A. R. (Arthur Reginald) Horwood.

A new British flora : British wild flowers in their natural haunts (Volume 3) online

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rapes, Toothwort, Bird's-nest Orchis, &c., that
live on the roots of trees, is another feature of
woods, and their dark character has perhaps
been here responsible for the differentiation o(
such groups.

Moisture of the Woods. Woods are the
principal agents in condensing the moisture
of the atmosphere in the bulk, and for this
reason their preservation is an actual neces-
sity. It is only since the greater part of the
wooded areas have been disafforested that the
climate of this country has become so much

One feature of woodland life that should be
noticed is the extraordinary wealth of the
lower plants or Cryptogams. These depend
upon water for the effective fertilization of the
ovum by the spermatozoid, which must meet
it in water. Hence the habitat they require
must be moist, and a woodland is an ideal
type of vegetation for this purpose.

Here, too, is the home of those higher
plants that are unable to exist in the open
glare of the sun and need moist conditions.
Another effect of the moisture of the woods
that must not be overlooked is the luxuriance
of the vegetative organs.

Coldness of the Woods. A condition that
regulates the distribution of plants is the

2 4


amount of heat available. This is little liable
to vary in open meadows and pastures within
several degrees of latitude. But in a wood
the temperature is considerably lower than
that of the surrounding' open country. Heat
and colour go together; hence it may be that
there is an absence of colour in the wood-

Moreover, each plant requires a definite
amount of heat before it will commence to
flower and later ripen seed. If one excepts
the bulbous plants that flower before the trees
are in leaf, and the trees themselves, the
generality of the woodland plants flower late,
in spite of their usually perennial character.

Temperature has also an effect upon the
general conditions of plant-life, and this
explains the absence of life (lower zones) in
a cold dry wood. The absence of moisture
with cold prevents the proper balancing of
conditions for assimilation ; respiration, tran-
spiration, and osmosis are slow.

Protection of the Woods. The denseness,
darkness, and coldness of woods generally
are retarding factors which may be well
compensated by another feature, and that
is their protection. The association of the
trees in a close formation, not only serves
as a protection in itself to the tree unit, but
it has a corresponding conservative effect
upon the rest of the flora of a wood. The
scrub layer and the ground flora are effectively
protected. Wind erosion is almost minimized
by the covering tree zone. The effect of frost
is also greatly reduced.

Trees further protect the soil from being
worn away by the denuding effect of rain or
hail. Where trees drip there is some local
erosion, but this is restricted in its work, and
the soil is not carried far away.

In a wood, also, the effect of a drought is
far less marked, though a clayey soil suffers
more severely in this respect. The scorching
heat of the sun in ordinary weather is again
moderated by the tree zone. Hence the pro-
tective effect of trees is, on the whole, decidedly
advantageous to woodland plants.

Wet and Dry Woods. Whilst the character
of the soil determines the type of woodland
there being live main types: pedunculate Oak,
M-^ile Oak, Birch, Beech, Ash, with com-
binationsthe water content of the soil has
a good deal to do with tree dispersal, and also
affects the scrub and ground flora.

Thus a wet clay is characterized by the
pedunculate Oak, whilst a dry, sandy soil is
occupied by the sessile Oak. The extent of
the effect of soil may be seen in the same
tract of wood, for on the siliceous slates of the
C'harnwood Forest region, which give rise to

a wet clay, Birch, which is a wet -soil type of
tree, is found, with Oak encircling it where
those rocks are in turn surrounded by the
drier, more sandy red marl.

The ground flora in a wet and dry wood
will differ correspondingly, such plants as
Bugle and Tussock Grass indicating a wet
wood. The extreme type of wet wood is
afforded by the Alder-Willow association,
which is characteristic of marshy or aquatic
plant formations.

Effect of Tree- felling on Rainfall. When
trees are felled, not only is the shade which
they afford at once lost and sunlight able
therefore to penetrate near to the surface,
but the removal of the trunk and branches,
with the numerous leaves, causes the moisture
which they accumulate to fall directly upon
the earth. Here, on a porous surface, the
water percolates and finds its way down to a
subterranean reservoir. Water accumulated
upon a clayey soil soon evaporates in the
open. Radiation is more rapid over a tree-
less area than in a forest area.

The retention of the moisture by the indi-
vidual trees may be, moreover, considered
apart from the aggregate amount of moisture
present in a forest, regarded as a unit in itself.
The association of numbers of trees causes
the atmosphere itself to remain charged with
moisture, and evaporation is consequently
slow. The preservation of moisture at the
surface by a tree layer, and its retention by the
lower strata of plants, are also features of a
woodland area that must be considered in
estimating the value of forests as water

The retention of dew is also an important

Effect of Woodlands upon Soil. Perhaps the
most outstanding feature of a wood or forest
is the part it plays in the accumulation of
organic matter, plant and animal, upon the
surface, which in course of time becomes a
valuable asset to the soil. This matter is
known as humus, and it is to the presence
of this in the soil that the woodland plants
owe their distribution to a great extent.
Whilst many plants that grow in a wood are
able to exist in the open upon other soils, or
those not rich (or even deficient) in humus,
some that grow in the open do not care for
humus. It is suggested that simple experi-
ments be made in growing plants in soil with
and without humus, and noting the effect.

Since the original vegetation was woodland,
it should be expected that the removal of this
from a large area by disafforestation has been
the cause of differentiation into meadow and
pasture, heath, and other types of vegetation



derived from woodland vegetation. It is pro-
bable that moisture and altered light-and-heat
conditions have played as important a part as
that of the absence of humus.

Woodlands also affect the water content and
physical character of the soil, preventing it
from becoming pulverized. All these points
should be carefully explained.

Causes of Cutting Down of Woodlands.
When the original area of woodland is com-
pared with its extent to-day (there are fourteen
national forests of insignificant total acreage)
it is obvious that the cause of the reduction in
forests has been multiple.

Primarily there was the need for wood for
fuel. In Saxon or Norman times, or later
even, only the churches, castles, &c., were
built of stone, and wood was used for dwell-
ings. From Alfred's day, also, till the time
of Nelson there was a constant demand upon
the forests for ship-building. Incidentally,
hunting and similar causes were responsible
for the clearing, of forests; and the need for
cultivating, especially from the Conqueror's
time, has finished the work of depletion.

Woodlands the Origin of many Fruit Trees,
&c. The origin of many of the fruit trees
of this country is wrapt in obscurity. It is
certain, however, that some, such as the
Cherry, were introduced from the south of
Europe, and the apples, plums, pears, peaches,
&c., that have been cultivated and improved
in orchards and kitchen gardens for centuries
have lost their original characters.

De Candolle has traced the history of many
of them by the comparative method, and if we
regard the quasi-wild or truly wild species,
such as the Crab, Wild Plum, Wild Pear, it
will be found that they are largely reversions
to a wild stock from cultivated plants. None
the less, there are a number of the smaller
fruit trees, such as the Sloe or Bullace, Rasp-
berry, Hazel, that certainly originated in our
woodlands, whilst the Currant and Goose-
berry, and the Plum are found in a wild state

The Value of Woodlands. Reference is made
elsewhere to some of the causes of the dis-
appearance of woodlands, which is one proof of
their value, economically considered. Another
reason for their preservation, to which allusion
has also been made, is their effect in preserving

A very prominent feature of woodlands also
is their beauty, and it is to be hoped that the
efforts to preserve beauty spots which has been
so well begun by the National Trust will be
fostered and extended in the future. The
afforestation of the whole country on scientific
lines is urgently required. The rising genera-

tion may lend their support by taking part in
Arbor Day, or the planting of trees on festive

Natural and Artificial Woodlands. It is very
important that a careful distinction should be
drawn between woods that are natural and
those that are artificial. Natural woodlands
upon clay and loam commonly consist of the
pedunculate Oak, while on sandy soil sessile
Oak prevails. This may occur also on siliceous
soils, which are also characterized by Birch
scrub. Heathy tracts also consist of Birch in
some areas, and on gravelly soils of the Pine.
Ash is the principal tree in limestone areas,
and also occurs on chalk. But the chief tree
on chalk and oolite is the Beech.

Where such conditions occur, the woodlands
may be regarded as natural.

All these trees are likewise found in a planted
state, but an examination of the ground flora
and scrub will reveal this as a rule. The
coniferous woods and plantations, except Pine
and Yew (the latter found on the chalk), are
artificial also. The distinguishing of the
characters of a wood will be an excellent piece
of work if skilfully directed.

The Home of the Lower Plants. Woodlands
are the particular resort of a variety of Crypto-
gams. The whole group of Fungi are espe-
cially fond of moisture, and as they can grow
in the shade they flourish in the woodlands.
They are to be found on the trunks of the
trees, to which they do a great deal of harm.
Old stumps are especially the habitat of many
fungi that flourish upon the putrescent wood.
Upon the sticks or dead (or living) under-
growth a large number of the microscopic
forms are to be found. Upon the grounds the
agarics and peziziform fungi grow, and the
beautiful earth-stars.

Lichens grow well in woodlands upon the
trunks, and where the woods are rocky on the
rocks. They need a clear atmosphere and
moisture. Here, too, those delicate, moisture-
loving plants known as Hepatics or Liverworts
are particularly at home. They grow upon
the base of the tree-trunks, amongst the under-
growth, on rocks, and upon the bare ground,
in open clearings and rides. The same re-
marks apply to Mosses. Horsetails and Ferns
are especially fond of moist habitats that are
to be found in woods.

Animal Life of the Wood. In all types of
vegetation there is an intimate connection be-
tween the plant and the animal life, but the
woodlands are the especial resort of many
types of animal life. The density of the woods
compared with the openness of the meadow or
pasture affords an additional means of protec-
tion. It is in the woods that those animals

46 a



called vermin by the game-keeper are especially
at home.

It is probable that a certain amount of dis-
persal of plants is effected by these animals,
the pads of the fox being often filled with clay
in which seeds maybe carried for long distances.
Upon the spines of the hedgehog large fruits
such as crabs may be transfixed, and burs may
stick to them.

Birds, especially in woodlands, act as carriers
of seeds from one place to another. The hard
seeds of fruits may be dropped after the soft
exterior has been eaten. In the same way
squirrels may disperse nuts, storing them and
forgetting them. Woodpeckers and titmice
are factors in a woodland to be considered,
because they aid the destruction in time of the
trunks, which they riddle with holes and expose
to air and rain, causing them to rot. The
innumerable interactions between plants and
animals are full of material for study.

Ancient Woodlands. The antiquity of the
woods and forests in this country is undoubted,
but as yet little definite information is avail-
able, from the absence of any clear evidence
earlier than the deposits that just precede the
Ice Age or the Cromer Forest bed. In addi-
tion to the numerous other plants, some, as
Trapa natans (Water Chestnut), denoting a
warmer climate, there were remains of the fol-
lowing frees: Elm, Oak, Beech, Hazel (rare),
Alder, White Birch, and three species of Wil-
low. These indicate the same type of wood-
land that is met with in this country to-day.
If one were to examine the flora of the earlier
Oligocene or Eocene one would find that the
climate was still warmer, and in the Bovey
Tracey beds the giant or mammoth tree type
of California, Cinnamons, Evergreen Oak,
Fig, Laurel, and in the Bournemouth beds of
the same age, Eucalyptus, Araucaria, Sequoia,
riatanns, are found, indicating as warm a

Between these beds and the Cromer Forest
bed we have no very clear connection, but Oak,
Elm, and Poplar of allied species occur. The
submerged forests around the coast belong to
a later period than the Cromer Forest bed, and
contain the present-day trees.

The Peat beds of Scotland have two forest
beds, the lower containing largely White Birch,
whilst the upper contains Pine, and these lie
over Glacial beds. In Norway there is a third
forest bed of Spruce. Thus, whilst we are
largely foiled by the influence of the Ice Age
in determining the area and age of ancient
woodlands, there are certain data which indi-
cate that they are Preglacial.

Tree Zones. The influence of altitude upon
plants varies in degree. The tree type is

especially affected by altitude, and in a corre-
sponding manner by latitude or climate. In
the tropics the belts as the loftier mountains
are ascended correspond with those which are
observed as one travels from the Equator to
tlie poles. Thus at the Equator there are wet
jungles of palms and bananas, followed by
Savannahs, 10 degrees north to 20 degrees.
Between 20 degrees and 30 degrees the main
deserts are met with. Then come the Steppes
and woods, made up of evergreen trees be-
tween 30 degrees and 45 degrees.

The large deciduous forests range between
45 degrees and 55 degrees, and it is in this
zone mainly, the cold temperature zone, that
the British Isles are included. Northward
from 55 degrees to 65 degrees come the Pine
forests of Norway and countries of the same
latitudes, as Canada in North America. The
frozen Tundras, all but treeless, come between
5 degrees and 75 degrees. The everlasting
snow lies north of this, and beyond the snow-
line only mosses and lichens will flourish as a

In ascending a tropical mountain there are
from sea-level to 4000 ft. tropical forests, from
this point to 8000 ft. sub-tropical forests, and
upward to 9500 ft. temperate deciduous forests.
A zone of conifers comes next between 9500
and 11,500, alpine shrubs between 11,500 and
13,300, alpine herbs up to the snowline, and
above it mosses and lichens.

Woodland Habitats and Associations.- Habi-
tats in general may be wet or dry, rocky or
not, upland or lowland. The wettest habitats
(especially E. Anglia) are afforded by the
Alder-Willow associations, where the scrub and
ground flora is made up of such plants as
Guelder Rose, Currant, Gooseberry, Meadow-
sweet, Yellow Flag, Reed, &c., Bitter-cress,
Kingcup, Figwort, Great Hairy Willow-herb,
Tussock Grass, &c. The tree types are scat-
tered, and the ground itself is open, allowing
such large herbaceous plants to thrive.

On clays and loams, sandy and siliceous
soils, the trees are Oak, pedunculate and
sessile, Birch, with other trees. The scrub
and ground flora are very variable. The
woodland may be close or open. On clays and
loams the ground flora is largely gregarious,
e.g. Bluebell, Bracken. On sandy soils more
often there is a good deal of bare rock surface
with deep soil elsewhere, giving a variety of
habitats. The same applies to a Birch wood.
Here also there are wide associations of grasses,
such as Heath Hair Grass, Matweed, &c., and
the heaths also form wide gregarious associa-
tions. These habitats are largely upland,
whilst the oak-woods are mainly lowland, the
sessile Oak not growing above 1500 ft. as a



rule. The pedunculate Oak has wet-soil con-
ditions, the sessile being adapted to dry-soil

The woodlands on calcareous soils (Carboni-
ferous Limestone, Chalk, Oolite) afford in the
case of Ash woods varied habitats or types of
association, the plants being often gregarious,
as in the case of Dog's Mercury and Arch-
angel. They rise to some altitude. On marls
the Ash-Oak woods are variable in the types
of association. In the case of Beech woods
the habitat is upland very largely, and dry,
there being a scanty scrub and ground flora.

The Habit of Woodland Plants. The wet
or dry character of the woodland determines
largely the nature of the habit. Thus in
Alder- Willow woodland associations the plants,
such as Rushes, Grasses, and Sedges, with the
grass habit are largely tufted or ca^spitose.
Even the rosette types are frequently tufted,
as in the case of Marsh Marigold and Bitter-
cress. The procumbent or trailing habit is
also characteristic. These habits are transi-
tional to the submerged and floating habits of
purely aquatic plants, which are intimately
associated with fen formations.

In the normal dry woodlands the tree habit
is the dominant one. The scrub is analogous
to that of the tree habit, but is always influenced
by the tree zone. The stems and branches are
less strong, and thick, the leaves are small,
and often several times pinnate. Spines are
more numerous, and the flowers are more
suited in most cases to pollination by insects.

The ground flora is variable in habit. There
is the climbing habit of the Ivy or the Honey-
suckle, &c. , adapted to reliance upon the sup-
port of trees or scrub. The bulbous or tuber-
ous habit is especially typical, e.g. Bluebell,
Orchids. A large number of plants are pros-
trate or procumbent, or provided with creeping
underground stems, as Strawberry, Wood

Flowering Seasons in the Woods. The shade
conditions in a woodland have a marked effect
upon the periods of flowering. There are thus,
apart from the general seasons of flowering in
May, June, and July, when the sunlight is fuller
and stronger, early-flowering plants and late-
flowering plants. Those plants that flower
early, seize the opportunity of doing so before
the leaves of the trees appear, or at least before
the foliage is fully developed. The growth
season of bulbous plants is short, and they
flower early in consequence.

The earlier plants to bloom in the woods are
the Winter Aconite, Snowdrop, Lesser Celan-
dine, Spurge Laurel, &c.

The trees themselves largely flower before
the leaves, owing to their adaptation for wind

pollination, as the pollen would be less likely
to be dispersed when the leaves are fully ex-
panded. The Willows depend partly on the
wind, partly on insects, and so flower early.

The scrub is largely influenced by the same
factors also. The Hazel relies on wind pol-
lination, and is the earliest to flower. The
Blackthorn also flowers before the leaves ap-
pear, since it is more conspicuous then than
later. The Grasses, in spite of the fact that
they are chiefly wind-pollinated, flower, as a
rule, rather late in the woods.

The late-flowering groups are chiefly the
Hawkweeds, rosette plants whose scapes are
long. The Brambles, owing to the great out-
put of stems and branches, also flower late.
The latest plant to flower of all plants is a
woodland plant, the Ivy.

Height of Woodland Plants. A particular
feature of the woodlands is the height of the
dominant type, the trees. It is largely owing
to their height, which is regulated to a con-
siderable extent by the wind and soil, that they
are the dominant type of plant, next to Grasses,
in the world flora itself.

This character enables them to outstrip other
plants in the struggle for sunlight and air.
They are thereby enabled to counteract the
influence of all other classes of plants, which
growing below do not affect them in these
respects. These facts require special emphasis.

The lower strata of plants are directly in-
fluenced as regards height (and other factors
equally) by the dominance of the tree zone.
This is seen in its greatest extreme in a Beech
wood, where the ground flora is often nil.

The scrub, e.g. Blackthorn, Elder, &c.,
suffers less than the ground flora, and this is
seen in clearings, where the scrub may rival
the younger trees in height, &c. Like the
tree zone, the scrub normally has a definite
upper limit. The undershrubs, that are in
turn dominated by the scrub or large shrubs
and smaller trees, also approximate in height
to a certain standard.

The ground flora is of course influenced
most by being covered by two strata above.
Consequently, as a rule, it also approximates
to a certain general height, e.g. Grasses, and
others with the grass habit. Orchids and
bulbous plants come next. Then there are
the trailers, such as the Barren Strawberry;
and lastly the mosses and hepatics.

Life Duration of Woodland Plants. As a rule,
shade plants are perennial, whilst the annuals
and the biennials are to be found amongst the
sun plants. A feature of the woods, dominated
by the tree type as they are, is the deciduous
character of the vegetation, at least in the cold
temperate zone. This is an adaptation to

46 a-

2 4 4


climatic conditions necessitated by the relation
of the cold winter period to that of summer.
No large tree in this country, except the Pine
and Yew, is evergreen. The Holly and the
Box are lesser trees which have adopted this

The scrub also consists almost entirely of
deciduous shrubs or trees. The hardy ligneous |
climbers are also deciduous, as the Honey-
suckle. The Ivy, however, is an evergreen.
A large part of the ground flora is made up
of deciduous herbaceous perennials. Unless
the woodland plants were as a whole perennial,
it is difficult to understand how as annuals
they could in the short growing period manage
to germinate, and develop stems, leaves,
flowers, and fruit ; for the light is so feeble
compared with that of the open pasture that
assimilation would not keep pace with the
demands of the plant for rapid growth. Hence
also the prevalence of vegetative modes of

Pollination of Woodland Plants. Apart from
grasses, docks, and plantains, &c., which are
largely pollinated by the wind, the bulk of the
meadow and pasture plants are pollinated by

The case is different in the woods. If one
excludes beetles, which are very partial in
their choice of plants for pollination, and cer-
tain types of Hymenoptera, the group of
flower-seeking insects is not so conspicuous in
close woods as in the open. True Lepidoptera,
especially moths, are frequent in woodlands,
but the majority are not bearers of pollen.
The Honeysuckle is a familiar example of the
dependence of long-tubed plants upon crepus-
cular moths with a long proboscis, such as the
Humming-bird Hawk Moth.

The main feature of woodland plants is the
prevalence of wind pollination in the case of
the trees. The Grasses are also pollinated by
the same agency. Another feature is the oc-
currence of cleistogamy, as illustrated by the
Violet and the Wood-sorrel. A considerable
proportion are monoecious plants adapted to
self-pollination, whereas the dioecious species
are in the majority in open habitats.

The Dispersal of Seeds in Woods. In a wood
the struggle for existence is so great, owing to
the abnormal conditions of light and heat and
the density of the vegetation, that plants must
necessarily adopt special means of dispersal to
a distance. The trees themselves have set the
example by being practically all dispersed by
tin- wind. In this, again, they have a pull

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Online LibraryA. R. (Arthur Reginald) HorwoodA new British flora : British wild flowers in their natural haunts (Volume 3) → online text (page 21 of 23)