To what extent can simple plant biological traits account for the response of the herbaceous layer to environmental changes in fallow-savanna vegetation (West Burkina Faso, West Africa)?

The ability of simple plant traits used as surrogate of species to reflect environmental variability of grasses and herbs in a West African savanna subject to fallow land rotation is assessed by referring to plants' functional attributes. The aim is to determine the nature and the importance of the loss of information associated with the trait-vs.-species simplification. The traits selected are easily observable and widely documented. They are related to plant responses to resource availability, environmental constraints/disturbances and to plant palatability and capacity to disperse. The co-inertia analyses of both species-environment and traits-environment are compared. Although selected traits account for only a part of the variability recorded by species, they are relevant and most of them have an ecological significance. Syndromes of attributes that reflect the functional plant-environment relationships of the grass layer along a twofold gradient of soil fertility and woody cover could then be established. Periodic clearing and soil fertility decline produced by the fallow system determine vegetation types dominated by herbaceous species ranging from competitive and ruderal-competitive on fertile and wooded sites to stress-tolerant ruderal on unfertile and non-wooded sites. Thus, selected traits do not reveal all functional aspects of the relationships of savanna plants to their environment, such as soil hydromorphy and depth of the clayey horizon. That is possibly due to the scarcity of traits that characterize the root system involved in the analysis.