around 1.6 Mt/year corresponding to a total of afforestation of 500,000 to
600,000 ha plus 4 Mt/year, corresponding to forest management activities in
existing forest areas.
The 1990s debate on climate change has since led to greater dissemination of
scientific information on the importance of forests. This has mainly resulted from
the widespread application of the eddy covariance method, spurred by research
programs like CARBOEUROPE between 2003 and 2008 (involving about 70
partners in Europe and 30 entities both within and outside Europe) as well as
parallel programs, such as Ameriflux implemented in North American, among
others. The global scientific network FLUXNET, involving partners of earlier
scientific programs, was also created. The outcome was an extended knowledge
base on the main factors that contribute to seasonal and annual variations of carbon
balance components with latitude (Falge et al. 2002).
The carbon balance termed net ecosystem exchange (NEE), and gross primary
assimilation (GPP ) in forest ecosystems are related to the biology of plants and
their physical environments such as the leaf area index, the temporal dynamics of
the microclimate variables, and the duration of growing season, temperature, and
soil moisture. NEE represents the net carbon dioxide measurable flux between a
given soil–plant ecosystem and the atmosphere.
GPP is the carbon dioxide uptake, resultant from the gross primary productivity
or gross photosynthesis by vegetal components of ecosystems such as trees and
understory species, e.g., bushes or grasses. Gross assimilation of carbon is particularly dependent on the intercepted solar radiation, mostly in the range of photosynthetic active radiation (PAR) and the total ecosystem respiration (TER) is
mainly associated with the air and soil temperatures (Carrara et al. 2004; Reichstein
et al. 2002).
In continental European forest stands TER increases with latitude. TER relates
to the additional flux of respired carbon dioxide with two components which are
autotrophic and heterotrophic respiration.
In this context, net ecosystem exchange can be defined as the difference between
GPP and TER, following a criterion wherein a loss of carbon to the atmosphere is
negative. Micrometeorological and edaphic variables are the main influencers
embedded within those processes. Evapotranspiration flux variations along with
several time scales and their interactions with, e.g., carbon dioxide exchange
dynamics can also be evaluated.
The soil respiration can be measured in the field with analyzers (Fig. 4.7).
Climate variability is one of the key features of climate change. In the case of the
Mediterranean areas, there is an increased tendency for droughts which cause
substantial reductions in both the NEE and GPP (Ciais et al. 2005; Granier et al.
2007; Pereira et al. 2007). In these regions, droughts are largely responsible for the
interannual variability of carbon fixation/sequestration, particularly due to stomatal
control of evapotranspiration (Tenhunen et al. 1985; Pereira et al. 1986) as well as
gas exchanges at the leaf level and photosynthesis. In northern Europe and North
America, these interactive effects between droughts and carbon sequestration are
not as pronounced.
4.6 Carbon Sequestration in Forests
125
600,000 ha plus 4 Mt/year, corresponding to forest management activities in
existing forest areas.
The 1990s debate on climate change has since led to greater dissemination of
scientific information on the importance of forests. This has mainly resulted from
the widespread application of the eddy covariance method, spurred by research
programs like CARBOEUROPE between 2003 and 2008 (involving about 70
partners in Europe and 30 entities both within and outside Europe) as well as
parallel programs, such as Ameriflux implemented in North American, among
others. The global scientific network FLUXNET, involving partners of earlier
scientific programs, was also created. The outcome was an extended knowledge
base on the main factors that contribute to seasonal and annual variations of carbon
balance components with latitude (Falge et al. 2002).
The carbon balance termed net ecosystem exchange (NEE), and gross primary
assimilation (GPP ) in forest ecosystems are related to the biology of plants and
their physical environments such as the leaf area index, the temporal dynamics of
the microclimate variables, and the duration of growing season, temperature, and
soil moisture. NEE represents the net carbon dioxide measurable flux between a
given soil–plant ecosystem and the atmosphere.
GPP is the carbon dioxide uptake, resultant from the gross primary productivity
or gross photosynthesis by vegetal components of ecosystems such as trees and
understory species, e.g., bushes or grasses. Gross assimilation of carbon is particularly dependent on the intercepted solar radiation, mostly in the range of photosynthetic active radiation (PAR) and the total ecosystem respiration (TER) is
mainly associated with the air and soil temperatures (Carrara et al. 2004; Reichstein
et al. 2002).
In continental European forest stands TER increases with latitude. TER relates
to the additional flux of respired carbon dioxide with two components which are
autotrophic and heterotrophic respiration.
In this context, net ecosystem exchange can be defined as the difference between
GPP and TER, following a criterion wherein a loss of carbon to the atmosphere is
negative. Micrometeorological and edaphic variables are the main influencers
embedded within those processes. Evapotranspiration flux variations along with
several time scales and their interactions with, e.g., carbon dioxide exchange
dynamics can also be evaluated.
The soil respiration can be measured in the field with analyzers (Fig. 4.7).
Climate variability is one of the key features of climate change. In the case of the
Mediterranean areas, there is an increased tendency for droughts which cause
substantial reductions in both the NEE and GPP (Ciais et al. 2005; Granier et al.
2007; Pereira et al. 2007). In these regions, droughts are largely responsible for the
interannual variability of carbon fixation/sequestration, particularly due to stomatal
control of evapotranspiration (Tenhunen et al. 1985; Pereira et al. 1986) as well as
gas exchanges at the leaf level and photosynthesis. In northern Europe and North
America, these interactive effects between droughts and carbon sequestration are
not as pronounced.
4.6 Carbon Sequestration in Forests
125