Question: What is the composition, ecology and distribution of the main plant communities on Santiago Island?
Location: Santiago Island (Cape Verde archipelago).
Methods: 308 plots were established using a stratified sampling system according to habitat type; random sampling was employed in each habitat type. Floristic and ecological (topographic, edaphic, climatic and land use) data were collected and analysed using classification and ordination methods and regression analysis.
Results: The classification results led to the recognition of ten plant communities. Ordination pointed to the importance of altitudinal gradient, slope angle and soil moisture in vegetation variation, as well as some categories of land use, land form or soil type. Regression analysis of sample distributions in ordination space and altitude, according to the two main types of slope aspect – leeward vs. windward – produced altitude differences of ca. 100 m. Variation in rainfall proved more effective at lower altitudes, resulting in the differentiation of more vegetation belts. Slope angle proved to be more important for vegetation differentiation when values exceeded 40°, particularly at medium and higher altitudes. Plant communities are mainly dominated by herbaceous annual species, many of which are exotic.
Conclusions: Two main phyto-ecological zones can be distinguished: a xerophilous zone (up to 300/400 m) and a mesophilous zone (above 300/400 m). The zonal communities (four mesophilous and three xerophilous) were distributed in altitudinal belts (mainly reflected in a precipitation gradient); different altitudinal ranges were estimated for these communities according to aspect. The two hygrophilous and one psammophilous communities presented an azonal distribution.