-1 Spatial variation and dynamics of flooding, canopy openness, and structure in a Neotropical swamp forest Alexandre F. Souza 1,3 and Fernando R. Martins 2, * 1 Programa de Po ´s-Graduac ¸a ˜o em Biologia: Diversidade e Manejo da Vida Silvestre, Universidade do Vale do Rio dos Sinos, Av. UNISINOS 950-C.P. 275, Sa ˜o Leopoldo 93022-000, RS, Brazil; 2 Departamento de Bota ˆnica, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, Campinas 13083-970, SP, Brazil; 3 Present address: Laborato ´rio de Ecologia Quantitativa, Departamento de Ecologia, IB, Universidade Federal do Rio Grande do Sul, Campus do Vale, Porto Alegre 91501-970, Av. Bento Gonc ¸ alves 9500, RS, Brazil; *Author for correspondence (e-mail: afsouza@unisinos.br; phone: +55-51-590-2122; fax: +55-51-590-8122) Received 13 November 2003; accepted in revised form 16 December 2004 Key words: Crown densiometry, Forest degradation, Forest dynamics, Ground-surface heterogeneity, Ripley’s K function Abstract Temporal changes and spatial variation of soil drainage and understory light availability in 2001 and 2002, small stem (5 £ dbh (diameter at breast height) < 10 cm) density, forest successional phase and large stem (dbh ‡ 10 cm) spatial distribution were investigated in 1 ha of tropical swamp forest in southeastern Brazil. Building patches and treefall gaps comprised, respectively, 69.75 and 7.5% of the area in 2002. Semivariograms indicated spatial segregation of successional phases, with mature areas predominating in the North and gaps aggregated into the South. Exclusion of outliers showed large unpredictability of background variation in canopy openness, but patches with high canopy openness values concentrated along the South and East plot borders. Overall canopy openness increased from 2001 to 2002, and was locally autocorrelated between years. In 2001, well-drained and flooded sites comprised 46.75 and 38.19% of the study area, respectively, and were not spatially autocorrelated. In the study period, the number of flooded sites decreased by 40.4%. Canopy openness and small stem density were independent from drainage and were not correlated. Large trees aggregated at scales larger than 40 m, while arborescent palms were aggregated at all scales. Our findings suggest that tropical swamp forests have architectural characteristics similar to that of young, secondary forests and treefall gaps in old-growth forests. Patterns at larger scales pointed to the occurrence of widespread forest degradation, which seems to be particularly advanced in some forest sectors. Introduction Although tropical forests have been the focus of a growing number of studies in the last two decades, only recently has the spatial heterogeneity of their constituent elements begun to be explicitly addressed (Nu` n˜ ez-Farfa´n and Dirzo 1988; Molofsky and Augspurger 1992; Trichon et al. 1998; Nicotra et al. 1999; Denslow and Guzman 2000; Montgomery and Chazdon 2001). Swamp forests, specifically, are characterized by high spatial and temporal variability (Klinge et al. 1990) largely due to the aquatic–terrestrial gradi- ent they represent (Malanson 1993). However, Plant Ecology (2005) 180: 161–173 Ó Springer 2005 DOI 10.1007/s11258-004-7811-7