Abstract
Rear‐edge tree populations are experiencing a combination of higher temperatures and more intense droughts that might push individuals beyond their tolerance limits. This trend towards ...rising atmospheric CO
2
is concurrent with an increase in intrinsic water use efficiency (iWUE), which theoretically enhances photosynthesis and decrease evapotranspiration rates, consequently improving tree resistance to drought. However, it remains unclear whether iWUE is favouring tree growth under current climate conditions, particularly when climate and iWUE legacy effects are simultaneously considered.
We evaluated this question with an extensive sampling along Iberian rear‐edge (dry) populations comprising four mountain ranges and two distinct altitudes. We simultaneously examined the effects of climate and iWUE on secondary growth using annually resolved basal area increments (BAIs) for the period 1901–2017. We used linear mixed models including second‐order autocorrelation and 1‐year legacy effects of iWUE and summer drought.
BAI and iWUE increased across the studied period. iWUE increase was driven by changes in atmospheric CO
2
concentration and water availability during the growing season. Climate and iWUE exerted direct and lagged effects on beech growth. Water availability during growing season was the main driver of tree growth, combining direct and indirect effects through its impact on iWUE. Legacy effects of water availability and iWUE were more important than growing season conditions. The net effect of iWUE shifted when lagged effects were considered, resulting in a net negative impact on tree growth.
Synthesis
: Our results reveal that climate and iWUE legacy effects must be considered to assess the net iWUE effect on secondary growth. Considering lagged effects, the current increase in iWUE is constraining tree growth. Modelling efforts of tree growth response to climate warming should include climate and iWUE legacy effects to adequately assess terrestrial ecosystem carbon balance.
Tree ring records are among the most valuable resources to create high-resolution climate reconstructions. Most climate reconstructions are based on old trees growing in inaccessible mountainous ...areas with low human activity. Therefore, reconstruction of climate conditions in lowlands is usually based on data from distant mountains. Albeit old trees can be common in humanized areas, they are not used for climate reconstructions. Pollarding was a common traditional management in Europe that enabled trees to maintain great vitality for periods exceeding the longevity of unmanaged trees. We evaluate the potential of pollarded deciduous oaks to record past climate signal. We sampled four pollarded woodlands in Central Spain under continental Mediterranean climate. We hypothesized that pollarded trees have a strong response to water availability during current period without pollarding management, but also in the period under traditional management if pruning was asynchronous among trees. Moreover, we hypothesized that if climate is a regional driver of oak secondary growth, chronologies from different woodlands will be correlated. Pollard oaks age exceeded 500 years with a strong response to Standardized Precipitation-Evapotranspiration Index (SPEI) from 9 to 11 months. Climate signal was exceptionally high in three of the sites (r2 = 0.443–0.655) during low management period (1962–2022). The largest fraction of this climate signal (≈70 %) could be retrieved during the traditional management period (1902–1961) in the three sites where pollarding was asynchronous. Chronologies were significantly correlated since the 19th century for all the studied period, highlighting a shared climate forcing. We identified critical points to optimize pollard tree sampling schema. Our results show the enormous potential of pollarded woodlands to reconstruct hydroclimate conditions in the Mediterranean with a fine spatial grain. Studying pollarded trees is an urgent task, since the temporal window to retrieve the valuable information in pollarded trees is closing as these giants collapse and their wood rots.
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•Pollarded trees are not used for climate reconstructions due to recurrent management.•Pollarded oaks can live >500 years in intensively managed territories.•Pollarded oaks secondary growth encapsulates valuable climate information.•We have few decades left to retrieve pollarded trees environmental information.
Key message
The post-fire growth responses and changes in wood C and N isotope composition depend on site water availability and fire severity in Mediterranean Aleppo pine forests.
Mediterranean ...forests are subjected to recurrent wildfires and summer droughts. Under warmer and drier conditions, it is required to determine how Mediterranean pines recover after wildfires, and how this translates into changes in tree radial growth and function (e.g. intrinsic water-use efficiency—iWUE). We analysed four Aleppo pine areas located in SE Spain affected by 1994 wildfires and subjected to different water availability, ranging from mesic to semi-arid conditions. We combined dendrochronological analyses with δ
13
C and δ
15
N wood isotopes to quantify the changes in radial growth (expressed as Basal Area Increment—BAI) and functional responses (iWUE and N cycling) to three fire severities (unburned sites, low and medium severities). We expected that the post-fire release in nutrients and a reduction in competition for water would enhance radial growth. We found that fire did not significantly alter growth patterns at the driest sites, but increased BAI at the wettest sites. δ
13
C was significantly (
P
≤ 0.01) more negative only in burned stands located at the wettest site indicating a decreased iWUE and thus improved water availability. However, the δ
15
N was higher in severely burned than in unburned plots from all sites but the wettest site, indicating a potential fertilization effect of fire in sites subjected to mild drought severity. Site water availability determined how fire affected subsequent modifications in growth and tree functioning of Aleppo pine forests, that is, changes in iWUE and N cycling. Therefore, site dryness should be explicitly considered to forecast the growth and functioning responses of Mediterranean pine forests to the predicted increasing recurrence of fire events due to global warming.
•Tree-ring growth data successfully validated modeled NPP in silver fir forests.•The main driver of growth and NPP was the summer evapotranspiration deficit.•Negative effects of drought override ...CO2-related enhancement of NPP in xeric sites.
Warming-induced drought stress has been hypothesized as a major driver of forest net primary production (NPP) reduction, but we lack reliable field data to assess if higher temperatures lead to forest NPP reduction, particularly in humid sites and at basin to landscape spatial scales. The use of a landscape approach would allow considering the feedbacks operating between climate, topography, soil vegetation and water resources. Here we follow that approach by simulating NPP using the regional hydro-ecologic simulation system (RHESSys) model and by comparing the results with radial growth data (tree-ring widths and intrinsic water-use efficiency – iWUE). We evaluate the relationships between climate, growth, NPP, atmospheric CO2 concentrations (ca) and iWUE in xeric and mesic silver fir forests subjected to contrasting water balances. The growth data successfully validated the 11-month NPP cumulated until spring. The main negative climatic driver of growth and NPP was the summer evapotranspiration deficit, which shows a negative association with tree-ring width indices. Sensitivity analyses indicate that rising ca do not compensate the severe NPP reduction associated to warmer and drier conditions. The positive effect of rising ca on NPP is mediated by climatic site conditions being detected only in mesic sites, whereas the negative effects of drought on NPP override any ca-related enhancement of NPP in xeric sites. Future warmer and drier conditions causing a higher evaporative demand by the atmosphere could lead to a NPP decline in temperate conifer forests subjected to episodic droughts.
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.
Theory predicts that the postindustrial rise in the concentration of CO₂in the atmosphere (cₐ) should enhance tree growth either through a direct fertilization effect or indirectly by improving water ...use efficiency in dry areas. However, this hypothesis has received little support in cold‐limited and subalpine forests where positive growth responses to either rising cₐor warmer temperatures are still under debate. In this study, we address this issue by analyzing an extensive dendrochronological network of high‐elevation Pinus uncinata forests in Spain (28 sites, 544 trees) encompassing the whole biogeographical extent of the species. We determine if the basal area increment (BAI) trends are linked to climate warming and increased cₐby focusing on region‐ and age‐dependent responses. The largest improvement in BAI over the past six centuries occurred during the last 150 years affecting young trees and being driven by recent warming. Indeed, most studied regions and age classes presented BAI patterns mainly controlled by temperature trends, while growing‐season precipitation was only relevant in the driest sites. Growth enhancement was linked to rising cₐin mature (151–300 year‐old trees) and old‐mature trees (301–450 year‐old trees) from the wettest sites only. This finding implies that any potential fertilization effect of elevated cₐon forest growth is contingent on tree features that vary with ontogeny and it depends on site conditions (for instance water availability). Furthermore, we found widespread growth decline in drought‐prone sites probably indicating that the rise in cₐdid not compensate for the reduction in water availability. Thus, warming‐triggered drought stress may become a more important direct driver of growth than rising cₐin similar subalpine forests. We argue that broad approaches in biogeographical and temporal terms are required to adequately evaluate any effect of rising cₐon forest growth.
•High variability in space and time of tree-growth response to climate in Spain.•Negative impact of low summer rainfall on growth increases at low elevations and high latitudes.•Growth at low ...elevations is more dependent on spring climate than at high elevations.•Negative impact of summer heat and drought has increased during the past decades.•Local adaptation to climate change is a key factor for future Mediterranean forests.
Scots pine forests subjected to continental Mediterranean climates undergo cold winter temperatures and drought stress. Recent climatic trends towards warmer and drier conditions across the Mediterranean Basin might render some of these pine populations more vulnerable to drought-induced growth decline at the Southernmost limit of the species distribution. We investigated how cold winters and dry growing seasons drive the radial growth of Scots pine subject to continental Mediterranean climates by relating growth to climate variables at local (elevational gradient) and regional (latitudinal gradient) scales. Local climate-growth relationships were quantified on different time scales (5-, 10- and 15-days) to evaluate the relative role of elevation and specific site characteristics. A negative water balance driven by high maximum temperatures in June (low-elevation sites) and July (high-elevation sites) was the major constraint on growth, particularly on a 5- to 10-day time scale. Warm nocturnal conditions in January were associated with wider rings at the high-elevation sites. At the regional scale, Scots pine growth mainly responded positively to July precipitation, with a stronger association at lower elevations and higher latitudes. January minimum temperatures showed similar patterns but played a secondary role as a driver of tree growth. The balance between positive and negative effects of summer precipitation and winter temperature on radial growth depends on elevation and latitude, with low-elevation populations being more prone to suffer drought and heat stress; whereas, high-elevation populations may be favoured by warmer winter conditions. This negative impact of summer heat and drought has increased during the past decades. This interaction between climate and site conditions and local adaptations is therefore decisive for the future performance and persistence of Scots pine populations in continental Mediterranean climates. Forecasting changes in the Scots pine range due to climate change should include this site-related information to obtain more realistic predictions, particularly in Mediterranean rear-edge areas.
Eventos extremos como las sequías severas modifican la dinámica de los bosques reduciendo su crecimiento y su capacidad de recuperación. En la cuenca Mediterránea los efectos de las sequías sobre los ...bosques pueden estar amplificados por el aumento de temperaturas. Además, ambos estreses actúan sobre bosques muy modificados por el hombre en los que el tamaño del árbol también depende del uso histórico. ¿Pueden entonces el crecimiento previo y el tamaño de los árboles condicionar la respuesta a una sequía en dos especies de Quercus que coexisten (Q. ilex - encina,Q. faginea - quejigo)? Para responder esta cuestión: (i) cuantificamos el número de pies y el tamaño de cada individuo en un monte bajo afectado por la sequía de 2011-2012 en el NE de España, (ii) reconstruimos el crecimiento radial de individuos poco o muy defoliados tras la sequía, y (iii) comparamos la anatomía del xilema (área transversal de los vasos) entre ambos grupos de defoliación en el caso de la encina. Los individuos más defoliados presentaron menor altura, y, en el caso de la encina, crecían menos y formaban vasos con áreas menores. Nuestros resultados indican que los individuos de encina que formaron vasos de área mayor y con mayor tasa de crecimiento fueron los menos vulnerables a la sequía. En el quejigo, los individuos más defoliados fueron los que mostraron una mayor pérdida de crecimiento en respuesta a temperaturas elevadas en primavera y verano.
Aim
Climate change is expected to modify growth trends of forests around the world. However, this modification may vary in strength and intensity across a species' biogeographical range. Here, we ...study European populations of silver fir (Abies alba) across its southern distribution limits in Spain, Italy and Romania. We hypothesized that growth trends of silver fir will differ across its distribution range, with a marked decline in growth in drought‐prone regions near the species' southernmost biogeographical limits.
Location
Europe (Spain, Italy, Romania).
Methods
We collected tree‐ring data from at least 1300 silver fir trees located in 111 sites. The dataset was used to assess and model growth trends, quantified as changes in basal area increment, and to determine how growth responds to climate.
Results
We found contrasting patterns of basal area increments among countries and sites. Populations of silver fir located outside the Mediterranean area (e.g. northern Italy, Romania) have shown a clear increase in growth over the last two decades, whereas most populations in Spain and southern Italy have displayed a marked decline in growth since the 1980s. The growth of silver fir forests at the south‐western distribution limit is severely constrained by low spring–summer water availability, whereas growth of silver fir forests in non‐Mediterranean areas is limited by cold conditions in late winter to early spring.
Main conclusions
Climate warming is distinctly modifying growth patterns and responses to climate in silver fir across most of the species' European distribution area. In south‐western Europe the reduction in growth of many populations is related to an observed increase in aridity, whereas in more temperate areas warming is enhancing growth. Our results confirm a decline in the growth of silver fir at its south‐western distribution limits as a consequence of climate warming.
El conocimiento de las interacciones existentes entre el cambio climático y el manejo del bosque en el decaimiento de ciertas especies forestales es necesario de cara al establecimiento de planes de ...conservación y gestión. En este trabajo hemos realizado una revisión bibliográfica y una síntesis de trabajos científicos centrados en el estudio de la causas del declive de los cedrales del Atlas (bosques de Cedrus atlantica), norte de Marruecos.Se han revisado trabajos sobre las tendencias climáticas y las propiedades del suelo y estudios dendroecológicos con el objetivo de determinar las relaciones existentes entre el patrón de crecimiento de los árboles, la degradación y el declive del bosque y el clima. Los bosques de cedro han sido severamente afectados por sequías, sobrepastoreo, talas y podas. Eventos recurrentes de intensa sequía, así como un incremento en la temperatura media, han sido identificados desde la década de 1970. El actual decaimiento de las poblaciones de cedro en bosques intensamente talados, podados y sobrepastoreados está propiciando su regresión y su sustitución por especies más resistentes a la sequía y las perturbaciones, como por ejemplo Quercus rotundifolia.
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