?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.aufirst=H+I+D&rft.au=Vierich%2C+H+I+D&rft.aulast=Vierich&rft.atitle=Changes+in+West+African+Savanna+agriculture+in+response+to+growing+population+and+continuing+low+rainfall&rft.title=Agriculture%2C+Ecosystems+and+Environment&rft.issn=0167-8809&rft.date=1990&rft.volume=31&rft.pages=115-132&rft.issue=2&rft.genre=article