iEcology reveals the importance of geography and genetic makeup in the flowering phenology of invasive Carpobrotus taxa

Abstract

Understanding the flowering phenology of invasive alien plants is essential for predicting their potential impacts on invaded ecosystems and developing effective management strategies. However, achieving this for globally widespread invasive species poses significant challenges. Digital data offer an efficient and scalable solution to studying the flowering phenology of plants across diverse regions and environments. Here, we apply this approach to taxa in the genus Carpobrotus, one of the most problematic groups of invasive plants in coastal areas worldwide. We collected geotagged photographs from widely used online platforms (i.e. Instagram, Google Maps, and iNaturalist) at key tourist sites in six countries spanning native (South Africa) and non-native (Argentina, New Zealand, Portugal, Spain and the United States) regions. These records were analysed to document the flowering phenology of Carpobrotus plants in different regions linked to their genetic lineages (clusters), focussing on the start, end and peak flowering periods. Our results show that broad floristic region and sampling locality, rather than genetic lineage, are the primary determinants of flowering phenology in the Carpobrotus taxa studied. Non-native populations often displayed extended flowering periods compared to native populations, potentially enhancing their pollen availability and seed production, contributing thus to increased propagule pressure or seed bank. Apparent differences among genetic clusters in single-model analyses were not retained once a site-level random effect was included, indicating that observed cluster contrasts reflect local environmental and sampling variation more than intrinsic genetic differences. Practical implication. This study highlights the use of digital data to address critical knowledge gaps in the flowering phenology of invasive plants across native and non-native ranges. By identifying extended flowering periods and their potential contribution to increased propagule pressure through prolonged seed production and subsequent accumulation in the soil seed bank, our findings provide valuable insights for developing targeted management strategies, such as optimizing intervention timing to coincide with flowering peaks.