Within-stand and seasonal variations of specific leaf area in a clonal Eucalyptus plantation in the Republic of Congo
Specific leaf area (SLA; m2 leaf kg_1 leaf) is a key ecophysiological parameter influencing leaf physiology, photosynthesis, and whole plant carbon gain. Both individual tree-based models and other forest process-based models are generally highly sensitive to this parameter, but information on its temporal or within-stand variability is still scarce. In a 2-4-year-old Eucalyptus plantation in Congo, prone to seasonal drought, the within-stand and seasonal variability in SLA were investigated by means of destructive sampling carried out at 2-month intervals, over a 2-year period. Within-crown vertical gradients of SLA were small. Highly significant relationships were found between tree-average SLA (SLAt) and tree size (tree height, Ht, or diameter at breast height, DBH): SLAt ranged from about 9 m2 kg_1 for dominant trees to about 14-15 m2 kg_1 for the smallest trees. The decrease in SLAt with increasing tree size was accurately predicted from DBH using power functions. Stand-average SLA varied by about 20% during the year, with lowest values at the end of the 5-month dry season, and highest values about 2-3 months after the onset of the wet season. Variability in leaf water status according to tree size and season is discussed as a possible determinant of both the within-stand and seasonal variations in SLA.