Dieback of rural trees in Australia

Much of Australia's woody vegetation has been cleared since European settlement, allowing extensive agricultural and pastoral industries to develop. Although scattered stands of native trees were often left on farmland, many of these trees are now in decline, particularly in regions where farm management is intensive. Rural dieback is a dramatic manifestation of this decline, and is characterized by a widespread, relatively recent upsurge of premature dieback and death of trees on farms. Comparatively little is known of its aetiology. Possible causal agents include insects, pathogens, drought and changes in the properties of soils or groundwater. We review and assess the evidence implicating each of these factors, and outline a conceptual model that demonstrates how several of them may be undesirable side effects of an intensification of pastoral management. The model shows how several different factors may interact to contribute to tree stress, and how dieback may eventuate if any one of them intensifies. Negative feedbacks operate between insect damage and the epicormic foliage that eucalypts produce in response to it, and also between dieback-related tree deaths and a worsening of the environmental degradation that contributed to the onset of dieback. These negative feedbacks will have most impact in those rural areas in which trees have become predisposed to chronic defoliation because of management practices or other environmental factors.     

Water contents, temperatures and diversity of the magmas of the catastrophic eruption of Nevado del Ruiz, Colombia, November 13, 1985

The petrology of the highly phyric two-pyroxene andesitic to dacitic pyroclastic rocks of the November 13, 1985 eruption of Nevado del Ruiz, Colombia, reveals evidence of: (1) increasingly fractionated bulk compositions with time; (2) tapping of a small magma chamber marginally zoned in regard to H₂O contents (1 to 4%), temperature (960–1090°C), and amount of residual melt (35 to 65%); (3) partial melting and assimilation of degassed zones in the hotter less dense interior of the magma chamber; (4) probable heating, thermal disruption and mineralogic and compositional contamination of the magma body by basaltic magma “underplating”; and (5) crustal contamination of the magmas during ascent and within the magma chamber. Near-crater fall-back or “spill-over” emitted in the middle of the eruptive sequence produced a small pyroclastic flow that became welded in its central and basal portions because of ponding and thus heat conservation on the flat glaciated summit near the Arenas crater. The heterogeneity of Ruiz magmas may be related to the comparatively small volume (0.03 km³) of the eruption, nearly ten times less than the 0.2 km³ of the Plinian phase of Mount St. Helens, and probable steep thermal and P_H2O gradients of a small source magma chamber, estimated at 300 m long and 100 m wide for an assumed ellipsoidal shape.     

Some problems in planning the office economy in a third world city: the example of Tunis

While the office economy has been studied extensively in the advanced industrial nation, it has been overlooked in the context of the developing country. Based on a case-study of Tunis it is shown how the growth of office activities in the central area has exacerbated the planning problems of the city's core. Planning policies designed to control the rate of office growth in the central area and encourage its suburban decentralization have been introduced. However, achievements to date on either of these two aims have been limited, reflecting political, administrative and fiscal problems which limit the effectiveness of planning in the city as a whole.     

Community structure of the demersal fish species of Laguna Joyuda,Puerto Rico

A year-long trawl survey of the mangrove-fringed Laguna Joyuda, Puerto Rico yielded 41 species of juvenile and adult fishes. Twelve percent of the species and 55% of the individuals were residents in the lagoon; 56% of the species and 44% of the individuals were cyclic visitors, mostly juveniles of species which spawn offshore. The lagoon yielded fewer species than tropical estuaries in continental regions of the Caribbean and temperate estuaries of North America. However, paralleling other estuarine habitats, Laguna Joyuda supported three primary types of fishes, a resident small flatfish (Achirus lineatus), a complex of transient juveniles (Gerreidae, paralleling the Sciaenidae of higher latitudes), and small planktivores (Anchoa spp.). Seasonal patterns in the abundance of individual species were not strong, but overall abundance showed a wet season maximum, particularly because of recruitment of anchovies and cyclic visitors in April, May, and June. Wet season abundance corresponded with highest water column productivity and detrital input to the benthos. Fishes associated with the water column appeared to show greater variation in abundance than those associated with more stable benthic food webs.     

Factors affecting boundary-layer wind shear over the Indian Ocean during FGGE

Statistics on the vertical wind shear in the boundary layer over the Indian Ocean were examined for the causes of regional and seasonal changes. Low-level cloud motions and surface ship wind reports were used to define the vertical shear. Temperature data from the ship reports were analyzed for boundary-layer stability related to the observed shears. Smaller wind shears were found in areas of large negative air-sea temperature difference (unstable boundary layers). The thermal wind effects were very small over most of the tropical Indian Ocean. The largest factor affecting the speed shear was the strength of the wind itself. Larger speed shear was found under high wind conditions. A small reduction in the direction difference between cloud and ship observations also was found under higher speeds. The scatter of cloud-ship comparisons around the mean (dispersion) also decreased for higher wind speeds. Daily gridded cloud motion and ship wind speed data had a correlation coefficient of 0.8 with a scatter of 1.9 m s^-1 (r.m.s.) around the mean difference.     

RbSr study of dolerite dikes and psammite from the Western Gneiss region of Norway

The Saetra Nappe, consisting of feldspathic psammite cut by pre-tectonic dolerite dikes, is a distinctive tectonostratigraphic unit of the Western Gneiss Region of Norway. Although the rocks were metamosphosed at amphibolite facies, RbSr whole-rock sf three well preserved dikes a date of $\text{745 ± 37}\text{Ma}$ with initial ${}^{87}\text{Sr}\text{/}{}^{86}\text{Sr}\text{= .7046}$, interpreted to record the dike intrusion. Analysis of small psammite samples collected in rows parallel to the foliation and in columns perpendicular to it, indicate that the RbSr isotopic systems were not equilibrated on the whole-rock scale. The Strata Nappe provides evidence of a strong Caledonian deformation/metamorphic event in the Western Gneiss Region of Norway.     

Alluvial, eolian and lacustrine sedimentology of a Paleoproterozoic half-graben, Baker Lake Basin, Nunavut, Canada

The northeast-trending Baker Lake sub-basin was a volcanically active, half-graben during deposition of ca. 1.85–1.76 Ga Baker Lake Group. Drainage was oriented along transverse and axial directions with flow to playa lake and deeper perennial lacustrine depocentres. Basin marginal, streamflow-dominated alluvial fans were concentrated along the southern margin, and provided sediment from Archean crystalline basement rocks. These fed transverse gravel- and sand-bed braided streams. Alluvial dynamics were characterized by channel aggradation and abandonment. Abandoned channel belts were sites of floodplain and eolian deposition. Basin axial braided streams fed northeast and southwest to a depocentre near Christopher Island, where eolian, playa and lacustrine environments were intimately linked. Felsic minette flows were initially erupted from localized centres; contemporaneous sedimentary deposits typically contain minor volcaniclastic components that increase in abundance basinward. Voluminous and widespread younger minette flows prograded outward from volcanic centres contributing significant additional basin-infill.