Natural variability of lotic Mediterranean ecosystems or wildfire perturbations: who will win?

This study evaluates the impacts of wildfires in lotic Mediterranean ecosystems. It was carried out at Monchique ridge after big wildfires occurred during 2002 and 2003. Deferential impacts were evaluated comparing historical results obtained before the wildfires (1999 and 2001), with the post fire ones (2006 and 2007). Physical and chemical parameters of the water, habitat morphology, diatoms, macrophytes, macroinvertebrates and fishes were evaluated at 10 collecting places, before and after wildfires. High recovering rates were observed to the vegetation, but it is still possible to found fire impacts over macrophytes and river morphology. Wildfires, contributed to canopy decrease and, consequently to the growth of plants that usually are controlled by shadow. As a result, vegetation biodiversity tend to increase. River banks tend also to be invaded by terrestrial plants. Higher post fires recover rates were observed to the more aquatic communities (diatoms, macroinvertebrates and fishes). For those communities, comparing spring situations before and after the fires no substantial differences were observed. Sometimes differences between consecutive years are even higher. So it can be concluded that magnitude of wildfire impacts is less than the natural inter-annual variability of Mediterranean rivers. Long-term effects of forest fires, resulting from large woody debries, were also detected by morphological alterations, like debries dams. Habitat diversity increase and impacts on aquatic communities are expected

Cataclysmic variables below the period gap : mass determinations of 14 eclipsing systems

We present high-speed, three-colour photometry of the eclipsing cataclysmic variables CTCV J1300-3052, CTCV J2354-4700 and SDSS J115207.00+404947.8. These systems have orbital periods of 128.07, 94.39 and 97.52 minutes respectively, placing all three systems below the observed “period gap” for cataclysmic variables. For each system we determine the system parameters by fitting a parameterised model to the observed eclipse light curve by χ2 minimisation. We also present an updated analysis of all other eclipsing systems previously analysed by our group. The updated analysis utilises Markov Chain Monte Carlo techniques which enable us to arrive confidently at the best fits for each system with more robust determinations of our errors. A new bright spot model is also adopted, that allows better modelling of bright-spot dominated systems. In addition, we correct a bug in the old code which resulted in the white dwarf radius being underestimated, and consequently both the white dwarf and donor mass being overestimated. New donor masses are generally between 1 and 2σ of those originally published, with the exception of SDSS 1502 (−2.9σ, Mr = −0.012M⊙) and DV UMa (+6.1σ, Mr = +0.039M⊙). We note that the donor mass of SDSS 1501 has been revised upwards by 0.024M⊙ (+1.9σ). This system was previously identified as having evolved passed the minimum orbital period for cataclysmic variables, but the new mass determination suggests otherwise. Our new analysis confirms that SDSS 1035 and SDSS 1433 have evolved past the period minimum for cataclysmic variables, corroborating our earlier studies. We find that the radii of donor stars are oversized when compared to theoretical models, by approximately 10 percent. We show that this can be explained by invoking either enhanced angular momentum loss, or by taking into account the effects of star spots. We are unable to favour one cause over the other, as we lack enough precise mass determinations for systems with orbital periods between 100 and 130 minutes, where evolutionary tracks begin to diverge significantly. We also find a strong tendency towards high white dwarf masses within our sample, and no evidence for any He-core white dwarfs. The dominance of high mass white dwarfs implies that erosion of the white dwarf during the nova outburst must be negligible, or that not all of the mass accreted is ejected during nova cycles, resulting in the white dwarf growing in mass