Week 44
What is it about autumn colours that are so pleasing? This year, for reasons I cannot explain, the colours on my land are wonderful. Strangely, colours can vary year-on-year. One year they will be dramatic, while the next they will disappoint. The autumn air is frequently clearer and the sun lower, which can exaggerate any colours that I might see. Autumn is the time to look for colours and this year the palette is remarkable.
The changing colour of autumn foliage is a simple chemistry lesson. Chlorophyll makes leaves green and enables plants to use sunlight to create their own food. As days become shorter and temperatures drop, chlorophyll production slows, and then stops so that other pigments in the leaves begin to appear.
The two primary pigments are carotenoids[i] that produce orange, yellow, and brown colours, and anthocyanins[ii] that are responsible for reds. The carotenoids are present in leaves throughout the year, although green chlorophyll is dominant during the growth season and prevents the carotenoids from being seen. The anthocyanins (reds) are created in the autumn in response to light, plant chemical changes, temperature, and water supply. This is how weather might affect the brilliance of a colour display. A succession of warm, sunny days and crisp but not freezing nights leads to the most spectacular colours. The first frost triggers a dramatic increase in the breakdown of chlorophyll and the yellow and orange carotenoids become the dominant colour seen in leaves[iii].
Moisture also plays a role. A late spring, or a severe summer drought, can delay the onset of autumn colours. A warm wet spring, favourable summer weather, and warm sunny autumn days with cool nights should produce the most brilliant autumn display[iv].
Other factors can also affect colours, especially in urban communities. For example, de-icing salts can injure and stress vegetation and delay or inhibit any colour display. Also, diseases such as powdery mildew[v] and tar spot[vi] can kill living cells and disrupt the metabolism of a leaf so that its seasonal display is reduced[vii].
As with humans, plants have a respiratory system that is vulnerable to air pollution. Pollution ranging from factories to car exhaust turns into a greyish brown smog that can have a substantial impact on trees and their leaves. Pollutants emitted from fossil fuels can bleach leaves white or turn them into traditional autumn colours before the season properly arrives. If enough leaves are prematurely impacted in this manner, an entire plant is at risk. Damage caused by air pollution is easy to spot. Sulphur dioxide converts into sulphuric acid which makes holes in leaves. Smog damage on leaves appears as mottled spots which range in colour from yellow to black or brown. Fluorides damage the edges of plants and cause them to turn brown or black[viii].
Although vegetation can suffer from the effects of pollution, it also has some ability to adapt to high pollution levels[ix], but this property is clearly not limitless. Even so, this can help control air pollution, especially as photosynthesis requires carbon dioxide (CO2) to proceed[x]. Vegetation can also reduce the effects of other pollutants and, for maximum effect, should be close to the source of pollution. The vegetation should also be sufficiently high and porous to allow air through but solid enough to ensure the air passes close to the vegetation’s surface[xi]. I am fortunate with my land, as it is bounded by private thoroughfares and the volume of traffic is low. Yet in the distance I can still hear the public roadways. Significant pollution is not far away, and coming ever closer if the planners have their way.
When it comes to noise, night-time is a good occasion to listen to my land. Sound is an important dimension that is so often ignored. As it becomes dark, as the traffic noise reduces, and when the builders nearby have gone home, so I can hear my land. There is the rustle of leaves in the trees and on the ground, the swish of bamboo and long grasses, birdsong, and the faint tinkle of flowing water[xii]. Spring is perhaps a noisier season, as that is when many animals gather to mate. At that time, frogs and toads are extremely vocal, while hedgehogs snort, snuffle, and grunt[xiii]. Right now, there is the occasional bark of a deer, certainly the distant honking of any geese that have not yet migrated, the occasional “twit-twoo” of an owl, and plenty of other birdcall. My land is a noisy place, and I will frequently sit in the open and listen. It goes a long way to helping me relax.
Surprisingly noisy are the bats, and the fluttering sound from their wings. Occasionally I can hear them scratching, when they use their wings, the so-called patagium[xiv], as hands to climb and crawl[xv]. I have plenty of bats on my land, although none that I can find roosting in my house. Bats live in many different locations - countryside, towns, and cities across the UK. They are most active in the summer months when they come out of hibernation, hunt insects, give birth, and raise their young. It is more likely one will see bats around sunset or sunrise in warm, dry weather. Some bats fly high in the sky while others fly low over water. Some prefer grassland while others stick close to hedges and trees[xvi].
Bats are more common than one thinks and comprise about 20% of all classified mammal species worldwide, with over 1400 species of bat in existence. Many are insectivores, but some are frugivores (fruit-eaters) or nectarivores (nectar-eaters)[xvii]. They are remarkable animals despite the existence of chiroptophobia, which is an irrational fear of bats[xviii]. Fortunately, this is uncommon. Not all bats hibernate, and they have few natural predators. Disease is their biggest threat, especially so-called white-nose syndrome[xix]. This condition is caused by a fungus called Pseudogymnoascus destructans but unlike the USA and Canada, where the fungus has been associated with mass mortalities, it less of a problem in Europe and the UK, where the fungus has also been found[xx].
Bats are incredibly useful animals. Without them, albeit overseas to the UK, there would be no bananas, avocados, and mangoes, as the animals aid their pollination. Bats are the only flying mammal and can reach speeds of over 161 kilometres/hour (100 mph). The longest living bat was an impressive 41 years old, and the animal spends a considerable amount of time cleaning and grooming itself. Approximately 80 medicines come from plants that rely on bats for their survival. Bats also have a belly button (umbilicus)[xxi], which is a feature of all mammals, even if the umbilicus is covered with fur. So, what is there not to like about a bat? They are fascinating animals and easy to see on my land.
In the UK, there are 18 species of bat, although sadly their numbers are dwindling[xxii]. This is partly because of modern agricultural practices. The most widespread bat in the UK, and on my land, is the common pipistrelle. This bat relies on buildings for making its roosts, so is vulnerable to building renovations, as well as the toxic chemicals used for the treatment of timber[xxiii]. It is a hard life being a UK bat. It is perhaps just as well that this week, the last week in October, is Bat Week worldwide[xxiv]. The animal needs our help.
My holly[xxv] trees are presently laden with red berries, unusually so, and I can confirm that on the nearby fells, the hawthorn trees are also dotted with red berries. With so many red berries, one old wives’ tale would claim there is a severe winter ahead[xxvi]. This would not surprise me as we have been receiving multiple weather warnings in recent times, indicative of an undeniable climate change that is taking place all around.
In addition, I recall thinking a few weeks ago that the geese were migrating south somewhat earlier than I would expect. Again, this is said to be a sign of a severe winter ahead. I will simply have to see but I will order in some extra warming blankets for my plants, especially if I am thinking of planting some new holm oaks for screening.
Holly is a very sturdy tree. On the fells I find hollies in often precarious and exposed locations. Meanwhile, on my land holly seedlings suddenly appear in unexpected places. As evidence of a holly’s toughness, I had one, about 20 feet high, that was toppled by the violent Storm Arwen in November 2021. I decided not to slice it up with a chainsaw but to bring it back to the vertical and hold it in position. I did so and, astonishingly, it is now growing brilliantly. I had another holly that developed fungal root rot and I believed it was a goner. However, I pruned it hard, applied regular phosphite biostimulant to its roots and it has also recovered. Hollies are remarkable.
Holly has been used to decorate homes for centuries and is particularly associated with mid-winter festivals. Its evergreen, prickly leaves around the front door of a house were thought to stop evil forces from entering. The leaves also have a high calorific value and, in the past, were used as fodder. The wood of the holly was also once used for making bobbins for the cotton industry. Although a holly’s berries are attractive, they are also toxic and can be violently emetic and purgative, so eating them is best avoided. This said, the leaves have been used as a tea substitute and roasted berries as a coffee alternative[xxvii]. The holly is what is called dioecious. That is, there are male and female trees. The female has the berries whereas the male does not. Telling the difference between the two is not simple unless there are flowers to see. The flower with four stamens is male while those with a green bump, the future berry, is female. In autumn, it is a fair bet that a holly with red berries is a female[xxviii].
A major advantage of renaturing is that the land keeps itself going. I rarely, if ever, need to visit a garden centre. Many people, especially those from urban surroundings, think that plants and trees come from shops. How wrong they are. My land has all it needs and there is little requirement to seek input from beyond. For example, a year ago we harvested seed from some wild oregano, loosestrife, and other plants as well, all of which were growing on my land. My main aim was to plant my dry stone Lakeland wall as I have long believed that to leave a wall unplanted is a true waste of space.
In Lakeland, dry stone walls are still common. In 1880, the United Kingdom had approximately 837,750 kilometres (520,554 miles) of dry stone walls[xxix], requiring 1.9 billion hours of work for their construction[xxx]. Many of these walls no longer exist. Today, there are about 290,000 kilometres (180,198 miles) remaining[xxxi], much of which needs repair. Dry stone walls are found in at least 35 countries and were designated an intangible cultural heritage of humanity by UNESCO in 2018[xxxii].
In the United Kingdom, free-standing walls are typically 1.4 metres high, while boundary walls may be slightly higher[xxxiii]. The Lakeland walls on my land are both free-standing and boundary. Discussions about these walls generally focus on the wall, stones, and techniques, and often neglect environmental benefits. However, a dry stone wall contains no cement or mortar. Cement production alone generates around 2.5 billion tonnes of CO2 each year, which is about 8% of the global total[xxxiv].
Because dry stone walls contain 15-25% air they are an excellent habitat for biodiversity[xxxv]. They provide homes for various animals, especially insects, and offer an environment conducive to the growth of lichens, mosses, and other plant species. Limited scientific studies have identified 149 plant species associated with dry stone walls[xxxvi]. Animals, too. Many thousands of different species of wildlife can be found in a dry stone wall, which is essentially a linear nature reserve that should be preserved[xxxvii]. This is how I see my own Lakeland walls.
More than 4.4 billion people now live in urban areas[xxxviii], representing over half of the global population. This societal shift, added to a greater focus on environmental protection, has led to the development of numerous vertical garden projects. Examples such as Milan's Bosco Verticale[xxxix], Paris' L'Oasis d'Aboukir[xl], and Singapore's Tree House[xli] exemplify this growing trend.
The existing 290,000 kilometres (180,198 miles) of dry stone walls in the United Kingdom represent a total length of 580,000 kilometres (360,395 miles) if each wall has two faces, although this is not always the situation. With a mean wall height of 1.4 metres, the total surface area reaches 81,200 hectares, surpassing the size of Paris, which covers 10,540 hectares.
Imagine using all this space for planting trees. With a mean of 1600 trees per hectare in mixed woodlands[xlii], this expanse of unused dry stone wall could theoretically support 130 million trees. If eight mature trees can provide sufficient oxygen for one person[xliii], the UK's dry stone walls, if planted, could theoretically supply sufficient oxygen for 16.25 million people. This is about 24% of the UK's population.
Dry stone walls are essentially vertical rockeries, and many types of vegetation will grow both in and on them. Stonecrop, houseleek, wall bellflower, ferns, phlox, speedwell, rosemary, strawberry, ivy, moss, lichens, and so much more, are very content to inhabit a dry stone wall[xliv]. These plants produce oxygen, absorb carbon dioxide, and are effective carbon sinks.
To fully harness the benefits of biodiversity and support various forms of life, I believe it is crucial to, what I call, "dress" dry stone walls before considering them complete. Dressing requires seeding or promoting the growth of plants from surrounding vegetation, even incorporating soil, as might be performed for a horizontal rockery. These practices contribute to environmental improvement while providing camouflage for the newly constructed wall and reducing the risk of physical damage.
We have done this on my own land, by shifting seed from elsewhere directly into crevices in the wall. The result has been remarkable. My Lakeland wall has burst into life.
Never leave a wall naked and do use your own seed to develop your land.
***
Acknowledgement
Take it from me - none of this would be possible without the help of RSG Horticulture. Rufus, who runs it, has far more energy than me and is full of ideas and skills. Do contact him through https://www.rsghorticulture.com.
Hashtags
#AutumnColors #Rewilding #Nature #FallFoliage #LeafPeeping #AutumnPalette #ChemistryOfNature #ClimateChange #AirPollution #Bats #Conservation #UKWildlife #HollyTrees #Lakeland #DryStoneWalls #UrbanGardens #VerticalGardens #Biodiversity #EnvironmentalProtection
References [i] Maoka T. Carotenoids as natural functional pigments. J Nat Med. 2020 Jan;74(1):1-16. doi: 10.1007/s11418-019-01364-x. Epub 2019 Oct 1. Carotenoids are essential pigments in photosynthetic organs along with chlorophylls. Carotenoids also act as photo-protectors, antioxidants, colour attractants, and precursors of plant hormones in non-photosynthetic organs of plants. [ii] Gould KS. Nature's Swiss Army Knife: The Diverse Protective Roles of Anthocyanins in Leaves. J Biomed Biotechnol. 2004;2004(5):314-320. doi: 10.1155/S1110724304406147. Anthocyanins protect leaves from the stress of photoinhibitory light fluxes by absorbing the excess photons that would otherwise be intercepted by chlorophyll. [iii] Schaberg P. The Biology of Fall Leaves: It’s all about Chemistry. 22 October 2015. See https://www.fs.usda.gov/features/biology-fall-leaves-its-all-about-chemistry. Accessed 26 October 2023. [iv] Hall J. Fall Foliage 101: Why Some Autumns are More Colorful. 15 October 2021. See https://www.gardenista.com/posts/fall-foliage-101-why-some-autumns-are-more-colorful/. Accessed 26 October 2023. [v] See weeks 37 & 38 entries. [vi] RHS. Tar spot of maple. See https://www.rhs.org.uk/disease/tar-spot-of-maple. Accessed 28 October 2023. [vii] Westover T, Smith KT. Science of Fall Colors. See https://www.fs.usda.gov/features/did-you-know-fall-color-begins-spring. Accessed 26 October 2023. [viii] Clean Air Council. Fall’s color is in danger. See https://cleanair.org/fallcolor/#:~:text=Sulfur%20dioxide%20converts%20into%20sulfuric,to%20turn%20brown%20or%20black. Accessed 26 October 2023. [ix] Molnár VÉ, Simon E, Tóthmérész B, Ninsawat S, Szabó S. Air pollution induced vegetation stress–the air pollution tolerance index as a quick tool for city health evaluation. Ecological Indicators. 2020 Jun 1;113:106234. [x] Gheorghe IF, Ion B. The effects of air pollutants on vegetation and the role of vegetation in reducing atmospheric pollution. The impact of air pollution on health, economy, environment and agricultural sources. 2011 Jul 29;29:241-80. [xi] Janhäll S. Review on urban vegetation and particle air pollution–Deposition and dispersion. Atmospheric environment. 2015 Mar 1;105:130-7. [xii] Thrive. Engaging our sense of hearing in the garden. See https://www.thrive.org.uk/get-gardening/engaging-our-sense-of-hearing-in-the-garden#:~:text=For%20example%2C%20the%20rustle%20of,unique%20sounds%20to%20the%20garden. Accessed 26 October 2023. [xiii] Kirkwood H. Things that go screech in the night. 9 November 2015. See https://www.countrylife.co.uk/country-life/things-that-go-screech-in-the-night-79023. Accessed 26 October 2023. [xiv] Chiroptera: more on morphology. See https://ucmp.berkeley.edu/mammal/eutheria/chiromm.html#:~:text=Unlike%20birds%20and%20pterosaurs%2C%20in,%2C%22%20for%20the%20bats). Accessed 29 October 2023. [xv] What sounds to bats make? See https://www.crittercontrol.com/wildlife/bats/bat-noises#:~:text=Bat%20Sounds%20at%20Night&text=The%20noises%20people%20are%20able,may%20hear%20scratching%20on%20walls. Accessed 26 October 2023. [xvi] Bat Conservation Trust. Where to see bats. See https://www.bats.org.uk/about-bats/where-do-bats-live/where-to-see-bats#:~:text=Bats%20live%20in%20the%20countryside,sunrise%20in%20warm%2C%20dry%20weather. Accessed 26 October 2023. [xvii] Wikipedia. Bat. See https://en.wikipedia.org/wiki/Bat. Accessed 26 October 2023. [xviii] Johnson E. What is chiroptophobia? See https://cpdonline.co.uk/knowledge-base/mental-health/chiroptophobia/. Accessed 26 October 2023. [xix] National Wildlife Health Center. White-nose syndrome. See https://www.usgs.gov/centers/nwhc/science/white-nose-syndrome?qt-science_center_objects=0#qt-science_center_objects. Accessed 26 October 2023. [xx] Bat Conservation Trust. White-nose syndrome. See https://www.bats.org.uk/about-bats/threats-to-bats/white-nose-syndrome/white-nose-syndrome-in-europe. Accessed 26 October 2023. [xxi] US Department of the Interior. 13 awesome facts about bats. 20 October 2021. See https://www.doi.gov/blog/13-facts-about-bats. Accessed 26 October 2023. [xxii] UK Bats. See https://www.bats.org.uk/about-bats/what-are-bats/uk-bats. Accessed 27 October 2023. [xxiii] Bat Conservation Trust. Common pipistrelle (Pipistrellus pipistrellus). See https://cdn.bats.org.uk/uploads/pdf/About%20Bats/commonpipistrelle_11.02.13.pdf?v=1541085177&_gl=1*1n44ku7*_ga*MTg5MjEwMTAwLjE2OTgzMzUxMzc.*_ga_G28378TB9V*MTY5ODQwNzE1Mi4yLjEuMTY5ODQwNzI4NS4wLjAuMA.. Accessed 27 October 2023. [xxiv] Bat Week. See https://batweek.org. Accessed 26 October 2023. [xxv] See weeks 3, 4, 23, 26 entries. [xxvi] Dick S. Signs of a harsh winter: Truth in the old wives tales? 15 September 2019. See https://www.heraldscotland.com/news/17903551.signs-harsh-winter-truth-old-wives-tales/. Accessed 27 October 2023. [xxvii] Plants For A Future. Ilex aquifolium. See https://pfaf.org/user/Plant.aspx?LatinName=Ilex+aquifolium. Accessed 27 October 2023. [xxviii] Tilley N. How To Tell The Difference Between A Male And Female Holly Bush. See https://www.gardeningknowhow.com/ornamental/shrubs/holly/how-to-tell-the-difference-between-a-male-and-female-holly-bush.htm. Accessed 29 October 2023. [xxix] Müller G. Europas Feldeinfriedungen, Wallhecken (Knicks), Hecken, Feldmauern, Flecht- und Biegehecken, traditionelle Zäune, 2013. [xxx] Aitken A. In Dry stone walling: materials and techniques. The Crowood Press, 2023, p4 [xxxi] Dry stone walling – introduction. See https://www.lowimpact.org/categories/dry-stone-walling#:~:text=Most%20are%20found%20along%20the,and%20unfit%20for%20keeping%20stock. Accessed 7 June 2023. [xxxii] UNESCO – Intangible Cultural Heritage. Art of dry stone walling, knowledge and techniques. See https://ich.unesco.org/en/RL/art-of-dry-stone-walling-knowledge-and-techniques-01393. Accessed 7 June 2023. [xxxiii] Spear T. The Stone Trust. Technical specifications for dry stone walls. See https://thestonetrust.org/tech-specs-for-dry-stone-walls/#:~:text=A%20standard%2C%20freestanding%20wall%20usually,1.6m%20(5ft%203in). Accessed 7 June 2023. [xxxiv] Science Museum. Building the modern world: concrete and our environment. 7 January 2021. See https://www.sciencemuseum.org.uk/objects-and-stories/everyday-wonders/building-modern-world-concrete-and-our-environment#:~:text=The%20environmental%20impact%20of%20concrete,-Concrete%20is%20now&text=Cement%20production%20alone%20generates%20around,to%20around%201%2C500°C. Accessed 27 October 2023. [xxxv] Paysalia – landscape, garden and sport exhibition. See https://www.paysalia.com/en/blog/expertise/durable-ecological-good-looking-dry-stone-walls-ideal-gardens#:~:text=When%20finished%2C%20dry%20stone%20walls,picked%20up%20in%20a%20field. Accessed 7 June 2023. [xxxvi] Bunce B. International Association for Landscape Ecology. The biodiversity of a dry-stone wall. See https://iale.uk/biodiversity-dry-stone-wall. Accessed 7 June 2023. [xxxvii] Dry Stone Walling Association of Great Britain. Dry stone walls and wildlife. See https://www.dswa.org.uk/wp-content/uploads/2018/07/Walls-Wildlife-Leaflet.pdf. Accessed 11 September 2023. [xxxviii] Urbanization over the past 12,000 years. See https://ourworldindata.org/urbanization#urbanization-over-the-past-12-000-years. Accessed 7 June 2023. [xxxix] Bosco Verticale. http://www.residenzeportanuova.com/it/residenze/bosco-verticale. Accessed 7 June 2023. [xl] Best vertical gardens around the world. See https://ferntasticagardens.com/best-vertical-gardens-around-world/. Accessed 7 June 2023. [xli] [xli] World’s largest vertical garden in Singapore breaks Guinness World Record! See https://www.1millionwomen.com.au/blog/worlds-largest-vertical-garden-singapore-breaks-guinness-world-record/. Accessed 7 June 2023. [xlii] [xlii] NHS Forest. How many trees per hectare? See https://nhsforest.org/how-many-trees-can-be-planted-hectare/. Accessed 7 June 2023. [xliii] [xliii] Villazon L. How many trees does it take to produce oxygen for one person? Science Focus. See https://www.sciencefocus.com/planet-earth/how-many-trees-does-it-take-to-produce-oxygen-for-one-person/. Accessed 7 June 2023. [xliv] Frederike. Dry stone walls for gardens: 5 tips for proper planting. See https://plantura.garden/uk/garden-design/dry-stone-walls-for-gardens#:~:text=Suitable%20plants%20for%20the%20dry%20stone%20wall,-Anyone%20wanting%20to&text=In%20fact%2C%20only%20plants%20that,planting%20a%20natural%20stone%20wall. Accessed 12 September 2023.
Comments