Perturbations in the carbon budget of the tropics

The carbon budget of the tropics has been perturbed as a result of human influences. Here, we attempt to construct a ‘bottom-up’ analysis of the biological components of the budget as they are affected by human activities. There are major uncertainties in the extent and carbon content of different vegetation types, the rates of land-use change and forest degradation, but recent developments in satellite remote sensing have gone far towards reducing these uncertainties. Stocks of carbon as biomass in tropical forests and woodlands add up to 271 ± 16 Pg with an even greater quantity of carbon as soil organic matter. Carbon loss from deforestation, degradation, harvesting and peat fires is estimated as 2.01 ± 1.1 Pg annum(−1); while carbon gain from forest and woodland growth is 1.85 ± 0.09 Pg annum(−1). We conclude that tropical lands are on average a small carbon source to the atmosphere, a result that is consistent with the ‘top-down’ result from measurements in the atmosphere. If they were to be conserved, they would be a substantial carbon sink. Release of carbon as carbon dioxide from fossil fuel burning in the tropics is 0.74 Pg annum(−1) or 0.57 MgC person(−1) annum(−1), much lower than the corresponding figures from developed regions of the world

Comunidades vegetales acuáticas del paraguay occidental

Se hace un estudio de las comunidades vegetales acuáticas del Paraguay occidental. Se describen una clase fitosociológica, un orden, una alianza y cuatro asociaciones como nuevas, que se detallan en el resumen en inglés.The aquatic plant communities of western Paraguay have been studied. As a result, one phytosociological class, one order, one alliance and four new associations are proposed: Eichhornietea crassipedis, Eichhornietalia crassipedis, Eichhornion crassipedis, Elodeo calIitrichoidis- Nymphaeetum amazoni, Hydrocleydo nymphoidis-Nymphoidetum humboldtianae, Rhabdadenio ragonesei-Cyperetum gigantei, Echinodoro grandiflori-Pontederietum cordatae

Linaria yusufeliensis, a replacement name for the Turkish Linaria turcica Makbul & Hamzaoglu (Plantaginaceae)

Galan de Mera, Antonio/0000-0002-1652-5931WOS: 000425091500016[No abstract available

Gas-phase reactions of chlorine atoms and CIO radicals with dimethyl sulfide. Rate coefficients and temperature dependences

The results of a discharge flow-mass spectrometric (DF-MS) kinetic study of the reaction between Cl and dimethylsulfide (DMS) (1) over the temperature range 259−364 K at low total pressure between 0.5 and 1 Torr with helium as carrier gas are reported. At room temperature and 1.0 Torr the main products of reaction 1 correspond to an abstraction channel leading to HCl and CH3SCH2 with k(1) = (6.9 ± 1.3) × 10-11 cm3 molecule-1 s-1. The association channel has also been confirmed by mass spectroscopic detection of the adduct CH3S(Cl)CH3 with a yield <0.05 under the experimental conditions used. It is now shown that the abstraction channel requires a slight activation energy, k(1) = (2.0 ± 1.2) × 10-10 exp[−(332 ± 173)/T] cm3 molecule-1 s-1. The kinetics and mechanism of the reaction ClO + DMS → products (2) over the temperature range 259−335 K at total pressures between 0.5 and 2 Torr have also been studied by DF-MS. By mass spectroscopic calibration of dimethyl sulfoxide, DMSO, the branching ratio of the channel leading to this product has been measured (0.90 ± 0.49). The rate constant of reaction 2 has been measured under pseudo-first-order conditions in excess of DMS over ClO:  k(2) = (1.2 ± 0.7) × 10-15 exp[(354 ± 163)/T] cm3 molecule-1 s-1 with k(2) = (3.9 ± 1.2) × 10-15 cm3 molecule-1 s-1 at 298 K. The reaction is postulated to proceed through a channel involving a long-lived intermediate [CH3S(OCl)CH3]* which may decompose back to reactants or to products. Finally, the atmospheric implications through the DMS chemistry of both reactions are discussed.We thank the European Commission for financial support within the “Energy, Environment and Sustainable Development” V Framework program (EVK2-CT-1999-00033 contract) and the Spanish Ministry of Science and Technology for the PB97-0432 contract.Peer reviewe

Phytogeographical data and modern pollen rain of the puna belt in southern Peru (Nevado Coropuna, Western Cordillera)

International audienc