African geoxyles evolved in response to fire; frost came later

It has been proposed in separate studies that fire or frost were the critical selective agents in the evolution of subshrub geoxyles (SGs) in African subtropical grasslands. We attempt to resolve this controversy by examining the evolution of SGs among the entire genus Protea that is widespread throughout southern/central Africa. We show that SGs are not confined to grasslands but occur in a wide range of non-forest vegetation types, including mediterranean shrublands. SG proteas arose 1–11 million years ago but their multiple origins among other geoxyles, confounded by strong intraspecific variability among grassland species, makes it impossible to identify the ancestral growth form. We conclude that the evolutionary history of SG proteas has occurred under lightning-prone conditions that promoted fire and were essentially frost-free; exposure to frost has been limited to certain elevated locations in more recent times. This is supported by many SGs having pyrogenic flowering and lack of seed storage among grassland species

Growth of monolayer graphene on 8deg off-axis 4H-SiC (000-1) substrates with application to quantum transport devices

Using high temperature annealing conditions with a graphite cap covering the C-face of an 8deg off-axis 4H-SiC sample, large and homogeneous single epitaxial graphene layers have been grown. Raman spectroscopy shows evidence of the almost free-standing character of these monolayer graphene sheets, which was confirmed by magneto-transport measurements. We find a moderate p-type doping, high carrier mobility and half integer Quantum Hall effect typical of high quality graphene samples. This opens the way to a fully compatible integration of graphene with SiC devices on the wafers that constitute the standard in today's SiC industry.Comment: 11 pages, 4 figures , Submitted in AP

Post-fire management of cork oak forests

28 páginas, 11 figuras.This chapter concerns the ecology and post-fire management of cork oak forests. It starts with a short overview of ecological and socio-economic context, continuing with an introduction on the cork oak post-fire regeneration strategies and the main factors affecting tree responses. Several post-fire management issues and alternatives, such as tree logging, assisting natural regeneration, reforestation, cork harvesting and pruning, or protecting against herbivory, are also presented and discussed.To all people who contributed in some way to the contents of this chapter, with special thanks to Francisco Rego, Paulo Fernandes and Thomas Curt. To Fundação para a Ciência e a Tecnologia (PhD grant SFRH/BD/65991/2009), FFP (project Recuperação de Áreas Ardidas), EU (COST FP0701 and TRANZFOR), and the Spanish government (project VARQUS, CGL2004-4325/BOS).Peer reviewe

Fuel loading and flammability in the Mediterranean Basin woody species with different post-fire regenerative strategies

12 páginas, 5 figuras, 3 tablas.The flammability and combustibility of plant communities are determined by species features related to growth-form, structure and physiology. In some ecosystems, such as the Mediterranean ones, these characteristics may contribute to the existence of fire-prone species. We measured several parameters associated with the flammability and fuel loading of dominant woody species with different post-fire regenerative strategies ( seeders and non-seeders) in shrublands in the western Mediterranean Basin. Overall, seeder species show lower fuel load but are more prone to burning owing to a higher dead-to-live fuel ratio, live fine-fuel proportion and dead fine-fuel proportion. Moreover, they burst into flame at lower temperatures than non-seeders. In the Mediterranean Basin, most seeder species emerged mainly during the Quaternary, under a highly fluctuating Mediterranean climate and during recurrent fires. We propose that properties related to the combustibility and flammability of seeders may be the result of selective pressures associated with both fire and climate. These results suggest that ecosystems dominated by seeder species are more susceptible to fire risk than those dominated by non-seeder species in the Mediterranean Basin. Therefore, the proportion of these types of species resulting from previous fire or management history is likely to determine the characteristics of future fire events.We thank M. Jané, E. Martí, A. Vilà-Cabrera, J. Garcia, B. Moreira, S. Ribeiro and C. Beseler for helping in the field and in the laboratory work. Also, special thanks are due to J. Piñol for his advice and suggestions, and to J. Peñuelas and G. Alessio for supporting the flammability tests. This study was funded by the Department of Universities, Research and Information Society of the Generalitat de Catalunya, the European social funds, and the Spanish Ministerio de Ciencia y Tecnología (MCYT) projects REN 2003–07198 and CGL2006–01293/BOS. It also contributes to the European research group (GDRE) ‘Mediterranean and mountain ecosystems in a changing world’ funded by the Generalitat de Catalunya and CNRS (Centre National de la Recherche Scientifique). CEAM (Fundación Centro de Estudios Ambientales del Mediterráneo) is supported by the Generalitat Valenciana and Bancaixa.Peer reviewe

Fires enhance flammability in Ulex parviflorus

6 páginas, 2 figuras, 2 tablas.This work was financed by the VIRRA project (CGL2009-12048 ⁄ BOS) from the Spanish Government. G.A.A. is supported by a Juan de la Cierva scholarship (JDC 2009-5067; Spanish Government) and B.M. by an FCT grant (SFRH ⁄BD⁄ 41343 ⁄ 2007; Portuguese Government). CIDE is supported by the Spanish National Research Council (CSIC), Generalitat Valenciana and the University of Valencia. We thank R. Bossi (CEAM, GRACCIE project, CONSOLIDERINGENIO 2010), E. Beltran, S. Paula, J. Chofre and O. González-Pelayo for their collaboration in the field and laboratory work, M. C. Castellanos for comments on an early version of the manuscript, and Fundación Caja Castellón-Bancaja for permission to work in Barranc dels Horts (Ares del Maestrat).Peer reviewe

Fire and plant diversification in mediterranean-climate regions

Despite decades of broad interest in global patterns of biodiversity, little attention has been given to understanding the remarkable levels of plant diversity present in the world’s five Mediterranean-type climate (MTC) regions, all of which are considered to be biodiversity hotspots. Comprising the Mediterranean Basin, California, central Chile, the Cape Region of South Africa, and southwestern Australia, these regions share the unusual climatic regime of mild wet winters and warm dry summers. Despite their small extent, covering only about 2.2% of world land area, these regions are home to approximately one-sixth of the world vascular plant flora. The onset of MTCs in the middle Miocene brought summer drought, a novel climatic condition, but also a regime of recurrent fire. Fire has been a significant agent of selection in assembling the modern floras of four of the five MTC regions, with central Chile an exception following the uplift of the Andes in the middle Miocene. Selection for persistence in a fire-prone environment as a key causal factor for species diversification in MTC regions has been under-appreciated or ignored. Mechanisms for fire-driven speciation are diverse and may include both directional (novel traits) and stabilizing selection (retained traits) for appropriate morphological and life-history traits. Both museum and nursery hypotheses have important relevance in explaining the extant species richness of the MTC floras, with fire as a strong stimulant for diversification in a manner distinct from other temperate floras. Spatial and temporal niche separation across topographic, climatic and edaphic gradients has occurred in all five regions. The Mediterranean Basin, California, and central Chile are seen as nurseries for strong but not spectacular rates of Neogene diversification, while the older landscapes of southwestern Australia and the Cape Region show significant components of both Paleogene and younger Neogene speciation in their diversity. Low rates of extinction suggesting a long association with fire more than high rates of speciation have been key to the extant levels of species richness

No evidence of suitability of prophylactic fluids for wildfire prevention at landscape scales

Yu et al. propose a viscoelastic fluid as a prophylactic fire-retardant treatment in landscapes at high risk of wildfires. We argue that, while the idea is worth exploring further, their data do not support its suitability for real landscape-scale applications.Peer reviewe

Interactions between biogeochemical and management factors explain soil organic carbon in Pyrenean grasslands

Grasslands are one of the major sinks of terrestrial soil organic carbon (SOC). Understanding how environmental and management factors drive SOC is challenging because they are scale-dependent, with large-scale drivers affecting SOC both directly and through drivers working at small scales. Here we addressed how regional, landscape and grazing management, soil properties and nutrients, and herbage quality factors affect 20 cm depth SOC stocks in mountain grasslands in the Pyrenees. Taking advantage of the high variety of environmental heterogeneity in the Pyrenees, we built a dataset (n = 128) that comprises a wide range of environmental and management conditions. This was used to understand the relationship between SOC stocks and their drivers considering multiple environments. We found that temperature seasonality (difference between mean summer temperature and mean annual temperature; TSIS) was the most important geophysical driver of SOC in our study, depending on topography and management. TSIS effects on SOC increased in exposed hillsides, slopy areas, and relatively intensively grazed grasslands. Increased TSIS probably favours plant biomass production, particularly at high altitudes, but landscape and grazing management factors regulate the accumulation of this biomass into SOC. Concerning biochemical SOC drivers, we found unexpected interactive effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial SOC driver as expected but modulated by livestock species and neutral detergent fibre contenting plant biomass; herbage recalcitrance effects varied depending on grazer species. These results highlight the gaps in knowledge about SOC drivers in grasslands under different environmental and management conditions. They may also serve to generate testable hypotheses in later/future studies directed to climate change mitigation policies

Amounts of litter fall in some pine forests in a European transect, in particular Scots pine.

Pine litter fall data, mainly needle litter, were available for 64 plots in a transect from the Arctic Circle in Fennoscandia (41 plots) to southern Spain (22 further plots in continental Europe) and one in the American Midwest). Data originated from a total of eight pine species. Regressions were calculated mainly for needle litter fall and to some extent for total litter fall. We obtained a highly significant linear relationship for needle litter fall and latitude (R 2adj = 0.285; n = 58; P < 0.001) when using needle litter fall data from all pine species. Combining sites in the boreal and Atlantic climates gave an R2 adj of 0.732 with n = 45 (P < 0.001). A multiple linear relationship using stand age, latitude and basal area was highly significant and gave an R2adj value of 0.412 (n = 54; P < 0.001). For the amount of Scots pine needle litter in Fennoscandia, the best simple linear relationships were obtained with site index (H 100) (R2 adj = 0.349), latitude (R2adj = 0.331) and basal area (R2adj = 0.324) as predictor variables, whereas the regressions on altitude and stand age were significant only with P < 0.01. An X2 function for stand age improved the relationship with age to R2adj = 0.243. Multiple regression relationships for Fennoscandia between needle litter fall and latitude plus basal area and that to latitude plus basal area plus age were highly significant (R2adj = 0.605 and 0.661, respectively, with n = 41). In a stepwise procedure using data from the same sites, combinations of the factors latitude, site index, basal area and stand age could explain as much as 78 % of the needle litter fall. For total litter fall as measured by the same method as needle litter we related data from 32 sites to that of needle litter fall and obtained highly significant relationships indicating that needle litter fall may be used as an index for total litter fall. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS.Chute de litière dans quelques forêts de pins, en particulier du Pin sylvestre, le long d'un transect européen. Les données de chute de litière, essentiellement des chutes d'aiguilles, étaient disponibles pour 64 sites le long d'un transect depuis le cercle polaire en Scandinavie (41 sites) jusqu'au Sud de l'Espagne (22 sites supplémentaires en Europe continentale) et un site dans le midouest américain. Les données proviennent de huit espèces de Pin. Des régressions ont été calculées principalement pour la chute d'aiguilles et dans certains cas pour la chute totale de litière. Il existe une relation linéaire hautement significative entre la chute des aiguilles et la latitude (R2adj = 0.285 ; n = 58; p < 0,001) lorsque l'ensemble des données pour toutes les espèces sont utilisées. La combinaisons des sites en climat boréal et atlantique donne un R2adj de 0.732 pour n = 45 (p < 0,001). Une relation linéaire multiple, utilisant l'âge du peuplement, la latitude et la surface terrière est hautement significative et donne un R 2∼ de 0.412 (n = 54; p < 0.001). La meilleure relation linéaire, pour les retours d'aiguilles chez le Pin sylvestre en Scandinavie a été obtenue en utilisant comme variables prédictives l'indice de fertilité stationnelle « H 100 » (R2 adj = 0.349), la latitude (Radj = 0331), et la surface terrière (R2adj = 0.324 ; alors que la régression sur les variables altitudes et âge des peuplements n'était significative seulement à p < 0,01. Une fonction X2 pour l'âge du peuplement améliore la relation avec l'âge, R2adj = 0,243. Les relations multiples entre la chute des aiguilles et la latitude associée à la surface terrière et celle associée à la surface terrière plus l'âge, pour les sites Scandinaves, sont hautement significatives (R2 adj = 0,605 et R2adj = 0,661, respectivement, avec n = 41 ). La procédure de régression progressive sur les données des mêmes sites, combinaisons des variables latitude, indice de fertilité, surface terrière et âge du peuplement permet d'expliquer 78 % de la variation de la chute des aiguilles. Des relations hautement significatives ont été calculées sur les données des retours totaux de litière, utilisant la même méthodologie sur 32 des sites. Elles démontrent que la quantité des chutes des seules aiguilles peut être utilisée comme indice pour la chute totale de la litière. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS