El paisatge vegetal dels Monegros : assaig d'interpretació

The vegetation of the plains in the central depression of the Ebro valley is conditioned by some remarkable factors, besides scarce rainfall(300-350 mm yearl). First, the frequent thermal inversions modify the local climate in the sense of increasing its montane character, a fact reflected in the presence of some species, specially Juniperus thurifera. When passing from the endorheic central plains to the peripheral areas of torrential relief connecting the plains to the Ebro river, thermal inversions become less important because of increased air turbulence. Second, relief features impose catenary systems in response to opposed gradients of soil water availability and soil salinity. Subdesertic grey soils are well represented and this does not support the hypothetical existence of a forested climax in the recent past. The landscape of the central plains, today profoundly transformed by man, is interpreted, in view of these factors and of floristic, chorological and phytosociological data from the literature as a soil-determined, pluriteselar complex linked to the pattems of relief. The Rharnno-Quercetum cocciferae macchia seems to have always had, at most, a partia1 dominance, and J. thurifera has been able to occupy only favourable parts of the mosaic. Pinus halepensis remains confined to hilltops and, together with most of the macchia species, to the inversion-free peripheral areas. Hence, we accept the hypothesis of a terminal vegetation of macchia with P. halepensis occupying these peripheral areas, while the central plains must have always been partially deforested since the end of the last glaciation and, indeed, most of the time since the late Miocene. The central plain and its characteristic vegetation is presently under regression because of erosion and climatic warming, but some species of steppic afinities have spread due to the anthropic degradation of the xerogamgue.El caràcter de la vegetació de la plana central de la depressió de ]'Ebre esti marcat per alguns fenòmens notables. La inversió tèrmica en primer lloc, dóna peu a una influència muntanyenca, reflectida en diverses especies, la més notable Juniperus thurifera. La topografia afecta a la circulació de l'aire i a l'existència o no de turbulències, que eliminen l'efecte d'inversió així que es passa a zones de relleu torrencial. En segon lloc, les característiques del relleu originen estructures catenals que responen a gradients d'humitat edifica i de salinitat d'efectes contraposats. La presència de sols grisos subdesèrtics sembla contrària a I'existència d'una "clímax" forestal en temps relativament recents. El paisatge de la zona central de la depressio, avui força transformat, s'interpreta a la vista d'aquests factors i de les dades florístiques, fitosociològiques i corològiques de la bibliografia, com un complex pluritessel·lar de causa edifica, lligada a la morfologia del relleu. La dominància del Rhamno-Quercetum cocciferae hi deu haver estat sempre parcial i J. thurifera ha pogut ocupar només alguns llocs privilegiats del mosaic. Pinus halepensis resta confinat a les elevacions o a les zones d'influència fluvial lliures d'inversió que voregen la plana, juntament amb la major part d'espècies de màquia. Per tant, s'accepta la idea d'una vegetació terminal de màquia amb pi blanc als voltants de la plana central, mentre que aquesta deu haver estat sempre parcialment desforestada des de la fi de la darrera glaciació, i quasi sempre en realitat des de finals del Miocè, trobant-se avui en regressió per l'erosió de la conca i el rescalfament climàtic, si bé alguns elements de caràcter estepari s'han estès per la degradació de la xero-gamga com a conseqüència de l'acció humana

MEOITERRANEAN WOOOY PLANT GROWTH-FORMS, BIOMASS ANO PROOUCTION IN THE EASTERN PART OF THE IBERIAN PENINSULA

The major physiognomic features of Mediterranean vegetation in the eastem part of the Iberian Peninsula are described considering a coastal and a continental gradient and oro-Mediterranean formations. The main communities include broadleaved evergreen forest, maquis, pine woodlands, "garigue", matorral, thom-scrub and dwarf-shrub steppes along mesic-xeric gradients, and pine-juniper woodlands and xeroacanthic cushion-like formations as altitudinal stages. We discuss sorne morphologico- functional traits of dominant plants from these different formations as related to environmental conditions, and their corresponding energy use strategies. Even though there are relatively few data on biomass and production, a broad synthetic approach is given, with sorne reference values

Els reptes socials del canvi climàtic i global

El canvi climàtic no és un fet nou, el que és realment novedós és que aquest canvi sigi per causa, almenys en una bona part, nostra, de les societats humanes. Hi ha una vulnerabilitat social al canvi, en l’economia, la salut, etc., que fins ara no havíem experimentat. Els canvis a què ens enfrontem, a més, no són només climàtics, altres canvis en la relació amb el nostre entorn poden tenir conseqüències directes per a la nostra societat i potser les societats humanes estan fent més atenció als processos de mitigació del canvi climàtic que no pas a la vulnerabilitat i l’adaptació a les conseqüències que se’n deriven.Climate change is nothing new, what is really new is that this change is due, at least in good part, to human societies. There is a vulnerability to social change in the fields of economy, health, etc. which we had not experimented until now. The changes that we face, moreover, are not just related to climate. Other changes in the relationship with our environment may have direct consequences for our society and it may be that human societies are paying more attention to the process of climate change mitigation than to the vulnerability and adaptation to its results

The planetary crisis of the Anthropocene : Cultural evolution and environmental change

We are living through a crisis which we call Anthropocene. The determining force in this period is the expansion of humankind as the result of a new biological process, cultural evolution. This has allowed us to construct an enormously extensive niche thanks, above all, to the increased use of exosomatic energy. The growth is accelerating rapidly and the impact on our socio-ecological structure is unpredictable. Environmental change exerts new selective pressures on human societies, which try to adapt, which in turn, forces new changes. Our demographic growth and improved living conditions are threatening resources and even our basic life-support processes but, even though we study their ecological impact, but their causes are social. The destruction of cultures and biodiversity is the heritage of colonialism, even though it is now following different paths or being played out by different actors. We need to generate universal messages, not attempt to perpetuate Western supremacy and the ideology of indefinite progress, but an intercultural effort to reach a consensus on universal values and to generate the corresponding institutions

Spatial Damping of Propagating Kink Waves Due to Resonant Absorption: Effect of Background Flow

Observations show the ubiquitous presence of propagating magnetohydrodynamic (MHD) kink waves in the solar atmosphere. Waves and flows are often observed simultaneously. Due to plasma inhomogeneity in the perpendicular direction to the magnetic field, kink waves are spatially damped by resonant absorption. The presence of flow may affect the wave spatial damping. Here, we investigate the effect of longitudinal background flow on the propagation and spatial damping of resonant kink waves in transversely nonuniform magnetic flux tubes. We combine approximate analytical theory with numerical investigation. The analytical theory uses the thin tube (TT) and thin boundary (TB) approximations to obtain expressions for the wavelength and the damping length. Numerically, we verify the previously obtained analytical expressions by means of the full solution of the resistive MHD eigenvalue problem beyond the TT and TB approximations. We find that the backward and forward propagating waves have different wavelengths and are damped on length scales that are inversely proportional to the frequency as in the static case. However, the factor of proportionality depends on the characteristics of the flow, so that the damping length differs from its static analogue. For slow, sub-Alfvenic flows the backward propagating wave gets damped on a shorter length scale than in the absence of flow, while for the forward propagating wave the damping length is longer. The different properties of the waves depending on their direction of propagation with respect to the background flow may be detected by the observations and may be relevant for seismological applications.Comment: Accepted for publication in Ap