Developmental dynamics of a beech-dominated ‘natural forest’ – permanent observation site on limestone in the Hainich National Park, Thuringia

Heute besteht bei Geoökologen und Forstleuten weitgehend Konsens darüber, dass die Wälder Mitteleuropas vor dem massiven menschlichen Einwirken, also vor etwa 2-3.000 Jahren weitgehend buchendominiert waren (BÜCKING et al. 1994, ELLENBERG 1996). Ihre Flächen wurden zunächst durch Rodung drastisch verringert. Später führte vor allem Brennholznutzung dazu, ihren Anteil in den übriggebliebenen Wäldern weiter zu reduzieren. Schließlich tat die Aufforstung und Umwandlung mit Nadelbäumen ein Übriges, um ihre Bedeutung einzuschränken. So kam es, dass ihr Anteil von ehemals ca. 70 auf heute noch 15 % in Deutschland sank (BMVEL 2004). Die verbliebenen Buchenwälder sind zudem stark durch forstliche Bewirtschaftung überprägt.A long term study of the natural dynamics of a semi-natural beech forest largely untouched for fifty years began in 1999. A part of the >150 year old beech/ash stand was completely inventoried (28 ha), and the gaps in the forest canopy measured repeatedly. The gaps ranged from 8 – 592 m², with a mean size of less than 150 m². There were, on average, 3 gaps/ha, occupying less than 4 % of the stand area. The establishment and survival rates of admixed species were low under the largely intact canopy. The total seedling number was only slightly higher in the gaps (approx. 7 plants/m²) than under the canopy (approx. 6 plants/m²). The problem of seedling establishment was exacerbated by the unregulated influence of deer. Ash seedlings rarely exceeded heights of 50 cm without the protection of fencing, and the development of the sycamores was halted at 90 cm. Even the unpalatable beech benefited slightly from fencing. The average volume of coarse woody debris (CWD) was 62 m³/ha, comprised chiefly of large lying timber, but also of large standing dead wood. The findings to date support the assumption that beech forests left to develop naturally regenerate gradually by means of numerous small scale disturbances, and tend towards an ever greater dominance of beech

The effect of aqueous alteration and metamorphism in the survival of presolar silicate grains in chondrites

Relatively small amounts (typically between 2-200 parts per million) of presolar grains have been preserved in the matrices of chondritic meteorites. The measured abundances of the different types of grains are highly variable from one chondrite to another, but are higher in unequilibrated chondrites that have experienced little or no aqueous alteration and/or metamorphic heating than in processed meteorites. A general overview of the abundances measured in presolar grains (particularly the recently identified presolar silicates) contained in primitive chondrites is presented. Here we will focus on the most primitive chondrite groups, as typically the highest measured abundances of presolar grains occur in primitive chondrites that have experienced little thermal metamorphism. Looking at the most aqueously altered chondrite groups, we find a clear pattern of decreasing abundance of presolar silicate grains with increasing level of aqueous alteration. We conclude that the measured abundances of presolar grains in altered chondrites are strongly biased by their peculiar histories. Scales quantifying the intensity of aqueous alteration and shock metamorphism in chondrites could correlate with the content in presolar silicates. To do this it would be required to infer the degree of destruction or homogenization of presolar grains in the matrices of primitive meteorites. To get an unbiased picture of the relative abundance of presolar grains in the different regions of the protoplanetary disk where first meteorites consolidated, future dedicated studies of primitive meteorites, IDPs, and collected materials from sample-return missions (like e.g. the planned Marco Polo) are urgently required.Comment: 15 pages, 3 figures, published in PASA as part of the Proceedings of the 2008 Torino Conference "The Origin of the Elements Heavier than Iron

Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank

9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved: the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and Conselleria de Pesca de la Xunta de GaliciaPeer reviewe

Change of land use in the Turkish Taurus Mountains

The effects of land use changes on forests and agricultural areas in the central Taurus Mountains of Turkey have been studied. In this region a progressive conversion of extensive grazing was observed towards more intensively farmed arable land in recent decades. The loss of forest land is obvious, and the remaining forests are currently severely degraded and fragmented. Based on a model area it was shown that forests accounted for more than 80% of the land cover in the 1960s. In the following decades the forest area decreased by more than 20%. To the same extent, the share of agricultural land increased, predominantly of the pastures, too. The use of pastures in turn was replaced in the 1990s by arable use, so that now for almost 30% of land use accont for production crop. Accordingly, the way of life of the rural population changed in the last 50 years. By the middle of the 20th century, people had mostly been living as nomads. Thereafter, they become increasingly stationary. While the population density decreased at the some time agriculture was intensified and livestock reduced. This change led to today to profound changes in the landscape of the Taurus Mountains and its unique habitats. Restrictive measures as a way to curb forest degradation and to intensify the use of arable land are discussed