Canopy and substratum heterogeneity influence recruitment of the mangrove Avicennia marina

Minchinton, TE

Te. Minchinton, Canopy and substratum heterogeneity influence recruitment of the mangrove Avicennia marina, J ECOLOGY, 89(5), 2001, pp. 888-902

70

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

89

5

2001

888 - 902

ISI

0022-0477(200110)89:5<888:CASHIR>2.0.ZU;2-H

1 Mangrove forests are structurally complex with canopy gaps generated by p hysical disturbances such as storms and mounds created on the forest floor by biotic disturbances such as crabs excavating burrows. 2 I studied how variations in canopy cover and substratum topography influe nce the recruitment and demography of the mangrove Avicennia marina in a te mperate forest in New South Wales, Australia. 3 Surveys showed that mounds covered up to 44% of the forest floor and were larger and covered more of the substratum under the canopy than in gaps. P ropagules and new seedlings (i.e. the most recently established cohort) wer e more abundant under the canopy than in gaps and on flat areas than on mou nds. 4 A field experiment tested whether the observed spatial distribution of ne w seedlings was due to differences in the secondary dispersal of propagules or in the establishment or early survivorship of seedlings. Propagules wer e supplied in equal densities on mounds and flats under the canopy and in g aps and then monitored for 10 months. 5 Four times as many propagules were dispersed away from mounds as from fla ts, and this difference was greater under the canopy than in gaps. In contr ast, seedlings established more successfully on mounds, particularly in gap s, suggesting that this is an important microhabitat for recruitment. Seedl ing survival to 9 months was independent of habitat structure. 6 The influence of mounds on dispersal was, however, much greater than on e stablishment, so that densities of new seedlings 9 months after establishme nt were greater on flats. Patterns of seedling abundance in the mangrove fo rest are thus primarily driven by the influence of habitat structure on the supply of propagules. 7 In contrast, saplings were most abundant on mounds in gaps. Thus, there i s a shift in the spatial distribution of the population from the early to t he later stages of life history in relation to habitat structure. Long-term survival of seedlings and their development into saplings may depend both on light availability in gaps and on sediment disturbance resulting from th e creation of mounds. The causative agent, crabs, may therefore be critical for regeneration of mangrove forests.