Abstract
Coastal sand dunes have attracted the attention of plant ecologists for over a century, but they have largely relied on correlations to explain dune plant community organization. We examined long-standing hypotheses experimentally that sand binding, inter-specific interactions, abiotic factors and seedling recruitment are drivers of sand dune plant community structure in Sardinia, Italy. Removing foundation species from the fore-, middle- and back-dune habitats over three years led to erosion and habitat loss on the fore-dune and limited plant recovery that increased with dune elevation. Reciprocal species removals in all zones suggested that inter-specific competition is common, but that dominance is transient, particularly due to sand burial disturbance in the middle-dune. A fully factorial 2-year manipulation of water, nutrient availability and substrate stability revealed no significant proximate response to these physical factors in any dune zone. In the fore- and middle-dune, plant seeds are trapped under adult plants during seed germination, and seedling survivorship and growth generally increase with dune height in spite of increased herbivory in the back-dune. Sand and seed erosion leads to limited seed recruitment on the fore-dune while high summer temperatures and preemption of space lead to competitive dominance of woody plants in the back-dune. Our results suggest that Sardinian sand dune plant communities are organized hierarchically, structured by sand binding foundation species on the fore-dune, sand burial in the middle-dune and increasingly successful seedling recruitment, growth and competitive dominance in the back-dune.
Highlights
Understanding the mechanisms biotic and abiotic that generate spatial patterns in natural communities is a major goal of ecology and is critical for developing ecology into a predictive science that can inform ecosystem management and contribute to conservation (Morin, 2011)
Previous studies of Sardinian sand dune plant communities reveal that they have high species richness, endemism (Bacchetta et al, 2008; Prisco, Acosta & Ercole, 2012) and species adapted to physical stress (Fenu et al, 2013)
Our results suggest that fore-dune foundation species are responsible for binding, stabilizing and maintaining sand dune communities, and that inter-specific plant interactions occur across the dune, but are generally overshadowed by physical stresses, sand burial in the middle-dune
Summary
Understanding the mechanisms biotic and abiotic that generate spatial patterns in natural communities is a major goal of ecology and is critical for developing ecology into a predictive science that can inform ecosystem management and contribute to conservation (Morin, 2011). Many natural communities are structured and defined by foundation species, sensu Dayton (1975). Foundation species are defined operationally as common, abundant species that build and maintain habitats, ameliorating potentially limiting physical and biological factors, providing habitat for other species How to cite this article Cusseddu et al (2016), Hierarchical organization of a Sardinian sand dune plant community. Examples of foundation species-dependent ecosystems include forests, coral reefs, salt marshes, mangroves, mussel and oyster reefs, which are all built and maintained by numericallydominant habitat forming foundation species (Bruno & Bertness, 2001). Amelioration of potentially limiting physical and/or biotic conditions is a hallmark of foundation speciesbased ecosystems. Coastal sand dunes are physically-harsh habitats for the xerophytic plants that dominate them and are best understood as foundation species-based ecosystems (Olff, Huisman & Van Tooren, 1993)
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