Rapid Changes in Soils Following Eucalyptus Afforestation in Hawaii

Abstract Intensively managed plantations of trees occupy vast areas of the tropics. The productivity of these forests depends strongly on nutrient supply, and nutrient supply may change rapidly under intensive management regimes. We documented changes in a Hawaiian soil after 32 mo of development of a plantation of eucalyptus [ Eucalyptus saligna (Sm.)]. Soil C did not change significantly (average = ‐23 g C m ‐2 yr ‐1 to 30 cm; 95% confidence −139 to +93 g C m ‐2 yr ‐1 ). This lack of change in soil C resulted from a rapid loss of older soil C derived from sugarcane (−191 g C m ‐2 yr ‐1 ) and a rapid gain of new soil C from eucalyptus (160 g C m ‐2 yr ‐1 ). Soil N declined by 19 g N m ‐2 yr ‐1 ( P = 0.08), despite fertilizer additions of 31 to 70 g m ‐2 . Large reductions in exchangeable Ca and Mg probably resulted from dissolution and leaching of residual lime from prior agricultural management. We conclude that intensive sampling regimes may detect relatively small changes in tropical forest soils, and that expectations of C accumulation in soils following afforestation may need to be reconsidered.