ArticlePDF Available

Harvesting in boreal forests and the biofuel carbon debt



Owing to the extensive critique of food-crop-based biofuels, attention has turned toward second-generation wood-based biofuels. A question is therefore whether timber taken from the vast boreal forests on an increasing scale should serve as a source of wood-based biofuels and whether this will be effective climate policy. In a typical boreal forest, it takes 70–120 years before a stand of trees is mature. When this time lag and the dynamics of boreal forests more generally are taken into account, it follows that a high level of harvest means that the carbon stock in the forest stabilizes at a lower level. Therefore, wood harvesting is not a carbon-neutral activity. Through model simulations, it is estimated that an increased harvest of a boreal forest will create a biofuel carbon debt that takes 190–340 years to repay. The length of the payback time is sensitive to the type of fossil fuels that wood energy replaces
Harvesting in boreal forests and the biofuel carbon debt
Bjart Holtsmark
Received: 5 January 2011 / Accepted: 9 August 2011 / Published online: 26 August 2011
Springer Science+Business Media B.V. 2011
Abstract Owing to the extensive critique of food-crop-based biofuels, attention has
turned toward second-generation wood-based biofuels. A question is therefore whether
timber taken from the vast boreal forests on an increasing scale should serve as a
source of wood-based biofuels and whether this will be effective climate policy. In a
typical boreal forest, it takes 70120 years before a stand of trees is mature. When this
time lag and the dynamics of boreal forests more generally are taken into account, it
follows that a high level of harvest means that the carbon stock in the forest stabilizes
at a lower level. Therefore, wood harvesting is not a carbon-neutral activity. Through
model simulations, it is estimated that an increased harvest of a boreal forest will create
a b iofuel carbon debt that takes 190340 years to repay. The length of the payback time
is sensitive to the type of fossil fuels that wood energy replaces
1 Introduction
Carbon neutrality of bioenergy combustion is incorporated into most countries
climate policies. No country imposes taxes on CO
emissions from the combustion of
bioenergy. Moreover, the European Union emissions trading scheme incorporates the
assumption that bioenergy is a carbon-neutral fuel; firms included in this market are not
committed to acquiring and surrendering allowances for emissions from the combustion
of bioenergy.
The reasoning behind the carbon neutrality assumption is that the harvest of one
crop is replaced by the growth of a new crop, which reabsorbs the quantity of carbon
that was released by burning the first crop. This is a reasonable argument in the case
of food-crop-based biofuels, as new crops replace those that are harvested, usually
within 1 year. However, the carbon neutrality of food-crop-based biofuels has recently
Climatic Change (2012) 112:415428
DOI 10.1007/s10584-011-0222-6
Electronic supplementary material The online version of this article (doi:10.1007/s10584-011-0222-6)
contains supplementary material, which is available to authorized users.
B. Holtsmark (*)
Statistics Norway, PO box 8131 Dep, 0033 Oslo, Norway
been questioned. Fargione et al. (2008) found that converting native habitats to cropland
releases CO
from both existing vegetation and carbon stored in soils. Fargione et al.
(2008) therefore concluded t hat production of food-crop-based biofuels may create a
biofuel carbon debt by releasing CO
at a level that is many times the level of annual
greenhouse gas reductions that these biofuels would provide by displacing fossil fuels.
Searchinger et al. (2008) analyzed the global effects of using grain or existing cropland
for biofuel production. They argued that most previous analyses failed to take account of
the carbon emissions that occur as farmers worldwide respond to higher crop prices and
convert forest and grassland to new cropland to replace the grain or cropland diverted to
biofuels; see also Gibbs et al. ( 2010 ); Gurgel et al. (2007); Lapola et al. (2010), and Melillo
et al. (2009), among others.
More generally, Wise et al. (2009) and Searchinger et al. (2009) underlined that the
current practice of accounting for CO
emissions from combustion of bioenergy as zero
means there are strong incentives to clear land, thus releasing large amounts of greenhouse
The criticism of food-crop-based biofuels has not been directed toward wood-based
biofuels to the same degree, at least not wood fuels from boreal forests. Even within the
research community it has been common to consider timber from boreal forests as a carbon-
neutral energy source; see for example Bright and Strømman (2009); Petersen and Solberg
(2005); Raymer (2006); Sjølie et al. (2010); Sjølie and Solberg (2009), and Zhang et al.
(2010). Especially, the possibility of producing liquid biofuels from cellulosic biomass
(second-generation biofuels) is considered a promising alternative to using food crops (Hill
et al. 2006).
This article therefore analyzes the effects of wood fuels from boreal forests with regard
to the release of CO
into the atmosphere. It would be reasonable to argue that wood fuels
are carbon neutral if new trees grew so fast that they replaced those that are felled a year
later or at least after only a few years. However, this is not the case in a boreal forest. Even
after 10 or 20 years, new trees are still only saplings. In typical boreal-forested areas, it
usually takes 70120 years before a stand of trees is mature (Storaunet and Rolstad 2002).
As will be shown in Section 3, this long growth period implies that a higher level of harvest
entails a lower stock of carbon stored in the forest. Hence, the assumption that wood fuels
from boreal forests are climate neutral should be replaced with realistic assumptions about
the dynamic consequences of harvest in a boreal forest.
In this article, I use model simulations to study how increasing the harvest from the
Norwegian forest by 30%, starting in 2010 will influence the net release of CO
into the
atmosphere. With regard to the use of the wood harvested, two cases are considered. In the
first case, I assume that the wood is used as the raw material for manufacturing pellets. The
pellets then replace coal in power plants. This is a relevant example because power
producers in Europe are committed to acquiring and surrendering allowances for emissions
resulting from fossil-fuel combustion only, not for emissions resulting from the combustion
of bioenergy. In the case of Norway the example has special relevance, as the worlds
second-largest wood-pellet production plant (BioWood Norway) h as recently been
established on the west coast of Norway, and it will manufacture pellets on a large scale
for this purpose.
In the second example, I look at the use of wood to produce second-generation liquid
biofuels. This example is relevant as NCPA (2010) presented ambitious scenarios for the
production of second-generation liquid biofuels based on wood.
The simulations show that increasing the harvest in a boreal forest will cause a
significant initial release of CO
. Along the lines of Fargione et al. (2008), I label this
416 Climatic Change (2012) 112:415428
release of CO
from the forest as a carbon debt. Over time, the carbon debt could be repaid
through regrowth in the harvested area and through replacement of fossil fuels as an energy
source. In this study, the payback time is found to be within the interval of 190340 years,
depending on the type of fossil fuel that the wood fuel replaces.
The model simulations in this article are based on the properties of a Norwegian forest.
However, the conclusions are relevant to boreal forests more generally. Additionally, it
should be kept in mind that boreal forests store almost twice as much carbon as tropical
forests (Kasischke 2000, p. 20).
A closely related study is that conducted by McKechnie et al. (2011), although they
studied a temperate forest in Ontario with faster regrowth. Their model simulations have a
timeframe of 100 years, while I present simulations 400 years into the future. In the case in
which pellets replace coal in power plants, McKechnie et al. (2011) deduced a payback time
shorter than that determined in this article. However, this is as expected after taking the
more rapid growth in temperate forests into account. McKechnie et al. (2011) did not
specify the payback time when wood fuels replace liquid fossil fuels, as this was beyond
their simulation timeframe.
Another closely related report is Biomass Sustainability and Carbon Policy Study
published by the Manomet Center for Conservation Sciences (2010). They calculated a
payback time shorter than that determined in this study. However, the Manomet report
considered single-harvest events only. As discussed in Section 3.1 and in the supplemental
online material, this makes a large difference.
It should also be mentioned that this article analyzes the consequences of taking
bioenergy from boreal forests when the supply of bioenergy is generated through increased
harvest. Using by-products from the forest industry as bioenergy is a different and less
controversial matter, and is not discussed in this article. One should, however, be aware that
increased demand for by-products from the forest industry could increase the harvest
through indirect market effects.
The next section presents the model and crucial assumptions made. Section 3 discusses a
number of model simulations. First, Section 3.1 considers the relationship between the
harvested volume and the forests carbon stock in long-term steady states. Second,
Section 3.2 describes the consequences in both the short and long terms of increasing the
annual harvested volume. Third, Section 3.3 studies the net effects on CO
emissions when
the increased harvest considered in Section 3.2 is used as bioenergy and replaces fossil
fuels. The findings are discussed in Section 4. The supplemental online material provides
firstly a detailed model description with all parameter values. Furthermore, the online
material (1) clarifies the importance of considering not only a single-harvest event in the
case where a permanently higher harvest level is to be analyzed, and (2) presents two
scenarios where greater harvest is achieved through expansion of the harvested area, rather
than adjusting the rotation length as considered in Sections 3.2 and 3.3.
2 Model and methods
The model contains a fixed set of 75 000 parcels, each parcel covering an area of
, and all having identical dynamic properties with regard to accumulation of dead
and living biomass. However, the time since the last clear-cutting in the parcel (i.e., the
parcels stand age) varies. The Norwegian forest has a high proportion of youn g stands;
see Larsson and Hylen (2007). On the basis of their work an age structure in the starting
year of the simulations is assumed such that the stand age for 37% of parcels is less than
Climatic Change (2012) 112:415428 417
30 years, while that for 21% is more than 80 years. Hence, the stand age for 42% of
parcels is between 30 and 80 years. For further details, see the supplemental online
Essential for the dynamics of the model is that immediately after clear-cutting has taken
place in a parcel, the parcels volume of living biomass drops to zero, and thereafter, the
growth path described in Fig. 1 begins again. The volume of living biomass in a single
parcel depends solely on the parcels stand age. The parcels productivity is fairly normal
for a boreal forest and is close to the growth path of productivity class 14 defined by
Braastad (1975 ).
An important part of the model is the module taking care of carbon stored in deadwood.
The trunks are assumed to constitute 48% of the living biomass. Hence, after clear-cutting a
significant amount of harvest residues is left on the parcel (see Fig. 1). Different cohorts
of natural deadwood and harvest residues are treated separately. With regard to the speed of
decomposition of deadwood, there is uncertainty. On the basis of the discussion presented
by Liski et al. (2005), I assumed that 75% of harvest residues and 70% of natural deadwood
decomposed in 50 years. After 100 years, both types of deadwood are assumed to have
decomposed completely. Owing to the uncertainty of these points, however, the
supplemental online material presents a number of sensitivity simulations with regard to
these assumptions.
The accumulation of natural dead wood in each parcel of forest after felling and
replanting is also shown in Fig. 1. Natural losses are low until the trees are 8090 years old,
increase sharply until the trees are 150 years old, and then gradually stabilize. Note that the
periodization (time unit) in the model is 5 years.
Changes in the stock of biomass in old forests are uncertain (Carey et al. 2001; Pregitzer
and Euskirchen 2004; Seely et al. 2002). It is here assumed that there is a constant volume
biomass of older stands; see Fig. 1. As more recent data suggest that old growth forests are
significant carbon sinks (see Luyssaert et al. 2008), this might be considered conservative.
Assuming that older stands continue to accumulate carbon would imply a longer payback
0 50 100 150 200 250 300 350 400
1000 m3 wood
Stock of dead and living wood (1000 tonnes carbon)
Stand a
Fig. 1 A single parcel. The development of the volumes of living wood, harvest residues and natural
deadwood after clear-cutting and replanting in the standard parcel. Stand age at time of last felling was
95 years
418 Climatic Change (2012) 112:415428
time of the carbon debt than found in this article. However, owing to the uncertainty of this
point, and claims that the probability of carbon loss due to different types of disturbances is
greater in older forests, Holtsmark (2010) assumed, as a very conservative estimate, that the
stock of wood and thus the carbon stored in the biomass decline substantially as a parcel
ages. Holtsmark (2010) therefore deduced a payback time shorter than that determined in
this article.
An important point is the role of soil as a carbon sink. In a boreal forest, in contrast
to a tropical rain forest, a large share of the carbon is stored in the soil. According to
Kjønaas et al. (2000), more than 80% of carbon in Norwegian forests is stored in the soil.
An important question is therefore whether harvest is likely to t rigger the r elease of
carbon from soil. As underlined by Fontaine et al. (2007); Friedland and Gillingham
(2010), and Nilsen et al. (2008), the accumulation and possible release of carbon from the
soil are complicated processes that are not easily modeled. I have therefore chosen to
ignore the possibility that harvesting may reduce the capacity of the soil as a carbon sink,
and have considered only how harvesting influ ences the stock of carbon stored in dead
and living biomass, although Nakane and L ee (1995) and Nilsen et al. (2008) suggest that
clear-cutting might trigger the release of carbon from soil, especially if tops and branches
are harvested in addition to trunks. This last point is further underlined by Holmgren et al.
(2007); Kujanpää et al. (2010 ); Kirkinen et al. ( 2008); Palosuo et al. (2001); Repo et al.
(2011), and Schlamadinger et al. (1995). Hence, the estimated payback time of the carbon
debt would probably have been longer if I had relied on less conservative assumptions at
this point.
The carbon content of a cubic meter of biomass depends on the woods density. I assume
throughout a density of 423 kg/m
, and that half of the mass is carbon. This gives 0.211
tonnes of carbon per m
, or 0.774 tonnes CO
per m
wood used as fuel. For further details,
see the supplemental online material.
3 Results
3.1 Relationship between the length of the rotation cycle and the carbon stock in different
steady states
Figure 2 provides relevant information for a discussion on carbon neutrality. It shows the
volume of timber felled annually (curve) and the entire forests stock of carbon in dead and
living wood (columns) for rotation cycles of different lengths (horizontal axis).
It should be noted that Fig. 2 considers the entire forest area of 75000 km
and shows
the forest in different steady states, in the sense that the length of the rotation cycle is
constant and has been constant for so long that both the harvest and standing volume are
also constant over time.
Figure 2 confirms that the maximum harvest (volume felled) is obtained with a rotation
cycle of 90 years. The carbon stock of dead and living biomass, on the other hand,
monotonously increases as the rotation period is extended.
The stock of carbon is almost twice as large with a 250-year rotation cycle as with a 90-year
rotation cycle. This may seem difficult to reconcile with Fig. 1, which shows that the stock of
carbon in a single parcel increases by less than 25% as the stand age increases from 90 to
250 years. The explanation is that as the length of the rotation cycle increases, there are fewer
and fewer parcels that have recently been clear-cut. In other words, if the rotation cycle is
long, a large share of the parcels will at any point in time carry a large stock of wood. If the
Climatic Change (2012) 112:415428 419
rotation cycle is short, on the other hand, a large proportion of the forest will at any point in
time be relatively recently felled, and its stock of wood will be correspondingly small.
Figure 2 indicates that it is misleading to claim that wood provides carbon-neutral
bioenergy, even in the long term. It shows that if the harvest is permanently large, which
requires short rotation cycles, the carbon pool of the forest will be permanently small. In
contrast, if the annual harvest is small, with correspondingly long rotation cycles, the
carbon pool will be permanently large. With a 90-year rotation cycle, for example, an area
of 833 km
can be felled each year, giving an annual harvest of 22.5 million cubic meters
) of timber and 467 million tonnes of carbon (MtC) stored in dead and living wood.
With a 250-year rotation cycle, 300 km
can be felled annually and the annual harvest is
only 9.5 Mm
; the carbon stored in dead and living wood, on the other hand, rises to 933
MtC (see Table 1).
In other words, increasing the harvest to a higher level on a permanent basis does not
merely result in a temporary drop in the forests carbon stock that will in the long term be
entirely counterbalanced by CO
uptake by the forest. On the contrary, a permanent
increase in the harvest results in a permanently lower forest carbon stock. Hence, increasing
the harvest level is not a carbon-neutral change, either in the short term or in the long term.
This also shows that the question of carbon neutrality cannot be resolved by studying the
effect of a single harvest in a single year with subsequent planting. Such a single-event
perspective is an oversimplification that does not incorporate the important long-term
0 50 100 150 200 250 300 350 400
th of rotation periods
Stock of dead and living wood (MtC)
Annual harvest (Mm3/year)
Living wood
Fig. 2 The entire forest. Annual volume of timber felled (black curve) and quantity of carbon stored in dead
and living wood (columns) in different steady states for rotation cycles of different lengths
Length of the
rotation cycle
Carbon stored in dead
and living biomass
90 22.5 833 467
250 9.5 300 933
Table 1 Example of two
different steady states
420 Climatic Change (2012) 112:415428
dynamic effects on the forests carbon stock (see the supplemental online material for
further discussion).
At this point, the report on biomass sustainability presented by the Manomet
Center for Conservation Sciences (2010) should be mentioned. This report considers
only a single-harvest event rather than conducting “…a more complicated series of
repeated harvest entries. (ibid. p. 85). The M anomet report is important along different
lines, as it contains new information and provides an interesting discussion on the carbon
neutrality of wood energy. However, the reports relatively optimistic conclusions with
regard to the time lag between harvest, the released volume of carbon dioxide, and the
payback time of the carbon debt reflect the reports single-harvest approach and therefore
do not take into account important features of the long-term effect of a hig her level of
harvest on the forests carbon stock. As shown in the supplemental online material,the
payback time mo re t han doubles if a series of subsequent h arvest events are considered
instead of a single-harvest event.
3.2 Short-term and long-term effects of increasing the harvest
The previous section considered the carbon stock of a forest in a steady state in the sense
that the rotation cycles were constant over time, giving the forest an even age structure.
This section describes the short-term and long-term effects of increasing the harvest in a
forest with an uneven age structure similar to the age structure found for a Norwegian
In the reference scenario, the annual harvest is 10 Mm
and no residues are harvested.
This is compared with a scenario where the annual harvest increases by 3 Mm
to 13 Mm
with 2010 as the first year of increased harvest. In addition, this scenario assumes that
0.6 Mm
of residues is harvested annually.
The chosen numerical example has relevance, as the annual harvest from Norwegian
forests has varied around 10 Mm
for several decades (NCPA 2010). However, the
Norwegian government wants to increase the harvest to increase the supply of bioenergy,
and an increase in the annual harvest to 13 Mm
is frequently discussed; see NCPA (2010).
What effect does a higher harvest level have?
Given the assumed age structure, with a large share of the parcels having a low stand
age, and because the annual harvest is limited to 10 Mm
in the reference scenario, the
forests carbon stock increases until the end of the 22nd century (see Fig. 3). Moreover,
even if the harvest is increased to 13 Mm
, the forests carbon stock increases over this
period, although at a lower rate. Recall here that the maximum harvest that could be
sustained in a steady state is 22.5 Mm
/year; see Fig. 2.
It is important to note that Fig. 2 shows different steady-state situations for rotation
cycles of different lengths, whereas Fig. 3 shows the transition from the current state of the
forest to towards a new steady state.
For further clarific ation, consider the ref erence (small-har vest) scenario as
illustrated by the upper curve in Fig. 3. The figure shows that b y 2100, the stock of
carbon has more than doub led from the 2005 level to 857 MtC (see a lso Table 2).
However, Figure 3 also shows that in the larger-harvest scenario, the carbon stock is only
775 MtC in 2100. In other wo rds, the increase in the harvest has resulted in a carbon
stock th at is 82 MtC lower in 2100 than it would have been with the lower harvest level.
More generally, the vertical distance between the upper and lower curves in Fig. 3 shows
the n et reduction in the forests carbon stock as a result of the greater harvest; see also the
red curve in Fig. 4.
Climatic Change (2012) 112:415428 421
3.3 Reducing the use of fossil energy by increasing the use of wood energy
The previous section considered how felling affects the stock of carbon stored in the forests
dead and living wood. The argument for felling more timber is precisely that using wood as
a source of bioenergy can reduce the use of fossil energy and thus cut CO
emissions. In
this section, I consider the extent to which increasing the timber harvest for bioenergy
production can replace the use of fossil energy. Taking account of both the replacement
effect on fossil fuel combustion and the effects on the forests carbon stock, it is possible to
calculate the net CO
effects of increased logging.
The quantity of fossil energy that wood fuels can replace varies widely depending on
precisely which technologies are involved. Here I discuss two examples that show how two
different types of wood fuels will affect net CO
emissions. In the first case, I have assumed
that the wood is used as the raw material for manufacturing pellets. The pellets then replace
coal in power plants. In the second example, I look at the use of wood to produce second-
generation liquid biofuels.
The exact volumes of CO
emissions that can be eliminated using wood energy are of
great importance. On the basis of the works of Sjølie and Solberg (2009) and Weisser
(2007), I have assumed that using 1 m
of wood, processed to pellets, instead of coal in a
power plant can eliminate 0.5 tonnes of fossil-generated CO
emissions. The method used
to calculate this figure is described in further detail in the supplemental online material.
2000 2100 2200 2300 2400
Million tonnes carbon
Reference scenario (low harvest) Hi
her harvest level with use of fellin
Fig. 3 Carbon stored in wood in the two scenarios considered in Sections 3.2 and 3.3
Table 2 Carbon stock, emission reductions, and remaining carbon debt in the scenarios considered in
Section 3.2. All figures are in millions of tonnes of carbon
2005 2100 2200 2300
Carbon stored in biomass in reference (small-harvest) scenario 417 857 915 918
Carbon stored in biomass in large-harvest scenario 417 775 820 822
Drop in carbon stock due to increased harvest 82 95 96
Accumulated reductions in fossil carbon emissionswood fuels replace coal 46 95 144
Remaining carbon debtwood fuels replace coal 36 0 48
Accumulated reductions in fossil carbon emissionswood fuels replace oil 26 54 81
Remaining carbon debtwood fuels replace oil 56 42 15
422 Climatic Change (2012) 112:415428
To calculate the volume of fossil emissions that can be eliminated using second-
generation biofuels, I followed NCPA (2011, p. 32). This report concludes that using 1 m
of wood processed to second-generation liquid biofuel can eliminate 0.28 tonnes of CO
emissions generated through the combustion of fossil fuels.
We are now ready to calculate the net effect of the increased harvest on
accumulated CO
emissions. Recall that the overall increase in the annual harvest is
3.6 Mm
when a share of the residues is also harvested. From Fig. 4 it is possible to gain
a visual impression of the results by comparing the lines with the curve. The red curve in
Fig. 4, the elevation of which is equal to the vertical distance between the curves in
Fig. 3, shows the difference in the carbon stock of the forest between the large- and small-
harvest scenarios. The lines show the accumulated fossil CO
emissions that can be
eliminated by increasing the volume of timber harvested and using this harvest to replace
fossil fuels in the two ways discussed. The remaining carb on debts in the two cases
considered are equal to the vertical distance between the red curve and the two lines in
Fig. 4. As long as the curve is above the considered l ine, the remaining carbon debt is
positive. When the line is above the curve, the carbon debt has been fully repaid and a
carbon dividend is collected, using the term introduced by Manomet Center for
Conservation Sciences (2010).
Firstly, consider the case where the wood is processed to pellets and replaces coal in a
power plant. In that case, each cubic meter of wood eliminates 0.5 tonnes of fossil-
generated CO
emissions. This means that 1.8 MtCO
or 0.5 MtC of fossil emissions are
eliminated each year. Hence, by 2100, fossil CO
emissions corresponding to 46 MtC have
been eliminated (see Table 2 and the broken line in Fig. 4).
As mentioned, the increased harvest means that the carbon stock of the forest by 2100 is
82 MtC less than it would have been if the annual harvest had been maintained at 10 Mm
Subtracting 46 MtC (the accumulated drop in fossil carbon emissions), it follows that in the
2000 2050 2100
2200 2250 2300 2350 2400
Million tonnes carbon
Drop in the forest carbon stock due to increased logging
Accumulated reduction in carbon emissions from coal combustion due to increased
supply of pellets
Accumulated reduction in carbon emissions from fossil fuels due to increased supply of
liquid biofuels
Fig. 4 The two straight lines show the accumulated reductions in CO
emissions from combustion of fossil
energy achieved by increasing the supply of bioenergy through a higher harvest level. The red curve in Fig. 4
shows the difference in the carbon stock between the small- and large-harvest scenarios
Climatic Change (2012) 112:415428 423
pellets case, the remaining carbon debt in 2100 is 36 MtC. In other words, although
increasing the harvest eliminates fossil CO
emissions from coal combustion corresponding
to 46 MtC, the net accumulated release of carbon to the atmosphere will be 36 MtC higher
in the period 20102100 in the large-harvest scenario than in the reference (small-harvest)
The development o f th e remaining carbon debt is shown in Fig. 5. Note that the
elevations of the curves in Fig. 5 are equal to the vertical distances between the red curve
and the two lines in Fig. 4. Figure 5 shows that i n the pellet case, the remaining carbon
debt is declining in 2100 and becomes negative around 2200, that is, 190 years after the
increase in the harvest. Hence, the analysis suggests that increasing the harvest and the
use of wood fuels to replace coal in power plants could, for a long period of time, result
in significantly greater CO
emissions than the combustion of the coal that the increased
harvest replaces.
Secondly, consider the effect of using the extra harvest of wood as raw material in the
production of second-generation liquid biofuels. In that case, each cubic meter of wood
eliminates 0.28 tonnes of fossil-generated CO
emissions. This means that 1.01 MtCO
0.27 MtC of fossil emissions are eliminated each year. Hence, by 2100, fossil CO
emissions corresponding to 26 MtC have been eliminated; see the level of the lower line in
2100 in Fig. 4, which shows the accumulated reduction in fossil carbon emissions in this
The lower line in Fig. 4 is below the red c urve through out the 21
, and 23
centuries, and crosses the red curve in 2350. Thus, the calculations indicate that using
second-generation liquid biofuels produced from boreal timber rather than continuing to
use fossil diesel may actually increase the net accumulated release of CO
for 340 years,
i.e. generate a carbon debt that w ill be repaid only after more than three centuries. This is
in contrast to the results obtained by assuming that wood is a climate-neutral fuel, where
the effect on the forests carbon stock is completely ignored and a carbon dividend i s thus
assumed to be generated from day one and to be equal to the elevation of the lines in
Fig. 4.
2000 2050 2100 2150 2200 2250 2300 2350 2400
Million tonnes carbon
Remaining carbon debt –second-generation biofuels replace petrol
carbon debt –pellets replace coal
Fig. 5 Development of the remaining carbon debt due to increased harvest when the increased harvest is
used to replace fossil fuels
424 Climatic Change (2012) 112:415428
4 Discussion and conclusion
Bioenergy is usually considered carbon neutral and an important part of a strategy for
reducing CO
emissions; see for example IPCC (2000). The generation of biomass in boreal
forests is significant and could potentially serve as an important source for an increased
supply of bioenergy.
The traditional assumption that wood fuels are carbon neutral would have been
appropriate if trees harvested were replaced by new trees within a short period of time.
However, the typical life cycle of a spruce tree in boreal forests includes a growth phase
that lasts about 100 years and then a phase in which the mass remains relatively stable for a
further 100 years. The tree then dies, but remains standing for about 30 years before falling
to the ground and gradually decaying over the course of the following 100 years (Storaunet
and Rolstad 2002).
From that point of view, it appears obvious that harvest from boreal forests is not a
climate-neutral activity. However, as should be made clear from the previous sections, forest
dynamics cannot be understood by studying individual trees or a single harvest and
subsequent regeneration of the felled trees. I have therefore described and simulated a
dynamic model of the Norwegian forest.
In the simulations presented in this article, the harvest is increased by 30%, while the
forest increment is still positive over the whole of the 21st century. Nevertheless, the
increase in the harvest means that the carbon stock in the stylized forest stabilizes at a
different level, as would be expected. Hence, even if the forest increment is positive, wood
harvesting and combustion are not carbon-neutral activities.
The article also presents calculations illustrating the net effect on the CO
release of
increased logging when the biomass made available replaces fossil fuels as energy sources.
Two examples are described: processing wood to pellets for use in coal-fired power plants,
and processing wood to liquid biofuels, which are used to replace fossil oil.
The articles first main finding is that increasing the use of wood from a boreal forest to
replace coal in power plants will create a carbon debt that will only be repaid after
approximately 190 years. Secondly, if the wood is used to produce second-generation liquid
biofuels and replaces fossil diesel, the payback time of the carbon debt is estimated to be
340 years.
In addition, it is important to remember that the analyses presented here do not take into
account the effect of providing subsidies for various alternative forms of energy as a means
of reducing the use of fossil energy. Such subsidies tend to increase overall energy use; see
for example Hutchinson et al. (2010). If this is taken into account, the emission-increasing
effect of using wood as energy will become even more pronounced. A complete analysis
should also include such effects.
An uncertain aspect of the parameterization of the model is the determination of changes
in the volume of deadwood over time. Sensitivity calculations were therefore carried out to
test the effect of varying the rate of decay for deadwood. These simulations show that the
parameterization is not a critical factor (see the supplemental online material).
Nevertheless, it should be stressed that the purpose of this article is not to provide
definitive answers but to draw attention to the importance of taking both short- and
long-term dynamic e ffects of increasing the timber harvest more fully into account
when evaluating the effect o n emissions of increasing the use of energy from wood
combustion. The analysis carri ed out here could be improved along several
dimensions, not least considering more heterogeneous forests with areas of different
productivity while taking fu ll account of how harvest in boreal forests influences the
Climatic Change (2012) 112:415428 425
amount of carbon stored in the soil. Anoth er topic for future research should be the
capacity of old growth forests as carbon stores when the likeliness of disturbance is
taken into account, and how the frequency of disturbance migh t change in a warmer
climate. And finally, it should be noted that this paper calculate estimates of the
effects on accumulated net release of CO
into the atmosphere along different time
horizons only. To provide a complete picture of the climatic effects of this would require a
model of the relationship between net release of CO
, its persistence in the atmosphere
and the corresponding effects on radiative forcing, a s well as possible albedo effects of
clear-cutting in boreal forests.
It should also be underlined that the analysis presented here does not make arguments
against the use of bioenergy from boreal forests in general. If bioenergy is obtained through
increased use of residues from different forest-related industries, the CO
effects are
probably favorable.
Nevertheless, the commonly applied assumption that wood fuels are climate neutral is
not tenable. If this assumption is reevaluated, it may also be necessary to reevaluate the
current taxes and subsidies that apply to bioenergy and forestry. It is not at all clear whether
current policy takes sufficient account of the potential of forests as carbon sinks or of the
fact that burning wood results in CO
emissions. As highlighted by Searchinger et al.
(2009), for example, putting a high price on CO
emissions from fossil energy emissions
while considering bioenergy to be carbon neutral would create strong incentives to clear
The claim that using wood fuels is carbon neutral is based on the approximation that
logging has a negligible effect on the forests carbon stock. This would be a reasonable
approximation if there were a negligible time lag between felling and full regrowth. The
carbon-neutrality claim ignores the significance of this time lag, and the dynamics that
follow, not least that there will be a permanent reduction in the stock of both dead and
living biomass in the forest if the harvest is permanently increased. Thus, making the
common assumption that using wood as bioenergy is carbon neutral also means that it is
assumed that all the effects on the forests carbon stock are so small that they can be
Acknowledgements Ketil Flugsrud, Hans Goksøyr, Henrik Lindgaard, Olav Norem, Hans Henrik Ramm,
and Trygve Refsdal provided important assistance and ideas at an early stage of this work. I also wish to
thank four anonymous referees as well as Iulie Aslaksen, Rasmus Astrup, Lise Dalsgaard, Per Arild
Garnåsjordet, Cathrine Hagem, Per Kr. Rørstad, Hanne K. Sjølie, and participants at a seminar held at the
University for Life Sciences in October 2010 for comments and suggestions that improved the manuscript
significantly. The Norwegian Research Council provided funding as part of the project Environmentally
friendly transport: How to design policies for sustainable introduction of biofuels.
Braastad H (1975) Yield Tables and Growth Models for Picea abies. Reports from The Norwegian Forest
Research Institute 31.9
Bright RM, Strømman AH (2009) Life cycle assessment of second generation bioethanol produced from
Scandinavian boreal forest resources. J Ind Ecol 13:514530
Carey EV, Sala A, Keane R, Callaway RM (2001) Are old forests underestimated as global carbon sinks?
Global Change Bio 7:339344
426 Climatic Change (2012) 112:415428
Fargione J, Hill J, Tilman D, Polasky S, Hawthorne P (2008) Land clearing and the biofuel carbon debt.
Science 319:12351238
Fontaine S, Barot S, Barré P, Bdioui N, Mary B, Rumpel C (2007) Stability of organic carbon in deep soil
layers controlled by fresh carbon supply. Nature 450:277281
Friedland AJ, Gillingham KT (2010) Carbon accounting a tricky business. Science 327:411412
Gibbs HK, Ruesch AS, Achard F, Clayton MK, Holmgren P, Ramankutty N, Foley JA (2010) Tropical forests
were the primary sources of new agricultural land in the 1980s and 1990s. P Natl Acad Sci 107:16732
Gurgel AJ, Reilly M, Paltsev S (2007) Potential land use implications of a global biofuels industry. J Agr
Food Ind Organ 5:134
Hill J, Nelson E, Tilman D, Polasky S, Tiffany D (2006) Environmental, economic, and energetic costs and
benefits of biodiesel and ethanol biofuels. P Natl Acad Sci 103:1120611210
Holmgren K, Eriksson E, Olsson O, Olsson M, Hillring B, Parikka M (2007) Biofuels and climate neutrality
system analysis of production and utilisation. Elforsk report 07:35
Holtsmark B (2010) Use of wood fuels from boreal forests will create a biofuel carbon debt with along
payback time. Discussion Paper 637. Statistics Norway
Hutchinson E, Kennedy PW, Martinez C (2010) Subsidies for the Production of Cleaner Energy: When do
they Cause Emissions to Rise? The B.E. Journal of Economic Analysis & Policy: Vol. 10, Iss. 1, Article
IPCC (2000) Special report on emissions scenarios. Working Group III, Intergovernmental Panel on Climate
Change (IPCC), Cambridge University Press, Cambridge
Kasischke ES (2000) Boreal ecosystems in the global carbon cycle. In: Kasischke ES, Stocks BJ (eds) Fire,
climate and carbon cycling in the boreal forest. Springer, New York
Kirkinen J, Palosuo T, Holmgren K, Savolainen I (2008) Greenhouse impact due to the use of combustible
fuels: life cycle viewpoint and relative radiative forcing commitment. Environ Manage 42:458469
Kjønaas O, Aalde JH, Dalen LS, de Wit HA, Eldhuset T, Øyen BH (2000) Carbon stocks in Norwegian
forested systems. Biotechnol Agron Soc Environ 4:311314
Kujanpää M, Eggers J, Verkerk H, Helin T, Lindner M, Wessman H (2010) Carbon balance of forest residue
collection and combustion in Southern Finland. Proceeding paper from the 18th European Biomass
Conference and Exhibition
Lapola D, Schaldach MR, Alcamo J, Bondeau A, Koch J, Koelking C, Priess JA (2010) Indirect land-use
changes can overcome carbon savings from biofuels in Brazil. P Natl Acad Sci 103:1120611210
Larsson JY, Hylen G (2007) Statistics of forest conditions and forest resources in Norway. Reports from The
Norwegian Forest Research Institute 1/07
Liski TP, Peltoniemi M, Sievänen R (2005) Carbon and decomposition model Yasso for forest soils. Ecol
Model 189:168182
Luyssaert S, Schulze ED, Börner A, Knohl A, Hessenmöller D, Law BE, Ciais P, Grace J (2008) Old-growth
forests as global carbon sinks. Nature 455:213215
Manomet Center for Conservation Sciences (2010) Massachusetts Biomass Sustainability and Carbon Policy
Study: Report to the Commonwealth of Massachusetts Department of Energy Resources. In Walker T
(ed) Natural Capital Initiative Report NCI-2010-03. Brunswick, ME, USA
McKechnie J, Colombo S, Chen J, Mabee W, Maclean HL (2011) Forest bioenergy of forest carbon? Assessing
trade-offs in greenhouse gas mitigation with wood-based fuels. Environ Sci Technol 45:789795
Melillo JM, Reilly JM, Kicklighter DW et al (2009) Indirect emissions from biofuels: how important?
Science 326:13971399
Nakane K, Lee NJ (1995) Simulation of soil carbon cycling and carbon balance following clear-
cutting in a mid-temperate forest and contribution to the sink of atmospheric C O
. Vegetatio
NCPA (2010) Tiltak og virkemidler for å norske klimamål mot 2020 (Efforts and policies for Norwegian
climate goals toward 2020). The Norwegian Climate and Pollution Agency (NCPA), Norwegian Water
Resources and Energy Directorate, The Norwegian Petroleum Directorate, Statistics Norway, The
Norwegian Public Road Administration. Report TA2590
NCPA (2011) Skog som biomasseressurs (Forests as biomass resources). Report from The Norwegian
Climate and Pollution Agency. Report TA 2762
Nilsen P, Hobbelstad K, Clarke N (2008) Opptak og utslipp av CO
i skog (Capture and Emission of CO
from Norwegian Forests). Norwegian Forest and Landscape Institute, report no. 06/2008
Palosuo T, Wihersaari M, Liski J (2001) Net greenhouse gas emissions due to energy use of forest residues
impact of soil carbon balance. EFI Proceedings no 39, Wood biomass as an energy source challenge in
Europe. European Forest Institute, Joensuu, 115130
Climatic Change (2012) 112:415428 427
Petersen AK, Solberg B (2005) Environmental and economic impacts of substitution between wood products
and alternative materials: a review of micro-level analyses from Norway and Sweden. Forest Policy
Econ 7:249259
Pregitzer KS, Euskirchen ES (2004) Carbon cycling and storage in world forests: biome patterns related to
forest age. Glob Change Biol 10:20522077
Raymer AKP (2006) A comparison of avoided greenhouse gas emissions when using different kinds of wood
energy. Biomass Bioenerg 30:605617
Repo A, Tuomi M, Liski J (2011) Indirect carbon dioxide emissions from producing bioenergy from forest
harvest residues. GCB Bioenergy 3:107115
Schlamadinger B, Spitzer J, Kohlmaier GH, Lüdeke M (1995) Carbon balance of bioenergy from logging
residues. Biomass Bioenerg 8:221234
Searchinger TD, Heimlich TD, Houghton RA et al (2008) Use of US croplands for biofuels increases
greenhouse gas through emissions from land-use change. Science 319:12381240
Searchinger TD, Hamburg SP, Melillo J et al (2009) Fixing a critical climate accounting error. Science
Seely B, Welham C, Kimmins H (2002) Carbon sequestration in a boreal forest ecosystem: results from the
ecosystem simulation model, FORECAST. Forest Ecol Manag 169:123135
Sjølie HK, Solberg B (2009) Greenhouse Gas Implications by Production of Wood Pellets at the BioWood
Norway plant at Averøy, Norway. Report drawn up for BioWood Norway. Department of Ecology and
Natural Resource Management, Norwegian University of Life Sciences
Sjølie HK, Trømborg E, Solberg B, Bolkesjø TF (2010) Effects and costs of policies to increase bioenergy
use and reduce GHG emissions from heating in Norway. Forest Policy Econ 12:5766
Storaunet KO, Rolstad J (2002) Time since death and fall of Norway spruce logs in old-growth and
selectively cut boreal forest. Can J For Res 32:18011812
Weisser D (2007) A guide to life-cycle greenhouse gas (GHG) emissions from electric supply technologies.
Energy 32:14531559
Wise M, Calvin K, Thomson A, Clarke L, Bond-Lamberty B, Sands R, Smith SJ, Janetos A, Edmonds J
(2009) Implications of limiting CO
concentrations for land use and energy. Science 324:11831186
Zhang Y, McKechnie J, Cormier D, Lyng R, Mabee W, Ogino A, MacLean HI (2010) Life cycle emissions
and cost of producing electricity from coal, natural gas, and wood pellets in Ontario, Canada. Environ
Sci Technol 44:538544
428 Climatic Change (2012) 112:415428
... On the other hand, it is argued that longer temporal boundaries should not be applied when assessing CN of biomass because they overshoot established Paris Agreement targets and hinder efforts to mitigate climate change (Diehl et al. 2020). In many cases, the actual carbon payback period is very long (Holtsmark 2012). When biomass is combusted, it immediately increases the concentration of C in the atmosphere, and it is theorized that a delay between C release and C sequestration could have a temporary warming effect (Muys et al. 2014). ...
Full-text available
The exploitation of forest biomass for bioenergy is commonly perceived as part of a broad strategy for climate change mitigation due to the view that forest biomass is carbon neutral. The aims of this study are to distinguish the most widely used definition of carbon neutrality and to identify the most frequently discussed aspects of the concept of carbon neutrality. This research is conducted in the form of a scoping review. The results of the scoping review demonstrated that there is no generally accepted definition of carbon neutrality. Eight main concepts of carbon neutrality were identified. The most frequently discussed aspects of the carbon neutrality concept were temporal and spatial boundaries, scenario-based assumptions, and the source of biomass feedstock. This research provides a comprehensive summary of the concept of carbon neutrality and contributes to the debate regarding forest biomass exploitation for bioenergy.
... They also emphasized that nitrous oxide emissions from the growing fertilizer use should also be taken into consideration when designing a GHG emission reduction scheme. B. Holtsmark [38] discussed whether wood harvesting is a carbon-neutral activity and proved that it is not. He estimated that it took 190~340 years to repay biofuel carbon debt generated from an increased harvest of a boreal forest and verified that high levels of harvest indeed lead to low levels of carbon stock. ...
Full-text available
Climate change is one of the most urgent challenges facing the world. All countries should take joint actions to achieve the goal of carbon neutrality, which include controlling global warming to within a 1.5 °C temperature rise, to mitigate the extreme harm caused by climate change. However, ways in which to achieve economically and environmentally sustainable carbon neutrality are yet to be established. Carbon neutrality appears frequently in international policy and the scientific literature, but there is little detailed literature. It is necessary to conduct an in-depth analysis of the development context of its research. This paper analyzed the literature on carbon neutrality using bibliometric methods. A total of 1383 research papers were collected from the “Web of Science core database” from 1995 to 2021. Descriptive statistical analysis and keyword co-occurrence and literature co-citation network analyses were utilized to sort the research hotspots, and the detected bursts, the top 30 keywords in terms of word frequency, and 12 clusters were selected. It was found that the existing carbon neutrality research literature mainly focuses on carbon neutrality energy transformation, carbon neutrality technology development, carbon neutrality effect evaluation, and carbon neutrality industry examples. The analysis process involved comprehensively reading the key articles and considering the co-citation, burstiness, centrality, and other indicators under clustering; the carbon neutrality research was then divided into three stages, and evolving themes were observed. Based on the burst detection, this paper holds that with the energy structure transformation, energy consumption assessment and carbon neutrality schemes of various industries, carbon dioxide capture technology, and biogas resource utilization, urban carbon neutrality policy will become a research hotspot in the future. This paper helps to provide a reference for scholars’ theoretical research and has important reference value for policymakers to formulate relevant policy measures. It is helpful for enterprises to make strategic decisions and determine the direction of technology, for R&D and investment, and it is of considerable significance to promote the research of carbon neutrality technology.
... At the local scale or stand level, the increased harvest of wood for bioenergy can cause a temporary loss of the carbon stock compared to what would otherwise happen without harvesting (Agostini et al., 2014;Högberg et al., 2021). However, it should be noted that forest dynamics cannot be understood by studying individual trees or a single harvest and subsequent regeneration of the felled trees (Holtsmark, 2012). The abovementioned studies highlighted that lack of methodological consensus related to handling biogenic carbon in climate impact assessments of forestry systems could lead to differences in results. ...
... Wood fuels emit more CO 2 per unit of energy than fossil fuels, and it requires a long time until a forest has regrown and absorbed the initially emitted carbon ("carbon debt," Cherubini et al., 2011). Consequently, wood-based fuels are not carbon-neutral, at least on short and medium time-scales (Booth et al., 2020;Cherubini et al., 2011;Holtsmark, 2012;Leturcq, 2020). It is crucial to take this into account, which is done here by considering the total carbon effect including stocks in forests and products, similarly as performed by Knauf et al. (2016). ...
Full-text available
Forests mitigate climate change by storing carbon and reducing emissions via substitution effects of wood products. Additionally, they provide many other important ecosystem services (ESs), but are vulnerable to climate change; therefore, adaptation is necessary. Climate-smart forestry combines mitigation with adaptation, whilst facilitating the provision of many ESs. This is particularly challenging due to large uncertainties about future climate. Here, we combined ecosystem modeling with robust multi-criteria optimization to assess how the provision of various ESs (climate change mitigation, timber provision, local cooling, water availability, and biodiversity habitat) can be guaranteed under a broad range of climate futures across Europe. Our optimized portfolios contain 29% unmanaged forests, and implicate a successive conversion of 34% of coniferous to broad-leaved forests (11% vice versa). Coppices practically vanish from Southern Europe, mainly due to their high water requirement. We find the high shares of unmanaged forests necessary to keep European forests a carbon sink while broad-leaved and unmanaged forests contribute to local cooling through biogeophysical effects. Unmanaged forests also pose the largest benefit for biodiversity habitat. However, the increased shares of unmanaged and broad-leaved forests lead to reductions in harvests. This raises the question of how to meet increasing wood demands without transferring ecological impacts elsewhere or enhancing the dependence on more carbon-intensive industries. Furthermore, the mitigation potential of forests depends on assumptions about the decarbonization of other industries and is consequently crucially dependent on the emission scenario. Our findings highlight that trade-offs must be assessed when developing concrete strategies for climate-smart forestry.
... When forest biomass burns, it releases CO 2 and black carbon into the atmosphere immediately. This creates a 'carbon debt' that will not be paid back through tree regrowth for many decades (Holtsmark, 2012;Leturcq, 2020). ...
Full-text available
Scientific studies show that fast actions to reduce near-term warming are essential to slowing self-reinforcing climate feedbacks and avoiding irreversible tipping points. Yet cutting CO 2 emissions only marginally impacts near-term warming. This study identifies two of the most effective mitigation strategies to limit near-term warming beyond CO 2 mitigation, namely reducing short-lived climate pollutants (SLCPs) and promoting targeted nature-based solutions (NbS), and comprehensively reviews the latest scientific progress in these fields. Studies show that quickly reducing SLCP emissions, particularly hydrofluorocarbons (HFCs), methane, and black carbon, from all relevant sectors can avoid up to 0.6 C of warming by 2050. Additionally, promoting targeted NbS that protect and enhance natural carbon sinks, including in forests, wetlands, grasslands, and agricultural lands, can avoid emissions of 23.8 Gt of CO 2 e per year in 2030, without jeopardizing food security and biodiversity. Based on the scientific evidence, we provided a series of policy recommendations on SLCPs and NbS, including: 1) implementing the Kigali Amendment to reduce HFC emissions; 2) deploying cost-effective, sector-based measures to reduce methane and black carbon emissions; and 3) implementing targeted NbS to protect and enhance existing carbon sinks and shifting away from forest-burning bioenergy. These fast-acting strategies on SLCPs and NbS will play a key role in securing the most avoided warming in the near-term and help countries meet their mid-century carbon neutrality goals. Finally, we proposed future research topics, including: improving measurement and monitoring systems and techniques for SLCP emissions; developing and improving assessments of marginal abatement costs for SLCP mitigation in different sectors; better quantifying the avoided warming potential from protecting different types of natural carbon sinks by 2030, 2050, and over longer periods; and identifying whether there are any biomass types for energy sources that are consistent with the United Nations Environment Assembly's 2022 resolution adopting a definition of NbS. Further research in these areas could help address barriers to adoption and assist countries with better integrating the most effective SLCP and NbS strategies into their climate policies.
The sustainability of air transport is increasingly studied in relation to climate issues. The objective of this paper is to provide the key elements for assessing whether a given transition scenario for aviation could be considered as sustainable in the context of the Paris Agreement. Addressing this question relies on a broad range of concepts which are reviewed. First, ethical considerations related to effort-sharing mitigation principles and physical considerations on climate impacts of aviation are introduced. Then, the technological levers of action for mitigating CO2 and non-CO2 effects are detailed. Concerning CO2 emissions, low-carbon alternative energy carriers represent the main lever, with a wide range of solutions with varying degrees of maturity and decarbonization potentials. Other significant CO2 levers include improving aircraft architecture efficiency and accelerating fleet renewal. Concerning non-CO2 effects, contrail effect mitigation through operational strategies is one of the most promising lever. Aviation transition scenarios are then reviewed, with a particular focus on scenario simulation and sustainability assessment methodologies. Prospective scenarios are a useful framework for assessing the impacts of technological levers on the achievement of climate objectives. This review leads to the conclusion that technological levers have an important role to play in making aviation sustainable; however, significant uncertainties weigh on their feasibility, particularly for the most ambitious scenarios which rely on strong technological and political trade-off assumptions. The paper ends by raising the question about the meaning of sustainable aviation, which must be based on technological but also, for instance, social, economic and ethical considerations.
Full-text available
Harvested wood products (HWP) can play an important role in climate-smart bioeconomic transformation. They contribute to climate change mitigation through two main mechanisms: carbon storage and substitution. Norway has ambitions to strengthen the contribution of its forest sector in climate change mitigation. Ideally, the future production and use of HWPs would increasingly shift towards products with high carbon storage and substitution benefits. We collected data from the literature and, when necessary, supplemented it with our own calculations, on carbon storage and substitution factors of HWPs that seemed relevant in evaluating the climate change mitigation potential in the context of the Norwegian forest sector. There are many uncertainties in the parameters. We identified and examined in more detail some uses of wood for industrial products that offer clear substitution benefits and, in some cases, long-term carbon storage. Wood-based construction materials, textile fibres, and insulation materials are examples of such products that could have high potential in the bioeconomy transformation in Norway.
Full-text available
We examine the evolution of European net sinks towards 2030 and the European Union's (EU) climate neutrality target by 2050. The EU's current land use policy for 2021-2030 is divided into two periods: 2021-2025 and 2026-2030. The national inventory data from several databases and statistical analyses are used to examine the trends and drivers and to forecast future forest sinks and the net sinks of the land use, land use change and forestry (LULUCF) sector. Our forecasts suggest that national forest sinks will be short of the agreed forest reference levels in most member states in 2021-2025, with a total of 128 MtCO 2 eq. For 2026-2030, the net sink for the whole EU LULUCF sector will be short of the EU target by 298 MtCO 2 eq. Thus, most member states must design more efficient LULUCF policies to fulfil their national targets. Furthermore, the decreasing trends in the LULUCF sinks also emphasize the need to reduce emissions and to increase the sinks in most member states so that the EU can achieve its climate neutrality goal by 2050.
Full-text available
Several key international policy frameworks involve forests, including the Paris Agreement on Climate Change and the Convention on Biological Diversity (CBD). However, rules and guidelines that treat forest types equally regardless of their ecosystem integrity and risk profiles in terms of forest and carbon loss limit policy effectiveness and can facilitate forest degradation. Here we assess the potential for using a framework of ecosystem integrity to guide policy goals. We review the theory and present a conceptual framework, compare elements of integrity between primary and human-modified forests, and discuss the policy and management implications. We find that primary forests consistently have higher levels of ecosystem integrity and lower risk profiles than human-modified forests. This underscores the need to protect primary forests, develop consistent large-scale data products to identify high-integrity forests, and operationalize a framework of ecosystem integrity. Doing so will optimize long-term carbon storage and the provision of other ecosystem services, and can help guide evolving forest policy at the nexus of the biodiversity and climate crises.
Full-text available
The visual analysis of carbon neutrality research can help better understand the development of the research field and explore the difficulties and hot spots in the research, thus making contributions to “carbon emission reduction,” environmental protection and human health. This paper makes a visual quantitative analysis of 2,819 research papers published in top international journals from 2008 to 2021 in the WOS core database. It is found that China, the United States, Britain, and Germany are leading the way in carbon neutrality research. The research hotspots are mainly divided into three dimensions: (1) biomass energy and the negative effects it might bring; (2) ways and methods of electrochemical reduction of carbon dioxide; (3) catalysts and catalytic environment. The research mainly went through the conceptual period of 1997–2007, the exploration period of bioenergy from 2008 to 2021, the criticized period of bioenergy sources from 2011 to 2013, and the carbon dioxide electroreduction period from 2013 to the present. In the future, the research direction of biomass energy is to find one kind of biomass energy source which can be stored in a low-carbon way, produced in large quantities at a low cost, and will not occupy forestland. The electrolysis of water to produce hydrogen and the synthesis of fuel with CO2 are two major research directions at present, whose aims are to find the suitable catalyst and environment for the reaction. Besides, more research can be done on “carbon neutrality” policies so as to reduce carbon dioxide emissions from the source, develop a low-carbon economy and protect human health.
Full-text available
Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.
Full-text available
Owing to the extensive critique of food-crop-based biofuels, attention and hopes have turned toward second-generation wood-based biofuels. An important question is therefore whether wood from boreal forests could serve as a source for biofuels. However, in a typical boreal forest, it takes 70–120 years before a stand of trees is mature. If this time lag and the real dynamics of the carbon stock of boreal forests more generally are taken into account, it becomes necessary to reconsider the potential mitigation effects of the increased use of wood fuels from boreal forests. This paper finds that the increased harvest of a boreal forest creates a biofuel carbon debt that takes 150–230 years to repay.
Full-text available
The accounting now used for assessing compliance with carbon limits in the Kyoto Protocol and in climate legislation contains a far-reaching but fixable flaw that will severely undermine greenhouse gas reduction goals (1). It does not count CO2 emitted from tailpipes and smokestacks when bioenergy is being used, but it also does not count changes in emissions from land use when biomass for energy is harvested or grown. This accounting erroneously treats all bioenergy as carbon neutral regardless of the source of the biomass, which may cause large differences in net emissions. For example, the clearing of long-established forests to burn wood or to grow energy crops is counted as a 100% reduction in energy emissions despite causing large releases of carbon.
To estimate the age of Norway spruce (Picea abies (L.) Karst.) logs by means of decay classes, and to assess how long it takes for downed logs to decompose, we dated logs dendrochronologically by applying 5- and 8-grade decay classification systems. Study sites were chosen in old-growth and previously selectively cut forest stands in boreal south-central Scandinavia; 113 logs were dated to the number of years since death, 120 were dated to the number of years since fall, and 61 logs were dated to both. The number of years from death to fall showed a negative exponential distribution, with a mean of 22 years and a range of 0–91 years. Decay classes of logs (8-grade scale) reflected time since fall (R2 = 0.58) better than time since death (R2 = 0.27) in a linear regression model. This result is due to the lower decomposition rate of standing snags. Therefore, the decomposition time of logs should be divided into two periods: time from death to fall, which varies considerably, and time after fall, which appears to follow a linear relationship with decay class. The model predicted that it takes 100 years after fall for downed logs to decompose completely (reaching decay class 8) in old-growth stands. Logs in selectively cut stands appeared to decompose faster (64 years), which is explained by a sample shortage of old logs resulting from previous cuttings. We conclude that the decomposition time of downed logs may be severely underestimated when data is retrospectively compiled from previously logged forest stands.
The boreal forests of Scandinavia offer a considerable resource base, and use of the resource for the production of less carbon-intensive alternative transport fuel is one strategy being considered in Norway. Here, we quantify the resource potential and investigate the environmental implications of wood-based transportation relative to a fossil reference system for a specific region in Norway. We apply a well-to-wheel life cycle assessment to evaluate four E85 production system designs based on two distinct wood-to-ethanol conversion technologies. We form best and worst case scenarios to assess the sensitivity of impact results through the adjustment of key parameters, such as biomass-to-ethanol conversion efficiency and upstream biomass transport distance. Depending on the system design, global warming emission reductions of 46% to 68% per-MJ-gasoline avoided can be realized in the region, along with reductions in most of the other environmental impact categories considered. We find that the region's surplus forest-bioenergy resources are vast; use for the production of bioethanol today would have resulted in the displacement of 55% to 68% of the region's gasoline-based global warming emission—or 6% to 8% of Norway's total global warming emissions associated with road transportation.
Old forests are important carbon pools, but are thought to be insignificant as current atmospheric carbon sinks. This perception is based on the assumption that changes in productivity with age in complex, multiaged, multispecies natural forests can be modelled simply as scaled-up versions of individual trees or even-aged stands. This assumption was tested by measuring the net primary productivity (NPP) of natural subalpine forests in the Northern Rocky Mountains, where NPP is from 50% to 100% higher than predicted by a model of an even-age forest composed of a single species. If process-based terrestrial carbon models underestimate NPP by 50% in just one quarter of the temperate coniferous forests throughout the world, then global NPP is being underestimated by 145 Tg of carbon annually. This is equivalent to 4.3–7.6% of the missing atmospheric carbon sink. These results emphasize the need to account for multiple-aged, species-diverse, mature forests in models of terrestrial carbon dynamics to approximate the global carbon budget.
Forest age, which is affected by stand-replacing ecosystem disturbances (such as forest fires, harvesting, or insects), plays a distinguishing role in determining the distribution of carbon (C) pools and fluxes in different forested ecosystems. In this synthesis, net primary productivity (NPP), net ecosystem productivity (NEP), and five pools of C (living biomass, coarse woody debris, organic soil horizons, soil, and total ecosystem) are summarized by age class for tropical, temperate, and boreal forest biomes. Estimates of variability in NPP, NEP, and C pools are provided for each biome-age class combination and the sources of variability are discussed. Aggregated biome-level estimates of NPP and NEP were higher in intermediate-aged forests (e.g., 30–120 years), while older forests (e.g., >120 years) were generally less productive. The mean NEP in the youngest forests (0–10 years) was negative (source to the atmosphere) in both boreal and temperate biomes (−0.1 and –1.9 Mg C ha−1 yr−1, respectively). Forest age is a highly significant source of variability in NEP at the biome scale; for example, mean temperate forest NEP was −1.9, 4.5, 2.4, 1.9 and 1.7 Mg C ha−1 yr−1 across five age classes (0–10, 11–30, 31–70, 71–120, 121–200 years, respectively). In general, median NPP and NEP are strongly correlated (R2=0.83) across all biomes and age classes, with the exception of the youngest temperate forests. Using the information gained from calculating the summary statistics for NPP and NEP, we calculated heterotrophic soil respiration (Rh) for each age class in each biome. The mean Rh was high in the youngest temperate age class (9.7 Mg C ha−1 yr−1) and declined with age, implying that forest ecosystem respiration peaks when forests are young, not old. With notable exceptions, carbon pool sizes increased with age in all biomes, including soil C. Age trends in C cycling and storage are very apparent in all three biomes and it is clear that a better understanding of how forest age and disturbance history interact will greatly improve our fundamental knowledge of the terrestrial C cycle.
A simulation model of soil carbon cycling was developed based on the data observed in a mid-temperate forest in Yoshiwa, Hiroshima Prefecture, Japan, and soil carbon cycling and carbon budget in a mature forest stand and following clear-cutting were calculated on a daily basis using daily air temperature and precipitation data. The seasonal change in the amount of the A0 layer was characterized by a decrease from spring to autumn due to rapid decomposition of litter, and recovery in late autumn due to a large litterfall input. There was little change in the amount of humus in mineral soil. These estimates coincides closely with those observed in the field. Most flow rates and the accumulation of soil carbon decreased very markedly just after clear-cutting. The A0 layer reached its minimum in 10 years, and recovered its loss within 50–60 years after cutting. A large loss of carbon was observed just after cutting, but the balance changed from negative to positive in 15 years after cutting. The total loss of soil carbon following cutting recovered within 30 years, and nearly the same amount of carbon as that stocked in the timber before harvesting accumulated 70–80 years after cutting. The calculation by the simulation model was made using the assumption that the increase in atmospheric CO2 promoted the primary production rate by 10% over the last three decades. The result suggests that about 8 t C ha-1 was sunk into soils of the mid-temperate forest over the same period. It indicates that forest soils may be one of the main sinks for atmospheric CO2.