|Beech Trees (Fagus) as Ecosystems
Beech trees are renown for their smooth grey bark (which lovers frequently engrave) and their massive straight
and tall slightly fluted column-like trunks. Indeed, they remind one of the ancient Greek temple columns.
However, despite their massive form, resembling sentries of stone, beech trees are not usually long lived by
tree standards, 200 years being their usual life-spans, though they may live for over a thousand years if
pollarded. One of the main reasons for their shorter lives is that they tend to have shallow roots and coupled
with their massive trunks this makes them prone to windfall, especially when they grow on chalky slopes. It
avoids extremely dry or extremely wet soils, but can grow well on most soils, but is often unable to out-compete
oak, except on lime-rich chalky soils, acidic flint soils and acidic sandy soils and gravels. On most clay soils, oak
out-competes the beech. Many of these chalky escarpments, such as in the Cotswalds in England, have quite
thin soils in any case, so the beech has adapted by having shallow roots that catch the rain before it drains
away from these highly porous soils.
More ancient beech trees often have hollow trunks, as do oaks and yews. Tree holes are an important part of
the ecosystem since they support a variety of life. Rot holes form when bark is damaged, either by wind,
animals or lightning or by pollarding, coppicing or pruning. Often, the tree will form scar tissue (calluses) which
will slowly close over the wound, over many years, preventing infection, but sometimes fungi take root and rot
the dead heartwood. Even if the wound closes over, fungi may have gotten inside and will slowly rot away the
heartwood. This is fine for an old thick tree, since it loses weight and so is more stable in high winds and the
fungi break down the heartwood and leave a nourishing compost inside the hollow trunk, into which trees grow
roots down the inside of their trunks, top absorb and recycle the valuable nutrients released.
Pans are shallow depressions in the tree, lined by unbroken bark, and a result of the natural growth of the tree.
They often form when overcrowding of branches distorts the trunk or its branches, perhaps as they fuse or
graft together. In beech trees they are often found among the buttress roots that flare out at the base of the
trunk. Buttress roots help support a big tree that is growing in shallow soil, and they also serve to direct rain
water flowing down the tree trunk to the absorbing roots - useful when one grows in thin, well-drained soils like
chalk. Indeed the whole beech tree is designed to accumulate rain water, which flows down the fluted trunk,
along the buttresses and straight to the young absorbing roots. Pans are less stable than rot holes, as they
periodically lose water by evaporation much more easily.
Rot holes and pans are found frequently in a number of hardwoods, such as beech, ash, oak and hornbeam,
but are less common in conifers, since conifers produce copious resin which seals wounds very quickly and
prevents their infection, though some conifers may have them, including the silver fir.
Dry tree holes harbour a different ecosystem, and are frequented by centipedes, spiders and overwintering
ladybirds and they make excellent homes for larger animals. Large holes may harbour owls, smaller holes
starlings, blue tits, great tits, nuthatches and pied flycatchers. These birds may modify the hole by lining it with
oak leaves, bark or grass, according to species. Holes high in the tree may be the home of squirrels or bats,
holes lower down may be the homes of mice, stoats and wildcats.
So you see, the old belief that a hollow tree was in ill health, weak and a danger to the public and so in need of
chopping down, is generally wrong on all counts. Eventually, a very old tree may become a liability if prone to
collapse, especially a very old pollard which has reacted to being repeatedly cut back by sprouting more
branches than its trunk can support in old age. Loss of living wood on one side of a hollow tree, such as due to
fire or disease, can also make trees prone to collapse, but generally hollowness does not indicate weakness.
Often removing the odd branch is all that is needed, these ancient trees are vital to the ecosystem since they
support so much biodiversity.
Above: a beech tree bearing bracket fungi. These
fungi may reach almost 2 metres in diameter and
may be soft and fleshy, tough and leathery or hard
and woody, depending upon the species. Some
species only eat the dead heartwood and so benefit
the tree by unlocking nutrients for it to recycle,
prolonging its life, but others are fierce parasites
that infiltrate the conducting wood and eventually kill
the tree. The tree is not helpless, however, for it can
sense the presence of harmful fungi and mobilise
various defences and weapons against them! Even
when these defenses ultimately fail, they may buy
the tree more years to scatter seed. What you see
is the 'fruit' of the fungus, a sporing body that
scatters thousands of spores to the winds. Beneath
this the fungus lives as a threadlike mass of fine
fibres that ramify throughout the wood. This bracket
fungus is Ganoderma applanatum, which is parasitic
on hardwood trees, especially beech.
Above: Bot's drawing of a beech tree (Fagus sylvatica) taken from a photo of a beech tree on Lewesdon Hill,
appearing in The Wildwood (Gareth Lovett Jones and Richard Mabey, Aurum press) - click to enlarge.
Lewesdon Hill in Dorset, England, contains eleven hectares of mixed ancient woodland, part of which is
dominated by beech and surrounds the site of an Iron Age fort. In drawing these trees I try to capture both the
form of the bole and the texture of the bark. This one looks splendid in the colour photograph - sheets of bright
green moss blend with the smooth dark grey bark which appears to have a damp sheen in places and looks
almost metallic. The smaller branches are especially smooth and carry a bright sheen in the light. Notice the
buttress roots that spread out to help support the tree (beech trees tend to have shallow roots as they grow on
thin soils) and also to convey rain water to the roots. In many ways this is reminiscent of the fig tree, whose
smooth grey bark also conducts water to buttress roots, though in the fig these roots can be greatly
exaggerated, often snaking for many metres across the ground. Younger beech tress seem to have much less
buttressing and this feature does seem very variable in mature individuals.
This beech tree, though rather stout still displays a prime characteristic of many modern British beech trees -
the vast, thick and very straight column like trunk. Some have argued that this is more a feature of beech trees
imported from abroad for timber, as many more native beech trees have much more twisted forms typical of the
oak (rather like the one above) but trees that are un-pollarded will grow straighter in any case. These trees
resemble huge living columns of grey limestone and look fit to support a cathedral roof, and to stand in a beech
grove always reminds me of being in a natural cathedral and such groves possess the same stately
atmosphere. Walking between a pair of mature beech trees is like passing between two silent and enormous
sentinels. Finally note the depressions sitting between the roots, these were full of leaves in the photo and no
doubt make good rot-holes in which a variety of microbes and fungi and arthropods (spiders, insects,
centipedes, millipedes and woodlice etc.) thrive.
In England, beechwoods occur in southern England, on the Chilterns and the Thames valley, on the Cotswolds,
around the Weald, alonge the Wye valley and in Wales on the hills above Cardiff and in Clydach valley near
Abergavenny. Beech trees produce large quantities of seeds only every few years, during so-called 'mast years'.
Beech trees have a very leafy canopy with close-set layers of leaves that let little light through. Their shallow
roots drain the top-soil dry, and their slowly rotting leaves form a deep carpet that discourages competing
plants. Thus, there is little undergrowth in beechwoods, except in clearings. In mid-summer beech woods can be
surprisingly dark. The beech mast provides food for many birds, such as finches, bramblings and chaffinches.
The felted beech-scale insect is able to suck sap from the tree's phloem by piercing the characteristicly thin
Above and below: bees were nesting in a dry hollow at the base of this beech tree.
Click here to see what may live inside the wetter hollows of a tree!
Note: The beech in the drawing is a different tree to
the one in the photographs. Observe the
rust-coloured spores which have coated large parts
of the tree!
A study on beech tree growth habit.
Symbiosis means 'living together' and refers specifically to close relationships between different
organisms which may benefit both (mutualism) or one partner without harming the other
(commensalism) or one partner to the detriment of the other (parasitism). We have already seen
examples of this above. More intricate relationships occur, however.
The Ghost Orchid (Epipogium aphyllum) and the Bird's-Nest Orchid (Neottia nidus-avis) lack
chlorophyll and do not photosynthesise (at least not to any appreciable degree). Both feed entirely
on soil fungi (they are mycotrophic) and prefer beech trees (Ghost orchid will also grow beneath oak
trees) in particular, suggesting that they feed upon fungi that form symbioses with the tree as
ectomycorrhizae (see mycorrhiza: fungi associated with the tree roots which provide the tree with
minerals from the soil in return for carbohydrates manufactured by the tree by photosynthesis - an
example of mutualistic symbiosis). In this way these orchids are secondarily parasitic on the trees
themselves. Lacking chlorophyll and finding alternative nourishment is particularly useful when
growing in the deep shade of beech trees.