The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events... more The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events could induce growth decline and die-off on tree populations located at the geographical distribution limit of the species. Understanding of adaptive capacity and regional vulnerability to climate change in Mediterranean forests is not well developed and requires more focused research efforts. We studied the relationships between spatiotemporal patterns of temperature and precipitation along the southwestern edge of the Betic range (southern Spain) and measured basal area increment (BAI) and carbon isotope (Δ) in tree ring series of Abies pinsapo and Pinus halepensis, two Mediterranean conifer trees with contrasting drought adaptive capacity. Climatic information was obtained from a network covering a wide range of elevations and distances from the Atlantic and Mediterranean coasts. Temperature trends were tested by the Mann–Kendall test, and precipitation was thoroughly analyzed by quantile regression. Climatic data showed a warming trend, enhanced since the 1970s, while quantile regressions revealed that drought events worsened during the course of the twentieth century. Long-term decrease of A. pinsapo BAI was related to regional warming and changing precipitation patterns, suggesting increasing drought stress on this species. Both temperature and precipitation in the summer influenced wood Δ in P. halepensis, whereas negative correlation between wood Δ and current autumn temperature was yielded for A. pinsapo. Increased intrinsic water use efficiency was inferred from wood Δ in both species; however, A. pinsapo showed sudden growth reductions under drier conditions, while pine trees were able to maintain almost constant BAI values and lower water costs under increasing long-term water stress.
The causal factors and effects of forest declines are not well understood in temperate conifer fo... more The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir (Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km 2 . We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.
The combined effects of changes in climate and land use on tree mortality and growth patterns hav... more The combined effects of changes in climate and land use on tree mortality and growth patterns have rarely been addressed. Relict tree species from the Mediterranean Basin serve as appropriate models to investigate these effects, since they grow in climatically stressed areas which have undergone intense cover changes. The aim is to use climate, aerial photographs, stand structure and radial-growth data to explain the mortality and historical patterns of growth of Abies pinsapo in the area where this relict species was first protected.
1. Long-term basal area increment (BAI) in Abies pinsapo was studied to investigate the way densi... more 1. 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.2. 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.3. 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.4. 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.
Introduction and statement of the research questions Gap dynamics have been widely studied in for... more Introduction and statement of the research questions Gap dynamics have been widely studied in forests of Abies spp. from temperate and boreal regions. The local microclimate and competition for light have been identified as the main factors controlling changes in species composition and canopy structure, however little is known on dynamics of such forests in Mediterranean. Experimental design and aims We studied forest structure and dynamics of Abies pinsapo stands in southern Spain, in contrasting habitats and successional status. In addition past regeneration patterns and their relationship to canopy structure, disturbances and forest-use history were investigated. Results Stands structure attributes were within the range described for temperate conifer biomes. The age structure revealed two main cohorts comprised of a few > 100 year-old trees and abundant younger trees established in a single recruitment event after the stands were protected in the 1950s. Initial growth-rate analyses indicated that A. pinsapo regenerated mainly in small canopy gaps, while only 15% recruited from the forest understorey. For the last ten years, basal area increment was lower than 10 cm2 y−1 in 91% of studied trees and growth rate differences between trees narrowed. Conclusion Stand dynamics in A. pinsapo forests maintain general features of temperate fir forests. Tree establishment over time and current stand structure fit to known changes in forest use. Widespread growth decline trends might be linked to stand stagnation and global warming. Introduction et état des questions de recherche Les dynamiques des trouées ont été largement étudiées dans les forêts d’Abies spp. à partir des régions tempérées et boréales. Le microclimat local et la compétition pour la lumière ont été identifiés comme les principaux facteurs de contrôle des changements dans la composition des espèces et la structure du couvert, mais on sait peu de choses sur la dynamique de ces forêts dans les écosystèmes méditerranéens. Plan expérimental et objectifs Nous avons étudié la structure de la forêt et la dynamique de peuplements d’Abies pinsapo dans le sud de l’Espagne, dans des habitats contrastés et dans des états d’évolution successifs. En outre, les modèles passés de régénération et leurs relations avec la structure du couvert, les perturbations et l’histoire de l’utilisation des forêts ont été étudiés. Résultats Les attributs de structure des peuplements se situent dans la gamme décrite pour les biomes de conifères tempérés. La structure des âges a révélé deux cohortes principales composées de quelques vieux arbres d’un âge supérieur à 100 ans, et de nombreux jeunes arbres établis dans un seul évènement de régénération après que les peuplements aient été protégés dans les années 1950. Les premières analyses des taux de croissance ont indiqué que A. pinsapo s’est régénéré principalement dans les petites trouées, tandis que seulement 15 % des arbres ont été recrutés dans le sous-bois. Au cours des dix dernières années, l’augmentation de la surface terrière a été inférieure à 10 cm2 an−1 chez 91 % des arbres étudiés et les différences entre les taux de croissance des arbres étaient réduites. Conclusion Les dynamique des peuplements d’A. pinsapo conservent les caractéristiques générales des forêts de sapins tempérés. L’installation des arbres et la structure actuelle des peuplements permettent de connaître les changements dans l’utilisation de la forêt. La baisse généralisée des tendances de croissance pourrait être liée à la stagnation du peuplement et au réchauffement de la planète.
The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events... more The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events could induce growth decline and die-off on tree populations located at the geographical distribution limit of the species. Understanding of adaptive capacity and regional vulnerability to climate change in Mediterranean forests is not well developed and requires more focused research efforts. We studied the relationships between spatiotemporal patterns of temperature and precipitation along the southwestern edge of the Betic range (southern Spain) and measured basal area increment (BAI) and carbon isotope (Δ) in tree ring series of Abies pinsapo and Pinus halepensis, two Mediterranean conifer trees with contrasting drought adaptive capacity. Climatic information was obtained from a network covering a wide range of elevations and distances from the Atlantic and Mediterranean coasts. Temperature trends were tested by the Mann–Kendall test, and precipitation was thoroughly analyzed by quantile regression. Climatic data showed a warming trend, enhanced since the 1970s, while quantile regressions revealed that drought events worsened during the course of the twentieth century. Long-term decrease of A. pinsapo BAI was related to regional warming and changing precipitation patterns, suggesting increasing drought stress on this species. Both temperature and precipitation in the summer influenced wood Δ in P. halepensis, whereas negative correlation between wood Δ and current autumn temperature was yielded for A. pinsapo. Increased intrinsic water use efficiency was inferred from wood Δ in both species; however, A. pinsapo showed sudden growth reductions under drier conditions, while pine trees were able to maintain almost constant BAI values and lower water costs under increasing long-term water stress.
The causal factors and effects of forest declines are not well understood in temperate conifer fo... more The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir (Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km 2 . We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.
The combined effects of changes in climate and land use on tree mortality and growth patterns hav... more The combined effects of changes in climate and land use on tree mortality and growth patterns have rarely been addressed. Relict tree species from the Mediterranean Basin serve as appropriate models to investigate these effects, since they grow in climatically stressed areas which have undergone intense cover changes. The aim is to use climate, aerial photographs, stand structure and radial-growth data to explain the mortality and historical patterns of growth of Abies pinsapo in the area where this relict species was first protected.
1. Long-term basal area increment (BAI) in Abies pinsapo was studied to investigate the way densi... more 1. 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.2. 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.3. 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.4. 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.
Introduction and statement of the research questions Gap dynamics have been widely studied in for... more Introduction and statement of the research questions Gap dynamics have been widely studied in forests of Abies spp. from temperate and boreal regions. The local microclimate and competition for light have been identified as the main factors controlling changes in species composition and canopy structure, however little is known on dynamics of such forests in Mediterranean. Experimental design and aims We studied forest structure and dynamics of Abies pinsapo stands in southern Spain, in contrasting habitats and successional status. In addition past regeneration patterns and their relationship to canopy structure, disturbances and forest-use history were investigated. Results Stands structure attributes were within the range described for temperate conifer biomes. The age structure revealed two main cohorts comprised of a few > 100 year-old trees and abundant younger trees established in a single recruitment event after the stands were protected in the 1950s. Initial growth-rate analyses indicated that A. pinsapo regenerated mainly in small canopy gaps, while only 15% recruited from the forest understorey. For the last ten years, basal area increment was lower than 10 cm2 y−1 in 91% of studied trees and growth rate differences between trees narrowed. Conclusion Stand dynamics in A. pinsapo forests maintain general features of temperate fir forests. Tree establishment over time and current stand structure fit to known changes in forest use. Widespread growth decline trends might be linked to stand stagnation and global warming. Introduction et état des questions de recherche Les dynamiques des trouées ont été largement étudiées dans les forêts d’Abies spp. à partir des régions tempérées et boréales. Le microclimat local et la compétition pour la lumière ont été identifiés comme les principaux facteurs de contrôle des changements dans la composition des espèces et la structure du couvert, mais on sait peu de choses sur la dynamique de ces forêts dans les écosystèmes méditerranéens. Plan expérimental et objectifs Nous avons étudié la structure de la forêt et la dynamique de peuplements d’Abies pinsapo dans le sud de l’Espagne, dans des habitats contrastés et dans des états d’évolution successifs. En outre, les modèles passés de régénération et leurs relations avec la structure du couvert, les perturbations et l’histoire de l’utilisation des forêts ont été étudiés. Résultats Les attributs de structure des peuplements se situent dans la gamme décrite pour les biomes de conifères tempérés. La structure des âges a révélé deux cohortes principales composées de quelques vieux arbres d’un âge supérieur à 100 ans, et de nombreux jeunes arbres établis dans un seul évènement de régénération après que les peuplements aient été protégés dans les années 1950. Les premières analyses des taux de croissance ont indiqué que A. pinsapo s’est régénéré principalement dans les petites trouées, tandis que seulement 15 % des arbres ont été recrutés dans le sous-bois. Au cours des dix dernières années, l’augmentation de la surface terrière a été inférieure à 10 cm2 an−1 chez 91 % des arbres étudiés et les différences entre les taux de croissance des arbres étaient réduites. Conclusion Les dynamique des peuplements d’A. pinsapo conservent les caractéristiques générales des forêts de sapins tempérés. L’installation des arbres et la structure actuelle des peuplements permettent de connaître les changements dans l’utilisation de la forêt. La baisse généralisée des tendances de croissance pourrait être liée à la stagnation du peuplement et au réchauffement de la planète.
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