Increasing Liana Abundance and Basal Area in a Tropical Forest: The Contribution of Long-distance Clonal Colonization

Authors

  • Suzanne R. Yorke,

    1. Department of Biological Sciences, University of Wisconsin-Milwaukee, U.S.A
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  • Stefan A. Schnitzer,

    Corresponding author
    1. Smithsonian Tropical Research Institute, Ancon, Panama, Republic of Panama
    • Department of Biological Sciences, University of Wisconsin-Milwaukee, U.S.A
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  • Joseph Mascaro,

    1. Department of Biological Sciences, University of Wisconsin-Milwaukee, U.S.A
    2. Smithsonian Tropical Research Institute, Ancon, Panama, Republic of Panama
    Current affiliation:
    1. Department of Global Ecology, Carnegie Institution for Science, Stanford, CA, U.S.A
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  • Susan G. Letcher,

    1. Department of Environmental Studies, Purchase College (SUNY), Purchase, NY, U.S.A
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  • Walter P. Carson

    1. Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, U.S.A
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Corresponding author; e-mail: S1@uwm.edu

Abstract

Recent evidence suggests that liana abundance and biomass are increasing in Neotropical forests, representing a major structural change to tropical ecosystems. Explanations for these increases, however, remain largely untested. Over an 8-yr period (1999–2007), we censused lianas in nine, 24 × 36 m permanent plots in old-growth and selectively logged forest at La Selva Biological Station, Costa Rica to test whether: (1) liana abundance and basal area are increasing in this forest; (2) the increase is being driven by increased recruitment, decreased mortality, or both; and (3) long-distance clonal colonization explains the increase in liana abundance and basal area. We defined long-distance clonal colonization as lianas that entered and rooted in the plots as vegetative propagules of stems that originated from outside or above the plot, and were present in 2007, but not in 1999 or 2002. Our hypotheses were supported in the old-growth forest: mean liana abundance and BA (≥1 cm diameter) increased 15 and 20 percent, respectively, and clonal colonization from outside of the plots contributed 19 and 60 percent (respectively) to these increases. Lianas colonized clonally by falling vertically from the forest canopy above or growing horizontally along the forest floor and re-rooting—common forms of colonization for many liana species. In the selectively logged forest, liana abundance and BA did not change, and thus the pattern of increasing lianas may be restricted to old-growth forests. In summary, our data support the hypothesis that lianas are increasing in old-growth forests, and that long-distance clonal colonization is a major contributor.

Resumen

Actualmente existe evidencia sustancial de que la abundancia y la biomasa de lianas en bosques tropicales va en aumento, lo cual es un cambio estructural profundo para estos ecosistemas. Sin embargo, hay pocas explicaciones para este fenómeno. Durante 8 años (1999–2007), hicimos un inventario de lianas en nueve parcelas permanentes de 24 × 36 m en un bosque primario y un bosque intervenido en la Estación Biológica La Selva, Costa Rica, para indagar (1) si la abundancia y la biomasa de lianas en este bosque han aumentado; (2) si el aumento ocurre gracias a un mayor reclutamiento, a una menor mortalidad, o por ambos mecanismos; y (3) si la colonización clonal de larga distancia explica el aumento de la abundancia y la biomasa. Definimos la colonización clonal de larga distancia como el reclutamiento de lianas que entraron a las parcelas y se establecieron como propágulos vegetativos de tallos que se originaron afuera de o arriba de las parcelas (i.e. echaron raices), y que estaban presentes en 2007 pero ausentes en 1999 y 2002. Hayamos evidencia para apoyar para nuestras hipótesis en el bosque primario: el diámetro promedio de las lianas aumentó en un 15%, el área basal de lianas ≥1cm diámetro aumentó en un 20%. La colonización clonal contribuyó en un 19% y 60%, respectivamente, de esos aumentos. Las lianas colonizaron las parcelas al caer verticalmente del dosel o por crecer horizontalmente sobre el suelo y luego echar raíces; formas comunes de colonización para muchas especies de lianas. En el bosque intervenido, no se presentaron cambios ni en la abundancia ni en la biomasa de lianas, así que el patrón de aumento podría ser un fenómeno restringido al bosque maduro. En resumen, los datos apoyan la hipótesis de que las lianas están aumentando en el bosque primario, y que la colonización clonal es un mecanismo importante.

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