How regeneration vs adult traits shift across environmental gradients at different spatial scales during post-fire recovery in Southern California shrublands

Meg Kargul and Loralee Larios, Botany and Plant Sciences, University of California-Riverside, Riverside, CA

Background/Question/Methods: With more frequent wildfires and variable precipitation events, understanding post-fire recovery mechanisms is vital to prevent plant invasions and habitat type conversion. Early life stage traits (regeneration traits) may mediate the recovery process, yet are largely understudied and may differ from adult traits commonly used to determine community structure and function. To better predict vegetation dynamics over time and across environmental gradients, understanding how traits vary across life stages and resource gradients acting at different spatial scales is needed. Therefore, our research objectives were to compare how regeneration vs adult traits shift across resource gradients at different spatial scales during woody post-fire recovery in Southern California shrublands. Specifically, we asked 1) how do regeneration traits differ from adult traits across regional and local resource gradients, and 2) how responsive are regeneration traits to different resource gradients compared to adults. To answer these questions, we collected leaf functional traits for regenerating species within three burn scars and for adults in nearby unburned areas across northeast and southwest aspects. The three burn scars occur across a regional increasing elevation gradient from the coast moving inland in Southern California, and the underlying resource gradients are quantified using a Digital Elevation Model and PCA.
Results/Conclusions: We found regeneration and adult traits to differ, where regeneration traits were indicative of resource-acquisitive functional strategies (ex. higher specific leaf area, lower leaf dry matter content) relative to adults, and this relationship was conserved across the regional resource gradient. Additionally, regeneration traits tend to decrease along the regional gradient more strongly than adult traits, indicating the environment has a strong impact on establishment traits that mediate recovery. Local aspect impacted trait values differently across life stage and regeneration strategy. On cooler, wetter northeast aspects, regenerating seeders had more resource-acquisitive traits while adults had conservative traits. For regenerating resprouters, the aspect supporting resource-acquisitive traits depended on the underlying regional resource gradient, where resource-acquisitive traits were found on northeast aspects only at medium resource stress. Because the local scale filters traits differently across life stages and regeneration strategies, management efforts must use the correct match between traits suitable for the local environment depending on life stage. Our results are a first step towards identifying the correct match between life stage, traits, and environment to promote successful establishment during recovery and restoration.