Crossing forest thresholds: inertia and collapse in a Holocene sequence from south-central Spain

A Holocene palaeoecological sequence from Villaverde, south-central Spain, is presented. The pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi-arid, plateau and mountain vegetation. From c. 9700–7530 cal. yr BP, Pinus is dominant, probably as a result of a combination of a relatively dry climate and natural fire disturbance. From c. 7530–5900 cal. yr BP, moderate invasion by Quercus appears to be a migrational response following increased moisture and temperature, but in part shaped by competitive adjustments. From c. 5900–5000 cal. yr BP, the pine forests are replaced by deciduous-Quercus forests with an important contribution from Corylus, Betula, Fraxinus and Alnus. Mediterranean-type forests spread from c. 5000 to 1920 cal. yr BP coincident with expansions of Artemisia, Juniperus and other xerophytes. From c. 1920–1160 cal. yr BP, Pinus becomes dominant after a disturbance- mediated invasion of the oak forests. Human impact upon the regional landscape was negligible during the Neolithic, and limited in the Bronze and Iron Ages. Local deforestation and the expansion of agro-pastoral activities occur after c. 1600 cal. yr BP.

The isolation and secondary functionalisation of the mer- and fac-isomers of tris(5-hydroxymethyl-2,2 '-bipyridine) complexes of ruthenium(II)

Tris-chelate 5-hydroxymethyl-2,2 '-bipyridine complexes of ruthenium (II) and the structurally related benzo- and naphthoesters have been isolated. The mer-isomer of the alcohol functionalised complex has been isolated by selective precipitation from methylene chloride and was subsequently functionalised to the benzoester with retention of the geometrical isomerism. The fac- and merisomeric forms of the ester complexes were separated using preparative plate silica chromatography and characterised by H-1 NMR spectroscopy. X-ray structural analysis of the fac-isomer of both the ester complexes confirmed the product assignment. The photophysical properties of the three isomers were investigated, indicating very similar absorption spectra to [Ru(biPY)(3)](2+). The emission wavelength was comparable in each case, with the aromatic ester complexes giving a much longer lifetime and higher quantum yields. (c) 2004 Elsevier B.V. All rights reserved.