Regeneration patterns of Cedrela lilloi (Meliaceae) in northwestern Argentina subtropical montane forests

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Abstract
All individuals of Cedrela lilloi (a valuable timber species of Meliaceae) > 4 cm DBH were sampled in three rectangular plots (c. 15 000 m2 each) in northwestern Argentina subtropical montane forests between 850 and 1350 m. Regeneration dynamics of C. lilloi was characterized by testing two hypotheses: (i) C. lilloi has a gap-phase regeneration mode, which implies a negative exponential size/age distribution at forest stand scale, growth releases due to canopy openings, and juvenile trees clumped at spatial scales of treefall gaps. (ii) There is a negative spatial association between adults and juveniles of C. lilloi which could be caused by density dependent mortality. Despite differences in age structure, diameter distribution approximated a negative exponential curve at all sites. Radial growth, measured as tree-ring widths, averaged between 2 and 4 mm y−1 which is comparable to fast growing tropical species in mature forests. Aggregation of juveniles peaked at radial distances of 8 to 15 m. Size structure, growth and spatial patterns of juveniles support the first hypothesis. In support of the second hypothesis, juveniles showed a negative spatial association with conspecific mature trees at spatial scales of less than 20 m. The Janzen–Connell model of density-dependence is one potential explanation for this pattern. Although regeneration and growth patterns of C. lilloi suggest a potential for sustainable management based on small-scale gaps, spatial dynamics at stand-scale need to be considered to ensure the regeneration of mature trees.

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