Thus in a survey of grasslands in the Pyrenees, we found that abandoned grasslands
had lower SOC stocks in the uppermost 20 cm of soil than grazed ones (Casals et al.
2004). However, this result may just reflect that the less productive grasslands were
abandoned. In summary, changes in soil C stocks of mountain grasslands as a
consequence of grazing abandonment are, at least in the short term, small and no
clear trends may be stated.
9.4.4 Effects of Shrub Encroachment on Soil C Dynamics
and Stocks
In the long term, grazing abandonment may involve a change in the dominant
functional groups and often leads to shrub encroachment (Fig. 9.5). This shift is
often observed in many mountain areas (MacDonald et al. 2000) and can lead to
long-term expansion of forests (Gehrig-Fasel et al. 2007; Améztegui et al. 2010).
Shrub encroachment into grasslands has been documented in the Pyrenees
(Molinillo et al. 1997; Roura-Pascual et al. 2005) and the Central System ranges of
the Iberian Peninsula (Sanz-Elorza et al. 2003). However, depending on the site
characteristics, this can be a slow process. Indeed, Pardo et al. (2015) did not
Fig. 9.5 Shrub encroachment (Cytisus balansae ssp. europaeus) into mountain grasslands. Durro
mountains (Alta Ribagorça, Central Pyrenees). Photo: Pere Casals
220
J. Garcia-Pausas et al.
had lower SOC stocks in the uppermost 20 cm of soil than grazed ones (Casals et al.
2004). However, this result may just reflect that the less productive grasslands were
abandoned. In summary, changes in soil C stocks of mountain grasslands as a
consequence of grazing abandonment are, at least in the short term, small and no
clear trends may be stated.
9.4.4 Effects of Shrub Encroachment on Soil C Dynamics
and Stocks
In the long term, grazing abandonment may involve a change in the dominant
functional groups and often leads to shrub encroachment (Fig. 9.5). This shift is
often observed in many mountain areas (MacDonald et al. 2000) and can lead to
long-term expansion of forests (Gehrig-Fasel et al. 2007; Améztegui et al. 2010).
Shrub encroachment into grasslands has been documented in the Pyrenees
(Molinillo et al. 1997; Roura-Pascual et al. 2005) and the Central System ranges of
the Iberian Peninsula (Sanz-Elorza et al. 2003). However, depending on the site
characteristics, this can be a slow process. Indeed, Pardo et al. (2015) did not
Fig. 9.5 Shrub encroachment (Cytisus balansae ssp. europaeus) into mountain grasslands. Durro
mountains (Alta Ribagorça, Central Pyrenees). Photo: Pere Casals
220
J. Garcia-Pausas et al.