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Short dry spells in the wet season increase mortality of tropical pioneer seedlings

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Abstract

Variation in plant species performance in response to water availability offers a potential axis for temporal and spatial habitat partitioning and may therefore affect community composition in tropical forests. We hypothesized that short dry spells during the wet season are a significant source of mortality for the newly emerging seedlings of pioneer species that recruit in treefall gaps in tropical forests. An analysis of a 49-year rainfall record for three forests across a rainfall gradient in central Panama confirmed that dry spells of ≥10 days during the wet season occur on average once a year in a deciduous forest, and once every other year in a semi-deciduous moist and an evergreen wet forest. The effect of wet season dry spells on the recruitment of pioneers was investigated by comparing seedling survival in rain-protected dry plots and irrigated control plots in four large artificially created treefall gaps in a semi-deciduous tropical forest. In rain-protected plots surface soil layers dried rapidly, leading to a strong gradient in water potential within the upper 10 cm of soil. Seedling survival for six pioneer species was significantly lower in rain-protected than in irrigated control plots after only 4 days. The strength of the irrigation effect differed among species, and first became apparent 3–10 days after treatments started. Root allocation patterns were significantly, or marginally significantly, different between species and between two groups of larger and smaller seeded species. However, they were not correlated with seedling drought sensitivity, suggesting allocation is not a key trait for drought sensitivity in pioneer seedlings. Our data provide strong evidence that short dry spells in the wet season differentially affect seedling survivorship of pioneer species, and may therefore have important implications to seedling demography and community dynamics.

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Acknowledgements

We thank Maria Pickering, Amy Faivre, Lauren Schachner and Didimo Moran for assistance with the field experiment, and Susanne Aref, Rachel Gallery and David Moore for statistical advice. We also thank all the BCI residents for their timely help in preparing seeds, for their willingness to spend evenings sorting toothpicks, as well as for moral support. The Smithsonian Tropical Research Institute provided excellent logistical support. Rainfall data were provided by the Terrestrial-Environmental Sciences Program of the Smithsonian Tropical Research Institute and by the Meteorology and Hydrology Branch of the Panama Canal Authority, Republic of Panama. The project was funded by the University of Utah, the USDA Forest Service, The Andrew W. Mellon Foundation and The Leverhulme Trust.

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Author notes

  1. Timothy R. H. Pearson

    Present address: Winrock International, 1621 North Kent Street, Suite 1200, Arlington, VA, 22209, USA

  2. David A. Gálvez

    Present address: Departamento de Psicologia, Universidad Magna, 77500, Cancún, Quintana Roo, México

  3. Tobias Koehler

    Present address: Department of Botany, University of Hawaii, Hawaii, HI, 96822-2279, USA

Authors and Affiliations

  1. Smithsonian Tropical Research Institute, Gamboa, P.O. Box 0843-03092, Panamá, Republica de Panamá

    Bettina M. J. Engelbrecht, James W. Dalling, Timothy R. H. Pearson, Robert L. Wolf, David A. Gálvez, Tobias Koehler, Melvin T. Tyree & Thomas A. Kursar

  2. Department of Plant Ecology and Systematics, Technische Universität Kaiserslautern, 67663, Kaiserslautern, Germany

    Bettina M. J. Engelbrecht

  3. Department of Plant Biology, University of Illinois, Urbana-Champaign, IL, 61801, USA

    James W. Dalling

  4. USDA Forest Service, P.O. Box 968, Burlington, VT, 05402, USA

    Melvin T. Tyree

  5. Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA

    Thomas A. Kursar

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  1. Bettina M. J. Engelbrecht
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Correspondence to Bettina M. J. Engelbrecht.

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Communicated by Jim Ehleringer

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Engelbrecht, B.M., Dalling, J.W., Pearson, T.R. et al. Short dry spells in the wet season increase mortality of tropical pioneer seedlings. Oecologia 148, 258–269 (2006). https://doi.org/10.1007/s00442-006-0368-5

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