Evaluating the restoration potential of soil seed banks in degraded semi-arid oak forests: Influence of canopy cover types and fire-related cues on seed germination

Abstract

Soil seed bank is an important driver of vegetation dynamics, particularly in fire-prone Mediterranean ecosystems. In this study, we disentangle the effects of fire-related cues on the dynamics of the soil seed bank in semiarid oak forests of western Iran. Soil samples were collected in two types of forests: below closed canopy or below the open canopy of more intensively used forests. In a greenhouse experiment, the effects of five treatments were tested application of: ash (Ash), smoke (Smoke), 50 °C temperature (Heat50), 100 °C temperature (Heat100) and control. Soil samples were regularly monitored and the number of germinated seeds (seedlings) by species were recorded in each treatment. Diversity indices were also computed. Knowing the effects of fire and its cues on fied 18 species from 16 genera and 9 families. 56 % of the seedlings emerged from the closed canopy forest soils and 44 % from the open canopy forests. Seedling density and diversity values were the lowest in the Heat100 treatment. No annual grasses and tree species were recorded in this treatment. In contrast, the influence of the other fire-related cues was mediated by the forest type cover: the number of emerged seedlings was the highest in Smoke and Heat50 in the open canopy and closed canopy, respectively. This mediation effect was also reflected in the composition of the control as tree species were only present in the closed canopy and annual forbs were less abundant there compared to the open canopy type. Considering all fire treatments together, the seedling density was significantly higher in the closed canopy type than in the open canopy (309.6 ± 28.03 vs 240.8 ± 20.78 seeds/m2). Our results showed that intense fires leading to high soil temperatures are largely detrimental to soil seed bank germination and species diversity, whereas less intense fires can be favourable depending on species life form and the type of forest. Our findings highlight that post-fire regeneration from the soil seed bank is more promising in closed forests than in forests with an open canopy in the studied ecosystem.