Effects of Exotic-Species Afforestation on the Understory Vegetation of Santo Antao, Cape Verde Islands

Abstract

The nation of Cape Verde is an isolated, geologically young Macaronesian archipelago off the west coast of Africa. The westernmost island, Santo Antão, ranks second in the archipelago in terms of area and altitude, possesses high topographic relief, and thus harbors some of the highest levels of native plant diversity in Cape Verde. After a history of denudation, exotic-species afforestations were established in the high altitude regions of Santo Antão in the mid-20th century in an effort to combat erosion, re-establish vegetative understories, increase water yield and infiltration, and provide socio-economic opportunities for the local populace. An evaluation of the afforestations has not been completed, particularly in terms of the effect on understory species. The central objective of this research was to determine the impact of exotic-species afforestations on the understory vegetation of the Planalto Leste region of the island of Santo Antão across three bioclimatic zones – humid, sub-humid, and semi-arid. A total of 42 plots were sampled in both afforested and natural habitats, and the data were analyzed to ascertain the afforestation’s effect on understory richness, cover, and composition. Afforestations were observed to exert a negative effect on understory vegetation abundance and diversity, and the magnitude of the effect is likely attributable to the formation of closed canopies and thick leaf litter layers, inhibiting understory growth. Negative effects were most pronounced in the humid zone, less pronounced in the sub-humid zone, and not present in the semi-arid zone. The original goals of afforestation are evaluated, and some stand management suggestions are given to improve native understory plant conservation.