Open Access
Drought limits tree growth more than greenness and reproduction: insights from five case studies in Spain
(KeAi Communications, 2025-08-01) Camarero, Jesús Julio; Rubio-Cuadrado, Álvaro; González de Andrés, Ester; Valeriano, Cristina; Pizarro, Manuel; Imbert Rodríguez, Bosco; Lo, Yueh-Hsin; Blanco Vaca, Juan Antonio; Ciencias; Zientziak; Institute for Multidisciplinary Research in Applied Biology - IMAB
Droughts impact forests by influencing various processes such as canopy greenness, tree growth, and reproduction, but most studies have only examined a few of these processes. More comprehensive assessments of forest responses to climate variability and water shortages are needed to improve forecasts of post-drought dynamics. Iberian forests are well-suited for evaluating these effects because they experience diverse climatic conditions and are dominated by various conifer and broadleaf species, many of which exhibit masting. We assessed how greenness, evaluated using the normalized difference vegetation index (NDVI), tree radial growth, and seed or cone production responded to drought in five tree species (three conifers: silver fir (Abies alba), Scots pine (Pinus sylvestris), and stone pine (Pinus pinea); two broadleaves: European beech (Fagus sylvatica) and holm oak (Quercus ilex) inhabiting sites with different aridity. We correlated these data with the standardized precipitation evapotranspiration index (SPEI) using the climate window analysis (climwin) package, which identifies the most relevant climate window. Drought constrained growth more than greenness and seed or cone production. Dry conditions led to high seed or cone production in species found in cool, moist sites (silver fir, beech, and Scots pine). We also found negative associations of cone production with summer SPEI in the drought-tolerant stone pine, which showed lagged growth−cone negative correlations. However, in the seasonally dry holm oak forests, severe droughts constrained both growth and acorn production, leading to a positive correlation between these variables. Drought impacts on greenness, growth, seed, and cone production depended on species phenology and site aridity. A negative correlation between growth and reproduction does not necessarily indicate trade-offs, as both may be influenced by similar climatic factors.
Open Access
Drought-induced changes in wood density are not prevented by thinning in Scots pine stands
(MDPI, 2018) Candel Pérez, David; Lo, Yueh-Hsin; Blanco Vaca, Juan Antonio; Chiu, Chih-Ming; Camarero, Jesús Julio; González de Andrés, Ester; Imbert Rodríguez, Bosco; Castillo Martínez, Federico; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Density is an important wood mechanical property and an indicator of xylem architecture and hydraulic conductivity. It can be influenced by forest management and climate. We studied the impact of thinning and climate variables on annual stem radial growth (ring width and ring density, and their earlywood and latewood components) in two contrasting Scots pine (Pinus sylvestris L.) stands in northern Spain (one continental, one Mediterranean). At each site, three thinning regimes (control or T0, removing 20% basal area or T20, and removing 30% or T30) were randomly applied to nine plots per site (three plots per treatment) in 1999. Thinning was repeated at the Mediterranean site in 2009 (increasing thinning intensity in T30 to 40%). Eight trees per plot were cored in spring 2014. Second thinning at the Mediterranean site and first thinning at the continental site generally caused significantly wider ring (RW), earlywood (EW) and latewood (LW) widths, although no differences between T20 and T30/40 were found, supporting in part the common observation that radial growth is enhanced following thinning as competition for water and nutrients is reduced. At the Mediterranean site, values of latewood density (LD) and maximum density (Dmax) relative to pre-thinning conditions were significantly lower in T0 than in T30. However, at the continental site, relative changes of ring density (RD) and LD were significantly higher in T0 than in T20 and T30. Climate significantly affected not only RWbut also RD, with significant RD drops during or right after unusually warm-dry years (e.g., 2003, 2011), which were characterized by LD reductions between 5.4 and 8.0%. Such RD decreases were quickly followed by recovery of pre-drought density values. These results indicate trees temporarily reduce LD as a way to enhance hydraulic conductivity during dry summers. However, climate effects on wood density were site-dependent. We also detected that the thinning effect was not intense enough to prevent drought-induced changes in wood density by altering water availability, but it could help to reduce wood properties fluctuations and therefore maintain more homogeneous wood mechanic features.
Open Access
Complex climate constraints of upper treeline formation in the Pyrenees
(Springer, 2015) González de Andrés, Ester; Camarero, Jesús Julio; Büntgen, Ulf; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Alpine treelines are often induced by a threshold of minimum temperatures above which tree growth is generally not possible anymore. However, this worldwide pattern may not account for more drought-prone mountains, where changes in precipitation can also affect ecosystem functioning and productivity at higher elevations. Here, we aim to determine if tree-ring formation in ecotones along the Pyrenees indeed primarily depends on temperature means or also reflects hydroclimatic changes. The mean duration of the growing season at Pyrenean treelines was 177 days, lasting from mid-May to early November, which corresponds to a mean root-zone temperature of 8.2 °C. Temperatures during the early and late growing season were most critical for mountain pine growth at highest elevations, and above average spring temperatures also contributed to radial enlargement of tracheids. Sites showing more similar soil temperatures also presented more similar long-term growth trends indicating that local conditions trace regional influences on growth. Nevertheless, more wet conditions in summer enhanced growth at treelines subjected to more Mediterranean influence and therefore having a higher summer water deficit. A broader perspective reveals that soil moisture availability during spring and summer, however, also influence ring width formation at other treelines located in mid-latitude mountains separating temperate and semi-arid biomes. Our results suggest re-evaluating the idea of purely temperature-limited treelines, especially in mid-latitude mountains that experience moisture seasonality or where precipitation decreases with increasing elevation.
Open Access
Constrained trait variation by water availability modulates radial growth in evergreen and deciduous mediterranean oaks
(Elsevier, 2024) González de Andrés, Ester; Serra-Maluquer, Xavier; Gazol, Antonio; Olano, José Miguel; García Plazaola, José Ignacio; Fernández Marín, Beatriz; Imbert Rodríguez, Bosco; Coll, Lluís; Ameztegui, Aitor; Espelta, Josep Maria; Alla, Arben Q.; Camarero, Jesús Julio; Ciencias; Zientziak; Institute for Multidisciplinary Research in Applied Biology - IMAB
Spatial and temporal variation in functional traits allows trees to adjust to shifting environmental conditions such as water stress. However, the change of traits, both mean and variances, along water availability gradients and across growing seasons, as well as their covariation with tree performance, have been rarely assessed. We examined intraspecific trait variation in coexisting evergreen (Quercus ilex ssp. ilex and Q. ilex ssp. ballota) and deciduous (Quercus faginea and Quercus humilis) Mediterranean oaks along a wide water availability gradient in northeastern Spain during six years. We measured leaf area (LA), shoot twig mass (Sm), leaf mass per area (LMA) and the ratio of shoot twig to leaf biomass (Sm:Lm). We characterized tree performance through basal area increment (BAI) and drought resilience indices. Higher variation was found within individuals than between individuals across populations and years. Within species, we found trait adjustments toward more conservative water-use (low LA and Sm and high LMA) with increasing drier conditions. Intraspecific trait variation was constrained by water availability, particularly on the deciduous species. In Q. ilex, trait variance of LMA positively covaried with annual BAI, whereas variance of LA, Sm and Sm:Lm was positively related to resistance and resilience against the severe 2012 drought in deciduous oaks. Our results support a tradeoff between the ability to tolerate drought and the capacity to cope with unpredictable changes in the environment through increased intraspecific trait variation, which may have implications on tree performance in the face of increased extreme events.
Open Access
Papel de los factores bióticos y las sequías en el decaimiento del bosque: aportaciones desde la dendroecología
(Asociación Española de Ecología Terrestre, 2015) Sangüesa Barreda, G.; Camarero, Jesús Julio; Linares, J.C.; Hernández, R.; Oliva Serrano, Jesús; Gazol, Antonio; González de Andrés, Ester; Montes, F.; García Martín, A.; Riva, J. de la; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
El aumento de la mortalidad y la pérdida de vitalidad de los bosques son procesos que afectan a diversas especies de árboles y biomas. Estos fenómenos de decaimiento forestal se han asociado a la interacción de múltiples factores relacionados con el cambio global, como el aumento de las sequías o la mayor incidencia de factores bióticos que generan estrés. Sin embargo, el papel que juegan estos organismos en el decaimiento del bosque en relación a la sequía no está del todo comprendido. En este trabajo caracterizamos retrospectivamente los efectos que ejercen dichos organismos sobre el crecimiento radial de árboles estresados por sequía utilizando dendrocronología. El efecto combinado del muérdago y las sequías reducen el crecimiento del pino silvestre y aumentan la defoliación, siendo estos efectos más evidentes en el ápice del árbol. La procesionaria induce pérdidas de crecimiento en pino laricio, pero en general se observa una recuperación dos años después. No encontramos un papel determinante de los hongos patógenos de raíz en el decaimiento del abeto. Finalmente, pinos carrasco muertos que presentaban ataques de insectos perforadores mostraron patrones de crecimiento similares a pinos vivos. Este estudio nos permite caracterizar algunos de los complejos y múltiples efectos de diferentes factores bióticos de estrés sobre el crecimiento y la vulnerabilidad de los bosques susceptibles a los efectos negativos de las sequías.
Open Access
Los precedentes y las respuestas de los árboles a sequías extremas revelan los procesos involucrados en el decaimiento de bosques mediterráneos de coníferas
(Asociación Española de Ecología Terrestre, 2012) Camarero, Jesús Julio; Sangüesa Barreda, G.; Alla, Arben Q.; González de Andrés, Ester; Maestro Martínez, M.; Vicente Serrano, S.M.; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
¿Qué determina la vulnerabilidad de las especies de árboles frente a eventos climáticos extremos en el contexto actual de calentamiento global? Sabemos que las sequías severas contribuyen al decaimiento del bosque pero desconocemos los procesos involucrados en el declive de crecimiento y la pérdida de vigor del árbol que pueden conducir a su muerte. Para profundizar en estos procesos combinamos datos retrospectivos de crecimiento secundario, obtenidos mediante dendrocronología, y variables funcionales potencialmente indicadoras de cambios de vigor (frondosidad, producción de albura, cambios en las concentraciones de carbohidratos no estructurales en acículas y albura del tronco) en bosques mediterráneos afectados por decaimiento inducido por sequía. Evaluamos las respuestas de tres especies de árboles (Abies alba, Pinus sylvestris y Pinus halepensis) a la sequía extrema del año 2012 caracterizada mediante un índice de sequía que considera la temperatura. En primavera y verano del año 2012 la sequía fue muy intensa debido a que las elevadas temperaturas máximas condujeron a condiciones de aridez que carecen de precedentes similares desde 1950. En las tres especies los árboles menos frondosos (más defoliados) formaban menos albura y ésta contenía una menor concentración de azúcares solubles que en los árboles más frondosos. Los árboles más defoliados presentaron también mayor similitud de crecimiento secundario entre años consecutivos que los poco defoliados. Los patrones de crecimiento difirieron entre especies y sugieren que en P. sylvestris el decaimiento responde a sequías extremas recurrentes durante el siglo pasado, mientras que A. alba y P. halepensis muestran patrones correspondientes a un declive durante la pasada década relacionado con el aumento de temperaturas que ha producido el decaimiento de individuos que durante episodios climáticamente benignos pasados mostraron altas tasas de crecimiento. Los diversos patrones descritos indican la necesidad de definir conceptos como la muerte del árbol o su recuperación post-decaimiento dentro de un marco de investigación objetivo, cuantitativo y verificable.
Open Access
Tree-to-tree competition in mixed European beech-Scots pine forests has different impacts on growth and water-use efficiency depending on site condition.
(Wiley, 2018) González de Andrés, Ester; Camarero, Jesús Julio; Blanco Vaca, Juan Antonio; Imbert Rodríguez, Bosco; Lo, Yueh-Hsin; Sangüesa Barreda, G.; Castillo Martínez, Federico; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Mixed conifer-hardwood forests can be more productive than pure forests and they are increasingly considered as ecosystems that could provide adaptation strategies in the face of global change. However, the combined effects of tree-to-tree competition, rising atmospheric CO2 concentrations and climate on such mixtures remain poorly characterized and understood.2. To fill this research gap, we reconstructed 34-year series (1980-2013) of growth (basal area increment, BAI) and intrinsic water-use efficiency (iWUE) of Scots pine (Pinus sylvestris L.)-European beech (Fagus sylvatica L.) mixed stands at two climati-cally contrasting sites located in the southwestern Pyrenees. We also gathered data on tree-to-tree competition and climate variables in order to test the hypotheses that (1) radial growth will be greater when exposed to inter- than to intraspecific competition, that is, when species complementarity occurs and (2) enhanced iWUE could be linked to improved stem radial growth.3. Growth of both species was reduced when intraspecific competition increased. Species complementarity was linked to improved growth of Scots pine at the continental site, while competition overrode any complementarity advantage at the drought-prone Mediterranean site. Beech growth did not show any significant response to pine admixture likely due to shade tolerance and the highly competitive nature of this species. Increasing interspecific competition drove recent iWUE changes, which increased in Scots pine but decreased in European beech. The iWUE enhancement did not involve any growth improvement in Scots pine. However, the positive BAIiWUE relationship found for beech suggests an enhanced beech growth in drought-prone sites due to improved water use.4. Synthesis. Complementarity may enhance growth in mixed forests. However, water scarcity can constrict light-related complementarity for shade intolerant species (Scots pine) in drought-prone sites. Basal area increment-intrinsic water-use efficiency relationships were negative for Scots pine and positive for European beech. These contrasting behaviours have got implications for coping with the expected increasing drought events in Scots pine-European beech mixtures located near ecological limit of the two species. Complementarity effects between tree species should be considered to avoid overestimating the degree of future carbon uptake by mixed conifer¿broadleaf forests.