Comparison between grassland communities with and without disturbances

Ronei Baldissera,Leila Fritz,Sandra Müller,Rita Rauber

doi:10.4013/nbc.2010.51.01

Ronei Baldissera, Leila Fritz + Show 2 more

Open Access

https://doi.org/10.4013/nbc.2010.51.01

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Abstract

Grassland management with fire and grazing is considered one of the main factors determining plant physiognomy and composition in grassland ecosystem. In that sense, it is thought that intermediate disturbances, neither high frequent and/or intense, nor absent, could enhance grasslands diversity by diminishing the competitive exclusion. Therefore, the present study evaluated the effect of disturbance exclusion over grassland plant communities in Plateau region of Southern Brazil. Two grasslands were sampled: one excluded of disturbances over the past 16 years, and other with fire and grazing disturbances. Six plots (1m2) were sorted inside each area. Inside each plot, plant species composition was described, while plant richness and evenness were assessed based on cover proportion of each species. The data analysis showed that the grassland without disturbances presented higher richness and evenness. Furthermore, there were differences in the species composition between the grasslands, with less tussock dominance in the disturbed grassland. In addition, plots’ compositions were more homogeneous in areas submitted to disturbances, despite of the high richness. It is concluded that dominant tussock grasses in the grassland without disturbances suppressed many forbs, leading to reducing the species richness and evenness. On the other hand, the presence of disturbances limits the tussocks growth allowing the development of other forbs species. Key words: grassland management, fire, cattle grazing, intermediate disturbance.

Highlights

Estimates about the number of phanerophytes species in Southern Brazil grassland ecosystems indicate the presence of ca. 3,000 to 4,000 species (Boldrini, 1997; Klein, 1975)
In Southern Brazil, grassland physiognomies occur mainly in the Southern half of RS, corresponding to Pampa biome (Brazilian biome’s classification: IBGE, 2004), but they occur associated with South Brazilian Plateau forest formations, especially in Northern half of RS and in Santa Catarina State, forming mosaics with Araucaria Forest (Mixed Ombrophyllus Forest)
Under the present climatic conditions in Southern Brazil, a major factor determining the physiognomy and floristic composition of grasslands is the management with fire and grazing, either combined or not, aiming mainly beef cattle production

Summary

Introduction

Estimates about the number of phanerophytes species in Southern Brazil grassland ecosystems indicate the presence of ca. 3,000 to 4,000 species (Boldrini, 1997; Klein, 1975). In Southern Brazil, grassland physiognomies occur mainly in the Southern half of RS, corresponding to Pampa biome (Brazilian biome’s classification: IBGE, 2004), but they occur associated with South Brazilian Plateau forest formations, especially in Northern half of RS and in Santa Catarina State, forming mosaics with Araucaria Forest (Mixed Ombrophyllus Forest). In this region, grasslands are known as Altitude Grasslands or Mountain Summit Grasslands (“Campos de Cima da Serra”) and are part of the Atlantic Forest biome (Teixeira et al, 1986; Overbeck et al, 2007). It could be expected to record an increase in species diversity due to the decreasing dominance of one or more species – strong competitors that tend to competitively exclude other species –, and the increasing spatial heterogeneity (Connell and Slatyer, 1977)

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