Mangrove Regeneration Research Articles

Using Melaleuca fences as soft coastal engineering for mangrove restoration in Kien Giang, Vietnam

Planting mangrove is an important work to respond to mangrove loss and erosion, a serious issue and exacerbated from climatic changes in coastal area of the Mekong Delta. However, the previous efforts have repeatedly been unsuccessful because planted seedlings have suffered complete loss due to the lack of protection from wave action and seasonal sediment movement. Two Melaleuca (Melaleuca cajuputi) fences (wave barrier and silt trap fences) were designed and set up for testing their effectiveness in assisting mangrove restoration in the erosion-prone area of the Kien Giang Province. The wave height of the shoreline behind the Melaleuca fence can reduced by 63% compared to the open coast. After 3 years, they retained from 45 to 47cm of mud inside the fence line. The survival rate of Avicennia alba (62% and 44%) was much higher than that of Rhizophora apiculata (35% and 14%) in both two fenced treatments. Growth rate of Avicennia seedlings was also much higher than Rhizophora in both treatments. There was a significant statistical difference between live seedlings and growth of Rhizophora and Avicennia in the two fenced treatments. Wild seedlings of Avicennia started colonizing the fenced area after 1.5 years of fence construction and regenerated seedling density varied from 2300 seedlings/ha in to 7100 seedlings/ha after 3 years. Species richness of benthos inside 2 fenced areas approached that in the natural forest area 1.5 years after fence construction. The study demonstrates the high potential of using Melaleuca fences to facilitate regeneration of mangrove and improves coastal protection in Kien Giang Province.

Mangrove Restoration and Regeneration Monitoring in Gulf of Kachchh, Gujarat State, India, Using Remote Sensing and Geo-Informatics

Indian coast harbors richly diverse and critical coastal habitats like coral reefs and mangroves. Mangroves form one of the most important ecosystems of coastal and marine areas. It safeguards the ecology of the coastal areas and provides livelihood opportunities to the fishermen and pastoral families living in these areas. In real sense, mangrove is the Kalpvriksh (divine tree which fulfills all the desires) for the coastal communities. The restoration and plantation of mangroves have received a lot of attentions worldwide. To assess the impact of mangrove plantation activities and to monitor the mangrove regeneration and restoration in various villages, a joint study under the Integrated Coastal Zone Management Project (ICZMP) was taken up by Gujarat Ecology Commission (GEC) and Bhaskaracharya Institute for Space Applications and Geo-Informatics (BISAG) in the Gulf of Kachchh, Gujarat State. The major objective of this study was to monitor the increase in mangrove cover in coastal areas of Gulf of Kachchh using the Indian Remote Sensing Satellite data of 2005, 2011 and 2014. The mangrove regeneration was monitored using multi-temporal Indian Remote Sensing Satellite (IRS) LISS-III and LISS-IV digital data covering Gulf of Kachchh region. The multi-temporal IRS LISS-III data covering Gulf of Kachchh of October-2005, November-2011 and LISS-IV data of April-2014 was analyzed. The mangrove density and mangrove area in different talukas was estimated based on the analysis of IRS LISS-III digital data. The mangroves have been delineated based on the pink colour observed on satellite images and the area was estimated in the Geographic Information System (GIS) environment. The taluka or block-level mangrove areas were estimated and changes in the areas were monitored during the period of six years from 2005 to 2011. It was observed that the areas where mangrove regeneration activities were carried out with active participation of Community Based Organizations (CBOs), mangrove density as well as mangrove area have substantially increased in the Gulf of Kachchh region.

Response of mangroves to the change in tidal and fresh water flow – A case study in Pichavaram, South India

Mangroves grow in intertidal zone of tropical coasts and nourished by the influence of freshwater and tidal water added to local rainfall. This study attempts to spatially analyse such hydrological influence on the mangrove area over seven decades in Pichavaram, a wetland of South Indian East coast. Analysis of local rainfall, freshwater and tidal flow and spatial maps derived using Geographic Information System was carried out to interpret the influence of hydrological parameters on the extent of mangroves. The analysis shows that mangrove area has a positive correlation of 0.98 with amount of freshwater and 0.66 with tidal flow in terms of estuarine dimensions till 1991. After 1991, mangrove area is increased even with reduced amount of freshwater. Major reason for the increase in mangrove forest cover was the restoration of the wetland by avoiding stagnation of tidal water in degraded area and thereby reducing soil to support mangrove regeneration. However, this manipulation of local hydrological condition supported only one species of mangroves Avicennia marina, which is tolerant to high salinity. As indicated in this study freshwater inflow is one of the main factors that determine species diversity of mangrove plants since most of the mangrove species requires moderate saline condition for their optimal growth and biomass production. However, due to increased demand for freshwater upstream, amount of freshwater reaching mangroves are reduced. It is suggested that in order to at sustain mangrove wetlands suitable management procedures need to be evolved and applied to ensure required quantity of freshwater flow into mangrove ecosystem for required duration.

Growth density and regeneration of afforested mangroves at Mirersarai forest range in Bangladesh

The aim of the study was to determine growth performance of planted mangroves at three beats of Mirersarai forest range in the Chittagong coastal afforestation division, Bangladesh. This 22–29-year-old mangrove plantation showed satisfactory growth and regeneration with variations among different study sites. The study revealed that individual species density and overall density (stem/ha) in the study sites varied significantly (p ≤ 0.05) where density of Sonneratia apetala was maximum among five species followed by Excoecaria agallocha, Avicennia officinalis, Ceriops decandra and Bruguiera sexangula. Sonneratia apetala attained the highest mean diameter at breast height (DBH) (cm) and height (m) among all the plantation species. It was found dominant at the middle section plantations of three beats, whereas Bruguiera sexangula and Ceriops decandra were found absent at seaside plantation sites. Overall tree density was found to be highest at the middle part (1880 stem/ha) followed by inland (1610 stem/ha) and seaside (1087 stem/ha) plantations. Mean annual increment of height and of DBH were significantly higher for Sonneratia apetala (0.42 m/year, 0.81 cm/year) followed by Avicennia officinalis (0.32 m/year, 0.67 cm/year), Bruguiera sexangula (0.18 m/year, 0.40 cm/year), Excoecaria agallocha (0.16 m/year, 0.30 cm/year) and Ceriops decandra (0.05 m/year, 0.10 cm/year), respectively. Regeneration of vegetations showed promising performance in three beats. Sonneratia apetala showed rich regeneration at seaside plantations than inner parts in northern beats than those of southern beats. For all beats this species has an increased regeneration from inland to seaside plantation strips. Avicennia officinalis seedlings were found highest at the middle part of the plantation, whereas Excoecaria agallocha was found to be regenerated with high density at the inland part with a decreasing trend toward seaside strips. However, Bruguiera sexangula was found to be regenerated only at inland strips. Thus, this suggests that a coastal afforestation program with different species will show varied growth, regeneration and density at different situations according to species ecology and adaptability to the sites along the coast .

Long-term vegetation changes in a tropical coastal lagoon system after interventions in the hydrological conditions

Over a period of 44 years, we observed the vegetation changes in the western part of the lagoon system of the Ciénaga Grande de Santa Marta, which is situated on the Caribbean coast of Colombia and is separated from the sea by a sandy barrier. Since the construction of the Barranquilla-Ciénaga Road between 1956 and 1960, the lagoon system has been exposed to different interventions in its hydrological make-up, as well as changes to the vegetation. During the time of our investigations, four periods with different plant cover were distinguished. In 1965, the road was bordered by dense mangrove forests. The low surface water salinity and the presence of freshwater plants indicated the influence of the Magdalena River. At the beginning of the seventies, the second period was marked by a decrease in the freshwater in-flow from the river, which led to an increase in salinity and a gradual decay of vegetation. In 1988, the areas formerly covered by mangroves had converted into salt flats. The third period began with the reconstruction of several channels (1995–1998) which renewed the freshwater in-flow from the river to the lagoons. The subsequent vegetation development was characterized by the establishment of Typha domingensis Pers. In 1999, a year with an unusually high amount of rainfall, this species covered most of the former mangrove area in the western part of the lagoon system. The very low surface water salinity favored its spread. The last period began in 2001/2002, when growth conditions for T. domingensis became unfavorable due to an increase in salinity. Instead, conditions for mangrove regeneration improved. This process was slower than expected and is still ongoing. The striking vegetation changes indicate the sensitivity of the coastal lagoon system to hydrological variability.

Respuesta de la regeneración natural en manglares del Golfo de Urabá (Colombia) a la variabilidad ambiental y climática intra-anual

The natural regeneration process allows the mangrove forests remain over time. Both, biological and physical factors can affect the establishment and early stages along the development of trees. This study examined the response of natural regeneration of mangroves in the Turbo River delta and El Uno bay (Urabá Gulf, Colombia) to intra-annual environmental variability. We quantified mortality, survival and recruitment of seedlings of three mangrove species, seasonally during one year, in 72 semi-permanent sub-plots of 1 m2. In the sub-plots, the total height and the diameter at the base of the stem of all mangrove seedlings with basal diameter less than 2.5cm were measured. Damage by herbivores was also recorded to each seedling. While Laguncularia racemosa recorded the highest rates of mortality, Rhizophora mangle showed the highest survival rate during the study period, although Avicennia germinans dominated the natural regeneration. Through a Redundancy Analysis these processes were associated to environmental variables such as: Direct Site Factor-DSF (sunlight), sediments input rate, herbivory, distances from mangroves to the river, to inner lakes, and to the coastline. These variables explained 43% of the natural regeneration variation; sedimentation rate was the most important variable, while light was very representative for the R. mangle survival. Based on historical records of precipitation, Turbo River flow rate and associated sediment loads, it was established that during the highest precipitation peak, the survival of all species decreases and during the dry season, when the conditions of flooding and sediments input were lower, it was improved. The results indicated that the sediments input rates and sunlight play an important role in the survival of natural regeneration of evaluated mangrove species.

Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms

Abstract. Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala–Chilaw Lagoon Complex (Sri Lanka) was studied by combining a hydrodynamic model with species-specific knowledge on propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind), trapping agents (retention by vegetation) and seed characteristics (buoyancy) on propagule dispersal patterns. Sensitivity analysis showed that smaller propagules, like the oval-shaped propagules of Avicennia officinalis, dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped propagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the propagules being retained within the vegetation. Only a small proportion (max. 5%) of propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows), was found to significantly affect the resultant quantities and species of inflowing propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the value of propagule dispersal modelling in guiding hydrological restoration efforts that aim to facilitate natural mangrove regeneration.

BIODIVERSITY AND ROLE OF BRACHYURAN CRABS IN LEAF LITTER DECOMPOSITION ON TYPHOON DESTROYED AREAS AT CAN GIO MANGROVE, HCMC

Natural enviroment of the destroyed zone in Can Gio mangrove by Durian typhoon had been serious bioturbation. The researches about the environment of this area and role of organisms are very important for the mangrove regeneration. There are 19 species of Brachyuran crabs belonged to 13 genus, 7 families such as Sesarmidae, Ocypodidae, Varunidae, Oziidae, Grapsidae, Leucosiidae and Camptadriidae. Perisesarma eumolpe is the dominated species and effects mangrove leaf litter decomposition in there. They consumed all of 3 Rhizophora apiculata leaf types and the brown leaf is the most consumed by them. The consumed leaf rate is 5.2% - 24.44% / wet weight leaf on 24 hours. Perisesarma eumolpe is the important link of the nutritional chain in this ecosystem. They help to return the nutrition for sediment, reduce the leaf litter mass which is lost by tide.

Sulfide Concentration and Redox Potential Patterns in Mangrove Forests of Dar es Salaam: Effects on <i>Avicennia Marina</i> and <i>Rhizophora Mucronata</i> Seedling Establishment

The mangrove species Avicennia marina and Rhizophora mucronata occur in coastal areas with reducing sediment that contain high sulfide concentrations. However, in this study a glasshouse experiment demonstrated that the establishment of seedlings from these species did not occur in sediment with high sulfide concentration (0.5-6 mM) and low redox potential (-27 to -198 mV). In situ measurements, conducted at Mtoni and Mbweni, Dar es Salaam, showed similar ranges. However, sediments with mangrove roots had significantly lower (P = 0.03) sulfide concentrations than the adjacent areas without roots. Corresponding redox potential was higher in the sediment with roots than without roots. At Mtoni, the sulfide concentrations ranged between 0.0025 to 0.96 mM and 1.5 to 24.5 mM in sediment with roots and without roots, respectively. At Mbweni, sulfide concentrations between 0.01-0.97 mM and 1.09-16.59 mM were detected in sediment with roots and without roots, respectively. The conclusion of these results is that spatial and temporal variation in the soil redox potential and sulfide concentrations, which are results of microbial activities in the sediment, influence mangrove seedling establishment. These soil factors are modified by the root systems, whereby sediments in areas with plenty of mangrove roots are oxidized and thus conducive for mangrove regeneration. Keywords : Mangrove seedling, sulfide concentration, redox potential, sulfate reducing bacteria West Indian Ocean Journal of Marine Science Vol. 4 (2) 2005: pp. 163-174

Struktur dan Kemampuan Tumbuh Kembali Hutan Mangrove Cikiperan Cilacap

Study was conducted to know forest structure and regeneration of mangrove Cikiperan Cilacap. Transect method was used for this study, the data of seedling were collected by quadrat method, sapling and tree were collected by quarter method. The result of this research showed there were 7 species seedling, 11 species sapling and 18 species trees. Dominant species was Rhizophora mucronata , Rhizophora apiculata , Bruguiera gymnorhiza , Avicenia alba , Aegiceros corniculatum , Nypa fruticans , and Ficus retusa . The forest of mangrove regeneration was generally very good. Seven species, however, were recorded in critical condition, i.e. Ceriops tagal , Sonneratia alba , Intsia bijuga , Cynometra ramniflora , Cerbera adolam , Leucaena leucodendrom , and Lumnitzera littorea .

Short-term mangrove browsing by feral water buffalo: conflict between natural resources, wildlife and subsistence interests?

Management of the natural environment and its resources leads to conflicts between different stake-holders worldwide. Recently mangrove browsing by feral water buffalo in the East-Godavari Delta (India) has been considered a threat to the regeneration of mangroves by the local Forest Department, which led to conflicts between the authorities and local herds-men who have an ancient tradition involving feral water buffalo. The impact of browsing and grazing of mangroves by feral water buffalo was monitored. Feral water buffalo consumed mangroves, but not to the extent claimed by the Forest Department, prefering Avicennia alba, A. marina and A. officinalis. Their browsing behaviour was not linked to a height zone, and buffalo preferred the fresh leaves from previously undamaged branches. Under experimental and natural conditions, browsing induced compensatory regrowth in Avicennia. The carrying capacity of the mangrove appears to be sufficient to accumulate impact. There are both positive and negative impacts of livestock animals on forest ecosystems, and sociocultural consequences must be carefully assessed prior to enforcing a change in natural resource or environmental management. Before banning feral water buffalo from the mangrove, forest managers should confront their prejudices about the real impact of feral herbivores on these forests.

Zonation Patterns of Belizean Offshore Mangrove Forests 41 Years After a Catastrophic Hurricane1

ABSTRACTMangroves are prone to bearing frequently the full brunt of hurricanes and tropical storms. The extent of destruction and early regeneration are widely studied. The purpose of this study was to add a long‐term view of mangrove regeneration and assess the potential effects on mangrove horizontal zonation patterns of catastrophic destruction. Hattie, a category five hurricane, hit the Belizean coast in 1961. It passed directly over the Turneffe Atoll where our study area, Calabash Cay, is located. At four sites on this island, we analyzed mangrove forest structure along transects parallel to the shoreline within zones delineated by species dominance and tree height. We propose an index based on the Simpson index of diversity to express changes in the heterogeneity of the species dominance. Physical–chemical parameters and nutrient availability were also measured. The destruction levels were estimated by analysis of the distribution of diameter at breast heights of the bigger trees in the inland zones. Variations in species dominance among sites and zones could be explained by interactions of various factors. Further, different levels of destruction between the two sides of the island had a significant effect on current patterns of species and structural zonation at Calabash. We conclude that disturbance regime in general should be considered as a factor potentially influencing mangrove horizontal zonation patterns.

An assessment of metal contamination in mangrove sediments and leaves from Punta Mala Bay, Pacific Panama

Due to the growing rate of urbanisation in many tropical coastal areas, there continues to be an increasing concern in relation to the impact of anthropogenic activities on mangrove forests. Punta Mala Bay is located on the Pacific coast of Panama and suffers from intense anthropogenic activities that are potentially harmful to the remaining mangrove forests. Field observations reveal that the mangrove stand within Punta Mala Bay receives high inputs of untreated domestic sewage, storm water run-off and a range of diffuse inputs from shipping activities. Results from analysis of eight metals (Mn, Cu, Zn, Ni, Pb, Fe, Cr, Cd) showed that Fe, Zn and Pb were in concentrations high enough to conclude moderate to serious contamination within the bay, and thus pose the most threat to the regeneration and growth of the mangrove. However, previous biological surveys indicate ongoing mangrove regeneration and domination of stand structure by Laguncularia racemosa, together with high numbers of seedlings and saplings.

Evolution of the Sungei Buloh–Kranji mangrove coast, Singapore

The mangroves from Sungei Buloh Wetland Reserve to Kranji Dam represent the largest intact mangrove forest left on mainland Singapore. Mangroves colonized the area around 6820 BP, as sea level rose following the last glacial maximum and a variable thickness of Holocene sands, muds and peats (generally ~1 to >3.8 m thick) were deposited over the pre-transgression land surface. An analysis of a time series of photographs covering the period from 1946 to 2001 has revealed major changes in the distribution of mangroves in the area resulting from development-induced changes in the local hydrodynamic regime and clearance for aquaculture. Mangroves covered 117.3 ha in the study area in 1946 and were actively advancing over the coastal mudflats until 1980. Despite the addition of 6.24 ha from mangrove colonization, the total area covered by mangroves was reduced by ~50% by 1980 due to clearance for aquaculture. Following 1980, a reduction in sediment supply possibly due to the construction of the Kranji Dam, immediately east of the study area, led to the initiation of erosion along much of the coastline, with the mangrove fringe having retreated by up to 50 m in 2001. Establishment of the wetland reserve in 1992 enabled the partial regeneration of mangroves in the area to 86.8 ha, 25% less than in 1946. Three areas of undisturbed old growth mangroves >55 years in age have been identified and are considered to be of high conservation value. Two of these areas are within the current boundaries of the Sungei Buloh Wetland Reserve, but are located along coastal areas that are undergoing severe erosion. The third area is located in the south of the study area, protected from coastal erosion, but outside the current nature reserve boundary and hence is susceptible to loss as a result of future development. This third area is possibly the oldest undisturbed fragment of mangrove forest on mainland Singapore.

Spatial variations in macrobenthic fauna recolonisation in a tropical mangrove bay

Recolonisation by crab species and sediment-infauna taxa (at class level) in artificially re- generated mangrove stands of Avicennia marina, Rhizophora mucronata and Sonneratia alba (5 yr old) were studied using respective bare sites (open without mangroves or denuded) and natural sites (rela- tively undisturbed) as controls. The controls were chosen based on site history, physical proximity and tidal inundation class in reference to the particular reforested mangrove stand and samples randomly taken. A number of environmental variables were measured; interstitial water salinity and temperature (measured at low tide) were lower, whereas sediment organic matter content was higher in the areas with mangrove cover, with the natural sites having the highest content. The bare sites were generally sandier, whereas the areas with mangrove cover had higher proportions of clay and silt. Generally, there was a higher crab density in the reforested sites than in the bare sites, whereas crab species diversity (Shannon diversity index) did not vary from one site to another for any of the mangrove species. In terms of crab species composition, the reforested sites were more similar (Sorensen similarity coefficient) to the natural sites and less to the bare controls. For sediment-infauna, the reforested sites had a significantly higher density than the respective bare controls, while the natural sites had the highest density. The number of sediment-infauna taxa in both the reforested and natural sites of all the mangrove species was similar and higher than in the comparable bare sites. The results suggest that the reforested sites are supporting more faunal recolonisation, and therefore becoming more akin to the natural mangrove sites in terms of the investigated functional indicators. The findings seem to support the use of artificial mangrove regeneration (in areas where natural regeneration has been impeded by physical conditions or otherwise) as an effective management tool in the restoration and conservation of the functional integrity of degraded mangrove habitats.

Remote Sensing of Mangrove Change Along the Tanzania Coast

This article contributes to the understanding of the changes in distribution and total area of mangrove forests along the mainland Tanzania coast over the past decade. Mangroves are recognized as critical coastal habitat requiring protection and special attention. The Tanzania coastline forms a suitable habitat for establishment of mangrove forests. Mangrove forests are distributed from Tanga in the north to Mtwara in the south covering approximately 109,593 hectares from 1988-1990 and about 108,138 hectares in 2000. The largest continuous mangrove stands are found in the districts of Rufiji, Kilwa, Tanga-Muheza, and Mtwara. Comparison of data between these two time periods shows that the geographic coverage of mangroves has no dramatic change in the past decade. The Tanzania Mangrove Management Project and other closely related programs and efforts pertaining to mangrove conservation contribute to direct restoration and natural regeneration of mangroves. This study documents the changes of mangroves and demonstrates that remote sensing and GIS offer important data and tools in the advancement of coastal resource management and ecosystem monitoring. Application of geographic information technologies is critical for improved coastal resources management and decision making for sustainable development in Tanzania.

Do Forest Gaps Influence the Population Structure and Species Composition of Mangrove Stands in Northern Australia?1

ABSTRACTGap‐phase regeneration of tropical mangroves was studied to test if there were significant environmental, structural, and floristic differences between canopy gaps and adjacent forests with intact canopies. Twenty‐five canopy gaps in the low to mid intertidal zone were sampled at two study areas in northern Australia. Canopy gaps at the more equatorial study area were larger and had a higher surrounding canopy. Soil analyses showed that sediment texture exerts strong control on conductivity, pH, organic matter, total P, total N and total S. Some soil factors differed between gaps and intact forest, and PAR was significantly higher in gaps. Despite this, propagule and young seedling abundances did not differ between gaps and adjacent forests due to the dominance of viviparous species. Enhanced recruitment of seedlings to the sapling stage was detected in many canopy gaps, although saplings were also present under mangrove forest canopies. Nevertheless, the overall floristic composition, species richness, and species rank abundance were similar between canopy gaps and forests with intact canopies. There appears to be little evidence for specialized gap colonists in tropical mangrove forest as distinct from other tropical forests. Instead, gap‐phase regeneration of mangroves appears to follow a simple “direct replacement” model in which a species population is replaced by members of the same species in forest gaps. The scope for gap‐dependent specialization in mangroves via seed dormancy and fast growth rates, common in rain forest pioneers, may be constrained by the intertidal environment in which mangroves occur.

Do Forest Gaps Influence the Population Structure and Species Composition of Mangrove Stands in Northern Australia?1

Gap-phase regeneration of tropical mangroves was studied to test if there were significant environmental, structural, and floristic differences between canopy gaps and adjacent forests with intact canopies. Twenty-five canopy gaps in the low to mid intertidal zone were sampled at two study areas in northern Australia. Canopy gaps at the more equatorial study area were larger and had a higher surrounding canopy. Soil analyses showed that sediment texture exerts strong control on conductivity, pH, organic matter, total P, total N and total S. Some soil factors differed between gaps and intact forest, and PAR was significantly higher in gaps. Despite this, propagule and young seedling abundances did not differ between gaps and adjacent forests due to the dominance of viviparous species. Enhanced recruitment of seedlings to the sapling stage was detected in many canopy gaps, although saplings were also present under mangrove forest canopies. Nevertheless, the overall floristic composition, species richness, and species rank abundance were similar between canopy gaps and forests with intact canopies. There appears to be little evidence for specialized gap colonists in tropical mangrove forest as distinct from other tropical forests. Instead, gap-phase regeneration of mangroves appears to follow a simple “direct replacement” model in which a species population is replaced by members of the same species in forest gaps. The scope for gap-dependent specialization in mangroves via seed dormancy and fast growth rates, common in rain forest pioneers, may be constrained by the intertidal environment in which mangroves occur.

The Mangrove Ecosystem of the Ciénaga Grande de Santa Marta (Colombia): Observations on Regeneration and Trace Metals in Sediment

Alteration of water flows and consequent hypersalinization caused the death of nearly 70% of mangroves at the Ciénaga Grande de Santa Marta, Colombia. Efforts to rehabilitate the ecosystem have been made through the construction of freshwater channels. Mangrove recovery was observed along a freshwater channel and at a small lagoon behind the beach ridge. Factors identified in this study influencing mangrove regeneration are: salinity of surface water, duration and height of flooding, leaching property of soils, dispersal of propagules and presence of fertile trees. Besides mangrove regeneration, a notable extension of freshwater plants was observed in the channel. Trace metal concentrations in sediments from the Magdalena River and its area of influence were investigated before the complete opening of the first channel. A relative comparison indicated that the highest concentrations of Cd, Cu, Ni and Zn were above international recommended limits. However, metal concentrations found in sediments at Cları́n Channel did not affect the mangrove recovery.

Impact of ecological factors on the regeneration of mangroves in the Ciénaga Grande de Santa Marta, Colombia

In the Cienaga Grande de Santa Marta, a brackish lagoon system on the Caribbean coast of Colombia, human-induced changes in the hydrological system caused hypersalinisation of the soils. As a result, 30 000 ha of originally 51 000 ha of the mangrove forests growing in the lagoon's flood plain died. Presently, efforts are being made to reestablish the original hydrological system. Reforestation of the bare areas is planned with the three dominating mangrove species Avicennia germinans, Laguncularia racemosa and Rhizophora mangle. The objective of the project presented here is to identify the regeneration patterns in the study area. Experiments under controlled conditions and measurements at bare and forested sites carried out from 1994 to 1996 showed that regeneration is possible. However, as the bare areas are large and presently very few or no propagules arrive naturally, regeneration will be slow. Therefore, reforestation is recommended to accelerate the process. In the forests, the seedling growth is mainly controlled by changes in salinity and the mortality by seasonal flooding, while in the bare areas, regeneration is aggravated by extremely high salinities, high soil temperatures and dessication of the top soil layers. The establishment of the small A. germinans and L. racemosa propagules is especially difficult, because they cannot establish themselves in flooded soils and in direct sunlight they dry out rapidly. The seedlings of both species are also very sensitive to changes in water level, wind, waves, temperatures exceeding 45 °C and dry soils. In A. germinans, phytophagous insects affect the chances for survival also. Therefore, mortality in both species is extremely high. R. mangle is much more resistant to most detrimental factors observed with the exception of high salinities. However, there is one favourable factor at the open sites. When sufficient water is present and salinities as well as temperatures are low enough, the high light availability increases growth rates and survival.