Germinable soil seed banks in a tropical savanna: seasonal dynamics and effects of fire.

Abstract

The germinable soil seed bank of a tropical eucalypt savanna of north-eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire-related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta , Pycnospora lutescens and Triumfetta rhomboidea . Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus . The germinable soil seed bank varied seasonally, increasing from the mid west season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.

Understanding relations between pastoralism and its changing natural environment

“…Seeds in the upper layer are more likely to have their dormancy broken by fire or water than seeds in the deeper layer (Williams et al, 2005). Such effect of vertical distribution on species richness is consistent with Savadogo et al (2016) in Burkina Faso and with Tessema et al (2012) in Ethiopia.…”

“…After seed production, seeds first arrive at soil surface where they are captured before entering the deeper soil layer (Thompson and Grime, 1979) and where their dormancy is likely broken by fire or water (Williams et al, 2005). Such effects of vertical distribution on plant abundance in the soil seed banks is consistent with Tessema et al (2012) in Ethiopia, and Savadogo et al (2016) in Burkina Faso.…”

¿Qué ocurre con el banco de semillas del suelo 17 años después del corte de la vegetación?

“…Consequently, seasonal differences in richness and density of seed in the soil bank may not occur (López, 2003) or may occur and sometimes be higher either in the dry season (Williams et al, 2005) or in the rainy season (Facelli, Chesson, & Barnes, 2005;Santos et al, 2010), being evidence that precipitation explains 5% of the density of the soil seed bank .…”

“…63 (2): 321-332. Epub 2015 June 01.Key words: semiarid, young forests, savanna, natural regeneration, resilience.The soil seed bank reflects the factors that affect plant reproduction and survival of seeds in time and space (Donohue, Casas, Burghardt, Kovach, & Willis, 2010;López, 2003;Pennington, Lavin, & Oliveira-Filho, 2009; Pugnaire, & Lázaro, 2000;Silva et al, 2013a), and may be depleted in disturbed areas (Mamede, & Araújo, 2008;Wang, Jiang, Toshio, & Zhou, 2013;Williams, Congdon, Grice, & Clarke, 2005). However, the influence of spatial and temporal heterogeneity on the soil seed bank of areas that have undergone the removal of vegetation is still poorly documented, making it difficult to assess the potential for restoration of anthropogenic forests, the resilience of which, among other factors, depends on the availability of seeds from the soil bank for recruitment (Baeten et al, 2009;Lopes et al, 2012;Wang et al, 2013).…”

“…In some dry forests, the thin layer of leaf litter houses a small amount of seeds when compared to the layers of soil (Costa, & Araújo, 2003;Santos et al, 2010), as the quantity of seeds decreases with increasing soil depth (Williams et al, 2005). The distinct microhabitats of forests are also of relevance for harboring different amount of seeds, explaining 31% of the density of the soil seed bank .…”