http://dx.doi.org/10.1590/1519-6984.08613 Original Article Effect of fire on a monodominant floating mat of Cyperus giganteus Vahl in a neotropical wetland Rocha, M.a*, Santos Júnior, CC.b, Damasceno-Júnior, GA.a, Pott, VJ.a and Pott, A.a aPrograma de Pós-graduação em Biologia Vegetal, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Mato Grosso do Sul – UFMS, Cidade Universitária, s/n, CP 549, CEP 79070-900, Campo Grande, MS, Brazil bCurso de Ciências Biológicas, Programa de Iniciação Científica, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Mato Grosso do Sul – UFMS, Cidade Universitária, s/n, CP 549, CEP 79070-900, Campo Grande, MS, Brazil *e-mail: [email protected] Received: May 22, 2013 – Accepted: January 6, 2014 – Distributed: March 31, 2015 (With 6 figures) Abstract The rhizomatous Cyperus giganteus, abundant in the Pantanal wetland, can dominate extense floodable areas as monodominant communities. The Jacadigo lake has a large area of C. giganteus, where we performed an evaluation on community structure during two months in 2010, before it was hit by a wildfire which top-killed the vegetation, compared to ten months post-fire. We utilized 40 plots of 1m × 1m, along permanent trails, assessing two strata: the upper, near the inflorescence of adult plants, and the lower, close to the water level. Our results show that fire does not affect dominance of C. giganteus, as it maintained the same cover as before fire; species richness is not much altered either - 28 before fire and 34 thereafter. Fire changed the floristic composition, due to the annual variation of species and the ability of some plants to colonize gaps and to regrow after fire from underground organs and seeds. The stratification of the vegetation with characteristic species of upper and lower strata was similar after fire. Keywords: Cyperaceae, floating meadow, diversity, Pantanal, plant succession. Efeito do fogo sobre uma comunidade monodominante de Cyperus giganteus Vahl em uma área úmida neotropical Resumo A planta rizomatosa Cyperus giganteus, encontrada no Pantanal, pode dominar extensas áreas inundáveis, formando uma comunidade monodominante chamada localmente de pirizal. A lagoa do Jacadigo, situada na sub-região de Nabileque, possui uma extensa área de pirizal onde foi realizada uma avaliação na estrutura da vegetação durante dois meses no período de 2010, antes de ser atingida por um incêndio que causou perda da cobertura aérea da vegetação e foi comparada com 10 meses de avaliação pós-fogo. Com indicações na literatura de que o rizoma da planta pode favorecer a espécie através de rebrotamento após um incêndio, o objetivo deste trabalho foi avaliar as variações na estrutura da vegetação de pirizal após um evento de fogo. Foram utilizadas 40 parcelas não fixas de 1m × 1m e alocadas sistematicamente através de trilhas avaliando dois estratos: o superior, próximo a inflorescência dos adultos e oinferior , próximo a lâmina d’água. Nos dois meses logo após o fogo, devido ao tamanho reduzido nos indivíduos de C. giganteus foi avaliado apenas um estrato denominado total. Os resultados mostram que o fogo não afeta a dominância de C. giganteus, que se mantém na mesma faixa de cobertura do período anterior ao fogo; a riqueza de espécies não é alterada, 28 no período anterior ao fogo e 34 no período posterior. Após o incêndio, a estrutura da comunidade sofre alteração na composição florística, devido a mudança anual de espécies e a capacidade que certas plantas possuem em colonizar clareiras e rebrotar após o fogo por meio de órgãos subterrâneos e sementes. A estratificação da vegetação com espécies características de estrato superior e inferior se manteve após o fogo, porém com diferença menos acentuada entre as espécies. Palavras-chave: Cyperaceae, baceiro, diversidade, Pantanal, sucessão vegetal. 1. Introduction In some wetlands fire is a frequent and important Gosselink, 2000). For instance, in the Okavango delta, disturbance, and only tolerant species persist; a wildfire floodplains can have high frequency of fire (Heinl et al., can open gaps in the vegetation, followed by secondary 2007). succession at recovery (Cronk and Fennessy, 2001). In Effects of fire can be detrimental or favorable. In a swamps, burnings are not frequent, due to standing water, monodominant bamboo Bambusa arnhemica stand, in but can be a significant factor during droughts (Mitsch and a floodable area in Australia, fire destroys some culms 114 Braz. J. Biol., 2015, vol. 75, no. 1, p. 114-124 Fire on monodominant Cyperus giganteus and reduces subsequent survival, leading to a decline (1948). Mean annual rainfall in 1975-1996 was 1,070.0 of tussock basal area (Franklin et al., 2010). In yearly mm (Soriano, 1997). burned grasslands in austral Brazil, some herbs present Our study was carried out in Jacadigo lake, a shallow higher abundance compared to areas protected from fresh water neotropical lake, with clayey-organic sediment, fire (Fidelis et al., 2007). In wet grasslands of cerrado, situated on the right margin of the Paraguay river (Bezerra burning favors some Eriocaulaceae but hinders others and Mozeto, 2008), in the sub-region of Nabileque (Silva (Neves et al., 2011). and Abdon, 1998), ca. 85 m altitude, in the municipality Consequences of fire on aquatic herbaceous monodominant of Corumbá (Pereira and Lapere, 2009). The lake is fed formations are yet little known in the Neotropics. by rain runoff and the Urucum creek, plus extraordinary Communities have dynamic species composition, with overflow from the Paraguay river (Pereira and Lapere, change of species continuously entering and leaving the 2009), ca. 40 km away. The overall vegetation is of foodable system, very evident when there is an external disturbance, savanna type and one of the outstanding herbaceous such as fire, capable to affect the ecological succession species is C. giganteus, which occurs in high frequency (Pinto-Coelho, 2000). The study of effects of fire allows within Copernicia alba stands (Allem and Valls, 1987) to understand survival mechanisms, such as underground and in this lake. storage organs in Richardia grandiflora and Vernonia The Jacadigo lake shrank in the decade 2000 (Pereira flexuosa which have regrowth capacity after loss of aerial and Lapere, 2009). Macedo et al. (2009) verified that biomass by fire (Fidelis et al., 2007). low water levels of the Paraguay river in 2008 and 2009, The Pantanal has a dynamic vegetation in time due to less rainfall on the watershed, caused increase of and space, due to factors which include hydrological wildfires in the Pantanal, due to drying off of floodable fluctuations, successional processes and intensity of land areas, making the vegetation fire-prone, from spread of use, such as fire (Pott and Pott, 2003). Burning in the natural or anthropogenic focuses. The studied vegetation region is traditionally used as management practice of burns every few years, when the lake level is low, like in natural grasslands, for renewal or control of coarse grasses 2010. The fire occurred in September 2010 and reached the (Allem and Valls, 1987; Couto et al., 2006). Wildfires are entire patch of C. giganteus in Jacadigo lake. We did not concentrated at the end of the dry season in August and measure duration of the fire, but we estimate that it lasted September, under low relative humidity, associated with up to two days, considering the size of the burned patch. accumulated flammable dry matter (Couto et al., 2006; The area of C. giganteus which partially covers the Crispim et al., 2009). Jacadigo lake has approximately 184,377m² and the study Effects of fire on the Pantanal flora are controversial, area 20,080 m², situated on the southeast portion of the lake, as they depend on vegetation type, if dry or wet grassland, close to the road BR-262, at the coordinates 19° 18’ 10” S cerrado savanna or forest, being detrimental on flood tolerant and 57° 36’ 28.2” W (Figure 1). The studied C. giganteus plants with exposed buds (Pott, 2007). Nevertheless, a stand is a floating mat on a histosol layer ca. 70 cm deep, high number of aquatic species is cited as fire tolerant in with entangled rhizomes of the sedge. the Pantanal, such as Cyperus giganteus, giant flatsedge, Monodominant stands of C. giganteus are very a rhizomatous herb which forms monodominat stands common in floodable areas, occurring from Mexico to (Pott and Pott, 2000). Dominance of C. giganteus has South America, in Brazil, Argentina, Uruguay, Paraguay indications in the literature of being favored by fire (Pott and Bolivia. It is a rhizomatous emergent aquatic herb, and Pott, 2000). resembling papyrus (C. papyrus L.), with thick and spongy In the Pantanal, the Jacadigo lake has an extense stem, 1.5-2.5m tall (Pott and Pott, 2000; Lorenzi, 2008). area covered by aquatic vegetation with monodominant The rhizomes are thick and rich in aerenchyma, growing community of C. giganteus. In 2010, during a survey on within the first 10 cm of soil (Schessl, 1999). It is one of this vegetation, a wildfire occurred, destroying all above the few aquatic species of the C4 type, doing photosynthesis ground biomass and we decided to assess its effects. even on the inflorescence, which may be sterile (Pott and So, our study aims to describe variations in community Pott, 2000). structure of C. giganteus before and after fire, testing the 2.2. Sampling of plant cover following hypothesis: fire contributes to increase dominance of C. giganteus. We performed monthly samplings from July 2010 to September 2011. We placed 40 quadrats systematically 2. Material and Methods along trails using a PVC frame (1 m × 1 m), separated by a distance of approximately 5 m, each month following trails 2.1. Study area established during field work.