ABSTRACT
Background: Invasive plants are associated with the decline of native plant richness, but the
impact of removal of invasives on native plant richness is often unknown.
Aims: We investigated whether the presence of the introduced plant Centaurea solstitialis
(Asteraceae) was correlated with reduced native plant richness; whether rain in late spring,
when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether
native species richness increased following the control of C. solstitialis.
Methods: From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20
1-m2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored
cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for
a total of 60 plots in two blocks.
Results: Native plant richness was lower in invaded than in non-invaded plots. More late spring
rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in
the six years after initial removal was slightly higher in removal plots than in untreated control
plots.
Conclusions: Centaurea solstitialis removal alone results in modest benefits for native plant
species richness. Managing this invasive requires more resources in years with more late spring
rainfall