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.
•Beech growth and vessel area respond to precipitation at disparate temporal domains.•Previous summer precipitation favors secondary growth.•Precipitation during vessel expansion phase controls ...vessel area variability.•Water-shortage constraints on growth and anatomy are shared along beech dry edge.
The response of European beech (Fagus sylvatica L.) to climate warming will depend on the ability of their populations to adjust tree performance to water shortage. By exploring inter- and intra-annual variations in secondary growth and mean vessel area (MVA), we assessed the effects of precipitation on cambial activity and hydraulic control during the vessel expansion phase along tree lifes. We sampled beech populations at low and high altitude from four mountain ranges across its southwestern distribution edge. We measured a total of 45,897 rings from 126 trees and 5.5 million vessels from 76 trees. We built chronologies for ring width and MVA between 1950 and 2017, calculated their climate responses and evaluated the effects of region, altitude and chronology type (ring-width vs. MVA) by means of ordinations (PCA) and constrained ordinations (pRDA). Precipitation controlled ring width and MVA along beech's southwestern distribution range, but at different time domains. Ring width responded primarily to summer precipitation during the previous growing season, whereas MVA responded to water availability during the vessel expansion phase, with timing shifting along the ring, according to the moment of vessel expansion. Regional differences were significant, but low, compared with the effect of chronology type. A large part of the variance explained by region was due to the strong difference between Western Pyrenees forests –growing under hyperhumid conditions– and the rest of forests under drier and warmer climate. Only minor differences between altitudes were found for the climate control of ring width and vessel size at annual scale, and no intra-annual effect on climate control of MVA. The stronger effect of chronology type on climatic response compared to the role of geographical location or altitude suggests common climate constraints on secondary growth and xylem anatomy along beech dry edge.
Key message
Sex and site conditions modulate intra- and inter-annual secondary growth and its climatic sensitivity in a dioecious Mediterranean conifer.
Divergent evolutionary pressures associated ...with differential reproductive costs in dioecious trees may lead to sex-related variation in non-reproductive functions. Sex-related differences may be site-dependent, with different outcomes depending on environmental conditions. We explored the effects of sex and environmental conditions on the climatic control of annual secondary growth and intra-annual wood density fluctuations (IADF) of a dioecious conifer (
Juniperus thurifera
L.) growing in two sites with contrasting hydrological conditions under a continental Mediterranean climate. Different sex-related strategies had variable effects on relative secondary growth, with females outperforming males under more favorable hydrological conditions, and males outperforming females under water-limited conditions. Ring width and IADF formation were driven by climatic factors occurring at different temporal scales. Tree-ring growth depended on factors acting prior to the initiation of the xylogenesis and to conditions directly affecting the duration and pace of cambial activity, and ring width, therefore, integrated a complex signal of factors occurring over a relatively long period, and on an annual cycle. In contrast, IADFs responded to singular short-term events that alleviated drought and promoted cambial reactivation during the summer arrest. Female trees showed a more opportunistic water use, displayed in the stronger ring-width response to June–July conditions. Enhanced cambial sensitivity in females set a lower threshold for IADF occurrence, leading to a higher frequency of IADFs irrespective of site. Intra-annual and inter-annual female growth patterns reflect an opportunistic strategy to benefit from favorable climatic windows.
Como regla general, la facilitación predomina sobre la competencia en ambientes con un alto grado de estrés, pero los niveles de estrés cambian a lo largo de la vida de las plantas. Resulta clave ...incluir el tiempo en los estudios de las interacciones planta-planta a través del monitoreo de las plantas a lo largo de sus ciclos vitales completos, pero captar la dimensión temporal requiere largos períodos de estudio. En este artículo se presentan distintas formas de incluir el tiempo en el estudio de las interacciones entre plantas utilizando técnicas dendrocronológicas. Mediante la presentación de distintos casos de estudio se desarrolla el modo de incluir la información que proporciona la edad de las plantas (control de la ontogenia y determinación de la estructura de edades de la población) y la anchura de anillos (crecimiento secundario) en estudios a nivel de comunidad, de población y de individuos. Se destaca la existencia de anillos de crecimiento en arbustos y herbáceas perennes y se pone de manifiesto el potencial que esto supone de cara a realizar estudios ecológicos. Para concluir se presentan otras variables que quedan registradas en los anillos de crecimiento y son susceptibles de ser utilizadas como complemento en los estudios de interacciones entre plantas, como los ratios isotópicos o distintas variables relacionadas con la anatomía cuantitativa de la madera.
Abstract
Forests are threatened globally by increased recurrence and intensity of hot droughts. Functionally close coexisting species may exhibit differences in drought vulnerability large enough to ...cause niche differentiation and affect forest dynamics. The effect of rising atmospheric CO2, which could partly alleviate the negative effects of drought, may also differ between species. We analysed functional plasticity in seedlings of two taxonomically close pine species (Pinus pinaster Ait., Pinus pinea L.) under different CO2 and water stress levels. The multidimensional functional trait variability was more influenced by water stress (preferentially xylem traits) and CO2 (mostly leaf traits) than by differences between species. However, we observed differences between species in the strategies followed to coordinate their hydraulic and structural traits under stress. Leaf 13C discrimination decreased with water stress and increased under elevated CO2. Under water stress both species increased their sapwood area to leaf area ratios, tracheid density and xylem cavitation, whereas they reduced tracheid lumen area and xylem conductivity. Pinus pinea was more anisohydric than P. pinaster. Pinus pinaster produced larger conduits under well-watered conditions than P. pinea. Pinus pinea was more tolerant to water stress and more resistant to xylem cavitation under low water potentials. The higher xylem plasticity in P. pinea, particularly in tracheid lumen area, expressed a higher capacity of acclimation to water stress than P. pinaster. In contrast, P. pinaster coped with water stress comparatively more by increasing plasticity of leaf hydraulic traits. Despite the small differences observed in the functional response to water stress and drought tolerance between species, these interspecific differences agreed with ongoing substitution of P. pinaster by P. pinea in forests where both species co-occur. Increased CO2 had little effect on the species-specific relative performance. Thus, a competitive advantage under moderate water stress of P. pinea compared with P. pinaster is expected to continue in the future.
•The P. nigra growth was enhanced by high spring precipitation.•Temperature explained a higher proportion of the BAI variance than precipitation.•Growth projections forecast a decline in BAI across ...all ecological regions.•The growth decline was lower in EN populations compared to the other populations.
Droughts chronically alter resource availability in forest ecosystems. The increased frequency and severity of such extreme climate events challenge the acclimation potential of tree species especially across the drought-prone Mediterranean region. Pinus nigra is a widely distributed tree species in the Mediterranean region and considered vulnerable to extreme droughts. We used a 1000 km latitudinal gradient from northern Morocco to north-eastern Spain incorporating four regions (Edge-South, Core-South, Core-North and Edge-North) and including different P. nigra provenances. We aim to identify the climate and forest structure related drivers that influence tree radial growth (BAI, basal area increment). We developed statistical models for BAI by incorporating the potential effects of climate and forest structure (diameter and age distributions). Then, we forecasted the future growth of P. nigra forests during the 21st century considering the emission scenario A2 with an expected increase of +2.7 °C at the end of this century. Our results showed large variability across P. nigra populations in terms of environmental conditions, forest structure, and growth. The northernmost P. nigra populations, subjected to wetter and cooler conditions were those presenting the lowest BAI (4.9 cm2), whereas the southernmost P. nigra populations subjected to drier and warmer conditions presented the highest BAI values (11.5 cm2). Pinus nigra growth was enhanced by high spring precipitation, but this positive effect was probably modulated by forest structure. Temperature explained a higher proportion of the BAI variance than precipitation, with warmer summer conditions decreasing growth. Growth projections forecasted a decline in BAI (from 9.6 to 7.0 cm2) across all ecological regions starting around the mid-21st century but being lower in Edge-North populations compared to the other populations. Our study provides quantitative knowledge related to how P. nigra populations have been growing across four distinctive ecological regions. We also provide a forecasting tool that incorporates both climate and stand structure related information to project dynamics in tree populations.
