OOS 36-5 - Vegetation dynamics after large-scale artificial canopy opening and detritus deposition in a tropical forest in Puerto Rico

Thursday, August 11, 2011: 9:20 AM
12A, Austin Convention Center
Aaron Shiels, Hawaii Field Station, USDA, APHIS, National Wildlife Research Center, Hilo, HI, Jess K. Zimmerman, Department of Environmental Science, University of Puerto Rico - Rio Piedras, San Juan, PR, Diana C. Garcia-Montiel, Institute for Tropical Ecosystem Estudies, University of Puerto Rico, Rio Piedras, PR, Inge Jonckheere, Biosystems Department, Geomatics Engineering Group, Katholieke Universiteit Leuven, Leuven, Belgium, Jennifer A. Holm, Earth Science Division, Climate Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, David Horton, Biology, Washington University in St. Louis, St. Louis, MO and Nicholas Brokaw, Institute for Tropical Ecosystem Studies University of Puerto Rico-Río Piedras, San Juan, PR

We artificially modified two key components of severe hurricane disturbance, canopy openness and detritus deposition, to determine the independent and interactive effects of these components on plant recruitment and forest structure. We increased canopy openness by trimming branches and added or subtracted canopy detritus in a factorial design.  Plant (seedlings and individuals ≥ 1 cm dbh) responses were measured during the 4 year study, which followed at least 1 year of pre-manipulation monitoring.  The physical conditions of canopy openness and detritus deposition in our experiment resembled the responses to Hurricane Hugo, a severe category 4 hurricane that struck this forest in 1989


Canopy detritus deposition killed existing seedlings and provided a mechanical barrier that suppressed seedling recruitment.  The increase in understory light caused by canopy trimming stimulated germination from the seed bank and increased seedling recruitment and density of pioneer species several hundred-fold when hurricane debris was absent.  Many significant interactions between trimming and detritus deposition were evident from the manner in which seedling density, recruitment, and mortality changed over time, and subsequently influenced the composition of individuals ≥ 1 cm dbh (i.e., stems). When the canopy was trimmed, stem densities increased > 2-fold and rates of recruitment into the stem (≥ 1 cm dbh) size class increased > 25-fold.  Trimming had no significant effect on stem mortality.  The two dominant species that flourished following canopy trimming were the pioneer species Cecropia schreberiana and Psychotria berteriana.  Deposition of canopy detritus had little effect on stems, although basal area increased slightly when detritus was added.  The separate and interactive effects of canopy openness and detritus deposition result in variable short-term trajectories of forest recovery.  However, the short interval of increased canopy openness from hurricane impacts and its influence on the recruitment of pioneer trees is the dominant factor that drives short-term forest recovery.

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