Litter context shapes seed persistence of an invasive pine in Patagonia

Abstract

Natural plant communities are highly vulnerable to invasion by neighboring invasive species. Understanding how litter influences invasive species establishment is essential for assessing its impact on invasion. We conducted a field experiment to investigate how litter context, related to disturbance and habitat type, affects the seed longevity of Pinus radiata, an invasive, fire-adapted species in Patagonia, Argentina. We simulated litter conditions that pine seeds may encounter along the edges of invasive pine-dominated areas, including post-fire scenarios. We examined the response of Pinus radiata seed viability to the combined effects of litter origin (native forest vs. pine-invaded forest), litter burn status (burned litter residue vs. unburned litter), and time since deposition in the field (4 months, 1 year, and 2 years). Burned litter generally reduced viability, though the effect was less pronounced in native litter than in pine forest litter. Pinus radiata seeds remained viable for at least one year in burned forest substrates, indicating that forests affected by fires are highly vulnerable to pine invasion. Burned litter residue, particularly from pine, promoted germination shortly after seeds were left in the field (pine litter: 30 % ± 1.4 vs. native litter: 17 % ± 1.1), compared to no germination in unburned litter, suggesting that burning accelerates pine colonization. The differing impacts of burned litter from different habitats on seed viability and germination emphasize that microcontext influences on regeneration are specific to each reproductive process. Prolonged seed deposition in the field reduced seed viability, yet some seeds remained viable after 2 years. Overall, these results highlight the role of disturbances in determining seed persistence and the potential for P. radiata to spread over time through the establishment of persistent soil seed banks.