Contribution of the soil SEED bank to the recovery of a Cytisus oromediterraneus shrubland after fuel reduction treatments

Abstract

Land managers need scientifically-based information to enable them to select the most appropriate treatments for reduction of high-severity wildfires in shrubland areas. The soil seed bank is known to play a key role in the post-disturbance recovery of shrubland communities, although information about how it is affected by fuel reduction treatments is still scarce. We carried out a combined greenhouse and field study to evaluate the effects of prescribed burning, clearing and mastication on the response of the soil seed bank and vegetation recovery in a Cytisus oromediterraneus (Spanish golden broom) shrubland area in central Spain. We determined the following variables: total seedling density in the greenhouse, broom density (in the greenhouse and field), vegetation cover recovery in the field, species richness (in the greenhouse and field) and similarity index between the floristic composition of the above-ground vegetation and soil seed bank. We also evaluated how the remaining soil organic cover and depth affected seedling emergence after treatments in the field. In addition, we explored the effect of soil thermal regime during prescribed burning on posterior seedling emergence.In the greenhouse experiment, a significantly greater number of seedlings emerged from the soil seed bank samples obtained after burning (1297 seedlings m−2) than from the seedlings obtained before burning (775 seedlings m−2) and after clearing (801 seedlings m−2) or mastication (705 seedlings m−2). The mechanical treatments did not induce any changes in the seedling emergence from the soil seed bank. Species richness in the soil seed bank was not altered by fuel reduction treatments. Post-burning seedling density was not significantly related to any of the soil thermal regime parameters during burning. Soil organic cover after the treatments negatively affected the response of the soil seed bank.The field study revealed no differences between treatments in relation to total vegetation cover, broom cover or grass cover. However, forbs cover was significantly higher in the prescribed burning treatment that is related with the higher density of seedlings of these species measured in the greenhouse experiment. C. oromediterraneus regenerated strongly via sprouting, being the seed germination rate in the field very low. That suggests that the soil seed bank makes little contribution to recovery of this species after fuel reduction treatments, and the same was observed for the remaining plant community.