Land use change and local forest dynamics in the forest-savannah boundary in central cameroon

transcript

Land-use change and

local forest dynamics in the forest-savannah boundary

in Central Cameroon

Taking stock of smallholders and community forestry Session 13

Impact of local forestry practices on landscapes

Let’s go to Central Cameroon

Fairly recent introgression of forest onto savannah

Ongoing afforestation on African forest margins

Attested throughout Western and Central Africa

Bioclimatic origin of this phenomenon that started 1,000 years BP

Local perceptions and attitudes vis-à-vis spontaneous afforestation are poorly documented

Humans are hardly responsible for past bioclimatic events…

… But they have co-influenced the impact of such events on the environment…

… Humans are becoming a major driving force in the dynamics of ecosystems

Multidisciplinary evidence of this extensive phenomenon

•  Phytogeography •  Botany •  Phytosociology •  Remote sensing •  Pedology •  Dendrochronology •  Isotopic biochemistry •  Sedimentology •  Phytolites •  Palynology •  Ecology •  Archeology •  Anthropology

Forest-savannah ecotone

•  Rich ecosystem - Diversified mosaic

- Forest plants and animals meet with savannah plants and animals

- Life forms specific to the ecotone

•  Dynamic ecosystem - Afforestation: 1 to 3 meters per year

- Changes perceptible in just a few years

- Ideal conditions to question adaptation to change

Ecological heterogeneity of the ecotone

forest/savannah ecotone in the southern area

forest/savannah ecotone in the northern area

Tikar…

•  Warlike and conquering stratified

society

•  Originally cereal cultivators

•  Brought their ecology with them

•  Sorghum progressively replaced

by maize

•  “Absorption” of populations met

along migration

•  Initiated into forest by Bedzan

Pygmies

and Bedzan

Forest swiddeners and savannah cultivators

Intercropped swidden under forest

Monocultural (cassava) field in the savannah

Non agricultural activities

hunting fishing

gathering

Afforestation between 1950 and 1989

Sectors of faster afforestation: former village settlements

Accelerated afforestation near residential sites Villages were built right up against the forest edge

Accelerated afforestation near residential sites

Temporary swidden camps

Seasonal fishing camps

In 35 years

Fragmented swidden area ⇒ fast afforestation

Single swidden area ⇒ slowed afforestation

Local strategies to control afforestation

Selective tree cutting by forest swiddeners

Seed rain and nucleation

Coffee agroforest

1970s: Permanent agroforest belt as a fence against afforestation

Agroforest trees as safety net Ictyotoxic bark of Albizia coriaria

Medicinal bark of Enantia chloranta

Storage of cola nuts in termites’ nests

Pan-tropical invasive shrub

Good for agronomy •  Voluntarily introduced as a cover crop

•  Improves soil structure (stops the leaching of mineral elements, increases the depth of

the humus stratum, reduces soil acidity)

•  Green manure

•  Nematicide properties

Bad for ecology •  Compromises forest regeneration

•  The African variegated grasshopper (Zonocerus variegatus, Orthoptera,

Pyrgomorphidae)

1980s: invasion by Chromolaena odorata (Asteraceae)

Suffrutescent plant: architecture smothers fire and protects tree seedlings of the forest edge

Abundant faunal circulation underneath (rodents) Early burned savannahs

Chromolaena facilitates afforestation Early burning of savannahs

Exhausting clearing of young fallows invaded by Chromolaena

Delayed burning of fallows

High caloric return of Chromolaena burning

Chromolaena compromises afforestation Delayed burning of fallows

Effect of Chromolaena on the fallowing rotation

•  No more forest regrowth •  Fallowing period reduced to 5 years

Socio-political system of savannah farmers more adapted to Chromolaena

Community farming activities and mutual aid

Increased man-days per hectare

In brief

1980s Invasion by

Chromolaena odorata

•  Coupled human-nature shaping of ecosystems

•  Analysis of biocultural interactions needed to catch local understanding

and influence of ecosystem dynamics (socioecological systems)

•  Local rationality differs from the scientific and conservationist views

•  Indigenous peoples are not de facto “conservationists”, but may

elaborate adaptive responses that are environmental-friendly

•  “Conservationist” does not mean “conservative”. Adaptive responses

may be stimulated by external factors (cash crop plantations ; invasive

shrub)

•  Innovative adoptions depend on socio-political features of the

considered community

Where do we go from here… … well, let’s go back to there!

Thank you for your attention!

Land use change and local forest dynamics in the forest-savannah boundary in central cameroon

Education