Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.     

A simple parameterization of sub-grid scale open water for climate models

The effects of small fractions ( < 30%) of open water covering a grid element are currently neglected even in atmospheric general circulation models (AGCMs) which incorporate complex land surface parameterization schemes. Here, a method for simulating sub-grid scale open water is proposed which permits any existing land surface model to be modified to account for open water. This new parameterization is tested as an addition to an advanced land surface scheme and, as expected, is shown to produce general increases in the surface latent heat flux at the expense of the surface sensible heat flux. Small changes in temperature are associated with this change in the partitioning of available energy which is driven by an increase in the wetness of the grid element. The sensitivity of the land surface to increasing amounts of open water is dependent upon the type of vegetation represented. Dense vegetation (with a high leaf area index) is shown to complicate the apparently simple model sensitivity and indicates that more advanced methods of incorporating open water into AGCMs need to be considered and compared against the parameterization suggested here. However, the sensitivity of one land surface model to incorporating open water is large enough to warrant consideration of its incorporation into climate models.     

Riverine dominance of a nearshore marine demersal food web: evidence from stable isotope and C/N ratio analysis

The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

A simple mechanism for the climatological midsummer drought along the Pacific coast of Central America

The global distribution, seasonal evolution, and underlying mechanisms for the climatological midsummer drought (MSD) are investigated using a suite of relatively high spatial and temporal resolution station observations and reanalysis data with particular focus on the Pacific coast of Central America and southern Mexico. Although the MSD of Central America stands out in terms of spatial scale and coherence, it is neither unique to the Greater Caribbean Region (GCR) nor necessarily the strongest MSD on Earth based on an objective analysis of several global precipitation data sets. A mechanism for the MSD is proposed that relates the latitudinal dependence of the two climatological precipitation maxima to the biannual crossing of the solar declination (SD), driving two peaks in convective instability and hence rainfall. In addition to this underlying local mechanism, a number of remote processes tend to peak during the apex of the MSD, including the North American monsoon, the Caribbean low-level jet, and the North Atlantic subtropical high which may also act to suppress rainfall along the Pacific coast of Central America and generate interannual variability in the strength or timing of the MSD. However, our findings challenge the existing paradigm that the MSD owes its existence to a precipitation-suppressing mechanism. Rather, aided by the analysis of higher-temporal resolution precipitation records and considering variations in latitude, we suggest the MSD is essentially the result of one precipitation-enhancing mechanism occurring twice.     

The population genetic structure of the waratah anemone (Actinia tenebrosa) around New Zealand

The genetic structure of populations is often shaped by the reproductive system and larval properties of the species. The waratah anemone (Actinia tenebrosa) reproduces through both asexual clones, which have very short-distance dispersal, and sexual larvae, which are believed to disperse much greater distances. The impact of this mixed strategy on the New Zealand population structure of Actinia tenebrosa was investigated using microsatellite markers. The analysis incorporated 24 sampling locations from around New Zealand and one Australian location, using four microsatellite markers, n = 420. We observed low connectivity and high genetic differentiation between all locations sampled, with a distinct pattern of isolation by distance. The most distinct grouping of locations sampled was the north-east of the North Island from Cape Reinga to East Cape, which was identified by SAMOVA and STRUCTURE analyses as being moderately diverged from the remainder of the country. A tentative correlation was observed between genetic clustering and biogeographic regionalisation, where the distribution of a number of genetic clusters matched previously defined biogeographic regions. Within each location sampled, large numbers of clones were present and a latitudinal cline was observed in the relative contribution of asexually and sexually generated recruits, with an increase in asexual recruits on the South Island's east coast.     

Interannual and decadal variability of the subsurface thermal structure in the Pacific Ocean: 1961–90

Heat content anomalies are analyzed to understand subsurface variability on both aparticular focus on the evolving basinwide patterns and oceanic connections between the extratropics and tropics. Various analyses indicate two distinct modes, one interannual and the other decadal, that involve the tropics and the North Pacific subtropical gyre, respectively. Interannual variability is associated with El Niño in the tropics, with a prominent “see-saw” pattern alternately on and off the equator, and in the east and west, respectively. The interannual cycle features a coherent propagation of subsurface signals around the tropical Pacific, eastward along the equator but westward off the equator at 10–15?°N. Decadal signals are dominant in the subtropics and midlatitudes but also have a tropical component that appears to be independent of interannual variations. An oceanic connection can be seen between subsurface anomalies in the midlatitudes, in the subtropics and tropics on decadal time scales. Subsurface thermal anomalies associated with midlatitude decadal variability can propagate through the subtropics into the tropics, which may modulate the intensity of interannual variability in the tropics. For example, in the middle and late 1970s, a significant warm temperature anomaly appeared to penetrate into the western and central tropics at depth, warming the tropical upper ocean and depressing the thermocline. During the development of El Niño, therefore, an extratropically preconditioned subsurface state (e.g., an enhanced positive heat content anomaly) in the western and central tropical Pacific would favor a warmer sea surface temperature anomaly in the eastern equatorial Pacific, potentially increasing the intensity of ocean-atmosphere coupling. These changes in the thermocline structure and possibly in the coupling strength can further alter the very character of tropical air-sea interactions. This may help to explain decadal variability of El Niño evolution in the tropical Pacific as observed in the 1980s. Our subsurface variability analysis presents observational evidence for the detailed space-time structure of decadal oceanic links between the extratropics and the tropics.     

Summer larval fish assemblages in the Southern Tyrrhenian Sea (Western Mediterranean Sea)

The purpose of this paper was to study the community structure, in terms of species composition, abundance and spatial distribution, of fish larvae in a wide coastal area of Sicily facing the Southeastern Tyrrhenian Sea, extending for 2300 km² from Cape Cefalù to the west, to Cape Rasocolmo in the east. This study analyses how species are assembled in relation to an inshore–offshore gradient and also how environmental conditions, determined by surface circulation patterns occurring in the Central Mediterranean at the local scale, determine the distribution patterns. Samples from 39 stations were collected using a 60‐cm Bongo net during an ichthyoplanktonic survey carried out in June 2006. In all, 62 taxa, representing 32 families, were identified. Cyclothone braueri (59.6%), Engraulis encrasicolus (9.2%) Lampanyctus crocodilus (4.3%) and Lampanyctus pusillus (4.1%) were the most abundant species. The results showed that the highest abundance value (14830.6 fish larvae per 10 m² sea surface) was observed in the western part of the study area. MDS, SIMPER and CCA analyses revealed well defined groups of stations and assemblages of larvae in accordance with an inshore–offshore gradient. The results of this study could have implications for the management of marine resources because the investigated area has already been identified as a nursery area for many pelagic and coastal fishes and a natural habitat for many species of high commercial interest.