The diversity of post‐fire regeneration strategies in the cerrado ground layer

Abstract

Disentangling species strategies that confer resilience to natural disturbances is key to conserving and restoring savanna ecosystems. Fire is a recurrent disturbance in savannas, and savanna vegetation is highly adapted to and often dependent on fire. However, although the woody component of tropical savannas is well studied, we still do not understand how ground‐layer plant communities respond to fire, limiting conservation and management actions. We investigated the effects of prescribed fire on community structure and composition, and evaluated which traits are involved in plant community regeneration after fire in the cerrado ground layer. We assessed traits related to species persistence and colonization capacity after fire, including resprouter type, underground structure, fire‐induced flowering, regeneration strategy and growth form. We searched for functional groups related to response to fire, to shed light on the main strategies of post‐fire recovery among species in the ground layer. Fire changed ground‐layer community structure and composition in the short term, leading to greater plant species richness, population densities and increasing bare soil, compared with unburned communities. Eight months after fire, species abundance did not differ from pre‐disturbance values for 86% of the species, demonstrating the resilience of this layer to fire. Only one ruderal species was disadvantaged by fire and 13% of the species benefited. Rapid recovery of soil cover by native vegetation in burned areas was driven by species with high capacity to resprout and spread vegetatively. Recovery of the savanna ground‐layer community, as a whole, resulted from a combination of different species traits. We summarized these traits into five large groups, encompassing key strategies involved in ground‐layer regeneration after fire. Synthesis. Fire dramatically changes the ground layer of savanna vegetation in the short term, but the system is highly resilient, quickly recovering the pre‐fire state. Recovery involves different strategies, which we categorized into five functional groups of plant species: grasses, seeders, bloomers, undergrounders and resprouters. Knowledge of these diverse strategies should be used as a tool to assess conservation and restoration status of fire‐resilient ecosystems in the cerrado.

Post‐fire regeneration strategies in a frequently burned Cerrado community

“…(a) resprouting ability after experimental fires, accounting for bud location; and (b) propagule stimulation and/or tolerance to heat shocks by evaluating seed germination and viability after laboratory trials. Since fire regime is expected to shape post-fire regeneration strategies (Bond & Midgley, 2003;Keeley et al, 2012), we expect resprouting to be the main regeneration strategy in the Cerrado (Bond & Midgley, 2001;Clarke et al, 2015;Pilon et al, 2020) Zirondi, José et al, 2019). We also expect propagules to be tolerant to fire-related temperatures (Daibes et al, 2019), remaining ungerminated (yet viable) until the onset of the rainy season (Escobar et al, 2018).…”

“…In the Cerrado, frequent fires have been present for at least four million years (Simon et al, 2009) and fire regimes are characterized by frequent (~3 to 5 years) surface fires of relatively low intensity fueled by grasses (Coutinho, 1982;Kauffman et al, 1994;Miranda et al, 2002Miranda et al, , 2009Pereira-Junior et al, 2014;Alvarado et al, 2017;Rissi et al, 2017). After fires, many woody and herbaceous species resprout from dormant buds (Coutinho, 1990;Medeiros & Miranda, 2008;Pausas et al, 2018;Pilon et al, 2020), but the role of post-fire seed germination as a regeneration mechanism in Cerrado remains unclear. Even though post-fire seed germination has been observed in grasslands and savannas that undergo surface fires (Overbeck & Pfadenhauer, 2007;Clarke et al, 2015;Ramos et al, 2019;Pilon et al, 2020), studies evaluating seed responses after heat shocks in the Cerrado have done so with few species (Ribeiro et al, 2013;Le Stradic et al, 2015;Fichino et al, 2016) or are restricted to certain clades (Ramos et al, 2016;Daibes et al, 2019;Zirondi, José, et al, 2019;Dairel & Fidelis, 2020), hindering the understanding of general postfire regeneration mechanisms at the community scale.…”

“…After fires, many woody and herbaceous species resprout from dormant buds (Coutinho, 1990;Medeiros & Miranda, 2008;Pausas et al, 2018;Pilon et al, 2020), but the role of post-fire seed germination as a regeneration mechanism in Cerrado remains unclear. Even though post-fire seed germination has been observed in grasslands and savannas that undergo surface fires (Overbeck & Pfadenhauer, 2007;Clarke et al, 2015;Ramos et al, 2019;Pilon et al, 2020), studies evaluating seed responses after heat shocks in the Cerrado have done so with few species (Ribeiro et al, 2013;Le Stradic et al, 2015;Fichino et al, 2016) or are restricted to certain clades (Ramos et al, 2016;Daibes et al, 2019;Zirondi, José, et al, 2019;Dairel & Fidelis, 2020), hindering the understanding of general postfire regeneration mechanisms at the community scale. Moreover, few studies addressing fire-related seed responses in the Cerrado have taken into account plant resprouting ability following experimental fires (but see Pilon et al, 2020).…”

Herbaceous-shrub species composition, diversity and soil attributes in moist grassland, shrub grassland and savanna in Central Brazil

“…The most species-rich families found in the shrub grassland and savanna belonged to Myrtaceae, Euphorbiaceae, Asteraceae and Fabaceae, which are well represented in floristic surveys in the Cerrado (e.g., Batalha and Mantovani 2001;Antar and Sano 2019). Species from these families in the Cerrado store reserves and biomass in a great diversity of thickened underground organs that can support regeneration of individual plants after seasonal droughts or fire (Simon et al 2009;Pausas et al 2018;Pilon et al 2020). Poaceae and Cyperaceae, the families with highest richness and cover in the moist grassland, are usually the richest families in wet open grassland ecosystems in the Cerrado (Amorim and Batalha 2007;Munhoz et al 2008;Bijos et al 2017).…”

“…Many species of Poaceae and Cyperaceae form dense clumps or rhizomatous individuals widely scattered in the vegetation, which increases their capacity to colonize and cover the soil (Filgueiras 2002). In addition, many grasses species occurring in fire-prone savannas present adaptations such as below ground rhizome buds that resprout after a fire in which aboveground matter is consumed, increasing their survival rate in areas with that kind of disturbance (Choczynska and Johnson 2009;Pilon et al 2020). Furthermore, the high occupancy rate of Poaceae individuals is due to the fact that most of these species are C 4 grasses adapted to direct incidence of sunlight, a condition found in open areas, which are ideal places for their establishment (Jacobs et al 1999;Parr et al 2014).…”