Coastal Swamp Forests Research Articles

Fire in the Swamp Forest: Palaeoecological Insights Into Natural and Human-Induced Burning in Intact Tropical Peatlands

Tropical peat swamp forests are invaluable for their role in storing atmospheric carbon, notably in their unique below-ground reservoirs. Differing from terra firme forests, the peat-forming function of tropical swamps relies on the integrity of discrete hydrological units, in turn intricately linked to the above-ground woody and herbaceous vegetation. Contemporary changes at a local, e.g. fire, to global level, e.g. climatic change, are impacting in the integrity and functioning of these ecosystems. In order to determine to what extent and predict their likely future response, it is essential to understand past ecosystem disturbance and resilience. Here, we explore the impact of burning on tropical peat swamp forests. Fires within degraded tropical peatlands are now commonplace; whilst fires within intact peat swamp forests are thought to be rare events. Yet little is known about their long-term natural fire regime. Using fossil pollen and charcoal data from three peat cores collected from Sarawak, Malaysian Borneo, we looked at the incidence and impact of local and regional fire on coastal peat swamp forests over the last 7000 years. Palaeoecological results demonstrate that burning has occurred in these wetland ecosystems throughout their history, with peaks corresponding to periods of strengthened ENSO. However, prior to the Colonial era c. 1839 when human presence in the coastal swamp forests was relatively minimal, neither local nor regional burning significantly impacted on the forest vegetation. After the mid-19th Century, at the onset of intensified land-use change, fire incidence elevated significantly within the peatlands. Although fire does not correlate with past vegetation changes, the long-term data reveal that open vegetation, a proxy for human forest clearance, does follow a similar pattern. Our results suggest that human activity may be strongly influencing and acting synergistically with fire in the recent past, leading to the enhanced degradation of these peatland ecosystems. However, intact tropical peat swamp forests can and did recover from local fire events. These findings support present-day concerns about the increase in fire incidence and combined impacts of fire, human disturbance and El Nino on peat swamp forests, with serious implications for biodiversity, human health and global climate change.

Impacts of alien grass invasion in coastal seed banks vary amongst native growth forms and dispersal strategies

Alien plant invaders frequently reduce biodiversity of native communities, but the mechanisms of impact remain poorly understood. We used the seedling emergence method to assess impacts of invasion by an alien, clonal grass (Stenotaphrum secundatum) on endangered coastal swamp forest seed banks of eastern Australia. We asked: do impacts vary amongst native plant growth forms and dispersal strategies, and are impacts driven by propagule or recruitment limitation? Invasion was associated with significant reductions in seed bank species richness and increased dissimilarity between the seed bank and standing vegetation. The rate of species loss was more than two times greater within the standing vegetation than seed bank, however, indicating that the primary mechanism of community change is limited recruitment from the seed bank rather than a reduction in the arrival and storage of propagules to invaded sites. Overall, species losses were observed for herbs, graminoids and vertebrate-dispersed species, whilst wind and water dispersed and woody species were unaffected by invasion. Overall, seed banks were substantially richer than the standing vegetation across both invaded and non-invaded sites, indicating a high potential for unassisted reestablishment of a species-rich standing vegetation from the seed bank following S. secundatum removal, although one unlikely to resemble the original community in structure, function and identity of species. Differential impacts across functional groups may result in regenerating communities relatively dominated by woody species, which may prevent subsequent recolonisation by herbs and graminoids. Monitoring will be required to identify whether these and other species require assisted reintroduction.

Foraging Ranges of Insectivorous Bats Shift Relative to Changes in Mosquito Abundance

The need to develop effective management strategies for insectivorous bat populations requires an understanding of factors influencing habitat use. Availability of pest prey, such as mosquitoes is likely to be one such factor. To assess whether this is the case, we radio-tracked Vespadelus vulturnus Thomas (little forest bat), a predator of Aedes vigilax Skuse (saltmarsh mosquito), in saltmarsh and adjacent coastal swamp forest during periods of high and low Ae. vigilax abundance. When mosquito abundance in structurally-open saltmarsh was similar to the more cluttered coastal swamp forest, use of saltmarsh by V. vulturnus was disproportionately greater than its availability, with saltmarsh selected preferentially for foraging. However, at times of low Ae. vigilax abundance in saltmarsh, use of saltmarsh by V. vulturnus was reduced and all habitats were used in proportion to availability in the study area. This is the first radio-tracking study to demonstrate a shift in foraging range by an insectivorous bat species correlated with fluctuations in the distribution and abundance of a particular prey resource. The shift in foraging range by V. vulturnus, corresponding with a spatio-temporal variation in abundance of Ae. vigilax highlights the importance of mosquitoes as a dietary item. Broadscale pest control of Ae. vigilax may have ecological implications for the diet and habitat use of V. vulturnus. An adaptive management approach is proposed, whereby careful monitoring of insectivorous bat populations is recommended before and after any application of broadscale mosquito control measures. We also suggest a precautionary approach is taken such that broadscale control of mosquitoes avoids the lactation period of bats, a time when their energetic demands are greatest and when there is reduced risk of contracting mosquito-borne diseases transmitted by Ae. vigilax.

Use of sediment amendments to rehabilitate sinking coastal swamp forests in Louisiana

Coastal wetlands are losing elevation worldwide, so that techniques to increase elevation such as sediment amendment might benefit these wetlands. This study examined the potential of sediment amendment to raise elevation and support the production and regeneration of vegetation in coastal forests in Louisiana. Before sediment amendment, the vegetation did not differ in these Taxodium distichum–Nyssa aquatica forests with respect to herbaceous and tree seedling composition, and sapling and tree characteristics. After the application of sediment in January 2007, sediment-amended swamps had higher elevations and salinity levels than natural swamps. The layer of sediment applied to Treasure Island in Jean Lafitte National Historic Park and Preserve was relatively deep (sediment depth at Site One and Site Two: 0.89 and 0.69m, respectively, six months after application), and may have exceeded an optimal threshold. Sediment-amended swamp with the highest elevation had some tree mortality and little tree growth of T. distichum. Also, sediment-amended swamp had higher root biomasses of ruderal species, and lower species richness and cover of herbaceous species. Nevertheless, during controlled water releases during an oil spill emergency in 2010, both sediment-amended and reference forest had higher production levels than in other years. While sediment amendment is a compelling management alternative for sinking coastal wetlands, optimal thresholds were not determined for these T. distichum–N. aquatica swamps.

Climate change threatens coexistence within communities of Mediterranean forested wetlands.

The Mediterranean region is one of the hot spots of climate change. This study aims at understanding what are the conditions sustaining tree diversity in Mediterranean wet forests under future scenarios of altered hydrological regimes. The core of the work is a quantitative, dynamic model describing the coexistence of different Mediterranean tree species, typical of arid or semi-arid wetlands. Two kind of species, i.e. Hygrophilous (drought sensitive, flood resistant) and Non-hygrophilous (drought resistant, flood sensitive), are broadly defined according to the distinct adaptive strategies of trees against water stress of summer drought and winter flooding. We argue that at intermediate levels of water supply the dual role of water (resource and stress) results in the coexistence of the two kind of species. A bifurcation analysis allows us to assess the effects of climate change on the coexistence of the two species in order to highlight the impacts of predicted climate scenarios on tree diversity. Specifically, the model has been applied to Mediterranean coastal swamp forests of Central Italy located at Castelporziano Estate and Circeo National Park. Our results show that there are distinct rainfall thresholds beyond which stable coexistence becomes impossible. Regional climatic projections show that the lower rainfall threshold may be approached or crossed during the XXI century, calling for an urgent adaptation and mitigation response to prevent biodiversity losses.

Individual-based modeling of flooding and salinity effects on a coastal swamp forest

Coastal swamps are among the rapidly vanishing wetland habitats in Louisiana. Increased flooding, nutrient and sediment deprivation, and salt-water intrusion have been implicated as probable causes of the decline of coastal swamps. We developed a two-species individual-based forest succession model to compare the growth and composition of a cypress-tupelo swamp under various combinations of flooding intensity and salinity levels, using historical time-series of stage and salinity data as inputs. Our model simulates forest succession over 500 years by representing the growth, mortality, and reproduction of individual Taxodium distichum (baldcypress) and Nyssa aquatica (water tupelo) trees in a 1-km 2 spatial grid of 10 m × 10 m cells that vary in water levels and salinity through differences in elevation. We independently adjusted the elevations of each cell to obtain different grid-wide mean elevations and standard deviations of elevation; this affected the temporal and spatial pattern of flooding. We calibrated the model by adjusting selected parameters until averaged basal area, stem density and wood production rates under two different mean elevations (partially versus highly flooded) were qualitatively similar to comparable values reported for swamps in the literature. Corroboration involved comparing model predictions to four well-monitored contrasting habitat sites within the Maurepas Basin, Louisiana, USA. Model predictions of both species combined showed the same patterns among sites as the data, but the model overestimated wood production and the dominance of T. distichum. Exploratory simulations predicted that increased flooding leads to swamps with reduced basal areas and stem densities, while increased salinity resulted in lower basal areas at low salinity concentration (∼1–3 psu) and complete tree mortality at higher salinity concentrations (∼2–6 psu). Our model can provide insight into the succession dynamics of coastal swamps and information for the effective design of restoration actions.

Restoration of a coastal swamp forest in southeast Brazil

Restoration of degraded swamps often requires strong human intervention because of their fragility. In Brazil, coastal swamp forests are now much reduced by anthropogenic action. This paper investigates survival and growth performance of nine native shrub and tree species introduced into a degraded swamp invaded by exotic grasses and sedges in coastal Rio de Janeiro. Our central aim was to evaluate which species were more appropriate for use in initial stages of revegetation. Additionally, in separate field experiments, we tested statistical hypotheses that higher survival and growth performance would be found for seedlings: (a) taller in height, (b) subjected to shorter duration of flooding, and (c) planted with addition of organic matter inside the planting holes. Results were analyzed after 3 years of planting. “Planting in mounds”, and a consequent reduction on the flooding period plants are exposed to, increased survival and growth. The use of taller seedlings often increased survival, and organic matter addition increased growth. Three (Myrsine rubra, Tabebuia cassinoides, and Calyptranthes brasiliensis) out of nine species tested showed high growth- and use-viability indices, and were therefore indicated for use in revegetation programs. Interspecific variation as regards responses to the treatments applied suggests that in the future, species evaluated for this purpose, should be examined on a case-by-case basis.

Akodon montensis (Thomas, 1913) (Muridae) as a disperser of endozoochoric seeds in a coastal swamp forest of southern Brazil

Akodon montensis (Thomas, 1913) (Muridae) as a disperser of endozoochoric seeds in a coastal swamp forest of southern Brazil

Orangutan Sociality, Tool Use, and Human CultureAmong Orangutans: Red Apes and the Rise of Human Culture. By Carel vanSchaik. Cambridge: Belknap Press of Harvard University Press, 2004.

It has long been believed that culture is one of the critical characters which divide human from other animals, but decades of animal research have revealed that cultural differences maintained by social transmission are found in many nonhuman primates and in other animals. In particular, it is now well-documented that wild chimpanzees show cultural variations between local communities in many behavioural traits such as tool use, grooming, and courtship signals (Whiten et al 1999). In captivity, orangutans seem as intelligent as chimpanzees. They are excellent tool users and specialists in escaping from a cage. In contrast to the hyperactive chimpanzees, they are curious and patient enough to open a door if they happen to have substitutes for the key or a bar. However, few toolusing behaviours had been reported from wild orangutan populations. Carel van Schaik and colleagues have made a breakthrough discovery in this area. Van Schaik has been studying wild orangutans at Ketambe, North Sumatra, Indonesia, since 1976, but the story of this book begins with the discovery in 1993 of a population in a coastal swamp forest at Suaq Balimbing with one of the highest population densities of orangutans in the world. Their density is due in part to the inaccessibility of the swamp forest to humans and in part to the abundance of food in the forest. These orangutans are also more social (i.e., interact with other orangutans more frequently) than others; the stereotypical images of orangutans as solitary philosophers in the forest do not apply well to them. Finally, they are excellent tool users. Why do the orangutans at Suaq differ so much from others? In his attempt to answer this question van Schaik provides an excellent introduction to the latest primate socioecological theories. Socioecology deals with the relationship between social characteristics of species or populations and ecological conditions such as the distribution and abundance of food or predators. In plain words, van Schaik shows how the availability of food might affect the orangutans’ social characteristics, why orangutans grow and breed in slow motion, and how infanticide risk influences females’ social behaviour. On the basis of his findings van Schaik advances a new hypothesis about the evolution of intelligence and emergence of cultures (van Schaik and Pradhan 2003). He argues that the combination of individual learning (innovation) and social learning capabilities can be achieved through natural selection and that a tolerant or egalitarian nature towards group members, or “sociability,” plays an important role in the evolution of a high level of intelligence. His social learning hypothesis for the evolution of intelligence is different from the Machiavellian intelligence hypothesis (Byrne and Whiten 1988; Whiten and Byrne 1997), which regards the requirements of everyday social life as the most important factor: intelligence has evolved to cope with cooperative and/or competitive relationships with group members. These two hypotheses are not mutually exclusive and appear to operate at different stages of evolution. Finally, van Schaik attempts to draw some inferences about human nature from his findings. It is inevitable at this stage that this final chapter contains considerable speculation, but now we have good working hypotheses and can move on to a better understanding. In 1997–98, the most severe El Nino events of the century caused large-scale forest fires in Indonesia. Several million hectares of potential habitat for orangutans disappeared. At the same time, economic crisis hit the Southeast Asian countries, and Indonesia suffered the most severe damage from it. This caused political instability in both central and local governments and conflict among local peoples. Illegal logging, further forest fires, and poaching did immeasurable damage to wildlife. Van Schaik’s narrative never becomes emotional and accuses no one, but his deep sorrow is palpable. He is concerned about local extinctions and a possible loss of cultural diversity among orangutans. I strongly hope that this unique creature and its cultures will survive these difficult years.

A Holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at Batulicin, South Kalimantan, Indonesia

Pollen analysis of a coastal peat swamp core representing 9100 BP from Batulicin, South Kalimantan, Indonesia, shows that mangrove forest, with Rhizophora as its main element has been established since the early Holocene. Vegetation development in general, and particularly mangrove forest, was influenced by Holocene environmental changes. The highest value of Rhizophora at ca. 8200 BP indicates an early Holocene sea level drop and implies sea level at ca. −9 m. Subsequently mangrove forest was severely disrupted by rapid sea level rise at ca. 6400 BP prior to the Holocene Maximum. However, it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca. 6000 BP and flourished until ca. 1000 BP. From ca. 6000 BP, the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation. Human influence is recognized from ca. 1600 BP.

Paleoenvironmental Changes in the Semiarid Coast of Chile (∼32°S) during the Last 6200 cal Years Inferred from a Swamp–Forest Pollen Record

Pollen analysis of two sediment records from a coastal swamp forest site in the Chilean semiarid region (31°50′S; 71°28′W) shows an alternation of dry and wet phases during the past ∼6100 cal yr B.P. The most prominent vegetation changes occur at ∼4200 cal yr B.P., with the expansion of the swamp forest taxa Luma chequen and Escallonia sp., followed by a regression of the forest beginning at ∼3200 cal yr B.P. and ending with its replacement by a xerophytic scrub, between ∼1800 and 1300 cal yr B.P. The swamp forest reexpanded after ∼1300 cal yr B.P. and persisted, with minor variation, until the present. We interpret the establishment of the swamp forest at the study site to be the result of a rising watertable in response to increased rainfalls from ∼4200 cal yr B.P. onward. Our results indicate that in north-central Chile the second half of the Holocene was climatically more variable than previously thought, suggesting significant changes in the position and/or intensity of the westerlies wind belt and possibly in the frequency of El Niño–Southern Oscillation events.

Estimating the extent of floods in Bangladesh using SPOT data

Nine SPOT XS scenes recorded during the dry season (January, February) and after cyclonic storms were analyzed to evaluate both the extent and consequences of floods in Bangladesh, in the deltaic complex of the Ganges. Digital and visual analysis showed the following results: 1) Near the capital, Dahka, within a SPOT scene (3600 km 2), the extent of water varies from 324 km 2 during the dry season to 1303 km 2 after a destructive flood. This means that flood-prone areas in this overpopulated deltaic region are at least four times larger than the hydrographic network observed during the dry season. 2) The Sunderbans are the world's largest mangroves (about 6000 km 2 in a single block); two-thirds of this forest (4050 km 2) are in Bangladesh, and the rest is in India. These ecosystems seem to resist cyclones. No sign of any kind of mangrove alteration is seen on SPOT images recorded a few weeks after disastrous cyclonic storms (20 August 1987 and 6 September 1988). This is an important fact since the protective role of these coastal swamp forests is tremendously important. 3) The islands located in the very exposed area at the mouth of the Meghna are densely populated (more than 1000 inhabitants/km 2). Hathya island has been carefully surveyed. According to the investigations carried out on SPOT images (25 February 1987 and 26 October 1988), the island seems to be at present satisfactorily protected against cyclones and tidal surges, behind newly planted mangroves (Sonneratia apetala Buch.-Ham.) and sheltered by a complex network of embankments which are visible on the images. It was concluded that the spectral separability of classes (water, natural plant communities, land use units) and the geometric accuracy of SPOT are suitable for coastal monitoring in this part of the Bangladesh.

Blade Tissue Organization of Foliage Leaves of Some Carolina Shrub-Bog Species as Compared with Their Appalachian Mountain Affinities

1. Leaf blades of twenty-seven woody species of North Carolina have been studied. Leaves of fourteen species were collected from coastal shrub bogs; two, from coastal swamp forests; and eleven, from mesic forest habitats of the Appalachian mountain slopes. The selection of species was based upon a list prepared by B. W. Wells, showing how the shrubbog species have arisen: by geographical isolation from the Appalachians; by northern migration from the tropics; or by southern extension of boreal forms. Thus, the mountain species chosen are those that have Carolina coastal affinities. Conclusions are based upon comparative descriptive and statistical data from the group analyses as well as from data of the eight individual species pairs. 2. The leaves from both the shrub-bog and the mountain mesic forest collections are elliptical or modified elliptical, but the shrub-bog leaves are more perfectly elliptical. 3. The shrub-bog leaves are thick and, for the most part, coriaceous, evergreen, and heavily cuticularized, while those of the mesic forest are thinner, deciduous, and less cuticularized. 4. Greater volumes of palisade mesophyll account for most of the greater blade thickness of shrub-bog leaves as compared with the mesic mountain forms. The actual dermal volume for the two groups is about the same; both the palisade and the spongy mesophyll volumes are greater for the shrub-bog leaves, but the palisade volume is porportionally greater. 5. The shrub-bog leaf blades are smaller than are those of the mesic forest. Correlated with the smaller blade areas of the shrub-bog leaves are smaller surface areas of individual epidermal cells, smaller stomates, and higher stomatal frequencies. 6. Although the surface areas of epidermal cells are smaller for shrub-bog leaves, the cross-sectional area of the palisade cells for most of these leaves is larger; thus, the epidermal-palisade-cell ratio is smaller-that is, fewer palisade cells are contiguous to an epidermal cell. 7. In general, the shrub-bog leaves show less contrast between palisade and spongy mesophyll than do the mountain mesic forest leaves. For many of the bog leaves the vertically oriented palisade intergrades with a predominantly vertically oriented spongy mesophyll. 8. The radial walls of the epidermal cells are less sinuous in the shrub-bog leaves, especially in the leaves with thick cuticles. 9. The shrub-bog leaves have denser vein patterns than do the mesic leaves. 10. In the shrub-bog leaves the denser vein patterns are associated with greater palisade volumes and vertically oriented spongy mesophyll. 11. Five minor vein categories are described. Although all five patterns occur in leaves of both major groups studied, the dendriform, imbedded pattern is more frequent among shrub-bog leaves; veins carrying bundle sheath extensions and anastomosing around polygonal units of chlorenchyma occur more frequently among the mountain mesic leaves. 12. Those shrub-bog leaves which have anastomosing veins with bundle sheath extensions are the ones most heavily cuticularized. 13. The dendroid, imbedded vein patterns in the shrub-bog leaves are related to all-palisade mesophylls or to spongy mesophylls with predominantly vertically elongate and contiguous cells or parts of cells. 14. Leaves of both series have uniseriate dermal layers. 15. Crystal idioblasts and sclereids are associated with particular genera rather than with habitat. 16. Bundle sheath extensions are associated with anastomosing vein patterns rather than with dendriform vein patterns. 17. Hypotheses are proposed concerning the significance of certain blade characteristics of shrub-bog and mesic forest leaves, as to whether they are static, inherent characteristics or plastic responses to the immediate environment. The hypotheses are ones of induction based upon the occurrence of the blade characteristics within species groups or within individual species of paired affinities. Conclusions must be based upon experimental evidence.