Yew (Taxus baccata L.) population dynamics in the Iberian Mediterranean Mountains: natural regeneration and expansion in East Central System (Spain)

Aim of study: To evaluate demographical dynamics of yew populations in the Iberian Mediterranean mountains in order to assess population trends and a hypothetical natural regeneration of the species.Area of study: Ayllón Mountain Range, Eastern end of Central Mountain Range, Spain.Material and methods: Afield survey was conducted on three yew groves, taking data of altitude, orientation, companion woody species, UTM coordinates, height, perimeter (at breast height, 120cm) and sex. Individuals were classified in four age groups, considering height and trunk perimeter: AgeGroup1, Seedling; AgeGroup2, Juvenile; AgeGroup3, Adult and AgeGroup4, Old. Finally Recruitment rate was calculated for each population.Main results: Surveyed yew populations include more than 1600 trees, showing elevated Recruitment rates, which indicates that there are more seedling and juvenile individuals (Group1 and Group2) than adult and old ones (Group3 and Group4).Research highlights: Surveyed yew populations show vigorous regeneration. These results lead us to reconsider the relictic character assigned to the species in the Iberian Mediterranean mountains.Key words: Ayllón; microclimatic; regeneration rate; relictic; survey

Needle senescence affects fire behavior in Aleppo pine (Pinus halepensis Mill.) stands: a simulation study

Research Highlights: Pre-programmed cell death in old Aleppo pine needles leads to low moisture contents in the forest canopy in July, the time when fire activity nears its peak in the Western Mediterranean Basin. Here, we show, for the first time, that such needle senescence may increase fire behavior and thus is a potential mechanism explaining why the bulk of the annual burned area in the region occurs in early summer. Background and Objectives: The brunt of the fire season in the Western Mediterranean Basin occurs at the beginning of July, when live fuel moisture content is near its maximum. Here, we test whether a potential explanation to this conundrum lies in Aleppo pine needle senescence, a result of pre-programmed cell death in 3-years-old needles, which typically occurs in the weeks preceding the peak in the burned area. Our objective was to simulate the effects of needle senescence on fire behavior. Materials and Methods: We simulated the effects of needle senescence on canopy moisture and structure. Fire behavior was simulated across different phenological scenarios and for two highly contrasting Aleppo pine stand structures, a forest, and a shrubland. Wildfire behavior simulations were done with BehavePlus6 across a wide range of wind speeds and of dead fine surface fuel moistures. Results: The transition from surface to passive crown fire occurred at lower wind speeds under simulated needle senescence in the forest and in the shrubland. Transitions to active crown fire only occurred in the shrubland under needle senescence. Maximum fire intensity and severity were always recorded in the needle senescence scenario. Conclusions: Aleppo pine needle senescence may enhance the probability of crown fire development at the onset of the fire season, and it could partly explain the concentration of fire activity in early July in the Western Mediterranean Basin.We acknowledge funding from the Natural Science Foundation in China (31850410483), the talent proposals from Sichuan Province (2020JDRC0065), the Southwest University of Science and Technology talents fund and the Spanish MICINN (AGL2015-69151-R). R.B.-R. acknowledges the Community of Madrid for the predoctoral contract PEJD-2019-PRE/AMB-15644 funded by the Youth Employment Initiative (YEI)

A semi-mechanistic model for predicting daily variations in species-level live fuel moisture content

Live Fuel Moisture Content (LFMC) is one of the main factors affecting forest ignitability as it determines the availability of existing live fuel to burn. Currently, LFMC is monitored through spectral vegetation indices or inferred from meteorological drought indices. While useful, neither approach provides mechanistic insights into species-specific LFMC variation and they are limited in the ability to forecast LFMC under altered future climates. Here, we developed a semi-mechanistic model to predict daily variation in LFMC across woody species from different functional types by adjusting a soil water balance model which estimates predawn leaf water potential (Ψpd). Our overarching goal was to balance the trade-off between biological realism, which enhances model applicability, and parameterization complexity, which may limit its value within operational settings. After calibration, model predictions were validated against a dataset comprising 1659 LFMC observations across peninsular Spain, belonging to different functional types and from contrasting climates. The overall goodness of fit for our model (R2 = 0.5) was better than that obtained by an existing models based on drought indices (R2 = 0.3) or spectral vegetation indices (R2 = 0.1). We observed the best predictive performance for seeding shrubs (R2 = 0.6) followed by trees (R2 = 0.5) and resprouting shrubs (R2 = 0.4). Through its relatively simple parameterization, the approach developed here may pave the way for a new generation of process-based models that can be used for operational purposes within fire risk mitigation scenarios.This work was partly founded by the Spanish Government, grant number RTI2018-094691-B-C31 (MCIU/AEI/FEDER, EU) . R.B-R. ac-knowledges the Community of Madrid for the predoctoral contract PEJD-2019-PRE/AMB-15,644 funded by the Youth Employment Initia-tive (YEI) . M. De C. was supported by the Spanish Ministry of Science and Innovation via competitive grant CGL2017-89149-C2-2-R. UNED founding for open access publishing

Yew (Taxus baccata L.) population dynamics in the Iberian Mediterranean Mountains: natural regeneration and expansion in East Central System (Spain)

Aim of study: To evaluate demographical dynamics of yew populations in the Iberian Mediterranean mountains in order to assess population trends and a hypothetical natural regeneration of the species. Area of study: Ayllón Mountain Range, Eastern end of Central Mountain Range, Spain. Material and methods: Afield survey was conducted on three yew groves, taking data of altitude, orientation, companion woody species, UTM coordinates, height, perimeter (at breast height, 120cm) and sex. Individuals were classified in four age groups, considering height and trunk perimeter: AgeGroup1, Seedling; AgeGroup2, Juvenile; AgeGroup3, Adult and AgeGroup4, Old. Finally Recruitment rate was calculated for each population. Main results: Surveyed yew populations include more than 1600 trees, showing elevated Recruitment rates, which indicates that there are more seedling and juvenile individuals (Group1 and Group2) than adult and old ones (Group3 and Group4). Research highlights: Surveyed yew populations show vigorous regeneration. These results lead us to reconsider the relictic character assigned to the species in the Iberian Mediterranean mountains

Short communication: The mosquito yew wood: Survey and analysis of Mediterranean Taxus baccata L. woods (Habitat 9580*)

Aim of study: To survey a yew tree grove and to evaluate its conservation status to ascertain whether its proposal to class it as Habitat 9580* is appropriate. Area of study: Eastern end of Central Mountain Range, Spain. Material and methods: We conducted a field survey collecting data of UTM coordinates, altitude, orientation, companion woody species, height, stem perimeter, sex and browsing evidence. Individuals were classified in four age groups, considering height and stem perimeter: 1) seedling, 2) juvenile, 3), adult and 4) old. Companion species were analysed to assess the presence of habitat 9580* according to the Habitats Directive. Population structural complexity, stability and compactness were analysed to assess the conservation status. Main results: We registered 8,304 yews along with seventeen distinctive accompanying species, thus confirming the presence of priority habitat of community interest 9580* "Mediterranean Taxus baccata woods”. Population analysis leads us to appreciate a favourable conservation status for the whole habitat in the study area. Research highlights: We have described the largest T. baccata grove registered to date in the Central Mountain Range of the Iberian Peninsula. We confirm the presence of priority habitat of community interest 9580* "Mediterranean Taxus baccata woods", being the first description of this habitat in the Community of Madrid. As the study area is located within a Special Area of Conservation (SAC), we propose its inclusion on the SAC habitats list

Evolution of fruit and seed traits during almond naturalization

We would like to thank Irene Martín Brull, Josep A. Ribera i Torró and Nuria García Díaz for their help in the field. This study was funded by the Spanish Ministry of Economy and Finance (grant CGL2016-79950- R) and the Junta de Andalucia I+D+i program (grant P18-RTJ- 4704).All data are available from the Dryad Digital Repository https://doi. org/10.5061/dryad.mcvdn ck29 (Rubio de Casas et al., 2021).The peer review history for this article is available at https://publons.com/publon/10.1111/1365-2745.13831.1. Cultivated plant species often naturalize and enter wild communities in a process known as feralization. To successfully feralize, crops must overcome ecological barriers and may undergo selection on certain traits, diverging phenotypically and genetically from their crop ancestors. In spite of the agronomic and ecological relevance of crop feralization, the eco-evolutionary dynamics driving it remain understudied. 2. In this paper, we evaluated phenotypic and genotypic differentiation in fruit and seed traits during the naturalization of the almond tree (Prunus dulcis (Mill.) D.A. Webb) in SE Iberia and evaluated the potential role of natural selection in this process. To do so, we investigated the patterns of genetic divergence between cultivated and feral populations using functional (the cyanogenesis Sk gene) and neutral (17 SSR loci) markers and analysed morphological and biochemical traits in kernels of 342 individuals from 15 cultivated and 24 feral populations. 3. We detected very little genetic differentiation in neutral markers between cultivated and feral populations. The majority of the observed genetic variation was due to differences within each type. Conversely, the recessive allele sk responsible for seed toxicity was significantly more frequent in feral populations. Phenotypic differentiation between cultivated and naturalized almond populations was also significant. Feral almond kernels were smaller and lighter, had denser and more resistant shells (endocarps) and more toxic seeds. Selection analyses indicated that these genetic and phenotypic patterns might be driven by directional selection on fruit and seed traits, potentially linked to defence against predation. 4. Synthesis. Our findings indicate that almond naturalization is consistent with strong directional selection on fruits and seeds, leading to smaller and more toxic seeds encased in harder endocarps. Accordingly, we propose that feralization of this crop is, at least to some degree, driven by adaptive evolution of dispersal and recruitment traits.Secretaría de Estado de Investigación, Desarrollo e Innovación, Grant/Award Number: CGL2016-79950- RJunta de Andalucia I+D+i program (grant P18-RTJ- 4704

Drivers and implications of the extreme 2022 wildfire season in Southwest Europe

Wildfire is a common phenomenon in Mediterranean countries but the 2022 fire season has been extreme in southwest Europe (Portugal, Spain and France). Here we provide a preliminary but comprehensive analysis of 2022's wildfire season in southwest Europe. Burned area has exceeded the 2001–2021 median by a factor of 52 in some regions and large wildfires (>500 ha) started to occur in June–July, earlier than the traditional fire season. These anomalies were associated with record-breaking values of fuel dryness, atmospheric water demand and pyrometeorological conditions. Live fuel moisture content was below the historical minima for almost 50 % of the season in some regions. A few large wildfires were responsible for 82 % of the burned area and, in turn, 47 % of the area burned occurred in protected areas. Shrublands, transitional woodlands and conifer forests (but not eucalypt plantations) were the land cover types most affected by extreme fires. As climate change intensifies, we can expect such fire seasons to become the new normal in large parts of the continent, potentially leading to major negative impacts on rural economies. These results highlight the need for landscape level fuel management also in protected areas, to avoid fire-induced biodiversity losses and landscape scale degradation. Our results have important policy implications and indicate that fire prevention should be explicitly addressed within continental forest legislation and strategies

Evolution of fruit and seed traits during almond naturalization

Cultivated plant species often naturalize and enter wild communities in a process known as feralization. To successfully feralize, crops must overcome ecological barriers and may undergo selection on certain traits, diverging phenotypically and genetically from their crop ancestors. In spite of the agronomic and ecological relevance of crop feralization, the eco-evolutionary dynamics driving it remain understudied. In this paper, we evaluated phenotypic and genotypic differentiation in fruit and seed traits during the naturalization of the almond tree (Prunus dulcis (Mill.) D.A. Webb) in SE Iberia and evaluated the potential role of natural selection in this process. To do so, we investigated the patterns of genetic divergence between cultivated and feral populations using functional (the cyanogenesis Sk gene) and neutral (17 SSR loci) markers and analysed morphological and biochemical traits in kernels of 342 individuals from 15 cultivated and 24 feral populations. We detected very little genetic differentiation in neutral markers between cultivated and feral populations. The majority of the observed genetic variation was due to differences within each type. Conversely, the recessive allele sk responsible for seed toxicity was significantly more frequent in feral populations. Phenotypic differentiation between cultivated and naturalized almond populations was also significant. Feral almond kernels were smaller and lighter, had denser and more resistant shells (endocarps) and more toxic seeds. Selection analyses indicated that these genetic and phenotypic patterns might be driven by directional selection on fruit and seed traits, potentially linked to defence against predation. Synthesis. Our findings indicate that almond naturalization is consistent with strong directional selection on fruits and seeds, leading to smaller and more toxic seeds encased in harder endocarps. Accordingly, we propose that feralization of this crop is, at least to some degree, driven by adaptive evolution of dispersal and recruitment traits.This study was funded by the Spanish Ministry of Economy and Finance (grant CGL2016-79950-R) and the Junta de Andalucia I+D+i program (grant P18-RTJ-4704)

Climate change induced declines in fuel moisture may turn currently fire-free Pyrenean mountain forests into fire-prone ecosystems

Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6–15 °C and 395–933 mm, respectively. We observed significant spatial variation in live (78–162%) and dead (10–15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|–|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006–2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the “safety margin” for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response