Although Towerhouse Wood is designated as semi-natural ancient woodland, several alien tree species occur, particularly to the north of the main public footpath (W9) that traverses the wood from East to West. Some of these have been deliberately planted, while others are probably escapes from local gardens. The average age of these alien trees appears to be about 50 years.
Adjacent to the notice board about half way along the main footpath is a cluster of Gymnosperms, notable among which is a Douglas Fir Pseudotsuga menziesii. This tree was first discovered by ArchiboldMenzies in 1793 on the West Coast of the United States. It was introduced to Britain by David Douglas in 1827. As his diary subsequently revealed, Douglas suffered great hardship in his plant collecting journeys. Eventually, these led to his untimely death at the age of 35. Since wild cattle introduced by Captain Vancouver into Hawaii, were becoming too numerous, pits were dug to trap these animals. Douglas came across one of these pits and fell in – unfortunately the pit also contained one of the animals and he was killed. Douglas introduced at least 200 plants to the UK, including Mahonia, Limnanthes, Escholtzia, Clarkia, Symphoricarpos, Picea sitchensis andAcer macrophyllum. Douglas fir is the tallest tree in the UK, growing to 61 metres in Dunkeld. It was used for ships masts in the age of sail, and is now widely grown for the construction industry.
Near to the Douglas Fir is a Monterey Cypress Cupressus macrocarpa, one of the parents of the now infamous Cupressus x leylandii, the other parent being the NootkaCypressChamaecyparis nootkatensis. C.J.Leyland was the owner of Haggerston Hall where the hybrid was first raised.
Further back into the Wood are thickets of Rhododendron ponticum from Spain, Cherry Laurel Prunus laurocerasus from the Balkans, Portuguese Laurel Prunus lusitanica, Box Honeysuckle Lonicera nitida from China, and Mock Orange Philadelphus coronarius from SE Europe. These plants are aggressive, suppressing the native flora, and are being progressively eliminated from the woodland as part of the management plan. The Rhododendron is particularly undesirable as virtually no animal eats it, it produces toxic honey and it is allelopathic to other plants.
Further along the footpath is a European Larch Larix decidua, introduced into the UK in 1610. This is now widely used for fencing panels (larch lap), and it is grown as a nursery in raising seedlings of less hardy trees. The wood is very resistant to fire. Close by, is a young Norway Spruce, better known as the ‘Christmas Tree’ Picea abies. Near the junction of footpaths W9 with W2 set well back from these paths, is a young Coast Redwood Sequoia sempervirens. This tree was discovered by ArchiboldMenzies in 1796, near to the coast of California. This tree should be distinguished from the Wellingtonia or Giant Redwood Sequoiadendron giganteum, an example of which may be seen outside the Police Station in the centre of Nailsea. The leaves of the Coast Redwood are like those of yew, while the leaves of the Wellingtonia are more like those on Cypress trees. Although both trees have spongy bark and may grow up to 50m in height, the Coast Redwood is the more desirable tree, with good quality wood and the ability to regenerate as coppice on being felled. The genus is named after the North American Red Indian who was the son of a Cherokee squaw and an English trader named George Giss. Sequoia became famous as a skilled silversmith but his greatest achievement was in devising a phonetic alphabet for the Red Indian language.
Further back along the footpath in the direction of Tickenham is the Sweet Chestnut Castanea sativa. This grows opposite to the Chestnut paling fence that is on the left of the path, an important use for the timber. This tree was probably introduced into England by the Romans who were notorious gourmets, together with the Walnut (not found in Towerhouse Wood). This specimen has been coppiced many years ago.
Although the Sycamore Acer pseudoplatanus is often considered to be native to the UK, it was probably not introduced until the 13th Century from mainland Europe. The first indication of its presence was the carved Sycamore leaf on the tomb of Saint Frideswide, patron saint of Oxford. Sycamore is very vigorous, possibly related to the fact that it appears to have hybrid origin with double the normal number of chromosomes found in the genus Acer. The Tolpuddle martyrs met under a Sycamore tree in 1834, before their deportation to Australia.. The white wood is used for making spoons and for the backs of violins.
There are many Turkey Oaks Quercus cerris in Towerhouse Wood, and it is intended to remove these if possible. This tree was introduced to the UK from Southern Europe in 1735. The wood is inferior to that of English Oak from which it is distinguished by its ‘mossy’ acorn cups. It is also the alternate host for the wasp causing the Knopper Gall Andricus quercuscalicis in English Oak, introduced in the 1960s, which destroys the acorns sometimes eliminating the entire harvest.