Climate change, tree species distributions and forest dynamics: A case study in the mixed conifer/northern hardwoods zone of northern Europe

Three bioclimate variables (growing degree days after budburst, temperature of the coldest month and a moisture index) are used in a model (STASH) to predict potential range limits of north European tree species. CO₂-induced climate warming scenarios cause major changes in these limits. The dominant conifers of the mixed conifer/northern hardwoods zone, Picea abies and Pinus sylvestris, retreat from the south and west while Fagus sylvatica and other temperate hardwoods spread to the north. A gap model (FORSKA 2) is used to simulate the associated transient responses of a forest reserve within this zone. In both dry Pinus- and moist Picea- dominated forest communities, Picea continues to increase while Pinus sooner or later declines. These changes are continuing successional (non-climatic) responses to the cessation of disturbance 150 years ago. Climate warming speeds up the succession, and allows Fagus to establish and increase. The eventual decline of Picea however is delayed due to the persistence of old-growth stands. Picea forests subject to continuing disturbance show a more rapid shift to dominance by Fagus and other temperate hardwoods. Delayed immigration of new species, including Fagus, would favour earlysuccessional species such as Betula pendula and Quercus spp. in a forest with reduced biomass and diversity. The results emphasise the complex and sometimes counter-intuitive nature of transient responses, and the importance of considering disturbance history and potential migration rates when predicting the impacts of rapid climate change on forests.     

Environmental variables and their association with faecal coliform and faecal streptococci densities at thirteen Sydney beaches

Environmental variables and their association with faecal coliform and streptococci densities were investigated at a number of Sydney's metropolitan beaches. High variability in faecal coliform and faecal streptococci densities was observed at most beaches. The ability of the various models to explain the observed variation in faecal coliform or streptococci levels was relatively low, although they did provide an insight into the more influential environmental factors involved. Rainfall has the single most important effect on faecal coliform and streptococci densities at Sydney beaches. Whether this is due to increased stormwater runoff at the beaches, increased discharge through the outfalls (both the deepwater ocean outfalls and the few remaining shoreline outfalls), or a combination of both is unclear and is likely to depend on the individual beach being considered. Elevated levels of faecal coliforms and streptococci are still occasionally observed at some beaches, but these levels are usually not as high nor as frequent as they were prior to commissioning of the deepwater outfalls. The significant associations of current and plume entrapment with faecal coliform and streptococci densities at some Sydney beaches suggest that under certain conditions, effluent from the deepwater ocean outfalls can still influence faecal coliform and streptococci densities at these beaches.     

Non-Newtonian effects during injection in partially crystallised magmas

Injection of Newtonian crystal-free magmas into a partially crystallised host which may exhibit non-Newtonian properties produces magmatic structures such as pipes, syn-plutonic dikes or dendritic structures. Field relationships between the structure and the host rock commonly indicate what the rheological contrasts during the injection were. The manner in which a magma deforms in response to injection is mainly linked to crystal content and strain rate (i.e., injection rate). Three kinds of behaviour can be distinguished: (1) Newtonian at low crystal contents; (2) Non-Newtonian at intermediate (40–60%) crystal contents, or at high crystal contents if the strain rate is small; and (3) brittle failure at high crystal content or strain rates.Petrologic observations indicate that injection can take place when the host magma still behaves as a fluid. To investigate the physics of the injection process we review the results of injection experiments in non-Newtonian fluids. These experiments were performed to study viscous fingering in 2-D Hele Shaw cells. They provide the first step to establishing the main non-Newtonian effects during the formation of interfacial instabilities arising when a Newtonian fluid is injected into a more viscous fluid or paste. The qualitative comparison of the morphological features of the interfaces between the fluids in the experiments with those in nature suggests that, in magmas, irregularities of the interfaces (dikes and dendrites) result from non-Newtonian properties of the host. We conclude that fluid-like deformation, rather than brittle behaviour of the host, during injection is likely to produce the general features observed on the field. Cooling effects might be responsible for the widespread phenomenon of fragmentation. We emphasise that the main effect of non-Newtonian properties in partially crystallised magmas is to generate strongly heterogeneous media producing discontinuities which could explain the main morphological features of syn-plutonic injection structures.     

A consistent map of the postglacial uplift of Fennoscandia

A consistent map of the recent postglacial rebound of Fennoscandia is constructed on the basis of sea-level records, lake-level records and repeated high-precision levellings.
The uplift rates calculated from the sea-level series form a consistent framework of the map. The sea-level stations used are 56 reliable stations in the Baltic Sea and adjacent waters with series spanning 60 years or more, many of them about 100 years. Using a reference station in the Baltic Sea and another one outside the Baltic, all results are reduced to a common time span, the 100-year-period 1892–1991, in order to eliminate oceanographic changes. Inland, uplift differences are obtained from the repeated national levellings and, in four of the large lakes, from long water level series in pairs. The levellings, however, yield less accurate land uplift values than the sea-level and lake-level data.
The resultant map shows a fairly smooth phenomenon, with a maximum apparent uplift in the Gulf of Bothnia of 9.0 mm yr^-1. The standard error is typically 0.2 mm yr^-I close to the sea level stations, larger inland.
Finally the pattern of the present uplift as determined here is observed to be very similar to that of the past uplift as determined from ancient shore-lines of the Litorina Sea. However, the ratio between the past uplift and the present uplift rate tends to increase somewhat towards the uplift centre. This might reflect a non-uniform mantle viscosity. Also, the uplift maximum seems to have migrated towards NNE.     

Measurements of Air Concentrations of SO2, NO2 and NH3 at Rural and Remote Sites in Asia

Sensitive diffusive samplers for concentration measurements in ambient airhave been used successfully in Sweden for several years. The samplers have theadvantage of being stable at room temperature before, as well as after,sampling, easy to handle, and cost-efficient. Furthermore, they do not requireelectricity or field calibration. In order to test their use in tropical andsubtropical environments and to obtain a preliminary set of data to validateatmospheric chemistry transport models in this part of the world, duplicatesamples were collected at 11 sites every second month during one year. Eightof the sites were background sites in Asia. It was not possible within theproject to compare the measured concentrations with other measurementtechniques. However, the reproducibility of the duplicates was satisfactoryover the whole measuring range (almost three orders of magnitude of theconcentration for SO₂) and reasonable agreement with modelcalculations was obtained at least for SO₂ andNH₃. Further testing of the measuring technique in tropicalareas is, however, warranted.     

An overview of a heavy rain event in southeastern Iberia: the role of large-scale meteorological conditions

The heavy rain event of 30 January to 4 February 1993 in the Segura Basin in SE Iberia is investigated. The study emphasizes the atmospheric processes that led to thunderstorm development. The meteorological scenario has been separated into preconvective and convective periods and into large-scale and subsynoptic settings. The warm, moist air now from the Mediterranean Sea, channelled by a high-over-low blocking pattern with a cold front over southeastern Iberia appears to be the main reason that helped trigger a severe weather occurrence. The study of the mesoscale environment parameters showed an enhanced conditional unstability through a deep troposphere layer with a moderate to strong vertical wind shear that promoted conditions to allow organization of long-lived convective structures.     

Seasonal variations in the loosely sorbed phosphorus fraction of the sediment of a shallow and hypereutrophic lake

On the basic of selective extractions, loosely sorbed phosphorus (ADS-P) has been shown to constitute much of the total phosphorus in the P-rich near-surface sediments of Lake Søbygaard, Denmark. The concentrations of ADS-P are seasonally variable, ranging from 0.2 mg Pg^?1 DW in the winter to more than 2 mg Pg^?1 DW in the summer. The variations can be observed as deep as 10 cm into the sediment but are most pronounced in the upper few centimeters. During the summer, lake and pore water pH levels are very high, and photosynthetic activity causes elevation to pH 10–11 in the lake. Laboratory experiments demonstrated a strong association between ADS-P and high pore water pH. It is likely that Lake Søbygaard represents an extreme example of pH control on sediment/water phosphorus equilibria in which high concentrations of internal ADS-P contribute significantly to the total P load of the Lake.