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 Ireland's
natve trees are not numerous compared for example to those
of Britan. They have also been subject to thousands of years
of use and abuse by human hands, so much so that this island
has become in more recent centuries almost denuded of tree
life. Though the 20th century has seen a rise in the
percentage of Ireland's area under woodland, most of this
has been in the form of commercial plantations, and of
exotic species such as Sitka Spruce, which originates in
northwestern North America. Despite this, none of our native
species seem to have become extinct, except perhaps Scots
Pine, though even that is a matter of debate. One of the
more interesting survivors is Alder which has, to be honest,
little commercial value and thus little or no chance of
being deliberately planted. Its survival seems to have come
mainly from its liking for poor land types, placing it often
in areas which tend to be last to undergo human
'improvement'.
Some
Like It Anaerobic…
It
is with this liking for sites which remain wet all year
round that we begin. To be specific, alder can thrive in
sites where the anaerobic or near-anaerobic soil conditions
- usually due to waterlogging - which would quickly weaken
and kill off most other tree species. It manages this feat
through a symbiotic relationship with a nitrogen-fixing
bacterium which occupies root nodules. The bacteria provide
the nitrates the tree needs while the tree seems to provide
a degree of physical and chemical protection to the
bacteria.
Not only
does this relationship allow alder to thrive in waterlogged
sites such as the edges of lakes and fens, forming alder
carrs, but also coastal dunes and even abandoned industrial
sites such as quarries. It is, to put it simply, a pioneer
species. While this ability to make use of otherwise
marginal or unusable sites has been taken advantage of
outside Ireland, for example in recovery of opencast mine
and quarry sites in North America and continental Europe, it
seems that Ireland still has no 'job' for the
alder.
This
is surprising, for alder not only makes use of marginal
sites but improves them; the bacteria it supports produce
much more nitrate than the tree itself requires. The result
is that the quality of the soil around the alder is improved
in exactly the way that nitrate fertilisers are designed to.
The real difference is that planting alder inserts the
nitrates into the soil itself rather than splashing them
across the soil surface, it is a slow, organic process
rather than an annual blitz approach which requires purchase
of fertiliser and use of equipment, and the trees themselves
look good and ultimately produce timber.
Oh, You Pretty
Things
So,
what
do alder trees actually look like? What are the
characteristics of their leaves, bark, catkins, or timber?
To start with the general features, alder is a deciduous
broadleaved tree usually with several main stems or trunks
and a broad, somewhat loose shape forming a pyramidal or
conical crown. The bark is initially smooth and grey to
purplish-brown in colour, turning to a darker brown with age
and developing shallow fissures between thick plates. It is
often covered over in lichens and as a result tends to have
a mottled appearance at first glance. The young shoots and
branches, before toughening to the grey or brown colour, are
green and have glands that secrete a sticky resin which
gives the species its Latin name: Alnus
glutinosa.
Getting
down to details, the leaves are broad, appear in May or
sometimes
April,
starting out light green and slightly sticky but soon
turning darker green with a tough glossy texture on top and
remaining a paler light green underneath. During autumn the
leaves turn a very dark green before falling in November and
December. They are, when full-grown, usually 6-10 cm long
and 5-7 cm wide with a form which has been best described as
a 'plump heart shape'. The margins of the leaves have a
ragged toothed form while underneath the veins stand out
almost completely from the leaf surface itself. There are
usually five to seven veins down each side which are covered
on light downy, cream-coloured hairs. As the 'heart shape'
description suggests, alder leaves are often inturned at the
tip, though it is not unusual to see them with a rounded
tip. The leaves are therefore a useful aid to
identification.
The
other main key to spotting alder are its fruit. These are
small, hard, ovoid,
cone-l
ike structures which grow in clusters once the flowers
ripen in April and May. Varying from one to three cm in
length, they are initially green but turn brown and woody in
texture once they have ripened nd shed their seed. They
remain as important identifiers almost all year round as
they remain on the tree through the winter until January and
can regularly be seen still in place beside the following
year's flowers.
The
flowers themselves come in catkins which develop, in the
case of male catkins, during winter and ripen around March
and April. Both male and female catkins appear on the same
tree, with the former 5-10cm and erect prior to release of
pollen and the latter just 0.5 to 1cm in length with a
browny-red stigma. The female catkin remins erect even while
ripening to fruit.
With
these details alone it should be possible to positively
identify an alder tree at any time of the year, but what of
the features which are not so easily seen in the field?
Alder roots come in two types. The upper layer are shallow
and spread widely; it is this root type that carries the
root nodules. The nodules themselves are either perennial or
ephemeral. Perennial nodules live normally for about five or
six years, are around five cm in diameter and located near
the root crown. Ephemeral nodules are much smaller at just
1.5 to 3mm in diamater and found throughout the surface root
system. The other root type is a large tap root which
normally reaches well below the normal water table. While
the surface roots allow alder to prosper in poor soil
conditions, the tap root overcomes occasional drought
situtions, which alder does not at all like, by giving
continuing access to water. The combination of widely spread
surface roots and deep tap roots tend to make alder a quite
stable species able to withstand a severe battering from
stormy weather. The other notable feature of alder is its
timber, which we look at in the next section.
Wooden
It Be Nice[alt text: with apologies to the Beach
Boys!]
So
far we've encountered several features of alder that are
either unique or very unusual among native Irish trees: its
root nodules, the leaf shape, those odd cone-like fruits. To
this list we can add its timber. When cut it is a pale
creamy white or slightly pink in colour, but almost
immediately turns to a vivid orange or yellowy-brown on
contact with the air, a process that is easily visible over
the course of a few minutes. Once dried, the wood loses some
of this striking and attractive colour and turns to a dusty
darkish red or ochre-brown. It is still quite an
attractively toned timber, however.
Timber
is generally looked on as the primary 'product' of a tree
used to justify its inclusion on commercially-oriented
plantings, so why does alder not get used for this
purpose in Ireland? One reason is the long-standing
emphasis on fast-growing non-native species, particularly
Sitka Spruce and to a lesser extent Lodgepole Pine which can
produce saleable timber in thirty to forty years. Another is
a peculiar feature of this most peculiar of Ireland's trees.
Alder wood becomes extremely hard and strong when wet but
soft and light when dry. In the process of wetting and
drying, the wood decays rapidly and therefore it has no real
use in outdoor settings as it has no staying power. Equally
it does not retain strength when dry and is of little use
for indoor structural applications. It is only where wood
capable of taking great stresses when constantly wet that
alder comes into its own. Many of the piles that Venice is
built on are of alder, and at this end of Europe the wood
has been mostly used for bridge and pier piles, for canal
sluice gates, and for making clogs: uses that are
specialised and today almost unneeded.
What
alder wood does have to offer is it colour, its fine grain,
its softness and disinclination to split, all of which make
it ideal for turning and carving. Because it has been little
planted, the wood does not tend to become available very
often in Ireland and its chracteristics are not generally
appreciated by Ireland's burgeoning wood turning hobbyists
and professionals. Beyond that, the only real commercial use
seems to be for the production of wood pulp, a market in
which it must compete with the faster-growing Sitka
Spruce.
Money, Money,
Money
So,
it would seem that alder, for all its unusual features, has
little if anything to recommend it to the commercial
planter. To draw this conclusion would be unfair, however,
as alder provides several advantages even when viewed purely
in commercial terms. Several studies and commercial practice
have proven alder to be a most beneficial nursery tree -
planted with more commercially valuable species to provide
wind protection and soil improvement through leaf litter and
leftover nitrates from the root nodules. It is quite fast
growing and can gain 1.5 to 2 metres per annum during the
first thirty or forty years, after which growth slows
markedly; by this time it has gained over sixty percent of
its full height, and is worth felling at between forty and
sixty years of age, making it actually a strong competitor
in the fast-growing wood pulp producer stakes. While sitka
spruce has been criticised for the effect it has on soil
quality and biodiversity, alder has a very positive effect
on soil quality mainly through the rapid decay of its
nitrate-rich leaf litter. More valuable species - usually
hardwoods - planted with alder tend to exceed expected
growth rates as a result, thereby reducing the timespan from
planting to felling.
Alder
has one other use, though not so much to create revenue as
to preserve existing revenue-producing sites. One of the
main purposes for which alder is planted is to stabilise the
banks of waterways, reducing or stopping erosion which can
cut into farmland or plantation land, or lead to the
destabilisation of field walls and so on. Here at least this
species' liking for wet sites is taken advantage
of.
Tree Steps To
Heaven[alt text: more apologies, this time to Eddie
Cochran]
Puns
aside, alder has three main attractions: its ability to
improve soil quality and as a nursery species, and its
usefulness for carving and turning and in specialist uses in
wet settings both of which we've looked at above. It is here
that I must voice my bias in advance as it will become
evident very shortly - alder is my favourite native Irish
tree species, bar none. Why? Partly from tree-nerd
fascination with its multiple unique and unusual features
discussed earlier, for which I make no apology. There is
more, however. Alder supports many species of lichen, its
fissured bark is an ideal lodging place for mosses (and even
at times for small ferns), and it supports some 141
phytophagous invertebrate species. Yes, that is a lot; a
figure less than half that is more normal for our native
tree species. It therefore plays an important role in
supporting biodiversity among the smaller plant and animal
species, while because of the high tannin content of its
bark it is unplatable to browsers such as deer and as a
result is suited to non-agricultural sites as well as
avoiding the attentions of cattle and sheep on the
farm.
Above
all it is the natural setting of alder that I think makes it
most attractive: the alder carr. A carr is an area which is
waterlogged most or all of the year with a soil pH which is
alkaline to very mildly acidic. Typically this will be
beside a fen, a lake or a river. Such sites, which tend to
be dominated by alder and oak, or alder and willow (or more
rarely alder alone), see Irish nature in action, shaping the
lndscape. Fens are intermediate stages between open water
and either dry land or the bogs that are such a feature of
the Irish landscape; rivers carve the land and redistribute
minerals and rock alike; our lakes are among our best known
natural features for example at Killarney, Lough Neagh,
Lough Derg and elsewhere. Above all Ireland's rain-dominated
climate - who could doubt that this summer? - makes this
island as much a place of water as of earth and stone, and
alder is the tree species that most takes advantage of this,
and gives back as much or more than it takes. When we see
misty-eyed images of romantic or 'Celtic' Ireland it is
almost a given that the scene will include water, in the
form of running or standing water or of mist moving through
the trees. Or all of these. Ireland is a place defined and
shaped by water, and alder, is our finest 'water tree', has,
I think, fair claim to the title of National Tree, a title
currently held by one of our two native oak
species.
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Alder in a typical setting - lining the
banks of a stream, Castlegregory, Co Kerry
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All
arguments and reasoning aside, though, alder is simply a
beautiful tree with an easy, spreading frame, doing no one
harm and benefitting many. The Cinderella of Irish trees,
living on the margins, unloved and shunned (even folklore
considers it an unlucky tree), the alder deserves our
attention, our appreciation, and no little
respect.
 ©
IRQUAS MMII
S MacA has a long-standing interest
in Irish woodlands, and is currently compiling an extensive
text and image database of all native Irish tree species for
IRQUAS. The information in this article has been taken from
the Alder entry in that database
All images © MMII S
MacA except the Ballyseedy, Dingle and
Castlegregory
ones, which are (c) Ray
Monahan, MMII.
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