Considering the Role of Grazing Disturbance in Shaping Seed Quality and Quantity in Arid Environments

Abstract

Vegetation dynamics typically relies on the availability of good seed quality. However, seed production depends on many factors and often involves a trade-off between quality and quantity, which can be affected by stress factors. Successional types of species (early, intermediate, and late) share life-history traits that may lead to contrasting responses to disturbance. To understand vegetation dynamics under disturbance in arid environments, we investigated how a grazing gradient affected seed quality and quantity of successional types of species in Monte Desert. We hypothesized that grazing would affect seed traits through maternal effects and that responses would differ among successional types. We measured plant biomass, reproductive effort, seed set and seed weight in ten species across ten independent rangelands with increasing stocking rates. Overall, grazing intensity was not associated with seed quantity or quality when species were analyzed together, disregarding interspecies variability. Species responses differed markedly according to successional type. Early and intermediate species showed compensatory responses to grazing, and higher biomass in intermediate species may confer greater nutrient availability and tolerance to disturbance. In contrast, the negative associations between seed traits, biomass, and reproduction of late species suggest a shift in resource allocation toward maintenance rather than reproduction. Successional strategies are key determinants of seed trait responses to disturbance. This results show that reproductive resilience in arid ecosystems emerges from the interaction among environmental constrains, functional strategy, plant biomass, and disturbance intensity. Recognizing this context dependency is fundamental for selecting species in restoration programs and for facilitating natural successional dynamics.