricans) and Silky Piggyback (Asterophora parasitica)
I have a love-hate relationship with russulas, the eye-catching, colourfully-capped mycorrhizal mushroom types known commonly as brittlegills. I love it when you chance upon a pristine specimen that has been unmunched upon by insects, slugs or squirrels. It seems impossible to resist the temptation to get down to ground level and take a snap. I hate the subsequent task of attempting to home in on an identification so you can put a label to the resulting photo. Identifying russulas is a painstaking process: determining which of the nearby tree species’ roots in a mixed woodlands it might be forming a mycorrhizal relationship with; in which range of hues does the highly variable cap colour fall within; sniffing to detect if there’s any hint of an aroma such as coconut or crab or strewed apples that goes beyond the simple description of “mushroomy”; the nibble-and-spit test to gauge whether its taste is peppery, acrid or bitter, or any of the other vague categories in between; the thorough examination of physical features such as gill spacing, stem width and how far the cap cuticle peels towards the centre; the rubbing with Guaiac and iron salts to see what colour the flesh changes... And this is before we even get to the microscope stage. [caption id="attachment_36165" align="aligncenter" width="650"] The Woodland Brittlegill, Russula silvestris, is one of many red-capped brittlegills that need much closer inspection to identify correctly[/caption] Yes, it takes many years in the field to get one’s head around the 200 or so species of brittlegills that have been recorded across the British Isles. Nevertheless, there is one that is not only almost conspicuous within this genus by its utter drabness, but the remnants of its fruitbody, once it has fulfilled its spore-distributing process, leave one in little doubt as to what it is. That is the Blackening Brittlegill (Russula nigricans), whose fruiting bodies are quite a bit larger than your average russula, getting up to around 20cm across as they expand and flatten out. They start out a grimy off-white colour before darkening through an ever-darkening range of slightly greenish greys and browns before eventually turning completely black. Unlike most fungi fruitbodies, these blackened caps don’t just turn to mush and rot back into the ground. They dry up so as to appear mummified, and you can find their black husk-like remnants lying around for months after the main fruiting season, often well into the following year. [caption id="attachment_36166" align="aligncenter" width="650"] The 'charred' remnants of the Blackening Brittlegill, Russula nigricans, distinguishable due to its relatively wide gill spacing as much as its black colour[/caption] The Blackening Brittlegill might seem pretty unique then, except that the mycological world is never that simple and the world of russulas even less so. In fact, there are a number of other species that blacken and desiccate in much the same way. The Fungi of Temperate Europe (2019) refers to them collectively under the category of ‘charred russulas’, and lists Russula adusta, Russula densifolia, Russula albonigra and Russula anthracina. The British Mycological Society website includes common names for some of these: R. anthracina is the Coal Brittlegill, in obvious reference to its colour, while R. adusta is the Winecork Brittlegill, as it reputedly smells of empty wine barrels. R. densifolia is the Crowded Brittlegill, due to its tightly packed gills – something which distinguishes it from the Blackening Brittlegill, which has unusually widely spaced ones. When it comes to the taste test, R. acrifolia has hot peppery gills, earning it the memorable title of the Hotlips Brittlegill. [caption id="attachment_36167" align="aligncenter" width="650"] The Crowded Brittlegill before desiccating looks very similar to other charred russulas like the Blackening Brittlegill[/caption] Other features distinguishing these various species include the way the inner flesh colour transforms from their original white when a fresh mushroom is cut in half: R. adusta, R. densifolia and R. nigricans for example turn red then black, while R. anthracina goes straight to brownish black. But let us not get waylaid by any of this, because the main reason for covering these charred russulas this month is due to the way that these or carbonised cap remnants serve as mini ecosystems in their own right as they persist beyond the initial fruiting stage. Look closely and you’ll see them crawling with near microscopic bugs and larvae, and beyond the scope of the naked eye, they swarm with bacteria and other microfungi. This is the case for many decaying fungal fruitbody, it is true, but the charred russulas also provide the substrate for two more conspicuous species of fungi – the Silky Piggyback and the Powdery Piggyback. [caption id="attachment_36168" align="aligncenter" width="650"] The underside of an old Blackening Brittlegill is a haven for insects and other fungi[/caption] I’ve covered a couple of examples of fungi that specifically grow on other fungi in my previous posts on the Bolete Eater, which forms a fishy-smelling bright yellow mould on certain bolete species, and the Common Tarcrust, which plays host to the tiny orange spheres of Dialonectria episphaeria. There’s also a more obviously mushroom shaped example in the form of the Parasitic Bolete (Pseudoboletus parasiticus), which grows out of or in association with earthballs as part of a relationship that doesn’t seem to be clearly understood. However, I don’t think you can find a more striking example of such mushroom-on-mushroom weirdness than the two Asterophora piggyback species. Both are dainty little types that have a similar form and colour to your basic supermarket button mushroom, although their caps only rarely get much bigger than 2cm in diameter and the stems are relatively longer and thinner. The gills of both start off white, then turn brownish. [caption id="attachment_36169" align="aligncenter" width="650"] A group of Silky Piggybacks growing on an old Blackening Russula cap[/caption] The two are pretty similar unless you look very closely, and even then it is not always clear. The cap of the Silky Piggyback (Asterophora parasitica) is fibrous, giving it the silky appearance that gives it its name. The Powdery Piggyback (Asterophora lycoperdoides) is slightly smaller, but its main distinguishing feature is the pale brown dusting on the upper side of its cap. This powder is made up of asexual spores knows as chlamidospores, and is as is noted on the First Nature website, is an unusual feature of basidiomycetes fungi, which produce sexual basidiospores on their gills or in pores (in such examples as the bolete fungi) – the Powdery Piggyback also produces these basidiospores on their gills. [caption id="attachment_36170" align="aligncenter" width="650"] Silky Piggybacks[/caption] One thing that is worth mentioning is that despite the ‘parasitica’ part of the Latin binomial name of the Silk Piggyback, neither are parasitic in any true sense of the word. They are in no way detrimental to their russula hosts. They just have evolved to grow on the long-lasting blackened remains of the various charred brittlegills (they can also be found on the decaying remnants of a number of milkcap species). And so now is the good time to find these curious types. The russulas in general tend to begin fruiting early during the summer months. The Blackening Brittlegill begins appearing in late summer and autumn in both coniferous and deciduous forests, but many will have gone over now and can be seen lying on the ground among the fallen leaves, beech mast, pinecones and other forest litter forming a mushroomy substrate for these two Piggyback species, which you might barely even notice unless you are looking closely at the ground beneath your feet. [caption id="attachment_36171" align="aligncenter" width="650"] Silky Piggybacks[/caption]
Woodland web updates- 8.
Migrating hoverflies. Hoverflies are important pollinators, plus they also act as important predators of crop pests such as Aphids. Some hoverflies (like the pied and yellow clubbed hoverflies) spend the summer in the U.K. but then fly to the Mediterranean or North Africa come the autumn. They begin these migrations on sunny days but simply flying towards the sun would take them on a rather long winded route. A study by a research team at Exeter University suggests that they are able to account for the sun’s movement using their circadian rhythm - an internal clock. If the circadian rhythm of the hoverfly is disrupted, then so is its flight path. Migrating cuckoos. Like many other birds, cuckoos are in decline. Some time back, the BTO set up a research unit to learn more about the decline and behaviour of cuckoos. The work of this group has revealed details of the cuckoos’ migration routes and its winter homelands. Cuckoos have two routes out of the UK : They migrate out south west via Spain and Morocco - the WEST route, or They take a south east route via Italy and the Balkans (the EAST route) but Both routes ultimately converge on the Congo Basin in Central Africa. However, the birds that take the WEST route leave some eight days later than those taken the EAST route, but were more likely to die en route. Most of the mortality of the birds occurs in the European section of the migration path. This may be a reflection of the status of their stop-over sites. Problems might include : Habitat change, droughts and wildfires Decline in food sources (e.g. large moth caterpillars). A lot more detail / information on this project can be found here. VOC’s The air around us is a mixture of different gases / particles / and aerosols. An aerosol is itself a ‘mixture’ of very small particles (solid or liquid) in air. These particles can come from a variety of sources :such as volcanoes, cars, trucks and wood fires. Examples of aerosols include mist, cigarette smoke, fires volcanoes car exhaust fumes. Some trees and plants also release volatile organic compounds (VOCs), for example Pine trees release alpha-pinene. Recent research has established that these volatile compounds / vapours are not only responsible for the characteristic scent, but are also important in the formation of aerosols found in the air in and around such woodlands and forests. Atmospheric aerosols scatter and absorb light, and also influence the formation of clouds, though these processes are not fully understood. Recent research by the University of East Finland has showed that biogenic aerosols (formed from VOCs) can reduce the amount of solar radiation that reaches the earth’ surface. They help scatter the radiation back into space. These biogenic aerosols increase the number of cloud droplets and make the clouds more reflective.
Woodland and forest cover
Compared to some of our European neighbours, it seems that our percentage woodland and forest cover is quite low at 13%; as was recently discussed on the BBC "More or less" programme. Only Denmark and the Netherlands have similar low levels of cover. Finland, on the other hand, has almost three quarters of its surface area covered with trees. After the end of the last ice age, trees gradually recolonised the exposed landscape so that vast swathes of the U.K. were covered with woodland/forest - the wildwood. It might be thought that our current low figure is due to increased urbanisation, road/motorway construction etc. In fact, the tree cover is remarkably similar to that at the end of the first millennium CE. More trees were ‘lost’ in succeeding centuries with the expansion of farming, and trees were harvested for boat building and house construction. The Mary Rose was built using oak and elm. It was the first big ship of the Tudor naval fleet. It has been estimated that over 600 trees were needed for its construction; that is equivalent to about 16 hectares of forest/woodland. Wood was also used to produce charcoal, which was used to smelt metals, particularly iron. The history of charcoal burners in the New Forest is well documented. Many woodlands / forests were the preserve of the landed gentry and the aristocracy and reserved for deer hunting. Anyone caught killing deer or boar from such woodlands could suffer terrible punishments but would more likely be fined.. Woodland and forest continued to be depleted so that by the end of the seventeenth century, the percentage cover had fallen to 8%. At the beginning of the twentieth century, the figure stood at a pitiful 5.2%. The Asquith administration in 1916 established a committee to report on the country’s woodlands and timber supplies. This lead to the setting up of the Forestry Commission which was not just concerned with established ‘strategic reserves of timber’ but also trying to create viable communities in marginal areas. Through its efforts over the succeeding decades, the U.K’s area of woodland and forest has increased significantly - though the Forestry Commission’s heavy use of coniferous species (particularly in the 60’s and 70’s) has been criticised. Coniferous woodland / plantations do not support such a wide range of plant and animal life as deciduous woodland. However, their current emphasis on diversity (and recreational use) favours a much wider range of species, including broadleaved/deciduous trees and the development of a richer ground flora.
What are Buckingham Palace Gardens like from the inside? And what are the Royal gardeners trying to achieve?
The main thing about the queen's gardens is that they are very private. They are large (39 acres) and surrounded by busy roads but not many people get a chance to go inside and even fewer get the inside story from the horse's mouth. So my guided tour around the gardens this week with the Head Gardener, Mark Lane, was an unusual insight, made possible by being a member of the Royal Forestry Society. Mark explained that the Queen wanted no photos whatsoever of the garden and he wouldn't even let me take a mugshot of him. Beyond the privacy that exists within the garden, there are extensive efforts to keep it hidden from the outside - the eight gardeners and dozens of contractors have planted evergreen trees and shrubs just inside the walls to shield the gardens from voyeurs in neighbouring high-rise buildings. And there's a lot to hide with a 3.5 acre lake, a tennis court, statues, a summer-house with its very own corgi (stuffed, I think), and a private borehole for watering and lake-filling. Mark Lane has been working in the garden for over 40 years, 30 of those as Head Gardener so the planting and design are very much a joint creation by him and the Queen herself, working to create a giant secret garden on what is, in essence, a triangular traffic island. They have tried to plant as many different species as possible so you are also in what could be thought of as an arboretum - I saw no weeds whatsoever so it's probably fair to say that there is not a tight budgetary constraint. Mark's bold claim is that "any habitat you can name we have an example of here." I walked along the herbaceous border for 150 metres without seeing the same plant twice, apart from the six or seven banana plants. This border runs along the edge of a lawn extensive enough for a helicopter to land. Indeed one chopper touched down just before the coronation in 1953 making it London's oldest helipad, now reinforced with matting underneath the lawn. Behind this is the lake with two islands, both rarely visited by Royals - or other humans - to encourage wildlife there. Another semi-secret element is the woodland path behind the herbaceous border for the Queen to use on occasions "when she wants some peace and quiet". Apart from creating a pleasure garden for the Royal family, the gardeners are focused on the three big garden parties the Queen holds in early summer each year (aside from Covid years). Each one is for 7,500 guests, who are allowed to roam freely around the gardens. Mark and his team are so concentrated on these events that his motto for each party day is, "not a leaf out of place". They also prune the roses in late autumn rather than Spring so that they bloom and are at their best for the parties. His main criteria for choosing the species of rose are that they should have maximum fragrance and be disease resistant. "Every garden," insists Mark, "should have a conservation plan" and Buckingham Palace Gardens has one: they recycle 99% of their waste, they have bee hives on the island, they retain rotting Robinia trees for the bats, and they have much increased their areas of meadow grasses. These grassy patches have been good for moths and butterflies and the gardeners can be sure of this because every year they choose several nights to set up overnight moth traps. Using a mercury light, they trap, count and then release dozens of species and they have a record of this annual audit going back to 1956. Other species are not so lucky - grey squirrels are "controlled" though Mark was too coy, even with the group of foresters I was accompanying, to say whether he shoots, traps or poisons these "tree rats" It seems that being Royal doesn't stop your trees or garden from suffering from pests and diseases. Honey fungus is a menace that they attack using fungicides and "air-spading", whilst Oak Processionary Moth nests are removed for incineration, and even their London Plane trees are attacked by the Massaria fungus which has been present in London since 2007. Buckingham Palace Gardens have a very long history and at one time had a four-acre mulberry garden to produce silk worms. The King at the time (King James 1st) was so keen on silk production that he ordered every county in the country to plant 1,000 Mulberry Trees, some of which still survive such as the ones at Charlton House in South East London. The variety and quality of trees mean that Buckingham Palace Gardens has 15 National Champion trees, three of which were planted by the Royal family. One of the most unusual plants we stumbled across was the Ilex vomitaria, a species of holly which, when eaten, makes the consumer vomit. But my favourite was the common hawthorn whose berries had been recently harvested - they are used to make Buckingham Palace Gin which for £30 a bottle is available commercially (who said the Queen doesn't share?!). All the hundreds of varieties of trees and shrubs are part of Mark Lane's aspiration as Head Gardener which he describes as "to create a garden that is notable not just because it's attached to Buckingham Palace but which stands on its own merit." He told us of an incident in the gardens, when the queen was meeting a man who was one of thousands of guests at one of the tea parties. His phone went off and he looked a bit confused, not sure whether to take the call. She advised encouragingly, "yes, take it - it might be someone important." Although photos are not allowed it seems some have been smuggled out. If you search "Buckingham Palace gardens" on Google images you'll find a nice collection of snaps. My pictures are all from outside, trying to look in. Have you visited? What was your impression?