Cerrado grasslands: characterization, ecology and conservation

Author(s)

Bruna Helena de Campos

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2023-04-11

Examining board members

Giselda Durigan; Marcelo Fragomeni Simon; Vania Regina Pivello; Sandra Cristina Müller

• Advisor: Giselda Durigan; Natashi Aparecida Lima Pilon

Abstract

Savannas and grasslands occupy about 20% of the Earth's surface. Yet, just recently open biomes have received the deserved attention about degradation and biodiversity loss. Open ecosystems negligence manifests in the lack of studies that characterise both the vegetation and the climatic, edaphic, and disturbance gradients to which these grasslands are subjected. Moreover, there is a gap in the characterisation of grassland vegetation, and little is known about the factors responsible for maintaining open ecosystems and the conservation status of the rare remnants of Cerrado grasslands. We sampled 15 natural remnants of Cerrado grasslands in five Brazilian states to fill the gaps regarding the ecology of these grasslands. In each site, we installed 30 plots of 1 m² within an area of 01 hectare for the floristic survey and plant community structure sampling. Additionally, we sampled soil, obtained climate descriptors, and reconstructed the fire history of each site. In the first chapter, we characterised the diversity, vegetation structure, climate, soils, and fire history of each site, generating an overview of the average values for the biotic and abiotic descriptors and their range of variation. We found often surprising similarities and differences between the grasslands sampled, sometimes contradicting theories that had been in place for decades. The soils were similar in terms of acidic pH and low fertility, but very different in terms of texture, aluminium saturation, organic matter content, and soil water content. Although mean annual values of precipitation and temperature were not very variable, we found large differences in extreme climate descriptors (e.g., number of frost days in a year, temperature of the hottest month, and maximum evapotranspiration). In the second chapter, we analysed how environmental factors affect the floristic composition, diversity, and structure of the vegetation. We verified that grasslands are not modulated by only one factor. The floristic composition was primarily associated with climatic factors, such as rainfall seasonality and minimum temperature. On the other hand, vegetation diversity was positively associated, above all, with fire frequency. Variables representing soil fertility, available water capacity, and extreme heat conditions influenced the vegetation structure, such as the aerial biomass and non-graminoid:graminoid coverage ratio. In the third chapter, we develop an analysis of the conservation status and threat factors in the studied Cerrado grasslands. We classified the species by their degree of extinction risk and report the main drivers of degradation that challenge the conservation of these grasslands. We verified that more than 80% of the registered species were not even evaluated regarding the degree of extinction risk and that 2.4% of the species are already recognized as threatened. Among the main threats, we found: (i) invasion by exotic grasses and/or tree species of the genus Pinus and (ii) fire suppression. Both processes may culminate in the extinction of a considerable fraction of the typical flora of natural grasslands. Diversity metrics were unrelated to the remnants size. However, we found an inverse association between the proportion of ruderal species and the distance from roads. The knowledge generated by this research advances the scientific field of ecology of open ecosystems, elucidating the factors and mechanisms involved in maintaining their diversity and making it possible to infer the assembly rules of these communities. By identifying the main threats to natural grasslands and discussing the challenges to face them, the results of this research support public policies, especially when dealing with actions aimed at the conservation and restoration of the open physiognomies of the Cerrado (AU)

• FAPESP's process: 19/03463-8 - Influence of environmental factors and fire history on structure, diversity and composition of savanna grasslands.
• Grantee: Bruna Helena de Campos
• Support Opportunities: Scholarships in Brazil - Doctorate