Plant resprouting: How many sprouts and how deep? Flexible modelling of multi-species experimental disturbances

Plants can respond to damage through regrowth from meristematic tissue, commonly concentrated in buds. Knowledge of the distribution and abundance of buds within plants can assist in understanding individual, population and species responses to disturbances. Yet belowground buds can be hard to study, as they may be cryptic until initiated in response to damage. Sprouts emerging following disturbance can be studied more easily and represent a realised bud bank.Here we aimed to characterise and compare the vertical distribution of sprouts from a previous study of clip and burn treatments for 42 species of grasses, forbs, subshrubs and woody plants in semiarid eastern Australia (Vesk et al., Oikos 2004 107:72–89). We tested whether depth distributions of sprouts could be explained by growth forms and plant traits, while also asking whether clip and burn treatments influenced those distributions. We combine function regression with a hurdle model to estimate simultaneously the probability of resprouting and the depth distribution of buds, conditional on resprouting (hereafter, sprouts). Function regression models the depth distribution of sprouts as a continuous function, rather than a single value. The hurdle model also allowed us to ask whether sprout depths and the probability of resprouting were similarly related to treatments, growth forms and traits.Depth distributions of sprouts in successfully resprouting plants differed among growth forms. Specifically, we observed similar distributions of sprouts in forbs and woody plants, more and deeper sprouts in grasses, fewer and mainly above-ground sprouts in subshrubs. However, because the probability of subshrubs resprouting was very low, the expected number of sprouts was very low too. Burning resulted in more and deeper sprouts on successfully resprouting plants. Further, species’ traits like maximum height and specific leaf area (SLA) were correlated with different sprout distributions. Taller species had fewer shallow sprouts in general, and high SLA species had more shallow sprouts under clipping but not under burning.This work points to experimental methods and statistical analyses to quantify the depth distribution of the buds from which plants resprout. This serves to inform comparative investigations of buds, sprouts, and disturbance responses, and is likely to improve predictions of responses to disturbances.