Common Mangrove Species Research Articles

Ecological effects of small-scale cutting of Philippine mangrove forests

Small-scale wood harvesting is one of the most ubiquitous forms of resource-use in the tropics, yet ecologists have barely studied it. This paper examines the effects of small-scale woodcutting on forest structure, composition and regeneration of mangrove forests in the Philippines. Information for the study was obtained through the application of extensive bio-ecological assessments of forests and interviews of forest users. Cut mangrove forests were characterized by smaller trees, less basal area and more canopy gaps. At least two-thirds of all canopy gaps were caused by cutting. In spite of these dramatic structural effects, there was little demographic evidence to suggest that significant changes to current species composition are occurring, although this may, in part, reflect that some species have already been eliminated from study areas by past cutting. Among common species, Rhizophora mucronata was the only one that appeared to be negatively impacted from cutting in terms of its relative abundance. Although abundance varied, seedlings of all common species measured were taller in canopy and/or expanded gap compared to understory, with Sonneratia spp. showing the greatest and Avicennia marina the least response. The particular success of A. marina in cut forests may be explained by the ability of its seedlings to better persist in the understory and thereby exploit gaps when these are created by cutting. Among common mangrove species, all but R. mucronata appear to be regenerating well in cut forests: Sonneratia sp., A. marina and R. apiculata regenerate well by coppice regrowth into the abundant small canopy gaps found in uncut and especially cut forests. Findings from this study highlight the significance of small-scale cutting disturbance and coppice regeneration as biotic factors in mangrove ecology.

Marine fungi from the Bahamas Islands

This study extends our knowledge of the marine fungi in the Bahamas Islands (Atlantic Ocean) and of subtropical mangroves in general. Ninety-two fungal taxa have been recorded from seven mangrove sites, of which 81 are new records, bringing the total number of species for the islands to 112. Fungi dominating the community were Lulworthia grandispora, Kallichroma tethys, Leptosphaeria australiensis and Verruculina enalia, all common mangrove species. The fungal community reported is, compared to that of the Atlantic Ocean, one of the least sampled locations for marine fungi. Many new taxa were encountered during the study and further ecological and taxonomical studies on the mangrove fungi of these islands are warranted.

Histological analysis in shoot organogenesis from hypocotyl explants of Kandelia candel (Rhizophoraceae)

In vitro culture of hypocotyl explants from Kandelia candel, a common mangrove species, on hormone-free Murashige and Skoog (MS) medium resulted in shoot formation. Since the hypocotyls showed good potential for in vitro shoot multiplication, the process of bud primordium formation was analyzed from a histological viewpoint. A wound periderm first appeared at the top, exposed cut surface of the explants. The wound-induced meristem continued to divide giving rise to suberized cells oriented towards the cut surface. After formation of the suberized cell layers, the meristem and its inner derivatives differentiated into multilayered, uniformly packed parenchyma cells. Bud primordia differentiated from the dense cytoplasmic cells of the wound-induced meristem just beneath the suberized layer near the severed vascular bundles. Each explant produced several visible shoot buds. Furthermore, histological sections revealed that additional bud primordia were present within the explant just underneath the suberized cells and that these bud primordia appeared to be arrested in their development. The fact that additional bud primordia were present within the explant suggests that further manipulation of the explant is helpful to maximize the potential of this system.

Severe hail damage to mangroves at Port Curtis, Australia

A hailstorm in October 1994 was found to have moderately or severely impacted on 5.3% of the mangrove forests in Port Curtis. All mangrove species showed evidence of hail damage, including the three most common species (Rhizophora stylosa, Ceriops tagal and Avicennia marina). Physical effects of hail damage included stripping of leaves from plants, holes punched through leaves, bruising to bark, divots removed from bark, branch and plant death. Species‐specific differences in vulnerability to the effects of hail were observed with C.tagal experiencing relatively higher mortality rates than the other two common mangrove species. A delayed pattern of mortality was observed in two species _ C.tagal and A.marina. Alterations to mangrove community structure included: (1) reductions in stem density, stem diameter and basal area, (2) reductions in canopy cover (based on a photographic index of foliage projective cover) and (3) changes in relative abundance of species in mangrove zones. Recovery was observed in some stands but others had not recovered to pre‐hail levels of canopy cover two years after the hailstorm. Recovery had occurred by regeneration of fresh leaves but no recruitment of young plants had been observed during the study. The forests in the impact area were dominated by either Ceriops tagal or Rhizophora stylosa with Avicennia marinaas a subdominant in places. C.tagal dominated forests within the impact area were relatively more severely affected (41.8% in the severe category) than R.stylosa dominated communities (only 17.4% in the severe category). This indicated that C.tagal dominated forests were more vulnerable to the effects of hail damage than R.stylosa dominated forests. In addition, hail‐impacted C.tagal dominated forests represented a relatively high percentage of the area of C.tagal dominated forests in Port Curtis (44.3%). This percentage was much higher than hail‐impacted R.stylosa dominated forests in Port Curtis (2.7%). These two factors – relatively severe impact on C.tagal communities and a relatively higher percentage affected within the Port Curtis area – illustrate that hailstorms, as a form of natural disturbance, are an important influence on the forest ecology of mangrove ecosystems in this region.

Increased groundwater abstration in Zanzibar: A threat to mangroves?

In 1993–94 a study was carried out to assess the feasibility of improving agricultural water supplies on the Zanzibar islands of Tanzania by increased groundwater abstraction. On the two main islands, there are 18 00 ha of mangrove, which are located in estuaries, but also in sheltered bays where the only freshwater input is via springs in the intertidal and subtidal zones. The extent to which the mangroves are dependent on freshwater was therefore examined, so that abstraction proposals could be developed which would not have adverse impacts. Surveys gave no evidence that the springs have a strong effect on salinity, and field observations and literature surveys indicated that the common mangrove species, which cover over 80 percent of the mangal area, are those that are tolerant to high salinities. Their associated fauna is also generally well adapted to varying environmental conditions. This and other evidence is discussed, and the conclusion is reached that a decrease in freshwater is unlikely to have major impacts on the mangrove ecosystem. Because of the importance of this habitat and its value as a natural resource, the following precautionary measures were recommended: In the unlikely event of adverse impacts becoming evidents, These safeguards will ensure an adequate response.

Pollen from four common new world mangroves in jamaica

Abstract Pollen descriptions of four common mangrove species Rhizophora mangle L. (Rhizophoraceae), Avicennia germinans (L.) L. (Avicenniaceae), Conocarpus erectus L. and Laguncularia racemosa (L.) Gaertn. f. (Combretaceae) are presented. These species dominate the mangrove communities in coastal wetlands in the Caribbean and their pollen is common in peat cores taken from such deposits. The identification of the pollen grains is fairly easy as the four species investigated have characteristic pollen, however it is difficult to distinguish between Rhizophora mangle and Laguncularia racemosa pollen when found in fossil material. Pollen from Conocarpus erectus and Rhizophora mangle tend to be over‐represented in pollen diagrams as these plants are prolific pollen producers and their pollen is probably wind distributed.