This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
In all types of vegetation there is an intimate connection between 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 protection. It is in the woods that those animals a called vermin by the game-keeper are especially at home.
It is probable that a certain amount of dispersal 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.
The antiquity of the woods and forests in this country is undoubted, but as yet little definite information is available, from the absence of any clear evidence earlier than the deposits that just precede the Ice Age or the Cromer Forest bed. In addition to the numerous other plants, some, as Trapa natans (Water Chestnut), denoting a warmer climate, there were remains of the following frees: Elm, Oak, Beech, Hazel (rare), Alder, White Birch, and three species of Willow. These indicate the same type of woodland 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, Platanus, are found, indicating as warm a climate.
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 indicate that they are Preglacial.
The influence of altitude upon plants varies in degree. The tree type is especially affected by altitude, and in a corresponding 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 the 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 between 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 65 degrees and 75 degrees. The everlasting snow lies north of this, and beyond the snowline only mosses and lichens will flourish as a whole.
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.