African archaeobotany watch: new data on the First Millennium BC 'crisis'

In the latest issue of Quaternary Research (May 2009), Ngomanda, Katarina Neumann and colleagues report new pollen data from Cameroun which address the nature of vegetation changes between the end of the Second Millennium BC and the end of the First Millennium BC, a period when archaeological settlements are thin on the ground in sub-Saharan West Africa. Elsewhere Neumann and others(Breunig) have written on the apparent crisis in which early agricultural settlements of the West African Neolithic (based on pearl millet agriculture) were abandoned and sedentary agricultural settlement (often with a different, broader agricultural package) re-emerged in the later First Millennium BC. In this paper they suggest some possible reasons. I have been struck by a somewhat parallel abandoment phase in peninsular (savanna) India between ca, 1200 and 600/400 BC, i.e. the Jorwe collapse in the North Deccan and the end of Southern Neolithic. Could there have been a parallel kind of ecological shift involved?