History of introduction of Invasive/Adventive plants in California

As a field botanists in California, I fully admit being uninterested in “weeds” early on.  So many cool. endemic plants to seek out.  Once enough experience is gained, this viewpoint fortunately changed, as it ought to, into a caution.  Invasive plant biology has become a looming problem for many regions: as a Mediterranean climate region, California is predisposed to the acquisition of adventives from other regions. 

Working recently to examine the history of non-native plant introductions into California, I downloaded >140,000 CCH database records and have begun to examine the data for pattern.  The graph above is the pattern of acquisitions: based on the first specimen record for 1506 taxa. 

The most and perhaps most important first observation I offer is this: the pace of introduction is, for all purposes, linear over time.  Contrary to the important 1993 review (post Jepson Manual Ed. 1) review of Rejmanek  (Madrono 41:161-177. 1994) the pace seems not to be neither logistic, nor slowing down.  Hope for a solution would offer that some point we would reach a saturation in exotic species richness: the bad problem is no longer getting worse.  The graph above suggests that point is not yet in view.   Trends such as this require more research least we find, that at some point, homogenization of our flora becomes too massive a problem to avoid.  If landscape-scale species richness is a zero-sum game, then we have little time to ramp up our surveillance, study and control of invasives in CA.  We best hurry up from the shape of this graph.  The overall pace 1880-2010 is about 10 plants per yr (10.3 exactly).