Climate Change Mitigation.
Are there any Forestry Options?

By Dr. Chris S. Papadopol
February 2001

The Author is Lead Scientist, Ecology of Intensive Plantations, with the Ontario Forest Research Institute in Sault Ste. Marie, Ontario, Canada. OFRI develops new scientific knowledge to support the sustainable management of forests, wildlife habitats and biodiversity.   → See also:

Abstract

In recent decades, convincing scientific evidence has been accumulated that climate change, caused mainly by increasing atmospheric CO2 concentration, has already begun. Forests, which are major carbon pools, and cover large areas, were identified as potential major contributors to the mitigation of climate warming through their C sequestering capacity.

Two are the most important characteristics of forecasted climate change:

  1. temperature increases of 3 ± 1.5 °C at the time of doubling CO2 concentration, with a more accentuated increase toward poles, and
  2. amplified climatic variability.

This paper suggests a series of comprehensive silvicultural interventions likely to achieve a more active CO2 sequestration, and an ensuing temporary climate change mitigation. The importance of this measures of general interest has grown sharply recently. A new assessment made in an IPCC report contends that the expected rise of temperature until the end of the 21st century will be in the range from 1.4 to 5.8 °C (IPCC 2001).

In concert with efforts aiming at increased conservation of fossil fuels, the suggested measures aim to increase the carbon, C, storage term in the C balance of future forests and soils, thus significantly enhancing the C «sink» role of forested areas. In comparison with the past, when enormous C pools were locked underground, in the future, sequestered C will pass through a chain of transitional pools and ultimately end up in the atmosphere. Forests and soil can only provide temporary C storage, while true mitigation can only be achieved through very long-term C removal, e.g. in durable goods.

All the recommended measures towards this aim fall in the «no regrets» category, enhancing the forest stewardship function that society expects from forest managers without affecting the status of forest industry.

Keywords: climate change, silviculture, carbon balance, afforestation, exotics.

Contents

Introduction

Climate warming entails complex changes in the atmosphere and ecosystems, including increased climatic variability (Gleick et al. 2000). The ecological conditions in which forests develop, especially the hydrology, will certainly be subjected in the future to an enhanced atmospheric demand for evapotranspiration (Papadopol 2000a), and to a greater frequency of extreme phenomena (Francis and Hengeveld 1998; Glantz and Wigley 1987). While experiencing a pressure to move northwardly, the existing forests may not be able to cope with this challenge unless new management approaches are adopted. Therefore, new strategies will need to consider ecological pressures exerted on existing ecosystems by the warming trend, which accentuates in time and from equator to poles (Bolin et al. 1986; Overpeck et al. 1991; Houghton 1997).

The underlying premise of this paper is that the already occurring shift of ecological conditions might have a destabilizing influence on the majority of ecosystems, especially those in the boreal forest. The occurring rapid «shift» of ecological conditions has already created a growing pressure for every ecosystem to migrate towards north (Roberts 1989; Pitelka 1997). It is therefore appropriate for forest management to anticipate this shift and expand northwardly, at least for a number of rotations, species that could thrive in the new conditions characterized by longer growing seasons (Murray et al. 1989) and increased water scarcity (Manabe and Wetherald 1986; Glantz and Wigley 1987).

Finally, there are some new aspects of climate change. Until recently, scientists involved with this issue debated whether human activities were altering the global climate. In a very short historic interval, the key questions of the climate change issue have become rather when, where and by how much. Also, the last decade has been the warmest in the 20th century and, indeed, the warmest for many centuries (IPCC 2001). With a lot of scientific evidence accumulating, and, especially in view of permafrost withdrawal, ancient glaciers melting, ice caps thinning and breaking up at an alarming rate, the object of climate change debate is changing into what steps can be taken by the international community to avoid major ecological disruption. This paper attempts to provide a realistic forestry perspective on this question.

Precursors of change

Climate change is a complex alteration of climate, subtle and continuous, yet extremely important through its consequences on vegetation of various types that thrived under «constant» climates. It was heralded by a gradual increase of atmospheric CO2 concentration, recorded first at Mauna Loa, Hawaii, and showing a marked seasonal variation, corresponding to photosynthetic activity of vegetation (Boden et al. 1994). Subsequently such determinations, considerably expanded geographically, as well as backward in time by using the analysis of air bubbles trapped in fossil ice, have shown a remarkable parallelism between atmospheric CO2 content and average air temperature (Chapellaz et al. 1990).

Some of the precursors of climate change, copiously reported in the media especially during the last decade, are:

Increasingly, we learn about the «fingerprints» of climate change such as polar warming, with ensuing glacier/permafrost melting causing the rising of ocean levels, as well as heat waves that affected various areas of earth in the last decade (Schneider 1994).

Obviously, these modifications of previously stable climates, implying a clear warming trend and a growing climatic variability, impact the existence of forest ecosystems, as we know them. At the same time, these phenomena appear to occur with increasing frequency leaving a clear impression that the pace of climate change is accelerating (Hessman 2000).

The role of global forest carbon cycling

In the past two centuries, roughly since the beginning of Industrial Revolution, the CO2 concentration in the atmosphere has increased from 280 to 370 parts per million as volume (ppmv), or approximately 30% (Bolin et al. 1986). This happened, primarily, as a result of burning fossil fuels for energy generation and transportation, with further increases probable, depending on patterns of energy generation in industrial and developing countries. To this we can add the continuous CO2 release from large and growing areas of arable lands, under a more intensive agriculture. In the last decade of the 20th century, on average, the combined discharges of CO2 in the atmosphere caused a rise of 1.5 ppmv annually, in a trend that was ascending exponentially (Boden et al. 1994). Between the major CO2 sources, electricity-generating power plants account for about one third of all CO2 released into the atmosphere worldwide (Herzog et al. 2000). Other major CO2 sources, especially in developed countries, include the extensive and growing use of fossil fuels (oil and coal) by transportation industry.

The effects of these large and increasing CO2 emissions were neglected until about three decades ago, when modeling attempts to understand the atmosphere-land-ocean systems yielded their first results (Bolin et al. 1986). Today it is well established that the largest carbon exchange occurs between the atmosphere and plants, with a mean residence time of a molecule of CO2 in the atmosphere of about 3 years (Schlesinger 1995). Through successively improved versions of general circulation models, GCMs, the currently accepted estimate of the warming trend was about 3 ± 1.5 °C, for a 2 x CO2 scenario (Houghton 1997), with regional temperature increases at mid- to high-latitudes possibly exceeding 10 °C (Overpeck et al. 1991). However, the pace of climate change seems to accelerate. In a new assessment, publicly released at the beginning of the new Millennium by IPCC, the warming rate of globe´s atmosphere until the end of the 21st century is given as being in the range 1.4 to 5.8 °C (IPCC 2001).

The key question is when this doubling of atmospheric CO2 content will occur ? Initially, it was thought it would happen by the end of the 21st century (Manabe and Wetherald 1975). More recently, the doubling of atmospheric CO2 is placed at the middle of the 21st century (Houghton 1997), being coincidental with the time when global population will surpass 9 billion. Consequently, forests created today, supposedly on sites optimally selected to match the species´ ecological requirements, will find themselves in a very different environment by rotation age. This warming influence, resulting in an unprecedented pressure to move in a northward direction, may lead to forest decline in just one generation (rotation). Among the most important implications of this situation for forest management, is the fact that natural regeneration will be affected in a difficult to predict way (Andrasko 1990; Cannell and Dewar 1995; Brown 1996). While it might be successful initially, as the trees approach maturity, the «shift» of ecological conditions might grow significantly, possibly resulting in forest decline. Likewise, the use of established seed zones will have to be reconsidered, because the original territory of a zone might become up to 10 °C warmer in just one century.

Already there are numerous reports of ecological changes resulting from warming, which range from insect ecology (Fleming and Volney 1995; Volney 1996) to severe melting of glaciers (Schindler 1998; Johannessen et al. 1999; Kerr 1999; Vinnikov et al. 1999; Wuethrich 1999). It is conceivable that, as the awareness of the current stage of the climate warming grows, international organizations and society at large will desire the return to Earth´s status quo before the Industrial Revolution. This is likely to become soon a strong political and social necessity, as the evidence of change amasses: retraction of glaciers, rising ocean levels, permafrost melting and aggravating climatic variability. As the scientific understanding of the forest C cycle advances, it is clear that the progression of changes, and their timing, strongly depend on

  1. environmental factors (increase of atmospheric CO2, accelerated nutrient mobilization especially of nitrogen and sulphur),
  2. human factors (demographics, economic growth, technology), and
  3. resource management policies.

These factors have numerous interactions, not always obvious, sometimes complicated by regional circumstances.

To a great extent, mitigation of climate change is a matter of understanding and manipulating the carbon cycle. Prior to the Industrial Revolution, the carbon - which is now floating in the atmosphere- was locked permanently in large underground pools (Schroeder and Ladd 1991; Rubin et al. 1992). Presently, over 8 bil. tons of C are added annually to atmosphere (IGBP Terrestrial Carbon Working Group 1998). While retrieval of the «extra» C from the atmosphere is feasible, it may not remain locked for too long in biomass. Instead, it will be passed through a chain of temporary storage, finally returning to atmosphere. Current estimates are that, all together, plants retain annually about 600 Gt (gigatons) of carbon, with another 1600 Gt in soil (Cooper 1983; Schroeder 1991; Herzog et al. 2000).

Unless a solution is found for the permanent retrieval and sequestering of a sizable proportion of the enormous amount of C floating now in the atmosphere -because of the unavoidable decomposition of biomass and soil organic matter - in the foreseeable future the retrieved C is vulnerable to return to the atmosphere in a century or so since re-capture. With other words, future sequestration of CO2 will be in transient, non-permanent pools. This is precisely the case of C sequestration in forest biomass and in soils (Anderson 1992; Bruce et al. 1999; Johnson 1992; Marland and Marland 1992). In this new scenario, soil and roots of terrestrial ecosystems are of particular importance, since about two-thirds of terrestrial C is found below-ground (Dixon et al. 1994; Schlesinger 1995). Adding to the importance of this sink is the fact that below-ground C has a slower turnover rates than the above-ground C, which means that it can be maintained in storage over longer periods of time, being more protected during fires and other disturbances (IGBP Terrestrial Carbon Working Group 1998). However, even small changes in such large pools of C would be expected to have dramatic impacts on the global climate system. Under a warmer atmosphere, sudden losses of organic soil matter could exacerbate global warming. On the other hand, increases of soil organic matter (e.g. from litter accumulation under more productive forests) could reduce the rise of atmospheric CO2 and provide negative feedback to global warming.

Although sequestering atmospheric C in forest biomass and soils is only a temporary solution, on a time scale of 50 to 100 years, this delay buys time for developing other solutions. It is conceivable that an active forestry program could hold C in forest biomass not intended for fuelwood, on average for at least 2-3 centuries (Kirschbaum and Fishlin 1996; MacLaren 1996; Dewar and Cannell 1992), while the C residence in soil, under forest, might be even longer (Post et al. 1982; Anderson 1991). Since the rates of soil CO2 efflux vary with soil temperature (Raich and Schlesinger 1992; Peterjohn 1993), it is to be expected that avoiding the exposure of soils to direct radiation and aeration would result in a substantial additional sink. Whereas it is estimated that soils will lose about 45 Pg (pentagrams, 109 g) C as the climate warms from today´s conditions to those anticipated with a doubling of CO2 (Schlesinger 1991), it appears that, through the manipulation of stand density and shadow of soil, it will be possible to reduce significantly this amount and take advantage of the additional sink thus created in forest soils.

As GCMs have shown, high- and mid-latitude forests are going to be more strongly influenced by changes in environment than the low-latitude forests (Pastor and Post 1988; Singh and Wheaton 1991; Rizzo and Wiken 1992). The most promising ways to increase C sequestration, appear to be

  1. restoring forest coverage,
  2. increasing forest productivity, and
  3. suppressing fires.

Also, an increase in overall C sequestration rates can be achieved through shorter rotations, since young forests have higher rates of net carbon accretion. The greatest gains in forest productivity (above- and below-ground) might come from the CO2 fertilization effect (Graham et al. 1990; Lindroth et al. 1993; Cannell et al. 1998). Results from a global biogeochemical model, BIOME, which considers only environmental factors, project that net primary productivity of forests may increase up to 25% (Dixon et al. 1994). In the model, improvements in productivity were attributed only to warmer ambient conditions, mineralisation of soil N, and CO2 enrichment. Nevertheless, these predictions still need to be confirmed by the large scale open-air experiments at the ecosystem level, evaluating the long-term impacts of CO2 enrichment on carbon cycling (McLeod and Long 1999).

However, attention must be given to all aspects of climate change, not just the temperature. For instance, demographic projections of increases in low-latitude human population and associated agricultural and industrial development in future decades suggest that these pressures will be great. Projected total future forest C emissions with climate-induced land-use change, without implementation of mitigation practices, amounts to between 4.4 and 6.0 Pg (pentagrams) year-1, encompassing large land uses shifts from forestry to agriculture (Dixon et al. 1994). However, this conflicts acutely with the accrued food needs of a fast growing human population.

In forest ecosystems, C recycling occurs continuously through photosynthesis and decomposition. Dixon et al. (1994) estimated annual C fluxes from forests by latitudinal belts. They found that mid- (temperate) and high-latitude (Canada´s and Russia´s) forests act as a net C sink, offsetting the deforestation still occurring in low-latitude forests at a rate of over 15 million ha year-1 (Andrasko 1990). The duration of C sequestration in vegetation and soil can extend from years to centuries, with the decomposition rate of biomass depending on: species, site conditions, disturbance (mainly fire), and management practices. Present estimates of global forest C sequestration potential, determined on the basis of C budget methodology applied to major vegetation formations, suggest that an annual biologic capability of 1 to 3 Pg of C, on the same area, remains unrealized due, mainly, to lack of coverage with vegetation. It would be realistic to project this capacity for at least a century, before the CO2 concentration of atmosphere will start to decrease, amounting to a storage capacity of approximately 200 Pg of C (Dixon et al. 1994).

The rise of atmospheric CO2 concentration in the last two centuries, has induced changes in the physiology of forest species. In the first place, this increase, which has the effect of CO2 fertilization, is expected to augment overall plant photosynthesis. In turn, this will lead to accelerated growth and yield and potential rotation shortening (McGuire and Joyce 1995; Mooney et al. 1991). A review conducted on this effect has shown that the growth-enhancing effect of CO2 fertilization is more pronounced when other resource limitations or environmental stresses are also present (Idso and Idso 1994).

The increased levels of atmospheric CO2 over the next 50-100 years are likely to increase both the rates of photosynthesis and the resistance to CO2 and water vapour exchange, resulting to the increase of number of CO2 molecules captured per unit of water transpired (Eamus and Jarvis 1989). This effect of increased water-use efficiency has been demonstrated in laboratory experiments, where the growth of broadleaved and conifer seedlings has increased by 20-120% under a double CO2 concentration. However, the magnitude of these effects is still unknown for mature trees. Also, responses to high CO2 levels may be influenced by other stresses (nutrient supply, water stress and atmospheric pollutants), with the water stress forecasted to accentuate. This effect is already manifest for aspen forests in central North America which present already a dry-climate analogue of future boreal forest (Karl et al. 1991; Alban and Perala 1992; Hogg and Hurdle 1995)

Large biomass accumulations due to a more active photosynthesis and an extended growing season under a changed climate with good water supply, amounting to a 25% increase of growing stock in 1990 compared to 1971, were documented for the European forests, especially in Austria, Finland, France, Germany, Sweden and Switzerland (Kauppi et al. 1992). Subsequently, their findings were confirmed and deepened for the Finish forests by Kellomaki et al. (1997).

In 1996, the annual wood harvest has reached 3.36 bil. m³. Approximately 55% of this amount was fuelwood while the balance was industrial sawlogs. Currently, the maximum per capita wood consumption in US is 2.3 m³ per person and year-1, while the world average is 0.58 m³ per person and year-1 (Sutton 1999). These figures have to be judged against the projected population growth, which is now slightly over 6 bil. and might surpass 9 bil. by 2050 (Population Reference Bureau 1999).

However, while the growth-enhancing effect is potentially very important, problems still exist with respect to scaling up from the level of leaf to forest (Jarvis and Dewar 1993). This effect is now investigated experimentally, for a score of commercially important forest species in US, using the open-air technique (DeLucia et al. 1999; McLeod and Long 1999). Although the cost of such an experiment is high, incorporation of acquired knowledge in new models describing tree response to climate change may prove of very great significance.

In summary, large uncertainty exists with our ability to project future forest distribution, composition, and productivity. In addition, global models that consider the role of improved forest management in mitigating C flux to the atmosphere have not been developed. The land-use effects most responsible for future C emissions, such as decline in forests and expansion of agriculture, should be considered in development of forest C conservation and sequestration options. With forests gaining such an importance as a vehicle for C sequestration, the future forest management practices will likely be evaluated on their effectiveness in fulfillment of this function, resulting in a pro-carbon silviculture. According to Houghton (1997), these practices can be grouped into four categories:

  1. slowing deforestation and forest degradation,
  2. expansion of existing C sinks through forest management,
  3. creation of new C sinks through expansion of forested area, and
  4. substitution of fossil fuels with renewable wood-based fuels.

Adoption of such long-term policy will have the added benefit of enhancing other environmental objectives, such as protection of biologic, water and soil resources.

Mitigation objectives

The effects of climate change have reached such a magnitude that irreversible changes in the functioning of the planet are seriously feared. It is therefore implacable for the international scientific community to use all existing knowledge to reverse this trend and restore atmospheric conditions to pre-Industrial Revolution levels. Some temporary measures to adapt existing forest ecosystems to limited changes are possible and have been suggested (Papadopol 2000b). However, if the warming trend accentuates or even continues at its current pace, these may soon prove insufficient. The objective of mitigation measures is therefore to attempt a gradual reversal of the effects caused by increased CO2 concentration, primarily through a more effective C sequestration by forests.

On the topic of climate change the goal that holds the greatest promise remains increased C conservation. This planetary effort can be helped substantially by a favorable manipulation of C cycle through forestry. This is why the Kyoto Protocol, focusing on using forest C sequestration to reduce the CO2 concentration of atmosphere, has set reduction targets by countries (IGBP Terrestrial Carbon Working Group 1998). In the meantime, other solutions, actively being searched by modern science, such as underground and underwater CO2 storage, may prove their technical feasibility (Herzog et al. 2000).

In the balance of this paper, a number of practical ways are suggested to manipulate the C cycle through silvicultural means, so as to increase the sequestration of C in tree biomass and, especially, in the forest soil. These measures are comprised in the «no regrets» category; actions that represent an implementation of principles of sustainable forestry. Their large-scale application will result in great amounts of biomass and soil humus. If their decomposition can be delayed, perhaps, in the meantime, a more permanent CO2 storage solution will appear. The suggested measures are by no means exhaustive, being somewhat adapted to the temperatezone. Conceivably, an extended, necessary discussion among informed foresters will reveal other useful facets of the C cycle that could be manipulated to the benefit of general objective: restoration of atmosphere´s condition prior to Industrial Revolution.

Suggested climate change mitigation measures

At this point in time, it appears that one of the main tasks of forest management is to prepare a portfolio of valid actions, differentiated by species and environments, emphasizing active CO2 sequestration and increased ecological stability of future forest ecosystems. The mitigation measures suggested below, especially for countries in the Northern Hemisphere covering the latitudinal range of temperate and boreal forests in Canada and US, are based on the need to have all territory allocated to forestry covered with active CO2 retrievers, in order to maximize the net photosynthetic product. Although the «area under forest» reported in many forest statistics seems quite large, actually much of it is not covered by trees, is poorly regenerated, or is covered by low-productivity species. The proposed mitigation measures are:

  1. Reforesting immediately after harvest

    This measure has several facets. First, the forest coverage should be restored to every surface that was previously covered by forest, as soon as possible after harvest, to maintain an active and almost continue C sequestration function. This refers chiefly to areas not successfully regenerated, where the species composition is undesirable, or with low productivity.

    Secondly, from the C sequestration viewpoint, this is the occasion when the foresters can change the composition of the forest, introducing new species that may be better adapted to changes in ecological conditions. Priority has to be given to species and silvicultural methods that will result in productive new forests, therefore having high sequestration efficiency. Although natural regeneration of recently harvested areas might be successful, the resulting stand may not be desirable or secure in the long run (50 to 100 years). Such a situation arises when the ecological conditions, favorable at regeneration time for a certain species, are expected to change so fast as to preclude the productive existence of the same species at maturity. Most likely, this is the case of forests at the southern limit of their range.

    Thirdly, reforesting immediately avoids long intervals with the forest soil exposed, when, because of decomposition of soil organic matter, the area may become a CO2 source. At the global scale, this measure has tremendous potential to offset deforestation and increase the effectiveness of forest carbon sinks, both in the low latitude forests of the Amazonian basin and in the wide band of temperate forests of Russia, Canada and the US.

  2. Restoring the productive forest cover

    This relates to bare areas that can sustain, and have sustained, forest production, thus re-establishing the CO2 sink function, as well as stopping erosion, where it is a problem.

    In many forest zones, large areas exist where the forest has been harvested, but, for various reasons, regeneration did not succeed. Such areas bear some pioneer, low-productivity forest types, are in marginal agricultural use, have been degraded, or are simply abandoned. In terms of land area, this is probably the largest area on the planet that could be covered with active CO2 retrievers, estimated at over 200 mil. ha (Dixon et al. 1994). However, in terms of feasibility, this situation is more complicate than the preceding one, because greater and more diversified efforts and investments willhave to be made with respect to vegetation management, which may make this proposition less attractive i.e. more expensive per land unit. In terms of biological potential of forest growth, the low latitudes exhibit the greatest potential for carbon sequestration, which should indicate the priority for action.

  3. Expanding existing forest carbon sinks

    Large areas of forest at all latitudes are not storing carbon at their potential. In North America, this is the case for areas where high grading has been repeatedly applied, resulting in lower-productivity, secondary forests. In the mid-latitude zones the net C accumulation of commercial timberland is also below its biologic capacity (Dixon et al. 1994; Overpeck et al. 1991; Vitousek 1991). These forests could sequester considerably more C in future decades, especially if management practices to expand forest sinks would be applied, thus favouring soil carbon pools, such as:

    1. reforesting to arrest erosion,
    2. adding chemical amendments to boost fertility,
    3. reducing shifting cultivation,
    4. reforesting marginal agricultural lands, and
    5. retaining litter/debris after logging operations.

    Regeneration of Canadian boreal forest under a changing climate will pose numerous challenges for forest managers. Foremost among these could be the need to establish extensive areas of plantations, in part for assisting the migration of tree species to future ranges, with species different from the present ones (Andrasko 1990; Davis 1989; Mackey and Sims 1993). If we assume that forecasted climate change will continue at its current pace, an assumption for which there is overwhelming evidence (Gleick and Adams 2000), then extensive stand establishment in the boreal region should occur immediately after an area is cleared, while the guiding principle should be to move the existing species, including the broad-leaved, aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.), 500 to 1000 km north of their current range.

    From an operational perspective, the optimal rotation age is dependent on the forest type, site productivity, and desired forest product. For instance, in 1990-1997, 55% of industrial wood harvested in Ontario was used for lumber and veneer, 39% for pulp and paper and 9% for fuelwood (Canadian Council of Forest Ministers 1999), with clear cutting and even-aged management used on large scale for jack pine (Pinus Banksiana Lamb.), upland black spruce (Picea mariana Mill.) and aspen forests. Management of these relatively short-rotation species for C storage in wood products may be preferable through extending their rotation length, particularly where there is a significant risk of stand replacing disturbance (Price et al. 1997). However, in plantations managed for pulpwood production, C storage can be made more effective increasing growth rate by planting on more productive sites, genetic improvement, or intensive management. Longer rotations than those in use today may be a more practical means of increasing C storage in black spruce lowland forests because the current and future risk of fire on these sites are lower. Carbon storage in longer-lived Great Lakes - St. Lawrence conifer and tolerant hardwood forest types, managed with partial cutting systems, can be augmented by increasing the age (and therefore the size) at which residual overstory trees are removed, or by permanent retention of a portion of the large, old canopy trees (Parker et al. 2000).

    In the special cases of poor soils, intensive management practices (soil preparation, weed control and fertilization) can increase greatly the C storage in timber biomass and soils, either directly or by shortening the rotation. Especially, improving soil fertility by the application of nitrogen fertilizers may expand the pool of C in forest soils, provided the «carbon costs» of fertilizer production do not exceed the gain in soil organic matter (Schlesinger 1995). However, in comparison with natural regeneration, these practices imply additional costs, or can have «secondary effects,» such as leaching fertilizers/pesticides to groundwater or water courses.

  4. Establishing new plantations

    Establishing plantations of productive species, including mono-specific, industrial plantations, managed on the basis of economic principles, on all suitable sites will satisfy both the requirements of traditional timber-related industries, especially for pulpwood, and the CO2 retrieval function (Woodward and Lee 1995). An important proportion of these plantations should replace existing low productivity forest vegetation on fertile soils. Potential concerns about the long-term adaptation of these plantations to changing conditions can be addressed based on

    1. shifting species 500 to 1000 km north from their current seed zone, for the first rotation, and
    2. using fast-growing genotypes which will shorten rotations by 5-15%.

    In view of the increasing frequency of extreme phenomena, understanding the growing conditions at the new location will be critical. This should cover especially two main aspects: extreme droughts and damaging winds (great gales). The first aspect requires existence of a deep soil, with a large ability to store water. On sites with high permeability, for 1-2 rotations, preference should be given to pioneer species, especially for their role of soil organic matter buildup. These soil characteristics will help future ecosystem to bear hydric stresses caused more frequently by irregular precipitation. Strong winds may cause windstorm problems, especially to shallow rooted species. Any increase in the incidence of such events would obviously be very damaging, and could potentially affect the profitability of long-rotation commercial forestry (Cannell et al. 1989).

  5. Shifting species

    Based on current climate change theory, there is already pressure for a northward shift of species ranges (Houghton 1997). This will surely be perceived differentially by the various species that compose certain ecosystems, and they will shift at individual paces, and not as entire ecosystems (Peters 1990). Some plant ranges could shift naturally by as much as 500 to 1000 km during the next 200 to 500 years (Andrasko 1990; Overpeck et al. 1991). This pressure might therefore result in unprecedented vegetation change. If the climate changes as predicted, forecasting the exact timing and patterns of change will not be exceedingly difficult, since - based on historical record - it can be assumed that the intensity of this pressure is tied to the speed of CO2 increase.

    Considering the delay before this measure will be effective, and the atmosphere will respond through a detectable reduction of CO2 concentration, it is reasonable to establish new forests with species shifted 500 to 1000 km north of the edge of their current natural ranges. Initially, such stands of trees may appear to be established in an environment that is too cold. However, because the warming process will continue for at least 100 to 200 years owing to atmosphere´s own inertia, these stands will find themselves in optimal climatic conditions close to the young-mature stage, when they have the highest sequestration ability, or productivity.

    Maintaining species of economic importance but with diminished natural genetic diversity and abundance, such as white pine (Pinus Strobus L.), red pine (Pinus resinosa Ait.), black spruce and red oak (Quercus borealis Michx.) may require establishment of gene bank plantations on north-south paths, resulting in transects of «reserves.» Assessing genetic variation within these species will help to determine the limits of transferability of these genotypes, i.e. identification and planting of southern ecotypes in more northerly regions.

  6. Replacing drought sensitive species

    GCMs predict potential consequences of climate warming, some of the most important affecting the water cycle. Although general influences were identified, only in a few places it is possible to indicate with certainty the magnitude of change in the hydrological cycle. For instance, while the growing season will become longer for various latitudinal stripes, eastern Ontario will remain wet, due to its clay substrate, while western Ontario, with a substrate of permeable materials, will become drier, especially because of scarcer precipitation. Obviously, this issue will have to wait more refined GCMs, so as to yield better predictions at the regional scale, and possibly take site quality into account.

    As the hydrology changes, the morphological ability of forest species to explore deeper soil layers will become more important. This will probably result in the screening out of shallow rooted species. In Ontario, Canada, and the northern US this may be the case of red pine and jack pine, economically important species, however with a root system that does not advance beyond 1.0 - 1.2 m, therefore unable to use water stored at deeper levels. For a while, the hydric stress to which such stands will be subjected could be eased through interventions such as thinnings, as has been recently demonstrated for Norway spruce (Vesterdahl et al. 1995) and red pine (Papadopol 2000b), which will help existing stands reach rotation age. However, in the long run, the risk for shallow rooted species to be replaced by more resilient, deeply rooted species, will increase, especially on permeable sites.

    Fortunately, with climate warming, the direction of ecological pressure is such that it will open more northerly areas for the deeply rooted red and white (Quercus alba L.) oaks. The same trend will prove auspicious for the reintroduction of American beech (Fagus grandifolia Ehrh.), first on drought sensitive sites (sandy, permeable), with the added benefit of annual production of a large amount of rich litter, an excellent vehicle for increasing soil C sequestration. Finally, the expansion of European larch (Larix decidua Mill.) and its ecotypes, deeply rooted and very productive entities, could be considered for large areas of Canadian boreal forest, as well as northern zones of US. Although European larch has no ecological limitations for this area, because no seed base exists, it will have to be considered, at least for a generation, for plantations. The only matter of potential concern in the case of European larch remains its, as yet unexplained, susceptibility to diseases. However, the strict expansion of those European provenances that are immune to its blister rust Lachnellula wilkommii (R. Hartig) Dennis (Dasyscypha wilkommii), and exclusion of sensitive provenances, a well known topic in European silviculture, could avoid this risk (Howse 1983). One way to solve this problem would be through promotion of vegetative propagation, which has a high success rate (e.g. over 80%), for rapid multiplication of immune provenances.

  7. Substituting wood fuels for fossil fuel

    An effort that could be very rewarding in terms of C conservation, applicable in all geographic zones, is the substitution of biomass energy, a renewable resource, for fossil fuel combustion. This measure does not change the C balance of atmosphere, since CO2 released from burning wood or biofuels is cycled back to forest biomass through photosynthesis. Short-rotation woody crops have the greatest potential here, provided the several advances in cultural techniques obtained in the last three to five decades are implemented (Dewar 1990; Alban and Perala 1992; Schlamadinger and Marland 1996). The productivity of these specialized crops can be further enhanced using the latest genetic progress related to fast growing species, particularly eucalypts (Eucalyptus sp.), poplars (Populus sp.), willows (Salix sp.) and other hardwoods, some of which are able to occupy narrow niches (e.g. bottomlands of major rivers), that otherwise remain unused. Some of these sites, especially the bottomlands, are very rich in nutrients, which are renewed annually during spring floods. On such sites the risk of nutrient exhaustion, a concern with intensive culture, does not exist. In terms of productivity, such sites might be among the best for short rotation forestry for biofuels.

    Conversely, longer rotations of managed forests increase bole size, and the proportion of the wood that can be used for longer-duration timber products. Adoption of this stance would allow, for some species used today mainly for pulp and grown on less fertile sites, to be grown at longer rotations and result in timber apt for durable uses, consequently, locking C in biomass for longer intervals.

  8. Increasing protection measures

    It is a known fact that the population dynamics of potential insect pests are highly dependent on temperature. Insect pest outbreaks result in considerable economic losses and accumulation of combustible material (dead biomass) in the forest. Conifer monocultures are especially vulnerable to such outbreaks (Cannell et al. 1989).

    At the same time, because the virulence of insect pest outbreaks is affected by the physiological state of trees, foresters should make every effort to ensure vigorous forest stands. With other words, before chemical means are used to fight the outbreaks, it is important to maintain, through silvicultural practices (sanitary operations), a state of active stand growth and to remove declining trees. These requirements can be effected through periodic thinning and removal of diseased trees. Although shorter rotations have been proposed to reduce stand vulnerability to outbreaks of spruce budworm and oak decline (Gottschalk 1995), such measures have only limited applicability, since certain timber products require longer rotations. However, when these interventions fail to prevent insect outbreaks, chemical insecticides may be required.

  9. Increasing fire prevention measures

    Increased risk of forest fires is expected in central North America, Ontario and Michigan, with climate change (Weber and Flannigan 1997), which means that the fire protection capacity will have to be expanded. Intensifying forest fire prevention activity is important to minimize economic losses, reduce the accidental release of CO2 into the atmosphere, maintain forest cover on soils, and allow existing CO2 sinks to remain effective.

    Fire risks are known to be increased by the amount of dead biomass left after logging, or litter in the forests (Torn and Fried 1992; Stocks 1993). Important are also the characteristics of these materials, especially the water content, which vary with rainfall, air temperature and air saturation deficit (Fosberg 1971). If the climate in central North America becomes drier, we might expect a higher frequency of forest fires. Clark, quoted by Cannell et al. (1989), using charcoal deposits in lake sediments, found that there was a higher frequency of fires in Minnesota during a warm period in the fifteenth and sixteenth centuries than at present. Fire risks are also going to increase in areas with high population density. More fire protection measures, such as fire breaks and fire fighting equipment may be needed for achieving the same level of fire protection in the future.

  10. Establishing surveillance systems

    With the development of advanced (spatial) surveillance technology, it is conceivable that such systems will be expanded to address forest health and productivity, monitoring biotic vectors and natural elements, as well as tree and stand responses. In the future, the main objective of surveillance activities will be minimize the «loss» of C from biomass to atmosphere, likely to be caused by either fire and insect outbreaks. In the absence of surveillance and prompt intervention with modern fighting means, fires and insect outbreaks will represent positive feedbacks to CO2 atmospheric concentration (Schindler 1998).

Discussion

All suggested actions fall in the category of «no regrets;» that is they involve good silviculture practices able to improve the quality of stands, lessen the impacts of climate change and adapt existing ecosystems to climate warming. The forecasted climatic change is of such magnitude that assessing its ecological and social implications can already be considered a new scientific field, with immediate and important practical applications. Modern science will have to rapidly assess the ecological consequences of warming and provide effective solutions to a score of emerging problems, made even more complicated in the context of unprecedented population growth, by the need to provide food and shelter in an increasingly variable climatic environment. For forestry, the above described measures attempt to provide some of the solutions, recognizing how complicate and costly their implementation might be. An additional aspect, still awaiting proper assessment, is CO2 fertilization. This is likely to increase the productivity of forest ecosystems and the C sequestration process, if vigorous action is taken immediately. When the biomass accumulated in the first rotation after the implementation of the pro-carbon silviculture will start to decompose, or release C accidentally (e.g. as a result of a major fire), the atmosphere will again be suddenly enriched with additional CO2. People should be under no illusions that these measures, although effective, are no more than means to delay grave ecological effects, that can only be prevented if a permanent solution is found for the permanent storage of the "extra" C, now present in the atmosphere (Herzog et al. 2000).

Regardless of which groups they fall into, all measures must be ecologically sustainable over time, technologically simple, capable of addressing the direct and indirect causes of forest loss by providing economically viable solutions, preferably with low start-up costs, be socially integrative, building on local needs and traditions, and be relatively adaptable to changing economic and ecological conditions (Houghton 1997). However, before any measures are adopted on a wide scale, their relative benefits must be determined. Thus, true net GHGs balances are necessary for the major forest ecosystems of the world, incorporating consideration of all fluxes of gases associated with all phases of growth, harvest, and final disposition of biomass/carbon incorporated in products having slow decomposition rates. Since all the effects of climate change depend on the evolution of temperature and precipitation, modeling of the effects of these primary elements on crop yields, including forest biomass, and water supplies will gain in importance. The scientific community will probably soon witness a new generation of regional models, apt to be used as tools for economic development.

Considering the time frame of climate change, in the short term, the establishment of new forests, especially intensive industrial plantations, has the highest potential for C sequestration. Second only to this, conservation of natural forests and their intensive management should aim at the restoration of their CO2 assimilative capacity, based on climax species. The effectiveness of carbon sequestration by these measures increases significantly when the timber produced is used in durable products, having low decomposition rates. However, in the long term, substitution of timber biomass for fossil fuels, to the extent feasible, appears more sustainable, emphasizing storage/release of energy in biomass without C balance variation (Schlamadinger and Marland 1996). Yet, although such a solution is feasible for a large range of societal needs, it may not appear practical in an energy-hungry world.

An important remark needs to be made concerning the suggested measures. Normally, in forestry, recommendations for change of policies affecting a large geographic area are made when a large number of pilot cultures have reached sufficient age to be evaluated. In the case of climate change, the pace of the warming is such that available time is very limited for this pattern to be effective. At the same time, the continuity and diversity of timber production have to be maintained, while the effectiveness of C sequestration has to be sharply increased. In devising forest management options for this new, pro-carbon silviculture, forest managers will have to integrate, more than in the past, the ecological and silvicultural knowledge and act courageously. The important paradigm here remains that shifting of ecological conditions induces changes in species performance and their ability to withstand adversities. Given the long rotations and the atmosphere´s inertia, for the forester to be able to make sound decisions, especially in regard to species expansions and withdrawals over a certain area, an imperious need exists for a comprehensive socio-political scenario to be developed. This relates to whether mankind is satisfied with stabilization of CO2 concentration at a certain level, accepting its ecological consequences, or would like to decrease it to the level prior to Industrial Revolution, i.e. down to 280 ppmv.

In using the forest ecosystems for C sequestration, the manager is interested to minimize the interval in which biomass accumulation is low, while the soil C losses are high. As we have seen, because of the shift of ecological conditions, although some sites might be well covered with advanced regeneration, it may not be of the species that will form the next generation of forest. Therefore, in the future, the forest managers will increasingly use plantation with species well adapted to warmer conditions. Prompt use of artificial regeneration has the advantage of shortening the transition phase by at least 5 to 15 years, representing an increase of total C storage of around 5% over the rotation (Kurz et al. 1995). Further reduction of the interval between generations and increased biomass accumulation can be obtained through tree improvement programs aimed at fast growth, hydric stress resistance, and response to CO2 fertilization, all these traits helping to reduce the regeneration phase and increase the amount of C stored per rotation. Where artificial regeneration is to be applied, site preparation and vegetation management can reduce substantially the competition and shorten the regeneration phase (Farnum et al. 1983; Schroeder 1991; Dixon 1997). In Ontario, Canada, vegetation management was applied annually on about 40% of area harvested between 1989-1996 (Parker et al. 2000), with herbicides as the most frequent agent of weed destruction (Canadian Council of Forest Ministers 1999). Herbicide use for site preparation causes less damage to the forest floor and does not impact the forest C sequestration.

There are several means through which C sequestration of forests can be enhanced. One of these, especially important for the boreal forest, is fertilization. It is known that growth response to fertilizers application depends on species and site quality, their effect being greatest on poor sites (Foster and Morrison 1983; Schroeder 1991). Although presently fertilization is applied only experimentally and on limited areas (Parker et al. 2000), the climate warming may rise the need for large scale use of fertilizers in boreal forests which, typically, lack nitrogen and respond with increased productivity to its addition, as was proven on jack pine by Morrison and Foster (1990) and Bell et al. (1997). However, additional research is necessary on the carbon balance of fertilization, before it will be applied on large scale for enhancing C sequestration through forestry. This is because important amounts of C are released during production, transportation and spreading of nitrogen fertilizers. Indications exist in the literature showing that even a small gain in productivity due to fertilization can offset the C emissions made for production of ammonia (Schroeder 1991), suggesting that nitrogen fertilization can influence positively the net C balance of boreal forest.

It is the opinion of author that climate warming will represent a dramatic change in harvesting, with preference being given to simple, brutal techniques, such as clearcuts. Such a change will probably be justified through its high operational effectiveness, as well as through the short delay in coverage between the old stand and the new plantation. Strictly, from the viewpoint of the net C balance, on sites where erosion does not present a problem, this change has the advantage of not letting the soil unprotected for a long interval, and not allowing the decomposition process to affect the C stored in soil and detritus. In contrast, any partial cutting system reduces the net CO2 stored, because large amounts of biomass and soil organic matter are exposed to elements for a longer interval. However, this is an issue that deserves more research thorough precise net site C balances, because the soil organic matter may be less affected when an overstory of weeds and advanced regeneration is present (Piene and Van Cleve 1978; Johnson 1992). At the same time, a high intensity of harvesting does not impact negatively the net C balance if a new cover is quickly established (Aber et al. 1978; Harmon et al. 1996).

It is also the opinion of author that, initially, for practical reasons, the atmospheric CO2 increase will continue, probably until an acceptable culmination of CO2 concentration will be attained, possibly, around 550 ppmv. This seems unavoidable since the fossil fuel conservation measures and afforestation/reforestation activities need time to be implemented and show their effect. Roughly, this coincides with the 2 x CO2 option of GCMs. Then, a gradual reversal of climate change will be attempted, through decreasing the CO2 concentration, with distinct targets, established mainly for the conservation of fossil fuels, for instance, for each half century. When such a «plan» for decreasing CO2 concentration is accepted and the time frame of this «pulse» of atmospheric CO2 concentration is known, the society could ask forest managers to implement the measures 4, 5 and 6, related, respectively, to establishing new plantations, shifting species and replacing the drought sensitive ones. Conversely, until the characteristics of such a CO2 «pulse» are known, any attempt to manipulate the forest ecosystems will remain haphazard.

Further research needs

Although the measures outlined above are realistic and could be implemented in Canada and the US over a period of 50 to 100 years, what will count the most is their technical effectiveness and cost. At this point in time, there are no certain data to estimate these aspects, except for typical «yield class» information assessing biomass over time for the major forest species, usually grown in extensive silvicultural systems. From these, approximate C budgets can be developed immediately and quickly validated in the field by means of existing permanent sample plots. To these budgets, data about other C fluxes, e.g. in soils, will have to be added.

A large body of information will have to be developed in a short interval related to:

It is obvious that developing this information, probably first for North America, will require considerable time, which does not exist. A first approximation should be developed immediately based on the best guesses of informed specialists, and fine tuned later, as research results become available.

The process launched by the Kyoto Protocol at end of 1997, recognizing only forest establishment activities in accounting for CO2, requires the 36 developed countries to reduce their C emissions with 6% by 2008 - 2012, compared to 1990 levels (Cannell 1999). However, at this stage, the protocol places no restrictions on C emissions from developing countries and does not consider the CO2 released by other forestry activities such as harvesting, site preparation, planting, fertilization and thinning. Moreover, the process does not acknowledge the potential contribution of forest productivity increases as a CO2 sink. For instance, in Ontario, Canada, over 13% of newly forested land is insufficiently regenerated or remains understocked (Natural Resources Canada 1999). Neglecting the potential of productivity increases to affect the C budget, basing it on a simple accounting of areas, the Kyoto process, as it is conceived today, misses the most important means of influencing this budget.

Finally, intensive silviculture, coupled with superior harvesting efficiency, as well as more efficient biomass burning technologies, leads to a greater efficiency of energy production areas, with no impact on the C budget, a desirable objective.

As a result of the pace set by the Kyoto process, latter in 2001, countries will be required to work with gross approximations, yet adhere to firm commitments. However, this process has at least put forestry on the agenda for future discussions. Possible outcomes of these deliberations might be a broad understanding that the capacity of forests to mitigate climate change, while real, is only temporary and much less effective that thought in the recent past (Cannell 1999). Relying too much on forestry for C sequestration carries a considerable risk, since the newly created C storage can be easily affected by great disturbances, such as geographic fires, that will suddenly release large amounts of C.

Conclusions

At the beginning of the new millennium, the importance of atmosphere´s condition for the quality of life on Earth has become critically important and is now much better understood than in the past. Consequently, the need for healthy forest ecosystems, that are able to restore the atmosphere to its pre-Industrial Revolution condition, is greater than at any time in modern history. For this to happen, the world´s forest ecosystem can be employed, at least as a temporary solution. Therefore, the answer to the question posed by the title of this paper is «Yes». There are definitely numerous forestry options and society must implement them, while searching for permanent solutions. Although intensified carbon sequestration in forests will not solve the complex effects of climate change, it can, nevertheless, make a timely and significant contribution.

With a population expected to reach over 9 billion and a doubling of atmospheric CO2 concentration in 50 years, to which increased climatic variability is added, every delay compounds the efforts that will be necessary to correct this situation. At the meeting in The Hague, Holland, in late 2000, countries were expected to make firm commitments of CO2 emission reduction quotas, an objective now postponed for mid 2001. Industrial countries, including Canada and US, have accepted a 6% emissions reduction target, to be phased in gradually by 2008-2012. This process will be helped by the fact that The World Bank has introduced in January 2000 a revolutionary system of credits, to reward countries that take positive action in the direction of CO2 sequestration through forestry, which is expected to stimulate creation of new forests, primarily in the developing countries.

In this context, the options discussed in this paper should be thoroughly analyzed, adapted to each country realities and implemented immediately. In the process, they will be refined and expanded through the contribution of numerous specialists. Apart from the possibility of restoring the previous condition of the atmosphere, application of these measures will result in an important economic gain and additional timber volume, resulting from CO2 fertilization effect, which will increase the effectiveness of carbon sequestration.

After the considerable efforts made by the science of climate change, the time for action has arrived, and urgent intervention is needed to offset major ecological disturbances.

Acknowledgments

Funding for this research was provided by Ontario Ministry of Natural Resources.

The author is indebted to Lisa Buse for manuscript review.

References

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