Extreme Drought Episodes Research Articles

Potential climatic influence on maximum stand carrying capacity for 15 Mediterranean coniferous and broadleaf species

Climate change projections for the Mediterranean basin predict a continuous increase in extreme drought and heat episodes, which will affect forest dynamics, structure and composition. Understanding how climate influences the maximum size-density relationship (MSDR) is therefore critical to designing adaptive silvicultural guidelines based on the potential stand carrying capacity of tree species. With this aim, data from the Third Spanish National Forest Inventory (3NFI) and WorldClim databases were used to analyze climate-related variations of the maximum stand carrying capacity for 15 species from the Pinus, Fagus and Quercus genera. First, basic MSDR were fitted using linear quantile regression and observed size-density data from monospecific 3NFI plots. Reference values for maximum stocking, expressed in terms of the Maximum Stand Density Index (SDImax), were estimated by species. Then, climate-dependent MSDR models including 35 annual and seasonal climatic variables were fitted. The best climate-dependent models, based on the Akaike Information Criteria (AIC) index, were used to determine the climatic drivers affecting MSDR, to analyze general and species-specific patterns and to quantify the impact of climate on maximum stand carrying capacity. The results showed that all the selected climate-dependent models improved the goodness of fit over the basic models. Among the climatic variables, spring and summer maximum temperatures were found to be key drivers affecting MSDR for the species studied. A common trend was also found across species, linking warmer and drier conditions to smaller SDImax values. Based on projected climate scenarios, this suggests potential reductions in maximum stocking for these species. In this study, a new index was proposed, the Q index, for evaluating the impact of climate on maximum stand carrying capacity. Our findings highlight the importance of using specific climatic variables to better characterize how they affect MSDR. The models presented in this study will allow us to better explain interactions between climate and MSDR while also providing more precise estimates concerning maximum stocking for different Mediterranean coniferous and broadleaf tree species.

A weekly spatio‐temporal distribution of drought events over the Po Plain (North Italy) in the last five decades

AbstractThe aim of this research is to identify and characterize, in terms of length, intensity, and spatial propagation, the main drought events which took place in the Po Valley (Italy) from 1965 to 2017. Two drought indices were applied, the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Precipitation Index (SPI). Daily precipitation and temperature series belonging to the National System for the Collection, Processing, and Dissemination of Climatic Data of Environmental Interest (SCIA) database were collected. Subsequent to an accurate quality control, the converted weekly climatic values were spatialized on a 20 × 20 km cell grid, and for each index, weekly severe and extreme drought episodes at a 12‐, 24‐, and 36‐month time scale were calculated. Results showed that the application of two indices is fundamental in the study of drought episodes, and that different triggering factors act over time. Especially, since the 2001 drought, episodes have become stronger in terms of frequency and length, and they seem to be mostly related to changes in the intra‐annual precipitation distribution. An analysis of the spatial propagation also indicates that two spatial gradients follow each other during the analysed period.

Data-driven control of water reservoirs using an emulator of the climate system

This study presents a novel approach to combine a data-driven control strategy with an emulator model of the climate system in order to make the optimal control of water systems more flexible and adaptive to the increasing frequency and intensity of extreme events. These latter are often associated with global climate anomalies, which are difficult to model and incorporate into optimal control algorithms. In this paper, we compare a traditional control policy conditioned only on the reservoir storage with an informed controller that enlarges the state space to include the emulated dynamics of global Sea Surface Temperature anomalies. The multi-purpose operations of Lake Como in Italy, accounting for flood control and water supply, is used as a case study. Numerical results show that the proposed approach provides a 59% improvement in system performance with respect to traditional solutions. This gain further increases during extreme drought episodes, which are influenced by global climate oscillations.

Drought spatiotemporal characterization using self-calibrating Palmer Drought Severity Index in the northern region of Nigeria

Abstract Hazards from drought events has made it of utmost importance for scientist to concentrate on the establishment of a dependable early warning systems that will enable stakeholders to effectively cope with the probable effect of this climatic phenomenon. Drought assessment in the northern region of Nigeria (NRN) was conducted majorly using a self-calibrated Palmer's Drought Severity Index (sc-PDSI). Between 1981 and 2015, the number of drought episodes identified ranged from 5 to 18. The most severe drought episodes took place from 1998 to 2001, next to it was between 2006 and 2008. The power spectral analysis of sc-PDSI timeseries identified periodicities ranging between 3 and 18 years. The spatial extent of extreme drought episodes shows that, the peak coverage area (10%) occurred at multiple times (August 1987, 2001, 2002 and 2009), most of which is in the 21st century. sc-PDSI reveals the long-term hydrological drought of River Niger indicated at Baro gauging station about 12 months before the low flow occurred. There is a need for policymakers to make adequate preparation by drawing out appropriate mitigation plans using established drought indices before future drought events occur.

Detecting the State of the Climate System via Artificial Intelligence to Improve Seasonal Forecasts and Inform Reservoir Operations

AbstractIncreasingly variable hydrologic regimes combined with more frequent and intense extreme events are challenging water systems management worldwide. These trends emphasize the need of accurate medium‐ to long‐term predictions to timely prompt anticipatory operations. Despite in some locations global climate oscillations and particularly the El Niño Southern Oscillation (ENSO) may contribute to extending forecast lead times, in other regions there is no consensus on how ENSO can be detected, and used as local conditions are also influenced by other concurrent climate signals. In this work, we introduce the Climate State Intelligence framework to capture the state of multiple global climate signals via artificial intelligence and improve seasonal forecasts. These forecasts are used as additional inputs for informing water system operations and their value is quantified as the corresponding gain in system performance. We apply the framework to the Lake Como basin, a regulated lake in northern Italy mainly operated for flood control and irrigation supply. Numerical results show the existence of notable teleconnection patterns dependent on both ENSO and the North Atlantic Oscillation over the Alpine region, which contribute in generating skilful seasonal precipitation and hydrologic forecasts. The use of this information for conditioning the lake operations produces an average 44% improvement in system performance with respect to a baseline solution not informed by any forecast, with this gain that further increases during extreme drought episodes. Our results also suggest that observed preseason sea surface temperature anomalies appear more valuable than hydrologic‐based seasonal forecasts, producing an average 59% improvement in system performance.

Drought Event Analysis and Projection of Future Precipitation Scenario in Abaya Chamo Sub-Basin, Ethiopia

Monthly observed and future precipitation magnitudes were subjected to statistical trend analysis to examine possible time series behavior. Future precipitation was downscaled from large-scale output through statistical downscaling. The observed and downscaled future precipitation was analyzed for drought events using the Standardized Precipitation Index (SPI) method. In the Abaya Chamo sub-basin, Ethiopia precipitation is explained by below average magnitudes in most of the low land area, characterized by moderate to extreme drought episodes. Nine drought events were discerned during the period of 1988 to 2015, i.e. once in three years, resulting in harvest failure and subsequent food insecurity. The NCEP-NCAR and CanESM2 model predictors were used to statistically downscale the precipitation data. The monthly observed and downscaled precipitation magnitudes were in good agreement. The RCP-2.6, RCP-4.5 and RCP-8.5 long-term future scenarios were computed to evaluate future drought patterns. The mean annual precipitation scenario decreased by 0.2% to 13.7%, 0.5% to 6.4% and 0.1% to 1.3% for the period from 2016 to 2040, 2050s and 2080s respectively. The increase in mean precipitation was projected to be 0.7% to 12.2%, 0.2% to 11.7% and 0.1% to 17.8% for the period from 2016 to 2040, 2050s and 2080s respectively. The present analysis may provide useful information associated to drought events to decision makers and can be used as a basis for future research in this area.

Late Middle Pleistocene Elephants from Natodomeri, Kenya and the Disappearance of Elephas (Proboscidea, Mammalia) in Africa

Comparative morphometric study of recently recovered fossil elephant molars from Natodomeri, Kenya identifies them as belonging to Elephas jolensis and confirms the presence of this species in Members I and II of the Kibish Formation. Improved datation of these geological units constrains them between 205 and 130 ka. Elephas jolensis is also reported from localities in northern, northwestern, eastern, and southern Africa. Thus, including its Natodomeri occurrence, E. jolensis appears to have been pan-African in distribution. Despite the wide geographic distribution of the species, molars of E. jolensis are remarkably uniform morphometrically. They are characterized by their extreme hypsodonty, high amplitude of enamel folding, high lamellar frequency, and plates that are anteroposteriorly thick relative to transverse valley interval spacing. In addition, they exhibit only a modest number of plates (<20 in M3/m3). Elephas jolensis either evolved from or represents the last stage of Elephas recki, the dominant elephant species in East Africa during the late Pliocene-Pleistocene. The dental morphology and isotopic composition of E. jolensis indicates that, like E. recki, it was a dedicated grazer. In the Kibish Formation, E. jolensis is succeeded by Loxodonta africana at 130 ka, coincident with an intensely cool, dry interval marked by episodes of extreme drought. This marked the extirpation of Elephas on the continent. The intensity and increased rate of climate fluctuation may have played an important role in the demise of the specialist, grazing E. recki-E. jolensis lineage in favor of a generalist, mixed feeder such as L. africana.

Climatic Suitability Derived from Species Distribution Models Captures Community Responses to an Extreme Drought Episode

The differential responses of co-occurring species in rich communities to climate change—particularly to drought episodes—have been fairly unexplored. Species distribution models (SDMs) are used to assess changes in species suitability under environmental shifts, but whether they can portray population and community responses is largely undetermined, especially in relation to extreme events. Here we studied a shrubland community in SE Spain because this region constitutes an ecotone between the Mediterranean biome and subtropical arid areas, and it has recently suffered its driest hydrological year on record. We used four different modeling algorithms (Mahalanobis distance, GAM, BRT, and MAXENT) to estimate species’ climatic suitability before (1950–2000) and during the extreme drought. For each SDM, we related species’ climatic suitability with their remaining green canopy as a proxy for species resistance to drought. We consistently found a positive correlation between remaining green canopy and species’ climatic suitability before the event. This relationship supports the hypothesis of a higher vulnerability of populations living closer to their species’ limits of aridity tolerance. Contrastingly, climatic suitability during the drought did not correlate with remaining green canopy, likely because the exceptional episode led to almost zero suitability values. Overall, our approach highlights climatic niche modeling as a robust approach to standardizing and comparing the behavior of different co-occurring species facing strong climatic fluctuations. Although many processes contribute to resistance to climatic extremes, the results confirm the relevance of populations’ position in the species’ climatic niche for explaining sensitivity to climate change.

Climatic suitability derived from species distribution models captures community responses to an extreme drought episode

Climatic suitability derived from species distribution models captures community responses to an extreme drought episode

A Lagrangian analysis of the moisture budget over the Fertile Crescent during two intense drought episodes

The Fertile Crescent (FC) region comprises the east coast of the Mediterranean Sea and the northern part of the Arabian Peninsula. The FC suffered two severe drought episodes separated by a 7-year period, in 1998–2000 and 2007–2009, which are considered the most severe episodes to hit the region in the last 50 years. A Lagrangian model (FLEXPART) and ERA-Interim data (with a 1° × 1° lat-long resolution) were used to identify for the first time the climatological sources of moisture for the FC and their characteristics. Variability and the source-receptor relationships, concerning their contribution to the precipitation, and the implications regarding the transport of moisture changes over the FC, during the wet season (October-May) from 1980 to 2014 were analysed. The main climatological moisture sources during this period were determined to be the FC itself, the eastern Mediterranean Sea, the Red Sea, the Persian Gulf, the Arabian Sea, the Caspian and Black Seas, and the central and western parts of the Mediterranean Sea.The analysis showed higher anomalous conditions in the moisture transport from some moisture sources during the two outstanding drought episodes. The key feature of the wet seasons during these episodes was a deficit in the moisture losses over the studied area related to the FC itself, the Red and Arabian Seas sources, followed and to a lesser extent by the eastern Mediterranean Sea over the northern part of the FC region. Nevertheless, the moisture supply deficit from the sources was much greater during the 2007–2009 drought event. The SPEI index at large scales (24 months) showed that the 2007–2009 episode was part of longer-term drought conditions that had been developing over the previous months, reinforcing the drought severity given recycling processes attributed to the FC. During the two extreme drought episodes, the mountainous terrain over the northern and eastern FC suffered the highest precipitation deficits, and these areas are, precisely, the most influenced by two of the major moisture sources, namely, the FC and eastern Mediterranean Sea. The decreased moisture contribution from these main sources led to more intense droughts over the region. As a result, both regions should be considered as hotspots to signal severe or extreme droughts in the region.

Meteorological drought assessment in north east highlands of Ethiopia

PurposeThe purpose of this paper is to investigate the patterns and trends of drought incidence in north east highlands of Ethiopia using monthly rainfall record for the period 1984-2014.Design/methodology/approachStandard precipitation index and Mann – Kendal test were used to analyze drought incident and trends of drought occurrences, respectively. The spatial extent of droughts in the study area has been interpolated by inverse distance weighted method using the spatial analyst tool of ArcGIS.FindingsMost of the studied stations experienced drought episodes in 1984, 1987/1988, 1992/1993, 1999, 2003/2004 and 2007/2008 which were among the worst drought years in the history of Ethiopia. The year 1984 was the most drastic and distinct-wide extreme drought episode in all studied stations. The Mann–Kendal test shows an increasing tendencies of drought at three-month (spring) timescale at all stations though significant (p < 0.05) only at Mekaneselam and decreasing tendencies at three-month (summer) and 12-month timescales at all stations. The frequency of total drought was the highest in central and north parts of the region in all study seasons.Originality/valueThis detail drought characterization can be used as bench mark to take comprehensive drought management measures such as early warning system, preparation and contingency planning, climate change adaptation programs.

Contrasting patterns of the extreme drought episodes of 2005, 2010 and 2015 in the Amazon Basin

Future climate scenarios point to an increase in the frequency of extreme droughts events, even in humid biomes. Throughout the 21st century, large areas of the Amazon basin experienced the most severe droughts ever recorded with special emphasis on the 2005 and 2010 events due to their severity and extent. Currently, there is an increased demand to understand the geographic extent and seasonal variability of climate variables during drought events, especially with respect to the social and environmental impacts. In this study, we aim to compare the observed climate conditions during the drought episodes of 2005, 2010 and 2015. We perform a detailed assessment of the measured precipitation, land‐surface temperature (LST) and solar radiation anomalies. We provide evidence that the anomalous precipitation deficit during 2015 exceeded the amplitude and spatial extent of the previous events, affecting more than 80% of Amazon basin, particularly the eastern portion. The pronounced lack of rainfall availability during late spring and early summer, coincident with radiation and temperature surpluses during these years are significant and notable. Changed meteorological spatial patterns were observed, with precipitation and radiation being the most prominent parameters in 2005, whereas precipitation and LST were most relevant in 2010. Understanding the behaviour and interactions of pertinent meteorological variables, as well as identifying similar or divergent patterns over the region during distinct extreme events, is essential for the improvement of our knowledge of Amazon forest vulnerability to climate fluctuation changes.

PADRÕES ATMOSFÉRICOS E OCEÂNICOS ASSOCIADOS A EVENTOS EXTREMOS NA BACIA AMAZÔNICA: UMA ANÁLISE DE COMPOSIÇÃO BASEADA NOS EPSÓDIOS SECOS DE 1982/83, 2004/05 E 2009/10

This study aimed to determine the atmospheric and oceanic patterns related to changes in precipitation over the Amazon basin during the episodes of extreme drought occurred in the years of 1982/83, 2004/2005 and 2009/10. Data from the zonal and meridional components of the wind vector, wind speed, omega, specific humidity, precipitation and sea surface temperature was used. The data was obtained from the reanalysis-2 NCPE/NCAR (except for the variable precipitation which was obtained from the CMAP). The anomalous composition method was used to determine the atmospheric and ocean fields that were characteristic of episodes of intense drought. The results show a deficit in rainfall in the rainy pre-season (SON) in part of the northern region of South America and northeastern Brazil. The lower level of rainfall also persists during the rainy season (December to April). Associated with these anomalous patterns of rainfall, positive anomalies of SST were observed which were similar to El Niño events, followed by anomalous subsidence in the Amazon. In the rainy pre-season, wind divergence over the state of Amazonas and the north of South America was observed. During the rainy season, the divergence in streamlines shows the weakening of the northeast trade winds. In addition, the anomalous divergence of vertically integrated moisture flux reveals consistency with rainfall deficits in theipre and rainy season in the Amazon basin.

Changes in the natural dynamics of Nothofagus dombeyi forests: population modeling with increasing drought frequencies

AbstractDrought‐induced episodes of tree mortality can determine forest dynamics and structure, particularly in forests dominated by single species. Short‐ and mid‐term climate projections indicate that strong changes in annual precipitation may strike more often in northern Patagonia. Data for recruitment, growth, and survival of Nothofagus dombeyi tree individuals were collected at several sites across the Nahuel Huapi National Park in Argentina. We combined mathematically all these different demographic stages into an Integral Projection Model to simulate 100‐yr projections of simulated stand structure under different frequencies of extreme drought episodes. We projected total basal area and the number of individuals for three different initial stand types (i.e., young, medium, and old) and for varying drought frequencies (i.e., from 1 to 5 drought events every 100 years). Recruitment into the dbh ≥ 10 cm size class under normal conditions (i.e., without drought) was higher than under episodic drought conditions. In addition, survival under normal conditions was higher than under drought conditions, especially for small trees. Differences in growth were also important, with trees growing more vigorously under normal than under drought conditions. Our simulations predicted that N. dombeyi populations would experience a reduction in tree density in the mid‐term if, as predicted by the IPCC projections, the frequency of future drought events increased. The simulations also showed that in those cases, young stands should suffer the most. Drought‐mediated changes may induce a decline in the development of N. dombeyi forests in the mid‐ and long term by a drastic reduction in tree density.

Exceptionally extreme drought in Madeira Archipelago in 2012: Vegetation impacts and driving conditions

This work aims at characterizing the exceptional drought that affected Madeira Archipelago (Portugal) during the 2011–2012 hydrological year while including some major impacts but also the main atmospheric circulation mechanism behind the event. Precipitation records from six meteorological stations are used to assess the extreme drought episode by means of a decile classification. The assessment of the drought duration and severity is further corroborated by the Standardized Precipitation Index (SPI) computed for the 3, 6, 12 and 24 months’ time scales which confirmed that the 2012 drought event was one of the events with higher drought intensity at all scales, being classified as extreme at the 6-month time sale (SPI6<−1.65) from December 2011 until May 2012 on the majority of the meteorological stations analysed. Long-term precipitation data available since 1865 for the station of Funchal confirm the exceptional dryness of this episode, particularly during the winter season (December to March) corresponding to the driest winter in 150 years.Vegetation activity is assessed through anomalies of NDVI (Normalized Difference Vegetation Index), confirming several large sectors of Madeira under vegetative stress. The southern sector of Madeira Island suffered up to seven months (out of nine) of extremely negative anomalies. From an operational point of view, obtained results reveal the ability of the developed methodology to monitor vegetation stress and droughts in Madeira. The extreme dryness of the Island favoured an unusually intense summer fire season of 2012 (between June and September) in Madeira being the year with highest number of fires in the last decade (with robust data). Furthermore, the main fire hotspots of the 2012 fire season are mostly coincident with the areas affected by drought.The large-scale atmospheric circulation responsible for the setting and intensification of the drought is evaluated using reanalysis data. An extensive high pressure anomaly (maximum above 12hPa in December) persisted over the North Atlantic during the extended winter months (October to April), centred between the Azores Islands and the UK. This feature is in agreement with a positive NAO index (2.25 in December), a negative EA index (−1.76 in January and −1.73 in February) and compatible with enhanced north-easterly trade winds over the region. As a consequence of this uncharacteristic dynamics there was a deficit of moisture availability over the region as evaluated by the vertically integrated horizontal water vapour transport with a negative anomaly up to −120kgm−1s−1.

Comparison of the Characteristics (Frequency and Timing) of Drought and Wetness Indices of Annual Mean Water Levels in the Five North American Great Lakes

In this study, we compared the frequency and timing of drought and wetness indices of annual mean water levels in the North American Great Lakes as they relate to teleconnection indices over the period from 1918 to 2012. In terms of timing, drought occurred in the Great Lakes watershed during the 1920, 1930 and 2000 decades, and was very intense in the East during the 1930’s and in the West during the 2000 decade. The main cause of extreme drought episodes in the 1920’s and 1930’s was a decrease in precipitation, while the 2000 decade drought is thought to be caused by increased water temperature (enhanced evaporation) due to a significant decrease in winter ice cover. The 1970 and 1980 decades were very wet over the whole watershed as a result of increased precipitation in the region. The succession of these dry and wet episodes did not have the same impacts on the stationarity of annual mean water levels in the five Great Lakes. Lake Superior shows an abrupt shift in mean in 1999, but a smoothed shift in variance since 1994, whereas Lake Erie shows four abrupt shifts in mean. Lake Ontario also shows the two first abrupt shift in mean and one abrupt change in variance. Extreme drought indices are negatively correlated with the North Atlantic Oscillation (NAO) for the two shallowest lakes (Ontario and Erie). In contrast, extreme wetness indices are positively correlated with PDO (positive correlation) and SOI (negative correlation) for Lake Superior only.

The extreme drought episode of August 2011–May 2012 in the Czech Republic

ABSTRACTThe weather conditions from August 2011 to May 2012 produced an extreme drought in the eastern Czech Republic (Moravia), whereas the patterns were nearly normal in its western region (Bohemia). The Southern and Central Moravia regions, which represent the most important agricultural areas, were most affected by the drought. The precipitation totals for the studied period were 50–70% of the long‐term mean, which was calculated for 1961–2000. In autumn 2011, the total precipitation accounted for 10–30% of the long‐term mean for most of Moravia, increasing to 30–50% in spring 2012. Moreover, 7.5% of the Czech Republic experienced a 100‐year drought; 20% of the country experienced a 20‐year drought. According to the Palmer Drought Severity Index, the 2012 drought was classified as the worst in the past 130 years. The drought patterns were related to the prevailing high‐pressure systems over Central Europe and the occurrence of weather types with different precipitation amounts in Bohemia and Moravia. The most substantial drought effects occurred in the agricultural sector. A decrease in cereal yields was observed in the analysed production areas in Moravia, which was unprecedented in the past 52 years. Moreover, winter crops were affected more than spring crops. An increased risk of fire occurred due to the drought conditions; the largest forest fire in the past 15 years was recorded during this period. Furthermore, signs of hydrological drought were also reported in rivers. The 2011–2012 drought was compared with the significant droughts in 2000, 2003 and 2007. Austria and Slovakia, which neighbour the Czech Republic, experienced a similar drought. Global circulation model sensitivity experiments appear to indicate that droughts similar to this episode may be occurring at a recurrence interval of 20 years by the 2050s.

Water-Deficit Inducible Expression of a Cytokinin Biosynthetic Gene IPT Improves Drought Tolerance in Cotton

Water-deficit stress is a major environmental factor that limits agricultural productivity worldwide. Recent episodes of extreme drought have severely affected cotton production in the Southwestern USA. There is a pressing need to develop cotton varieties with improved tolerance to water-deficit stress for sustainable production in water-limited regions. One approach to engineer drought tolerance is by delaying drought-induced senescence via up-regulation of cytokinin biosynthesis. The isopentenyltransferase gene (IPT) that encodes a rate limiting enzyme in cytokinin biosynthesis, under the control of a water-deficit responsive and maturation specific promoter PSARK was introduced into cotton and the performance of the PSARK::IPT transgenic cotton plants was analyzed in the greenhouse and growth chamber conditions. The data indicate that PSARK::IPT-transgenic cotton plants displayed delayed senescence under water deficit conditions in the greenhouse. These plants produced more root and shoot biomass, dropped fewer flowers, maintained higher chlorophyll content, and higher photosynthetic rates under reduced irrigation conditions in comparison to wild-type and segregated non-transgenic lines. Furthermore, PSARK::IPT-transgenic cotton plants grown in growth chamber condition also displayed greater drought tolerance. These results indicate that water-deficit induced expression of an isopentenyltransferase gene in cotton could significantly improve drought tolerance.

Vulnerabilidad y resiliencia de ecosistemas forestales frente a episodios extremos de sequía

Lloret, F. (2012). Vulnerability and resilience of forest ecosystems to extreme drought episodes. Ecosistemas 21(3):85-90. Doi.:10.7818/ECOS.2012.21-3.11 Drought-induced forest die-off has been recently reported in many locations abroad, and also in some shrublands. The phenomena show recognizable spatial patterns and it is not homogenous in localities with similar climatic characteristics. Therefore, we can identify different drivers contributing to die-off, for instance soil properties related soil availability, but also the existence of a remarkable resilience in these ecosystems. In fact, population decline would occur as a result of the unbalance between mortality and recruitment. Any factor contributing to diminish mortality or favouring recruitment would enhance resilience, and shifts in community composition would occur when the balance between mortality and recruitment will be different across species. Also, the impacts of these events would be intensified by the synergy with other disturbances, such as wildfires in Mediterranean-type ecosystems, particularly if these disturbance generate conditions similar to those resulting from the climatic anomaly. The die-off events can help to incorporate climate change context to forest management. Particularly, a pro-active approach by favouring the mechanisms contributing to forest resilience would be desirable. These actions include species and genotypes selection, forest structure adequate to optimize resource use in the oncoming climatic conditions, and distribution of these elements at landscape level.

Plant competition and facilitation after extreme drought episodes in Mediterranean shrubland: does damage to vegetation cover trigger replacement by juniper woodland?

AbstractQuestionWe analyse the contribution of plant–plant interactions, particularly the outcome of plant competition and plant facilitation, on vegetation dynamics as a result of extreme drought episodes. These events will likely become more frequent under climate change, can induce vegetation die‐off and alter community dynamics. We study succession in a shrubland that tends to be replaced by juniper (Juniperus phoenicea) woodland. Due to drought, shrubland die‐off may result in competition release favouring J. phoenicea juveniles, and accelerating shrubland replacement. Alternatively, deleterious abiotic stress may increase after loss of vegetation cover protection.LocationMediterranean coastal shrublands, South Spain (Doñana National Park).MethodsField estimates of plant growth, production of needle‐like leaves, water‐use efficiency (WUE; leaf δ13C) and N leaf content of J. phoenicea juveniles in relation to plant size, drought‐induced damage, cover and habit characteristics of surrounding vegetation, and drought‐induced defoliation of the surrounding vegetation.ResultsJuniperus phoenicea juveniles growing beneath a dense vegetation canopy, particularly trees and large shrubs, were less damaged during the extreme drought episode. Plant size correlated negatively with damage. Post‐drought growth was higher in juveniles partially released from the vegetation canopy, supporting the existence of a balance between competition and facilitation. Cover of pines, large shrubs and spiny shrubs favoured growth of juveniles. Needle‐like juvenile leaves were more abundant in plants covered by the surrounding vegetation or in moderately damaged plants, but less abundant in plants without damage. Higher leaf δ13C values – indicating water stress – were measured in plants more damaged by drought and in those without canopy protection, or under vegetation strongly affected by drought. Leaf N content was lower in undamaged plants and individuals covered by surrounding vegetation.ConclusionWe did not find evidence that gaps opened by drought promoted growth of the potential replacing J. phoenicea. Thus, drought‐induced enhancement of successional replacement of shrublands with woodlands was not supported; instead, our findings foresee shrubland prevalence under future climate change conditions. Plant facilitation will play a relevant role in this process. Thus, we herein extend the relevance of plant–plant interactions to extreme drought episodes related to climate change, highlighting their role as drivers of community dynamics.