Species richness increases the resilience of wetland plant communities in a tropical floodplain PRISCILLA CARVALHO, 1 * SIDINEI MAGELA THOMAZ, 1 JOSILAINE TAECO KOBAYASHI 1 AND LUIS MAURICIO BINI 2 1 Universidade Estadual de Maringá, Nupelia, PEA-UEM, Av. Colombo, 5790, CEP: 87020-900, Maringá, PR, Brazil (Email: carvalhop@hotmail.com), and 2 Universidade Federal de Goiás, ICB, Departamento de Ecologia, Goiânia, GO, Brazil Abstract In the last two decades, the relationship between diversity and stability/ecosystem functioning has been widely discussed and has become a central issue in ecology. Here, we assessed the relationship between wetland plant diversity and community resilience after a disturbance. Our study area was located in the Upper Paraná River floodplain (Brazil). An experiment was carried out in situ (18 1 m ¥ 1 m plots with richness varying from 1 to 18 species). In each plot, we recorded the number of species, total per cent vegetation cover and per cent age cover of each species. The above-ground biomass of wetland plants was removed, simulating a disturbance by animal trampling or an extreme flood. The recovery of vegetation was monitored over 3 months. According to a linear regression, the recovery of wetland plants was positively correlated with diversity. Comparisons with plots con- taining monocultures of one of the dominant species (Polygonum stelligerum) suggested that this species did not overyield in mixed cultures. Thus, our experiments indicate that the higher resilience in richer plots after a disturbance is mainly due to the fact that species have different resource use requirements (complementarity effect) and not due to the presence of a single, more productive species. Our experiment carried out in a more real condition (in situ) showed that biodiversity is important to wetland functioning and stability, paralleling the results obtained in laboratory and mesocosms experiments.These results also suggest that the loss of plant diversity in our study area could compromise community recovery following strong disturbances. Key words: disturbance, diversity, field experiment, resilience, wetland plant. INTRODUCTION The intuitive idea that high species diversity confers stability on communities was proposed by early natu- ralists and ecologists (e.g. Darwin 1859; Forbes 1887; Elton 1958). In the last few years, several studies have recognized that the loss of species may affect ecosys- tem functions, such as productivity (Naeem et al. 1994; Tilman & Downing 1994; Tilman et al. 1996; Engelhardt & Kadlec 2001; Engelhardt & Ritchie 2001), invasion resistance (Naeem et al. 2000; Lanta & Lepš 2008), nutrient retention (Engelhardt & Ritchie 2001) and stability (Frank & McNaughton 1991; McGrady-Steed et al. 1997; Tilman et al. 2006; see Cardinale et al. 2012 for a recent review). Given the high rates of species extinction as a function of human land use (Jenkins 2003; Dudgeon et al. 2006), it is critical to understand how the loss of biodiversity influences the stability and function of ecosystems. Two central hypotheses have been argued to explain positive relationships between biodiversity and ecosys- tem function or stability: the niche-differentiation effect and the sampling effect. The former can occur when species within a community use resources in complementary ways (Naeem et al. 2002), while the latter suggests that there is an increased probability of including keystone species or superior competitors in richer communities (Huston 1997). There is a clear bias of studies focusing on the biodiversity–ecosystem function and biodiversity– stability in terrestrial, compared with the aquatic eco- systems (Srivastava & Vellend 2005; Caliman et al. 2010). Similarly to what is observed in terrestrial eco- systems, studies carried out in wetlands also suggest the importance of diversity for ecosystem function and stability. For example, mesocosm studies have shown that plant biomass increased and methane efflux decreased with increasing richness of plant functional groups (Bouchard et al. 2007), while algal biomass increased and phosphorus loss decreased in meso- cosms containing higher number of macrophyte species (Engelhardt & Ritchie 2001). Differently, plant biomass was negatively correlated with plant richness and carbon cycling was better predicted by plant com- munity composition than diversity in a field study carried out in a north-temperate wetland (Schultz et al. 2011). One of the few studies carried out in *Corresponding author. Accepted for publication September 2012. Austral Ecology (2013) 38, 592–598 © 2012 The Authors doi:10.1111/aec.12003 Austral Ecology © 2012 Ecological Society of Australia