Mary Ann Riley
Historically the oak is seen to represent power and strength. It was under the oak tree that the Gauls rendered justice. Among the Romans, receiving a crown of oak leaves was a form of reward! (Lauriault, p.372). Even today the oak tree is seen as a symbol of strength and durability.
The bur oak is one of the many oaks in the genus Quercus. Bur oak, Quercus macrocarpa, is the most wide spread of all oaks native to Canada. Quercus is derived from the Celtic language and means "tree above all others". Macrocarpa is from the Greek makros meaning large and karpos meaning fruit (Lauriault, p.372). Acorns of bur oak are the largest of our indigenous oaks. It is believed by some ecologists that the bur oak is the predecessor of all white oak tribes in North America (Reed, p.216).
This profile of the majestic bur oak will provide information on; identifying features; habitat conditions; early growth and development; growth in woodlots; potential of the bur oak in Agroforestry; and pests that infest the bur oak.
Identifying Features of the Bur Oak (Farrar, p.258)
Leaves- The leaves are 15-30 cm long and of variables shape. Some bur oak trees have leaves with a broadly expanded portion above two deep notches, the lower portion with a few short, rounded lobes. Other leaves resemble white oak with 7-9 deep lobes. On all bur oak leaves the upper surface is shiny green. The underside is pale and hairy. Stipules are often present.
Lobed leaf with largest lobe at the top of leaf. Large acorn cap with fringed edge.
Buds- The terminal bud is 3-6 mm long, blunt, brown, hairy and often surrounded by a number of elongated, pointed scales. The lateral buds are pressed against the twigs.
Twigs - The twigs are stout, yellowish- brown and slightly hairy. Branchlets often have corky ridges.
Coarse, yellowish branches.
Flowers - Bur Oaks are monoecious, male and female flowers are on the same tree. Male flowers are small catkins developing from buds on previous year's twigs or on the base of new shoots. Female flowers are small and either solitary or in few flowered clusters in the axils of leaves on new shoots. The flowers appear as the leaves are developing and are wind pollinated.
Seeds - The seeds of the bur oak are one of the sweetest of the white oak group. The white nut is considered edible and is a favourite of forest animals including squirrels and deer.
Fruit - The acorns are one seeded nuts 20-30 mm long. They are usually solitary, stalkless or have a short-stalk.. The cup is large, enclosing one-half or more of the acorn. The inside of the cup is hairless. Knobby scales and a conspicuous fringe surround the cup. The acorns mature after the first year on new twigs. The acorns are shed in autumn soon after ripening. The nut usually remains with the cup. A good crop of bur oak acorns occur at intervals of 2-6 years.
Bark - The young bark is brown, furrowed and rough. The mature bark is deeply furrowed with ridges broken into irregular, thick, dark, grey scales. Due to the thickness of the bark, the bur oak is fire-resistant.
Grey bark, deeply furrowed with large irregular ridges.
Size and form - The bur oak, when grown in Canada, is considered a small tree, 12-18 m high and 60-80 cm in diameter. It lives to 200 years old' however, in parts of the United States, bur oaks have lived 200 to 400 years and the largest bur oak reaches the height of 29 m and 2.6 m in diameter (Sternberg). The trunk is straight and tall with principal branches ascending in the upper crown and nearly horizontal in the lower crown. New shoots (epicormic branches) often occur along the trunk. The root system is a deep wide spreading taproot.
Open grown bur oak with short trunk and large crown.
Main branches ascending in upper crown and nearly horizontal in lower crown.
Botanical Range of the Species
There are 500 to 600 species of oaks in the genus Quercus. Eleven species can be found in Canada (Farrar, p. 246). Oaks are subdivided into two main groups, red and white. This division is based on the appearance of the leaves and the acorns.
Trees in the red oak grouping have leaves with bristle-tipped lobes, the veins extend beyond the leaf margins in sharp points. The acorn matures in two years. The cup of the acorn has thin scales and is lined with a hairy coat. Included in the red oak group are red oak, black, pin, northern pin, Shumard and scarlet.
Trees in the white oak grouping have leaves with rounded lobes or large regular teeth. The acorn matures is one year. The acorn cup has thicker scales and a smooth inner surface. The species in the white group are white, bur, swamp white, chinquapin, dwarf chinquapin, Garry, English and chestnut oak.
The bur oak is the native white oak most commonly found in Canada. It is distributed from southeastern Saskatchewan, southern Manitoba, Ontario and Quebec and east to New Brunswick. More specifically it is found in the Deciduous Forest Region and in scattered groupings throughout the Great Lakes-St. Lawrence Forest Region. It is in the central portion of the Acadian Forest Region and in the area of transition between the Grasslands and the Boreal Forest Region (Lauriault, p.372).
The bur oak hybridizes easily with other white oak species. This ease of hybridization may explain the wide range of leaf shape of bur oaks. In Canada bur oak has hybridized with the swamp white oak (Farrar, p. 258). The Oikos Tree Crops, a tree nursery based in Kalamazoo, sells hybrid species of oaks. The ease of hybridization allows for trees that can flourish in a wide range of soil types and climates (Oikos Tree Crops).
The bur oak grows best on deep, dry, rich bottom lands. Its preference is for well drained sandy or clay loam soils. It also occurs on upland limestone soils and at the northern limits of its range, on shallow soil over granite bedrock. Trees maybe stunted on exposed shallow soils. Its strong early root growth and its deep tap root system allows it to pioneer on dry exposed locations and compete with prairie shrubs and grasses (Fowells, p. 565).
Years ago bur oak could be found in pure oak stands. In Canada it now tends to be mixed with other hardwood species and conifers. In A Nut Growers Manual for Eastern Ontario it is noted that the bur oak " is associated with upland hardwoods of mid-tolerance including cherry, basswood and white ash. It is occasionally found with white elm and soft maple in better drained bottom lands. It is semi-tolerant, so does well in the open or in openings in a woodlot." (Schaefer, p.56 & 60). Interestingly the bur oak has been used as an ornamental tree in urban areas because it is able to tolerate urban conditions.
Generally nut trees grow best in temperate climates. However, the bur oak, like other native hardy nut trees (heartnut, shagbark hickory), is able to survive fairly difficult climates. The bur oak will survive with a minimum temperature of -30C and a period of one hundred and fifty frost free days (Schaefer, p. 4). Fluctuations in temperature during the winter and early spring can cause more injury than sustained cold. Late spring frost and early fall frost can potentially damage the fruiting capacity of the tree. Also, low lying areas that act as frost pockets are undesirable locations. Microclimates can protect trees from the elements. Large bodies of water will moderate winter cold extremes. Trees on a north facing gentle slope will break bud later and are less likely to be damaged by late frost. Bur oak grown in a woodlot setting, at the edge of a woodlot or protected by a conifer wind break will fair well. Moisture is another climatic factor effecting tree growth. The bur oak grows best in moist but well drained soils. It is the most drought resistant of all the oaks so is able to withstand periodic dry conditions or sites that are typically dry.
Reproduction and Early Growth in Woodlands
The literature varies on the age at which the bur oak produces acorns. The range is any where from 10 to 20 to 35 to 50 years and some numbers in between. Some of this range can be explained by the climate in which the tree grows. Good seed crops occur every two to three years with light production in the years in between. The bur oak is considered a productive tree though no yield amounts could be located. For some comparison, the English oak, a somewhat more productive oak, can yield 50 to 100 lbs. of acorns in a year (Asmus, p. 1).
The bur oak flowers shortly after the leaves appear, sometime between March and late May depending on latitude. First 2 to 3 inch catkins are produced. Then 5 to 10 days later, it produces either individual or pairs of pistillate flowers. Though monoecious, the pollen from one tree appears to germinate better on the stigmas of another, favouring cross-pollination (Fowells, p. 565).
Research on white oak found weather conditions seem to play a major role in reproduction (Light). On average it takes 3 days for pollen to be disseminated. In wet weather the anthers close and stop shedding pollen until conditions improve. Dry wind and freezing weather can have an adverse effect on reproduction. Acorn crops are good when there is 10 days of warm weather followed by 13 to 20 days of cool weather, and poor crops of acorns occur when cool weather is followed by warm weather during flowering. It takes approximately 120 days for the acorns to mature, and they begin to fall 25 days later, for about 30 days.
Acorns are disseminated by rodents, gravity, water and wind. A great many bur oak acorns are eaten by wildlife and are considered to be a preferred forest food. For the acorns that remain, a good seedbed is comprised of litter or leaf cover on the forest floor, and is located in partial shade to full sun and dry to moist soil (Beattie et al, 1983, p. 126). In contrast, another report stated that acorns on a litter seedbed were found to be more susceptible to pilferage by rodents, and the newly developed seedlings were in contact with fungus and insect attack (Fowells, p.565). Germination usually takes place soon after the seed falls. Seedlings have a scaly shoot with a cluster of 2-5 unlobed leaves at the tip. The cotyledons are retained within the seed shell. A terminal bud forms and may show in a few weeks producing a second producing a second shoot with another cluster of leaves (Farrar, p. 247). The initial growth of the root is rapid, the taproot penetrating deeply into the soil before the leaves unfold. The taproot of the bur oak can grow up to 1 metre within the first year.
Sprout growth following fire or cutting of pole size trees is vigorous but the quality is usually poor.
Growth Within Woodlots
Due to its semi-tolerant nature, bur oak tends to be found on edges of the woodlot, forming a fringe along open fields or grasslands or in woodlot openings. If competition for light with neighbouring trees is too fierce, the bur oak's growth will be suppressed. In heavy shade, trees can die out and be replaced with more tolerant maple and ash. In a forest stand it forms a tall, straight trunk with a small crown, compared with a short trunk with a wide crown when open grown. Bur oak is considered to be a slow growing tree. In his article on white oak, Bobby Light noted that the "mean annual increment (MAI) for pure and mixed unthinned stands over a 60 year period ranged from 0.95 m3/ha on poor to fair sites to 2.2 m3/ha on good sites. However, if the stands are thinned, a 60 year old stand could have an MAI of 3.9 m3/ha." (Light, p.1). He also indicated that the rotation length for white oak is usually 120 years or more. When a stand is thinned at 10 years and every following 10 years, to 60% of the original volume, yields were approximately double an unthinned stand (Light, p.1). The information cited here is for white oak, but similarity in growth of bur oak allows for some comparison.
Opportunities in Agroforestry
Traditionally bur oak is considered with white oak in its use as a tree for lumber. It produces a high quality lumber used in flooring, veneer, furniture, boats and cooperage for whisky barrels. The wood is ring porous, heavy, hard, strong, brownish in colour with the sapwood being paler(Schaefer, p. 56). Species of white oak are used for cooperage because the vessels not located in the current growth increment are blocked with tyloses (Shigo). Tyloses are made up of bubble - like tissue that forms in openings of vessels, closing the vessel. The result is a wood that is waterproof.
Both the strength and weakness of white oak has been the quality of its wood. In Canada, much of the bur oak has been removed and not replaced at a rate that will sustain it as a ongoing lumber source. In conversation with a mill operator from the Arnprior area, he stated that any white oak that came to the mill was only suitable for pulp and paper. What then is the opportunity of the bur oak in Agroforestry today?
The opportunity in Agroforestry for the bur oak is to re-establish it on farms where it grows well. This time the bur oak can be considered of value for not only a lumber producing tree. Many believe the bur oak has potential as an edible nut.
Native Americans use acorns from white oak for food, soaking them in water to lessen the acidity produced by tannins. The acorn has been a staple food in countries from Iran to Japan. They are still eaten regularly in Korea and North Africa (Bainbridge, 1991).
Proponents of acorns as food cite research that looks at the nutritional value of the acorn (Bainbridge, 1991, p. 186). Its starch structure falls between that of corn and potatoes. It is a good source of both vitamin C and vitamin A. An analysis of the nutritional value of 18 species has been completed. Acorn oil is used as a cooking oil and has been found to be comparable to olive oil. The taste of the acorns eaten raw vary greatly with the species. A high tannic acid content produces a bitter taste. Tannins can be leached with water, hot water hastens the process, without loss of essential amino acids. Bur oak has a fairly low tannic acid content and is considered a sweet acorn. One researcher compared the taste of oaks with a sweet chestnut and found bur oak to be one of the best but still left a lingering bitterness (Asmus, p. 1).
D.A. Bainbridge, a strong advocate of oaks as an edible nut, suggests that further searches for edible acorns should be carried out in the hopes of rediscovering ones particularly in Europe and Asia. He also suggests that breeding oaks for flavour is possible due to the ease with which oaks hybridize (Bainbridge, p. 190). In the meantime for a sustainable acorn industry to begin he feels we must begin by selecting existing trees with high productivity, early bearing and pest resistance.
A group of local individuals and companies sees the potential of developing an edible nut industry in Eastern Ontario. They have researched trees that grow and produce well in the soils and climate of the area. The bur oak is one of the indigenous nut trees selected for research. A test plot exists at The Baxter Conservation Area, and the members of the Eastern Chapter of the Society of Ontario Nut Growers (ECSONG) are using their own experience as nut growers to verify the potential. The industry would be based on utilizing the nut trees already producing and encouraging individuals to plant hardy species now for use in the future. Equipment for the collection, hulling and grinding of nuts will be required on a scale much smaller then that for which the existing equipment has been developed. Finally determining the products and the best ways of marketing the final products both within Canada and to foreign markets requires research and planning.
The second opportunity for the bur oak is to continue to use it as a source of quality lumber. However, to ensure a sustainable product the bur oak can be grown as a crop much like a farmer does with corn and grain. The various methods proposed yield twofold. The nut tree is grown both to produce edible nuts and when trained properly thinned as a timber crop. Nut trees take up considerable land so intercropping, growing the bur oak with field crops, makes use of the land between trees while the trees are young. Possible crops include soybeans, wheat or cash crops (Schaefer, p.5). In Nut Culture in Ontario, it suggests soybeans may compete excessively with the trees because their growing cycles coincide. Winter wheat may be more suitable since most of the growth occurs when trees are dormant (Gardner, p.24). Intercropping has been successful with barley, maize, wheat and other crops (Bainbridge, p. 186). The oak is able to benefit from its deep tap root and mycorrhizal fungus (beneficial relationship with soil fungus) to produce good yields even when other crops may do poorly. Nut trees can also be planted on oddly shaped fields or on land that is sloping and unavailable for tillage because of the potential for erosion (Gardner, p. 3). The bur oak can be grown in a open field mixture with black cherry and white ash or in a pine stand (Schaefer, p. 60). The choose of how the bur oak is planted depends on the goals of the grower and the land that is available.
A study currently being conducted by Agriculture Canada, Prairie Farm Rehabilitation Administration based in Indian Head, Saskatchewan, and reported in the 1993 Report of the PFRA Shelterbelt Centre, may provide insight into the process and value of planting bur oak for Agroforestry purposes (Prairie Farm Rehabilitation Administration, p.7). The objectives of the study are to determine the types and extent of genetic variation among bur oak families from selected sources in the Great Plains, and to provide for shelterbelts and Agroforestry planting genetically improved bur oak seed. Three plots were planted, one in loam soil and second in clay loam soil and the third in silty clay soil. All sites were mulched with fibre and one metre tree shelters erected. Survival rates after one season have been 99 percent, 99 percent and 98 percent, respectively. It will be interesting to learn of the progress of the trees and how the bur oak fares as a tree for Agroforestry.
Best Silvicultural Practices
The information provided here will be for planting bur oak for the purposes of producing edible nuts and a quality wood product. The information for this section is obtained from A Nut Growers Manual for Eastern Ontario and Nut Culture in Ontario. More detailed information can be obtained by consulting these texts.
An ideal site is a well drained, sandy or clay loam soil with a minimum of one meter depth. An open area or opening in the wood will ensure adequate light. A conifer windbreak is advisable for plantation type planting.
The more preparation done prior to planting the less post planting tending will be required. Preparation by ploughing and discing should be done the year before planting. Frequent discing will help to minimize weeds. Weeds can also be removed chemically (Roundup) though care must be taken with amounts used. Ploughing strips two meters wide at five meter spacing minimizes soil erosion. Between strips are appropriate for intercropping or if vegetation remains mowing twice a year will discourage voles and mice.
Stock is obtained by seed or seedling. Care must be taken to ensure stock that meets the requirements of both a good nut and lumber producing tree. A suitable timber tree is tall, straight, fine branching, has a strong crown and a clear trunk. A strong, full crown is also necessary for good nut production as well as large nuts that crack easily, have good tasting nut meat and are disease free.
Stock can be obtained through specialist nurseries or through seed collection areas recognized by Ontario Ministry of Natural Resources, the ECSONG's "Inventree" file or personal knowledge.
It must be remembered that trees grown from seed do not always display all the characteristics of the parent tree.
Nut trees in plantations are generally spaced about 12 m apart to avoid shading. This will yield 85 trees per hectare. However, for the purposes of timber trees a closer spacing is desirable to provide the competition necessary for a straight trunk. Is this a conflict? Perhaps and perhaps not. In the case of heartnut trees when planted at closer spacing (6m x 6 m) acceleration in growth in the early years resulted and at approximately 12 years when crowding occurred trees were removed to allow crown development (Garner, p.24). Choices in preferred trees could be made at this point.
The advantages of spacing trees at a wider distance include: a rapid diameter growth; lower initial planting costs; few or delayed thinnings; and easier use of large equipment. The disadvantages are: the inefficient use of growing space; delay in canopy cover which delays weed control by shading; poor stem form and heavy branching which results in higher pruning costs; and a possible shortage of crop trees. The choice must rest with the grower.
Bur oak seeds start to germinate shortly after falling so they are best planted in the fall. Plant 2 or 3 seeds horizontally about 2-3 inches deep. Protect seeds from rodents with wire mesh. Mulch to minimize competition from weeds. After germination, remove the weaker seedlings. Directly seeding into the desired location helps to avoid the shock that occurs with transplanting.
To ensure the tap root can be totally included with the seedling it is best to transplant bur oak seedlings at one year. It should have a good root system with a well formed top. Damaged and uneven length roots are removed. The seedlings are planted into a hole prepared with about a half kilogram of bone meal mixed into the soil and deep enough to ensure adequate spreading of tree roots. Soil is tamped around the root with a tamping stick. Water, mulch and if the tree is large enough apply a rodent collar.
It is necessary to maintain an area free of weeds for at least one square meter around young trees and up to four square meters as the tree matures. Mulch 5 centimetres with wood chips or straw. Mulch will help to conserve moisture and maintain a more porous soil allowing better water infiltration. It has been seen that in heavily mulched orchards there is an increase in usable nitrate, potassium, magnesium and phosphorus. A higher population of mycorrhizal fungi exist, and there is increased moisture, nutrient supply and root activity (Gardner, p. 25). Though labour intensive, weeds that grow through mulch can be manually removed. Discs, harrows and shallow rototillers can be used with care so as not damage feeder roots near the surface. Chemical weed control is expensive on large areas. Intercropping can reduce difficulties with weeds and provide further income. A pre-emergent weed control can also be used.
Soil testing each year will indicate the level of phosphorous and potassium required. Visible symptoms of nutrient deficiency include off-colour foliage, poor shoot growth, insects and disease. Fertilizer is not required in the first year. In the following years commercial fertilizer 10-lO-10 can be applied in the spring somewhat beyond the spread of the tree and not too near the trunk. A suggested rate is one half kilogram per three centimetre of tree diameter. Manure can be applied instead of the commercial fertilizer. Nutrient value of manure is harder to determine, though testing can be done on manure samples.
Pruning is necessary to develop new wood; maintain vigour and fruitfulness of spurs; control the size of trees; remove dead or diseased branches and direct the framework of tree to support nuts and ensure ease of nut removal (Gardner, p. 25). When both timber and nut production is desired pruning results in a long trunk and large full crown. Pruning is done after the spring sap run is over to avoid sap bleeding. With timber production in mind one central leader is desired early in the trees growth (2 or 3 years after planting), other potential leaders being cut back to avoid competition. Lower branches should be pruned before they are two inches in diameter just to the outside of the growth rings to ensure a knot free wood. This type of pruning is done until the trunk is a least 3 meters high for veneer log or about 6 meters high for timber. Pruning in the crown results in the removal of narrow branch angles and the spacing of main branches on the trunk to be alternate so no two are at the same level.
Specific information is not available on growing bur oak for veneer quality wood. The information available is on the general principles of central leader pruning of hardwood (Leuty).
The scarceness of white oak is obvious when attempting to find information on harvesting for its wood. List of wood prices from a number of mills did not provide prices for white oak. The criteria for red oak may provide the closest comparison and is included here.
The criteria for harvesting red oak for veneer quality is specified by each mill. The following are the specifications from the Agawa Forest Products Ltd. (Agawa Forest Products). What is obviously lacking is an idea of the number of years the bur oak would have to grow to obtain the desired height and diameter.
|Grade 1||14 " and up straight and clean;|
no surface defects
|Grade 2|| 12" and 13" no surface defect and straight;|
14" and up with one 3" surface defect;
no seams permitted
|Grade 3||11 " butt log with no surface defects and straight;|
12" with one 3" surface defect - 10% sweep allowed;
13" and up with two 3" defect - 10% sweep
|Other features-no star heart,worm holes, bird pecks; 12" may have 3" max. end defect if well centred; all logs must be fresh cut and well trimmed|
Presently as there is no North American market for acorns, harvesting equipment specific to acorns does not appear to exist. Nuts that are presently harvested in large quantities have various methods of collection based on the ease or difficulty at which they detach from the tree, if the nuts are clustered, do the nuts fall away from their covering, etc. Available are equipment that shake nuts from the tree, self-propelled vacuums and sweep conveyor-type harvesters that are capable of separating husk and chaff from nuts. Knowing the qualities of the bur oak as well as other white oak will help to determine the type of equipment needed. Bur oak fruit drop in the year of growth and will begin germination soon after falling. The nuts will need to be picked up soon after falling or shaken down. They are best eaten fresh so processing must occur soon after harvesting. This is all speculation and will require research if the industry is to develop.
Disease and Pest
Bur Oak, as with most nut trees, are generally quite resistant to disease. Two visible effects of pest on the bur oak as well as other oaks are oak galls and shredded leaves.
Oak Galls are formed by infestation of gall makers. There are hundreds of different types of gall makers including gall wasps, midges, aphids and mites. The tree is stimulated by the presence of these organisms to produce abnormal plant cells that serve as protection for the pests. The inner wall of the galls provide a source of protein for the young larvae. The appearance of galls varies in the size, colour, shape and hairiness. The variation depends on the type of gall maker infecting the tree. The galls are obvious growths on tree branches detracting from the overall appearance of the tree. The tree is usually able to withstand the presence of galls and maintain its health. The galls protect the developing pests so insecticides are unable to reach them. Twigs and branches that have galls can be removed and destroyed (Turner, p. 36). The picture shows galls found on a local bur oak
Galls on bur oak branch caused by unknown insect.
Oak Leafshredder, Croesia semipurpurana, is a pest that effects red oak and other oak species. It is able to cause severe defoliation that if it occurs over a number of years can cause the decline in the trees health and in the presence of other stresses such as drought the death of the tree (Grant, P. 149). The eggs, which over winter in leaf debris, batch in April and early May when the leaf buds begin to swell. The yellowish-brown larvae bore into the bud and feed at the folds of the leaf margin or on leaves that it attaches by strands of silk. The leaves appear very much like they have been shredded. The photosynthetic capacity of the leaf and the over all tree is reduced. In the fourth stage of development the pest, referred to as an instar, lowers itself to the ground and forms a pupae in the leaf litter. After about 10 days small yellow moths emerge. Four weeks later the moths lay eggs in the apical of the branch amongst the nodes or bark. Over wintering occurs and the cycle begins again.
The bur oak cuts a majestic form on the landscape. Within forests and woodlots it is a favourite nut for wildlife. Where present it is a valuable source of lumber. The presence of bur oak has declined over the years due to overcutting. However, as a native tree that has proven itself hardy both as a producer of nuts and a lumber tree, it is worthy of consideration for planting for both of these values. Its slow growing habit is a discouraging factor when considering growing a plantation. There is however our children and our children's children that can benefit from the foresight that tree growers show today.
1) Agawa Forest Products Ltd, 45 Third Line West., Sault Ste. Marie., Ontario.
2) Asmus, Ken. (1989) Oaks for Edible Acorns. St Catherine: 80th Annual Report of the Northern Nut Growers Association.
3) Bainbridge, D.A. (1991) The Oaks. 82nd Annua1 Report of the Northern Nut Growers Association. Corvallis: Oregon State University.
4) Beattie, Mollie and Charles Thompson and Lynn Levine. (1983) Working with Your Woodland. Hanover: University Press of New England.
5) Farrar, John Laird. (1995) Trees in Canada. Markham: Fitzhenry & Whiteside Limited.
6) Fowells, H.A. ed. (1965) Silvics of Forest Trees of the United States, Washington D.C; U.S. Department of Agriculture.
7) Gardner, J.O. ed. (1992) Nut Culture in Ontario. Toronto: Queen's Printer for Ontario.
8) Grant, G. G., et al (1995) Oak Leafshredder, Croesia semipurpurana. Forest Insects Pests in Canada. Ottawa: Canadian Forest Service.
9) Lauriault, Jean (1989) Identification Guide to the Trees of Canada. Markham: Fitzhenry and Whiteside.
10) Leuty, Todd. Central Leader Pruning for Hardwood Trees. Ontario Ministry of Agriculture, Food and Rura1 Affairs.
11) Light, Bobby. White Oak. Internet/World Wide Web http://www.forestry.auburn.edu/coops/sfnmc.
12) Oikos Trees Crops. P.O. Box 19425, Kalamazoo, MI, USA 49019.
13) Prairie Farm Rehabilitation Administration. 1993 Report of the PFRA Shelterbelt Centre. Indian Head, Saskatchewan: Agriculture Canada.
14) Reed, Clarence. (1958). The Improved Nut Trees of North America and How to Grow Them. New York: The Devin-Adair Company.
15) Schaefer, Mark (1988) The Nut Growers Manual for Eastern Ontario. Ottawa Chapter of the Society of Ontario Nut Growers.
16) Shigo, Alex L. (1994) Tree Anatomy. Littleton.
17) Sternberg, Guy and Jim Wilson. (1995). Landscaping with Native Trees. Vermont: Chapters Publishing Ltd.
18) Turner, K.B. et al. (1975). Common Pests of Ornamental Trees and Shrubs. Ontario Ministry of Natural Resources.
"Species Profile of Bur Oak"
A paper submitted by
Mary Ann Riley
in partial fulfilment of the requirements for the course
at Kemptville College of the University of Guelph
APRIL 3, 1997
Instructor: Dave Chapeskie