Oaks of the Castlemaine Botanical Gardens

Pin Oak dominates wet woods and river flats in its native habitat of eastern North America where soils are flooded annually.

Palustrine means swampy. Its ability to tolerate flooding and resultant low root oxygen makes it ideal for cultivation in compacted soils of urban environments; it is the most widely planted tree in North America.

Pin Oak is one of the easiest oaks to identify, its upper branches show strong apical dominance, lateral branches are strongly horizontal and lower branches angle downwards; its distinctive silhouette is striking.

The vernacular name “Pin” oak derives from use of its long flexible shoots as pins in construction of early settlers’ timber houses. Its timber cracks too readily to have general construction value.

With its demand for moisture Pin Oak is a tree that may prove more difficult to grow in Castlemaine as conditions become hotter and dryer.

Widely distributed in central Asia, Banjh Oak is the most useful tree of the Himalayas, its foliage being cut annually to provide fodder for stock. Older wood produces hot fire and is used as domestic fuel and for construction.

Its native habitat is mild and moist with poor clay soils it shares with Chir Pine (Pinus roxburghii) and Rhododendrons (Rhododendron arboreum).

Local people use Banjh Oak for many purposes, gum from old trees being used against colds and as an analgesic and the acorns ground for flour and as medicine.

Among its distinct features are its leathery evergreen leaves with white-woolly hair beneath and white-woolly young shoots.

Readily identified by the bristles at the apex of its ‘sawtooth’ leaf, the Sawtooth Oak extends over large areas of eastern Asia. Widely introduced, it has become invasive though important for food for native animals in eastern USA where a cultivar ‘Gobbler’ with smaller acorns has been introduced specifically for food for Bush Turkeys.

In Japan, charcoal from Sawtooth Oak is used in brassieres to provide the fuel for the traditional Japanese tea ceremony.

Growing over much of Europe, this species is separated from English Oak (Quercus robur), by growing at higher altitudes in shallow, often poorer soils and differentiated by the absence of a stalk to the acorns, the origin of the common name.

It has been estimated that 326 species of British wildlife depend upon this oak for some aspect of their lifecycle including insects, birds, mosses, lichens, liverworts, butterflies, beetles and bats, the latter roosting in cavities. Every ten years or so it produces a mast year when up to 10,000 acorns can be produced by a mature tree!

English Oak grows throughout Europe and provides important ecological benefits as well as economic benefits in many areas. It is the type species of the genus, the species that establishes the characteristics against which other oaks are assessed.

English Oak is the subject of myth and legend in many European cultures especially to gods associated with thunder and lightning, Zeus, Jupiter and Dagda. Being the tallest feature in the landscape they were often struck by lightning.

English Oak is one of the two main oaks that provide materials for French oak barrels so prized for wine production. The best timber comes from central France where annual auctions are held selling oak wood not only for cooperage but for cabinet making, panels, railroad ties and firewood.

Approximately 40% of Europe’s forests are in France, predominantly oak forest managed for timber production. Oaks used as a source of cooperage timber are upwards of 110 years old with the best, tightest grained timber said to originate from the centre of stands.

Cork from Cork Oaks has been used as a stopper for containers since at least 5,000BCE when it is recorded as sealing containers. Shakespeare describes the use of cork stoppers and bungs though bottles and corks for champagne were matched as late as 1670! Robert Hooke, the British scientist, used a microscope to investigate cork which led to his discovering and naming the cell.

Cork trees need to be about 30 years old before they can be stripped, nine years later this can be repeated, with cork from the third strip being suited to use for wine corks. Early production is used for shoes, flooring and other less demanding purposes. Bark is cut by hand by scoring around the top and base and then cutting down the tree carefully severing broad bark planks. The process can be repeated in approximately 10 years and continued for 200 years or more.

Cork is stored for a year and then steamed to remove tannins and to make the cork more malleable. Bottle corks are then cut from bark strips.

Cork is the natural adaptation of the tree to protect itself from the temperature changes and frequent fires of the Mediterranean basin and the cork acts as an effective insulator.

In Spain it grows with Holm Oak and its acorns provide valuable food for Iberian pigs to produce pata negra, best quality Iberian ham from black pigs introduced by the Phoenicians 2000 years ago. The Romans recognised the flavour of Iberian ham, Pliny the Elder saying “the flesh of these hogs has nearly fifty flavours”. Pigs feed on the dehesa, open woodland rich in wildflowers but dotted with oaks where they gorge on acorns eating 9 kilograms of acorns each day! It is these acorns that contribute to the remarkable flavour of the best of Iberian hams. So valuable are the acorns in pig raising that in 1957 acorns represented one sixth of the value of Spain’s timber products.

Amongst the fastest growing oaks, Water Oak is also amongst the shortest lived being a pioneer species of wet swampy areas, ponds, river margins, stream banks and the like. It is extremely tolerant of soil compaction and extensively used in programs of land rehabilitation but tolerates no shade and rarely lives beyond 60 years.

It has been amongst timbers used by settlers in North America since the seventeenth century though its quality varies considerably. The acorns are used by native Americans as food.

Red Oaks have increased in their native forests of northern New England and east coast USA since colonisation because White Oak, once more numerous, has been selectively felled for lumber; Red Oak has filled forest gaps and is now the second commonest north American oak after Pin Oak.

Red Oak forms new season’s leaves when day length reaches 13 hours, regardless of temperature, so in its northernmost distribution late frosts may kill the flowers produced with the leaves resulting in no acorn production. Leaf fall begins when day length drops below 11 hours. Acorns drop in the second year with the leaves and are disguised from seed eaters and protected from cold, only germinating when temperatures reach 21 degrees C. Even then acorns must have experienced a minimum of three months’ exposure to temperatures below 4 degrees C. Given the species’ distribution down the east coast there can be a three-week variation in leaf development and leaf loss from north to south of its range.

Red Oak is one of the most important North American timber trees used for internal construction and veneer.

The evergreen leaves of Holm Oak resemble the leaves of Holly (Ilex aquifolium). Ilex was the original classical name for Holm Oak though as a botanic name it was given to Holly! Holm is an ancient name for Holly now given to the Oak! In both cases thick evergreen foliage can be edged with spines to discourage browsing though both plants have foliage without spines often higher in the tree where browsing is less likely. Holly leaves are more undulating and have a shiny upper surface.

Quercus rotundifolium from the Iberian peninsula is sometimes considered a variety of Holm Oak and is valued for its sweet acorns.

Blue Oak is endemic to California and amongst its most familiar trees growing in the foothill ranges and is California’s most drought tolerant deciduous oak. It achieves this by reducing its foliage density, producing wax coated leathery leaves that lose less water and become more blue and reflective of sunlight in drought conditions. If conditions become really dry it drops leaves and sometimes its acorn crop in summer before re-leafing next spring.

Blue Oak was collected by David Douglas, 1799-1834, a Scottish botanist, commemorated in the names of more than 80 plants and animals. He introduced more than 240 plants to Britain from his three North American expeditions between 1823 and 1834. His most important introduction was Douglas Fir (Pseudotsuga menziesii).

Tannins in acorns discourage their consumption by herbivores but local native animals have enzymes in their saliva that allow their digestion. With increasing numbers of native herbivores including squirrels, gophers, mice and Mule Deer as a result of selective extermination of predators, acorns are being consumed in greater numbers reducing the population of young trees and placing the future of Blue Oaks in doubt.

Blue Oak produces especially edible acorns and both native Americans and settlers ate it, soaking it to remove tannins and then grinding it to produce flour for porridge, cakes, soup and bread.

Bur Oak grows in fire prone native American savanna grasslands and is protected from severe damage by its thick insulating bark layer. It gets its name, macrocarpa, from its very large acorns, up to 50mm across.

Bur Oak exhibits a common oak characteristic of ‘masting’. In one year in 10 years, the oak produces prodigious quantities of acorns, more than all its seed predators can possibly eat, ensuring the germination of significant numbers of trees and the species’ survival.

Turkey Oak is a fast-growing oak that is native to south-eastern Europe and Asia Minor though before the last Ice Age, 120,000 years ago, it grew more widely extending both further west and north. Re-introduced into Britain as part of the eighteenth century landscape craze it has now naturalised even hybridising with Cork Oak (Q.suber) to provide a fertile hybrid, Luscombe Oak (Q. x crenata), named Luscombe after the nursery where it was first identified.

Mature trees reach 40 metres with a trunk to 2 metre diameter, deciduous foliage with leaves glossy dark green above and softly hairy below to 140mm long and 50mm across. An easy way to differentiate them from English Oak is by their acorns, 40mm long, orange to the base and green towards the tip but more significantly housed in a 20mm cup covered with “moss”.

Turkey Oak was widely coppiced for timber in Mediterranean areas. Its ground acorns produced a high-quality bread, a staple diet in rural Greece during World War II.

Native to river flats, stream borders and lake and pond margins, Swamp White oak (Quercus bicolor) is named for its two-colour foliage, whitish beneath and green above. It grows fast to 24 metres, forming a rather narrow canopy.

The deciduous foliage grows to 180mm with a width of 110mm but, unlike many American oaks, it colours in bronze and yellow brown without giving highlight colours. It stretches through much of central northern USA from Nova Scotia to South Carolina and as far west as Minnesota and Tennessee.