Causes and consequences ofCedrela odoratainvasion in West African semi-deciduous tropical forests

Most of the West African forests have disappeared or have been deeply fragmented. This deforestation dynamic is still ongoing under a strong demographic pressure, forests being mostly replaced by agricultural lands. On the other hand, some reforestation projects are also undertaken, in particular by planting non-native species likeCedrela odorata. To our knowledge, this study is the first to investigate the causes and consequences ofCedrela odorataspread in West African natural forests. We studied a 400ha area of natural forest where 100ha of permanent plots have been affected by a major fire in 1983. Within these permanent plots, 21,444 trees were mapped, botanically determined and their diameters at breast height were measured in 2018. Using a bayesian hierarchical framework, we modelled the causes of the spread ofCedrela odoratain the studied plots, and its consequences on aboveground biomass and tree community diversity. Regarding the causes, the occurrence ofCedrela odoratais significantly linked to the fire occurence 25 years ago, to the proximity of the forest edge and to the presence of hydromorphic soils. Regarding the consequences,Cedrela odoratainvasion doesn't have any significant impact on the above-ground biomass but has a strong negative effect on the tree community diversity, as far as decreasing Simpson diversity in Hill numbers from 27 equivalent species in slightly invaded plots to 2 equivalent species in largely invaded plots. Our results highlight the long-lasting impacts of human disturbance (fire,Cedrela odorataintroduction) on forest ecosystems and the need to use local species for ongoing reforestation plans in West African semi-deciduous forests.

Automated summary

Most of the West African forests have disappeared or been fragmented due to deforestation, with reforestation projects also underway. The spread of Cedrela odorata in West African forests is linked to factors such as past fire occurrences, forest edge proximity, and hydromorphic soils. While the invasion of Cedrela odorata does not significantly impact above-ground biomass, it does have a strong negative effect on tree community diversity.