Reproductive Ecology of Black Mangrove (<Emphasis Type="Italic">Avicennia germinans</Emphasis>) Along the Louisiana Coast: Propagule Production Cycles,Dispersal Limitations,and Establishment Elevations

Black mangrove (Avicennia germinans) reproduces by producing propagules through the process of cryptovivipary, which requires a significant energy investment. We conducted a series of field and greenhouse studies to track propagule production in years of high and low disturbances (i.e., hurricanes), the effects of time and salinity on propagule dispersal potential, and the relationship between hydrology and propagule establishment elevations. Trees tended to produce greater numbers of propagules in years after hurricanes, and individual trees alternated the amount of energy they invested in reproduction in consecutive years. In the greenhouse, propagule buoyancy was affected by salinity with propagules in 36 remaining buoyant for over 110 days and establishment success decreasing with dispersal period length. Finally, a field survey across five sites in southeastern Louisiana revealed that the 2009 cohort of propagules established at significantly lower elevations than mature trees occurred. These findings elucidate some salient features of black mangrove reproductive biology in the northern portion of its North American distribution.     

Use of Fossil Bryozoans in Sourcing Lithic Artifacts

This study reviews the occurrence and potential of bryozoans within lithic artifacts and also sets out a methodology for their use in sourcing and discusses the advantages and disadvantages of this approach. We present case studies from our own research and from the literature on using bryozoans in sourcing archaeological lithic artifacts. Fossil bryozoans of different ages and clades can be effectively used to determine the material source of lithic artifacts from a variety of prehistoric ages. The case studies included in this report span the stratigraphic range of bryozoans from the Ordovician to the Neogene. The bryozoans came from four different orders: trepostome, fenestrate, cyclostome, and cheilostome. The use of these lithic artifacts ranged back to 25 ka. Although the majority of the fossil bryozoans were incidental in the artifacts, the bryozoans were still useful for determining their original source rock. The improved searchable online paleontologic databases allow for more efficient use of fossil bryozoans to constrain the stratigraphic and paleogeographic distribution of source outcrops. Although generally underutilized in sourcing prehistoric lithic artifacts, it is clear that by analyzing bryozoans, an increased understanding of the lithologic nature of these materials could be gained by the archaeological community.     

Cassini RADAR observations of Enceladus, Tethys, Dione, Rhea, Iapetus, Hyperion, and Phoebe

Cassini 2.2-cm radar and radiometric observations of seven of Saturn's icy satellites yield properties that apparently are dominated by subsurface volume scattering and are similar to those of the icy Galilean satellites. Average radar albedos decrease in the order Enceladus/Tethys, Hyperion, Rhea, Dione, Iapetus, and Phoebe. This sequence most likely corresponds to increasing contamination of near-surface water ice, which is intrinsically very transparent at radio wavelengths. Plausible candidates for contaminants include ammonia, silicates, metallic oxides, and polar organics (ranging from nitriles like HCN to complex tholins). There is correlation of our targets' radar and optical albedos, probably due to variations in the concentration of optically dark contaminants in near-surface water ice and the resulting variable attenuation of the high-order multiple scattering responsible for high radar albedos. Our highest radar albedos, for Enceladus and Tethys, probably require that at least the uppermost one to several decimeters of the surface be extremely clean water ice regolith that is structurally complex (i.e., mature) enough for there to be high-order multiple scattering within it. At the other extreme, Phoebe has an asteroidal radar reflectivity that may be due to a combination of single and volume scattering. Iapetus' 2.2-cm radar albedo is dramatically higher on the optically bright trailing side than the optically dark leading side, whereas 13-cm results reported by Black et al. [Black, G.J., Campbell, D.B., Carter, L.M., Ostro, S.J., 2004. Science 304, 553] show hardly any hemispheric asymmetry and give a mean radar reflectivity several times lower than the reflectivity measured at 2.2 cm. These Iapetus results are understandable if ammonia is much less abundant on both sides within the upper one to several decimeters than at greater depths, and if the leading side's optically dark contaminant is present to depths of at least one to several decimeters. As argued by Lanzerotti et al. [Lanzerotti, L.J., Brown, W.L., Marcantonio, K.J., Johnson, R.E., 1984. Nature 312, 139-140], a combination of ion erosion and micrometeoroid gardening may have depleted ammonia from the surfaces of Saturn's icy satellites. Given the hypersensitivity of water ice's absorption length to ammonia concentration, an increase in ammonia with depth could allow efficient 2.2-cm scattering from within the top one to several decimeters while attenuating 13-cm echoes, which would require a six-fold thicker scattering layer. If so, we would expect each of the icy satellites' average radar albedos to be higher at 2.2 cm than at 13 cm, as is the case so far with Rhea [Black, G., Campbell, D., 2004. Bull. Am. Astron. Soc. 36, 1123] as well as Iapetus.     

The impacts of the 2004 hurricanes on hydrology, water quality, and seagrass in the Central Indian River Lagoon, Florida

Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, and Jeanne) affected the central Indian River Lagoon (IRL). The central IRL received a prodigious amount of rainfall for the 2 mo, between 72 and 83 cm, which is a once-in-50-yr rainfall event. High stream discharges were generated that, combined with wind-suspended sediments, significantly reduced salinities and water transparency. In September, salinities among central IRL segments dropped from 30 psu or more to ≤15 psu, color increased from a low of 10 pcu to ≥100 pcu, and turbidity increased from ≤3 NTU up to 14 NTU. Evidence of the hurricanes' physical effects on seagrasses (burial, no scour) was limited to just one of the more than 25 sites inspected. Within 2 to 3 mo following the hurricane period, most parameters related to water transparency returned to or showed improvement over their prehurricane (February–July 2004) levels. Unseasonably low salinities (<20 psu) and moderately high color (>20 pcu) were observed through spring 2005, largely attributable to a relatively long residence time and a wetter-than-average spring season in 2005. By the end of the study period (July 2006), the central IRL generally showed a continuation of two opposite seagrass trends—an increase in depthlimit coverage but a decline in coverage density—that began before 2004. Also, within a limited reach of the central IRL, there was a temporary shift in species composition in summer 2005 (Ruppia maritima increased asHalodule wrightü decreased). It is likely that the persistently low salinities (not color) in 2004–2005 affected the species composition and coverage density. This study reveals that seagrasses are resilient to the acute effects of hurricanes and underscores the need to reduce chronic, an thropogenic effects on seagrasses.     

Delving into Allende's dark secrets

What are the strange dark clasts within carbonaceous chondrites? How did they form? And what do they tell us about the early solar system? Mark Sephton, one of a team investigating the Allende meteorite, summarizes their findings.     

Resident action groups in Sydney: people power or rat‐bags?

This paper presents an analysis of a neglected area of study by geographers; that of resident action groups. During the 1980s there has been a significant increase in the number of resident action groups throughout Sydney. Resident activism has influenced local planning processes, the location of noxious facilities and subsequent urban form. This has initiated important reactions by government at both the local and State levels. Urban collective activisms have been hypothesised as single‐issue, self‐serving nimby groups. However, RAGs are also empowering forces, in which women and men are introduced to the political structures and become engaged in protest and resistance that can challenge the social and spatial order. RAGs can, either singularly or cumulatively, force a re‐aligning of existing power relations, and they can necessitate changed modes of governance (or govern‐mentality).     

Annual growth zones in stems of Hypericum irazuense (Guttiferae) in the Costa Rican páramos

The high peaks of the Cordillera de Talamanca in Costa Rica support shrub- and grass-dominated páramo ecosystems that experience stand-replacing wildfires. The dry season that facilitates these fires results in dormancy in plant growth and provides an opportunity to use dendrochronological analyses to determine ages of plants in burn sites to support studies of fire history and postfire vegetation recovery. This study investigates the formation of annual growth zones in stems of the common shrub Hypericum irazuense. Unlike other páramo shrubs, H. irazuense rarely resprouts following fire, instead recovering through seedling recruitment following seed dispersal from the unburned periphery. Laboratory analysis of 19 prepared cross sections from 15 stems shows that samples of H. irazuense from burned areas can provide an estimate of the minimum number of years since the previous fire, supporting earlier work based on field examination of stems. Including a time lag for seedling recruitment or resprouting refines that estimate. Counts of growth zones in most sections coincided with dates of the last known fires. The presence of annual growth zones in H. irazuense places the species within a relatively small group of woody Neotropical species for which annual rings or growth zones have been demonstrated.     

Book reviews

BURNING BUSH: a fire history of Australia by S.J. Pyne. 15 × 23 cm, xix + 520 pp. Allen & Unwin, Sydney 1992. (ISBN 1–86373–194–6) $19–95 (soft).

ADVANCES IN RESOURCE MANAGEMENT: tributes to W.R. Derrick Sewell edited by H.D. Foster. 15 × 23 cm, viii + 366 pp. Belhaven Press, London 1992 (ISBN 1–85293–292‐ 9) £39.50 (hard).

FEMINISM AND GEOGRAPHY: the limits to geographical knowledge by G. Rose. 15 × 23 cm, 205 pp. Polity Press, Cambridge 1993. (ISBN 0–7456–1156–7) $34.95 (soft).

EVERYDAY LIFE: women's adaptive strategies in time and space (Lund Studies in Geography, Ser.B Human Geography 55) by T. Friberg (translated by M. Gray). 16 × 24 cm, 217 pp. Lund University Press, Lund, and Chartwell‐Bratt, Bromley 1993. (ISBN 0‐ 86238–345–5)

NATURAL DISASTERS by D. Alexander. 16 × 23 cm, xix + 632 pp. University College London Press, London 1993 (ISBN 1–85728–094–6) $55.00 (soft).