31 Archer, S TW Boutton KA Hibbard 2001 Trees in grasslands: biogeochemical consequences of woody plant expansion ED Schulze SP Harrison M Heimann EA Holland J Lloyd IC Prentice D Schimel Global Biogeochemical Cycles in the Climate System San Diego Academic Press 115-137 savannas, shrublands, vegetation change, woody plant encroachment http://ag.arizona.edu/research/archer/pubs/reprints/Archer_etal_JenaChapter.pdf