Seed Rain in Subtropical Grasslands Under Different Grazing Intensities

Question

Seed rain maintains propagule stocks in the seed bank and governs plant recruitment and community composition. However, seed rain studies in Southern Hemisphere grasslands remain scarce, and little is known about the effects of grazing on seed rain. We evaluated the seed rain in grasslands with distinct grazing intensities (high, moderate, low, very low, and not grazed) in subtropical southern Brazil.

Location

Long-term cattle grazing management experiment in subtropical Campos grassland, southern Brazil.

Methods

Seed rain was collected, using pot traps with sterile soil, monthly for one year. Additionally, we recorded species in the fruiting phase present in the vegetation. The seed rain was estimated by the seedling emergence method. We performed randomization tests to compare seed rain density and composition among managements and seasons, and evaluated functional composition of the seed rain (broad functional groups of plants and dispersal traits).

Results

We observed high numbers (up to 106,070 seedlings/m², representing the maximum annual sum) in seed rain samples, with seeds from 90 species. The ungrazed treatment showed the highest number of seedlings. Across seasons, no significant differences were found, due to large variation. Similarity between seed rain and vegetation was low (Sørensen index values between 13% and 30%).

Conclusion

Our results indicate that large numbers of seeds are dispersed and potentially incorporated into the soil seed bank at the grassland site. This study contributes to understanding the dynamics of subtropical grasslands under different grazing regimes. Our findings can guide grazing management strategies to enhance the dispersal of target species, supporting effective conservation and restoration efforts.