Role of Major Forest Biomes in Climate Change Mitigation …
497
also referred to as the net ecosystem productivity, is the total carbon accumulated by
the forest ecosystem in its various carbon pools, subtracted by the amounts of carbon
lost due to microbial respiration, soil respiration, mortality, etc. (Hui et al. 2017).
Different carbon pools are living biomass (of both trees and understorey vegetation),
dead biomass (detritus and litter), soil (on-site carbon pools) and wood products
(off-site carbon pool) (Bettinger et al. 2017). Carbon is represented as 45–50% of
the dry vegetation biomass (Birdsey 1992; Bettinger et al. 2017). Vegetation biomass
is considered a major carbon pool as the sequestered carbon of forest vegetation
amounts to around 359 billion tonnes (Allen et al. 2010; Hui et al. 2017). Soil is
also another important huge carbon pool consisting of approximately 2344 Pg C in
the top 3 m (Jobbagy and Jackson 2000). According to United Nations Framework
Convention on Climate Change (UNFCCC 2010), around 283, 38 and 317 Gt of
carbon are stored in biomass, deadwood and litter plus soils (top 30 cm) respectively
(Fiorese and Guariso 2013). As per the report of FAO (2015), 296 Gt of carbon are
contained in biomass alone in all of the world’s forests (Guo and Gong 2017). These
figures highlight the immense ability of forests to sequester atmospheric carbon.
As reported by Lorenz and Lal (2010), carbon sequestration occurs in forest
ecosystems mainly when (i) the total organic carbon of a forest (inclusive of all the
carbon pools) increases in a specified time interval by absorbing atmospheric carbon
dioxide and (ii) the pool of organic compounds present in the vegetation, detritus and
soil of a forest vegetation contain long carbon residence time that increases over time.
However, climate change has a profound influential role in global carbon cycling.
Therefore, a forest ecosystem may function either as a sink or a source depending
upon its environmental conditions. Climate change could stimulate photosynthesis
due to increased carbon dioxide concentration in the atmosphere (carbon fertilization)
might favour biomass accumulation, in which case the forest may function as a
net carbon sink. On the other hand, warmer temperatures can enhance the rates
of microbial and soil respiration processes, in which case, the forest may act as
a carbon sources. Therefore, a forest’s role in carbon sequestration (a source or a
sink) is determined by the difference between the gross primary productivity and
ecosystem respiration (Field et al. 2007; Hui et al. 2017). However, although forests
function as carbon sinks due to carbon fertilization, Mooney et al. (2009) suggest
that their absorptive capacity is getting saturated and they may hence switch their
role from sinks to sources by the end of this century.
Carbon cycling, which is a crucial regulatory cycle of forests, is being controlled
by various environmental drivers. Some of those drivers are temperature, precipitation, nitrogen deposition, atmospheric carbon dioxide concentration, soil quality,
soil nutrients, soil moisture, etc. (Beedlow et al. 2004; Kets et al. 2010; de Vries et al.
2017). As many regions in the warmer world are likely to become drought-prone,
water deficits would possibly lead to tree mortality, either directly by carbon starvation and hydraulic failure or indirectly by increasing the vulnerability to insect and
pest attacks (McDowell et al. 2008; Hisano et al. 2018). Even without water deficits,
tree longevity is expected to be reduced and trees may compete severely for resources
(Luo and Chen 2015; Hisano et al. 2018). Carbon cycling is also adversely influenced
497
also referred to as the net ecosystem productivity, is the total carbon accumulated by
the forest ecosystem in its various carbon pools, subtracted by the amounts of carbon
lost due to microbial respiration, soil respiration, mortality, etc. (Hui et al. 2017).
Different carbon pools are living biomass (of both trees and understorey vegetation),
dead biomass (detritus and litter), soil (on-site carbon pools) and wood products
(off-site carbon pool) (Bettinger et al. 2017). Carbon is represented as 45–50% of
the dry vegetation biomass (Birdsey 1992; Bettinger et al. 2017). Vegetation biomass
is considered a major carbon pool as the sequestered carbon of forest vegetation
amounts to around 359 billion tonnes (Allen et al. 2010; Hui et al. 2017). Soil is
also another important huge carbon pool consisting of approximately 2344 Pg C in
the top 3 m (Jobbagy and Jackson 2000). According to United Nations Framework
Convention on Climate Change (UNFCCC 2010), around 283, 38 and 317 Gt of
carbon are stored in biomass, deadwood and litter plus soils (top 30 cm) respectively
(Fiorese and Guariso 2013). As per the report of FAO (2015), 296 Gt of carbon are
contained in biomass alone in all of the world’s forests (Guo and Gong 2017). These
figures highlight the immense ability of forests to sequester atmospheric carbon.
As reported by Lorenz and Lal (2010), carbon sequestration occurs in forest
ecosystems mainly when (i) the total organic carbon of a forest (inclusive of all the
carbon pools) increases in a specified time interval by absorbing atmospheric carbon
dioxide and (ii) the pool of organic compounds present in the vegetation, detritus and
soil of a forest vegetation contain long carbon residence time that increases over time.
However, climate change has a profound influential role in global carbon cycling.
Therefore, a forest ecosystem may function either as a sink or a source depending
upon its environmental conditions. Climate change could stimulate photosynthesis
due to increased carbon dioxide concentration in the atmosphere (carbon fertilization)
might favour biomass accumulation, in which case the forest may function as a
net carbon sink. On the other hand, warmer temperatures can enhance the rates
of microbial and soil respiration processes, in which case, the forest may act as
a carbon sources. Therefore, a forest’s role in carbon sequestration (a source or a
sink) is determined by the difference between the gross primary productivity and
ecosystem respiration (Field et al. 2007; Hui et al. 2017). However, although forests
function as carbon sinks due to carbon fertilization, Mooney et al. (2009) suggest
that their absorptive capacity is getting saturated and they may hence switch their
role from sinks to sources by the end of this century.
Carbon cycling, which is a crucial regulatory cycle of forests, is being controlled
by various environmental drivers. Some of those drivers are temperature, precipitation, nitrogen deposition, atmospheric carbon dioxide concentration, soil quality,
soil nutrients, soil moisture, etc. (Beedlow et al. 2004; Kets et al. 2010; de Vries et al.
2017). As many regions in the warmer world are likely to become drought-prone,
water deficits would possibly lead to tree mortality, either directly by carbon starvation and hydraulic failure or indirectly by increasing the vulnerability to insect and
pest attacks (McDowell et al. 2008; Hisano et al. 2018). Even without water deficits,
tree longevity is expected to be reduced and trees may compete severely for resources
(Luo and Chen 2015; Hisano et al. 2018). Carbon cycling is also adversely influenced