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Differential plant damage due to litterfall in palm-dominated forest stands in a Central Pacific atoll

Published online by Cambridge University Press:  13 March 2014

Hillary S. Young*
Affiliation:
Department of Biology, Stanford University, 371 Serra Mall, Stanford CA, 94305, USA Division of Vertebrate Zoology, Smithsonian Institution, PO Box 37012, MRC 108, Washington DC, 20013, USA
Douglas J. McCauley
Affiliation:
Hopkins Marine Station, Stanford University, 120 Oceanview Blvd, Pacific Grove, CA 93950, USA
Amanda Pollock
Affiliation:
US Fish and Wildlife Service, Honolulu HI, USA
Rodolfo Dirzo
Affiliation:
Department of Biology, Stanford University, 371 Serra Mall, Stanford CA, 94305, USA
*
1Corresponding author. Email: hyoung@fas.harvard.edu

Abstract:

High densities of palms are common in many tropical forests. In some cases, the dominance of palms has been associated with a depauperate understorey and high rates of native seedling mortality. A variety of different potential mechanisms has been suggested to explain the sustained palm dominance in the understorey and canopy of these forests. Working in a Cocos nucifera-dominated wet tropical forest at Palmyra Atoll in the central Pacific, we examine how litterfall from this pantropical, and economically important palm, impacts seedling survival. We compare rates of litterfall, and rates of litterfall-associated damage, between forest stands dominated by C. nucifera (coconut palm) and forest stands with low abundance of C. nucifera. To assess litterfall damage we survey damage to both artificial seedlings (n = 711), outplanted real seedlings of two species (with and without protection via caging; n = 204), and standing rates of litterfall damage. We find that rates of large-litterfall damage were an average of five times higher in sites with high densities of C. nucifera. Associated with these increases we observe that levels of physical damage to artificial model seedlings caused by litterfall over a 4-mo period increased from 4.9% in sites with low abundance of C. nucifera to 16.1% in sites with high abundance of C. nucifera. Extrapolated to annual rates, litterfall damage of this magnitude exceeds the average levels observed in other published studies. Living native seedlings also showed more than 300% higher levels of mortality in forest stands with high densities of C. nucifera, a difference that was greatly reduced when protected by caging from litterfall. In contrast, uncaged C. nucifera seedlings actually had slightly higher survivorship in habitats dominated by conspecifics. We suggest that litterfall damage may be an important mechanism by which this tropical palm reaches and maintains near monodominance in many coastal and insular habitats.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2014 

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Footnotes

2

Current address: Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, CA, 93106, USA

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