Search Results for: fungi

Boreal forests are usually associated with the coniferous trees which predominate in them. However, if they were to be typified by their most widely-distributed tree, then it would be aspen which best characterises these northern forests. European aspen (Populus tremula) is one of the most widely distributed trees in the world, occurring from the Arctic Circle in Scandinavia to North Africa, and from Britain across most of Europe and north Asia to China and Japan, while quaking or trembling aspen (Populus tremuloides) is the tree with the greatest range in North America, stretching from Alaska through all of Canada to Newfoundland and southwards to Virginia, and in the Rocky Mountains as far south as northern Mexico. Between them, these two closely-related aspen species cover virtually the entire boreal biome. Because they are so similar, ‘aspen’ will be used in this article as a generic term for both species, except where it is specified otherwise.

It is not only the range of aspen that is remarkable, though, as it has a number of other unusual characteristics which have been drawing increasing attention from scientists, researchers and conservationists in recent years. As a fast-growing pioneer species, aspen regenerates profusely after disturbance such as fire, and often occurs as dense stands of even-aged trees. This regeneration takes place almost entirely by vegetative reproduction, as aspen rarely propagates from seeds. Instead, new shoots, or ramets, grow from the roots of a parent tree, and these stay connected underground, even once the shoots have matured into trees. All the interconnected trees are a single organism, known as a clone, which exhibits synchronous behaviour – for example, all the component trees will come into leaf at the same time. Because aspen is dioecious, an individual clone is either male or female, and research on Populus tremuloides in the USA has revealed how large individual clones can be. One clone in Utah, nicknamed ‘Pando’ (from the Latin for ‘I spread’), contains over 47,000 individual stems and covers an area of 43 hectares – with an estimated weight of over 6,000 tonnes, this is the world’s largest known organism.

The clonal reproductive strategy of aspen also means that it is extremely long-lived. Although individual stems may only survive for a maximum of 200 years, the clone itself lives for much longer, as new stems grow to replace those which die. Some clones of Populus tremuloides in the USA have been estimated to be at least 8,000 years old, making them possibly the oldest organisms on the planet. It has even been speculated that aspen is ‘theoretically immortal’, and some researchers have suggested that clones may reach an age of a million years or more, based on the resemblance of the leaves on aspen trees today to fossilised ones!

Another interesting feature of aspen’s clonal reproduction method is that the roots of a tree can survive underground after the death of the trunks above ground. The roots will continue to produce new ramets, and they in turn provide enough nutrients through photosynthesis to keep the roots alive until some ramets can grow successfully into new trees. A further feature which helps aspen in its growth is its ability to absorb the sun’s energy through its trunk – the greenish tinge often seen on aspen trunks indicates the presence of chlorophyll there, which carries out the photosynthesis.

In Europe, recent research has highlighted the ecological importance of Populus tremula for a wide range of forest species, from mosses and lichens to fungi and insects. Notable species associated with aspen include the aspen bracket fungus (Phellinus tremulae) which is pathogenic and therefore a significant cause of mortality for the tree; aspen brittle-moss (Orthotrichum gymnostomum); and the dark bordered-beauty moth (Epione vespertaria). There is also a unique community of saproxylic insects (ie insects which depend on dead wood) associated with dead aspen trees, many of which are rare in Europe, and in 1997 researchers studying this community in Scotland discovered a previously-unknown species of fly (Ectaetia christiei). Aspen is also drawing attention in Scotland in the light of the proposed reintroduction of European beavers scheduled for 2003. Aspen is a key winter food for this aquatic rodent, which was extirpated from the UK in the 16th century, as a result of hunting for its fur.

Trees for Life has been working to protect and restore aspen in the Highlands of Scotland since 1991, and we are currently seeking funds to expand this programme significantly, with a full-time project officer dedicated to it for the next 3 years. Our work includes the surveying of existing aspen sites (212 mapped to date), propagation of aspens from root sections (7,500 grown by 2002), the protection of regenerating ramets at existing sites and a research programme, in cooperation with Edinburgh University, into the ecology of aspen. The next steps are focussed on restoring the habitat for the aspen-dependent species of flora and fauna, through expanding and linking up existing aspen stands and creating new ones in appropriate locations. In doing so, we aim to produce and implement an aspen recovery plan which will provide a viable future for aspen and all its associated species in the northern Highlands.

In conclusion, aspen is a charismatic species displaying a number of spectacular characteristics, and it also supports a unique assemblage of other organisms. Occurring throughout the boreal zone, it can be seen as a unifying symbol of the northern forests and can act as a flagship species for their conservation.

Alan Watson Featherstone

(This article featured in the publication Taiga News in 2003)

Return to the Writing page.

A long time ago, before there were any galaxies far, far away, a remarkable transformational event took place. About 13.8 billion years ago, a singularity – a point of infinite density and extreme heat – began expanding, giving birth to the physical parameters of space and time, and the universe came into existence. Energy was transformed into matter, which cooled as it separated out through the expansion process, taking the form of elementary particles. These merged to create atoms, and the first elements – hydrogen and helium – appeared. As matter continued to form, areas of differing density of cosmic gas occurred, and these collapsed due to gravity, giving rise to nuclear fusion and the birth of quasars and then stars.

The first stars were massive in size and relatively short-lived, burning up and exploding as supernovas, with their remains fuelling further cycles of star formation. Over billions of years, gravitational attraction pulled hundreds of billions of stars into galaxies, which spread further and further apart as the universe expanded. About 9 billion years after the universe came into being, a star was formed in one of these 100 billion galaxies, half way out on a spiral arm, adding to the billions of other stars in the galaxy. The collapsing molecular cloud that gave birth to the star also provided the material for a number of planets to coalesce, and in time those formed a solar system, orbiting the star.

The third planet around the star was bombarded by comets and meteors in the millions of years after its formation, which added a greater diversity of elements, water and organic compounds to its composition. About a billion years after the planet’s creation, microbial organic life appeared in its oceans and began to spread. After another almost 3 billion years, multicellular organisms evolved and the diversity and complexity of life increased rapidly, initially in the seas and then on land and in the air. Despite occasional mass extinctions caused by asteroid impacts and large-scale volcanic activity, organic life forms, from bacteria and viruses to massive trees, large dinosaurs and giant whales, colonised all environments and habitats on the planet. They formed a biosphere containing millions of interdependent species, with countless complex ecological relationships, and together helped to maintain environmental factors such as temperature and rainfall at an optimum for life.

About 150 million years ago, the conifers, or cone-bearing plants, which had already been present on the planet for over 100 million years, went through a period of speciation that gave birth to the pine family of trees. After another 100 million years, the pines had diversified into more than 100 different species, including one that would come to be known as Scots pine…

On a spring day in the mountains of an island at the western edge of one of the planet’s main continents, the heat of the sun caused a cone high on the branches of a Scots pine tree to dry and open its scales slightly. A small winged seed less than 1 cm in length was dislodged by a gentle breeze, and began spinning in its perfectly evolved way to drift and sail in the air currents, away from its parent tree. Its spiralling aerial journey took it about 100 metres, and ended in a small clearing on a knoll in the forest. This seed was one of the exceptional few from the thousands produced by the tree that came to rest in favourable conditions.

Soon after landing, a tiny root emerged from the seed, probing into the earth in its quest for nutrients and water. In the knoll’s soil it found the ideal supply of minerals – a gift of the glaciers that had scoured the land for thousands of years – and it grew rapidly, sending its first needles up into the air to harvest the sun’s energy through photosynthesis. The roots branched and spread out, encountering the hyphae of various fungi in the soil. These thread-like filaments wrapped around the young pine’s roots, and a mutually-beneficial exchange of nutrients – carbohydrates and sugars from the tree and minerals from the fungi – began, that would last for the tree’s lifetime. This aided the young pine’s growth, and each year it gained height and lateral spread to its branches, punctuated by the dormancy of winters in between.

Although it initially grew in a conical form, several events in its younger years contributed to what would become a unique, multi-stemmed spreading shape when it was mature. These included the feeding effects of capercaillie, which ate the leader shoots one winter, causing the lateral shoots to take over, and an infestation of sawfly larvae another year, which fed on the needles on one side of the tree, creating a gap in its branches.

By the time 30 years had passed, the pine was a healthy young tree that was flowering each year, and producing seeds of its own, which ripened in the cones two years after being pollinated by the wind. Heather rags lichen had begun to grow on part of the trunk, and blaeberry and cowberry plants had become established under the shade of the tree. Their berries attracted birds and mammals such as the pine marten, which also chased the red squirrels that had started visiting the young pine, to feed on the seeds in its cones.

As the pine grew, it stored a record of the annual climatic variations in the size of the growth rings in its heartwood. Some years were mast ones, in which it produced large quantities of seeds, while in others there were very few at all. As the tree increased in size, insects and other invertebrates such as springtails came to live in the crevices between the plates of its bark, hidden by the lichens on much of its trunk and main branches. However, birds such as the treecreeper and crested tit were expert at searching out the insects, while another common visitor was the Scottish crossbill, which specialised in extracting seeds from the pine cones.

Several species of aphids, some of them tended by wood ants, fed on the twigs of the pine each year. They sucked the sap of the tree and their liquid waste, called honeydew, formed a primary food source for the ants, which climbed the trunk of the pine along chemically-marked trails to find the aphids. The ants also found caterpillars of the pine looper moth, perfectly camouflaged amongst the needles where they fed, and took them back to their nest not far from the base of the tree to feed to their own larvae.  The ants were preyed on by the wood ant spider, which specialised in spinning strands of silk across the crevices on the trunk to ensnare them as they went up or down.

Nourished in part by their symbiotic relationship with the tree, fungi fruited regularly on the forest floor, providing food for a range of organisms, from black slugs to badgers and wild boar. Deer that passed by the pine defecated near the base of its trunk, and their dung became the habitat for other fungi, while dung beetles used the droppings as a food source for their larvae. Dead pine branches, old needles and fallen pine cones all hosted fungi of their own, which broke down and recycled the organic matter contained within them, making the nutrients available for other organisms in the forest.

The decades passed into centuries, and although the pine continued to grow, it was not increasing in height any more – its canopy had become dome-shaped and flattened at the top, instead of the arrowhead shape of its younger years. However, each season new needles replaced those that were two or three years of age, and some lower branches continued to extend as they reached for the light in gaps that had appeared in the canopy above. In good seed years it produced about 3,000 cones annually. Several lichens that favoured old trees had begun to grow on the pine, and a handful of rowan seedlings had sprouted in the forks where large branches separated from the tree’s several main trunks. The rowans had germinated from seeds deposited in the droppings of birds that perched in the canopy above, and grew from nutrients derived from needles and other organic debris that had accumulated in the forks. Most of these young rowans were very small, although occasionally one would grow to three metres or so. Some of those larger ones flowered, with the berries being eaten by birds for dispersal elsewhere, and they also hosted galls that were induced by a mite on their leaves.

For almost 20 years a pair of ospreys had been nesting in the top of the pine’s canopy. The nest had reached a metre in height as more sticks were added to it each year, and sparrows and starlings occasionally built their own nests within it. As a piscivorous raptor, the osprey helped to return nutrients from water to land, and fish scraps that fell out of the nest acted as fertiliser on the forest floor below.

By this time, the wolves that had once made their den near the pine were a distant memory, and it had been many decades since the howling of those apex predators had been heard anywhere in the forest. In their absence, red deer often sheltered for the night near the base of the pine now, and as a result the carpet of blaeberries under the tree was much reduced in height from their grazing, while the creeping lady’s tresses orchids that formerly grew there had vanished from the vicinity. The boar had also not been seen for a long time.

The pine continued its own life journey though, and as it aged it became the host for additional species. Some branches that had been snapped off from the weight of accumulated snow during a particularly cold winter had left wounds where several different fungi grew in the exposed wood. Their fruiting bodies – tough wood-like brackets – occasionally appeared on the pine’s trunk and persisted for several years, as they carried out their function of breaking down the tree’s lignin and cellulose. Some of these fungi were the breeding ground for fungus gnats, and others hosted beetles whose larvae fed inside the brackets. Meanwhile, in the fork where a large branch came out of the main trunk, water had accumulated in the hollow, forming a rot-hole, which became the breeding site for the rare furry pine hoverfly.

Now almost 30 metres tall, the pine had lifted 20 tonnes of organic material from the earth up into the air as it grew its several trunks, many branches and countless needles. It supported 172 species of insects, as well as various plants, lichens and mosses, and was a home to numerous birds and several mammals. Underground, it was connected through its roots and the hyphal network of fungi to the other trees nearby, all of which communicated with each other through the movement of chemical signals, forming a literal ‘Undernet’. As the largest tree in this part of the forest the pine played a vital keystone role in the interconnected community that comprised the woodland ecosystem…

After 379 years, the pine’s life came to a sudden and dramatic end. A group of humans entered the forest carrying large metal saws, and, in a matter of hours, felled the tree and all its neighbours. The fallen trunks were cut up and dragged away by horses, crushing the understorey vegetation and leaving the former forest as a devastated landscape, devoid of almost all its inhabitants, which fled as the destruction took place. Thousands of years of continuous forest cover, and millions of years of co-evolutionary development of many species were terminated in the briefest of moments in the planet’s history.

For a century and a half the area remained barren and desolate, as deer and sheep increased in numbers and ate the surviving vegetation down to the ground. The richness, diversity and vast three dimensional habitat of the former forest was reduced to a near monoculture of grasses, and held at this minimal level, shaved by relentless grazing to closely follow the contours of the land.

Then, one day, another group of humans appeared, carrying spades and young Scots pine seedlings. One of them noticed the stump of the old pine, which had survived relatively unchanged since the tree’s felling, due to the natural preservative effect of the resin in its wood. Sensing it was a good place for a pine to grow, she carefully planted the tiny seedling. Thus began the restoration of the forest community, enabling it to continue its age-old evolutionary journey after what was a very brief interruption in the time scale of the planet and the universe…

Alan Watson Featherstone

(This article featured as the introductory essay in the 2017 edition of the Trees for Life Engagement Diary)

Return to the Writing page.

I have spoken at events all over the world and can deliver inspiring and stimulating talks on a wide range of subjects, including:

The Caledonian Forest

• Restoring the Caledonian Forest
• Glen Affric: a vision for a wild forest     
• The Importance of Aspen in restoring the Caledonian Forest
  
• An Introduction to Plant Galls
• The Ecology of Aphids
• The World of Wood Ants
• Details of many elements of the Caledonian Forest, from fungi and lichens to slime moulds and spiders – I can do a specific presentation on each of these

Rewilding and Ecological Restoration

• Restoring the Earth: The Essential Work of the 21st Century
• Rewilding the world, rewilding ourselves

Other ecosystems

• Araucaria: Ancient Forests of the Andes
• Tropical rainforests – the womb of life
• Mangroves: Tidal forests of the tropics
• Castles of Sand: the sandstone coastline of Moray in Scotland
• Biodiversity of the Findhorn Hinterland area in Moray, Scotland

Other presentations

• Climate change and consciousness
• The Planetary Benefits of a Plant-based Diet
• The power to make a positive difference – how we can each find our personal power to make a meaningful positive contribution in the world
  

All of these are accompanied by my own high quality photographs.

I’m also happy to prepare a custom presentation, if there is a specific subject or theme that is of particular interest.

If you’d like me to give a talk to your group or event, please contact me.