of land-use changes on C stocks are the result of the changes in the inputs and
output drivers in the short- and long term after abandonment. Land-use changes
may also affect the biochemical quality of litter inputs, which is a major factor
influencing the organic C accumulation in soils (Liao and Boutton 2008). In
ecosystems with high belowground allocation, such as grasslands, root dynamics
represent the primary source for building up soil organic matter (Rasse et al. 2005;
Piñeiro et al. 2006). This situation mostly applies to grazed grasslands, where a
substantial amount of aboveground production is removed by grazing animals.
When grass species are not palatable, both above- and belowground productions
may be of the same order of magnitude. For example, in subalpine Festuca eskia
grasslands in the Pyrenees, Montané et al. (2010) estimated an aboveground production of about 200 g m
−2 year
−1 while the root production estimated by
15 cm-depth ingrowth cores was about 150 g m
−2 year
−1
.
Belowground biomass production and turnover have been related to microclimate as well as to land-use management (Guo et al. 2007; Leifeld et al. 2015). In
the short term, grazing abandonment of subalpine grasslands allows higher
aboveground biomass and accumulation of substantial amounts of necromass, but
the effects on belowground biomass remain controversial. In general, belowground
productivity increases in response to grazing removal (Ruess et al. 1998; Johnson
and Matchett 2001; Smit and Kooijman 2001) but some studies did not find significant effects (McNaughton et al. 1998; Bazot et al. 2005) or even negative effects
(Frank et al. 2002; Pucheta et al. 2004). Controversial findings may be partly
explained by the physiological responses of plants to defoliation, but also by
changes in plant species composition that may translate to differences in productivity, C allocation patterns and rooting depths at the ecosystem level. Indeed, Lanta
et al. (2009) reported changes in plant species composition and richness in a 3-year
field experiment with grazing and abandonment, and also showed a reduction of
belowground biomass in non-grazed grasslands of the White Carpathians in the
Czech Republic. In a 2-year grazing exclusion experiment in the Pyrenees, root
production decreased in grazed grasslands in comparison with non-grazed ones.
This response occurred right after the grazing event, and no apparent effects on
yearly belowground C input were found (Garcia-Pausas et al. 2011).
9.4.3 Soil C Stocks in Grazed and Ungrazed Mountain
Grasslands
The effect of grazing abandonment on soil C stocks has mostly been studied through
the comparison of grazed and ungrazed areas, but the short-term effects of grazing on
SOC is inconsistent to date, with both increases and decreases reported in response
to increased grazing pressure. Although the effect of herbivory on plant productivity
and C allocation is still under debate, abandonment of light, extensive grazing
management might reduce soil stocks (Schuman et al. 1999; Pucheta et al. 2004).
9 Are Soil Carbon Stocks in Mountain Grasslands …
219
output drivers in the short- and long term after abandonment. Land-use changes
may also affect the biochemical quality of litter inputs, which is a major factor
influencing the organic C accumulation in soils (Liao and Boutton 2008). In
ecosystems with high belowground allocation, such as grasslands, root dynamics
represent the primary source for building up soil organic matter (Rasse et al. 2005;
Piñeiro et al. 2006). This situation mostly applies to grazed grasslands, where a
substantial amount of aboveground production is removed by grazing animals.
When grass species are not palatable, both above- and belowground productions
may be of the same order of magnitude. For example, in subalpine Festuca eskia
grasslands in the Pyrenees, Montané et al. (2010) estimated an aboveground production of about 200 g m
−2 year
−1 while the root production estimated by
15 cm-depth ingrowth cores was about 150 g m
−2 year
−1
.
Belowground biomass production and turnover have been related to microclimate as well as to land-use management (Guo et al. 2007; Leifeld et al. 2015). In
the short term, grazing abandonment of subalpine grasslands allows higher
aboveground biomass and accumulation of substantial amounts of necromass, but
the effects on belowground biomass remain controversial. In general, belowground
productivity increases in response to grazing removal (Ruess et al. 1998; Johnson
and Matchett 2001; Smit and Kooijman 2001) but some studies did not find significant effects (McNaughton et al. 1998; Bazot et al. 2005) or even negative effects
(Frank et al. 2002; Pucheta et al. 2004). Controversial findings may be partly
explained by the physiological responses of plants to defoliation, but also by
changes in plant species composition that may translate to differences in productivity, C allocation patterns and rooting depths at the ecosystem level. Indeed, Lanta
et al. (2009) reported changes in plant species composition and richness in a 3-year
field experiment with grazing and abandonment, and also showed a reduction of
belowground biomass in non-grazed grasslands of the White Carpathians in the
Czech Republic. In a 2-year grazing exclusion experiment in the Pyrenees, root
production decreased in grazed grasslands in comparison with non-grazed ones.
This response occurred right after the grazing event, and no apparent effects on
yearly belowground C input were found (Garcia-Pausas et al. 2011).
9.4.3 Soil C Stocks in Grazed and Ungrazed Mountain
Grasslands
The effect of grazing abandonment on soil C stocks has mostly been studied through
the comparison of grazed and ungrazed areas, but the short-term effects of grazing on
SOC is inconsistent to date, with both increases and decreases reported in response
to increased grazing pressure. Although the effect of herbivory on plant productivity
and C allocation is still under debate, abandonment of light, extensive grazing
management might reduce soil stocks (Schuman et al. 1999; Pucheta et al. 2004).
9 Are Soil Carbon Stocks in Mountain Grasslands …
219