Vegetation dynamics in a corridor between protected areas after slash-and-burn cultivation in south-eastern Madagascar

Slash-and-burn cultivation is a major cause of deforestation in Madagascar, and abandonment leads to the secondary vegetation dynamics, i.e. colonization by herbaceous vegetation, shrubs and trees. The study was conducted in south-eastern Madagascar in a steep transition zone along an altitudinal and a sharp precipitation gradient between a high altitude rainforest and a lowland dry tropical forest. The restoration of gaps created by abandoned fields in this narrow, winding corridor could be essential to maintain connectivity between two areas (areas 1 and 2) of Andohahela National Park. Prior to implementing restoration, baseline ecological information is needed on the reference ecosystem and vegetation resilience must be studied to identify restoration needs. This study aims to (1) assess whether cultivation practices (irrigated rice vs. cassava, maize and sweet potato) influence vegetation dynamics after abandonment; (2) study vegetation dynamics and soils over time since abandonment, and (3) compare secondary forest vegetation and soils with those of mature forest patches. Surveys of vegetation and soil were conducted in 26 secondary forest patches abandoned from 3 to >25 years (synchronic approach) and in 19 adjacent mature forest patches (controls). No relationship between age of abandonment and vegetation species richness, composition or structure was found, but clear differences were detected between secondary and mature forest patches. Secondary forests are not colonized by species from mature forests, but instead their vegetation dynamics appear to lead to the establishment of thorny thickets dominated by Mimosa delicatula, which is absent from the mature forest.

► Vegetation dynamics and soil were studied after the abandonment of cultivated plots.
► 26 plots abandoned between 3 and 33 years and 19 adjacent forests were studied.
► No clear link between the age of abandonment and vegetation characteristics is shown.
► Secondary forest patches are not colonized by mature forest species.
► Vegetation dynamics on secondary forest lead to Mimosa delicatula thorny thickets.