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 Californiaʹs 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.