The impacts of serial land-use changes and biological invasions on soil water resources in California, USA

Land-use changes and biological invasions have converted the vegetation of California's Central Valley and surrounding foothills from a mixture of perennial forbs and grasses and spring- and summer-flowering annuals to vegetation dominated by Eurasian spring-flowering annual grasses. The exotic annual grass communities are now rapidly being invaded by a Eurasian summer-flowering annual thistle that has caused losses of soil moisture resources on invaded sites of 15-25 % of mean annual precipitation. A rough preliminary estimate indicates that the value of the lost water may range from 16 to 75 million dollars per year in the Sacramento River watershed alone. (C) 2003 Elsevier Ltd. All rights reserved.