Abstract
An increased production of cashew
(Anacardium Occidentale L.) in the forest-savanna transition zone of
Côte d’Ivoire calls for an understanding of the biophysical, ecological
as well as climate change implications that may be associated with its
production. This study aimed to deepen knowledge on how expansive cashew
production impacts on land use/ land cover and its consequences on
biodiversity and carbon stocks. Using the maximum likelihood
classification algorithm and post-classification change detection
procedure, the spatial-temporal dynamics of land use/ land cover was
assessed based on a series of Landsat images for 1988, 2001 and 2014.
Vegetation inventories were carried out to determine the composition and
structure of cashew plantations and natural vegetation.
From
the diameter and species identification as well as soil samples data
collected in inventory, the biomass and for that matter carbon stock was
calculated. Multiple linear regression analysis was used to examine the
main drivers of cashew expansion at household level, and GIS and
multicriteria analysis were used to analyse the natural vegetations’
vulnerability to future cashew expansion. The results identified cashew
expansion (a rate of 26.78% and 7.24% per annum for the periods
1988-2001 and 2001-2013, respectively) as major land use changes. From
1988 to 2014, 26.4% and 34.1% of forest/woodland and savanna areas
respectively were converted to cashew plantations, given a natural
vegetation conversion rate of 2.35 to 2.88% per annum.
There was
a decrease in tree species richness and evenness from natural
vegetation to cashew plantations. In terms of vegetation structure
however, mature plantation had basal area similar to forest/woodland.
The total carbon stocks in Mg C ha-1 t/ha were low in cashew
plantations, where mature stands had 21.826 ± 3.23 (Mean ± SE), young
iii 25.927 ± 6.53 and juvenile 16.732 ± 2.96 compared with natural
vegetation (forest/woodland 64.375 ± 12.43, tree savannas 23.94 ± 3.3
and tree/shrub savannas 21.012 ± 10.12). There was no significant
difference in soil organic carbon and total soil carbon stocks under
different land use types, except between forest (24.67 ± 5.37 Mg C ha-1)
and tree/shrub savanna (8.92 ± 1.57 Mg C ha-1). The long drought
episode of the early 1980s was identified as the trigger for cashew
plantation establishment, whilst better income and lack of technical
support were the main drivers for expansion. Plantation size of
households was influenced by two demographic factors of age and gender
farmers (P < 0.05 and 0.305 R2-adjusted). Natural vegetation
vulnerability to future cashew expansion was in the descending order of
forest/woodland (21.43%), tree savanna (11.87%) and tree/shrub savanna
(8.27%).
This implies that cashew expansion is of higher threat
to more woody vegetation which has serious implication in terms of
conservation and carbon emissions. There is therefore a need for a more
sustainable management approach to cashew agriculture practices to
ensure optimum production for farmers, while conserving the
forest-savanna ecosystem.