Kym Knight and Bob Boardman.
Arborist; Consultant:‘Tree-environs’.
Silviculturalist & Guide, Waite Arboretum

  1. Brief outline of the significance of oaks in nature, history and features of their silviculture/cultivation.
  2. Evaluation of the oak spp. For uses in southern Australia from their performance in the Arboretum and elsewhere.

Bob Boardman – Significance of oaks in nature, history and features of their silviculture and cultivation.

Genus Quercus

The name is from Latin and which was used widely through the Roman Empire for oaks of all kinds.  It was derived from the Greek word ‘drys’ that was used for the wood most heavily utilized in the pre-Hellenic world.  This points to the widespread abundance of oak forest and woodland in the  NW Mediterranean on land below 800m a millennium or more before the Christian era. Many place  names incorporating ‘Drys’ have survived in classic literature testify to this.  The Greeks, however, whilst distinguishing between four main kinds of oak trees did not have consistent local names for them; the Romans did, and so botanists gave oaks the Latin sobriquet.

Classification: recognizes 2 Subgenera: Quercus with 5 Sections, Quercus, Mesobalanus, Cerris, Protobalanus and Lobatae;  and Subgenus Cyclobalanopsis (mainly confined to Central and Eastern Asia).  The distribution of evergreen, or ‘Live’ species is not confined to any one subgenus or section. This points to the evolution of deciduousness in response to climate changes affecting the survivors of previous wide-spread populations or refinement of traits aiding migration, especially, latterly, during the fluctuations of N. Hemisphere Ice Ages.

Distribution

World-wide in Northern Hemisphere (in contrast with our native Eucalypts also a genus with evolution into hundreds of living species) – from western N. America to China and Korea in the east; from the Tropics to Latitude 60º- N, The bulk of the natural distribution lies between Latitudes 30º N to 50ºN.  Paleobotanically, the genus appears to have evolved from ancestors within the tropics and sub- tropics, where  related genera still exist.  Quercus has the largest number of species of any trees in the Northern Hemisphere, about 400 spp.  Over 200 spp. are of former- or still-current socially-economic, cultural and religious interest to humans. These have now been significant for three millennia, since birth of civilization in China and in south-western Asia [Middle-east] to the present day.  The July 2010 edition of The English Garden has a 3-page article on manufactures of oak garden furniture and fittings.

Cultural interests:

Agriculture:

Animal and human shelter. Human & animal food: acorns. Normally abundant supply most years. 6-month or 18-month ripening periods subject to spp. Range in flavour from sweet to very bitter depends on tannin content; over-feeding may create a potential toxicity to livestock.  Wildlife food source: birds and animals: e.g. Possums like Cork oak (Quercus suber) besides humans.

Religion

Pagan rites, worship in open glades in oak woodland, as with Druids; wreaths of oak-leave and mistletoe; idols; protection from calamity and sickness – statues and ships’ figureheads; New Age significance.

Commemorations

‘Winners’ wreaths especially for endurance sports events; historical significance to rulers & governments (Federation Tree, outside Houses of Parliament, Melbourne, 1904; Quercus canariensis planted by PM Parkes, 1908); Major Oak in Sherwood Forest, UK.)  Avenues: trees,  especially trimmed or fastigate Q.fastigata, similar varieties, lead the eye to focal points – often worth using stock from clonal replication (like oaks, Q. robur, in Osmond Terrace, Norwood, and the elm  avenue in the Waite arboretum.  Memorial avenues; – for fallen in wars, like that Alexandra Avenue in Rose Park.   Many opportunities for other commemorative plantings in groups, avenues and as single park trees.  Oaks from Palestine and Gallipoli campaigns of WWI and training areas in Palestine for the   ‘Desert rats’ in WWII. : Tabor or Valonia oak (Quercus macrolepis), Kermes Oak (Q. coccifera, syn. calliprinos); Turkey oak (Q. cerris). Oaks from wider N. African and Mediterranean campaigns in WWII involving Anzac soldiers and airmen: Aegean islands, Morocco, Algeria, Tunisia, Crete, Sicily and Italy: Holm oak, (Q. ilex), Algerian oak (Q. canariensis), Cork oak, (Q. suber), Cyprus Oak (Q. boissieri).

Landscaping

Normally dense and strong green colour foliage and rounded form a visual contrast with many taller native tree species. Wide variation in leaf shape adds variety in closer view and adds to amenity values.

Local Government: City environs – Osmond Parade, Rose Park & Norwood, Q. robur. Street and roadside planting – fastigate oaks on Portrush Road at Glenunga. Avenues along through paths within SA town and city Parklands; Parks and recreation areas of various sizes from fifth ha, upwards.  Carbon sequestration plantings with amenity values, shade, shelter from winds, but enough space to prevent soil compaction around trees.

What have we got to show?

Good performers

Much of value on oaks potential has been augmented by the “Homoclime” studies of trees from regions, world-wide, having a Mediterranean-type climate. Collaboration between Prof. J.B.Prescott and Prof. Lindsay Pryor, ANU; with two test areas, planted 1948-1956 respectively, located in Adelaide (Waite Arboretum) and in Canberra,. (ACT arboreta and ACT Parks and Gardens.)

European

Tolerance of dry summers, often base-rich soils, and evergreen or deciduous foliage, variety of crown shape: Tabor or Valonia oak (Quercus macrolepis (formerly known as Q. ithaburensis or Q.aegilops); Kermes Oak (Q. calliprinos); Turkey oak (Q. cerris); Holm oak, (Q. ilex), Algerian oak (Q. canariensis), Cork oak, (Q. suber),

Eastern N. America

Attractive leaves with spiny pointed lobes, Pin oak, Q.palustris, and several Red oaks, with vivid autumn foliage – Southern red oak, Q.falcata, Scarlet oak, Q.coccinea, northern red oak, Q. rubra. Also smooth-edged leaves: Laurel oak, laurifolia, and Willow oak, Q. phellos.

Western N.America & Mexico

Closely-matched climate, evergreen or deciduous foliage, variety of leaf shape: California Black oak, Q. kelloggii; Interior live oak, Q. wislizenii; Coast live oak, Q. agrifolia; Valley oak, Q. lobata; Blue oak, Q. douglasii; Oregon oak, Q. garryana.

Hybridization

frequent almost totally limited to spp. within same Sections.  Most are fertile.  Many found in cultivation where spp. from different geographic areas become closely associated.

Kym Knight

Will deal with Arboricultural aspects. Fact Sheets for several oak species that perform well in the arboretum describe features and include experience.

Tree character

Provide a wide mixture of textural variety in leaf shape. Height†: Tall or short stature depending on whether wide-spaced (solitary) from neighbouring trees in begin in closer-spaced groups or plantation. Oaks planted closely then thinned out to favour the best in later life grow to be up to double the height of open-grown specimens. Prefers loamy to ‘stiff’ clay texture soils rather than light sands; moist, not waterlogged; neutral to acid and well-drained soils.  Some species are tolerant of base-rich soils.  They tend to grow best naturally on lower slopes of valleys, getting extra moisture from down slope drainage.  Oaks rRoot deeply with a prominent taproot, so benefit from good planting technique and avoidance ofsites with a high water table. Evergreen, sub-evergreen and deciduous species.  They occur in all Sections and most regions.

Propagation of desirable spp

Sow acorns soon after they fall, soon lose viability; should not be allowed to dry out.  Strict selection advisable within seedling offspring for straightness and vigour. Noted that some hybrids breed ‘true’ to parental form.  Hybrids – there is potential for selection of locally adapted varieties. Nursery at Urrbrae TAFE, is raising plants from arboretum and significant trees.  Needs:

Conservation, pruning, disease detection and remedies:

Disease detection and remedies:

Honey fungus (Armillaria luteobubalina) a native species on Q. douglasii [Californian blue oak]; Remedial work with  Trichoderma (a natural parasitic fungus) applications. Mildews:  Oak Mildew (Oidium quercinum), typical gray coating on leaves and defoliation. Is most serious in nursery stock. Remedies: (1) Dry dusting sulphur or wash with colloidal spray. (2) A parasitic fungus Ciccinobolus spp. used overseas. Red spider mite Oak leaf roller moth (Tortrix viridana): defoliation but rarely fatal.

Pruning

All pruning should follow accepted formative pruning practices and conform to AS 4373 – 2007  ‘Pruning of amenity trees’.  A clean bole is desirable: trimming off branches to head height on young trees, 3m or taller, is tolerated as these shoots usually grazed by sheep and cattle in park-pastures, and by goats and deer in woodland grazing situations. Further ‘lifts’ to 9m  in open-grown or specimen trees can best remove small diameter branches and simulate the effect of close-grown forest trees, [SEE note† above.] Pruning large branches or ‘dead-wooding’ older tree crowns needs care, sharp, clean tools,

Conservation

Soil compaction problems can arise with concentrated human foot and cloven-hoofed grazing animals. Waterlogging and salinityA maintenance programme needs to specify particular needs of each kind: arboretum; street plantings and memorial avenues; landscaping in urban parks – single tree, small group and avenue situations.

Quercus douglasii – Blue Oak

The Blue Oak originates in the hot, dry foothills of California’s interior, in areas receiving 375‐875mm rainfall annually. At the most extreme end of its range it extends to the lowest, hottest and generally most inhospitable areas of that state, usually on poor soils.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • douglasii is an attractive small to medium sized deciduous tree normally 10‐12m tall but may be up to 20m in ideal conditions, with a rounded, compact crown.
  • A tree of good form. (Seed source is important) Often has an erect slender crown when young, widening with age
  • Highly drought tolerant. Watering at establishment only Waite trees are not irrigated.
  • Tolerant of pruning.
  • Tolerant of frost.
  • The trunk rarely exceeds 600mm diameter. TDR ratio 1.4. (Based on 3 Waite Arboretum trees only)
  • The majority of the species range occurs in lowland savannah of grasses and herbs. It will grow equally well in parks (in lawns) or gardens
  • Suitable for avenue plantings, medium sized verges, medians and reserves.

The species possesses a range of unique characteristics that enable it to survive during periods of prolonged moisture stress.

  • Rapid germination whenever conditions are suitable, regardless of time of year.
  • Rapid root growth to aid in establishment and in competing with other plants
  • Roots continue to grow in cooler soil in the winter months.
  • The Blue Oak retains a proportionally small crown in relation to the root system when compared to other less drought tolerate Oak species.
  • Numerous water conservation measures are present in foliage, including small overall size, upper surface covered by a waxy coating giving the tree its bluish appearance, leaves are reinforced by lignin and cellulose during extreme stress to increase resistance to dehydration, internal salt content of leaves is adjusted to prevent wilting, enabling them to lose up to 30% of their water in extremely dry air to prevent wilting. Blue Oaks can also resort to dormancy in extreme drought, dropping their leaves and resuming growth when conditions improve.

Problems

  • Pest and disease issues in Oz are largely unknown. No pests are apparent in the Waite Arboretum trees.
  • The species is susceptible to Armillaria
    luteobubalina Australian Honey Fungus.
    One of the Waite trees is presently
  • Acorns are produced These may cause trip hazards or other litter problems in
    unsuitable environments.

Quercus kelloggii – Black Oak

Q. kelloggii is a tall deciduous tree with ascending limbs and an open elegant crown. It originates in mountainous areas of Oregon & California, being found between 350‐2,700m altitudes, receiving an average of 625mm rainfall annually. It is also common in large stands in lowland valleys around Napa and Santa Rosa where it is a feature of the landscape. Soils are usually coarse and well drained in the mountains. It occurs on heavier clay soils at low altitude sites. In its natural habitat it is subjected to periods of drought, moderate to intense heat and extreme cold.

  • The acorns of the Black Oak were considered the best of all the Oaks for human consumption by the native American Indian
  • Black Oak timber, once thought to be worthless, is now highly prized for fine furniture and other special uses.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • The Black Oak is a medium sized deciduous tree to 10‐28m tall, with a rounded, compact crown, a straight trunk often branching near the ground, particularly on the tougher DBH usually below 1m. The largest Black Oak found to date is in Placer County, California. It has a DBH of 2.9m and is estimated to be 450 years old.
  • The lustrous deep green foliage of summer turns a vibrant yellow This is contrasted against the almost black bark to create a stunning ornamental tree.
  • Fire Resistant.
  • Variable form, but tolerant of pruning.
  • Suitable for avenue plantings, medium sized verges, gardens and reserves.
  • Water required at establishment only, however the Black Oak will grow faster if irrigated.
  • TDR ratio of 1.8. (Based on 1 Waite Arboretum tree only)

Problems:

  • Pest and disease issues in Oz are
    largely unknown.No pests are apparent
    in the Waite Arboretum trees.
  • Acorns are produced prolifically.
    These may cause trip hazards or other litter
    problems in unsuitable environments.
  • Finding a good seed source from a
    suitable provenance may prove difficult.

Quercus suber – Cork Oak

Quercus suber is a medium‐sized, evergreen tree native to southwest Europe and northwest Africa.  It grows 12‐20 m tall x 12‐20m wide depending upon growing conditions. The cork Oak is a highly ornamental medium sized evergreen tree with a stout, often twisted trunk and spreading limbs. The dense rounded crown, often has a weeping appearance resulting from the drooping habit of smaller limbs. Check out the avenue at Grant Burge Winery, Rowland Flat, SA if you get the chance.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • Long 150‐250 years.
  • Moderate growth rate.
  • Tolerant of The thick bark protects epicormic buds, enabling rapid regeneration of the crownafter fire.
  • Tolerant of drought, frost, indirect salt and all but the worst of urban conditions.
  • Provides large areas of dense shade.
  • Will grow in a wide range of soil types and pH’s.
  • Pest and disease issues are rare.
  • Good tolerance to pruning*.
  • Highly suited to avenue plantings, medium sized verges, reserves and gardens.
  • Water required at establishment only but the Cork Oak will reward occasional irrigation in summer.
  • TDR ratio around 1.363. Waite Arboretum trees (2), 1.46.

Problems:

  • May be slow to establish at sites with drainage problems.
  • Acorns are produced These may cause trip hazards or other litter problems in unsuitable environments.
  • Bark inclusions may occur. Choose your stock or seed source with care and make sure trees are formatively pruned until good form is established.
  • *Weeping habit may increase clearance pruning requirements for trees with low limbs.
  • Trees with limited root space may damage surrounding in
  • The Oak Leaf‐miner, Phyllonorycter messaniella is a minor pest of foliage in some

Quercus canariensis – Algerian Oak

Originating from a variety of habitats in Spain, Portugal and North Africa, (introduced to the Canary Islands) this superb tree has a tall spreading crown of numerous heavy stems and large spreading limbs. Achieving between 15‐30 m tall depending upon conditions; the trunk will grow to 1m or more in diameter.
The Algerian Oak is only partly deciduous in mild climates, retaining some of its large, bright green foliage year round on most trees. Leaf fall occurs in late winter when some leaves turn light golden brown before falling.

There are many subspecies of Q. canariensis, with several varieties described:

  • var. salzmanianna: leaves 12 cm long, elliptical, elongated, flat, very leathery, with margins slightly wavy.
  • var. mirbeckii: leaves 20 cm long and more, oblong, base attenuate, margin wavy with numerous lobes, petiole 4 cm long
  • var. carpinifolia: leaves 8 cm long, elliptic‐oboval or obtriangular, with pointed lobes
  • var. elongata: leaves 10 x 2‐4 cm, narrow, with whitish fasciate hairs below; 5 short (less than 1 cm),. round lobes each side; 4‐8 vein pairs; petiole 2‐1.5 cm long, hairy; bud oboval, light tawny, 7 x 5 cm.
  • var. fissa: few, pointed lobes with sinuses reaching halfway to midrib.
  • var. ovata: leaves oval, 7 x 4‐5 cm, petiole 4 cm long.
  • var. pseudocastanea: leaves resembling those of the Chestnut.
  • var. suborbicularis: leaves 15 x 10 cm, elliptic; few, shallow, regular lobes.

It is fast growing and long lived; reaching 300 years of age or more.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • Large, bright green foliage and good form make this an extremely attractive specimen or avenue tree
  • Upright form when young, spreading with Easy to establish suitable structure.
  • Water required at establishment only.
  • Tolerant of alkaline sites and heavy
  • Fire retarding/resistant. Reputedly 100% survival rate.
  • Tolerant of cold to ‐100ºC.
  • Average tolerance of waterlogging and soil compaction.
  • Good tolerance to pruning
  • TDR ratio of 46. (Based on 4 Waite Arboretum trees only)
  • Suitable for avenue plantings, medium sized verges, gardens and reserves.

Problems:

  • Can be slow to start, but rapid growth occurs once established.
  • Pest and disease issues are largely unknown.
    No pests are apparent in the Waite Arboretum trees
  • Finding a reliable non hybridized seed source may prove

Quercus Lobata – Valley Oak

Endemic to California, the Valley Oak is found in the valleys and foothills of the inner coast ranges and on the islands of Santa Cruz and Santa Catalina. It grows on lowland fertile soils, often with Q. douglasii. It also occurs up to 1700m altitude. The Valley Oak is a tall tree 20‐30m high, with a short trunk and a spreading, broadly rounded crown. In its native environment the Valley Oak receives between 500‐2000mm of rainfall in coastal areas of its range and as little as 150‐750mm at inland sites. At dry sites access to ground water, preferably at around 10m depth will be important to success.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • A large, well‐structured specimen tree of good form, the Valley Oak is a handsome tree that deserves wider use in appropriate locations
  • Ecologically adapted to regular Will regrow from epicormic shoots.
  • Moderate growth rate.
  • Long lived; 300‐400 years.
  • Deep rooted species typically with several large roots tapping ground water in similar fashion to Eucalyptus camaldulensis
  • Tolerant of pruning and urban A tough tree.
  • Suitable for avenue plantings, wide verges, gardens and reserves.
  • TDR ratio of 71. (Based on 3 Waite Arboretum trees only)
  • Based on the species performance at Waite there is considerable potential for use in selected urban sites.
  • Tolerant of moderate waterlogging.
  • Moderately shade tolerant.

Problems:

  • Pest and disease issues in Oz are unknown. No
    pests are apparent in the Waite Arboretum trees.
  • Acorns are produced prolifically every 3rd
    These may cause trip hazards or other
    litter problems in unsuitable environments.

Quercus englemannii – Englemann Oak

Englemann Oak is a small to medium‐sized, evergreen tree native to south western California where it grows on dry rolling hills in well drained sandy loam soils. It grows 10‐18m tall and equally as wide, developing an open spreading crown in dense stands.

Factors that make this tree suitable for ornamental use in Southern Australia.

  • A handsome tree with real character, casting dense shade
  • Ecologically adapted to regular Will regrow from epicormic shoots.
  • Moderate growth rate.
  • Tolerant of drought and frost.
  • Suitable for shelterbelts, small avenue plantings, wide verges, gardens and reserves.
  • Shade tolerant as a young tree.
  • TDR ratio 1.5 Waite Arboretum trees only (3).
  • Based on the performance of trees at the Waite, this species will tolerate heavier soils.

Problems:

  • May be slow to establish at sites with drainage problem
  • Low open growing habit may increase clearance pruning requirements for trees in verges
  • Semi evergreen. May sometimes loose its leaves in summer in response to drought.

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