Oak Woodlands Research Articles

Interaction between weeding, outplanting date and site in open oak woodland plantations

In this paper we explore ways of improving the field performance of oak plantations for the regeneration of open woodlands in Mediterranean environments. Using the evergreen, sclerophyllous holm oak species (Quercus ilex L. subsp. ballota (Desf.) Samp.), we analyzed the effects of the outplanting date (October vs. February), vegetation competition (weeding vs. untreated), the environmental conditions imposed by the outplanting site, and the interactions between all these factors. For test purposes, 3 blocks of 200 one-year-old holm oak nursery-grown seedlings were set up in four sites in SE Spain (Becerra, Mágina, Jarosa and Hinojosa). Half of each block (plot) was weeded to prevent competition from other vegetation. In each plot (weeded or not) half of the seedlings were outplanted in October 2019 and the other half in February 2020. In total, 2400 holm oak seedlings were planted to be monitored over the course of two growing seasons. Survival and growth-related parameters such as height, root collar diameter, number of leaves and total and fractional aerial biomass were recorded. Weeding was shown to be the most important factor affecting both survival and seedling growth, especially in sites with a milder autumn and winter, and a long, intense summer, such as Jarosa and Hinojosa. In colder locations, however, October outplanting was more advantageous, especially if accompanied by weeding (Becerra and Mágina). In cases where competition from native species is not controlled, it would be advisable to plant in October, in terms of both survival and development of the seedlings, especially in colder sites. In general terms, the best option was outplanting in October plus weeding, while the worst option was outplanting in February with no weeding. This study provides new tested recommendations on how to improve the success of oak plantations in different Mediterranean environments.

Fuel build-up promotes an increase in fire severity of reburned areas in fire-prone ecosystems of the western Mediterranean Basin

BackgroundFire-vegetation feedbacks can modulate the global change effects conducive to extreme fire behavior and high fire severity of subsequent wildfires in reburn areas by altering the composition, flammability traits, and spatial arrangement of fuels. Repeated, high-severity wildfires at short return intervals may trigger long-term vegetation state transitions. However, empirical evidence about these feedbacks is absent in fire-prone ecosystems of the western Mediterranean Basin, where the response of fire activity has been enhanced by contemporary socioeconomic and land-use changes. Here, we evaluated whether fire severity differs between initial burns and subsequent wildfires in reburn areas (fire-free periods = 10–15 years) of maritime pine and Aleppo pine forests, holm oak woodlands, and shrublands in the western Mediterranean Basin, and whether there is a relationship between the severity of such interactive wildfire disturbances. We also tested how the type of ecosystem and changes in vegetation structure after the initial wildfires influence these relationships. We leveraged Landsat-based fire severity estimates for initial and last wildfires using the Relativized Burn Ratio (RBR) and Light Detection and Ranging (LiDAR) data acquired before the last wildfire.ResultsFire severity of the last wildfire was significantly higher than that of the initial wildfire for each dominant ecosystem type in reburn areas. These differences were very pronounced in maritime pine forests and shrublands. For consistency, the same patterns were evidenced for the fire severity in reburn and first-entry areas of the last wildfire for each dominant ecosystem type. Fire severity of the last wildfire in forests and woodlands (particularly maritime pine-dominated) raised with increasing severity of the previous wildfire to a greater extent than in shrublands. Pre-fire fuel density in the lower vegetation strata (up to 4 m high in maritime and Aleppo pine forests, as well as in shrublands, and up to 2 m high in holm oak forests) was significantly higher in reburn than in first-entry areas of the last wildfire.ConclusionsOur results suggest that land managers should promote more fire-resistant landscapes to high fire severity by minimizing fuel build-up and thus fire hazard through pre-fire fuel reduction treatments such as prescribed burning.

Decline in small mammal species richness in coastal-central California, 1997-2013.

The richness and composition of a small mammal community inhabiting semiarid California oak woodland may be changing in response to climate change, but we know little about the causes or consequence of these changes. We applied a capture-mark-recapture model to 17 years (1997-2013) of live trapping data to estimate species-specificabundances. The big-eared woodrat was the most frequently captured species in the area, contributing 58% of total captures. All small mammal populations exhibited seasonal fluctuations, whereas those of the California mouse, brush mouse, and pinyon mouse declined during the study period. We also applied a multispecies dynamic occupancy model to our small mammal detection history data to estimate species richness, occupancy (), detection (p), local extinction (), and colonization () probabilities, and to discern factors affecting these parameters. We found that decreased from 0.369 ± 0.088 in 1997 to 0.248 ± 0.054 in 2013; was lower during the dry season (May-September) than the wet season (October-April) and was positively influenced by total seasonal rainfall (slope parameter, = 0.859 ± 0.371; 95% CI = 0.132-1.587). Mean mammalian species richness decreased from 11.943 ± 0.461 in 1997 to 7.185 ± 0.425 in 2013. With highly variable climatic patterns expected in the future, especially increased frequency and intensity of droughts,itis important to monitor small mammal communities inhabiting threatened California oak woodlands.

Diversified vegetation types on rangelands promote multiple soil‐based ecosystem services

AbstractRangelands have the potential to be provisioners of ecosystem services, including livestock products, carbon storage and greenhouse gas regulation, water and nutrient cycling, wildlife habitat, and biodiversity. Due to their vast extent and landscape heterogeneity, the degree to which different ecological components of rangelands contribute to ecosystem services can be varied. Soils are the foundation of rangeland health and associated ecosystem services. While many studies have examined the effect of grazing intensity on rangeland ecosystem services, few studies have looked at the broader rangeland landscape and how managing varying vegetation types can influence soil‐based ecosystem services. In this study, a suite of physical, chemical, and biological soil health indicators were measured in various vegetation types found within a working cattle ranch, including coastal live oak woodlands, coastal scrublands, annual grassland, and restored native perennial grassland. Based on the measured soil health indicators, results from this study show scrubland significantly diverges from other vegetation types, having higher water infiltration and plant available water, carbon stocks, and a more diverse microbial community that drives more dynamic cycling of carbon and nitrogen. Strategically maintaining scrubland on unproductive, highly erosive slopes downgradient of highly productive grassland areas could maintain forage production while protecting water quality and increasing carbon storage. These results highlight the relevance of holistically evaluating rangeland operations to assess soil function and ecosystem services and the potential risks and co‐benefits of varying vegetation types. Ultimately, process‐based linkages described here may provide a working example of how to manage ranches as functional mosaics of strategically maintained vegetation types.

Elevated CO2 does not improve seedling performance in a naturally regenerated oak woodland exposed to biotic stressors

IntroductionInsect herbivores and biotrophic pathogens are major stressors influencing natural regeneration in woodlands. Information on the effect of elevated CO2 (eCO2) on plant-insect-pathogen interactions under natural conditions is lacking.MethodsWe studied the effects of eCO2 on leaf-out phenology, as well as on levels of insect herbivory and powdery mildew (PM), i.e., reduction of leaf photosynthetic material. We then assessed the combined impacts of these biotic stressors and eCO2 on seedling photosynthesis and growth. A total of 92 naturally recruited and 114 potted seedlings of 5 temperate tree species (Quercus robur, Acer pseudoplatanus, Corylus avellana, Crataegus monogyna, and Ilex aquifolium) within a mature oak woodland were studied.ResultsWe found that eCO2 advanced leaf-out phenology and was a significant explanatory variable for growth and physiological performance in potted seedlings. Potted oak seedlings experienced 11-fold higher tissue loss from insect herbivory than natural seedlings. The earliest leaf-flushing species, hawthorn, and the evergreen holly were resistant to insect attack and were not affected by PM. Oak was defoliated most but showed the highest regeneration capacity. Hazel was more resistant to PM infection than oak and sycamore. Despite being highly infected by PM, sycamore was less affected than oak. The more vigorous sycamore and oak seedlings suffered more severe PM disease.ConclusionNo evidence emerged that eCO2 enhances natural regeneration under biotic stress for any of the species studied.

Plant remains preserved in products of metal corrosion: source of evidence on ancient plant materials and environment from burial contexts

By-products of metal corrosion, when coming into contact with organic matter, have the capacity to preserve it from decay. A pilot study was conducted aiming to explore the potential and limitations of plant remains preserved in by-products of metal corrosion for archaeobotanical research. The organic remains considered come from the surface/immediate proximity of the metal funerary artefacts of two ancient cemeteries—Varna and Messambria, Eastern Bulgaria. Metal corrosion by-products were observed and sampled, under a low magnification stereo microscope. Subsequently, the plant macrofossils recognised were analysed under reflected light and a scanning electron microscope (SEM). Additionally, pollen was extracted from the metal corrosion by-products, using standard acetolysis. The analyses from the graves of both cemeteries allowed identification of textiles and plant fibres, as well as wood (Cornus sp., Pinus sp., Viburnum sp.). At Varna cemetery epidermis fragments of Juncus sp. were recognized, while at Messambria necropolis fruits of almond were found. The pollen analysis from Varna points to use of flowers in the ritual (Daphne tetrads were recorded) and shows a notably open landscape with 77% non-arboreal pollen (NAP). The palynological analysis from the Messambria necropolis revealed the use of flowers in the burial ritual indicated by clusters of Vitis, Cistus and Rosaceae pollen. The surrounding vegetation was dominated by open oak woodland and open habitats (43% NAP) with a strong presence of anthropogenic indicators. The outcome of the study proved to be promising for reconstructing details of the burial rituals including associated plant materials, as well as the surrounding plant habitats during the functioning of the cemeteries.

Grazing hinders seed dispersal during crop failure in a declining oak woodland

Masting, the synchronized production of variable quantities of seeds, is a global phenomenon in diverse ecosystems, including treed grazing systems where trees and grazing animals coexist. This phenomenon can be interspersed with years of extreme crop failure, whose frequency and unpredictability are increasing. Yet, the combined impact of crop failure and grazing on seed dispersal and seed-to-seedling transition remains poorly understood. To address this concern, we investigated rodent-mediated cork-oak (Quercus suber) acorn predation, dispersal, and seedling emergence in cattle grazed and non-grazed areas in central Portugal during years with contrasting masting seasons. We found that the acorns supplied in the crop failure year were dispersed more rapidly and over longer distances than those supplied in the crop success year when other acorns were naturally available. The crop failure year also had 83 % more dispersal events and 84 % more predated acorns than the reproductive success year. However, the higher acorn predation was offset by a 2.4-fold higher percentage of unpredated dispersed acorns recruiting into seedlings. Both years ended up recruiting a similar number of seedlings. Acorns emerged seedlings 3.4 times farther in the crop failure year than in the crop success year. Cattle grazing was the main constraint on seed dispersal distance by rodents, reducing it by 53 %. Our study provides empirical evidence that cattle grazing modulates how an extreme crop failure year can surprisingly be an opportunity for the few existing acorns to have seedlings established farther apart than in a crop success year. If we are to better manage and preserve the high conservation and socio-economic value of Mediterranean cork oak woodlands in the face of climate change, we must prioritize fecund trees and carefully manage seed dispersal factors such as cattle grazing, particularly during years of crop failure.

Uncovering historical roots of nature-based solutions: Christian Ludwig Krause's approaches to restoring degraded land in an 18th-century European landscape

Nature-based solutions (NBS) represent a recent umbrella concept to tackle land degradation and other urgent challenges. The concept has deep, often-hidden historical roots. To shed light on these origins, this paper examines 18th-century approaches to combat land degradation in a central European landscape, as documented in a 1773 book by Christian Ludwig Krause. First, historical sources on overexploitation and degradation of forests and grasslands in 18th-century Brandenburg (now part of Germany) are examined to illustrate major challenges of that period. Then, an analysis of Krause's book identifies the problems he addressed and the solutions he proposed in response. Krause astutely diagnosed the interaction of different land uses that led to the loss or degradation of forests and grasslands and then to wind erosion that severely affected agricultural fields. He identified reduced flower availability due to overgrazing as a threat to bees and honey production. His main recommendations include restoration of oak woodlands, establishment of tree plantations, recovery of degraded sandy areas, planting of hedgerows as living fences, and bee gardens. He justified these solutions by highlighting negative socioeconomic consequences of land degradation, such as timber shortages and reduced agricultural yields. He addressed farmers and other stakeholders directly, illustrating expected economic benefits of proposed interventions, including for the well-being of future generations. Krause's ideas stand out for several reasons: (i) they are underpinned by a clear-sighted understanding of natural components and processes, combined with practical experience; (ii) he treated land degradation as a social-environmental phenomenon, highlighting the responsibility of various stakeholders for problems and their solutions, supported by economic reasoning; (iii) he linked different land-use systems and local to regional scales, even incorporating urban-rural coupling of nutrient cycles. Most of his suggestions meet present-day criteria of NBS. Two aspects of his work fall outside the NBS framework: (i) historical data on the efficiency of the proposals are missing and (ii) biodiversity gains are not explicitly included in his proposals - although many of them would result in improved biodiversity. Christian Ludwig Krause can be considered an 18th-century pioneer of NBS, with his systems-based thinking serving as a model even today, and he was also a pioneer of ecological restoration and sustainable land use.

Predator odor can reduce acorn removal by granivorous rodents in mixed oak forest stands

Developing better practices for rodent pest control is of high importance to reduce damage during forest restoration and in crop production. For example, during direct seeding with large and highly attractive seeds such as acorns, most seeds will disappear due to consumption or dispersal if not protected. An unexplored concept in reducing rodent damage is the use of repellents derived from predators. We tested the efficiency of three volatile compounds (2-propylthietane, 2-phenylethylamine and indole) associated with predators as rodent repellent candidates and scored the reduction of acorn (Quercus petraea) removal at two field sites in southern Sweden. We further investigated at what distance (5 cm, 10 cm, and 15 cm) from the odor source the odors were efficient in lowering the removal of acorns. Removal was lowest with 2-propylthietane (25–45 % of acorn removal), followed by 2-phenylethylamine (75–95% acorn removal) at 5 cm. Indole failed to decrease acorn removal and did not differ significantly from the control treatments. In the control treatments, almost all acorns (95–100%) were removed from the plots during the 48-hour sessions at both sites, and the acorns were removed faster than in the other treatments. Removal increased with distance from the 2-propylthietane odor dispenser at both field sites. Here, the lowest acorn removal occurred at 5 cm from the odor disperser. Our short time experiment shows for the first time the potential of using 2-propylthietane for short-term protection of acorns from foraging by granivorous rodents in oak woodlands. To help increase the reliability of direct seeding as a method for regenerating and restoring forests, future studies should investigate whether the range and longevity in the field of predator odor formulations can be improved.

Elevated CO2 alters photosynthesis, growth and susceptibility to powdery mildew of oak seedlings.

Elevated CO2 (eCO2) is a determinant factor of climate change and is known to alter plant processes such as physiology, growth and resistance to pathogens. Quercus robur, a tree species integrated in most forest regeneration strategies, shows high vulnerability to powdery mildew (PM) disease at the seedling stage. PM is present in most oak forests and it is considered a bottleneck for oak woodland regeneration. Our study aims to decipher the effect of eCO2 on plant responses to PM. Oak seedlings were grown in controlled environment at ambient (aCO2, ∼400 ppm) and eCO2 (∼1000 ppm), and infected with Erysiphe alphitoides, the causal agent of oak PM. Plant growth, physiological parameters and disease progression were monitored. In addition, to evaluate the effect of eCO2 on induced resistance (IR), these parameters were assessed after treatments with IR elicitor β-aminobutyric acid (BABA). Our results show that eCO2 increases photosynthetic rates and aerial growth but in contrast, reduces root length. Importantly, under eCO2 seedlings were more susceptible to PM. Treatments with BABA protected seedlings against PM and this protection was maintained under eCO2. Moreover, irrespectively of the concentration of CO2, BABA did not significantly change aerial growth but resulted in longer radicular systems, thus mitigating the effect of eCO2 in root shortening. Our results demonstrate the impact of eCO2 in plant physiology, growth and defence, and warrant further biomolecular studies to unravel the mechanisms by which eCO2 increases oak seedling susceptibility to PM.

Key factors in direct acorn seeding for the successful restoration of open oak woodlands

Little is known about the effectiveness of direct acorn seeding when subjected to different environmental conditions, but without the interference of acorn predation. In order to assess and improve its success, a total of 2400 holm oak acorns from 20 mother trees were sown in three blocks across four sites from southern Spain. Each block was divided into two subplots, in one of which weed competition was mechanically controlled over the study period. Acorns were weighed, protected by a seed shelter, and sown at four different dates between December 2019 and March 2020. Emergence, survival and growth were registered until November 2021. In this last sampling, the aboveground biomass was harvested. Emergence varied from 53.7% of acorns sown in December to 29.4% of those sown in March while survival success after two growing seasons was 27.1% for acorns sown in December as compared to 9.2% of acorns sown in March. Survival success clearly decreased at a higher rate over time in non-treated subplots (12.7%) as opposed to those where the weeds were controlled (22.5%). Emergence, growth, and survival success were highly dependent on the site and the mother tree from which the acorn came. The mass of the emerged acorns was higher than the mass of those that did not emerge. The mean acorn mass of each mother tree was positively correlated with the germination rate and emergence of the seedlings, and with the survival of emerged seedlings and final survival success. In conclusion, we recommend selecting large acorns, sowing early (December), controlling weed competition over time, and selecting mother trees with high germination potential. Seeding success will be lower in drier sites and drier years.

Legacies of historical management practices in the large-scale distribution pattern of oak-hornbeam woodlands in Czechia

Historical woodland management practices like coppicing and grazing have formed the diversity and structure of oak-hornbeam woodlands. We analysed large-scale, high-resolution spatial data on the distribution of woodland communities in Czechia to find out whether past human impacts influenced the distribution of oak-hornbeam woodlands in present-day landscapes. We tested the relation of oak-hornbeam woodlands to the past and current settlement distribution pattern, woodland continuity since about 1840 and distance to the woodland edge, on top of natural environmental predictors, using generalized additive mixed-effects models (GAMM).The results show a positive association between oak-hornbeam woodlands and current towns and villages, but only at higher elevations at the edge of the supposed natural distribution of oak-hornbeam woodlands. This effect was enhanced in the vicinity of old (pre-1450) settlements. By contrast, we found no effect of distance to current settlements in the elevational optimum of oak-hornbeam woodlands and even a decreasing trend of oak-hornbeam at the lowest elevations. In addition, oak-hornbeam stands often occur on former agricultural land and close to the woodland edges.Our results do not contradict the traditional view of oak-hornbeam woodlands as natural vegetation in the lowlands and at middle elevations. However, they clearly show that this natural range was extended to higher elevations by past human influence, probably at the expense of beech woodlands. Additionally, historical woodland management probably supported thermophilous oak woodlands at the lowest elevations. These past human activities are still detectable in the current distribution pattern of woodland communities.

Drought conditions, aridity and forest structure control the responses of Iberian holm oak woodlands to extreme droughts: A large-scale remote-sensing exploration in eastern Spain

Understanding how Mediterranean forests respond to the increasing frequency of extreme droughts and forest densification is crucial for effective land management in the present context of climate change and land abandonment. We study the responses of Iberian holm oak (Quercus ilex L.) woodlands to recent extreme droughts during 2000–2019 along broad gradients of climate aridity and forest structure. To this purpose, we apply large-scale remote-sensing using MODIS EVI as a primary production proxy in 5274 Q. ilex sites distributed within a 100,000 km2 region in eastern Spain. These woodlands were extensively affected by two extreme drought events in 2005 and 2012. Resistance, assessed as the capacity of the ecosystems to maintain primary production during drought, was significantly lower for semi-arid than for sub-humid and dry-transition conditions. Holm oak woodlands located in semi-arid areas of the region showed also poorer resilience to drought, characterized by low capacity to fully recover to their pre-drought production levels. Further, drought intensity and both pre- and post-drought hydric conditions controlled the variations of resistance, recovery and resilience between the two analyzed extreme drought events. Drought effects were particularly negative for dense Q. ilex stands under semi-arid climate conditions, where strong competition for scarce water resources reduced drought resistance. The observed drought vulnerability of semi-arid holm oak woodlands may affect the long-term stability of these dry forests. Adaptive management strategies, such as selective forest thinning, may be useful for improving drought responses in these more vulnerable semi-arid woodlands. Conversely, natural rewilding may more appropriately guide management actions for more humid areas, where densely developed Q. ilex woodlands show in general a high ability to maintain ecosystem primary production during drought.

Deforestation and Its Effect on Surface Albedo and Weather Patterns

Deforestation is an important environmental problem and a key promoter of regional climate change through modifying the surface albedo. The objective of this research was to characterize the impact of deforestation and land use changes on surface albedo (α) and climate patterns in a tropical highland region of Mexico, between the years 2014 and 2021. The main land cover types are coniferous forests (CF), oak and gallery woodlands (OGW), and annual agriculture (AA), which represent more than 88% of the regional territory. We used 2014 and 2021 Landsat 8 OLI images with topographic and atmospheric correction in order to develop an inventory of albedo values for each land cover type in both time scenarios. Albedo images were generated by using the equation proposed by Liang in 2001, which is based on the reflectance of the bands 2, 3, 4, 5, and 7. Differences in albedo values were calculated between the years 2014 and 2021, and those differences were correlated with variations in climate parameters, for which we used climate data derived from the WRF model. In addition, the different land use changes found were classified in terms of triggers for increasing or decreasing surface albedo. We used the Mann–Whitney U Test to compare the 2021 − 2014 climatic deviations in two samples: Sample A, which included sites without albedo change in 2021; and Sample B, including sites with albedo change in 2021. Results showed that between 2014 and 2021, at least 38 events of land use change or deforestation occurred, with albedo increments between 1 and 11%, which triggered an average increment of 2.16% (p < 0.01; Mann–Whitney U Test) of the regional surface albedo in comparison to the 2014 scenario. In this period, the albedo for CF, OGW, and AA also increased significantly (p < 0.001; Mann–Whitney U Test) by +79, +12, and +9%, respectively. In addition, the regional albedo increment was found to be significant and negatively correlated (p < 0.01 Spearman’s coefficient) with relative humidity (RH), maximum temperature (Tmax), and minimum temperature (Tmin), and correlated (p < 0.01) positively with diurnal temperature range (DTR). The Mann–Whitney U Test revealed that 2021 climatic variations in Sample B sites are statistically different (p < 0.05) to 2021 climatic variations in Sample A sites, which demonstrates that albedo changes are linked to a decrease in minimum temperature and relative humidity and an increase in DTR. Conversion of CF and OGW into AA, perennial agriculture (PA), or grassland (GR) always yielded an albedo increment, whilst the conversion of AA to irrigation agriculture (IA) or PA triggered a decrease in albedo, and finally, the pass from GR or AA to protected agriculture (PA) caused albedo to increase or decrease, depending on the greenhouse covers materials. Reducing deforestation of CF and OGW, conversion of AA or GR into PA, and selecting adequate greenhouse covers could help to mitigate regional climate change.

Vegetation and climate dynamics at the dawn of human settlement: multiproxy palaeoenvironmental evidence from the Hashilan Wetland, western Iran

ABSTRACTThe scarcity of high‐resolution palaeoclimate records from the interior of West Asia has limited our understanding of the mechanisms of past climate change and their potential impacts on early human societies of the Eastern Fertile Crescent. Here, we present a multiproxy sedimentological, geochemical and palynological record from the Hashilan Wetland in the central Zagros Mountains, spanning the time interval from 22 to 2.2 kcal bp. Our results indicate a cold, dry climate for the last deglaciation (22 to 10 kcal bp) with amplified aridity during the Last Glacial Maximum, Heinrich Stadial 1, the Younger Dryas and the 8.2 and 3.2 ka events. The Early Holocene (11.6 to 7.8 kcal bp) is characterised by prolonged dry summers, frequent spring/summer dust storms and restricted oak woodlands that gradually expanded as summers shortened toward the second half of the Holocene (<6 kcal bp). We show an out‐of‐phase Holocene moisture variation between the interior of West Asia and the Indian Summer Monsoon domain and conclude that summer insolation‐driven latitudinal shifts of the Hadley cell played a key role in seasonality changes in the interior of West Asia by modulating the strength and pathway of the subtropical high‐pressure cells. Finally, we explore possible impacts of these changes on regional prehistoric human communities.

Multi-site archaeobotanical analysis reveals wood-fuel supply, woodland impact and land use around Roman urban centres: The case of Barcino (Barcelona, NE Iberia)

Woodlands are especially important spaces for city fuel provisioning. During Roman times urban centres carried out numerous activities with frequent wood-energy requirements, and as a result, they potentially impacted the composition of the surrounding forests.Considering this premise, this study discusses the wood fuel economy and the configuration of the landscape around the Roman colony of Barcino (present-day Barcelona), located on the NW Mediterranean coast. We approached the topic starting from an analysis of wood charcoal fragments and pollen remains sampled from several rescue archaeological excavations along the perimeter wall of the Roman city, in order to shed light on the composition of the urban wood fuel exploited and the land cover of the suburban area between the 1st and the 6th centuries CE.The charcoal analysis revealed that most of the fuel procured for Barcino came from holm oak woodlands, with Quercus ilex, Arbutus unedo and Erica arborea woods predominantly being harvested. Furthermore, the composition of the fuel charcoal debris appeared similar in the different excavation-sectors as well as constant through time, suggesting the existence of a fuel supply economy common to the whole city and sustainable woodland management to fulfil these needs.Moreover, pollen analysis detected an important deforestation process in the ager of the city, accompanied by an increase in cereal and vine cultivation. In addition, either pollen and/or charcoal findings assessed the introduction of new fruit trees in the area (Castanea sativa, Juglans regia, Maloideae, Citrus sp., Punica granatum, Prunus sp.). Overall, these data suggest the fragmentation and ever-increasing shift of forested areas in the hinterland of the Barcelona plain, as well as on the hills.

Mammalian resistance to megafire in western U.S. woodland savannas

AbstractIncreasingly frequent megafires are dramatically altering landscapes and critical habitats around the world. Across the western United States, megafires have become an almost annual occurrence, but the implication of these fires for the conservation of native wildlife remains relatively unknown. Woodland savannas are among the world's most biodiverse ecosystems and provide important food and structural resources to a variety of wildlife, but they are threatened by megafires. Despite this, the great majority of fire impact studies have only been conducted in coniferous forests. Understanding the resistance and resilience of wildlife assemblages following these extreme perturbations can help inform future management interventions that limit biodiversity loss due to megafire. We assessed the resistance of a woodland savanna mammal community to the short‐term impacts of megafire using camera trap data collected before, during, and after the fire. Specifically, we utilized a 5‐year camera trap data set (2016–2020) from the Hopland Research and Extension Center to examine the impacts of the 2018 Mendocino Complex Fire, California's largest recorded wildfire at the time, on the distributions of eight observed mammal species. We used a multispecies occupancy model to quantify the effects of megafire on species' space use, to assess the impact on species size and diet groups, and to create robust estimates of fire's impacts on species diversity across space and time. Megafire had a negative effect on the detection of certain mammal species, but overall, most species showed high resistance to the disturbance and returned to detection and site use levels comparable to unburned sites by the end of the study period. Following megafire, species richness was higher in burned areas that retained higher canopy cover relative to unburned and burned sites with low canopy cover. Fire management that prevents large‐scale canopy loss is critical to providing refugia for vulnerable species immediately following fire in oak woodlands, and likely other mixed‐forest landscapes.

A Drone-Powered Deep Learning Methodology for High Precision Remote Sensing in California’s Coastal Shrubs

Wildland conservation efforts require accurate maps of plant species distribution across large spatial scales. High-resolution species mapping is difficult in diverse, dense plant communities, where extensive ground-based surveys are labor-intensive and risk damaging sensitive flora. High-resolution satellite imagery is available at scales needed for plant community conservation across large areas, but can be cost prohibitive and lack resolution to identify species. Deep learning analysis of drone-based imagery can aid in accurate classification of plant species in these communities across large regions. This study assessed whether drone-based imagery and deep learning modeling approaches could be used to map species in complex chaparral, coastal sage scrub, and oak woodland communities. We tested the effectiveness of random forest, support vector machine, and convolutional neural network (CNN) coupled with object-based image analysis (OBIA) for mapping in diverse shrublands. Our CNN + OBIA approach outperformed random forest and support vector machine methods to accurately identify tree and shrub species, vegetation gaps, and communities, even distinguishing two congeneric shrub species with similar morphological characteristics. Similar accuracies were attained when applied to neighboring sites. This work is key to the accurate species identification and large scale mapping needed for conservation research and monitoring in chaparral and other wildland plant communities. Uncertainty in model application is associated with less common species and intermixed canopies.

Woodland wildfire enables fungal colonization of encroaching Douglas‐fir

Abstract Self‐reinforcing differences in fire frequency help closed‐canopy forests, which resist fire, and open woodlands, which naturally burn often, to co‐occur stably at landscape scales. Forest tree seedlings, which could otherwise encroach and overgrow woodlands, are killed by regular fire, yet fire has other effects that may also influence these feedbacks. In particular, many forest trees require symbiotic ectomycorrhizal fungi in order to establish. By restructuring soil fungal communities, fire might affect the availability of symbionts or the potential for symbiont sharing between encroaching trees and woodland vegetation. To investigate this possibility, we performed a soil bioassay experiment using inoculum from burned and unburned oak woodlands and Douglas‐fir forests. We examined how fire, ecosystem type, and neighboring heterospecific seedlings affect fungal root community assembly of Douglas‐firs and oaks. We asked whether heterospecific seedlings facilitated fungal colonization of seedling roots in non‐native soil, and if so, whether fire influenced this interaction. External fungal colonization of oak roots was more influenced by fire and ecosystem type than by the presence of a Douglas‐fir, and oaks increased the likelihood that Douglas‐fir roots would be colonized by fungi in oak woodland soil. Yet, fire increased colonization of Douglas‐fir in oak soil, diminishing the otherwise crucial role played by oak facilitation. Fire also strengthened the positive effect of Douglas‐firs on oak root‐associated fungal diversity in Douglas‐fir forest soil. Prior work shows that fire supports woodland ecosystems by stemming recruitment of encroaching seedlings. Here, we find evidence that it may contrastingly reduce fungal limitation of invasive seedling growth and establishment, otherwise relieved only by facilitation. Future work can investigate how these opposing effects might contribute to the net impact of changes in fire regime on landcover stability. Read the free Plain Language Summary for this article on the Journal blog.

Urban land cover and El Niño events negatively impact population viability of an endangered North American songbird

AbstractPopulation dynamics of migratory species are influenced by land use and climate patterns experienced across the full annual cycle. Identifying environmental factors influencing productivity, survival, and their relative contributions to abundance and population growth is critical for the recovery and management of at‐risk species in the face of continuing global change. The golden‐cheeked warbler (Setophaga chrysoparia) is an endangered passerine that breeds exclusively in the mixed Ashe juniper (Juniperus ashei)–oak (Quercus) woodlands of Central Texas, USA, and winters at high elevations in Central America. We evaluated the effects of precipitation, climate, and land cover on golden‐cheeked warbler productivity, adult male survival, and territory abundance using data from a long‐term monitoring site, the Balcones Canyonlands Preserve, in Austin, Texas. We jointly analyzed annual productivity, mark–recapture, and territory count data collected on 10 plots from 2011 to 2019 in an integrated population model. The number of young fledged per male territory was negatively related to percent urban land cover within 1 km of monitoring plots, and adult male survival was negatively related to a strong El Niño event. Estimates of population growth and abundance indicated a decline in abundance across our study period. We forecasted population viability 25 years into the future given increases in urban development and frequency of El Niño events. Quasi‐extinction probability increased from 0.17 under current urban land cover conditions and El Niño frequency to 0.41 under the scenario of a 10% increase in urban development around all plots and an increase in El Niño frequency. Productivity and adult survival were positively correlated with population growth, highlighting the need for conservation and management actions to maximize these vital rates on the breeding grounds and range‐wide.