From stars to dust: looking into a circumstellar disk through chondritic meteorites

One of the most fundamental questions in planetary science is, How did the solar system form? In this special issue, astronomical observations and theories constraining circumstellar disks, their lifetimes, and the formation of planetary to subplanetary objects are reviewed. At present, it is difficult to observe what is happening within disks and to determine if another disk environment is comparable to the early solar system disk environment (called the protoplanetary disk). Fortunately, we have chondritic meteorites, which provide a record of the processes that operated and materials present within the protoplanetary disk.     

Spatial structure of semi-natural and plantation stands of Scots pine (Pinus sylvestris L.) in northern Scotland

The success of current initiatives to maintain and enhance thearea of and the special habitats provided by the remnant semi-naturalpinewoods of northern Scotland will depend upon foresters' abilityto foster more natural structures in even-aged plantations throughstand manipulation. However, there is little information onthe structures and spatial patterns that can be found in Scottishpinewoods; such knowledge could be used to design appropriatesilvicultural regimes. A study was carried out to compare spatialstructure in three 0.8–1.0 ha plots in the CairngormsNational Park; one plot was a 78-year-old plantation stand,the other two were semi-natural stands with trees up to 300years old. Basic mensurational data showed that the semi-naturalstands were characterized by a wider range of tree sizes andmore large (>50 cm d.b.h.) trees. Spatial structure was evaluatedwith a range of different indices: the aggregation index ofClark–Evans (CE), the uniform angle and diameter differentiationindices, Ripley's L function of tree spatial distribution, pairand mark correlation functions and experimental variograms oftree diameter. The CE revealed a regular distribution in theplantation with the semi-natural stands having a random pattern.Further analysis of the latter stands indicated that, in eachcase, the older trees in the stand were regularly distributedwhile the younger ones were clustered. There was little differencein uniform angle values between the stands while the diameterdifferentiation distributions suggested greater variety in diameterwithin the semi-natural stands than in the plantation. The Ripley'sL function showed that trees in the plantation were regularlydistributed at close distances but clustered over wider distances.There were differences in pattern between the semi-natural stands;in one, trees were clustered because the positions of the youngertrees were influenced by past regeneration trials, whereas inthe other stand a random pattern was observed. Similarly, thevariogram indicated widespread homogeneity in diameter withinthe plantation, while the semi-natural stands showed high variationat close spacing because of competition followed by spatialautocorrelation up to 20 m distance. Thereafter, one of thesestands had a very different pattern because of a more intensiveregeneration history. All the indices, apart from uniform angle,were able to discriminate between the plantation and the twosemi-natural stands, but only the more detailed spatial indiceswere capable of identifying differences within the latter. Theimplications of these results for management strategies in plantationsare discussed.     

The assessment of fishery status depends on fish habitats

At the crux of the debate over the global sustainability of fisheries is what society must do to prevent over‐exploitation and aid recovery of fisheries that have historically been over‐exploited. The focus of debates has been on controlling fishing pressure, and assessments have not considered that stock production may be affected by changes in fish habitat. Fish habitats are being modified by climate change, built infrastructure, destructive fishing practices and pollution. We conceptualize how the classification of stock status can be biased by habitat change. Habitat loss and degradation can result in either overly optimistic or overly conservative assessment of stock status. The classification of stock status depends on how habitat affects fish demography and what reference points management uses to assess status. Nearly half of the 418 stocks in a global stock assessment database use seagrass, mangroves, coral reefs and macroalgae habitats that have well‐documented trends. There is also considerable circumstantial evidence that habitat change has contributed to over‐exploitation or enhanced production of data‐poor fisheries, like inland and subsistence fisheries. Globally many habitats are in decline, so the role of habitat should be considered when assessing the global status of fisheries. New methods and global databases of habitat trends and use of habitats by fishery species are required to properly attribute causes of decline in fisheries and are likely to raise the profile of habitat protection as an important complementary aim for fisheries management.     

Using rainfall simulation to guide planning and management of rehabilitated areas: Part II. Computer simulations using parameters from rainfall simulation

This paper reports computer simulations carried out using data from a rainfall simulator study on a steeply sloping revegetated area (a soundbund) at the NorthParkes Mine, near Parkes in New South Wales, Australia. Simulations of slope stability used a combination of daily time‐step models to consider soil water balances and runoff, growth of grass/legume pasture and soil erosion. Simulations indicated that long‐term erosion rates on the soundbund would be low (1·01–1·27 t ha⁻¹ yr⁻¹) due to low runoff rates and good vegetative cover. The simulations highlighted that peak vegetative growth occurred prior to the period of peak erosion hazard, with carry‐over dry matter being crucial for erosion control during the period of peak rainfall erosivity. This, in turn, indicated that grazing during the periods of peak growth and peak erosion hazard should be avoided (to avoid loss of dry matter). It also indicated that there was value in establishing grass species that would give greater growth during summer months, and that may produce dry matter that is more persistent through time. Simulations of stormwater flows in channels draining various lifts on the soundbund compared a range of alternatives with respect to channel length, gradient and roughness. The simulations indicated little effect of channel length on peak flow rates or depths once channel lengths exceeded 250 m and also showed little effect of vegetative roughness on peak flow rates or depths once Manning's n values exceeded 0·05. Implications of these results for design of drainage channels and drop structures on the soundbund are discussed. Copyright © 2000 John Wiley & Sons, Ltd.