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Dive into the research topics where Arben Q. Alla is active.

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Featured researches published by Arben Q. Alla.


Arctic, Antarctic, and Alpine Research | 2015

Recent and Intense Dynamics in a Formerly Static Pyrenean Treeline

J. Julio Camarero; José María García-Ruiz; Gabriel Sangüesa-Barreda; Juan Diego Galván; Arben Q. Alla; Yasmina Sanjuán; Santiago Beguería; Emilia Gutiérrez

Abstract Alpine treelines are considered monitors of the effects of climate on forest growth and dynamics. Treelines are expected to react to current climate warming by showing upslope migrations. However, treeline dynamics are often characterized by lagged responses to rising temperatures, that is, treeline inertia. In addition, encroachment within the treeline ecotone seems to be a more widespread response to climate warming than treeline ascent. We investigate how the treeline responds to climate in a Pyrenean site with an intense Mountain pine (Pinus uncinata) regeneration but also abundant dead trees. We use dendrochronology to reconstruct treeline dynamics (growth, tree recruitment, and death) and to build an age structure of Pyrenean Mountain pine forests, and relate them to temperature reconstructions of the study area. We also describe the spatial structure and estimate the size reproductive threshold of pine recruits. The study treeline showed profuse pine recruitment in the 1980s. These recruits were spatially aggregated and reached the 50% probability of reproduction at 24 years old. Most Pyrenean Mountain pines were recruited in the first half of the 18th century, a warm period when growth was stable, while old treeline trees recruited not only in those decades but also in previous warm periods. Pine deaths concentrated in the cool transition between the mid 17th and the early 18th centuries and mainly from 1820 to 1860, when growth declined as a consequence of temperatures rapidly dropping at the end of the Little Ice Age. Only the amount of dead pines at the treeline was negatively related to temperatures, indicating that cool periods cause high adult mortality rates and trigger long-term treeline decline. But this decline was interrupted by intense regeneration and treeline encroachment, two features that characterize recent treeline dynamics in some mountains. This concurs with the view of a rapid response of alpine treelines to climate during the late 20th century.


Trees-structure and Function | 2012

Acorn production is linked to secondary growth but not to declining carbohydrate concentrations in current-year shoots of two oak species

Arben Q. Alla; J. Julio Camarero; M. Maestro-Martínez; Gabriel Montserrat-Martí

In trees, reproduction constitutes an important resource investment which may compete with growth for resources. However, detailed analyses on how growth and fruit production interact at the shoot level are scarce. Primary canopy growth depends on the development of current-year shoots and their secondary growth might also influence the number and size of fruits supported by them. We hypothesise that an enhanced thickening of current-year shoots is linked positively to acorn production in oaks. We analysed the effect of acorn production on shoot growth of two co-occurring Mediterranean oak species with contrasting leaf habit (Quercus ilex, Quercus faginea). Length and cross-sectional area of current-year shoots, apical bud mass, number of leaves and acorns, xylem and conductive area, number of vessels of acorn-bearing and non-bearing shoots were measured in summer and autumn. Nitrogen and carbohydrates analyses were also performed in stems and leaves of both shoot types. Stem cross-sectional area increased in acorn-bearing shoots when compared with non-bearing shoots for both species and such surplus secondary growth was observed since summer. In bearing shoots, the total transversal area occupied by vessels decreased significantly from basal to apical positions along the stem as did the xylem area and the number of vessels. Leaves of bearing shoots showed lower nitrogen concentration than those of non-bearing shoots. Carbohydrate concentrations did not differ in stems and leaves as a function of the presence of acorns. Such results suggest that carbohydrates may preferentially be allocated towards reproductive shoots, possibly through enhanced secondary growth, satisfying all their carbon demands for growth and reproduction. Our findings indicate that acorn production in the two studied oaks depends on shoot secondary growth.


Annals of Forest Science | 2011

Variant allometric scaling relationships between bud size and secondary shoot growth in Quercus faginea: implications for the climatic modulation of canopy growth

Arben Q. Alla; J. Julio Camarero; Pilar Rivera; Gabriel Montserrat-Martí

Abstract• Introduction and statement of the research questionsThe relationships between primary and secondary growth in tree populations of contrasting climates are poorly understood. We tested the hypotheses that bud size and stem cross-sectional area are related through allometric relationship in shoots and that their scaling slopes change in response to climatic stress.• MethodsWe sampled three Quercus faginea populations subjected to contrasting climates and elevations. The main components of the current-year shoots (length, cross-sectional area, apical bud mass, and number of buds) were measured in ten trees per site, and the relationships among them were analyzed using structural equation models.• ResultsCross-sectional area and apical bud mass were allometrically related and they were higher in the mid-elevation site than elsewhere. In the mid-elevation site, the relationship between cross-sectional area and apical bud mass was the strongest and its scaling slope was the highest. Hence, for a given increase in shoot cross-sectional area, trees from the mid-elevation site produced bigger buds than trees from the other sites.• ConclusionsTrees from the mid-elevation site showed a greater potential for primary growth since mild temperatures and low-drought stress improve secondary shoot growth leading to an increased bud size. Therefore, secondary growth affects to a great extent bud size through allometric scaling which is modulated by climatic stress.


Annals of Botany | 2013

Seasonal and inter-annual variability of bud development as related to climate in two coexisting Mediterranean Quercus species

Arben Q. Alla; J. Julio Camarero; Gabriel Montserrat-Martí

BACKGROUND AND AIMS In trees, bud development is driven by endogenous and exogenous factors such as species and climate, respectively. However, knowledge is scarce on how these factors drive changes in bud size across different time scales. METHODS The seasonal patterns of apical bud enlargement are related to primary and secondary growth in two coexisting Mediterranean oaks with contrasting leaf habit (Quercus ilex, evergreen; Quercus faginea, deciduous) over three years. In addition, the climatic factors driving changes in bud size of the two oak species were determined by correlating bud mass with climatic variables at different time scales (from 5 to 30 d) over a 15-year period. KEY RESULTS The maximum enlargement rate of buds was reached between late July and mid-August in both species. Moreover, apical bud size increased with minimum air temperatures during the period of maximum bud enlargement rates. CONCLUSIONS The forecasted rising minimum air temperatures predicted by climatic models may affect bud size and consequently alter crown architecture differentially in sympatric Mediterranean oaks. However, the involvement of several drivers controlling the final size of buds makes it difficult to predict the changes in bud size as related to ongoing climate warming.


Proceedings of the National Academy of Sciences of the United States of America | 2017

Climate extremes and predicted warming threaten Mediterranean Holocene firs forests refugia

Raúl Sánchez-Salguero; J. Julio Camarero; Marco Carrer; Emilia Gutiérrez; Arben Q. Alla; Laia Andreu-Hayles; Andrea Hevia; Athanasios Koutavas; Elisabet Martínez-Sancho; Paola Nola; Andreas Papadopoulos; Edmond Pasho; Ervin Toromani; José A. Carreira; Juan Carlos Linares

Significance Climate extremes are major drivers of long-term forest growth trends, but we still lack appropriate knowledge to anticipate their effects. Here, we apply a conceptual framework to assess the vulnerability of Circum-Mediterranean Abies refugia in response to climate warming, droughts, and heat waves. Using a tree-ring network and a process-based model, we assess the future vulnerability of Mediterranean Abies forests. Models anticipate abrupt growth reductions for the late 21st century when climatic conditions will be analogous to the most severe dry/heat spells causing forest die-off in the past decades. However, growth would increase in moist refugia. Circum-Mediterranean fir forests currently subjected to warm and dry conditions will be the most vulnerable according to the climate model predictions for the late 21st century. Warmer and drier climatic conditions are projected for the 21st century; however, the role played by extreme climatic events on forest vulnerability is still little understood. For example, more severe droughts and heat waves could threaten quaternary relict tree refugia such as Circum-Mediterranean fir forests (CMFF). Using tree-ring data and a process-based model, we characterized the major climate constraints of recent (1950–2010) CMFF growth to project their vulnerability to 21st-century climate. Simulations predict a 30% growth reduction in some fir species with the 2050s business-as-usual emission scenario, whereas growth would increase in moist refugia due to a longer and warmer growing season. Fir populations currently subjected to warm and dry conditions will be the most vulnerable in the late 21st century when climatic conditions will be analogous to the most severe dry/heat spells causing dieback in the late 20th century. Quantification of growth trends based on climate scenarios could allow defining vulnerability thresholds in tree populations. The presented predictions call for conservation strategies to safeguard relict tree populations and anticipate how many refugia could be threatened by 21st-century dry spells.


European Journal of Forest Research | 2012

Contrasting responses of radial growth and wood anatomy to climate in a Mediterranean ring-porous oak: implications for its future persistence or why the variance matters more than the mean

Arben Q. Alla; J. Julio Camarero


Journal of Ecology | 2012

Sapwood area drives growth in mountain conifer forests

J. Diego Galván; J. Julio Camarero; Gabriel Sangüesa-Barreda; Arben Q. Alla; Emilia Gutiérrez


Trees-structure and Function | 2013

Revisiting the fate of buds: size and position drive bud mortality and bursting in two coexisting Mediterranean Quercus species with contrasting leaf habit

Arben Q. Alla; J. Julio Camarero; Sara Palacio; Gabriel Montserrat-Martí


Canadian Journal of Forest Research | 2015

Climate impacts on radial growth and vegetation activity of two co-existing Mediterranean pine species

Edmond Pasho; Arben Q. Alla


Agricultural and Forest Meteorology | 2017

Aged but withstanding: Maintenance of growth rates in old pines is not related to enhanced water-use efficiency

Elena Granda; J. Julio Camarero; J. Diego Galván; Gabriel Sangüesa-Barreda; Arben Q. Alla; Emilia Gutiérrez; Isabel Dorado-Liñán; Laia Andreu-Hayles; Inga Labuhn; Håkan Grudd; Jordi Voltas

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J. Julio Camarero

Spanish National Research Council

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Gabriel Montserrat-Martí

Spanish National Research Council

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Edmond Pasho

Spanish National Research Council

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Gabriel Sangüesa-Barreda

Spanish National Research Council

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J. Diego Galván

Spanish National Research Council

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Raúl Sánchez-Salguero

Spanish National Research Council

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