Rhizophora Seedlings Research Articles

Antibacterial Activity of Organic Fertilizer and Pesticidal Effects on Rhizophora Seedlings

Antibacterial Activity of Organic Fertilizer and Pesticidal Effects on Rhizophora Seedlings

Growth Performance of Planted Mangroves in the Philippines: Revisiting Forest Management Strategies

The effort toward restoring lost mangroves in the Philippines has been commendably immense, specifically during the past two decades. In light of such, it is important to evaluate outcomes and, where appropriate, apply the lessons learned to the current strategies in mangrove forest management. This article synthesizes the results from several research projects assessing the performance of planted mangroves across the country. Overall, there is a widespread tendency to plant mangroves in areas that are not the natural habitat of mangroves, converting mudflats, sandflats, and seagrass meadows into often monospecific Rhizophora mangrove forests. In these nonmangrove areas, the Rhizophora seedlings experienced high mortality. Of the few that survived (often through persistent and redundant replanting), the young Rhizophora individuals planted in these nonmangrove and often low intertidal zones had dismally stunted growth relative to the corresponding growth performance of individuals thriving at the high intertidal position and natural mangrove sites. From this evidence, this article argues that a more rational focus of the restoration effort should be the replanting of mangroves in the brackish-water aquaculture pond environments, the original habitat of mangroves. For such, a number of management options can be explored, the implementation of which will ultimately depend on the political will of local and national governments.

Nitrogen-fixing azotobacters from mangrove habitat and their utility as marine biofertilizers

A dearth of information is available for nitrogen-fixing bacteria in coastal mangroves, and hence, the present study has been undertaken to analyse 44 root and associated soil samples, derived from a mangrove habitat of southeast coast of India. The root samples exhibit high counts of total heterotrophic bacteria and azotobacters along with high rates of nitrogen fixation, as compared to the rhizosphere soil samples. Among the plant species, Bruguiera cylindrica records high microbial counts and nitrogen fixation. From the samples analysed, three species of Azotobacter, viz., A. chroococcum, A. virelandii and A. beijerinckii were isolated, purified and identified. These species exhibit high growth, nitrogen fixation and in vitro production of phytohormone (Indole Acetic Acid, IAA) at NaCl salinity of 30 g l −1. The azotobacters, which were inoculated with Rhizophora seedlings, increased significantly the average root biomass up to by 98.2%, the root length by 48.45%, the leaf area by 277.86%, the shoot biomass by 29.49% as compared to controls and they also increased the levels of total chlorophylls and carotenoids up to by 151.0% and 158.73%, respectively. Thus, azotobacterisation is beneficial in raising vigorous seedlings of mangroves in coastal wetlands.

Recruitment, mortality and growth of mangrove (Rhizophora sp.) seedlings in Ulugan Bay, Palawan, Philippines

Propagule dispersal, establishment and recruitment to the sapling stage are critical steps in the life cycle of mangroves. Specific (i.e., per capita) rates of recruitment and mortality, and the growth rates of Rhizophora seedlings in three mangrove stands in Ulugan Bay (Palawan, Philippines) were estimated between March 1999 and February 2001. Recruitment and mortality were variable in space and time, with mortality exceeding rates of recruitment at all sites. The specific rates of seedling recruitment and mortality were higher in Buenavista (0.66 year−1 and −1.67 year−1) than in Umalagan (0.05 year−1 and −0.33 year−1) and Oyster Bay (0.13 year−1 and −0.24 year−1). The annual rate of production of internodes by the main stem was similar at the three sites (5.4–5.5 internodes year−1), but the annual rate of elongation of the main stem was higher in Buenavista (10.6 cm year−1) than in Oyster Bay (7.6 cm year−1) and Umalagan (5.6 cm year−1).

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

Current theory predicts that in low-density, seed-limited plant populations, seed predation will be more important than competition in determining the number of individuals that reach maturity. However, when plant density is high, competition for microsites suitable for establishment and growth is expected to have a relatively greater effect. This dichotomous perspective does not account for situations in which the risk of seed predation differs inside versus outside recruitment microsites. We report the results of a field experiment and sampling studies that demonstrate such an interaction between microsite quality and the risk of propagule predation in mangrove forests on the Caribbean coast of Panama, where it appears to play a key role in shaping the demography and dynamics of the mangrove, Rhizophora mangle. Rhizophora's water-borne propagules establish wherever they strand, but long-term sampling revealed that only those that do so in or near lightning-created canopy gaps survive and grow to maturity. These microsites afford better growth conditions than the surrounding understory and, as importantly, provide a refuge from predation by the scolytid beetle, Coccotrypes rhizophorae. This refuge effect was confirmed with a field experiment in which Rhizophora seedlings were planted at different positions relative to gap edges, from 5 m inside to 20 m outside the gap. Mortality due to beetle attack increased linearly from an average of 10% inside a gap to 72% at 20 m into the forest. The interaction between canopy disturbance and propagule predation may be having a large impact on the composition of our study forests. Being shade-tolerant, Rhizophora seedlings that escape or survive beetle attack can persist in the understory for years. However, the high rate of beetle-induced mortality effectively eliminates the contribution of advance regeneration by Rhizophora saplings to gap succession. This may explain why the shade-intolerant mangrove, Laguncularia racemosa, is able to co-dominate the canopy in low intertidal forests at our study sites.

Regeneration in fringe mangrove forests damaged by Hurricane Andrew

Mangrove forests along many tropical coastlines are frequently andseverely damaged by hurricanes. The ability of mangrove forests to regeneratefollowing hurricanes has been noted, but changes that occur in vegetationfollowing disturbance by hurricane winds and storm tides have not been studied.We measured changes in plant community structure and environmental variables intwo fringe mangrove forests in south Florida, USA that experienced high windvelocities and storm tides associated with Hurricane Andrew (August1992). Loss of the forest canopy stimulated regeneration via seedlinggrowth and recruitment, as well as resprouting of some trees that survived thehurricane. Initial regeneration differed among species in both forests:Rhizophora mangle L. regenerated primarily via growth ofseedlings present at the time of the hurricane (i.e., release of advancerecruits), but many trees of Avicennia germinans(L.) Stearn and Laguncularia racemosa Gaertn.f.resprouted profusely from dormant epicormic buds. In one forest, which wasformerly dominated by Laguncularia, high densities ofRhizophora seedlings survived the hurricane and grew toform dense stands of saplings and small trees ofRhizophora. In the other forest, there were lowerdensitiesof surviving Rhizophora seedlings (possibly due tohigher storm tide), and extensive bare areas that were colonized byAvicennia, Laguncularia, andherbaceous species. This forest, predominantly Rhizophoraat the time of the hurricane, now contains stands of saplings and small treesofall three species, interspersed with patches dominated by herbaceous plants.These findings indicate that moderately damaged fringe forests may regenerateprimarily via release of Rhizophora advance recruits,leading to single-species stands. In severely damaged forests, seedlingrecruitment may be more important and lead to mixed-species stands.Regeneration of mangrove forests following hurricanes can involve differentpathways produced by complex interactions between resprouting capability,seedling survival, post-hurricane seedling recruitment, and colonizationby herbaceous vegetation. These differences in relative importance ofregeneration pathways, which may result in post-hurricane forestsdifferent from their pre-hurricane structure, suggest that models forregeneration of mangrove forests will be more complex than “directregeneration” models proposed for other tropical forests whereregeneration after hurricanes is dominated by resprouting.

The abundance and growth of Avicennia marina and Rhizophora stylosa in the low shore zone of Darwin Harbour, Northern Territory

Abstract The growth and distribution of the two mangrove seedling species, Avicennia marina (Forsk.) Vierh. and Rhizophora stylosa Griff., were studied in the low‐shore zone at three locations along two estuaries of Darwin Harbour to determine how growth varied along the estuary and within the habitats of the low shore zone. The low shore environment was heterogenous for factors such as salinity and light, with substantial variation within and between locations. Seedlings of Avicennia were in higher densities in light gaps than in the adjacent forest, and density in both habitats decreased towards the mouth of the estuary. Growth of Avicennia seedlings, as measured through in situ growth trials and plant harvests, increased towards the mouth of the estuary. Results for Rhizophora seedlings were more complex although some similar trends were evident. This may have been due to the greater early survival of Rhizophora seedlings compared to Avicennia seedlings. The importance of propagule origin was investigated, for Rhizophora, by transplanting propagules between locations along one estuary. Increased seedling survival was observed at the propagule source site; however, this effect was subtle and probably not the most important factor affecting seedling survival at a site.

Seedling survivorship, growth, and response to disturbance in Belizean mangal

Species zonation patterns across tidal gradients in mangrove forests are formed by successful seedling establishment and maintained by replacement of adults by conspecific seedlings. These two processes rarely have been examined experimentally in neotropical mangal. We studied survivorship and growth of seedlings of two species of mangrove, Rhizophora mangle L. and Avicennia germinans (L.) Steam, across a tidal gradient in Belize, Central America. Propagules of each species were planted in common gardens at tidal elevations corresponding to lowest low water (LLW), mean water (MW), and highest high water (HHW). Sixty‐nine percent of Rhizophora seedlings planted at MW and 56% of those planted at LLW survived 1 year. Forty‐seven percent of MW Avicennia seedlings also survived 1 year. No individuals of either species survived at HHW, and neither did any LLW Avicennia seedlings. Among the surviving Rhizophora seedlings, LLW seedlings grew more rapidly in terms of height, diameter, leaf production, and biomass than did MW seedlings. Insect herbivory was twice as high on MW seedlings as on LLW Rhizophora seedlings. We also examined the response of established Rhizophora seedlings to experimental removal of the adult Rhizophora canopy. Seedlings in canopy removal areas had higher survivorship, grew twice as fast, produced more leaves, and had less than half the herbivory of seedlings growing beneath an intact canopy. These results provide insights into underlying causes and maintenance of zonation in Caribbean mangrove forests.

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 $\pm$ 0.3) to 7.0 (SE $\pm$ 0.6) nodes$\cdot$ shoot$^{-1} \cdot$ 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.

Patterns of Herbivory in Belizean Mangrove Swamps

We quantified herbivory on leaves of two mangrove species, Rhizophora mangle and Avicennia germinans, at eight sites in Belize. Amounts and types of damage were compared among three mainland sites and five mangrove cays off the coast. Several environmental and autecological factors that potentially influence herbivory were examined, including canopy cover, tree age, leaf age, tidal height, and nutrient enrichment. Herbivores damaged 4.3 percent to 25.3 percent of Rhizophora leaf area and 7.7 percent to 36.1 percent of Avicennia leaf area, figures comparable to other mangal throughout the world. On average, Avicennia was less frequently damaged than Rhizophora at all sites but one. Herbivory at a bird rookery was not significantly higher than elsewhere, indicating that nutrient enrichment of leaves did not stimulate herbivory at this site. Significant but inconsistent differences in damage were detected between the cays and mainland sites. Significant differences, dependent on tidal height, were found between seedlings and trees. Rhizophora seedlings growing under a canopy of adult conspecifics suffered twice as much damage as seedlings growing in areas where the adult canopy was removed. Damage types occurring on each species were consistent across all sites, but the two species did not share the same herbivores.