- Fine-scale post-fire dynamics in southern Brazilian subtropical grassland - 655 Journal of Vegetation Science 16: 655-664, 2005 © IAVS; Opulus Press Uppsala. Abstract Question: How does fire influence species richness and diver- sity in subtropical grassland in southern Brazil? Location: Recurrently burned grassland in Porto Alegre, Bra- zil (30°03' S, 51°07' W; max. altitude 311 m a.s.l.) and aban- doned grassland near São Francisco de Paula, Brazil (29°47' S, 50°22' W; ca. 900 m a.s.l.). Methods: In the burned grassland, between-year changes in community composition and single-plot diversity, species number and vegetation structure were analysed in two con- secutive years for plots with different time since last fire. Responses to fire of individual species were analysed. At the abandoned site, diversity, species number and vegetation struc- ture were examined. Results: Species number and small-scale species turnover were highest ca. one year after the burn, and decreased as caespitose grasses increased in cover with time since fire until reaching a stable, but less diverse state three to four years after a fire. The abandoned grassland showed higher dominance of caespitose grasses and lower richness and diversity. Conclusions: Fire clearly leads to a short-term increase in species richness and diversity at the plot scale, as competitive interactions are being reduced and recruitment possibilities are high in early post-fire vegetation development. Overall community composition does not change after a fire. While small herbs seem to be slightly favoured in the early post-fire environment, no clear group of fire following species (absent in vegetation unburned for longer) was observed. The results indicate that the community is adapted to the current fire regime and is being maintained under the influence of fire. Keywords: Burn; Campos; Disturbance; Diversity; Species richness; Vegetation dynamics. Fine-scale post-fire dynamics in southern Brazilian subtropical grassland Overbeck, Gerhard Ernst 1* ; Müller, Sandra Cristina 2,3 ; Pillar, Valério DePatta 2,4 & Pfadenhauer, Jörg 1,5 1 Vegetation Ecology, Technische Universität München, Freising-Weihenstephan, Germany; 2 Departamento de Ecologia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; 3 E-mail smuller@ecologia.ufrgs.br; 4 E-mail vpillar@ecologia.ufrgs.br; 5 E-mail pfadenhauer@wzw.tum.de; * Corresponding author; Fax +49 8161714143; E-mail overbeck@wzw.tum.de Introduction Disturbance is an important component of natural systems (e.g. Grime 1979; Souza 1984; Pickett & White 1985; Pickett et al. 1989; Hobbs & Huenneke 1992). In general, disturbance enhances species richness by low- ering dominance of one or more species and by increas- ing spatial heterogeneity (Denslow 1985). Species rich- ness is hypothesized to be highest at intermediate levels of disturbance (Grime 1973; Connell 1978; Huston 1979), or under regimes similar to historic, i.e. natural, rates of disturbance (Denslow 1980), where regenera- tion conditions for the majority of species present should be met. In many grassland systems, fire increases species richness, with peaks sometimes after one (e.g. Collins 1987; Harrison et al. 2003), or a few years after burning (Gibson & Hulbert 1987). High richness has been attrib- uted to the presence of mixtures of invaders, opportunis- tic pioneer species and annuals and perennials with different life spans (Vogl 1974). Thus, diversity of functional groups may be related to the burning cycle (Gibson 1988) with, for example, small-sized and small- seeded species (Leach & Givnish 1996) or annual/bien- nial species (e.g. Ramsay & Oxley 1986; Lunt & Morgan 2001; Ghermandi et al. 2004) appearing only in early post-fire stages. In other cases, however, dominant species may be favoured by fire (Collins & Glenn 1991; Collins et al. 1995). Effects of fire on grassland diversity vary between grasslands according to general climatic conditions and corresponding functional plant composi- tion (e.g. arid vs humid, temperate vs. tropical grass- lands), differences in topography and year to year cli- matic conditions, and interactions with other disturbances (Collins 1987). This makes generalizations difficult and calls for local studies to understand the effect of fire on plant diversity in a particular system (Uys et al. 2004). In subtropical southern Brazil, fire and grazing are thought to be responsible for the persistence of mosaics of grassland and forest under a climate suitable for