Aging Rhizophora seedlings from leaf scar nodes: a technique for studying recruitment and growth in mangrove forests

This paper proposes a rapid and non-destructive technique to age Rhizophora seedlings in the field, using the sequence of leaf nodes along main stems. Based on three- to four-year-old R. mangle seedlings planted in a bay on the Caribbean coast of Panama, it was found that rates of annual node production (=half of leaf production) in the terminal shoot was relatively constant between individuals in the same and similar sites, and for each individual when remeasured three or four times over 19 months. Marked differences, however, were scored between sites under obviously different light conditions, notably in shade (closed canopy) or sun (open canopy); estimates range from 3.8 (SE ± 0.3) to 7.0 (SE ± O.6) nodes.shoot-1.year-1, respectively (note, these were comparable with branch shoots on mature trees nearby).Therefore, neighbouring seedlings in sites with the same light condition could be aged by dividing total counts of main stem nodes by the respective rate. But, of greater interest, seedlings in open sites were found to have annual peaks of internodal extension along their main stems. It followed that seedlings like these could be aged by counting the number of peaks. This provided a more robust means to age seedlings having unknown growth histories, since it did not assume constant annual node production. These characteristics of seedling growth offer a relatively simple means to age individuals, and to quickly characterize demographic patterns in seedling communities. The technique is limited by bark development obscuring nodes on lower stems, occurring after approximately six or more years in R. mangle. Furthermore, because node production was not apparently influenced by age, the technique may also apply to distal branches of larger trees in appropriate light conditions