Based on an article by Sue Parker in Algarve Resident, October 2014. Algarve Resident is the leading English-language newspaper and the source of essential information for Residents and would-be Residents in the Algarve. More information about Algarve Resident...
Pity the pine on poor pasture, where poisons impoverished the earth or clear felling killed the soil-dwelling organisms necessary for seedlings to thrive. Yet in such places conifer plantations are seen as secure long-term investments. If we entrust our savings to a bank laden with toxic assets, can we expect a risk-free return on our investment? In either instance only a substantial injection of capital can avert disaster. Following the economic crash, banks received public money; pines on toxic land need something similar.
In a healthy woodland environment, trees live not in harmony with everything else in the forest but in balance. There is a balance of prey and predator, and interactions between plants, animals, fungi, bacteria and many other microorganisms. We understand little about these complex interrelationships, and we disrupt them at our peril.
Pine saplings in ancient woodland share their habitat with other trees and a diverse understory of smaller plants. Mature pines shed so many needles that seeds rarely germinate in the shaded dry litter beneath them, but within the soil there is a living labyrinth of fungal threads connected via coral-like mycorrhizas that encase the finest rootlets of the tree. These threads of fungus mycelium reach out to soil nutrients well beyond the spread of the pine’s branches; they scavenge the soil, channelling water and trace elements back to the tree’s roots. Mycorrhizas enable a pine tree to grow far more vigorously than it could without these symbiotic servants. In return the tree shares with its fungal partners some of the energy-rich sugars it produces by photosynthesis - a trick which, like us, fungi have never mastered.
Trees are not without enemies, some much older and far more numerous than axes and chainsaws - and just as devastating. Fungal friendship is a tree’s best ally in adversity: with the right kind of support, threats to a tree’s health are more easily shrugged off.
Chenille is the French word for caterpillar; it also means a hairy yarn that looks like a nose-to-tail procession of furry caterpillars. If you see what looks like brown chenille littering the countryside, the chances are that it is indeed a procession of caterpillars. Toxic to touch, these bristly bugs are not to be sniffed at. Their tiny hairs readily become detached and can cause a painful rash if they contact human skin.
The Pine Processionary Caterpillar Thaumetopoea pityocampa feeds on the living needles of pine trees (and certain other conifers). In large numbers these bugs can severely defoliate trees, making them more susceptible to attack by other pests or diseases, and more vulnerable to environmental stress caused by drought. What chance a new pine plantation on poor, sandy and contaminated land?
Cometh the menace, cometh the mushroom. Pisolithus arrhizus, commonly referred to as the Dyeball because historically it was used to dye fabrics, forms mycorrhizas with almost any kind of root. This fungus is frequently used by foresters (and in recent years by gardeners, too) to promote sapling growth - particularly in remediation of degraded or polluted land or in formerly clear-felled forest sites where, having lost their tree partners, other mycorrhizal fungi have died. Before planting out, the sapling’s roots are coated with a paste (known as a mycorrhizal inoculant) containing Pisolithus spores.
Land reclamation using fungi requires knowledge, skill and patience, but once the fungi get to work they can produce amazing results. Unfortunately, foresters in northern climes have not found it easy to introduce Pisolithus fungi into land intended as pine plantations. Inoculation of seedlings helps, but its effects cannot compare with those of naturally-occurring mature fungi.
Pisolithus arrhizus is rare in northern Europe, where it presents little opportunity either for dyeing or for preventing trees from dying. Not so in the Algarve, where this dingy-looking fungus favours dry sandy soil – land of little agricultural value except for growing drought-tolerant trees such as Stone Pines. Dyeball fungi strengthen our pines, which is just as well because our climate also favours one of the pine trees deadliest enemies, the Pine Processionary Moth. Larvae of this Mediterranean moth live in communal tent-like nests in pine trees, and at night their hungry hordes foray forth to prey on the pine tree’s nourishing needles.
Those strange nose-to-tail processions along the ground are mature caterpillars off in search of underground bunkers in which to pupate prior to emerging as moths. Dyeballs and Pine Processionary Moths seem to be well-matched adversaries here in the Algarve - yet another example of how the individual components of an ecosystem are not good or bad but simply necessary for maintaining that all-important balance.
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