Tree species display a wide variety of water‐use strategies, growth rates and capacity to tolerate drought. However, if we want to forecast species capacity to cope with increasing aridity and ...drought, we need to identify which measurable traits confer resilience to drought across species. Here, we use a global tree ring network (65 species; 1931 site series of ring‐width indices—RWI) to evaluate the relationship of long‐term growth‐drought sensitivity (RWI‐SPEI drought index relationship) and short‐term growth response to extreme drought episodes (resistance, recovery and resilience indices) with functional traits related to leaf, wood and hydraulic properties. Furthermore, we assess the influence of climate (temperature, precipitation and climatic water deficit) on these trait‐growth relationships. We found a close correspondence between the long‐term relationship between RWI and SPEI and resistance and recovery of tree growth to severe drought episodes. Species displaying a stronger RWI‐SPEI relationship to drought and low resistance and high recovery to extreme drought episodes tended to have a higher wood density (WD) and more negative leaf minimum water potential (Ψmin). Such associations were largely maintained when accounting for direct climate effects. Our results indicate that, at a cross‐species level and global scale, wood and hydraulic functional traits explain species’ growth responses to drought at short‐ and long‐term scales. These trait‐growth response relationships can improve our understanding of the cross‐species capacity to withstand climate change and inform models to better predict drought effects on forest ecosystem dynamics.
This study evaluates de covariation between short‐term growth response to drought (resistance, recovery and resilience), long‐term growth drought relationship and functional traits related to leaf, wood and hydraulic properties. We found that species displaying a strong relationship between growth and drought (Ring Width Index ~Standardized Precipitation and Evapotranspiration Index relationship), low resistance and high recovery to extreme drought episodes tend to have higher wood density and more negative leaf minimum water potential.
see also the Commentary: https://doi.org/10.1111/gcb.16157.
Climate extremes, such as abnormally dry and wet conditions, generate abrupt shifts in tree growth, a situation which is expected to increase under predicted climate conditions. Thus, it is crucial ...to understand factors determining short‐ and long‐term tree performance in response to higher frequency and intensity of climate extremes.
We evaluated how three successive droughts and wet years influenced short‐ and long‐term growth of six dominant Iberian tree species. Within species variation in growth response to repeated dry and wet years was evaluated as a function of individual traits related to resource and water use (diameter at breast height DBH, wood density WD and specific leaf area SLA) and tree‐to‐tree competition across climatically contrasted populations. Furthermore, we assessed how short‐term accumulated impacts of the repeated dry and wet years influenced long‐term growth performance.
All species showed strong short‐term growth decreases and enhancements due to repeated dry and wet years. However, patterns of accumulated growth decreases (AcGD) and enhancements (AcGE) across climatically contrasting populations were species‐specific. Furthermore, individual trait data were weakly associated with either AcGD or AcGE and the few relevant associations were found for conifers. Intraspecific variations in tree growth responses to repeated climates extremes were large, and not explained by intraspecific variability in SLA and WD. Accumulated impacts of repeated dry and wet years were related to long‐term growth trends, showing how the recurrence of climate extremes can determine growth trajectories. The relationships of AcGD and AcGE with long‐term growth trends were more common in conifers species.
Synthesis. Repeated climate extremes do not only cause short‐term growth reductions and enhancements but also determine long‐term tree growth trajectories. This result shows how repeated droughts can lead to growth decline. Conifers were more susceptible to the accumulated effects of extreme weather events indicating that in the future, more intense and frequent climate extremes will alter growth performance in forests dominated by these species.
Repeated climate extremes do not only cause short‐term growth reductions and enhancements but also determine long‐term tree growth trajectories. This result shows how repeated droughts can lead to growth decline. Conifers were more susceptible to the accumulated effects of extreme weather events indicating that in the future, more intense and frequent climate extremes will alter growth performance in forests dominated by these species.
Drought-triggered declines in forest productivity and associated die-off events have increased considerably due to climate warming in the last decades. There is an increasing interest in quantifying ...the resilience capacity of forests against climate warming and drought to uncover how different stands and tree species will resist and recover after more frequent and intense droughts. Trees form annual growth rings that represent an accurate record of how forest growth responded to past droughts. Here we use dendrochronology to quantify the radial growth of different forests subjected to contrasting climatic conditions in Spain during the last half century. Particularly, we considered four climatically contrasting areas where dominant forests showed clear signs of drought-induced dieback. Studied forests included wet sites dominated by silver fir (Abies alba) in the Pyrenees and beech (Fagus sylvatica) stands in northern Spain, and drought-prone sites dominated by Scots pine (Pinus sylvestris) in eastern Spain and black pine (Pinus nigra) in the semi-arid south-eastern Spain. We quantified the growth reduction caused by different droughts and assessed the short-and long-term resilience capacity of declining vs. non-declining trees in each forest. In all cases, drought induced a marked growth reduction regardless tree vigor. However, the capacity to recover after drought (resilience) at short- and long-term scales varied greatly between declining and non-declining individuals. In the case of beech and silver fir, non-declining individuals presented greater growth rates and capacity to recover after drought than declining individuals. For Scots pine, the resilience to drought was found to be lower in recent years regardless the tree vigor, but the growth reduction caused by successive droughts was more pronounced in declining than in non-declining individuals. In the black pine forest an extreme drought induced a marked growth reduction in declining individuals when accounting for age effects on growth rates. We demonstrate the potential of tree-ring data to record short- and long-term impacts of drought on forest growth and to quantify the resilience capacity of trees.
Tree‐ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes ...in forest dynamics. Here, we related tree‐ring growth chronologies and stand‐level forest changes in basal area from two independent data sets to test if tree‐ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree‐ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981–2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree‐ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought‐prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought‐induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought‐prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought‐induced growth reductions and their cumulative impacts have strong potential to be used as early‐warning indicators of regional forest vulnerability.
The increase in frequency and intensity of droughts due to climate change might threaten forests under stress levels causing dieback and mortality episodes. Thus, deciphering how tree species from ...within a region respond to drought along environmental gradients should help us to understand forest vulnerability to climate change. To enlighten contrasting drought responses of dominant tree species, we reconstructed vegetation activity using Normalized Difference Vegetation Index (NDVI) and radial growth using tree-ring width series. We studied six tree species, three angiosperms (
Fagus sylvatica
,
Quercus humilis
, and
Quercus ilex
) and three gymnosperms (
Pinus sylvestris
,
Pinus nigra
, and
Pinus halepensis
), inhabiting a Mediterranean region in north-eastern Spain. We investigated if reduced growth resilience and increased growth synchrony after successive droughts (1986, 1989, 2005, and 2012): (i) were related to cumulative drought stress and (ii) preceded forest dieback in dry sites as compared to wet sites. In 2016, dieback affected
Q. ilex
and
P. sylvestris
stands in dry sites showing lower growth rates and NDVI. No dieback symptoms were observed in other species from dry (
P. nigra
,
P. halepensis
) or wet (
F. sylvatica
,
Q. humilis
,
P. sylvestris
) sites. Hot and dry summer conditions constrained growth and reduced NDVI. During 2005, a severe drought affected all species, but growth drops were more marked in dry places. All species were able to recover after extreme droughts, albeit angiosperms displayed lower than expected values of growth after the 2012 drought. Growth synchrony was higher in dry sites than in wet sites, and the differences were higher after the 2005 drought. This study reveals that the sensitivity of tree species to drought in species inhabiting the same region is species dependent, and it is contingent on local conditions with higher effects in dry sites than in wet sites. We describe how a cumulative impact of successive droughts increases growth synchrony and triggers the occurrence of dieback events in Mediterranean forests.
•Droughts and frosts impact growth in species southernmost distribution limits.•Droughts and frosts impair Silver fir and European beech radial growth.•Silver fir growth is more affected by drought ...than by late frosts.•European beech growth is more affected by late frosts than by drought.•We could not find interactive effects of drought and late frosts on growth.
Climate warming has lengthened the growing season by advancing leaf unfolding in many temperate tree species. However, an earlier leaf unfolding increases also the risk of frost damage in spring which may reduce tree radial growth. In equatorward populations of temperate tree species, both late frosts and summer droughts impose two constraints to tree growth, but their effects on growth are understudied. We used a tree-ring network of 71 forests to evaluate the potential influence of late frosts and summer droughts on growth in two tree species that reach their southern distribution limits in north-eastern Spain: the deciduous European beech (Fagus sylvatica L.) and the evergreen Silver fir (Abies alba Mill). The occurrence of late frost events and summer drought was quantified by using a high-resolution daily temperature and precipitation dataset considering the period 1950–2012. Late frosts were defined as days with average temperature below 0 °C in the site-specific frost-free period, whereas drought was quantified using the 18 month-long August Standardized Precipitation Evapotranspiration Index (SPEI). The growth of European beech and Silver fir was reduced by the occurrence of both late frost events and summer drought. However, we did not find a significant interaction on growth of these two climate extremes. Beech was more negatively impacted by late frosts, whereas Silver fir was more impacted by summer drought. Further studies could use remote-sensing information or in situ phenological records to refine our frost index and better elucidate how late frosts affect growth, whether they interact with drought to constrain growth, and how resilience mechanisms related to post-frost refoliation operate in beech.
•Tree neighbourhood identity influences soil microbial composition.•Tree size, competition and growth vary as a function of neighbour type.•Network of relationships between Silver fir neighbourhood, ...tree and soil features.•Mixture effects are complex and depend on soil, tree and neighbour interactions.
Mixed forests are expected to be more productive and resilient against disturbances than pure forests. However, tree to tree interactions are complex and vary depending on tree characteristics and multiple site features including soil properties. Such complexity is not normally accounted for in studies of mixing effects on tree response to drought. Here, we evaluate if neighbourhood tree identity influence soil biotic and abiotic characteristics in three mature, mixed Silver fir (Abies alba) forests. Further, we investigate the relationships between radial growth response to drought, tree characteristics (growth rate, size and competition pressure), tree neighbourhood, and soil physico-chemical and biological properties. Patterns of covariation between tree size, competition pressure, soil microbial composition, and growth recovery after drought were observed among different neighbourhood types. Slow-growing, small Silver fir trees experiencing high competitive pressure were associated with higher proportions of Scots pine (Pinus sylvestris) in the neighbourhood, high soil C:N ratios, and showed a faster growth recovery after drought. A neighbourhood dominated by broadleaf species (mainly European beech, Fagus sylvatica) was associated with high biomass of arbuscular mycorrhizal fungi, and low biomass of Gram-positive bacteria and Eukaryote, together with lower tree growth recovery. Therefore, coexistence with other Silver fir, Scots pine or European beech trees is associated to different covariation patterns of tree, soil and drought performance variables of the target Silver fir trees. Finally, our study remarks that combining tree, soil and neighbour variables at individual level helps to understand patterns of tree growth and growth response to drought under different stand mixtures.
The negative impacts of drought on forest growth and productivity last for several years generating legacies, although the factors that determine why such legacies vary across sites and tree species ...remain unclear.
We used an extensive network of tree‐ring width (RWI, ring‐width index) records of 16 tree species from 567 forests, and high‐resolution climate and normalized difference vegetation index (NDVI) datasets across Spain during the common period 1982‒2008 to test the hypothesis that climate conditions and growth features modulate legacy effects of drought on forests. Legacy effects of drought were calculated as the differences between detrended‐only RWI and NDVI series (i.e. after removing long‐term growth trends) and pre‐whitened RWI and NDVI series predicted by a model including drought intensity. Superposed Epoch Analysis (SEA) was used to estimate whether legacy effects differed from random. Finally, legacy effects were related to water balance, growth persistence and variability, and tree species identity.
We found a widespread occurrence of drought legacy effects on both RWI and NDVI, but they were seldom significant. According to SEA, first‐year drought legacies were negative and different from random in 9% and 5% of the RWI and NDVI series respectively. The number of significant second‐ and third‐year legacies was substantially lower. Differences between RWI and NDVI legacies indicate that canopy greenness and radial growth responses to drought are decoupled. We found variations in legacies between tree species with gymnosperms presenting larger first‐year drought legacies than angiosperms, which were exposed to less severe droughts. Greater growth variability can explain the presence of first‐year RWI legacies in gymnosperms from dry sites despite that the relationship between growth variability and legacies was complex.
Synthesis. Accounting for species and site responses to drought provides a better understanding of the magnitude and duration of drought legacies on forest growth and productivity. Despite the widespread occurrence of growth reductions in the years during and after drought occurrence, significant legacies were not very common, mostly lasted one year, and were more widespread in gymnosperms. These are relevant factors to be considered in the future when studying the consequences of drought on forest productivity and tree growth.
Legacy effects of drought on tree growth (RWI, ring‐width indices) and forest productivity (NDVI) vary between tree species. Drought legacies are more common for gymnosperms than for angiosperms and usually last for one year. Growth variability partially explains the variation in drought legacies between species despite the fact that this relationship is complex and species‐specific.
Warming-related growth decrease on southern Fagus sylvatica forests has been observed in different regions; however, whether it is a generalized fact or not remains unclear. Here we investigate the ...geographical pattern on growth response of the southwestern European beech forests to the warming climate shift which started in the 1980s. We sampled 15 beech forests (215 trees) across four climatically contrasting regions (Mediterranean, Pyrenean, low- and high-elevation Atlantic areas) near the southern distribution limit of the species in the Iberian Peninsula. Dendrochronological analyses were carried out to evaluate the growth of European beech since the 1950s. Growth responses quantified as pointer years, abrupt growth changes and long-term growth trends were compared between periods (before and after the 1980s climate shift), geographical regions and tree sizes. Analyses of the studied variables indicated a growth decrease in basal area increment after the climate shift in three of the four studied regions. Pyrenean stands were not negatively influenced by the climate shift, although an increase in the frequency of negative abrupt growth changes was also found there. Growth after the climate shift presented divergent patterns depending on the geographical region. Although Mediterranean and Atlantic stands presented different indicators of constrained growth, Pyrenean stands showed rising long-term growth trends. Such results suggest that regional characteristics differentially determine the growth response of the southern European beech forests to recent warming periods. Iberian beech forests located at the Pyrenees would benefit from forecasted warming conditions, whereas Atlantic and Mediterranean forests would be more prone to suffer warming-related growth decline.
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