Small‐scale disturbance and regeneration dynamics in a neotropical mangrove forest

Abstract

Summary1 Mangrove forests are aected by a variety of natural disturbances that dier in scale, intensity and frequency. Small canopy gaps, although common, have not been well studied. We examined the role of lightning-created canopy gaps in the dynamics of a 47-km 2 intertidal mangrove community in the Dominican Republic, by quantifying the spatial patterns of overstorey tree distributions, spatial and temporal patterns of gap formation, and tree regeneration in gaps and beneath the closed forest. We hypothesized that regeneration in these gaps would maintain and reinforce species' distribution patterns across the intertidal gradient in this mangrove ecosystem. 2 All 52 gaps surveyed in the ®eld were nearly circular canopy openings created by lightning. Expanded gap size indicated an average diameter of 30.4 m. The total area of forest in the gap-phase is currently 1.9%, with an annual formation rate of 0.23% year À 1. Canopy turnover was calculated to range from 421 to 842 years; however, gaps were not randomly distributed across the mangrove forest and canopy turnover in the most gap-prone areas ranged from 194 to 386 years. 3 Seedling density was not dierent under gaps and under the forest canopy, but sapling density and sapling growth rates of three species were signi®cantly greater in canopy gaps. The annual mortality rate of Rhizophora mangle (9%) in canopy gaps was signi®cantly lower than either Laguncularia racemosa (32%) or Avicennia germinans (56%). Gap regeneration was dominated by R. mangle throughout the forest. 4 The results of this study do not support our initial hypothesis but suggest that the distribution and abundance of R. mangle will increase throughout the forest over time, given the present disturbance regime. Field observations indicated that the peat mat collapses in lightning-created gaps following their formation, resulting in increased levels of standing water. We suggest the successful regeneration of R. mangle is favoured in these gaps because of its greater tolerance to¯ooding conditions.

Regeneration of Rhizophora mangle in a Caribbean mangrove forest: interacting effects of canopy disturbance and a stem-boring beetle

“…At our sites, lightning strikes kill or injure taller trees, but do not damage understory vegetation growing below about 3-4 m, including advance regeneration in the form of suppressed seedlings and saplings. This contrasts with the observation of Sherman et al (2000) that lightning strikes kill both overstory and understory vegetation in Dominican Republic mangrove forests.…”

“…f. (Combretaceae), and Rhizophora mangle L. (Rhizophoraceae). In these forests, as elsewhere (Davis 1940;Schaeffer-Novelli et al 1990;McKee 1995;Imbert and Menard 1997;Sherman et al 2000), the three species are distributed differentially with distance from the water's edge, but their distributions overlap to varying degrees (W. Sousa and B. Mitchell, unpublished data). In our study forests, several zones of differing canopy composition occur along the tidal gradient.…”

“…In this area, lightning strikes are the primary cause of canopy tree mortality, and the light gaps they produce are sites of vigorous regeneration as evidenced by the high density of saplings as compared to the understory (W. Sousa and B. Mitchell, unpublished data). Lightning gaps have been recognized as key sites of regeneration in mangrove forests throughout the tropics (Craighead 1971;Paijmans and Rollet 1977;Odum et al 1982;Smith 1992;Smith et al 1994;Sousa and Mitchell 1999;Clarke and Kerrigan 2000;Sherman et al 2000).…”

THE RECOVERY OF A DEGRADED MANGROVE IN CEARÁ THROUGH THE PRODUCTION OF Laguncularia racemosa (L.) C.F. Gaertn. (Combretaceae) AND Avicennia sp. Stapf ex Ridl (Acanthaceae) SEEDLINGS

“…The different plant species are distributed in mangroves in separate zones, which follow a tidal gradient (SHERMAN et al, 2000;LONDE et al, 2013.). Generally, the red mangrove, Rhizophora mangle (L.) (Rhizophoraceae), occupies locations near the sea, rivers, or muddy places while the black mangrove, Avicennia germinans (L.) Stearn (Avicenniaceae), and the white mangrove, Laguncularia racemosa (L.) Gaertn.…”

Coastal Systems and Low-Lying Areas

“…Nevertheless, it seems highly likely that similar principles are in operation and that the sedimentary response of the shoreline is a function of both the availability of sediment (Walsh and Nittrouer, 2004) and the ability of the organic production by mangroves themselves to fill accommodation space provided by sea-level rise (Simas et al, 2001). Mangroves are able to produce root material that builds up the substrate beneath them (Middleton and McKee, 2001;Jennerjahn and Ittekkot, 2002), but collapse of peat occurs rapidly in the absence of new root growth, as observed after Hurricane Mitch (Cahoon et al, 2003) and after lightning strikes (Sherman et al, 2000). Groundwater levels play an important role in the elevation of mangrove soils by processes affecting soil shrink and swell.…”