Linking plant functional traits with post-fire sprouting vigour in woody species in central Argentina

Sprouting vigour is determined by the plant amount of reserves and intrinsic growth rate of plants. While the first factor has been well studied, the second is far less understood. Although a higher growth rate would imply a higher sprouting vigour, fast-growing species may have less below-ground reserves, and thus, a lower sprouting potential. The relative importance of both opposite effects was little explored in the literature. To analyse the influence of growth rate on sprouting vigour, one growth season after a fire we measured plant height of the old (pre-fire) and new (post-fire) tissue in 194 individuals of 14 woody species from a woodland in central Argentina. We calculated a mean value of pre- and post-fire height for each species, and obtained from a data-base potential height at maturity, wood density (WD) and specific leaf area (SLA), as surrogates of intrinsic growth rate. We performed a forward stepwise multiple regression using WD and SLA, together with mean pre-fire height or potential height as independent variables, and mean post-fire height (as an indicator of resprout vigour) as the dependent variable. Interactions were also tested. Pre-fire height, WD and their interaction term were the variables that best explained post-fire height. We also analysed the relationship between pre- and post-fire size for each species independently by fitting hyperbolic functions. Then we correlated both parameters of the functions to species characteristics (WD, SLA, potential height and mean pre-fire height). Both parameters of the hyperbolic functions were significantly correlated only with WD, but not with the other species characteristics. All results together indicate that species with low WD (i.e. high potential growth rate) regrow more vigorously than species with high WD when pre-fire individuals were tall. In contrast, when pre-fire individuals were small, WD had no influence on sprout vigour. A trade-off between allocation of biomass to underground reserves and shoot growth seems to be responsible for the patterns obtained. For small individuals, below-ground reserves seem to play a more important role than inherent growth rate (here measured through WD) in determining the sprouting vigour, while for large individuals, growth rate seems more important than reserves.