Testing for the influence of niche and neutral factors on sapling community assembly beneath isolated woody plants in grasslands

Abstract

Questions: Perching and nursing effects drive initial steps of forest expansion over grasslands. Nursing effect is obviously related to niche mechanisms, while perching effect is likely to result both from neutral and niche factors. This study assessed the effect of neutral and niche factors on species composition in sapling communities developing beneath isolated trees/shrubs (ITS) in grassland. Location: A mosaic of Campos grassland and Araucaria forest in São Francisco de Paula, southern Brazil (29°28′S, 50°13′W). Methods: We described sapling communities beneath 32 ITS using mean number of forest woody saplings of different species. We performed a stepwise canonical correspondence analysis (CCA) to select ITS traits that maximized the association with species composition. Then we evaluated the contribution of distance from seed source, ITS traits and distance‐structured ITS traits on sapling community assembly using a variation partitioning method based on CCA and partial CCA. Results: Sapling species composition was significantly explained by ITS traits (ITS dispersal mode, ITS growth form, crown area:ITS height ratio, crown area, ITS height and crown area:volume ratio). Distance from seed sources explained only a minor, non‐significant fraction of sapling species composition. Distance‐structured trait variation was negligible. Conclusions: Sapling community assembly beneath ITS was mostly explained by niche factors related to both nursing and perching effects. Dispersal limitation explained only a small fraction of variation in species composition beneath ITS, suggesting that neutral‐based perching effect had a minor role in community assembly.

Species-specific associations between overstory and understory tree species in a semideciduous tropical forest

“…Instead, they state that succession is driven by stochastic events (see review in Brokaw & Busing 2000;Hubbell 2001). The existence of speciesspecific associations suggested by our study reinforces the importance of non-random processes (niche partitioning) in community organization (Duarte et al 2010;Long et al 2013) and suggest that the influence of overstory species on understory species in high-diversity forests may be more significant than previously thought.…”

“…Among the positive effects, the benefactor may, for example, provide more favorable sites for germination and seedling establishment under their canopies (Tirado & Pugnaire 2005), amelioration of harmful microenvironmental conditions (Wang et al 2008;Cavieres & Badano 2009), and a higher supply of nutrients (Souza et al 2013), water (Rigg et al 2002, and light (Tomita & Seiwa 2004;Souza et al 2014). Greater seed deposition rates by dispersers (Dias et al 2005;Duarte et al 2010) is also an important factor contributing to higher density or species richness under certain species, although this would not be considered true facilitation (Callaway 2007). Competition for abiotic resources (e.g., light, water, nutrients), as reported by many authors, is also an important structuring mechanism in plant communities (Callaway & Walker 1997;Maestre et al 2009;Long et al 2013).…”

Elementos nucleadores da paisagem influenciam a dispersão zoocórica em áreas campestres alto-montanas

“…A Área 3 foi a exceção, visto que neste local foi observada baixa densidade de indivíduos regenerantes para todas as síndromes de dispersão. Esse resultado reforça a ideia de que elementos nucleadores são importantes facilitadores do processo de regeneração natural em áreas abertas (Oliveira & Pillar 2004), com influência sobre a dispersão realizada por animais (Duarte et al 2010). Supostamente, animais utilizam os elementos nucleadores como hábitat e/ou, poleiro em todas as áreas, porém, a inexistência de associação na Área 3 pode estar relacionada com fatores limitantes à regeneração natural, como as condições ambientais existentes.…”

Chuva de sementes de espécies lenhosas florestais em mosaicos de floresta com Araucária e campos no Sul do Brasil

“…10 m de BO). Como poleiros (indivíduos isolados no campo), foram selecionados 14 indivíduos de A. angustifolia (AA) e 14 de B. uncinella (BU), por serem importantes no processo de expansão fl orestal em áreas de campo excluído no planalto sul-brasileiro (Oliveira & Pillar 2004;Duarte et al 2006a;Dos Santos & Pillar 2007;Duarte et al 2010). Como critério de isolamento, considerou-se a ausência de qualquer outro indivíduo lenhoso inserido na matriz campestre num raio mínimo de 20 m e localizados a uma distância máxima de 100 m da borda fl orestal mais próxima.…”