Predicting the retreat and migration of tidal forests along the northern Gulf of Mexico under sea-level rise

Tidal freshwater forests in coastal regions of the southeastern United States are undergoing dieback and retreat from increasing tidal inundation and saltwater intrusion attributed to climate variability and sea-level rise. In many areas, tidal saltwater forests (mangroves) contrastingly are expanding landward in subtropical coastal reaches succeeding freshwater marsh and forest zones. Hydrological characteristics of these low-relief coastal forests in intertidal settings are dictated by the influence of tidal and freshwater forcing. In this paper, we describe the application of the Sea Level Over Proportional Elevation (SLOPE) model to predict coastal forest retreat and migration from projected sea-level rise based on a proxy relationship of saltmarsh/mangrove area and tidal range. The SLOPE model assumes that the sum area of saltmarsh/mangrove habitat along any given coastal reach is determined by the slope of the landform and vertical tide forcing. Model results indicated that saltmarsh and mangrove migration from sea-level rise will vary by county and watershed but greater in western Gulf States than in the eastern Gulf States where millions of hectares of coastal forest will be displaced over the next century with a near meter rise in relative sea level alone. Substantial losses of coastal forests will also occur in the eastern Gulf but mangrove forests in subtropical zones of Florida are expected to replace retreating freshwater forest and affect regional biodiversity. Accelerated global eustacy from climate change will compound the degree of predicted retreat and migration of coastal forests with expected implications for ecosystem management of State and Federal lands in the absence of adaptive coastal management.     

Predicting youth participation in urban agriculture in Malaysia: insights from the theory of planned behavior and the functional approach to volunteer motivation

This study examines factors associated with the decision of Malaysian youth to participate in a voluntary urban agriculture program. Urban agriculture has generated significant interest in developing countries to address concerns over food security, growing urbanization and employment. While an abundance of data shows attracting the participation of young people in traditional agriculture has become a challenge for many countries, few empirical studies have been conducted on youth motivation to participate in urban agriculture programs, particularly in non-Western settings. Drawing on the theories of planned behavior and the functional approach to volunteer motivation, we surveyed 890 students from a public university in Malaysia about their intention to join a new urban agriculture program. Hierarchical regression findings indicated that the strongest predictor of participation was students’ attitude toward urban agriculture, followed by subjective norms, career motives and perceived barriers to participation. The findings from this study may provide useful information to the university program planners in Malaysia in identifying mechanisms for future students’ involvement in the program.     

Leaf gas exchange characteristics of three neotropical mangrove species in response to varying hydroperiod

We determined how different hydroperiods affected leaf gas exchange characteristics of greenhouse-grown seedlings (2002) and saplings (2003) of the mangrove species Avicennia germinans (L.) Stearn., Laguncularia racemosa (L.) Gaertn. f., and Rhizophora mangle L. Hydroperiod treatments included no flooding (unflooded), intermittent flooding (intermittent), and permanent flooding (flooded). Plants in the intermittent treatment were measured under both flooded and drained states and compared separately. In the greenhouse study, plants of all species maintained different leaf areas in the contrasting hydroperiods during both years. Assimilation-light response curves indicated that the different hydroperiods had little effect on leaf gas exchange characteristics in either seedlings or saplings. However, short-term intermittent flooding for between 6 and 22 days caused a 20% reduction in maximum leaf-level carbon assimilation rate, a 51% lower light requirement to attain 50% of maximum assimilation, and a 38% higher demand from dark respiration. Although interspecific differences were evident for nearly all measured parameters in both years, there was little consistency in ranking of the interspecific responses. Species by hydroperiod interactions were significant only for sapling leaf area. In a field study, R. mangle saplings along the Shark River in the Everglades National Park either demonstrated no significant effect or slight enhancement of carbon assimilation and water-use efficiency while flooded. We obtained little evidence that contrasting hydroperiods affect leaf gas exchange characteristics of mangrove seedlings or saplings over long time intervals; however, intermittent flooding may cause short-term depressions in leaf gas exchange. The resilience of mangrove systems to flooding, as demonstrated in the permanently flooded treatments, will likely promote photosynthetic and morphological adjustment to slight hydroperiod shifts in many settings.     

Pea Aphids (Hemiptera: Aphididae) Have Diurnal Rhythms When Raised Independently of a Host Plant

Seasonal timing is assumed to involve the circadian clock, an endogenous mechanism to track time and measure day length. Some debate persists, however, and aphids were among the first organisms for which circadian clock involvement was questioned. Inferences about links to phenology are problematic, as the clock itself is little investigated in aphids. For instance, it is unknown whether aphids possess diurnal rhythms at all. Possibly, the close interaction with host plants prevents independent measurements of rhythmicity. We reared the pea aphid Acyrthosiphon pisum (Harris) on an artificial diet, and recorded survival, moulting, and honeydew excretion. Despite their plant-dependent life style, aphids were independently rhythmic under light–dark conditions. This first demonstration of diurnal aphid rhythms shows that aphids do not simply track the host plant’s rhythmicity.     

Stimulation of nicotine demethylation by NaHCO(3) treatment using greenhouse-grown burley tobacco

Experiments were conducted in tobacco (Nicotiana tabacum L.) to investigate the effect of sodium bicarbonate (NaHCO(3)) on the conversion of nicotine to nornicotine, a secondary alkaloid that can form the tobacco-specific nitrosamine N-nitrosonornicotine (NNN). The results showed that, under optimum conditions, NaHCO(3) stimulated nicotine conversion in converter plants to the maximum level predetermined by the genetic background. The conversion level in NaHCO(3)-treated leaves was 2-3 times higher than that in control leaves. For young seedlings the optimum concentration of sodium bicarbonate was 0.8% aqueous solution, and for adult plants the optimum concentration was 1%. Lower concentrations resulted in partial stimulation, whereas higher concentration damaged leaf tissue and resulted in a lower conversion level. Studies with different temperatures (from 22 to 43 degrees C) showed that 37 degrees C was optimal. This temperature allowed the least amount of time, 2-3 days for mature leaves and 4-6 days for green leaves, for the major converters to reach >95% of nicotine conversion. An examination of leaves from different growth stages and stalk positions showed that the amount of time needed for conversion was longer for young leaves and shorter for mature leaves. Treatment of leaves with NaHCO(3) affords a rapid and convenient means of identifying and removing nornicotine converter plants during growth in the greenhouse or field.     

PAHs in SD:Polycyclic aromatic hydrocarbons levels in street dust in the central area of Niterói City, RJ, Brazil

Polycyclic aromatic hydrocarbons (PAHs) were studied in street dust (SD) samples collected in the center of Niterói, a tropical city located in the State of Rio de Janeiro, Brazil, at the margins of Guanabara Bay. Sampling was carried out monthly during the year of 2002 in order to evaluate seasonal variation of PAH concentrations. Samples were extracted by ultrasonic treatment with dichloromethane, cleaned up by solid phase extraction and analyzed by gas chromatography-mass spectrometry. The concentrations of the twenty one analyzed PAHs ranged from 3.2 to 132 ng/g. Of all PAHs, pyrene, fluoranthene and naphthalene showed the highest geometric means. Total PAH concentration (σPAH) ranged from 434 to 1247 ng/g with levels of carcinogenic PAHs (σCARC) representing 29 to 45% of σPAHs. The highest value of σPAH occurred in July 2002, when the lowest temperatures were measured in the Central Area of Niterói City. σPAH and σCARC showed significant correlations with daily mean and minimum temperature, as well as with temperature during sampling, indicating that both are influenced by these parameters. The obtained results suggest that a seasonal variation of total PAH levels in SD may occur in the studied area.     

How do local habitat management and landscape structure at different spatial scales affect fritillary butterfly distribution on fragmented wetlands?

Habitat fragmentation, patch quality and landscape structure are important predictors for species richness. However, conservation strategies targeting single species mainly focus on habitat patches and neglect possible effects of the surrounding landscape. This project assesses the impact of management, habitat fragmentation and landscape structure at different spatial scales on the distribution of three endangered butterfly species, Boloria selene, Boloria titania and Brenthis ino. We selected 36 study sites in the Swiss Alps differing in (1) the proportion of suitable habitat (i.e., wetlands); (2) the proportion of potential dispersal barriers (forest) in the surrounding landscape; (3) altitude; (4) habitat area and (5) management (mowing versus grazing). Three surveys per study site were conducted during the adult flight period to estimate occurrence and density of each species. For the best disperser B. selene the probability of occurrence was positively related to increasing proportion of wetland on a large spatial scale (radius: 4,000 m), for the medium disperser B. ino on an intermediate spatial scale (2,000 m) and for the poorest disperser B. titania on a small spatial scale (1,000 m). Nearby forest did not negatively affect butterfly species distribution but instead enhanced the probability of occurrence and the population density of B. titania. The fen-specialist B. selene had a higher probability of occurrence and higher population densities on grazed compared to mown fens. The altitude of the habitat patches affected the occurrence of the three species and increasing habitat area enhanced the probability of occurrence of B. selene and B. ino. We conclude that, the surrounding landscape is of relevance for species distribution, but management and habitat fragmentation are often more important. We suggest that butterfly conservation should not focus only on a patch scale, but also on a landscape scale, taking into account species-specific dispersal abilities.     

Salinity effects and differential germination of several half-sib families of baldcypress from different seed sources

Saltwater intrusion is responsible for the destruction of large expanses of baldcypress swamps along the Gulf of Mexico in the southern United States. Recent restoration efforts have focused on the identification, and subsequent planting, of moderately salt-tolerant plant material within these ghost forests. The long-term persistence of cypress swamps in these areas, however, will ultimately depend on the germination of seeds from the improved parent trees. This study investigates the germination capacity of seeds collected from baldcypress parent trees, located in both freshwater and brackish water environments. Seeds were tested at four different salinity levels under controlled conditions for a period of 65 days. Mean germination under the 0, 2, 4, and 6 g l^-1 seawater treatments was 26.3, 22.9, 15.4, and 10.2%, respectively. Although none of the eight families used in this study had a germination greater than 50%, three families demonstrated superiority in their germination capacity under all four salinity treatments. In general, brackish water seed sources had greater germination success than the two families from freshwater sources. Results indicate that families previously identified as moderately salt-tolerant based on physiological and morphological parameters may be equally successful in seed germination capacity under moderately saline conditions.     

Pests and diseases in agroforestry systems of the humid tropics

Few studies have included detailed investigations of the interactions of agroforestry techniques with pests and diseases, although the relevance of such interactions has long been recognized. The objectives of this review are to provide basic information on pests and diseases in tropical agroforestry systems and to develop concepts which can assist in the future in the systematic data collection and analysis in this field. The emphasis is on simultaneous agroforestry systems with annual and perennial crops, although rotational systems are also discussed. Crop rotation is an important pest and disease control strategy in annual cropping systems, and the principle of altering host with non-host plants can also be applied in improved fallow systems, provided that hosts of crop pests and diseases are avoided when selecting the fallow species. When annual cropping systems are transformed into simultaneous agroforestry, the control strategy of frequent disturbance of pest and disease populations is to some extent substituted for the strategy of increased stability and internal control mechanisms. However, reduced pest and disease risk is not automatically achieved by introducing perennial plants and increasing the plant diversity in a system. If plant species are introduced that harbor pests or diseases of other species in the system, the risk of pest and disease outbreaks may actually increase. For evaluating such risks, it is important to consider host-ranges of diseases on the pathovar instead of the species level. Beside the selection of compatible plant species, their spatial arrangement may be important for reducing the spread of pest and disease organisms through the system, although little information is available on such effects, and they may be largely irrelevant for organisms with efficient dispersal mechanisms such as wind-dispersed fungi. In addition to the species-specific, biological effects of plants on pests and diseases, their unspecific, physical effects can be of major relevance for pest and disease development as well as the susceptibility of the affected plant species. Increased pest and disease incidence has often been observed directly at the tree-crop interface, caused by the humid microclimate, physical protection of mammal and bird pests by the trees and eventually reduced pest and disease tolerance of competition-stressed crops. Linear tree plantings and hedgerows affect the wind transport of small insects and disease propagules, the active immigration and emigration of pest organisms as well as the populations of natural enemies. Similarly, overhead shade has a major effect on the micro-climatic conditions under which pest and disease organisms, their natural enemies and the crops themselves develop, and its optimization is a highly efficient control strategy for many pests and diseases. On infertile soils, the susceptibility of crops to pests and diseases is strongly affected by the availability of plant nutrients, which may be influenced by agroforestry techniques in various ways. Soil management measures such as mulching and planting cover crops may affect crop health by improving soil fertility and by directly acting on pest and disease populations. The importance of a more systematic collection of pest and disease related information for agroforestry, e.g., in a central database, and of the development of strategies for reducing pest and disease risks in agroforestry in cooperation with farmers is stressed.This revised version was published online in November 2005 with corrections to the Cover Date.