savannas contain gallery forests and forest patches. Mesic savannas were then seen
as relatively new and formed through anthropogenic activity (Aubréville 1939,
1947; Bond and Zaloumis 2016). During this period, many fire suppression policies
were developed in an attempt to protect tropical forests (see Bond and Zaloumis
2016). Fire practices were heavily modified, triggering changes in fire regimes, and
ultimately leading to woody encroachment in savannas (Aubréville 1947).
More recently, Sahelian pastoralists from west and central Africa started migrating in mesic savannas in the 1960s, in areas where Mbororo farmers dominated
historically the agricultural landscape (Bassett and Boutrais 2000; Ankogui-Mpoko
2003). This has led to important land conflicts between pastoralists and farmers in
the CAR (Ankogui-Mpoko 2003) and Cameroon (Ouikon 2003), and ultimately
changed the vegetation structure (Bassett and Boutrais 2000). In particular, changes
in agricultural practices modified the fire regime (i.e., from large fires for hunting, to
small and early fires for cattle herding), which, coupled with overgrazing, resulted in
woody encroachment (Bassett and Boutrais 2000).
6 Pasturelands became less productive “forcing” cattle herders to migrate southwards (Ankogui-Mpoko 2003).
9.2.2 Data Collection and Analysis
9.2.2.1 Reconstruction of Past Vegetation Changes
In this chapter, we conduct a meta-analysis of published studies to better understand
and illustrate past changes on vegetation cover, and their determinants (e.g., fires,
human presence, and climate) since the Last Glacial Maximum (~21,000 cal yr BP)
(see Sect. 9.3.1). We specifically focus on vegetation reconstruction studies from
14 paleo-ecological sites (Table 9.2), for which palynological information is
available.
Pollen preserved in lake sediments can be used to infer past vegetation composition and structure (Vincens et al. 1999). For example, we used data downloaded
from the African Pollen Database
7 to explain composition changes at Lake Barombi
Mbo. Each of the different pollen sites was recorded, and then plotted on a map of
central Africa. Dated charred material (e.g., oil palm endocarps, charcoals) can be
used as a proxy for local past fire events (Vleminckx et al. 2014). We plotted this
information on the same map described above to illustrate the location of past fire
events, even those located very deeply within the forest block.
We also reviewed the evidence of past human presence and activity in central
Africa, using all of the dated information on human presence assembled by Oslisly
6 Woody encroachment in savannas is currently widespread throughout SSA, and even in other parts
of the world (Stevens et al. 2017). While local encroachment has been directly linked to land use
change, global climate change, and specifically CO 2 fertilization, has also been identified as a
possible driver (Buitenwerf et al. 2012).
7 For more information refer to: http://fpd.sedoo.fr/fpd/
288
J. C. Aleman and A. Fayolle
as relatively new and formed through anthropogenic activity (Aubréville 1939,
1947; Bond and Zaloumis 2016). During this period, many fire suppression policies
were developed in an attempt to protect tropical forests (see Bond and Zaloumis
2016). Fire practices were heavily modified, triggering changes in fire regimes, and
ultimately leading to woody encroachment in savannas (Aubréville 1947).
More recently, Sahelian pastoralists from west and central Africa started migrating in mesic savannas in the 1960s, in areas where Mbororo farmers dominated
historically the agricultural landscape (Bassett and Boutrais 2000; Ankogui-Mpoko
2003). This has led to important land conflicts between pastoralists and farmers in
the CAR (Ankogui-Mpoko 2003) and Cameroon (Ouikon 2003), and ultimately
changed the vegetation structure (Bassett and Boutrais 2000). In particular, changes
in agricultural practices modified the fire regime (i.e., from large fires for hunting, to
small and early fires for cattle herding), which, coupled with overgrazing, resulted in
woody encroachment (Bassett and Boutrais 2000).
6 Pasturelands became less productive “forcing” cattle herders to migrate southwards (Ankogui-Mpoko 2003).
9.2.2 Data Collection and Analysis
9.2.2.1 Reconstruction of Past Vegetation Changes
In this chapter, we conduct a meta-analysis of published studies to better understand
and illustrate past changes on vegetation cover, and their determinants (e.g., fires,
human presence, and climate) since the Last Glacial Maximum (~21,000 cal yr BP)
(see Sect. 9.3.1). We specifically focus on vegetation reconstruction studies from
14 paleo-ecological sites (Table 9.2), for which palynological information is
available.
Pollen preserved in lake sediments can be used to infer past vegetation composition and structure (Vincens et al. 1999). For example, we used data downloaded
from the African Pollen Database
7 to explain composition changes at Lake Barombi
Mbo. Each of the different pollen sites was recorded, and then plotted on a map of
central Africa. Dated charred material (e.g., oil palm endocarps, charcoals) can be
used as a proxy for local past fire events (Vleminckx et al. 2014). We plotted this
information on the same map described above to illustrate the location of past fire
events, even those located very deeply within the forest block.
We also reviewed the evidence of past human presence and activity in central
Africa, using all of the dated information on human presence assembled by Oslisly
6 Woody encroachment in savannas is currently widespread throughout SSA, and even in other parts
of the world (Stevens et al. 2017). While local encroachment has been directly linked to land use
change, global climate change, and specifically CO 2 fertilization, has also been identified as a
possible driver (Buitenwerf et al. 2012).
7 For more information refer to: http://fpd.sedoo.fr/fpd/
288
J. C. Aleman and A. Fayolle