Quantifying seed rain patterns in a remnant and a chronosequence of restored tallgrass prairies in north central Missouri

Abstract

Seed rain is an influential process related to plant community diversity, composition, and regeneration. However, knowledge of seed rain patterns is limited to those observed in forests and late-assembling grasslands, which might not reflect early-assembling communities such as newly restored grasslands. Resolving this gap in our understanding provides further insight into the role of seed dispersal. Here, we measured seed rain in a remnant tallgrass prairie, which was the site of the foundational grassland seed rain study in 1978, and a nearby chronosequence of tallgrass prairie restorations. We sought to determine how the quantity, seed mass traits, timing, diversity, and composition of seed rain changed (1) long-term and (2) during community assembly. To do so, we deployed artificial turf grass seed traps into 2-year-old, 5-6-year-old, and 15-year-old restored prairies and the remnant prairie, replacing traps every two weeks from May to December 2019. We captured over twice the density and richness of seed rain in the remnant prairie in 2019 compared to 1978. We also found that seed rain patterns changed as prairies aged, with each prairie possessing a distinct community of dispersing species. Significantly more seeds, seed biomass, and species were captured in the youngest restored prairie. However, seed mass traits were similar in all prairies. Except for composition, all other seed rain metrics in the oldest restoration were eventually comparable to the remnant prairie. Synthesis and Applications: Our results revealed that grasslands, notably young prairies, produce larger quantities of seed rain than previously known (124,806 seeds m−2 year −1, 97.24 g m−2 year −1), and seed input in all sampled prairies far exceeded restoration broadcast seeding densities. We further found that decreases in seed rain quantity across the chronosequence did not correspond with increases in seed mass, suggesting a lack of tradeoffs between these metrics. Furthermore, tallgrass prairie restorations have not replicated the composition of seed rain seen in remnant systems. Increasing restoration seeding rates of desirable species may be needed to meet composition goals since current rates may not compete with the propagule pressure of undesirable species found in newly restored prairies.