Anja Murray: Learn to leave — and love — the leaves
A late autumn day in St Stephen's Green in Dublin. Picture: Brian Lawless/PA
Windy gusts have been doing their work of loosening the last of leaves from overhead branches — swirling yellows, rust-brown, and ochre-tinted leaves in the air before sweeping them into colourful drifts around field edges, town parks and tree-lined city streets. Each mottled golden canopy has its own palette of pigments on display, and each swathe of colourfully crinkled fallen leaves its own reassuring blend of warm amber, cinnamon, and vivid rusty brown.
Crisp dry fallen leaves are one of the nicest things about this time of year. Most of us have the luxury of winter woollies and waterproof jackets to insulate ourselves against the elements. Trees, on the other hand, have to be a little more self-sufficient in how they cope with winter weather. For most deciduous trees, the effort required to sustain leaves through the darker months is more than the gains to be had from photosynthesis when sunlight is so scant.
But the reasons why tree leaves turn such a vivid array of colour before letting go their leaves is not exactly clear. As yet, there is no single agreed explanation for why this spectacle occurs each year.
The first step in the process is well understood, when leaves reabsorb their green chlorophyll pigment once it is no longer needed.
But for the next step, not all trees are alike. Each species has evolved its own time-honed strategy for rendering pigments before the leaves are let go. Among the rowan and cherry trees, the willows, chestnut, oak, beech, hazel, birch, and sycamores, each has a tendency to a different hue in autumn. The redness of beech leaves always stands out, for example; oak leaves tend to turn consistently brown; and tall, wispy birch trees always let their leaves turn a glorious deep golden yellow.
The flamboyant reds that rowan, sycamore and beech display come from the pigment anthocyanin, produced especially at the end of the growing season. One theory is that anthocyanin protects against harmful UV light, allowing the leaf to continue photosynthesising in the harsh combination of cold temperatures and bright autumn light. Another theory is that the red anthocyanin pigment repels insects from laying their eggs among the canopy, helping lessen the attack from insect larvae come springtime.
Birch trees, on the other hand, don’t produce these red pigments in any quantity, instead they simply reabsorb all the protein-rich chlorophyll pigment from the leaves before letting them fall, leaving yellow pigments show through instead of green. Retaining the reabsorbed nutrients and storing them away for the winter is an adaptation to harsh environments where birch has learned to thrive.
Not only are fallen leaves from deciduous trees a splash of welcome vibrant colour in these dark months, but they are also a core part of the seasonal cycling of life and death throughout the year. Songbirds, bees, butterflies, and other wild creatures that depend on the bounty of trees have finished up the annual task of caring for and fledging their next generation, and most wild plants and animals will be preoccupied with conserving energy until springtime.
Many smaller creatures are busy recycling the nutrients contained in fallen leaves. A bustling community of beneficial bacteria, symbiotic mycorrhizal fungi, protozoa, a multitude of different types of mites, millipedes, springtails, beetles, earthworms, and nematodes are breaking down all the spent leaves into smaller components and assimilating nutrients back into the soil. Each of the thousands of soil organisms has a role in processing and modifying the mineral and organic materials, recombining and making them available for plants to use once again, in advance of another not-so-distant season of growth and reproduction.
As well as those breaking down fallen leaves, twigs, branches and seeds, there many animals that spend the winter sheltering among leaf litter. Some moths, for example, lay their eggs among fallen leaves, their larvae insulated there until spring. In turn, chaffinches, robins, wrens, blackbirds, and thrushes pick through the fallen leaves for tasty grubs and sleepy invertebrates hiding out in the piles.
Knowing this, it is hard to understand people’s propensity for leaf blowers and the practices of local authorities that spend a small fortune gathering up leaves from beneath parkland trees. Clearing the sludge of fallen leaves from pavements and pathways is understandable, where those who are not so steady on their feet, or people pushing buggies or using mobility aids might be deterred by the hazards of mushy leaves. Leaves that need to be cleared from pathways can be composted to make leaf mold — an excellent mulch and growing medium for garden plants.
But clearing leaves from open ground beneath trees, whether in a park or a private garden, makes very little sense. I find the noise, the diesel fumes, and the futility of leaf blowers baffling. I wish that parks department staff who drive their mini-tractors around trees in the park to chop and gather up the leaves there could be deployed on more nature-friendly tasks.
Our perception of nature is at the heart of this matter. Swathes of golden leaves gathering in drifts beneath parkland trees are seen by some as messy. People still prefer to impose order and control over natural processes, even in the absence of a logical or scientific basis for doing so. But in the natural world, fallen leaves have a vital role in enriching soil and providing a healthy growing medium for young plants. Leaves help protect the ground from drying out during periods of low rainfall, and the leaf mold that they break down into is naturally cycled back into the ground to nourish next year’s growth of trees and spring flowers. Biodiversity is both directly and indirectly bolstered by winter leaves.
Learning to leave the leaves is an exercise in perception, an opportunity for us to reconsider the origin of our aesthetic preferences and embrace the natural beauty of fallen leaves.
