TREES are not a separate botanical class, but a form of growth found in many different families of plants, which may include various forms. For instance, most conifers and most members of the oak, beech and poplar families are trees, though some are low shrubs; whereas the rose and pea families include a variety of herbs and shrubs and trees.

Trees occur sporadically throughout the two Classes of Flowering Plants – Gymnosperms and Angiosperms.

Gymnosperms [naked seed] include the Ginkgo, cycads, gnetophytes and the conifers, which are nearly all trees and bear cones rather than flowers, although the *gnetophytes can bear both flowers and cones. Conifers are typically evergreen, retaining their leaves all year round each year although the Larch [genus Larix, in the family Pinaceae] is an exception to that rule being deciduous and shedding its leaves during winter.

Angiosperms [hidden seed], also known as broadleaved trees, which are typically deciduous, include all our familiar garden plants and wild flowers, bulbs, palms, sedges, rushes, reeds and grasses.

Some of the Angiosperm families like Beech, Elm and Lime are nearly all trees.

In others like Pea and Rose, trees are in a minority; although the Rose family contains many of our herbaceous fruits such as; strawberries, in a genus of their own known as Fragaria, raspberries and blackberries [Rubus] and their hybrid cousins loganberries.

The Rose family also includes aside from the Hawthorn and the Sorbus varieties of Rowan, Whitebeam and Wild Service Tree, most of our fruit trees such as Apple [Malus], Pear [Pyrus], Plum, Cherry, Peach, Apricot and Almond [Prunus].

The Foxglove family has only one genus of tree, Paulownia.

The Primrose Family has none.

The Angiosperms are further subdivided into the monocots and dicots.

The monocots have leaves with veins that run parallel from stem to tip, while the dicots veins are netted or webbed across the whole surface from the leaf centre.

The Monocots include all the grasses, grains, palms, pineapple and other bromeliads, bananas, lilies, irises and orchids.

The Dicots comprise amongst many others, the rose, pea, buttercup, cabbage and daisy families.

Where a tree or shrub differs from other forms of growth is in making wood. A bud growing on any plant leaves behind a shoot of pith cells, which conduct sap. In non-woody plants that is all and the shoot dies back at the end of the season.

But in woody plants, the shoots, stems and roots are all enclosed by a single layer of cells called the cambium, which spend the growing season actively dividing and making new cells, both inside and out. This thickens and hardens the stem, which can then survive the winter and continue its growth the next season.

Cambial growth such as this builds up inner and outer layers which are used to conduct food manufactured by photosynthesis ** using Chlorophyll *** in the leaves down to the roots, while conducting sap up from the roots containing water and liquid nutrients extracted from the soil.

As these inner cells build in girth, the outer layers are later filled with lignin, a biopolymer [exceeded in botanical abundance only by cellulose] strengthening wood cells, and essential to the tree for resisting the stresses of the wind and bearing the weight of the branches.

The cell walls of plant vascular systems [circulatory vessels], being composed of cellulose are highly hydrophilic and thus permeable to water, whereas lignin is more hydrophobic. Therefore, having opposite physical characteristics and affinities to cellulose, the lignin outer layer makes it possible for the plant’s vascular tissue to conduct water efficiently.

The vascular systems consist of two structures, the xylem and the phloem.

The xylem helps to transport water and minerals from the root to the other parts of the plant and the phloem transports food that is made in the leaves to the storage organs. These vascular systems are arranged in a circular manner around the edge of the stem.

Another form of protection against the forces of nature that the trees have is, messenger chemicals, sent out to warn neighbouring trees when they are invaded by parasitic insects, which they have then encased in an enclosed compartment called a gall, thus isolating the invader.

Trees have various ways of protecting themselves, but there is a limit to their abilities when it comes to an army of voracious caterpillars or a swarm of ravaging locusts, and being rooted to the spot and immobile, they are powerless against the axes and chainsaws, the dangers, devices and pollutants of mankind, or indeed, the rampant forces of nature.

It is usually only the trees considered useful for their fruits and spices or some other commodity that are spared – unless of course, that commodity happens to be their timber. In the case of timber-bearing trees, they are often harvested and protected in manmade plantations and come to dominate larger areas than they sometimes would, like wheat, which has come to dominate nearly half the fertile land area of this world. This artificial arrangement is not beneficial to the Earth’s ecological balance. These plantations often come to take over the areas inhabited by a wide variety of naturally occurring tree species.

Adversely, trees like Sycamores and Limes become like weeds by producing a sticky resin for protection against parasites and are therefore also less beneficial to their surroundings, as they tend to proliferate by this method, outcompeting rival contenders and thereby taking over the space needed for more environmentally useful Broad-leaved species to flourish.

Most deciduous trees are generally more ecologically viable and help to enrich the soil. Coniferous trees however, tend to impoverish it, shedding layer upon layer of hard waxy needles in a thick impenetrable carpet upon the forest floor. This provides no immediate nourishment for wildlife and not much purchase for microbial organisms to work with, taking decades to break down into the soil.

Wherever there is a deciduous or broadleaf forest, there will be an environment that is ecologically richer, more varied and more productive.

Together with the carpets of plankton floating upon the ocean surfaces, trees provide most of the oxygen in this world, absorbing most of the excess greenhouse gases ** ** [carbon dioxide, methane] produced by human activity in the process – yet more and more forests all over the world are cleared for logging, lumber, food-cultivation, industry, and for housing as the human population increases at an ever-alarming rate, usually at the expense of other species.

Thus humans could be viewed as a rampant infestation grown to plague proportions endangering and diminishing the Earth’s ecological balance in the process.

In simulations of the future ocean, an international group of scientists measured an increased CO2 uptake of up to 39%. The unexpected positive effect for the global climate system harbours at the same time considerable risks for the oceans and their ecosystems.

The forests will be needed even more to rectify this ecological imbalance. Lets hope humanity does not become a plague devouring them.

Without the trees, we would be lost. We just could not survive.

The featured image is of untouched native woodland, its floor bathed in rays of sunlight slanting down through the gaps far above. It is part of a theme that I’ve used at least several times. This particular view and rendering of the subject is the original template, and with variations, was based on a photograph in a Natural History or British Countryside book.

It was painted in water colours in 1983 and the theme has been used in several other illustrations on this website, including ‘At Woodland’s Heart’ and ‘Warden’s Wood’, both rendered in Oil Pastels in 1986.

All three illustrations can be located under Landscape in the Art section of the Pulldown Menu.

In conclusion I have set a slideshow comprised of 8 versions of the same image. They are listed as Follows:

Sundrenched Woodland
Emerald Woodland
Woodland Moonlight
Moonlit Woodland
Lavender Moonglow
Woodland Sunset
Sundrenched Gold
Lemon Sunshine

Dave Draper July 2014

Click on each image in the slideshow to enlarge and view.
Place and run cursor over image to reveal centrally-placed arrows to move back & forth manually through slideshow. Alternatively, click on (play slideshow) in the description beneath to automatically scan through the images.

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The information for parts of the dendrological *** *** content in this article comes from various online and literary sources, which I have gathered, assembled, and supplemented with additional data and comments. The main data on woodlands and trees and their structure and functioning systems comes from textual content by Allan Mitchell in The Trees of Britain and Northern Europe published by William Collins Sons & Co Ltd in 1978 and 1982.

Details concerning vascular systems and their hydrophilic properties with xylem and phloem come from other online sources.

The data for messenger chemicals between individual trees, and the oxygen/carbon-dioxide recycling properties of ocean plankton and the world’s natural forests comes from natural history television programmes presented by Sir David Attenborough.

Dave Draper May 2015

INFORMATION for all above text shown in Bold and marked with an asterisk or asterisks is contained in the notes section below:

VNotes