Valor T., Pique M., Lopez B.C., Gonzalez-Olabarria J.R. (2013) Influence of tree size, reduced competition, and climate on the growth response of Pinus nigra Arn. salzmannii after fire. Annals of Forest Science. 70: 503-513.EnllaçDoi: 10.1007/s13595-013-0284-x
Context: After wildfire, surviving trees are of major ecological importance as they can help in the post-fire regeneration process. Although these trees may be damaged, they may also benefit from reduced fuel hazard and competition. However, little is known about the long-term growth response of surviving trees. Aims: This study aims to explain short- to long-term variations in the postfire growth of surviving black pines in an area burnt in 1994, focusing on levels of fire severity and tree sizes. Methods: Relative basal area increments were used to detect time-course variations in postfire radial tree growth depending on fire severity. Linear mixed-effects models were used to describe the factors affecting postfire ring growth. Results: In the short term, fire caused stronger reduction in growth in small trees with increasing bole char height. However, as time since fire increased, a positive effect of fire on growth due to reduced competition counteracted the short-term fire impacts. Indeed, small surviving trees demonstrated a surge in growth 15 years after the fire. Conclusion: It was concluded that reduced competition might offset the short-term negative effects of fire in surviving black pines. © 2013 INRA and Springer-Verlag France.
Arnan X., López B.C., Martínez-Vilalta J., Estorach M., Poyatos R. (2012) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronologia. 30: 11-14.EnllaçDoi: 10.1016/j.dendro.2011.02.002
Trees can reach ages that in some cases amount to thousands of years. In the Mediterranean region, olive trees (Olea europaea) have traditionally been considered a particularly long-lived species. The main objective of this study was to assess the age of large olive trees considered to be millenarian and classified as monumental trees in northeastern Spain. We extracted cores of 14 individuals and obtained 8 sections of trees which had already been cut in the area where the largest olive trees in the northeastern Iberian Peninsula are found. The age of the sampled olive trees was assessed by counting the number of annual growth rings. Tree rings did not cross-date well, neither within nor between individuals, but boundaries between likely annual rings were clearly distinct. We found a linear relationship between DBH and tree age (in years) (Age=2.11×diameter(cm)+88.93, R2=0.80), which was used to estimate the age of unsampled olive trees. The maximum estimated age (627±110 years) is among the greatest ages reported for olive trees around the world (700 years) and among the oldest trees in Mediterranean ecosystems. © 2011 Istituto Italiano di Dendrocronologia.
Hereş A.-M., Martínez-Vilalta J., López B.C. (2012) Growth patterns in relation to drought-induced mortality at two Scots pine (Pinus sylvestris L.) sites in NE Iberian Peninsula. Trees - Structure and Function. 26: 621-630.EnllaçDoi: 10.1007/s00468-011-0628-9
Drought-related tree mortality has become a widespread phenomenon. Scots pine (Pinus sylvestris L.) is a boreal species with high ecological amplitude that reaches its southwestern limit in the Iberian Peninsula. Thus, Iberian Scots pine populations are particularly good models to study the effects of the increase in aridity predicted by climate change models. A total of 78 living and 39 dead Scots pines trees were sampled at two sites located in the NE of the Iberian Peninsula, where recent mortality events have been recorded. Annual tree rings were used to (1) date dead trees; (2) investigate if there was an association between the occurrence of tree death and severe drought periods characterized by exceptionally low ratios of summer precipitation to potential evapotranspiration (P/PET); and (3) to compare the growth patterns of trees that died with those of surviving ones. Mixed models were used to describe the relationships between tree growth (in terms of basal area increment, BAI, and the percentage of latewood, LW%) and climate variables. Our results showed a direct association between Scots pine mortality and severe drought periods characterized by low summer water availability. At the two sites, the growth patterns of dead trees were clearly distinguishable from those of the trees that survived. In particular, the BAI of dead trees was more sensitive to climate dryness (low P/PET summer, high temperatures) and started to decline below the values of surviving neighbors 15-40 years before the time of death, implying a slow process of growth decline preceding mortality. © 2011 Springer-Verlag.
Lurgi M., López B.C., Montoya J.M. (2012) Novel communities from climate change. Philosophical Transactions of the Royal Society B: Biological Sciences. 367: 2913-2922.EnllaçDoi: 10.1098/rstb.2012.0238
Climate change is generating novel communities composed of new combinations of species. These result from different degrees of species adaptations to changing biotic and abiotic conditions, and from differential range shifts of species. To determine whether the responses of organisms are determined by particular species traits and how species interactions and community dynamics are likely to be disrupted is a challenge.Here, we focus on two key traits: body size and ecological specialization.We present theoretical expectations and empirical evidence on how climate change affects these traitswithin communities. We then explore howthese traits predispose species to shift or expand their distribution ranges, and associated changes on community size structure, food web organization and dynamics.We identify three major broad changes: (i) Shift in the distribution of body sizes towards smaller sizes, (ii) dominance of generalized interactions and the loss of specialized interactions, and (iii) changes in the balance of strong andweak interaction strengths in the short term. We finally identify two major uncertainties: (i) whether largebodied species tend to preferentially shift their ranges more than small-bodied ones, and (ii) how interaction strengths will change in the long term and in the case of newly interacting species. © 2012 The Royal Society.
Lurgi M., López B.C., Montoya J.M. (2012) Climate change impacts on body size and food web structure on mountain ecosystems. Philosophical Transactions of the Royal Society B: Biological Sciences. 367: 3050-3057.EnllaçDoi: 10.1098/rstb.2012.0239
The current distribution of climatic conditions will be rearranged on the globe. To survive, species will have to keep pace with climates as they move. Mountains are among the most affected regions owing to both climate and land-use change. Here, we explore the effects of climate change in the vertebrate food web of the Pyrenees. We investigate elevation range expansions between two time-periods illustrative of warming conditions, to assess: (i) the taxonomic composition of range expanders; (ii) changes in food web properties such as the distribution of links per species and community size-structure; and (iii) what are the specific traits of range expanders that set them apart from the other species in the community-in particular, body mass, diet generalism, vulnerability and trophic position within the food web. We found an upward expansion of species at all elevations, which was not even for all taxonomic groups and trophic positions. At low and intermediate elevations, predator: prey mass ratios were significantly reduced. Expanders were larger, had fewer predators and were, in general, more specialists. Our study shows that elevation range expansions as climate warms have important and predictable impacts on the structure and size distribution of food webs across space. © 2012 The Royal Society.
Martínez-Vilalta J., López B.C., Loepfe L., Lloret F. (2012) Stand- and tree-level determinants of the drought response of Scots pine radial growth. Oecologia. 168: 877-888.EnllaçDoi: 10.1007/s00442-011-2132-8
Characterizing the responses of key tree species to extreme climatic events may provide important information for predicting future forest responses to increased climatic variability. Here we aimed at determining which tree- and stand-level attributes were more closely associated with the effect of a severe drought on the radial growth of Scots pine, both in terms of immediate impact and recovery after the drought event. Our dataset included tree-ring series from 393 plots located close to the dry limit of the species range. Time series analysis and mixed-effects models were used to study the growth of each tree and its detailed response to a severe drought event that occurred in 1986. Our results showed that the radial growth responses of Scots pine were determined primarily by tree-level characteristics, such as age and previous growth rate, and secondarily by stand basal area and species richness, whereas local climate had a relatively minor effect. Fast-growing trees were more severely affected by the drought and retained proportionally lower growth rates up to three years after the episode. In absolute terms, however, fast-growing trees performed better both during and after the event. Older trees were found to be less resilient to drought. The effect of stand basal area and species richness indicated that competition for resources worsened the effects of drought, and suggested that the effect of interspecific competition may be particularly detrimental during the drought year. © 2011 Springer-Verlag.
Arnan X, López BC, Martínez-Vilalta J, Estorach M, Poyatos R (2011) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronología doi: 10.1016/j.dendro.2011.02.002.
Lopez B.C., Potrony D., López A., Badosa E., Bonada A., Saló R. (2010) Nest-box use by Boreal Owls (Aegolius funereus) in the Pyrenees Mountains in Spain. Journal of Raptor Research. 44: 40-49.EnllaçDoi: 10.3356/JRR-09-32.1
The Boreal Owl (Aegolius funereus) is a nocturnal forest-dwelling species widely distributed throughout the world. One of the least studied and most southerly populations of this species lives in the Pyrenees Mountains. This population, 500600 pairs, probably suffered a slight decline during recent decades due to forestry management practices. The use of nest boxes may become necessary to protect this species in southern Europe. The objective of this study was to establish a standard protocol for nest-box installation, based on the analysis of occupation rates of nest boxes installed during the last 20 yr and the comparison of reproductive data for nest boxes and natural nest cavities. Our results indicated that nest boxes should be installed at high elevations (above 2000 m asl), below 4 m aboveground, and preferably facing south or southeast. We also found that most territories are located where maximum July temperatures are
López B.C., Pino J., López A. (2010) Explaining the successful introduction of the alpine marmot in the Pyrenees. Biological Invasions. 12: 3205-3217.EnllaçDoi: 10.1007/s10530-010-9712-0
Alpine marmots were introduced into the northern Pyrenees between 1948 and 1988 from individuals captured in the French Alps, in order to bolster food sources for the golden eagle and brown bear. The marmot's subsequent occupation of the southern Pyrenees has been extremely fast. From an initial population of ~400 individuals, the present population in the southern Pyrenees is estimated to be of more than 10,000 individuals. The objective of this study was to assess what were the mechanisms that have enabled such a fast occupation of the territory. We studied habitat preferences and habitat selection of the alpine marmot in the southern Pyrenees both at the micro- and meso-scale, and compared our results with similar data in the bibliography on their native region. We also compared climatic data from both the native and introduction sites. Our results indicate relatively low climate (precipitation and temperature) matching between the two sites but a relatively high habitat matching. Marmots negatively select high woody cover and the presence of conifers in their home range, while they choose alpine and sub-alpine meadows close to rivers with boulders. Furthermore, the marmot population is independent of snow cover duration. We conclude that the successful establishment in the Pyrenees by the alpine marmot is explained both by the habitat- and climate-matching mechanisms. In both aspects, marmots show a generalist response. Meso-scale GIS-derived variables were non significant when analyzed together with local, micro-scale variables from field measurements. © 2010 Springer Science+Business Media B.V.
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