Seasonal Patterns of Longevity and Germination in Grass Species Determine the Vegetation Recovery Potential of Degraded Semi‐Arid Savannas

ABSTRACT

Studies indicate that soil seed bank (SSB) could play an important role in triggering the recovery of grass vegetation after degradation. However, the dissimilarity between SSB composition and aboveground vegetation (AGV) is reported in semi‐arid African savannas, which could be due to differences in seed longevity, as determined by seed dormancy and germination. Therefore, the longevity and germination success of 16 grass species collected in semi‐arid savannas of Ethiopia were studied to test whether the poor vegetation recovery of degraded semi‐arid savannas could be attributed to the low germination rate and long dormancy of grass seeds, and whether the difference in species composition between the AGV and SSB could be explained by differences in germination rates between annual and perennial grass species. Our results showed that perennial grass (PG) species had a higher viability and germination rates than the annual grass (AG) species. The mean viability of AG and PG species was 12% (range: 0%–38%) and 46% (20%–90%), respectively. Similarly, the mean germination rates of AG and PG species were 5% (0%–8%) and 33% (6%–90%), respectively. The germination rates of PG species peaked after 8 months since the seeds were placed for germination study. Our study confirmed that differences in germination rates between AG and PG species partly explained the variations in difference in species compositions between the AGV and SSBs. From this study, we concluded that PG species had a high germination rate and a low dormancy indicating that they could not form persistent SSB, and can therefore disappear rapidly after germination, such as under the influence of grazing and trampling, erratic rainfall events, or prolonged dry periods, which is a typical feature of the semi‐arid African savannas.