S. Hagner
This article deals with silviculture in boreal forest areas. The signature of forestry carried out in such areas today is its close linkage to industrial processing and its great importance for the livelihood of local people, forest owners and the national economies of countries in the boreal forest zone, particularly Sweden, Finland and Canada.
Stig Hagner is a retired professor of silviculture who was with the Swedish University of Agricultural Sciences. He is also a former director of forestry operations at SCA, a major Swedish forest owner and wood and wood products processing corporation. He is based in Sundsvall, Sweden.
The northernmost forest cover on earth is called the boreal forest (after Boreas, the personification of the north wind in Greek mythology). Encompassing approximately 920 million ha (of which some 820 million ha are potentially exploitable), it encircles the globe and forms a more or less continuous belt through Eurasia and North America. The boreal forest falls mainly within the borders of the Nordic countries (Norway, Sweden and Finland) which have 5 percent, the Russian Federation, which has 73 percent and Canada and the United States (Alaska) which have 22 percent. Boreal forests include vast, remote and sparsely populated wilderness areas, until now beyond the reach of large-scale wood harvesting, as well as areas that have long been an important resource for humans as providers of wood raw material, originally destined for local use but increasingly used for industrial processing at both national and international levels. Currently. boreal forests yield about 500 million m³ of industrial timber per year, equal to 37 percent of the world's total demand, and 45 percent of all coniferous timber harvested. [Ed. note: see Unasylva, 43(170) for a comprehensive description and analysis of the various characteristics of this forest zone.]
The history of industrial utilization of boreal forests varies in length from two centuries to nil, depending on factors such as distance to consumers and accessibility. Therefore, some boreal forests harvested today are the result of humans, silvicultural practices in the past while, in other areas, the trees currently being cut were sown centuries ago by nature alone.
In Europe, large-scale utilization of boreal forests started around the mid-1800s. Initially, the natural forests were exploited in a similar way to mining. This exploitation was the basis for the establishment of mills and surrounding communities. Silvicultural investments aimed at rejuvenating the resource were either low or nonexistent at this time. However, after a few decades or so of forest exploitation, an area's forest resource created by nature alone began to dwindle. Hauling distances to existing wood processing industries increased, as did the costs, but the mills and surrounding communities could not easily be moved, as they represented huge investments and social benefits. What could be done to sustain and improve wood harvesting in nearby areas? This is the transition stage when the role of silviculture is usually recognized.
The ecology of the boreal forests was poorly understood at that time and the selection cutting systems that had been developed and successfully implemented in the more southerly forests of the continent were introduced and widely used. In theory' they seemed ideal: there were no costs for planting and tending and the forest was to be kept in good and productive shape by a skilful use of the axe alone. In many places, however, these practices developed into biological disasters. Without active site preparation, many logged-over areas became covered with dominating aggressive brush vegetation. Only shade-tolerant climax trees that already existed as undergrowth in the previous stand could survive, for example spruce and fir, and thus the forests took on a completely different species composition. Millions of hectares of open, scrub, slow-growing and commercially worthless forests accumulated where the advocates had promised a garden of Eden. In the absence of strong disturbances, either natural or human-caused (the natural occurrence of fire was largely suppressed), the forests' life processes stagnated.
It was not until the 1940s that the failure of selection cutting as a general practice in northern European boreal forestry was commonly understood and accepted. Since then, a formidable restoration programme has turned these spoiled forest areas into a forceful new generation of young, fast-growing trees.
Of the total annual removals of industrial timber, 80 percent or more come from large-scale final felling in natural forests situated on public land in the Russian Federation and Canada. Here, "large-scale" means removals concentrated on the clear-felling of tracts that often cover 50 to 100 ha or more and yield tens of thousands of cubic metres of wood. In the Nordic countries the large forest industry corporations operate their forests in a similar way, although these are second- or third-generation forests as opposed to primary growth. Taking a global view, forestry in the boreal zone is therefore mainly of the large-scale type. Consequently, silvicultural practices used in industrial forestry are characterized by mechanization and a concern about profitability, cost efficiency, operations control, etc.
Private, small-scale boreal forestry is practiced mainly in the Nordic countries and in eastern Canada, where hundreds of thousands of small woodlot owners share a major portion of the forest. Despite the different situation, silvicultural systems used in these forests do not drastically differ from those of the larger owners. One reason is that the development of alternative silvicultural methods that would better suit the needs of small-scale boreal forestry was given a low priority in the past. Another is the increasing tendency of small private forest owners to sell their wood on stump and let the buyer - industry - carry out any obligatory silvicultural measures.
Guided by research and experience gained over the past century, forestry in the Nordic boreal forest zone has developed silvicultural systems that are intended to be rational from an operational point of view and that give reasonably safe and satisfactory biological results. During the past decades, the predominant regeneration method has been planting preceded by mechanical site preparation. In the late 1980s, approximately 750 million trees were planted annually on some 3001300 ha of clear-felled boreal forest.
Experience shows that the rate of regeneration failure is comparatively low in plantation forestry planted seedlings give the new forest stand a quick start; the most suitable tree species can be chosen for each site and, often, the seedlings originate from genetically improved seed, measures needed to establish the new stand are simple to plan and administer; the whole regeneration process is finished in a short time and the results are easy to check while corrective measures can be carried out quickly; and, for standardized methods such as planting, expenditures on personnel and other overhead costs can be kept low.
In plantation forestry, seed is a critical commodity. The collection of seed in the boreal forest is a laborious activity and not always possible because of the winter climate. Large forest areas exist in the boreal zone where the summer climate is frequently so chilly that tree seed only ripens on rare occasions. In addition, some conifers in the boreal forest, for example the spruces, are unreliable seed producers. Others, for example fir and larch, shed their seeds only during a short period after the cones have ripened. Therefore, a large portion of tree seed used in plantation forestry today is produced in seed orchards throughout the boreal forest zone. This seed also is produced from selected trees and hence has genetically improved properties.
A scarcity of labour and cost factors have led to the development of tree nurseries which produce seedlings grown in containers suitable for fast and easy planting, either manual or mechanical. These nurseries can be quite big, producing 50 to 70 million seedlings per year. Because of fairly high investment costs, they seldom have an annual capacity of less than 15 million seedlings. Under Swedish conditions, it has been possible to quadruple manual planting performance by using container seedlings instead of bare root seedlings. The planting rate per hour doubled, as did the length of the planting season. Container seedlings are also more suitable for being fed into planting machines than the bare root seedlings.
The importance of appropriate containers is worth mentioning. If grown in inappropriate containers, seedlings of numerous species, particularly pine, can suffer from instability after planting out. Such poor containers were in use initially and hence early pine plantations were negatively affected in the Nordic countries. Since then, new containers have been adopted which allow the roots of planted pines a more satisfactory development.
So-called "natural regeneration" is also widely practiced in the Nordic countries. Some boreal forest sites are not suitable for planting. They are to be found on both the wet and dry extremes on the scale of forest sites. Here, nature often provides the seedlings free if the rejuvenation process is skilfully handled by the forester. However, even on sites that are usually planted, natural regeneration under seed trees of pine can be a good alternative - on the condition, however, that the site can be satisfactorily prepared by scarification or controlled burning and that the local climate is adequately warm to allow the tree seed to ripen. In contrast to pine, spruces are usually not sufficiently wind-hardy to function as solitary seed trees and they are unreliable as seed producers.
In earlier days, frequent commercial thinnings were regarded as an important means to improve growth and value and to reduce natural mortality among pine and spruce trees in Nordic boreal forests. However, research and experience have shown that, in managed stands, foresters can decide within wide limits the amount of wood they want to harvest in the form of thinnings or final harvest. Without influencing the total yield of wood too much, they can choose either: a programme with a few or even no thinnings, harvesting most of the total yield in one single operation at the end of the rotation; or programmes with frequent light thinnings or just a few heavy thinnings. The choice of stand treatment programmes therefore depends more on economic factors, such as the price of wood assortments produced and harvesting costs. It should be noted that the same liberties might not exist in boreal forest zones where other conifers, for example Larix spp., are dominant.
Fertilization with nitrogen has been used during the past decades to maintain the harvest level of wood in some boreal forest areas, for example Sweden and parts of Canada, without risking the long-term supply. In Sweden, tens of millions of cubic metres of wood were produced with the help of aerial applications of urea and ammonium nitrate during a critical period in the 1970s and early 1980s when the resource of forests ready for harvest was temporarily in short supply. By adding extra growth to the growing stock of middle-aged and older forest stands on a large scale, forest owners were able to compensate for the temporary shortage in the age class distribution, which would otherwise have implied a considerable reduction in annual harvests over time. Today, fertilization is frequently used by the bigger forest owners to improve tree growth after thinning.
Mechanization has become an important component of boreal silviculture. Mechanical site preparation replaced the labour-intensive controlled burning at an early stage. More recently, there have been attempts at fully mechanized planting and precommercial thinning. Machine planting is a difficult task in some boreal forest areas because of the very rocky morainic soils. Today, however, planting machines with impressive performance capacities are working under these conditions, preparing the planting spot and planting container seedlings in one operation. One such machine in Sweden, working three shifts per day, can plant three million seedlings during the snow-free season.
An important part of boreal silviculture involves matching provenances to site conditions. Many boreal forest tree species can be grown far away from their place of origin in other parts of the boreal forest zone, provided the right provenances are used. In Sweden, for example, American lodgepole pine (Pinus contorta, var. latifolia) has been planted on more than half a million hectares and, on suitable sites, surpasses the increment of the Swedish pine and spruce by 40 to 60 percent. However, in the development of Nordic silviculture, rules for provenance choice had to be sharpened several times before plantations established far north and/or on high elevations showed acceptable survival. Large areas had to be replanted because of fungal disease on weakened trees, basically caused by climatic maladjustment.
With time it has become obvious that boreal forestry also needs alternative silvicultural systems that are useful for "difficult" forest sites, for the production of special wood assortments and for sites which need special consideration on the grounds of nature values. In the Nordic countries, silvicultural research is now engaged in developing such systems.
Planted and/or thinned trees, given a quick start in life, respond by forming relatively wide annual rings and thick branches. This is in contrast to many trees in the natural forest which were suppressed when young. Such initially slow-growing trees, sought after by the lumber industry for their high-quality sawnwood, will become rare as a result of present day silvicultural practices. Boreal silviculture shares this dilemma of volume yield versus wood quality with many other wood-producing areas of the world. In the Nordic countries, research in boreal silviculture is focusing on the prospects of modifications in order to improve the quality of tomorrow's planted forest.
In areas where harvest levels depend on yield-sustaining measures, for example in the Nordic countries, silviculture has become a necessary and even unavoidable part of sustained yield forest management. New trees have to be grown and stands tended at least at the same rate as harvesting proceeds. Under these conditions, silviculture tends to become a significant activity and cost item. Its cost must be judged against the gains in economic terms; hence boreal silviculture must be rational and production-oriented. On the other hand, it must also respect the needs of nature conservation and that of other forest users.
In this situation, silvicultural costs can no longer be regarded - as the German forest economist Pressler taught - as isolated investments directed ascertain stands in the forest. Instead, the composition and cost of a forest owner's silvicultural programme must be assessed against the forest's sustained yield level under this treatment only. The programme must be balanced so that the last dollar, rouble or crown spent gives a return that corresponds to the marginal income from wood or other forest benefits produced as a result of this expense.
This somewhat new way of appreciating costs for silviculture more as a maintenance cost than an investment, and hence of taking immediate advantage of the measure's effect on the condition of the whole forest apparatus, can most easily be understood and utilized by private owners or forest-owning enterprises where forest and forest industries are managed in close combination. In Sweden, where big enterprises own 50 percent of the forest, decisions to start intensive silviculture were rapidly taken in the boardrooms of forest-owning corporations when the need was clearly demonstrated half a century ago. Through legislative measures and public financial support, these programmes also spread rapidly to the smaller private forestry operations.
In other countries, for example Canada, where state ownership dominates, forest industries usually extract their wood from leased forest land. The silvicultural programmes needed to reforest the harvested areas are generally defrayed by the forest owner (the state) as part of the general budget. As a result, in times of poor economy (but not only then), silvicultural measures have often been neglected or underfinanced. In Canada the discussions went on for decades before the need for more targeted large-scale silviculture was generally understood and accepted in political circles and the necessary programmes financed and implemented. In the meantime, the forest's general condition suffered. Enormous areas of backlog and huge needs for forest restoration accumulated. Even though improvements have been made, this questionable system of divided responsibility for financing forest operations persists.
Since the start of the new era of boreal forest management in the Nordic countries 40 to 50 years ago, about 40 percent of the total area has been covered with new forests as a result of active silvicultural measures. The middle-aged forest has been thinned and large areas fertilized. As a means to improve forest growth, many owners have saved the better portion of the old forest from final felling and instead directed this activity towards poorer stands. Progress has been monitored through national forest inventories and, overall, the growing stock in the Nordic countries has increased by 23 percent during the past 40 years while the annual increment has been increased by as much as 36 percent, reflecting the creation of a more vital forest capital.
Today we know that the yield capacity of well-tended forest is generally 25 to 30 percent higher than yesterday's predictions. As a result of this as well as other positive changes in forest conditions, wood harvesting budgets have been successively upgraded and are reaching increasingly higher allowable cut levels. Long-term predictions for Sweden's boreal forests show the prospect of increasing the sustainable harvest rates by another 55 percent over today's level. Highly profitable measures, including forest fertilization and the planting of fast-growing trees such as Pinus contorta, have motivated an immediate increase in the annual harvest by 20 percent in large forest estates belonging to some Swedish corporations.
During the past two decades, increasing research resources have been spent on studies of the natural processes in boreal forest ecosystems. As a result, the influence of modern forestry practices on nature values and biodiversity in these forests can be better understood and predicted than before, and they have come under debate in wide circles. As elsewhere, environmentally engaged interest groups are advocating a ban on the utilization of forests in some areas. The ongoing process of converting natural boreal forests into production forests is criticized. Supposedly more indulgent and environmentally sound forestry practices than those used at present are suggested.
The silvicultural methods used today are, of course, undergoing continued development and modification as a result of changes in society, research findings and practical experience. However, there are some important basics in boreal forestry that should be made clear to "environmentalists".
The challenge that boreal forestry faces today and tomorrow is to reconcile rational and economically successful silviculture with good conservation practices. The economic frames within which boreal forestry, and consequently the societies dependent on them, can exist do not allow the same direction of development as that which characterizes the heavily subsidized forestry carried out in many central European communal and state forests, for example. There, the recreation demands of the surrounding dense human population as well as far-reaching nature conservation intentions (partly spurred by pollution damages) have raised the cost of silviculture far beyond the levels of profitability. Boreal forestry must include the cost of nature conservation in its own budget and still be able to survive.
The importance of the boreal forest for supplying humankind with wood-based commodities was stressed earlier. On a global scale, it would be physically impossible to substitute the industrial wood that is currently harvested in the boreal forest by increasing removals elsewhere, and any attempt in that direction would probably bring about other unacceptable environmental effects.
The main portion of industrial wood obtained from boreal forests is still extracted from natural stands, and this situation will persist for a long time to come. For many economic and biological reasons, it is hard to see any advantage in giving up today's harvesting methods and appropriate silvicultural measures in favour of something totally different in these forests. Selection cutting, which has been suggested as a general, "nature friendly" practice in natural boreal forests, would not only be killing for money, it would also repeat the mistakes of the past and seriously damage many boreal forest ecosystems.
Harvesting and silviculture in the boreal forest seldom affect more than a portion of the total landscape. This is an important observation when discussing the impact of large-scale commercial forestry on nature values. The natural mosaic of the terrain can be utilized as part of forest operations aimed at forming a web of small-scale reserves and corridors which are important for sustaining biodiversity and natural ecological processes alongside production-oriented silviculture.
Even where clear-felling takes place, environmental considerations to improve biodiversity must be an important part of planning and execution. The key person to decide which trees to cut and which to save is the machine operator or the person with the power-saw. Operators must be trained to understand the need and be given the responsibility for leaving groups of dead trees and large hardwoods, standing and fallen snags, to save brooks and marshes, etc. Appropriate ecological considerations should also be pan of all ensuing silvicultural work, from reforestation to thinning. In Sweden, practically all forestry personnel and a large number of private forest owners have been trained in nature conservation. Forestry workers and forest ecologists have collaborated to produce illustrated manuals demonstrating the practices to be applied in various forestry activities in order to conserve biodiversity.
A rather unexpected effect of the great forest restoration programmes on both sides of the Atlantic has been the strong positive impact on certain wildlife populations as a result of the changing forest conditions. Clear-felled and planted areas covered with grass, herbs and bushes offer food in abundance for many animals. The formerly fairly small moose populations in the Nordic countries have increased enormously as a result of new silvicultural practices, in fact to the point that winter browsing on young pine trees has become a great problem for forestry. The number of moose has had to be drastically reduced in Sweden: the peak year was 1982 when 175 000 animals were killed. The population, now under control, is still far larger than it has ever been in modern times and allows an annual harvest of more than 100 000 animals.
When discussing the economy of forest industries located in different pans of the boreal forest zone, a question that is often raised is how the high costs of intensive silvicultural systems can be absorbed as pan of the wood cost in some areas while the same cost would be completely devastating for the wood buyer in another region of the boreal forest. To understand the underlying dynamics, it must be realized that forests and forest industry often exist in a kind of symbiosis. The fact that the forest industry in a region is able to accept the cost of a comprehensive silviculture (a cost that is reflected in the wood price) can only be the result of a long development process. With time, a fair portion of the processing profit has had to be allocated to the forest, thus enabling measures to sustain and improve the forest yield to the benefit of the industry's continued existence. Needless to say, such industries must be strategically located in relation to the forest and the market, be cost-efficient and produce a palette of competitive commodities.
If profitability in forest industry remains acceptable, such relatively costly silvicultural systems, which have long served well-established industries, can be expected to be practiced over increasingly larger areas. A development in this direction can be clearly observed during the past decades in Canada. In areas where natural boreal forest has been cut for decades, it may be expected that more comprehensive silvicultural concepts will be introduced successively. However, new untapped areas will simultaneously come under harvest both in Eurasia and North America where less far-reaching and costly silvicultural systems still need to be practiced. For a long time, therefore, great differences will exist in the way and in the extent to which silviculture is carried out in the various parts of the boreal forest zone.
