Land transformation on multi-decadal timescales reveals expanding croplands and settlements at the expense of tree-covered areas and mangroves in Nigeria

Akinyemi, Felicia O.; Ifejika Speranza, Chinwe (2024). Land transformation on multi-decadal timescales reveals expanding croplands and settlements at the expense of tree-covered areas and mangroves in Nigeria (EarthArXiv). 10.31223/X5VD6K

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Evaluating how land-cover is being transformed is essential to identify
patterns necessary to infer the change trajectories and the driving
factors. This study considers the case of Nigeria, where various natural
ecosystems are being converted and for which a current national scale
assessment is lacking. Producing Landsat-based time-series, we analyze
change among land-cover types (i.e., tree-covered area, grassland,
wetland, waterbody, cropland, artificial surfaces and otherland) across
seven agroecological zones. The annual intensity of change was assessed
at multi-levels across two time-intervals (i.e., 2000 – 2013, 2013 –
2022). Distinguishing between natural land-cover and human activity related
land-use, we estimate the extent of change signifying how
humans have appropriated natural land-cover. Insights from analysis at
the interval level reveal that land transformation accelerated from 3.3%
in 2000 – 2013 to 4.5% during 2013–2022 in all agroecological zones
(e.g., rainforest, mangrove), except in Sudan and Sahel savannah where
speed was higher in 2000–2013 as grasslands were increasingly
cultivated. Cropland expanded two-fold (22% to 37%), whereas treecover
declined from 50% to 31% and wetland from 7% to 3.7% over the
23 years. Much loss of natural land-cover (e.g., tree-cover, grassland
and wetland) to cropland mainly occurred in 2000 – 2013 (22%) when
most irrigation schemes in Nigeria were established. In contrast, the loss
of natural land-cover to settlement (0.9%) during 2000 – 2013 increased
to 2.0% in 2013 – 2022. Of all agroecological zones, the mangrove zone
was most disturbed as its persisting land-cover areas reduced from 69%
to 5% between 2000–2013 and 2013–2022. The amount of persisting
land-cover was highest in the Sudan Savannah at 44% in 2000–2013
and 49% in 2013–2022. Processes of human appropriated natural land-cover in Nigeria are related to urbanization and cropland expansion into
natural areas with some instances of natural regeneration, especially in
abandoned croplands and settlement areas.

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