TAIGA BIOLOGICAL STATION
FREQUENTLY ANSWERED QUESTIONS
INTRODUCTION | OBITUARY for DR. WILLIAM O. PRUITT, JR
Updated March 23, 2010
Because we receive so many questions from students who have been assigned the "Taiga" as a class project or a subject of inquiry, the following exposé has been developed in an attempt to answer some of their questions and to generate further study.
"Here in the northern forest we can see the direct effects of physical factors on organisms, we can unravel the simplified food web and examine the component food chains, we can see and experience directly the effects of seasonal changes in light. A number of ecological principles are put on display in graphic clarity. In the taiga, students of ecology can easily grasp the fundamental concepts of the science as they are laid bare around them."
William Pruitt, "Wild Harmony"
1. What is the "taiga?"
The boreal forest is the taiga. Originally a Russian language word meaning "a marshy forest in Siberia" the word has come to mean the circumpolar coniferous forest. It is the same level of general ecological classification as "tundra" for the land beyond the poleward limit of trees or "steppe" for grasslands or prairie. Between the taiga and the tundra is a transition zone or ecotone of varying width, sometimes as much as several hundred kilometres. This is the forest-tundra. Forest-tundra can occur in two different aspects. There may be scattered trees, with shrubs between, or there may be isolated bits of forest in protected sites. I differentiate between taiga and forest-tundra by restricting taiga to be where a red squirrel (Tamiasciurus) can travel from tree to tree without having to come down to the ground.
In the south, the edge of the taiga is more difficult to define. Here the coniferous forest intergrades with a complex of vegetation types - northern hardwoods type, prairie type through the forest-steppe or aspen parkland type and many interdigitating types in the mountains.
Because the dominant trees are conifers, particularly spruce, the general aspect of the taiga is essentially the same wherever it is found: spire-like spruces against the skyline, lumpy pines, with feathery larches, white-barked birches and dense stands of alders, together forming a mosaic pattern when viewed from the air. The climate, soils, plants and animals are an interacting fabric that is distinct from other associations adjacent to it. Although there are a number of important regional variations to the taiga, they are but phases of what is obviously the same biotic association.
The taiga consists primarily of highly resinous coniferous trees and is, therefore, extremely susceptible to fire. Although wildfire was a regular occurrence in pre-contact times in North America, since the taiga was invaded by European cultures the frequency of wildfire has increased enormously. In interior Alaska about three-quarters of the spruce-birch taiga has burned and in other regions of North America such as northern Saskatchewan virtually all of the spruce taiga has burned. In northwestern North America the taiga characteristically regenerates through stages of fireweed (Epilobium), birch (Betula) and aspen (Populus tremuloides), but on the Canadian Shield after spruce taiga is destroyed by fire jackpine (Pinus banksiana) stages persist for many, many years. Alders (Alnus) frequently form impassable chaparral-like thickets. Here they function as nitrogen-fixers.
An important aspect of taiga vegetation is the presence of berry-bearing shrubs. Such plants as blueberry (Vaccinium), high-bush cranberry (Viburnum), low-bush cranberry (Vaccinium vitis-idaea), crowberry (Empetrum), cloudberry (Rubus chamaemorus) and rowan (Sorbus) are important in the lives of taiga birds, mammals and people.
The taiga is truly vast in extent. It makes up 27 percent of the world's total forest or 17 x 106 km2 and occupies 11 percent of the land area of the Northern Hemisphere. In North America north of Panama the taiga occupies 17 percent of the land area of the continent. Eighty-three percent of the total taiga is in Alaska, Canada and the former USSR.
The Siberian taiga is the largest forest in the world, stretching some 5,700 km from west to east and some 1,000 km from north to south. In North America the taiga encompasses area extending some 6,200 km from west to east and 500 to 1,000 km north to south.
In North America taiga meets tundra at the base of the Seward Peninsula in western Alaska, sweeps across the continent, swinging south of Hudson Bay and encompasses most of the island of Newfoundland. In Eurasia it begins in Norway, encompasses most of Sweden and Finland, then sweeps across Russia to Chukotka.
Taiga is trees, mainly evergreen trees. This is more than a statement of the obvious because the tree growth habit influences many aspects of the ecology of northern regions. The usual reason given for most northern trees being evergreen is that there is not sufficient time to grow leaves afresh every spring. It is true that in evergreens photosynthesis can proceed immediately the leaf achieves some minimum temperature, but then why don't larches have evergreen needles? And why are birches and aspens so successful in the taiga?
As far as snow cover is concerned, there are two main classes of trees in the taiga. The spruces and pines stand straight and tall and are relatively stiff. The spire-like outline, the downward sweep of the lower branches, combined with (or perhaps because of ?) the heritage character of evergreen foliage, enables the spruce to exist even though for long periods of the year it may be loaded with masses of snow or qali. They resist qali. Birches and alders and young aspen, on the other hand, lose their leaves, and their twigs and branches are remarkably limber and bend beneath the load of qali but recover in the spring. The limber alder bends nearly flat under its load of qali, but the following spring resumes its upright posture.
Because the angle of incidence of the incoming solar radiation is low, twilight lasts many hours in the taiga. Long summer mornings and afternoons when the low-lying sun shines under the canopy of spruces are characteristic, as well as long periods of twilight in the winter when, even though the sun itself has dipped below the horizon, there is light sufficient for small birds to feed. Moreover, in the winter, when the solar radiation is restricted, there is a cover of snow to reflect what available light there is. Therefore the yearly total of effective visible light in the taiga is probably more than in other ecological associations on earth.
While the annual temperature regime of the taiga may vary widely from place to place, certain patterns are characteristic of this ecological association because of its general geographical position. During the long days of summer the temperature is strongly influenced by the incoming solar radiation and may fluctuate accordingly. During the short or non-existent positive radiation periods in winter, however, the influence of solar radiation becomes negligible. At this season the taiga exhibits an "air mass" climate. That is, the ambient temperatures depend to a large extent on the characteristics of the air mass that overlies the region. An air mass that contains much water vapour (clouds) impedes the loss of radiant heat to space and the ambient temperature remains relatively high. When this air mass is replaced by one containing very little water vapour there is less to prevent the escape of heat to space and the air chills rapidly. Moreover, any warm body exposed to the clear sky loses heat rapidly by radiation. Research in the subarctic taiga of interior Alaska showed a sky radiant temperature of -75°C with an air temperature of only -36°C in late January. During such periods of extreme radiant heat-loss some taiga mammals, such as the snowshoe hare, which live on the snow surface, spend much time beneath qali-laden spruces and alders where they are protected from the infinite radiation heat-sink of the night sky.
The network of green, needle-covered branches that makes up the taiga traps incoming radiation, bounces it back and forth and eventually absorbs a goodly proportion of it, with only a small part lost back to space.
Within the forest, then, the ambient temperature is usually somewhat higher than that outside the forest; the extremes are not as wide. Also, the needles and twigs catch the wind and slow it down so that windchill is less within the forest than outside it.
Because of the ever-present chlorophyll-loaded needles, photosynthesis can take place even in winter, sometimes, if there is intense sunlight. This means that atmospheric carbon dioxide may be less within the forest than outside it.
The most common precipitation pattern, the only one common to all facies of the taiga, is the presence of an annual snow cover. This may last only a few weeks in some parts of the taiga, while in other regions it may last 230 or more days. In comparison with some associations that border it (the tundra and aspen parkland, for example) the taiga has remarkably little wind. Because of this factor (as well as because winter temperatures are usually continuously sub-freezing) the snow cover of the taiga is typically soft and of low density, even though varying greatly in thickness from place to place and from year to year.
One of the characteristics of the taiga is the usual presence of podzol soils. Podzols typically possess a surface humus layer of slowly decomposing coniferous litter, underlain by a light grey or nearly white mineral layer, which, in turn, is underlain by a brownish or reddish layer. The humus is typically strongly acid. The light grey horizon results from the massive leaching of nutrients; they are deposited lower down, in the reddish layer. When a podzol is ploughed, planted and exposed to air and rain the grey layer frequently coalesces into a "hard-pan" and is quite impermeable to water. It may then remain in such a condition for many years.
2. Threats to the future of the taiga
(a) From Newfoundland to Alaska, this biome is undergoing more change and habitat loss than any other. Fires, pulp cutting, logging, spraying, clearing for agriculture are the major factors. Alberta has committed 220,000 km2 of its taiga to be cut down over the next 60 years. Manitoba has signed over 20 percent of the total area of the Province for cutting by a single company. The area signed away consists of 40 percent of the productive taiga in the Province, or 198,000 km2. This is equivalent in size to the US state of North Dakota.
One of the characteristic large mammals of the taiga is the Woodland Caribou. They are few in number, have a low reproductive potential, are secretive, live in small bands and are terribly vulnerable to clear-cutting, forest fires, "sports" hunting, poaching and legal hunting by Treaty Indians. A recent study in Manitoba showed that it is not the loss of lichens that triggers a loss of Woodland Caribou in a region, but the jackstraw tangle of downed , burned trees that occurs when the roots of the fire-killed trees rot about 5 years after the fire. The animals show remarkable fidelity to ancestral range until the physical barrier of metre-high tangles stop them.
No Woodland Caribou band has ever survived even moderately intensive clear-cutting on their home range. Woodland Caribou in Alberta, Saskatchewan, Manitoba and northwestern Ontario are now classified as "threatened" by COSEWIC (Committee on the Status of Endangered Wildlife in Canada).
Loss of habitat continues in many regions. In one region of Manitoba the percentage of land cleared and cultivated increased from 58 percent in 1948 to 85 percent in 1974, with most of the increase occurring between 1964 and 1970. In the Interlake region of Manitoba, clearing of mature forest for agriculture makes up as much as 7.5 percent of the total area per year. Most of the clearing is subsidized by Provincial and Federal agricultural agencies.
Labrador is one of the few remaining areas in North America, other than the tundra, where large areas are unexploited for timber. In recent years much of the change/loss has been instigated by governmental initiatives. For example, in Labrador, since about 1900, government financing has supported a series of large-scale logging-pulp operations. All have failed, but before failing, they have cut much of the best and easily-accessible timber. Each failed venture has meant reduced chances for real ecologically-sustainable forest operations because less of the commercial-quality easily-accessible forest remains.
Loss of stable-aged ("old-growth") taiga and temperate rain forest is not just incidental to other uses of the forests. In forest succession, maximum productivity of fibre is in "middle-age." Stable-aged forests parcel energy and materials into increasingly complex numbers of species, microhabitats, etc. rather than adding large amounts of fibre. Consequently, the aim of market-driven industrial forestry is to eliminate stable-aged forests and substitute young, preferably monoculture, "tree farms" for maximum production of fibre when they reach "middle-age." Such management is based on the premise that logged areas will never again be permitted to reach an old-growth or "stable-aged" phase. Preservation of biologically-complex, stable-aged conditions by selective logging is anathema to capitalist-oriented industrial forestry.
(b) One of the main environmental concerns of the present is the "enhanced greenhouse effect" caused by the marked increase in atmospheric carbon (in compounds such as methane, carbon dioxide, etc.) There is still some disagreement in the public mind about the reality of atmospheric change but no longer much disagreement in the scientific community. Because it has the potential of being second only to "nuclear winter" as a world-wide ecological calamity, prudence dictates that we give serious consideration to all aspects and potential effects of climate change. It is now clear that our use of fossil fuels is one of the major sources of atmospheric carbon. What is not generally appreciated is that about half of the atmospheric carbon dioxide since about 1860 has resulted from forest clearing; indeed, possibly 10 percent of the total atmospheric carbon dioxide has resulted from the marked human invasion and almost explosive clearing of forests in the 30 years between 1860 and 1890.
The carbon locked up in the living plants of the taiga is about 8.8 kg/m2 for a total of 84 x 109 T C (giga-tonnes). When the taiga is clear-cut most of the carbon begins to be released into the atmosphere. When the protective canopy is removed there is a dramatic change in the microclimate. There is an increase in air temperature, increase in the extremes of soil temperature, increased wind, decrease in soil moisture and degradation of permafrost. There is, of course, loss of the vegetation on the forest floor, especially lichens. There is total loss of arboreal lichens. The heat and loss of moisture cause the complex carbon compounds to break down and almost all of the 8.8 kg/m2 carbon is released into the atmosphere to become the so-called greenhouse gases. Of course, the carbon in the wood begins to be released, also. It makes no difference if the wood is turned into toilet paper, disposable diapers, newspapers or 2x4s, when the tree is cut down it begins to change from lignins to greenhouse atmospheric carbon compounds.
In some aspects of the taiga, and in associated bogs, carbon has been locked up in peat for hundreds, even thousands of years. Not only is there carbon locked up in the peat, but the energy that went into synthesizing the chemical compounds (lignins, cellulose, other carbohydrates, fats, etc.) is still there in the chemical bonds holding them all together. The cold, wet, acidic and anaerobic environment of the peat has preserved the materials with their energy bonds virtually intact. In Manitoba, carbon is about 40 percent of the biomass of peat and is sequestered here at the rate of 372 kg/ha/yr. Twenty-five percent of the world's pool of soil carbon is in boreal and wetland ecosystems. The total peat in Canada and Russia contains 5.6 X 1021 Joules of energy, the equivalent of twice the capacity of all the potential hydroelectric sites in the world. Carbon released from drained bogs ~10 T/ha. Drained bogs now give off more atmospheric C than the remaining bogs can absorb.
An unknown factor in all calculations regarding the "greenhouse effect" is: How much atmospheric carbon is required to cause global warming to become a positive feedback loop? In other words, when will the drying and oxidation of the taiga and its peat cause global warming to cause further drying and oxidation to cause global warming to become uncontrollable, no matter what we do? I do wish the people with tunnel vision who say, "Bring on global warming so we can grow more wheat." would take a world view and consider this aspect. I suspect if the 5.6 x 1021 Joules locked up in the peat of Russia and Canada were released there would be no return. Is the present-day annual release from drying peat of 3.68 x 108 T of carbon already too much?
Even if dramatic changes in our life-styles result in effective recycling of all items and goods and gross reduction in the manufacture of most items, as well as great reduction in use of fossil fuels by reducing energy demands and increasing use of non-fossil energy sources, there will still be a need for some dimension lumber and pulp. But taiga, because of its slow growth is more valuable to the world as a carbon sink than as a source of dimension lumber and pulp. Bogs have too much carbon and energy locked up in them to allow them to be drained for any purpose.
Projections of future greenhouse-dominated climates postulate that the taiga will undergo more changes than any other forest-type, possibly a large reduction in area from about 17 x 106 km2 to about 10.5 x 106 km2 and a poleward shift in its southern boundary. Some estimates go so far as to predict loss of 90 percent of the taiga.
Recall the present distribution of taiga in Canada. Environment Canada projects the taiga with 2X atmospheric carbon as being reduced to about 3 isolated areas, remnants in the northern portion of the present-day taiga. The southern border is projected to retreat because of prolonged drought, massive insect invasion onto the weakened trees, followed by massive wildfire. The resulting burned landscape would be susceptible to invasion by grasses and other wind-borne plant seeds.
The best interpretation I can derive is loss of very large areas of forest cover in the southern half of the taiga, especially the western half, first to insect outbreaks and then massive fires. There is no uniform sequence of post-fire seral stage succession. Post-fire succession depends to a great extent on the type of fire. For example, the 1980 Lyon burn around Taiga Biological Station in southeastern Manitoba was uniformly hot. Recovery even today is primarily jackpine but there are areas still essentially bare with blueberries and widely-scattered young pines. In contrast, the 1987 burn to the south of Wallace Lake was irregular in intensity with large areas now thick with (Populus) from sprouts. If the new climate does not allow such stages to cover the soil, then grasses could invade and direct succession in an entirely different direction. Predictions are that the southerntaiga of Manitoba and Saskatchewan will be replaced by aspen parkland or even steppe, with new plant communities scattered throughout. The rock ridges of the Shield will probably not recover to either forest or grassland but will remain, hot and dry.
Most predictions are that the weather will be much more variable with more violent episodes. The period of snow cover is predicted to shorten by about 30 days but with more variation in the characteristics of the snow cover. That is, the more frequent invasions of warm, moist air and thaws will harden the snow cover. This could have severe effects on survival of Woodland Caribou and subnivean small mammals.
The important point to consider is that the northern border cannot move northward in response to the northward retreat by the southern border. The present northern limit of trees is governed by a complex of factors: soil, moisture, exposure, temperature, and especially genetic factors. It is well known that seeds from trees at one latitude cannot be successfully grown at more southern or northern latitudes. The stock at a given latitude is highly selected to break dormancy and germinate at given photoperiods. For example, in nature white spruce can advance at a maximum of about 300 metres per year.
I have proposed that forests of tropical and subtropical regions, because of their much faster growth rate (shorter cutting rotation and consequent greater flexibility to meet changes in demand) be used as sources of lumber and pulp while taiga remains uncut and used as a carbon sink. This would be a service to all human-kind and the countries or regions undergoing the change-over and furnishing this service should be compensated by the United Nations or from some special international fund set up for this purpose. But where would the money come from to pay for such a massive program? For Canada, the change would be relatively easy. The value of the Canadian pulp and lumber industry could be compensated annually by what the world still spends on arms every 2 weeks. The woods workers would still be woods workers, only now they would be engaged in planting and caring for forests instead of cutting down trees. Other workers, such as those in the mills and transportation would still be employed in supplying and assisting the woods workers.
Obviously, such a change will require dramatic modifications in economic and social strategies and systems. Our governments are not making these changes. Indeed, they are continuing the same old "business as usual" routines.
Here are the addresses of web sites of some organizations or groups interested in the future of the taiga, the plants, animals and people that live in it:
www.globalforestwatch.orgAn important publication by them is:
Smith, W. et al. 2000. Canada's Forests at a Crossroads: An Assessment in the Year 2000.
www.cnf.orgCanadian Nature Federation website
www.taigarescue.org or email: firstname.lastname@example.orgTaiga Rescue Network
A very active and valuable group, headquartered in Sweden.
www.manitobanature.caManitoba Naturalists Society
4. Terrestrial Food Web of the Taiga Biological Station Research Area
This outline of the Terrestrial Food Web of the Taiga Biological Station Research Area encompasses about 60,000 ha in the southern portion of Atikaki Provincial Wilderness Park in southeastern Manitoba. The arrows trace the direction of energy flow; solid arrows indicate usual or common foods, dashed arrows indicate uncommon foods. Data originate from some publications (see TBS bibliography) and from information in unpublished TBS files.
Food webs are important basic information, but are exceedingly difficult to delimit; quantified food webs are virtually non-existent. They require natural history field skills such as ability to interpret tracks and identification of scats (droppings) as well as ability to identify seeds, bits of vegetation, hair and fur, teeth and chips of bone. They also require a research protocol that provides techniques for extrapolating quantities of useful calories of food from the scraps of undigested material passed through the animal's digestive tract.
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This page created January 27, 2001.
INTRODUCTION | OBITUARY for DR. WILLIAM O. PRUITT, JR
Copyright © 2001 Taiga Biological Station