Soil Seed Banks of Dry Tropical Forests under Different Land Management

Abstract

The objectives of this study were to evaluate woody-species composition and seed density in the soil seed bank (SSB) in a dry subtropical forest with different disturbance regimes and assess the role of leaf litter as a seed reservoir in disturbed forests. Study area: the western Argentine Chaco region. Climate is seasonal and semiarid, and the fire season coincides with the dry and cool periods. In the first step, we evaluated the composition of species and seed density in the soils of forests with four different combinations of disturbances (wildfires, livestock, roller-chopping, and logging) using a systematic sampling design. In the second step, we assessed the seed density in the soil and litter fractions under focal individuals of six native woody species in two forest types (undisturbed/disturbed by roller-chopper and wildfires). Soil samples were extracted by core following standard methods for SSB studies. Eleven woody species were found in the SSB. The seed density varied between 17.78 seeds/samples in the reference condition forest and 5.46 seeds/samples in the more intensively disturbed forest (wildfires and livestock). The tree seed abundance was reduced in the disturbed forest SSB and the shrubby species increased. There were no significant differences in the seed density among the soil and litter fractions of each type of forest, but disturbances reduced the seed density in the litter fraction. The leaf litter is a seed reservoir in the soils of the Chaco forests, but this localization could promote loss by fires and desiccation. Our results could improve the forestry management plans in areas exposed to climate and land-use change.