Week 40
I see it as being any moment, as my deciduous trees begin to turn brown, and their leaves start to curl. Next will be the glances and messages from others, asking that I clear fallen leaves. My thoughts are straightforward - the only reason for leaf-tidying on renatured land is for appearance. I can think of little convincing biological benefit of leaf clearance at all[i]. I can certainly think of disadvantages, not least the time clearance can take. It is perhaps why there is a growing movement to let fallen leaves lie, and not just in UK. Take The Netherlands as an example, where Eindhoven council has specifically asked its citizens to either place their leaves in special leaf baskets[ii] so that leaf mulch can develop, or to leave the leaves alone. This is part of an attempt to change public perception of how land might be used and judged[iii].
Last year I cleared only a small proportion of the leaves that fell, and I also created some leaf mulchers. The mulchers are working magnificently, as their leaf content is softening, and mulch is starting to appear. Meanwhile those leaves that I allowed to lie where they fell have vanished. There is not even one to see. Flowers have appeared where once there was leaf and the long grass around is healthy. In addition, wildlife has flocked to the area and set up home. My grass is now crammed with walkers, hoppers, crawlers and slitherers that believe I should not be there.
I once thought that when a deciduous tree lost its leaves then the tree no longer had purpose. I now realise I was wrong, and that the loss of leaves is an integral part in the life cycle of a tree and something I must support. The starting point is chlorophyll, the chemical that produces a leaf’s green colour and that is essential to photosynthesis. This is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar[iv]. By autumn, and as sunlight reduces, the trees have generated and stored sufficient energy and sugars to see them through the winter months. This is almost a form of tree hibernation. As the chlorophyll reduces, it leaves behind carotenes, which are yellow. They have been there all the time but have been masked by the chlorophyll. For red leaves, this colour is created by anthocyanins, although the temperature generally must stay above freezing for these to have an effect. It is why trees can have a mixture of green, yellow, and red as their leaves begin to turn.
Where a leaf joins a branch, there is a layer of cells called the abscission layer. During the growing season this layer allows energy formed in the leaves to enter the branch and pass from there to the trunk to be stored. This transfer is aided by a hormone called auxin. As daylight reduces and the weather cools, so the amount of auxin reduces, the transfer of energy declines, and the abscission layer weakens. Eventually the leaf falls[v].
The loss of a leaf is an essential part of life for a deciduous tree. It means that the tree expends less energy during the winter and has stored sufficient energy to see it through to warmer times as well. The tree conserves moisture within its trunk thereby preventing it from drying out. As the leaves fall around the base of the tree, they provide a mulch layer that protects the roots against the frost. The leaves rot rapidly, within approximately six months[vi], and increase the nutrition of the soil around the tree so that growth can continue. The loss of leaf also reduces the wind resistance of a tree leading to less chance of the tree toppling during stormy weather. Winter, especially in Lakeland, has plenty of bad weather. Leaf fall is thus a critical part of a deciduous tree’s existence.
Conifers are different, as their needles can be impregnated with resin to resist cold and wet weather. Needles are better at this than leaves. Conifers, by being generally narrower than deciduous trees, use their thin shape to reduce wind resistance. Sadly, this attribute did not appear especially helpful during Storm Arwen in November 2021, with its winds of up to 100mph and the most severe disruption to power supplies since 2005[vii], as most of the Lakeland trees to fall were conifers. Many of the deciduous trees survived. Some conifers can also move water from the interior of their cells during icy weather. This means that if water freezes there is less chance a cell can be damaged.
Autumn perhaps shows the differences between deciduous and conifer trees more obviously than at any other time of the year. The two types of tree are very different, with each having its own processes for survival.
Because deciduous trees lose their leaves, they need to maximise the amount of light they can absorb during the periods they have them, and therefore most deciduous trees are broadleaved. The larger surface area of the leaves means that there is a greater expanse in which photosynthesis can take place. The trees also bear fruits or capsules that contain seeds. These seeds are protected by either a hard shell (e.g. the acorn from an oak) or form part of a fleshy fruit (e.g. plums). Their seeds are often dispersed by animals eating or moving them. Most deciduous trees flower and are thus angiosperms[viii]. They usually flower before the leaves grow or early in the growing season, while leaves are small, to optimise pollen transmission by the wind. Deciduous trees also tend to grow outwards to optimise the absorption of light.
Meanwhile conifers mostly have leaves in all seasons but gradually lose and replace them throughout the year. There are exceptions, for example the larch[ix], which loses its needles each year. The ability to recycle nutrients, especially nitrogen, which is what losing a leaf or needle encourages, is an important advantage in nutrient-poor environments. In addition, larches also grow in snowy climates where heavy snow loads are less likely to break bare branches compared with trees burdened with needles during the winter. Its deciduous nature also makes the larch especially resistant to fire and resilient to injury. The fire-resistance is further supplemented by a larch’s bark, which is thick, and helps protect the tree’s trunk[x]. All these reasons give the larch a competitive advantage over other conifers where it grows. However, sadly, the larch is very susceptible to the root fungus Phytophthora ramorum[xi], and the number of larches in the United Kingdom is plummeting as a result.
Most coniferous trees, however, have compact and pointed, needle-like or scale-like leaves with a waxy coating and a cuticle. This leaf structure minimises water loss from evaporation and is hardier, less palatable to pests, and more waterproof and windproof. The leaf structure allows conifers to photosynthesise throughout the year and makes them better adapted to harsh habitats, for example very cold or scorching environments. Conifers do not produce flowers, so are gymnosperms[xii]. Their seeds are protected by a sharp-toothed cone, which releases seeds by opening its scales. Conifers tend to grow upwards and in a triangular shape[xiii].
What is clear is that autumn and winter are critical parts of the life of a tree, and leaf fall forms part of that. It sets the scene for the year to follow, so as humans we tamper with this at our peril.
When I was a child, I read Wind in the Willows by Kenneth Grahame and grew to like the character called Mole. The moral of the book, not that it was necessarily written with a moral in mind, was that good friendship can overcome all obstacles[xiv]. The story centres around Rat, Mole, and Badger trying to keep their friend Toad out of trouble and help him reclaim his home. How true a lesson that is. In the story, Mole is kind and thoughtful and is loyal to his friends. But genuine moles are very different. In real life they are antisocial, violent, and terrible parents. Their forepaws are also stronger than human hands and a mole will eat its body weight in worms every 12 hours[xv]. Moles are nocturnal animals and mate in the early spring, giving birth to a litter of 2-5 pups in the late spring or early summer. A mole will live for 2-3 years[xvi].
I have moles on my land, and although they are small, their mole hills are clear to see. They are invariably somewhere with only moderate moisture, so I will not find them in an area of possible surface flooding. The higher up the hill a mole hill is found, the wetter the weather is likely to be. Moles like moisture, but just the right amount. Too dry and they will not find food, too wet and their tunnels may become impassable. Changes in the weather are critical for moles, with flooding the greatest hazard. It is said that during frosty weather, if a mole throws up fresh earth, there will be a thaw within 48 hours. If a mole throws up more earth than usual, then there is rain on the way. Moles are also useful for long-term forecasting. If a mole makes a cache of worms to see them through winter, then there is a hard winter ahead. If there are fewer caches than normal, then the winter is likely to be mild[xvii]. It is thus worth keeping one eye open for mole behaviour.
Moles need tunnels and can dig several hundred feet of tunnel in one day. There are two types of tunnel - surface or deep - the latter being more permanent. The tunnels are used while a mole searches for food, and for communication between moles, as well as avoiding being seen by predators. Mole hills are essential as well and have many advantages. They aerate the soil and tend to have a better nutrient content, as the mole has brought up the soil from deeper down. The tunnels and soil disturbance work wonders for biodiversity while a mole hill is an indication that the soil is healthy.
A mole hill is typically conical and created by a mole as it digs through the soil and pushes the excess dirt up and out of its tunnels. Large mole hills suggest a mature, experienced mole that has been in an area for quite a while. Smaller mole hills are often created by younger moles. Clusters of mole hills suggest a mole has established its territory while scattered mole hills imply it is still searching for an area to call home. The texture of the soil in a mole hill is also a valuable observation. When the soil is loose and crumbly, it implies the mole is eating well and is healthy. If the soil is hard and compacted, it suggests the mole may be struggling.
Moles can also be troublesome, and it is this that leads to so many people hating the animals and putting them to death on sight. The tunnelling can weaken the soil and create a trip hazard, while the mole hills can smother grass and other plants so that light cannot reach them. There are financial losses, too, when gardeners must repair the damage a mole has created. Personally, I do not bother, as with my land I am seeking function, not appearance.
Rather than putting moles to death, often for no logic, the animals can be discouraged rather than killed. On my land I allow moles to do whatever they wish. If I wanted to discourage them, and believe me they are not a major problem, then there are several options available to me. I can reduce watering, remove grubs[xviii], apply nematodes[xix] to the garden to reduce the earthworm population, or remove compost piles. There are certain eco-friendly repellents that can also be used, such as daffodils[xx], alliums[xxi], and fritillaries[xxii], which deter moles thanks to their strong odour. There are also chemical repellents - not for me, thank you - and traps and professional services.
I will leave my moles alone, while watching their molehills like a hawk. What better way of learning what weather lies ahead?
***
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
References
[i] See week 5 entry. [ii] Bladkorven in Eindhoven (transl. “Leaf baskets in Eindhoven). See https://www.eindhovenduurzaam.nl/bladkorven-in-eindhoven. Accessed 23 September 2023. [iii] Boztas S. Let fallen leaves lie, gardeners in Netherlands town urged. 24 October 2022. See https://www.theguardian.com/environment/2022/oct/24/let-fallen-leaves-lie-gardeners-in-netherlands-town-urged-eindhoven. Accessed 23 September 2023. [iv] National Geographic. Photosynthesis. See https://education.nationalgeographic.org/resource/photosynthesis/#. Accessed 30 September 2023. [v] Forestry and Land Scotland. Why do trees lose their leaves? 30 October 2020. https://forestryandland.gov.scot/blog/trees-in-autumn#:~:text=There%20are%20several%20reasons%20why,in%20winter%20storms%20and%20gales. Accessed 24 September 2023. [vi] Slippery Rock University. SRU composting advocates ‘break down’ options for fallen leaves. See https://www.sru.edu/news/110220a#:~:text=%22Leaves%20can%20take%20about%20six,soil)%2C%22%20Laurence%20said. Accessed 24 September 2023. [vii] Peachey J. Storm Arwen: from devastation to woodland regeneration. 20 January 2022. See https://insidedio.blog.gov.uk/2022/01/20/storm-arwen-from-devastation-to-woodland-regeneration/. Accessed 24 September 2023. [viii] Zimmermann MH, Dilcher DL, Cronquist A, Stevens P, Stevenson DW, Berry PE. "angiosperm". Encyclopedia Britannica, 3 Jun. 2023, https://www.britannica.com/plant/angiosperm. Accessed 30 September 2023. [ix] See weeks 23 & 38 entries. [x] Why do larches turn yellow? 6 December 2022. See https://www.fs.usda.gov/research/rmrs/news/featured/why-do-larches-turn-yellow#:~:text=Unlike%20pines%20they%20are%20not,saving%20nutrients%20to%20use%20later. Accessed 26 September 2023. [xi] Woodland Trust. Phytophthora ramorum. See https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/tree-pests-and-diseases/key-tree-pests-and-diseases/phytophthora-ramorum/. Accessed 30 September 2023. [xii] Delevoryas T. "gymnosperm". Encyclopedia Britannica, 13 Sep. 2023, https://www.britannica.com/plant/gymnosperm. Accessed 30 September 2023. [xiii] What’s the Difference between Deciduous and Coniferous Trees? 21 January 2020. See https://directree.org/deciduous-coniferous/#:~:text=Deciduous%20trees%20generally%20have%20smooth,bark%20from%20a%20young%20age. Accessed 26 September 2023. [xiv] See https://study.com/learn/lesson/the-wind-in-the-willows-kenneth-grahame-summary-characters.html#:~:text=While%20not%20written%20with%20a,friendship%20can%20overcome%20all%20obstacles. Accessed 25 September 2023. [xv] Brown A. Don’t kill moles, warns former catcher Marc Hamer at Hay festival. 29 May 2019. See https://www.theguardian.com/world/2019/may/29/dont-kill-moles-former-catcher-marc-hamer-warns-at-hay-festival. Accessed 25 September 2023. [xvi] See https://molescontrol.com/moles-hills/. Accessed 25 September 2023. [xvii] Moss S. Weatherwatch: meteorologist moles. 13 May 2011. See https://www.theguardian.com/news/2011/may/13/weatherwatch-moles-floods-droughts-forecast. Accessed 29 September 2023. [xviii] Britannica. The young form of an insect in which it looks like a small worm. https://www.britannica.com/dictionary/grub. Accessed 1 October 2023. [xix] Wikipedia. Nematode. The nematodes (/ˈnɛmətoʊdz/ NEM-ə-tohdz or NEEM-; Greek: Νηματώδη; Latin: Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They have successfully adapted to nearly every ecosystem: from marine (salt) to fresh water, soils, from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are found in every part of the earth's lithosphere, even at great depths, 0.9–3.6 km (3,000–12,000 ft) below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor. In total, 4.4 × 1020 nematodes inhabit the Earth's topsoil, or approximately 60 billion for each human. See https://en.wikipedia.org/wiki/Nematode. Accessed 30 September 2023. [xx] See weeks 3, 4, 7, 9, 10, 11, 12, 14, 15, 19, 21, 24 entries.
[xxi] RHS. Alliums include many familiar edible plants. Their common name is ornamental onion. Seehttps://www.rhs.org.uk/plants/allium. Accessed 26 September 2023. [xxii] Wikipedia. Fritillaria. Fritillaria (fritillaries) is a genus of spring flowering herbaceous bulbous perennial plants in the lily family (Liliaceae). The type species, Fritillaria meleagris, was first described in Europe in 1571, while other species from the Middle East and Asia were also introduced to Europe at that time. Fritillaria are distributed in most temperate zone of the Northern Hemisphere, from western North America, through Europe, the Mediterranean, Middle East and Central Asia to China and Japan. The majority of species are spring flowering. Most fritillaries contain poisonous steroidal alkaloids such as imperialin in the bulbs and some may even be deadly if ingested in quantity. The bulbs of a few species, such as F. affinis, F. camschatcensis, and F. pudica, are edible if prepared carefully. They were commonly eaten by indigenous peoples of the Pacific Northwest coast of North America. See https://en.wikipedia.org/wiki/Fritillaria. Accessed 26 September 2023.
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