Abstract Many exotic plants utilize early suc- cessional traits to invade disturbed sites, but in some cases these same species appear able to prevent re-establishment of late-successional and native species. Between 2002 and 2004, I studied 25 fields that represent a 52-year chronosequence of agricultural abandonment in a shrub-steppe ecosystem in Washington State, USA, to deter- mine if exotic plants behaved as early succes- sional species (i.e., became less abundant over time) or if they established persistent communi- ties. Exotics maintained dominance in tilled (73% of total cover) relative to never-tilled (6% of total cover) fields throughout the chronosequence. Exotic community composition, however, chan- ged on annual and decadal timescales. Changes in exotic community composition did not reflect typical successional patterns. For example, some exotic perennial species (e.g., Centaurea diffusa and Medicago sativa) were less common and some exotic annual species (e.g., Sissymbrium loeselii and S. altissimum) were more common in older relative to younger fields. Exotics in the study area appeared to establish communities that are resistant to re-invasion by natives, resilient to losses of individual exotic species, and as a result, maintain total exotic cover over both the short- and long-term: exotics replaced exotics. Exotics did not invade native communities and natives did not invade exotic communities across the chronosequence. These results suggest that, in disturbed sites, exotic plants establish an alter- native community type that while widely variable in composition, maintains total cover over annual and decadal timescales. Identifying alternative state exotic communities and the mechanisms that explain their growth is likely to be essential for native plant restoration. Keywords Chronosequence Æ Facilitation Æ nMDS Æ Old-field Æ Shrub-steppe Æ Stable state Introduction In many areas of the world, exotic plant species (exotics) form the dominant vegetation, especially in disturbed sites (Sheley and Petroff 1999; Den- slow and Hughes 2004). In some cases, these exotic invaders use traits (e.g., allelopathy, high combustibility, and plant-soil feedbacks) that alter their environment in a way that could be expected to improve their own growth (Mack and D’Antonio 1998; Klironomos 2002; Callaway et al. 2004). While rarely considered, it is also possible that assemblages of exotics, and not just A. Kulmatiski (&) Department of Forest, Range, and Wildlife Sciences and the Ecology Center, Utah State University, Logan, UT 84322-5230, USA e-mail: andrew@biology.usu.edu Plant Ecol (2006) 187:261–275 DOI 10.1007/s11258-006-9140-5 123 ORIGINAL PAPER Exotic plants establish persistent communities Andrew Kulmatiski Received: 24 June 2005 / Accepted: 13 March 2006 / Published online: 21 April 2006 Ó Springer Science+Business Media, Inc. 2006