The fate of herbaceous seeds during topsoil stockpiling: Restoration potential of seed banks

Abstract

Topsoil removed during linear infrastructure construction is one of the most valuable resources for the ecological restoration of roadslopes, as it contains high concentrations of micro-organisms, nutrients and seeds. During construction work, topsoil is stockpiled in a way that can harm seed germination and survival capacity. In order to assess the effects of topsoil storage time and seed burial depth on seed survival, germination and mortality, an experiment with three replicates was conducted using two factors: time (1–6 months) and burial depth (0, 5, 30 and 50cm). At each stockpile depth we buried 25 seeds from 10 natural grassland species (5 families) in permeable nylon sachets. Seed mass and seed functional responses to light (LI) and diurnal temperature fluctuations (DTF) were also measured for each species. Seed survival, germination and mortality during stockpiling were analyzed using binomial GLMs. Explanatory variables were family, depth of burial, time, seed mass, LI and DTF responses. Seed survival decreased with storage time but increases with depth. Seed losses were due to seed germination and mortality in the stockpile. Germination percentage increased with time but decreased with burial depth. This parameter was negatively related to LI and DTF. Mortality increased significantly with time and depth and was negatively related to seed mass.Results show that there may be a loss of viable seeds in topsoil stockpiles, particularly in the case of large seeds. Our results also underline the functional role of light requirements for germination and the detection of diurnal temperature fluctuations as mechanisms to achieve higher soil seed persistence. The correct management of topsoil is decisive for the restoration of roadslopes. Seed germination potential decrease with time of storage and burial depth, consequently a serious loss of seeds conducts an impoverishing of topsoil, which is the main natural resource for the restoration of these disturbed ecosystems. Viable seed loss is lower in deeper layers of the stockpile, so short-period topsoil storage and bigger stockpiles could reduce seed loss and increase thus the restoration potential of topsoil.