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Seedling surprise: Recruitment onto rotting logs in a humid tropical forest in Caribbean Costa Rica.

Schiller, Anja*,1, 1 The Evergreen State College, Olympia, WA, USA

ABSTRACT- The importance of decomposing logs for seedling recruitment is well established in temperate forests; however, few studies have examined their role in humid tropical forests. I compared the density of seedlings (<2 m high) of the families Arecaceae, Cyclanthaceae, and Melastomataceae on 37 downed logs and the adjacent forest floor in an old-growth forest at La Selva Biological Station on the Caribbean lowlands of Costa Rica. Seedling density differed among families and between microsite types. Cyclanthaceae had the highest density of seedlings on the log microsite (2.09 stems/m2), whereas Arecaceae (0.94 stems/m2) and Melastomatace (0.80 stems/m2) exhibited lower densities. On the forest floor, Arecaceae was the densest (1.06 stems/m2) whereas Cyclanthaceae and Melastomataceae had very low densities (0.15 and 0.12 stems/m2 respectively). Both Cyclanthaceae and Melastomataceae were significantly more common (14 and 6.5 times greater density respectively) on the log than on the forest floor (p < 0.002). At the genus level, Asplundia and Dicranopygium in Cyclanthaceae and Miconia in Melastomataceae were significantly denser on the log than the forest floor (p < 0.002). Genera within Arecaceae showed various patterns for microsite preference. Geonoma was significantly denser on the forest floor than on logs (p < 0.02). All other genera did not show a significant habitat preference. Taxa colonizing rotting logs all had small seeds; suggesting that life history strategy is important in establishing regeneration niches. This study indicates that rotting logs are important microsites in low land tropical rain forest regeneration. Consequently, leaving downed logs in forest clearings created by logging and natural disturbance events may accelerate forest regeneration.

Key words: nurse logs, seedling recruitment, rain forest, Neotropics

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