D. Andrew White M.Sc. 09/30/2009
Climatic factors have the greatest overall influence on soil structure and composition. Climate largely controls organic matter production and its rate of decay. Climate also influences the rates of erosion and leaching. Nevertheless, the parent material from which the soil derives does have some influence on the types of plants the soil can support. Vegetation type has a very large impact on the kind of soil. However, the vegetation to a large extent reflects the climate.
Soils are generally profiled in terms of their three prominent horizons: A, B and C. The 'Aoo' layer is basically dead plant material, or mor, before it has been mixed into the soil. Whereas the 'A' proper is the upper layer of the soil itself. Soil layers are often visible as the gradation between the dark humus rich 'A' surface layer and the 'C' layer, which is composed mostly of parent material sans humus. Bedrock, or other base material, composes the 'D' horizon. Below, are some examples of common soil orders found in eastern Canada. They are here named according to the Canadian System of Soil Classification. The FAO Unesco system is very similar to the Canadian. The USDA & Soil Survey's system is somewhat different.
Ontario’s boreal forests are typified by the Brunisolic and Podzolic soils. Brunisol is a fairly rich brown soil, that corresponds to the FAO's 'Cambisol' Order. Brown soil is commonest in the more arid west side of Ontario. The leached podzolic soils are more prevalent in the humid east. Luvisolic soils occur mostly in the Carolinian Forest zone. These are the soils with clayey bases and fairly rich humus. They have been heavily exploited as cropland. Near the Lake Erie shore the sandy Gleysolic soils are fairly common. These sandy loams can be excellent soils for crops. Most of Ontario's orchards and vinyards grow on Gleysolic soils.
A few of the tropical soils are similar to soils elsewhere. The tropical brown soils are basically similar to temperate Solonetzic, Luvisolic and Gleysolic soils. The podzolic soils occur in the tropics also. However, some kinds of tropical soils are quite distinctive. One common trait of tropical soils is that the humus rots-away fairly quickly. Basically, decomposition is more rapid in warm and wet climates. One common feature of these soils is that they tend to range from red to chestnut-brown in colour. These colours are due to the soils generally being very old and leached-out.
Where there is constant rainfall, both the carbonates and finer silica clays to leach away. This makes the 'laterites' reddish, as the less-soluble sesquioxides that are left-behind are often quite reddish (Ferralsol). If there is a long dry season, the leaching may not be too extreme. The soils in drought-then-monsoon prone places do tend to retain a fair bit of clay. These are the soils that crack into hexagons and crevasses during the dry seasons. Such 'black earths' are more likely to be dark coloured, at least under the surface (Vertisol). There are in-between soils. Some of the tropical soils are leached and clayey. They tend to be reddish-brown. These soils grade from chestnut-brown to quite red versions (Nitisol). These in turn garde into the true 'red clay' soils (Acrisol). These semi-leached red clay soils are common in the tropics and in the warmer temperate zones.
Brown soils and red soils are similar to what in the USDA system are considered to be the ‘Alfisol’ Order. These soils are sometimes called ‘Nitosols’, but the proper FAO name is now ‘Nitisol’. They resemble Solonetz and Luvisol, in that they have both a clayey and carbonate laden base. They are called 'terras roxas' in parts of Brazil. In Australia they are sometimes called 'red earths'. Being among the best agricultural soils, they are now heavily exploited. They are another example of how humans have changed nature. Pristine examples of these riparian soils are becoming increasingly rare.
The first fully scientific soil classification systems were developed in the USSR. Soil scientists (pedologists) often named the great soil groups and orders in the Russian language. Dark prairie soil for example, is called chernozem, the Russian name for ‘black earth’. Parkland soils sometimes have a carbonate, or even salt, hardpan layer under the humus. This kind of soil is called solonetz, after the Russian word for ‘salty’. Even the common word podzol is a Russian term describing the ‘ashy’ colour of the lower-layers in such soils.
Podzolic soils occur mostly under woodlands, in fairly moist climates. In these soils, the upper ‘A’ layers are can become quite leached out. It is largely the acidic nature of the surface humus that decelerates decay. But the ample rain allows some leaching to occur. Leaching accelerate the removal of clay particles and soluble minerals from the surface to the lower ‘C’ horizon. The less soluble sesquioxides of iron and aluminium are left behind in the ‘B’ layer. This causes the orange or reddish appearance of the ‘B’ horizon (Podzol). The 'C' layer can accummulate the leached materials. Sometimes even this layer becomes partly leached-out. Mostly podzols occur under pine forests, but other kinds of sub-humid forests can also develop podzolised soil.
Something like podzolisation can occur in the rainy tropics. In these environs, leaching can take the soluble minerals deep into the soil, even leaching the ‘C’ horizon. Often this results in ‘red clay’ soils - which still have a fair amount of clay (Acrisol). Taken to an extreme, laterites or latosols can form. These laterites are very reddish in colour. These soils even are short of clay - i.e. the finer silica particles are largely leached out. The clays of aluminium and iron sesquioxides remain. This makes the soil quite reddish (Ferralsol). Such soils can harden into a rock-like crust - if they are allowed to dry-out. These reddish soils are usually very infertile for plants. In rainforests the tree roots are largely confined to the surface layer of humus.
Rainwater is a mild solution of carbonic acid (H2CO3).
Upon contact with a mineral surface this acid dissolves alkali and alkaline elements to form carbonates
MgCO3 & CaCO3).
The alkali halides or 'salts' (NaCl & KCl) can also form via this rainwater action.
Therefore, while rain tends to drive soils toward the acidic range (low pH), electropositive ions tend to force the soil to become more basic (high pH).
Organics: Trees generally grow best when the organic content of the ‘A’ and 'B' horizons are at least three percent (3%). Usually, the more humus the better the soil is for plants. (Within limits.) Where humus accumulation is extreme, the milieu can become very acidic. In such soils, the cation exchange capacity can become too low for proper plant growth. This excessive acidification tends to happen mostly in bogs, muskeg or other unusual situations. Thick soils in the Organic order (Histosols) are more likely to lack sufficient amounts of the heavier nutrient elements. After many generations of plants growing on dead plants, the lighter elements can be lost faster than they are added. The other elements can become diluted as the mass of dead plant tissue expands. Bog soils may even lose so much phosphorus over time that they become very poor at supporting plant growth.
Sand: Sand is composed of small (2.0-0.05 mm) particles of assorted silicates. Often these grains are dominated by quartz. Quartz has a low solubility in water. It is the most common mineral ‘left behind’ when granite erodes. Course quartz sand has a very low capacity to hold ions. Sand can easily loose plant-useable ions to leaching. On the plus side, sand does allow for the diffusion of both air and water through the soil.
Silt: Silt is composed of medium sized particles (0.05-0.002 mm). These grains often consist of assorted silicates, such as feldspar, mica, and quartz. Silt has a medium ability to absorb ions. It has a fairly good porosity, and allows for fairly good diffusion of air and water through the soil.
Clay: Clay is composed of very fine particles ( <0.002 mm). Clay is composed predominantly of mica crystals and other aluminium silicates. These particles are the fine debris from erosion upstream. These flecks are generally carried long distances by water prior to being deposited. These tiny flake-like particles have a very high cation exchange capacity. The mica crystals hold plant-useable ions very well. On the downside, clay is relatively impermeable. Air and water do not move well through compact clay.
Loam: Loam is a mixture of silt, sand and clay. Loamy soils are generally better than other soil textures for supporting plant growth. Such soils are preferred for both agricultural and silvicultural purposes.
Solod / Solonetz: Sometimes in very arid environments, with intermittent rains, carbonates are carried into the deeper soil layers by water. Without a sufficiently constant water flow these carbonates can build-up into concretions in the C horizon, or lower. Significant accumulations of salt can also build-up in semi-arid regions. Often the alkaline layer is deep enough not to greatly harm plants. In fact, the upper layers can have near neutral pH levels (~ pH 7). Mildly basic upper soils layers are actually beneficial. Higher pH levels tend to make many ions more mobile, and more plant-useable. Chernozemic soils have such a limey layer, although it is not as extreme as it is in Solonetzic soils. Solonetzic soils are extreme versions of carbonate enriched soils. These soils may even have carbonate concretions in their 'B' horizon. Such soils are called 'solods'.
Tufo: Tuff or tufo is basically volcanic ash. The particles start out in assorted sizes (c 2.0-0.002 mm) and of assorted minerals. Tufo is mineral rich and it is a fertile base for agricultural soil. However, it eventual leaches and erodes into more ‘normal’ soil. In Ontario tufo has, for the most part, long ago been degraded.
Loess: Loess is a kind of fine sand and clay mixture. It is composed of very fine particles of quartz, mica and other common minerals. Loess makes a good base material for fertile loam soils. These deposits originated from windborne dust, i.e. they are basically aeolian dust. The dust came mostly from the exposed barrens left after the retreat of the glaciers - after the last Ice Age. Thick loess deposits occur mostly south of the Great Lakes, and not so much in Ontario.
Till: Till is composed of assorted rubble, varying from erratic boulders, to gravel, to sand and even silt. Drumlins and moraines are composed of this ‘glacial till’. In Ontario till was mostly produced by glacial action during the last Ice Age. Till is common around the southern rim of the Canadian Shield.
Mineral Nutrients: Mineral elements play a crucial role in plant health. Nitrogen, phosphorus and potassium are the mineral nutrients most commonly lacking in soils. In certain soils essential nutrients may be in forms that are not plant-useable. Sometimes minerals are rendered unavailable to plants because of low pH, or some other factor.
Agriculture Canada. 1987. The Canadian System of Soil Classification. Second Edition.Canadian Government Publishing Centre. Ottawa.
Gourou, Pierre. 1982. Terres de bonne espérance - le monde tropical. Édition Plon. Paris. pp 89-97, 192-196.
Eyre, S.R. 1968. Vegetation and Soils - a world picture. Second Edition. Aldine Publishing Company. Chicago.
Sims, R.A., Kershaw, H.M. and Wickware, G.M. 1990. The Autecology of Major Tree Species in the North Central Region of Ontario. COFRDA Report 3302, NWOFTDU Technical Report 48. Ontario Ministry of Natural Resources. Thunder Bay.
Pender, Terry. 2003. Our Stressed-out Trees. Ontario Arborist. International society of Arboriculture. 31(6): 10-12.
Soil Nutrient Deficiencies
The elements nitrogen (N), phosphorus (P) and potassium (K) are the mineral nutrients most commonly lacking in soils. Generally this is not because they are totally absent, but rather because they are in a form unusable by plants. Nutrient deficiencies often have tell-tale symptoms in plants. Most of the essential nutrient elements are in the 'upper' part of the Periodic Table. Some elements are essential, and are necessary for the production of proteins, carbohydrates, lipids and nucleic acids. In particular, hydrogen (H), carbon (C), nitrogen (N), oxygen (O) and phosphorus (P) appear to be necessary for all known life forms.
Biological Periodic Table
In the tables below, the 'Symptom' boxes refer to a plant's symptoms when the element is lacking or less than optimal. The 'Physio' boxes indicate what physiological role the nutrient has for plants.
Plants require some of the transition metals as components of their enzymes, co-enzymes, proteins and other important metal-organic compounds. Cadmium, palladium, silver, mercury and even tungsten are used by some organisms. Higher plants do not seem to require most of these metals. Nevertheless, some transition metals are essential for plant metallo-enzymes. Some of the transition metals required by plants include:
Plants require oxygen for respiration, just as animals do. Usually photosynthetic plants liberate more oxygen than they consume, and they absorb more carbon dioxide than they 'exhale'. But plants do 'breathe'. The roots of a plant absorb oxygen from the air for respiration. Respiration in plants is often quite localised, tissues obtaining it from the nearest source. For most trees this oxygen diffuses through the spaces between soil particles. Which is why soil should not be compacted or waterlogged. Plants have a difficult time growing in soil with a low porosity. Filling these spaces with stationary water can also cause problems. If the water is too immobile the dissolved oxygen can be used up by respiration and the water around the roots becomes anoxic (no oxygen) or hypoxic (low oxygen).
Most municipal forestry services have explicit prohibitions of grade modifications in or around city trees. I have seen trees die because of as little as six centimetres of clayey luvisolic soil piled over their root-systems. Even the standard practice of raising grades with light sand does not always work. Sometimes trees do not survive even the best planned grade modifications.
Fertiliers should only be applied if they are actually required. It is important to diagnose soil nutrient problems correctly before applying fertilisers. When trees flush in the spring they tend to use as much of their stored carbohydrates for shoot elongation as they can afford. If the soil is richly endowed with nutrients, a tree can act as if these nutrients surpluses are going to persist throughout the season. When the nutrient surplus in the soil is exhausted, the tree suddenly has to revert to normal rates of growth. Excessive fertilisation can raise the proportion of shoot growth, at the expense of the root growth. Excessive shoot elongation can also come at the expense of the production of protective chemicals. In other words, too much spring fertiliser can cause trees to be less drought-hardy, and less resistant to parasites and herbivores.
Atkins, P.W. 1995. The Periodic Kingdom. BasicBooks. New York.
Daniel, W.D., Helms, J.A. and Baker, F.S. 1979. Principles of Silviculture. McGraw-Hill Book Company. New York.
Emsley, John. 2001. Nature's Building Blocks - an A-Z guide to the elements. Oxford University Press. Oxford.
Morrison, R.T. and Boyd, R.N. 1980. Organic Chemistry. Allyn and Bacon Inc. Boston.
Scharenbroch, B.C. and Lloyd, J.E. 2004. A literature review of nitrogen availability indices for use in urban landscapes. Journal of Arboriculture. 30(4): 214-230.
Smiley, E.T. and Shirazi, A.M. 2003. Fall fertilization and cold hardiness in landscape trees. Journal of Arboriculture. 29(6): 342-346.
Struve, Daniel K. 2002. A review of shade tree nitrogen fertilization research in the United States. Journal of Arboriculture. 28(6): 252-263.
Watson, G.W. 2002. Soil replacement: long-term results. Journal of Arboriculture. 28(5): 229-230.
When a tree is drought stressed they first conserve water by holding it back from their leaves. This causes semi-wilting, and eventually dying of the leaf margins. Water translocation is more difficult to outer twigs. Thus drought stress is first manifest in the upper crowns. As the stress gets more severe upper leaves may fall, and buds set, similar to the physiological preparations for autumn. Early leaf fall may means that there are too few hours of photosynthesis. Photosynthates stored in the roots and stem may not be enough to survive the winter. More importantly, if the water reserves in the soil are too low to last the winter, the tree may be stressed again in the spring. Consequently, the tree may die from the water stress disorder, and its ramifications.
Trees that show signs of drought stress can be watered. It is not a good idea to let the water run all night. Nor should one continue watering if the soil is saturated to the point of being muddy, or if it is pooling. Conserve water, water only the trees showing obvious signs of drought stress. The stressed tree is probably stressed because of local drainage conditions, or because it is a sensitive species.
The cambium of dicot trees usually grows in two directions. The inner layer produces xylem (wood), the outer produces layer phloem (bark). Thus wood is oldest on the inside, and bark oldest on the outside. Stems that grow at small angles to each other can produce bark surfaces that press against each other. Such areas of apressed bark often occur in narrow branch crotches. Bark inclusion can also occur between two trees which are closely appressed together. In both cases the two bark layers can prevent the two stems from ever fusing together. The seam that forms along this bark inclusion is structurally weaker than normal wood.
Large branches that break during windstorms often break along the seam of bark inclusion. Likewise two individual trees with a seam of included bark between them can be very dangerous. Sometimes such trees have two totally independent and lopsided root systems. Such half-circle root spreads are very unstable. It matters little whether the two trees were always separate individuals or if they were clones. If their roots are disconnected they are risk trees. Trees with a seam of included bark that start at ground level are especially hazardous. In public places one or the other of the twin stems should be removed before the trees become too large. Such trees should be monitored, or an arborist's appraisal should be sought. Sometimes cable bracing can be installed to prevent the crotch from splitting.
Too often trees planted from nursery stock develop 'root girdling'. This girdling is caused by roots growing tangentially to the trunk. Eventually the 'sideways' growing roots can conflict with the outward growing trunk. With time this can strangle the xylem cutting off sap flow. This manifests itself as a generalised decline with branch dieback and necrotic shards in the trunk.. Strangely, root girdling can manifest itself decades after planting. Sometimes a whole set of trees from the same nursery succumb to girdling within a short span of a decade or so.
Girdling is often the result of nursery trees being left too long in their growing container. Girdling can be caused by the fine roots growing tangentially along a container's inner wall. When these rootlets enlarge, they can become girdling roots. Sometimes the offending root can be seen bulging-up near the base of the tree. One remedy is to dig up the soil around the root, if it is visible, and cut-out the girdling section. The bark and cambium of the trunk should not be harmed - if possible. This solution has a chance of efficacy if only a few of the tree's major roots are causing the girdling. Still, the tree may die from root loss. (This cheapo solution is worth a try. In my humble opinion.)
Buszacki, Stefan and Harris, Keith. 1998. Pest, Diseases & Disorders of Garden Plants. Harper Collins Publishers. London. 598-599.
Ontario’s Oak Savannah
Oak openings, oak opens, oak parkland, oak woodland and oak savannah are several names for a recurring vegetation type. There is a strange similarity between forests on a rocky alvar in Pelee Island, the woodlands of Ontario’s Pinery Provincial Park, Toronto’s High Park, the oak openings of Missouri, Oregon’s ‘oak savanna’, and even the dry montane forests of Honduras. These places look very much like the forest-steppes of Eurasia. The mature forests have an oak dominated canopy, often interspersed with pine, and generally an open tallgrass under-storey. Basically, these woodlands look like some kind of savannah.
Oak openings occur in areas that are either semi-arid, or where the soil is periodically dry. These kinds of growing conditions occur mostly in the prairies (i.e. steppes) or on the margins thereof. In Ontario, oak openings are commonest on old dunes, in sandy barrens, or on rocky alvars. It is not always a lack of rain per se that explains oak openings. Many species of oak (Quercus spp.) are well adapted to dry spells. This is why oaks often occur where it is too dry for other kinds of trees. It also explains how they can live on soils that are dry because of rapid drainage – even if there is a lot of rain.
Oak openings are a kind of the ‘parkland’ or ‘forest-steppe’ vegetation. Oak openings grade into aspen parkland in the north. To the south, the oak openings tend to grade into pinewoods or flatwoods. In these parklands the tree roots spread broadly, and the root and crown competition tends to suppress the smaller groundcover plants. In many parkland areas ground-fires were once fairly common. These fires also helped to clear the groundcover.
In the American Midwest, burloak (Quercus macrocarpa) and chinkapin oak (Q. muhlenbergii) can dominate the oak openings. In the eastern Great Lakes area, it is black oak (Q. velutina) that is most dominant. There are oak openings on the margins of the palouse prairies in the Plateau Country of the western USA. Garry oak (Q. garryana) is common in these parklands. In the mid-latitudes of Eurasia, the pollardo oak (Q. robur) and durmast oak (Q. petraea) are very common forest-steppe species.
Believe it or not, outliers of prairie once extended into southern Ontario. They differ from the full-prairies in that Ontario is rainier. The Great Plains can have between 100 mm and 500 mm of rain per year Whereas, the driest corner of southern Ontario usually has at least 600 mm of rain per year. These outlier grasslands usually have light-brown soils, and not the dark-brown soils of the Great Plains. It is the sandy soils that seem to encourage the tallgrass - not the climate per se. A few remnants of this tallgrass ‘prairie’ still exist in the Windsor-Essex to Pelee corridor. A mixture of tallgrass and savannah also used to stretch between Long Point and Brantford. Similar vegetation could be found from Toronto's lakeshore to the environs of Rice Lake. Oak openings were most common near these patches of grassland. Human activities, of course, have vastly reduced the oak openings as well as the tallgrass prairies. By some estimates, less than 0.1 percent of this forest-stepe vegetation still exists in Ontario.
The best examples of tallgrass prairies occur near Lake Huron and Lake Erie. An especially intact example of this grassland occurs in the Pinery Provincial Park, on the Huron shore. These areas are dominated by robust grasses with wide spreading mats of rhizomes. These tallgrasses can grow upwards of two metres tall. The coastal sand dunes are often colonised by switch grass (Panicum virgatum). Indian grass (Sorghastrum nutans) occurs on more established sandy areas. Little-bluestem (Andropogon scoparius) and big-bluestem (A. gerardii) grasses are also fairly common. These species also occur in the eastern side of the Great Plains. Though, of course, the real prairies have a broader range of species.
In sundry parts of the world one can find forest tracts wherein most of the canopy trees are pines (Pinus). Enigmatically, sometimes these forests seem to have little in common, except for the fact that pines are one of the dominant plants. The hard needled pines are pre-adapted to periods of water-stress. This is why pines are especially common on barren-lands. They can retain their water very well during droughts. Furthermore, being evergreen they can also take advantage of short growing seasons. This is why pines dominate in both the high boreal forests, and in the dry parklands to the south. Paradoxically, high alpine forests can also be pine dominated. This is because of the rapid drainage and the short growing-hours during the day.
In the highlands of Mesoamerica and in the Greater Antilles pinewoods are common (eg. P. caribaea). Oaks and palms often occur along with these pines. From Alberta to Quebec, jack pine (P. banksiana) parklands occur in the dry barrens of the boreal forest. Southern Ontario has a few white pine (P. strobus) dominated stands in the sandy barrens along the Lake Huron shoreline. In the southern USA the ‘southern pines’ are a common sight (eg. P. palustris). In northern Florida these pine-parklands are called the ‘flatwoods’. Similarly, open forests dominated by Aleppo pine (P. halepensis) can occur in the drier parts of Mediterranean Europe. These pinewoods are most common on limestone alvars or on sandy barrens.
The secret of all of these pinewoods is the pines themselves. Pines are, in general, tolerant of water-stress and they are tolerant of short growing-periods. Pines have some water-retaining and drought-resisting traits in common with succulents. Thus it is not surprising that semi-arid forests and parklands tend to support pines. At the same time, very cold locals can also become dominated by pines. This is true in the far north, with its short growing season. It is also true in alpine locals, where the growing-period of the day is short. Cold air can also desiccate plants. Both arctic and alpine plants need to be tolerant of water-stress. Pines are paradoxical plants.
Pines can tolerate dry conditions, and junipers more-so. Junipers, and to a lesser extent thujas and pines, are said to have ‘sclerophyllous’ features. This means that these plants loose relatively little water through transpiration. The leaves have thick cuticles, few stomata, and small surface. The leaves may also be closely spaced, so as to cover a greater surface area on the twig. These features may hinder photosynthesis to some extent. Nevertheless, they also help the plants to retain their water in habitats that are often extremely arid.
Juniper woodlands tend to occur in the transitions between montane forests and the drier rain-shadows. Such is the case on the east sides of the Santa Ana, Sierra Nevada and Cascade mountain ranges. In the subalpine forests one may find stunted whitebark pine (P. albicaulis) or limber pine (P. flexilis), firs and other conifers. The limiting factor is daily temperature, not rainfall. Lower in the montane forests, between 2700 and 3200 metres altitude, there occur tall forests of ponderosa pine (P. ponderosa), Douglas fir (Pseudotsuga menziesii), and other conifers. These montane forests have adequate rainfall (250-1000 mm/yr), at least during the winter months. The rain-shadow vegetation varies more greatly with latitude. East of the southern Sierra Nevada and Santa Ana mountains the montane forest grades into juniper-pinyon pine woodland. Further down-slope, the juniper-pinyon pine woodlands grade into the Mohave Desert. This is the desert with the diverse cacti and yuccas. At the north end of the range there are colder winters, and somewhat more rainfall. In the Cascade Range the rain-shadow woodlands are dominated by a mixture of junipers, pines and oaks. These dry-woodlands grade eastward into the grass dominated Palouse prairies. In all of these places the foothills have a sort of lower 'tree-line'. There is an altitude below which trees give way to scrubland and/or grassland.
It is on the east side of Sierra Nevada range that juniper woodlands are most fully developed. Western juniper (J. occidentalis) dominated forests grade into Utah juniper (J. osteosperma) woodlands. These Utah junipers are widely spaced, due to root competition and the poor Regosolic soils. Below about 1500 metres altitude, with less annual precipitation (100-200 mm/yr), these scrublands become nearly treeless. Sagebrush (Artemisia tridentata) and other sclerophyllous shrubs dominate in the chaparral lands of the Great Basin. Oddly, there are relatively few cacti in these scrublands.
In Ontario there are no chaparral lands or scrublands per se. Nevertheless, on extremely sandy slopes, or on thin soils, junipers and white cedars can come to dominate. In places where there were formerly sand dunes, white cedar (Thuja occidentalis) can form almost pure stands. Thujas can tolerate rocky or sandy soils with very little humus. On rocky alvars, or on eroded clear-cuts, red-cedars (Juniper virginiana) can be the dominant tree. Old fields and eroded roadsides are often be colonised by stands of common juniper (J. communis). One subspecies of common juniper (J. communis var. depressa) grows as a ground-hugging shrub. The creeping juniper (J. horizontalis) is a prostrate shrub. Both kinds of ground-juniper are common on rocky shorelines within the Canadian Shield. In these cases some scrubland-like features exist on account of the poor drainage conditions. The soil in these areas does not retain rainwater very well. These areas are, in effect, little pockets of scrubland within the lush forests of the East.
Easterly, Nathan William. 1979. Rare and Infrequent Plant Species In the Oak Openings of Northwestern Ohio. Ohio J. Sci. 79(2): 51-79.
Eyre, S.R. 1968. Vegetation and Soils a world picture. 2nd Edition. Aldine Publishing Company. Chicago.pp 118-121.
Munz, P.A. 1963. California Mountain Flowers. University of California Press. Berkeley.
Petrides, G.A. and Petrides, O. 1992. Western Trees. Peterson Field Guide Series. Houghton Mifflin Company. Boston.
Szeicz, J. M. and MacDonald, G. M. 1991. Postglacial vegetation history of oak savanna in southern Ontario. Can. J. Bot. 69(7): 1507–1519.
Tallgrass Ontario. 2009. Ontario Tallgrass. The Prairie and Savanna Association: www.TallgrassOntario.org.
Web page designed by D. Andrew White M.Sc.©
MM anno domini