Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

Forest¿woodland¿savannah mosaics are a common feature in the East African landscape. For the conservation of the woody species that occur in such landscapes, the species patterns and the factors that maintain it need to be understood. We studied the woody species distribution in a forest¿woodland¿savannah mosaic in Budongo Forest Reserve, Uganda. The existing vegetation gradients were analyzed using data from a total of 591 plots of 400 or 500 m2 each. Remotely sensed data was used to explore current vegetation cover and the gradients there in for the whole area. A clear species gradient exists in the study area ranging from forest, where there is least disturbance, to wooded grassland, where frequent fire disturbance occurs. Most species are not limited to a specific part of the gradient although many show a maximum abundance at some point along the gradient. Fire and accessibility to the protected area were closely related to variation in species composition along the ordination axis with species like Cynometra alexandri and Uvariopsis congensis occurring at one end of the gradient and Combretum guenzi and Lonchocarpus laxiflorus at the other. The vegetation cover classes identified in the area differed in diversity, density and, especially, basal area. All vegetation cover classes, except open woodland, had indicator species. Diospyros abyssinica, Uvariopsis congensis, Holoptelea grandis and all Celtis species were the indicator species for the forest class, Terminalia velutina and Albizia grandbracteata for closed woodland, Grewia mollis and Combretum mole for very open woodland and Lonchocarpus laxiflorus, Grewia bicolor and Combretum guenzi for the wooded grassland class. Eleven of the species occurred in all cover classes and most of the species that occurred in more than one vegetation cover class showed peak abundance in a specific cover class. Species composition in the study area changes gradually from forest to savannah. Along the gradient, the cover classes are distinguishable in terms of species composition and vegetation structure. These classes are, however, interrelated in species composition. For conservation of the full range of the species within this East African landscape, the mosaic has to be managed as an integrated whole. Burning should be varied over the area with the forest not being burnt at all and the wooded grassland burnt regularly. The different vegetation types that occur between these two extremes should be maintained using a varied fire regim

Hydrothermal alteration in the lower part of an early Proterozoic greenstone complex at Palovaara, Enontekiö, northwestern Finland

The lower part of the early Proterozoic greenstone complex at Palovaara, northwestern Finnish Lapland, comprises a quartzite formation overlain by intermediate and felsic tuffs and tuffites with some lava flows, mostly intermediate in chemical composition. They are intruded by numerous sills of albite diabase and also by some minor keratophyric dykes. The lithology and geochemistry of the rocks are similar to those of the spilitekeratophyre association and provide evidence that the rocks were thoroughly altered by postcrystallization processes. Geochemically, all the rock types, including the extrusive and subvolcanic varieties, are greatly enriched in Na and depleted in K and Mn. The alteration resembles that observed in recent submarine volcanics, whose mineralogy is largely governed by the water/rock ratio during alteration. Subsequent regional metamorphism had only a minor, if any, effect on the geochemistry of the rocks but adjusted the mineralogy to the conditions of epidote-amphibolite facies. The analytical data on lavas and albite diabases suggest an increase in Na, Si, Al and Ti and a decrease in total Fe, Mn, Mg and Ca, with an increase in w/r ratios from low to moderate values, thus reflecting intensifying albitization of the host rock. Further intensification of the water-rock interaction resulted in a dramatic change in alteration. The most permeable parts of the rocks, such as the interpillow matrices, pillow selvages and some of the fractures plus their wall rocks, acquired an ultramafic mineral composition with a marked increase in Fe and Ca and a decrease in Si and Na. A K-metasomatic event that postdated the general hydrothermal alteration locally raised the K-content of the rocks

Governing change towards sustainable economy in the Arctic

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Cobalt resources in Europe and the potential for new discoveries

Global demand for cobalt is increasing rapidly as we transition to a low-carbon economy. In order to ensure secure and sustainable supplies of this critical metal there is considerable interest in Europe in understanding the availability of cobalt from indigenous resources. This study reviews information on cobalt resources in Europe and evaluates the potential for additional discoveries. Based on published information and a survey of national mineral resource agencies, 509 cobalt-bearing deposits and occurrences have been identified in 25 countries in Europe. Harmonised cobalt resources, classified using the United Nations Framework Classification (UNFC), have been estimated for 151 deposits in 12 countries where data are available. The calculated total resource comprises 1 342 649 tonnes of contained cobalt metal. This includes: 114 638 tonnes in commercial projects with current cobalt extraction; 370 409 tonnes in potentially commercial projects; 111 107 tonnes in historic estimates compliant with modern reporting; and 746 495 tonnes in non-compliant historic estimates. Analysis of these data reveals that cobalt resources are widely distributed across Europe in deposits of several different types. Global mine production of cobalt is dominated by stratiform sediment-hosted copper deposits, magmatic nickel-copper deposits and nickel laterite deposits, but other deposit types may also be significantly enriched in cobalt. In Europe, current cobalt production is derived from three mines in Finland: the magmatic sulfide deposit at Kevitsa; the Kylylahti deposit of volcanogenic massive sulfide (VMS) affinity; and the black shale-hosted deposit at Sotkamo (Talvivaara). This study has identified 104 deposits in Europe that are currently being explored for cobalt, of which 79 are located in Finland, Norway and Sweden. The Fennoscandian Shield and the Caledonian Belt in these countries are high priority exploration terrains for a variety of cobalt-bearing deposits, notably magmatic Ni-Cu-Co deposits. The Svecofennian, Sveconorwegian and the Caledonian orogenies in Fennoscandia also resulted in the formation of several other cobalt-enriched deposit types. These include chiefly metasediment- and metavolcanic-hosted Co-Cu-Au, VMS, skarn and polymetallic vein deposits. The Kupferschiefer deposits in Poland and Germany are stratiform sediment-hosted Cu deposits with some similarities to the Central African Copperbelt, which is the predominant global producer. However, the cobalt grade in the Kupferschiefer deposits is relatively low (0.005–0.008% Co) and not currently economic to exploit without significant improvement in extraction technology. In the Balkans and Turkey cobalt grades and tonnages are known in 27 nickel laterite deposits, with several containing more than 10 000 tonnes of cobalt metal. Only nickel is currently recovered from these deposits, but new processing technologies such as high-pressure acid leaching could enable cobalt recovery in the future. Small polymetallic cobalt-bearing vein deposits in several European countries have been historic producers of cobalt. Today most are uneconomic, but new technologies and the drive towards locally-sourced raw materials could make them viable future sources of cobalt. Our analysis suggests that geological availability in Europe is not a problem. However, many economic, technological, environmental and social challenges will have to be overcome for exploration projects to become commercial

Geochemical distribution of precious metals in European soil

Contenuti riportati in: Geophysical Research Abstracts, Vol. 16, EGU201