(forest), while the other is dominated by grasses (savanna). The two alternative states
are maintained through a positive feedback between fire and an open canopy, with
fire being common in savannas (Fig. 9.3d), while nearly absent in forests (Fig. 9.3b).
This seems to be the legacy of long-term vegetation distribution, and not some kind
of founder effect.
Finally, even though rainfall and fire are important determinants of the distribution of tropical forests and savannas, other drivers can also become significant,
including soils (Lloyd et al. 2015), and herbivores, specifically mammal browsers
(Charles-Dominique et al. 2016). However, we have not addressed these effects in
this chapter.
9.3.3 Changes in Vegetation
9.3.3.1 Ongoing Vegetation Changes
The remotely sensed data indicate strong ongoing vegetation changes, and specifically deforestation and forest degradation in the forests and woody encroachment in
savannas (see Mitchard et al. 2011). At the regional scale, tree cover loss is far more
prevalent in forests than in savannas (Fig. 9.4a). Overall, although deforestation is
relatively low in central Africa (Pan et al. 2011; Achard et al. 2014; Aleman et al.
2018), tree cover loss can be extremely important locally, especially along the main
roads and the surroundings of major cities, specifically in the DRC (Fig. 9.4a). This
trend is due to the increasing fuelwood demand and need for agricultural lands, as
population grows (Schure et al. 2014; see also Chaps. 7 and 10, Vol. 1). Logging is
also responsible for forest degradation and fragmentation, as tree cover loss is much
more prevalent in logging concessions than in protected areas (Fig. 9.4b). Approximately 29% of the forests in central Africa are currently granted to logging
companies, ranging, however, from 13% in DRC to more than 60% of Gabon and
Congo (Fig. 9.4b, Laporte et al. 2007). Although selective logging (Ruiz Pérez et al.
2005), specifically under Forest Stewardship Council (FSC) criteria, might not be
very detrimental to forest biodiversity (Putz et al. 2012), the sustainability of
conventional logging practices elsewhere in the region is certainly questionable,
especially due to the progression of logging roads (Laporte et al. 2007).
In this chapter, we only analyzed tree cover loss between 2000 and 2015.
However, there is a longer term trend of woody encroachment in savannas areas
across SSA (Stevens et al. 2017), and also more regionally in central Africa (Youta
Happi 1998; Mitchard et al. 2009). Soil carbon isotopes signature analysis has
demonstrated forest encroachment into savanna areas over the past century in the
CAR (Runge 2002), Gabon (Delègue et al. 2001), and Cameroon (Guillet et al.
2001). However, the causes of this widespread woody encroachment in savannas are
hotly debated in the academic literature (Devine et al. 2017). Some scholars have
proposed that this is a response to fire suppression policies during the last century
9 Long-Term Vegetation Change in Central Africa: The Need for an Integrated. . .
297
are maintained through a positive feedback between fire and an open canopy, with
fire being common in savannas (Fig. 9.3d), while nearly absent in forests (Fig. 9.3b).
This seems to be the legacy of long-term vegetation distribution, and not some kind
of founder effect.
Finally, even though rainfall and fire are important determinants of the distribution of tropical forests and savannas, other drivers can also become significant,
including soils (Lloyd et al. 2015), and herbivores, specifically mammal browsers
(Charles-Dominique et al. 2016). However, we have not addressed these effects in
this chapter.
9.3.3 Changes in Vegetation
9.3.3.1 Ongoing Vegetation Changes
The remotely sensed data indicate strong ongoing vegetation changes, and specifically deforestation and forest degradation in the forests and woody encroachment in
savannas (see Mitchard et al. 2011). At the regional scale, tree cover loss is far more
prevalent in forests than in savannas (Fig. 9.4a). Overall, although deforestation is
relatively low in central Africa (Pan et al. 2011; Achard et al. 2014; Aleman et al.
2018), tree cover loss can be extremely important locally, especially along the main
roads and the surroundings of major cities, specifically in the DRC (Fig. 9.4a). This
trend is due to the increasing fuelwood demand and need for agricultural lands, as
population grows (Schure et al. 2014; see also Chaps. 7 and 10, Vol. 1). Logging is
also responsible for forest degradation and fragmentation, as tree cover loss is much
more prevalent in logging concessions than in protected areas (Fig. 9.4b). Approximately 29% of the forests in central Africa are currently granted to logging
companies, ranging, however, from 13% in DRC to more than 60% of Gabon and
Congo (Fig. 9.4b, Laporte et al. 2007). Although selective logging (Ruiz Pérez et al.
2005), specifically under Forest Stewardship Council (FSC) criteria, might not be
very detrimental to forest biodiversity (Putz et al. 2012), the sustainability of
conventional logging practices elsewhere in the region is certainly questionable,
especially due to the progression of logging roads (Laporte et al. 2007).
In this chapter, we only analyzed tree cover loss between 2000 and 2015.
However, there is a longer term trend of woody encroachment in savannas areas
across SSA (Stevens et al. 2017), and also more regionally in central Africa (Youta
Happi 1998; Mitchard et al. 2009). Soil carbon isotopes signature analysis has
demonstrated forest encroachment into savanna areas over the past century in the
CAR (Runge 2002), Gabon (Delègue et al. 2001), and Cameroon (Guillet et al.
2001). However, the causes of this widespread woody encroachment in savannas are
hotly debated in the academic literature (Devine et al. 2017). Some scholars have
proposed that this is a response to fire suppression policies during the last century
9 Long-Term Vegetation Change in Central Africa: The Need for an Integrated. . .
297