Abstract
ABSTRACT Th e interplay betwe en plant-plant interactions and light heterogeneity in the understory of tropical forests has rarely been examined. We aimed to identify the relative importance of the understory light environment and terrestrial bromeliads in explaining the abundance and spatial organization of diff erent plant life forms along a coastal forest gradient from seashore inland in southeastern Brazil. We estimated the abundance of various life forms (herbs, woody plants, bromeliads, climbers, and palms) and the degree of light availability using hemispherical photographs in 165 plots (1 m 2 ) within a 1.75 ha site. We used ordination methods, partial redundancy analysis (pRDA), spatial fi ltering using Moran’s eigenvector mapping, and Moran’s I splines. Forest cover was highly heterogeneous, but did not explain variation in abundance of life forms. Spatially, bromeliads were negatively associated with woody saplings, herbs and climbing plants at scales between 5-20 m, while the distance to seashore was found to be unrelated to these patterns. Our fi ndings revealed that terrestrial bromeliads play an important role in the spatial organization of various life forms near the forest fl oor. Overall, the presence of terrestrial bromeliads and the plant area index better explained the understory vegetation than forest cover and distance to seashore.
Highlights
Light is commonly viewed as the most important resource determining establishment, reproduction and growth of plants within forests and, not surprisingly, it is the most heterogeneous in time and space (Pearcy 2007)
We aimed to identify the relative importance of the understory light environment and terrestrial bromeliads in explaining the abundance and spatial organization of different plant life forms along a coastal forest gradient from seashore inland in southeastern Brazil
Only a few studies ever quantified the patchiness of forest light conditions (Clark 1996; Nicotra et al 1999; Valladares & Guzmán 2006) or examined how spatial variation in light conditions relates to the spatial organization of herb layers in tropical forests (Montgomery 2004), especially in coastal systems (Souza & Martins 2005)
Summary
Light is commonly viewed as the most important resource determining establishment, reproduction and growth of plants within forests and, not surprisingly, it is the most heterogeneous in time and space (Pearcy 2007). The light environment is mainly determined by canopy structure, which directly affects growth and survival of seedlings and saplings (Kabakoff & Chazdon 1996; Nicotra et al 1999; Montgomery & Chazdon 2001; Melo et al 2007) This is because light availability has strong effects on the physiological processes of forest plants (Denslow et al 1990). Even though light can have a strong filtering effect on the organization of understory vegetation, the spatial organization of plant communities is a result of many different processes Because these competing hypotheses are not mutually exclusive (Uriarte et al 2005), quantitative data are needed to understand the relative contribution of factors that determine spatial patterns of the shrub layer
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