CONICET | Buscador de Institutos y Recursos Humanos

AimsIncreasing evidence worldwide indicates that high mountainregions are not immune to invasion by alien plants. Here, we aimedto address whether three major woody invaders of low-mountainareas are constrained to lower altitudes due to climatic restrictionsor just by low propagule pressure. We hypothesize that the increasingclimatic harshness towards higher altitudes restricts seedlingestablishment and survival of these woody invaders and thus theirpotential for altitudinal expansion.MethodsThe study was carried out in the Sierras Grandes Mountains,Córdoba, central Argentina (32º50′S, 64º90′W). We addressedthe hypothesis with an experimental approach, dissociating theeffect of the environmental gradient from that of propagule pressure,by discarding the influence of seed sources. We translocatedseeds of Gleditsia triacanthos L., Ligustrum lucidum W.T. Aiton. andPyracantha angustifolia (Franch.) C.K.Schneid. along the altitudinalgradient (from 900 to 2700 m asl). Seven sites were selected alongthe altitudinal gradient, spaced every 200?400 m. Three plots (4 × 4m) were selected within each altitudinal site and excluded fromlivestock; 100 seeds of each species were sown within each plot(6300 seeds in total). Seedling emergence and survival was monitoredduring two growing seasons and soil temperature and moisturewas recorded as well. The field experiment was complementedwith lab assaysImportant FindingsClimate along this altitudinal gradient might be least restrictive at midelevations, as a result of the intersection between opposite soil temperatureand moisture gradients. Sown seeds germinated along the wholealtitudinal gradient and seedlings successfully established and overwinteredwell above their current altitudinal distribution (up to 2200m for Ligustrum and 2400 m for Gleditsia and Pyracantha). Additionallab assays confirmed field patterns and gave some insights into contrastingregeneration strategies between these invaders that might helpto overcome stochastic environmental constraints in the germinationstage. Overall, seedlings of three major woody invaders of low-mountainwoodlands can establish and survive at higher elevations thantheir current distribution. In contrast to natives, they seem to be broadclimate tolerators, rather than specialized stress tolerators, capable ofgerminating and growing across a wide elevational range. While longtermexperiments might be necessary to fully address the potentials foraltitudinal expansion, out results on early lifecycle stage suggest that theinvaders studied here would have mostly a dispersal barrier rather thana climate barrier to establish in the upper belt of the Sierras Grandes.

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