Plant diversity and carbon storage in roadside trees in Cotonou (Republic of Benin)

Abstract

The purpose of this paper was to assess the diversity of roadside trees and their capacity in the storage of carbon in Cotonou. This study has been posited as a prerequisite for urban greening management for the mitigation of the ongoing global warming. Purposive sampling was used involving four (04) Avenues, namely Canada, Proche, Missèbo-Zono and Marina, selected using the cartographic data from the DST (Direction des Services Techniques). The sampling was carried out using the sum of distances planted with alignment trees on the four investigated Avenues. Plant diversity was analyzed while dendrometric and plant community structure were characterized. The floristic inventory on the roadside trees of the four (04) avenues reported a total of 1075 plants belonging to 12 species, 11 genera and 9 families. The most abundant tree species was Khaya senegalensis (67.82 %), followed by Terminalia mentaly (21.15 %). The least represented species was Roystonea regia (2.01 %) found only on the Marina Avenue. Average Shannon Diversity Index and Pielou evenness values were respectively 1.93 bit and 0.55 indicating a weak diversity of tree species along the four Avenues. Noticeable high difference was observed in the floristic composition on the four Avenues regarding species, genera and family richness. Marina (9 species, 8 genera and 7 families) appeared to be the most diversified while Proche (3 species, 3 genera and 3 families) was the least. Non native tree species were the most dominant. Stored C mean in these roadside trees ranged between 5,877.8 tons C and 6,311 tons C, corresponding to the values of 744.03 kg C/ha and 798.87 kg C /ha. These results provided an evidence of the purification role of trees and posit urban forest as a solution to be encouraged to the ongoing pollution of the environment in cities.

Keywords: Urban forestry, roadside trees, carbon stock, Cotonou, Bénin