Estructura en l'espai del sotabosc als boscos pirinencs de pi roig (Pinus sylvestris L.)

A partir d'un mostreig basat en transectes a 59 parcel·les de bosc de pi roig (Pinus sylvestris L.), s'estudia el comportament en l'espai (dins les parce1,les) que presenten les espècies. El mètode utilitzat es basa en el càlcul del coeficient d'autocorrelació de cada espècie en cada parcel·la. Els resultats suggereixen que les espècies als boscos estudiats tendeixen a distribuir-se formant claps (distribució agregada), i no pas amb una distribució uniforme o a l'atzar, i que existeix certa relació entre el patró de distribució de les diferentes espècies i la seva forma vital.Spatial pattern of understorey species in Pyrenean Scots pine forests was studied from transect data in 59 plots. Autocorrelation coefficient was computed for each species in each plot. The results suggest that most of the species tend to show a clumped pattern, rather than random or uniform pattern, and that there is some relationship between the spatial pattern of the different species and their life form

Relació entre la vegetació i els paràmetres ambientals als boscos pirinencs de pi roig (Pinus sylvestris L.)

S'estudia la relació de la vegetació dels boscos pirinencs de pi roig (Pinus sylvestris L.) amb els paràmetres ambientals (p.e., altitud, radiació solar, nutrients al sòl, etc.) mitjançant mètodes d'andisi multivariant (ordenació, classificació i anàlisi canònica). Els resultats suggereixen que existeix una forta relació entre la vegetació i els paràmetres ambientals. Aquests boscos on l'única espècie arbòria és el pi roig, poden ser dividits en diierentes comunitats ecològicament diferenciades. Els principals paràmetres que determinen la vegetació corresponen a la capacitat de bescanvi catiònic del sòl i a la radiació solar incident.The relation between vegetation and their environment (e.g., altitude, solar radiation, soil nutrients) is studied in Pyrenean Scots pine (Pinus sylvestris L.) forests by means of multivariate analyses (i.e., ordination, classification and canonical analysis). The results suggest a strong correlation between vegetation and the environment. Although these forests are dominated by one overstorey species they can be subdivided into several ecologically differentiated communities. Cation exchange capacity and incoming solar radiation are the main parameters determining the vegetation composition

Genetic component of flammability variation in a Mediterranean shrub

Recurrent fires impose a strong selection pressure in many ecosystems worldwide. In such ecosystems, plant flammability is of paramount importance because it enhances population persistence, particularly in non‐resprouting species. Indeed, there is evidence of phenotypic divergence of flammability under different fire regimes. Our general hypothesis is that flammability‐enhancing traits are adaptive; here, we test whether they have a genetic component. To test this hypothesis, we used the postfire obligate seeder Ulex parviflorus from sites historically exposed to different fire recurrence. We associated molecular variation in potentially adaptive loci detected with a genomic scan (using AFLP markers) with individual phenotypic variability in flammability across fire regimes. We found that at least 42% of the phenotypic variation in flammability was explained by the genetic divergence in a subset of AFLP loci. In spite of generalized gene flow, the genetic variability was structured by differences in fire recurrence. Our results provide the first field evidence supporting that traits enhancing plant flammability have a genetic component and thus can be responding to natural selection driven by fire. These results highlight the importance of flammability as an adaptive trait in fire‐prone ecosystems

Disturbance ecology in human societies

1. We define societal disturbances as discrete events that abruptly disrupt the functioning of human societies. There is a variety of such events, including hurricanes, floods, epidemics, nuclear accidents, earthquakes and wars, among others. These disturbances can interact, further increasing their impacts. The severity of disturbances does not only depend on their intrinsic properties (type, intensity and magnitude) but also greatly on human aspects (socioeconomic, historical, political and cultural aspects that define vulnerability). 2. Very large or severe disturbances are infrequent and unpredictable. Yet societal disturbances are intrinsic to human societies; they have occurred through the entire human history and will continue to occur in the future. We can increase preparedness and recovery capacity but cannot avoid disturbances. The type, regime and scale of disturbances change with the development of societies. The increase in population density and complexity also increases the severity of many disturbances. 3. Societal disturbances can temporarily disrupt the functioning of societies. However, when those disturbances are frequent, societies adapt to them and thus disturbances contribute to shape cultural evolution. That is, societal disturbances have a cost at short temporal scales, but they can build up resilience at mid-to long-term scales. 4. Understanding this dynamic view of human systems is becoming more important as climate is changing, humans are overexploiting natural resources and humanity is dense and hyperconnected. We need to take advantage of frequent small disturbances, as they can build resilience and reduce the likelihood of infrequent large and severe disturbances. Our challenge is to encourage actions and policies to be prepared for unknown, unpredictable and unprecedented (infrequent) large-scale societal disturbances that will surely arrive

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

Differential pollinator response underlies plant reproductive resilience after fires

Background and aims Assessing the resilience of plant-animal interactions is critical to understanding how plant communities respond to habitat disturbances. Most ecosystems experience some level of natural disturbance (e. g., wildfires) to which many organisms are adapted to. Wildfires have structured biotic communities for millennia; however, the effects of fire on interactions such as pollination have only recently received attention. A few studies have shown that generalist plants can buffer the impact of fires by pollinator replacement, suggesting that the resilience to disturbance could depend on the level of specialization of the interactions. Here, we hypothesize that i) fires could impose negative effects on plants with specialized pollination systems, and ii) in large wildfires, these negative effects will be stronger with increasing distance inside the burnt because pollinators will need more time to recolonize. Methods These questions were tested in the specialized pollination system of a widespread Mediterranean palm, Chamaerops humilis. The postfire pollination resilience was assessed in replicated wildfires representing three postfire ages by measuring the abundance of beetle pollinators and by estimating fruit set (i.e., proportion of flowers setting fruits) in burnt and unburned areas. To test for distance effects, plants were sampled along transects inside the burnt. Key results This study revealed that despite a marked postfire decline in the specialist pollinator, exacerbated by the distance from the fire’s edge, the palm’s fruit set was barely affected. The temporary replacement by a sap beetle at burnt sites - an effective pollinator that had not been previously recognized - provided postfire reproductive resilience. Conclusions The study shows that differential pollinator responses to disturbance can ensure plant success even in plants with only two functionally similar pollinators. This highlights the importance of pollinator 1 replacement and dynamics for the resilience of interactions and ultimately of plant reproduction in disturbance-prone ecosystems

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