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Camarero J.J.,CSIC - Pyrenean Institute of Ecology | Olano J.M.,Area de Biologia Vegetal | Parras A.,CSIC - Pyrenean Institute of Ecology
New Phytologist | Year: 2010

Seasonal radial-increment and xylogenesis data can help to elucidate how climate modulates wood formation in conifers. Few xylogenesis studies have assessed how plastic xylogenesis is in sympatric conifer species from continental Mediterranean areas, where low winter temperatures and summer drought constrain growth. Here, we analysed intra-annual patterns of secondary growth in sympatric conifer species (Juniperus thurifera, Pinus halepensis and Pinus sylvestris). Two field sites (xeric and mesic) were evaluated using dendrometers, microcores and climatic data. A bimodal pattern of xylogenesis characterized by spring and autumn precipitation and subsequent cambial reactivation was detected in J. thurifera at both study sites and in P. halepensis at the xeric site, but was absent in P. sylvestris where growth was largely controlled by day length. In the xeric site J. thurifera exhibited an increased response to water availability in autumn relative to P. halepensis and summer cambial suppression was more marked in J. thurifera than in P. halepensis. Juniperus thurifera exhibited increased plasticity in its xylogenesis pattern compared with sympatric pines, enabling this species to occupy sites with more variable climatic conditions. The plastic xylogenesis patterns of junipers in drought-stressed areas may also provide them with a competitive advantage against co-occurring pines. © 2009 New Phytologist.


Moreno-Mateos D.,University of California at Berkeley | Moreno-Mateos D.,Stanford University | Power M.E.,University of California at Berkeley | Comin F.A.,CSIC - Pyrenean Institute of Ecology | Yockteng R.,CNRS Systematics, Biodiversity and Evolution Institute
PLoS Biology | Year: 2012

Wetlands are among the most productive and economically valuable ecosystems in the world. However, because of human activities, over half of the wetland ecosystems existing in North America, Europe, Australia, and China in the early 20th century have been lost. Ecological restoration to recover critical ecosystem services has been widely attempted, but the degree of actual recovery of ecosystem functioning and structure from these efforts remains uncertain. Our results from a meta-analysis of 621 wetland sites from throughout the world show that even a century after restoration efforts, biological structure (driven mostly by plant assemblages), and biogeochemical functioning (driven primarily by the storage of carbon in wetland soils), remained on average 26% and 23% lower, respectively, than in reference sites. Either recovery has been very slow, or postdisturbance systems have moved towards alternative states that differ from reference conditions. We also found significant effects of environmental settings on the rate and degree of recovery. Large wetland areas (>100 ha) and wetlands restored in warm (temperate and tropical) climates recovered more rapidly than smaller wetlands and wetlands restored in cold climates. Also, wetlands experiencing more (riverine and tidal) hydrologic exchange recovered more rapidly than depressional wetlands. Restoration performance is limited: current restoration practice fails to recover original levels of wetland ecosystem functions, even after many decades. If restoration as currently practiced is used to justify further degradation, global loss of wetland ecosystem function and structure will spread. © 2012 Moreno Mateos et al.


Linares J.C.,Pablo De Olavide University | Camarero J.J.,CSIC - Pyrenean Institute of Ecology | Carreira J.A.,University of Jaén
Journal of Ecology | Year: 2010

Long-term basal area increment (BAI) in Abies pinsapo was studied to investigate the way density-dependent factors modulate the responses of radial growth to climatic stresses in relict stands of a drought-sensitive Mediterranean fir. First, we verified that spatially explicit competition predicts mean A. pinsapo BAI at our study site; i.e. it modulates the degree to which the average climate-driven potential for growth is expressed. Second, we verified that the long-term pattern of temperature predicts the long-term pattern of BAI, estimated as the main trend over a time period of c. 40 years. Finally, we assessed whether the intensity of tree-to-tree competition restrains the potential improvements achieved by our model of BAI when a short-term, high-frequency stressor such as drought (inter-annual precipitation variability) is introduced. We applied Dynamic Factor Analysis (DFA) to characterize regional climatic trends and to test the hypothesis that trees subjected to contrasting competition intensity may differ in their growth pattern. Significant long-term climate trends obtained by DFA were used as predictors of long-term BAI. The mean BAI was mainly determined by competition, whereas growth trends obtained by DFA did not differ among dominant, suppressed and dying trees. Common trends of growth decline were strongly related to long-term, late-winter to summer temperatures, while the residuals were related to total annual precipitation, although with decreasing significance as competition increased. Our results support the contention that the reported patterns of A. pinsapo growth decline and death occur as a result of the interacting effects of both competition and climate stressors acting at long- and short-term time scales.5.Synthesis. Long-term climatic drought stress was the main driving factor of growth decline in A. pinsapo. Moreover, trees already suffering from competition (a long-term stress) were predisposed to decline given an additional short-term stress, such as a severe drought. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.


Vicente-Serrano S.M.,CSIC - Pyrenean Institute of Ecology | Begueria S.,CSIC - Aula Dei Experimental Station | Lopez-Moreno J.I.,CSIC - Pyrenean Institute of Ecology
Journal of Climate | Year: 2010

The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an increase in drought severity associated with higher water demand as a result of evapotranspiration. Relative to the sc-PDSI, the SPEI has the advantage of being multiscalar, which is crucial for drought analysis and monitoring. © 2010 American Meteorological Society.


Garcia M.B.,CSIC - Pyrenean Institute of Ecology | Dahlgren J.P.,University of Stockholm | Ehrlen J.,University of Stockholm
Journal of Ecology | Year: 2011

1. Understanding how vital rates and reproductive value change with age is fundamental to demography, life history evolution and population genetics. The universality of organism senescence has been questioned on both theoretical and empirical grounds, and the prevalence and strength of senescence remain a controversial issue. Plants are particularly interesting for studies of senescence since individuals of many species have been reported to reach very high ages. 2. In this study, we examined whether the herb Borderea pyrenaica, known to reach ages of more than 300years, experiences senescence. We collected detailed demographic information from male and female individuals in two populations over 5years. An unusual morphological feature in this species enabled us to obtain exact age estimates for each of the individuals at the end of the demographic study. 3. We used restricted cubic regression splines and generalized linear models to determine nonlinear effects of age and size on vital rates. We then incorporated the effects of age and size in integral projection models of demography for determining the relationship between age and reproductive value. As the species is dioecious, we performed analyses separately for males and females and examined also the hypothesis that a larger reproductive effort in females comes at a senescence cost. 4. We found no evidence for senescence. Recorded individuals reached 260years, but growth and fecundity of female and male individuals did not decrease at high ages, and survival and reproductive value increased with age. The results were qualitatively similar also when accounting for size and among-individual vital rate heterogeneity, with the exception that male flowering probability decreased with age when accounting for size increases. 5. Synthesis. Overall, our results show that performance of both male and female plants of B. pyrenaica may increase rather than decrease at ages up to several centuries, and they support the notion that senescence may be negligible in long-lived modular organisms. This highlights the need to explore mechanisms that enable some species to maintain high reproductive values also at very high ages and to identify the evolutionary reasons why some organisms appear to experience no or negligible senescence. © 2011 The Authors. Journal of Ecology © 2011 British Ecological Society.


Vicente-Serrano S.M.,CSIC - Pyrenean Institute of Ecology | Zouber A.,Agriculture and Agri Food Canada | Lasanta T.,CSIC - Pyrenean Institute of Ecology | Pueyo Y.,CSIC - Pyrenean Institute of Ecology
Ecological Monographs | Year: 2012

Semiarid Mediterranean regions are highly susceptible to desertification processes. This study investigated the influence of increasing climate aridity in explaining the decline in vegetation cover in highly vulnerable gypsum semiarid shrublands of the Mediterranean region. For this purpose, we have used time series of percent cover of vegetation obtained from remote sensing imagery (Landsat satellites). We found a dominant trend toward decreased vegetation cover, mainly in summer and in areas affected by the most severe water stress conditions (low precipitation, higher evapotranspiration rates, and sunexposed slopes). We show that past human management and current climate trends interact with local environmental conditions to determine the occurrence of vegetation degradation processes. The results suggest that degradation could be a consequence of the past overexploitation that has characterized this area (and many others in the Mediterranean region), but increased aridity, mainly related to global warming, may be triggering and/or accelerating the degradation processes. The observed pattern may be an early warning of processes potentially affecting more areas of the Mediterranean, according to the most up-todate climate change models for the 21st century. © 2012 by the Ecological Society of America.


Garcia-Ruiz J.M.,CSIC - Pyrenean Institute of Ecology
Catena | Year: 2010

Soil erosion is a key factor in Mediterranean environments, and is not only closely related to geoecological factors (lithology, topography, and climatology) but also to land-use and plant cover changes. The long history of human activity in Spain explains the development of erosion landscapes and sedimentary structures (recent alluvial plains, alluvial fans, deltas and flat valleys infilled of sediment). For example, the expansion of cereal agriculture and transhumant livestock between the 16th and 19th centuries resulted in episodes of extensive soil erosion. During the 20th century farmland abandonment prevailed in mountain areas, resulting in a reduction of soil erosion due to vegetation recolonization whereas sheet-wash erosion, piping and gullying affected abandoned fields in semi-arid environments. The EU Agrarian Policy and the strengthening of national and international markets encouraged the expansion of almond and olive orchards into marginal lands, including steep, stony hill slopes. Vineyards also expanded to steep slopes, sometimes on new unstable bench terraces, thus leading to increased soil erosion particularly during intense rainstorms. The expansion of irrigated areas, partially on salty and poorly structured soils, resulted in piping development and salinization of effluents and the fluvial network. The trend towards larger fields and farms in both dry farming and irrigated systems has resulted in a relaxation of soil conservation practices. © 2009 Elsevier B.V. All rights reserved.


Saiz H.,CSIC - Pyrenean Institute of Ecology | Alados C.L.,CSIC - Pyrenean Institute of Ecology
PLoS ONE | Year: 2012

In semi-arid ecosystems, vegetation is heterogeneously distributed, with plant species often associating in patches. These associations between species are not constant, but depend on the particular response of each species to environmental factors. Here, we investigated how plant species associations change in response to livestock grazing in a semi-arid ecosystem, Cabo de Gata-Níjar Natural Park in South East Spain. We established linear point-intercept transects at four sites with different grazing intensity, and recorded all species at each point. We investigated plant associations by comparing the number of times that each pair of species occurred at the same spatial point (co-occurrences), with the expected number of times based on species abundances. We also assessed associations for each shrub and grass species by considering all their pairs of associations and for the whole plant community by considering all pairs of associations on each site. At all sites, the plant community had a negative pattern of association, with fewer co-occurrences than expected. Negative association in the plant community increased at maximum grazing intensity. Most species associated as expected, particularly grass species, and positive associations were most important at intermediate grazing intensities. No species changed its type of association along the grazing gradient. We conclude that in the present plant community, grazing-resistant species compete among themselves and segregate in space. Some shrub species act as refuges for grazing-sensitive species that benefit from being spatially associated with shrub species, particularly at intermediate grazing intensities where positive associations were highest. At high grazing intensity, these shrubs can no longer persist and positive associations decrease due to the disappearance of refuges. Spatial associations between plant species and their response to grazing help identify the factors that organize plant communities, and may contribute to improving management of semi-arid ecosystems. © 2012 Saiz, Alados.


Linares J.C.,Pablo De Olavide University | Camarero J.J.,CSIC - Pyrenean Institute of Ecology
Global Change Biology | Year: 2012

The rise in atmospheric CO 2 concentrations (Ca) has been related to tree growth enhancement and increasing intrinsic water-use efficiency (iWUE). However, the extent that rising Ca has led to increased long-term iWUE and whether climate could explain deviations from expected Ca-induced growth enhancement are still poorly understood. The aim of this research was to use Ca and local climatic variability to explain changes during the 20th century in growth and tree ring and needle δ 13C in declining and nondeclining Abies alba stands from the Spanish Pyrenees, near the southern distribution limit of this species. The temporal trends of iWUE were calculated under three theoretical scenarios for the regulation of plant-gas exchange at increasing Ca. We tested different linear mixed-effects models by multimodel selection criteria to predict basal area increment (BAI), a proxy of tree radial growth, using these scenarios and local temperature together with precipitation data as predictors. The theoretical scenario assuming the strongest response to Ca explained 66-81% of the iWUE variance and 28-56% of the observed BAI variance, whereas local climatic variables together explained less than 11-21% of the BAI variance. Our results are consistent with a drought-induced limitation of the tree growth response to rising CO 2 and a decreasing rate of iWUE improvement from the 1980s onward in declining A. alba stands subjected to lower water availability. © 2011 Blackwell Publishing Ltd.


Lasanta T.,CSIC - Pyrenean Institute of Ecology | Vicente-Serrano S.M.,CSIC - Pyrenean Institute of Ecology
Remote Sensing of Environment | Year: 2012

In this study we used Landsat images to analyze land cover change processes since 1984 in the middle Ebro valley (Spain). The purpose was to identify abrupt changes suggesting modification of the land cover category, and gradual changes not associated with a change in the land cover type but potentially indicative of significant changes in natural areas. The results showed that: i) in analysis of land cover change the seasonality of vegetation cover is an important factor that must be taken into account in identifying the various change processes that may affect a region; ii) the major land cover changes in the study area were related to very diverse processes including urban expansion, industrial activities, the establishment of land irrigation, land extensification, natural revegetation following rural abandonment, forest fires, and changes in natural vegetated areas related to global warming and drought. With the exception of the occurrence of forest fires, the changes in natural areas (forest, shrubs and steppes) tended to be gradual with respect to both positive (forest colonization following rural abandonment and land extensification) and negative (land degradation and forest decline) processes. These areas showed rates of change that were lower in magnitude than those directly transformed by human activities. We found that time series of high spatial resolution satellite images and the application of change statistics provided a useful approach to the identification of abrupt changes, and gradual land cover change processes that are not commonly revealed using classical analytical approaches. © 2012 Elsevier Inc.

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