Traditional knowledge:
The-Tree also offers a page where
you can read the entry for Aspen
from "A Modern Herbal" (Mrs. M. Grieve, ed. Mrs.
C.F.Leyel) published in 1931. Obviously things have moved on
since then, yet this book is still often unsurpassed in its scope
and depth of traditional knowledge. The page pops up in a new
window. Close it to return to the Tree Gallery.
Picture on
the right:
A crane unloads aspen from a full lumber truck at the
Alberta Pacific Forest Industries pulp mill in Alberta,
Canada. Sixty percent of Alberta's lumber, siding and
paper is exported to the United States.
Sacramento Bee/José M. Osorio |
|
Aspen - Boreal
Symbol
by Alan Watson
Featherston
(from Trees for Life, Scotland)
Aspen is a
charismatic species displaying a number of spectacular
characteristics, including prolific propagation from its roots, 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.
Boreal forests are
usually associated with the coniferous trees that predominate in
them. However, if they were to be typified by their most widely
distributed tree, it would be aspen that best characterises the
northern forests.
European aspen (Populus tremula) is one of the most widely
distributed trees in the world, occurring from the Arctic Circle 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, however, 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 ha. With an estimated weight of over 6000 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 8000 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 that 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 (i.e. insects that 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 (Ecataetia 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 (7500 grown by 2002), the protection of
regenerating ramets at existing sites and a research programme, in
co-operation with Edinburgh University, into the ecology of aspen.
The next steps are focused 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 that will provide a viable future for aspen
and all its associated species in the northern Highlands.
***
The above article
has been reproduced from the Spring 2003 Issue of Taiga-News,
the newsletter on Boreal forests. Please see also:
Trees
for life - Aspen Information Resource
|
Note from Anna
(webmother) to page visitors: