Seed and seedbank dynamics of the highly invasive weed Yellow starthistle

LORTIE, C., J.L. HIERRO, AND D. VILLARREAL

Portland, Oregon, Estados Unidos

Congreso; Ecological Society of America Annual Conference; 2004

In a recent report by The Royal Society, 'Measuring biodiversity forconservation', unprecedented rates of introduction of non-native speciesand change in global climate are identified as two key processes impactingnatural ecosystems primarily through loss of biodiversity.  Every ecosystemworldwide is now subject to both processes, often simultaneously, and thesuccess of native and invasive plant species is highly context dependent.To this end, it is crucial that we begin to address various ecologicalaspects of invasion in the context of variation between geographicalregions.  For instance, why is it that an introduced species is successfulin one region and not another?  More importantly, why is it that the samespecies is often not dominant in its place of origin?  Yellow starthistle(Yst) is a highly successful invader in many regions including Californiaand Argentina.  The success of Yst is likely influenced by a suite offactors, yet seedbank dynamics, one of the least studied aspects ofinvasion ecology may be the key to understanding invasion dynamics for thisspecies.  An explicitly biogeographical approach was used to (i) compareproperties of the local seed banks being invaded; (ii) compare ecologicalattributes of Yst seeds and plants in each region; and (iii) experimentallytest for seed-seed interactions.  Seeds and seedbank from within its homerange (the Republic of Georgia) were also tested.  There was significantvariation between Yst plant density and seed density between regions withCalifornia having the highest density of both seeds and plants.Interestingly, California also had the most diverse and dense localseedbanks yet was the most invaded by Yst.  There was no significantrelationship between the persistent seedbank of Yst and its emergent plantdensity which suggests that seedbank dynamics are decoupled from plantcommunity interactions.  Finally, in experimental tests for seed-seedinteractions, Yst germination and establishment functioned in a densitydependent manner which suggests there may negative interactions with otherYst seeds and plants but that these effects do not translate into reduceddominance within natural plant communities.