Living in a world of fire: the population dynamic of Mulinum spinosum in Northwestern Patagonia grasslands
DE TORRES CURT M.; GHERMANDI L.; ZIMMERMAN V.
Lugar: Berlin; Año: 2020
Questions How do fire frequency and fire size affectthe long-term population dynamics of Mulinumspinosum? Which demographic parameters contributemost to the overall effect of fire on population growth?What is the relative importance of resprouting insustaining population increase?Location Grass-shrub northwestern Patagoniansteppe, Argentina.Methods We monitored five permanent plotsexcluded from grazing for 6 years. We measuredshrub abundance, dimensions, reproductive status,seedling emergence, and the size structure of M.spinosum, a resprouting native shrub inhabiting thenorthwest Patagonian steppe. Data were used toparametrize a stochastic matrix model developed toexplore the influence of fire frequency and fire size onlong-term population dynamics. We analyzed hypotheticalscenarios that included fire frequencies rangingfrom one per year up to exclusion.Results Except for annual fires, projections showgrowing populations regardless of fire frequency. Forfire return intervals greater than 50 years, the populationbecomes independent of fires, with an annualpopulation growth rate of 5.6%. The results suggesttwo relevant aspects of the population dynamics of thisspecies: M. spinosum is well adapted to the current firefrequency and its resprouting capability will allow M.spinosum to survive and persist in the community,even under frequent fires.Conclusions Climate change models forecast anincrease in summer temperature in NW Patagoniaand, consequently, an enhanced fire frequency. Fire isa driver of M. spinosum encroachment that gets worsein overgrazed grasslands. Mulinum spinosumencroachment derivate in a relative replacement ofpalatable grasses by shrubs changes the ecosystemfunctionality and reduces productivity. Controllingthis process is highly difficult and we suggest a changein the land use for the areas already deteriorated.