The most common approach centers seed traps or transects on one or more adult plants, generating the data necessary to construct dispersal curves and estimate seed shadows (i.e., the spatial distribution of seed-fall). Quantifying seed dispersal patterns in closed canopy forests is notoriously difficult. Additional mechanistic explanations for poor post-logging regeneration of mahogany in Mexican and Brazilian forests include insufficient light levels in the forest understory and logging gaps, and irregular supra-annual fruiting patterns by individuals and populations. This risks regeneration failure by strengthening pre-existing seed and/or establishment limitations, which in turn may jeopardise local population persistence. Local negative density-dependence (NDD) in juvenile tree recruitment and mortality is not uncommon in tropical forests, but likely stronger and more common in the critical seed-to-seedling and seedling-to-sapling stages (i.e., >1/ha, but these are the first to be logged out entirely. Together, these events help structure tree population sizes and distributions, influencing the composition of adult forest trees at a given time and place –. Patterns of seed-fall set the stage for a suite of post-dispersal events that can affect recruitment rates, including seed predation and germination, herbivory and competition, resource use and acquisition, and overhead canopy disturbances –. This is especially true in tropical forests where most tree species are rare and thought to be severely seed limited –. Seed dispersal is a critical life phase for plants that plays a key role in driving the dynamics, distribution, and persistence of plant populations and communities –. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. Nordin Prize from the Faculty of Forestry. JMN is grateful for a University of Toronto Fellowship and V. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: This study was partly funded by a Grant for Graduate Research Abroad from OAS (Organisation of American States) to JMN, and from the USDA Forest Service's International Institute of Tropical Forestry to JG. Received: AugAccepted: FebruPublished: March 7, 2011Ĭopyright: © 2011 Norghauer et al. PLoS ONE 6(3):Įditor: Andrew Hector, University of Zurich, Switzerland Our results have important implications for management and conservation of big-leaf mahogany populations, and may apply to other threatened wind-dispersed Meliaceae trees.Ĭitation: Norghauer JM, Nock CA, Grogan J (2011) The Importance of Tree Size and Fecundity for Wind Dispersal of Big-Leaf Mahogany. Tree seed production did not necessarily scale up proportionately with diameter, and was not consistent across years, and this resulting intraspecific variation can have important consequences for local patterns of dispersal in forests. Mean seed arrival into canopy gaps >30 m downwind was more than 3× greater for large, high fecundity trees than small, high-fecundity trees. Using the 2Dt model fits to predict seed densities downwind, coupled with known fecundity data for 2000–2009, we evaluated potential Swietenia regeneration near adults (≤30 m dispersal) and beyond 30 m. Although most seeds fell within 30 m of parent trees, relatively few juveniles were found within this distance, resulting in juvenile-to-seed ratios peaking at c. 25 m) for large, high-fecundity trees with the inverse Gaussian and Weibull functions providing comparable fits that were slightly better than the lognormal. When seedfall downwind was modelled in two dimensions using a normalised sample, it peaked furthest downwind (c. distance in one dimension, the Student- t (2Dt) generally fit best (compared to the negative exponential and inverse power). Among three empirical models fitted to seed density vs. Tree diameter and fecundity correlated positively with increased seed shadow extent but in combination large, high fecundity trees contributed disproportionately to longer-distance dispersal events (>60 m). We measured seed dispersal by the endangered neotropical timber species big-leaf mahogany ( Swietenia macrophylla King, Meliaceae) in the Brazilian Amazon at 25 relatively isolated trees using multiple 1-m wide belt transects extended 100 m downwind. How tree size and fecundity affect this process at the population level remains largely unknown because of insufficient replication across adults. Seed dispersal by wind is a critical yet poorly understood process in tropical forest trees.
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