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

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.