Climatic Fluctuations Research Articles

Uncovering glacial footprints and identifying phylogeographic units in the freshwater crab Potamon elbursi Pretzmann, 1962 (Decapoda: Potamidae) based on mitochondrial data

The current patterns of biodiversity have significantly been affected by glacial-interglacial cycles during the Pleistocene period. True freshwater crabs are considered as poor dispersers and terrestrial barriers restrict gene flow between their local populations. Recent studies, however, suggest that certain environmental conditions, such as periods of heavy rainfall and humidity, can facilitate their between-drainage dispersal and will result in the evolution of homogenous genetic patterns among different drainage systems. Here we tested this hypothesis by comparing populations of the endemic freshwater crab Potamon elbursi Pretzmann, 1962 distributed in two drainage systems, the Caspian Sea and Namak Lake, in northern Iran. Our results based on the genetic analysis of 70 new and 61 previously published sequences of the mitochondrial cytochrome oxidase subunit I gene revealed a substantial haplotype diversity in some populations and high levels of local population structuring in others. Initially, we found mixed evidence of genetic differentiation and connectivity among drainages and populations. Genetic differentiation between the two drainages only became apparent after the Sepirdood population (which belongs to the Caspian Sea drainage) was excluded. Subsequently, the two drainages showed significant genetic distinctions, with a limited gene flow between them. Our demographic analyses supported recent population bottlenecks, followed by a rapid demographic and/or spatial expansion dating back to the Pleistocene climatic fluctuations. Species distribution modelling suggests that precipitation during warm weather conditions profoundly affects the distribution of P. elbursi. This study indicates that freshwater crabs can override short land barriers under favorable weather conditions and will have conservation implications in the face of contemporary climatic fluctuations.

Cyclic and linear trajectories of ecosystem evolution on sand dunes in Siberian taiga: A comprehensive analysis

Extensive unforested sandy areas on the margins of floodplains and riverbeds, formed by dunes, barchans, and accumulation berms, are a ubiquitous feature across northern Eurasia and Alaska. These dynamic landscapes, which bear witness to the complex Holocene and modern climatic fluctuations, provide a unique opportunity to study ecosystem evolution. Within this heterogeneous assemblage, active dunes, characterized by their very sparse plant communities, contrast sharply with the surrounding taiga (boreal) forests common for the stabilized dunes. This juxtaposition makes these regions to natural laboratories to study vegetation succession and soil development. Through a comprehensive analysis of climate, geomorphology, vegetation, soil properties, and microbiome composition, we elucidate the intricacies of cyclic and linear ecosystem evolution within a representative sandy area located along the lower Nadym River in Siberia, approximately 100 km south of the Arctic Circle. The shift in the Holocene wind regime and the slow development of vegetation under harsh climatic conditions promoted cyclical ecosystem dynamics that precluded the attainment of a steady state. This cyclical trajectory is exemplified by Arenosols, characterized by extremely sparse vegetation and undifferentiated horizons. Conversely, accelerated vegetation growth within wind-protected enclaves on marginally stabilized soils facilitated sand stabilization and subsequent pedogenesis towards Podzols. Based on soil acidification due to litter input (mainly needles, lichens, and mosses) and the succession of microbial communities, we investigated constraints on carbon and nutrient availability during the initial stages of pedogenesis. In summary, the comprehensive study of initial ecosystem development on sand dunes within taiga forests has facilitated the elucidation of both common phases and spatiotemporal dynamics of vegetation and soil succession. This analysis has further clarified the existence of both cyclic and linear trajectories within the successional processes of ecosystem evolution.

Genomic divergence and mutation load in the Begonia masoniana complex from limestone karsts

Understanding genome-wide diversity, inbreeding, and the burden of accumulated deleterious mutations in small and isolated populations is essential for predicting and enhancing population persistence and resilience. However, these effects are rarely studied in limestone karst plants. Here, we re-sequenced the nuclear genomes of 62 individuals of the Begonia masoniana complex (B. liuyanii, B. longgangensis, B. masoniana and B. variegata) and investigated genomic divergence and genetic load for these four species. Our analyses revealed four distinct clusters corresponding to each species within the complex. Notably, there was only limited admixture between B. liuyanii and B. longgangensis occurring in overlapping geographic regions. All species experienced historical bottlenecks during the Pleistocene, which were likely caused by glacial climate fluctuations. We detected an asymmetric historical gene flow between group pairs within this timeframe, highlighting a distinctive pattern of interspecific divergence attributable to karst geographic isolation. We found that isolated populations of B. masoniana have limited gene flow, the smallest recent population size, the highest inbreeding coefficients, and the greatest accumulation of recessive deleterious mutations. These findings underscore the urgency to prioritize conservation efforts for these isolated population. This study is among the first to disentangle the genetic differentiation and specific demographic history of karst Begonia plants at the whole-genome level, shedding light on the potential risks associated with the accumulation of deleterious mutations over generations of inbreeding. Moreover, our findings may facilitate conservation planning by providing critical baseline genetic data and a better understanding of the historical events that have shaped current population structure of rare and endangered karst plants.

Circular genetic structure of the Abies nephrolepis species complex shaped by the circular landform of Northeast Asia

AbstractAimPinaceae have been noted for their tendency towards reticulation as a result of interspecific hybridization. Here, we demonstrated the phylogeographic dynamics of the native Northeast Asian sub‐alpine conifer, Abies nephrolepis species complex (ANSC), evolving in circular overlaps along the Northeast Asian landform, which functions as a corridor with the sea, thus acting as a geographic barrier.LocationNortheast Asia: the Korean Peninsula, Japanese Archipelago, Russian Far East and northeastern China.TaxonAbies nephrolepis species complex (Family Pinaceae, Genus Abies, Section Balsamea, Abies nephrolepis, A. koreana, A. veitchii and A. sachalinensis).MethodsA total of 728 individuals from 38 ANSC populations were analysed using multiplexed inter‐simple sequence repeat genotyping by sequencing to capture variations in biparental nuclear genomes. Eight mitochondrial regions and eight chloroplast regions of each individual were sequenced using the MiSeq platform and Sanger sequencing. Species distribution models were generated.ResultsBayesian clustering with 507 nuclear single nucleotide polymorphisms and the discrepancy between cytoplasmic and nuclear genome lineages implied contemporary and ancient connections between neighbouring species in the form of circular overlap. This genetic connectivity was supported by principal component analysis. Strong correlations between genetic distance and geographic distance were observed, suggesting that gene flow occurs through a continuous chain around the sea. We also found that gene flow direction and intensity changed over time, with support from palaeodistribution modelling.ConclusionPast hybridization events were captured in cytoplasmic genomes, generating heterogeneity across maternal ancestries. This intensive phylogeographic study demonstrates speciation with incomplete reproductive isolation (continuous gene flow) among neighbouring species with an alteration of the direction and intensity of gene flow due to climate change. The divergence of ANSC due to repeated isolation and reconnection caused by heterogenous physiological environments and climate fluctuation provides a model to solve evolutionary scenarios for reticulate evolution in Pinaceae and other plants.

Holocene utopias and dystopias: Views of the Holocene in the Anthropocene and their impact on defining the Anthropocene

In delineating the Anthropocene, the Holocene is being redefined as the formative epoch of human development leading to the Anthropocene. This has led to a diversity of views of the Holocene and Holocene humanity in the Anthropocene, the extremes of which may be described as “Holocene utopianism” and “Holocene dystopianism.” The former views the Holocene as a solution to the predicament of the Anthropocene, as an idealized past of human activities and stable climate that must be aspired to. The latter perceives the Holocene and Holocene humanity as the root cause of the ills of the Anthropocene that must be avoided in the future. These views reflect a gross simplification of human activities and the environment of the Holocene. Human activity in the Holocene is characterized by diverse human behaviors that can be perceived as both destructive and sustaining to the earth’s ecological systems, and in many cases, emerged as a response to fluctuations in the Holocene climate. The Holocene does not provide an escape from the Anthropocene, as a solution or as a cautionary tale. Nonetheless, future human endeavors must necessarily draw from the diversity of human activities and systems of organization observed in the Holocene, but do so carefully.

ENSO dataset & comparison of deep learning models for ENSO forecasting

Forecasting the El Nino-Southern Oscillation (ENSO) is a challenging task in climatology. It is one of the main factors responsible for the Earth’s interannual climatic fluctuation and can result in many climatic anomalies. The impacts include natural disasters (floods, droughts), low & high agriculture yields, price fluctuation, energy demand, availability of water resources, animal movement, and many more. This study presents a comprehensive ENSO dataset containing standard indicators and other relevant data to facilitate ENSO analysis and forecasting. To ensure the dataset's validity and reliability, we performed extensive data analysis and trained four basic deep models for time series forecasting (i.e. CNN, RNN, LSTM, and hybrids). The data analysis confirmed the accuracy and suitability of the dataset for ENSO forecasting. The LSTM model achieved the best fit to the data, leading to superior performance in forecasting ENSO events.

Multiomics data integration, limitations, and prospects to reveal the metabolic activity of the coral holobiont.

Since their radiation in the Middle Triassic period ∼240 million years ago, stony corals have survived past climate fluctuations and five mass extinctions. Their long-term survival underscores the inherent resilience of corals, particularly when considering the nutrient-poor marine environments in which they have thrived. However, coral bleaching has emerged as a global threat to coral survival, requiring rapid advancements in coral research to understand holobiont stress responses and allow for interventions before extensive bleaching occurs. This review encompasses the potential, as well as the limits, of multiomics data applications when applied to the coral holobiont. Synopses for how different omics tools have been applied to date and their current restrictions are discussed, in addition to ways these restrictions may be overcome, such as recruiting new technology to studies, utilizing novel bioinformatics approaches, and generally integrating omics data. Lastly, this review presents considerations for the design of holobiont multiomics studies to support lab-to-field advancements of coral stress marker monitoring systems. Although much of the bleaching mechanism has eluded investigation to date, multiomic studies have already produced key findings regarding the holobiont's stress response, and have the potential to advance the field further.

Hyperconcentrated flows shape bedrock channels

AbstractGeomorphological evidence of incised bedrock channels is widespread in all mountain landscapes worldwide. However, the processes controlling incision and gorge formation in bedrock have not directly been observed in an actualistic way. Here, we show a LiDAR change detection deciphering the erosive power of a 60,000 m3 hyperconcentrated flow (transition between flood and debris flow) in a deeply incised rock gorge in June, 2020. The flow laterally eroded up to 1 m of massive limestone and widened a 4 m narrow section of the gorge by up to 15%. Sinuosity, convergence, and gradient of the channel were proven to not influence erosivity indicating the hyperconcentrated nature of erosion. Furthermore, other than in prior studies no abrasion of thin rock veneer dominates erosion but mechanically excited breakout of rock fragments. Magnitude-frequency relations of eroded volumes mimic subaerial rock wall retreat. We show how single hyperconcentrated flows can erode bedrock channels far more efficient than decades of turbulent flows and hypothesise that repeated hyperconcentrated flows in phases of enhanced precipitation or by elevated material supply could control erosion boosts in gorge formation, e.g. in the Lateglacial or during climatic fluctuations.

Region-Specific Genetic Diversity of Black Rats (Rattus rattus Complex) in Southeast and East Asia Shaped by Rapid Population Expansion Events.

Among the six mitochondrial DNA lineages of the black rat (Rattus rattus Complex; RrC), lineages II and IV are widespread in Southeast and East Asia. This study explored their demographic history using 17 new sequences from the Miyako Islands in the Ryukyu archipelago, together with 178 publicly available cytochrome b sequences. We defined six and two haplotype groups showing rapid population expansion signals in Lineages II and IV, respectively. The six haplotype groups of Lineage II were represented by haplotypes from 1) Myanmar/Bangladesh/Northeast India, 2) Laos, 3) Thailand, 4) Indonesia/Philippines, 5) Vietnam/southern China, and 6) the Ryukyu archipelago. These expansion times were estimated using time-dependent evolutionary rates to be 115,300 years ago (ya), 128,500 ya, 9600 ya, 10,600 ya, 7200 ya, and 1400 ya, respectively, although all had large confidence intervals. The two groups of Lineage IV were recovered from the mainland and islands of Southeast Asia with predicted expansion times of 197,000 ya and 5800 ya, respectively. These results suggest that climatic fluctuations during the last 200,000 years of the Quaternary, affected the population dynamics in subtropical areas at different times. Furthermore, the results of the younger rapid expansion events of RrC suggest the possibility of agricultural advancement and dispersal of Neolithic farmers to different areas within the mainland and islands of Southeast Asia during the Holocene. A subset of rats from the Miyako Islands were found to have the same lineage IV haplotypes as those in Southeast Asia, suggesting a recent introduction of these new lineages.

High risk, high gain? Trade-offs between growth and resistance to extreme events differ in northern red oak (Quercus rubra L.).

Information about the resistance and adaptive potential of tree species and provenances is needed to select suitable planting material in times of rapidly changing climate conditions. In this study, we evaluate growth responses to climatic fluctuations and extreme events for 12 provenances of northern red oak (Quercus rubra L.) that were tested across three trial sites with distinct environmental conditions in Germany. Six provenances each were sourced from the natural distribution in North America and from introduced stands in Germany. We collected increment cores of 16 trees per provenance and site. Dendroecological methods were used to compare provenance performance and establish climate-growth relationships to identify the main growth limiting factors. To evaluate the provenance response to extreme drought and frost events, three site-specific drought years were selected according to the Standardized Precipitation Evapotranspiration Index (SPEI) and 2010 as a year with an extreme late frost event. Resistance indices for these years were calculated and assessed in relation to overall growth performance. We observed a high variation in growth and in the climate sensitivity between sites depending on the prevailing climatic conditions, as well as a high intra-specific variation. Overall, summer drought and low temperatures in the early growing season appear to constrain the growth of red oak. The resistance of provenances within sites and extreme years showed considerable rank changes and interaction effects. We did not find a trade-off between growth and resistance to late frost, namely, fast growing provenances had a high frost hardiness. Further, there was no evidence for a trade-off between growth and drought hardiness. Still, responses to drought or late frost differ between provenances, pointing to dissimilar adaptive strategies. Provenances from introduced (i.e. German) stands represent suitable seed sources, as they combine a higher growth and frost hardiness compared to their North American counterparts. Drought hardiness was slightly higher in the slow-growing provenances. The results provide a better understanding of the variable adaptive strategies between provenances and help to select suitable planting material for adaptive forest management.

Biological factor controls the variations in water use efficiency of an alpine meadow during the growing season in a permafrost region of the Qinghai-Tibet Plateau

The alpine meadow located in permafrost is crucial for ecosystem services of the Qinghai-Tibet Plateau (QTP), which is experiencing precipitation changes in most areas. Water use efficiency (WUE) can quantify the inextricable link between carbon assimilation and water loss in terrestrial ecosystems. However, the temporal variations in WUE and its driving factors across different precipitation years still need to be clarified in alpine meadows on the QTP. Therefore, 4-year carbon and water flux data were used to elucidate the mechanisms behind seasonal and interannual variations in WUE of an alpine meadow in the hinterland of the QTP. Noticeable seasonal variations in WUE were observed during the studied period, with the highest value (1.38±0.38 g C kg−1 H2O) occurring during the mid-growing season (MG, starting around 166 DOY), approximately 2 and 3 times those during the late-growing season (LG, starting around 256 DOY and ending around 282 DOY) and early-growing season (EG, starting around 140 DOY), respectively. Standardized total effects in the structural equation models from NDVI to WUE were highest in all seasons, indicating that NDVI was the primary controlling factor for daily WUE variations. Additionally, energy factors (temperature and solar radiation) also significantly influenced daily WUE variations. The highest mean daily WUE (1.23±0.65 g C kg−1 H2O) was in the mild dry year (2016). However, no significant differences were noted in mean daily WUE in severe dry (2015) and wet (2019) years compared to the normal year (2020) during GS. This can be attributed to the varying sensitivity of carbon assimilation and water loss to biotic and abiotic changes across divergent precipitation years, with WUE exhibiting a greater sensitive to gross primary productivity than to evapotranspiration. These findings suggest that alpine meadows have endured in its harsh environment and have adapted to climatic fluctuations through long-term evolution.

Genetic structure and landscape effects on gene flow in the Neotropical lizard Norops brasiliensis (Squamata: Dactyloidae)

One key research goal of evolutionary biology is to understand the origin and maintenance of genetic variation. In the Cerrado, the South American savanna located primarily in the Central Brazilian Plateau, many hypotheses have been proposed to explain how landscape features (e.g., geographic distance, river barriers, topographic compartmentalization, and historical climatic fluctuations) have promoted genetic structure by mediating gene flow. Here, we asked whether these landscape features have influenced the genetic structure and differentiation in the lizard species Norops brasiliensis (Squamata: Dactyloidae). To achieve our goal, we used a genetic clustering analysis and estimate an effective migration surface to assess genetic structure in the focal species. Optimized isolation-by-resistance models and a simulation-based approach combined with machine learning (convolutional neural network; CNN) were then used to infer current and historical effects on population genetic structure through 12 unique landscape models. We recovered five geographically distributed populations that are separated by regions of lower-than-expected gene flow. The results of the CNN showed that geographic distance is the sole predictor of genetic variation in N. brasiliensis, and that slope, rivers, and historical climate had no discernible influence on gene flow. Our novel CNN approach was accurate (89.5%) in differentiating each landscape model. CNN and other machine learning approaches are still largely unexplored in landscape genetics studies, representing promising avenues for future research with increasingly accessible genomic datasets.

Archaeology as a method and tool for resilience

ABSTRACT Climate change is having an immediate and devastating effect on archaeological sites in Florida. The Florida Public Archaeology Network's Heritage Monitoring Scouts (HMS Florida) program empowers local communities to document the impacts of climate change at sites throughout the state. Our ability to document sites shows humanity's resilience to climate fluctuations in the past while also making it clear that adaptation and mitigation of coastal areas in the face of modern anthropogenic climate change must be paramount. This article describes two case studies from coastal Florida that have served as visceral points of focus for local communities to see the impacts of climate change. At Shell Bluff Landing in the northeast part of the state a site stewardship program was developed to closely document changes in time starting in 2016 with alarming results. In the opposite corner of the state at Calusa Island, a private land trust was created to protect local natural environments from the impacts of development. The coastal island has subsequently seen massive loss due to erosion. The article concludes with actions archaeologists can take today to make the communities they work with more resilient, using a prioritization system developed with Palm Beach County as an example.

Phylogeography and population structure of Lagocephalus spadiceus (Richardson, 1845) (Tetraodontiformes, Tetraodontidae) in the South China Sea.

The climate fluctuations during the Late Pleistocene significantly influenced the phylogeographic structure and historical dynamics of marine fishes in the marginal seas of the western Pacific Ocean. The puffer fish, Lagocephalus spadiceus, holds substantial nutritional and economic value in the South China Sea. To investigate the demographic history and population structure of the L. spadiceus, the mitochondrial DNA COI and Cyt b gene datasets from 300 individuals across eight populations in the South China Sea were sequenced. Our findings revealed high haplotype diversity (0.874 ± 0.013) and low nucleotide diversity (0.00075 ± 0.00058). The phylogenetic tree and haplotype networks revealed no significant genetic differentiation along the northern coast of South China Sea. Neutrality tests, mismatch distribution analyses, and Bayesian skyline plots suggested that L. spadiceus underwent population expansion during the Late Pleistocene. Both ocean currents and climate change significantly influenced the geographical distribution and genetic population structure of L. spadiceus.

Genetically- and environmentally-dependent processes drive interspecific and intraspecific divergence in the Chinese relict endemic genus Dipteronia

China is a hotspot of relict plant species that were once widespread throughout the Northern Hemisphere. Recent research has demonstrated that the occurrence of long-term stable refugia in the mountainous regions of central and south-western China allowed their persistence through the late Neogene climate fluctuations. One of these relict lineages is Dipteronia, an oligotypic tree genus with a fossil record extending to the Paleocene. Here, we investigated the genetic variability, demographic dynamics and diversification patterns of the two currently recognized Dipteronia species (Dipteroniasinensis and D.dyeriana). Molecular data were obtained from 45 populations of Dipteronia by genotyping three cpDNA regions, two single copy nuclear genes and 15 simple sequence repeat loci. The genetic study was combined with niche comparison analyses on the environmental space, ecological niche modeling, and landscape connectivity analysis. We found that the two Dipteronia species have highly diverged both in genetic and ecological terms. Despite the incipient speciation processes that can be observed in D. sinensis, the occurrence of long-term stable refugia and, particularly, a dispersal corridor along Daba Shan-west Qinling, likely ensured its genetic and ecological integrity to date. Our study will not only help us to understand how populations of Dipteronia species responded to the tectonic and climatic changes of the Cenozoic, but also provide insight into how Arcto-Tertiary relict plants in East Asia survived, evolved, and diversified.

Spatial Pattern of Genetic Diversity and Demographic History Revealed by Population Genomic Analysis: Resilience to Climate Fluctuations of Acer truncatum Bunge

Whole genome sequencing techniques are capable of providing insights into plant genetic adaptation to climate oscillations. Acer truncatum Bunge is a new resource tree for food with ornamental, timber and medicinal value. However, it has been listed as a near-threatened species because of the decreasing number of natural populations. In order to develop conservation strategies and sustainable innovative utilization for genetic resources, spatial pattern of genetic diversity and demographic history of A. truncatum from 13 natural populations, which cover the entire range, were analyzed by 9,086,353 single nucleotide polymorphisms (SNPs) through whole genome resequencing. The genetic diversity of natural populations was high (He = 0.289, I = 0.449), and genetic variations mainly resided within populations (82.47%) by AMOVA analysis. Cluster analysis showed that 13 natural populations mainly originated from three common gene pools. Therefore, it is recommended that the natural populations (LBGM, BTM, WLS and DQT) with high genetic diversity in different groups were given priority for in situ conservation and the genetic resources from these populations were collected for ex situ conservation. The effective population size of A. truncatum experienced two large-scale sharp contractions and currently decreased to its bottom in history. Nonetheless, A. truncatum could have expanded its effective population size to its historical peak after the last glacial period, indicating that it is highly resilient to fluctuations of temperature and humidity.

Unraveling goitered gazelle (Gazella subgutturosa) diversification: insights from phylogeography and species distribution modeling

Abstract The impact of climate fluctuations on the genetic diversity and distribution of species is of particular concern for large mammals that are already at risk of extinction. In this study, we investigated the genetic status of populations, the evolutionary relationships, and the current and future state of population dispersion of the goitered gazelle, Gazella subgutturosa, using 109 mtDNA sequences (cytb) and species distribution modeling. We assessed the impact of past (Last Glacial Maximum [lgm: 21 Kya] and Mid-Holocene [6 Kya]), current, and future (2070) climate on the phylogeography and spatial distribution of the species. Our results indicate evidence of divergence of two main clades (G. subgutturosa subgutturosa, and G. subgutturosa yarkandensis) (1.052 Mya) and a further split between two clades of G. s. subgutturosa (Middle Eastern and Central Iranian) in the middle Pleistocene. Historical species distribution models suggest the species’ range has not changed much across all periods examined, but there has been a decreasing trend from 21k to the current. Future climate projections (bcc-csm1 and ccsm4, rcp s 4.5 and 6 scenarios) predict a contraction of suitable habitat at the northern and southern edges of the species’ current distribution, shifting the range to the center of the study area. Biogeographic analyses suggest that vicariance and dispersal events have shaped the genetic structure of G. subgutturosa. Our findings suggest that the current genetic structure of the species is potentially related to Pleistocene climatic fluctuations and refuges (Alborz, Zagros, and Kope Dagh Mountains) during cold periods. The study highlights the importance of understanding the genetic status of populations and their evolutionary relationships to effectively prevent further declines of species at risk of extinction.

The Influence of Ozone Depletion Potential Weighted Anthropogenic Emissions of Nitrous Oxide

The effects of anthropogenic emissions of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4), and halocarbons on stratospheric ozone (O3) over the twentieth and twenty-first centuries are divided using a chemical model of the stratosphere. As halocarbon levels revert to pre-industrial levels, N2O and CO2 will likely play the primary roles in the evolution of ozone in the future. It is unable to distinguish clearly between these gases’ effects on ozone due to nonlinear interactions between them. The work was conducted using the monthly and annual data of the gases in the stratospheric layer to determine the overlap between N2O and O3 for the Iraq station and for the period (2003-2016). The strength of the association between gases was determined using the Spearman rho test (rs). It was found that there is a very high positive relationship between the N2O and O3 in Nasriyah station, which is 0.807 which indicates a strong association. This is because meteorological conditions, climatic fluctuations, and atmospheric location all affect correlation. The ozone layer is destroyed by nitrous oxide at high concentrations through the stratosphere layer and the tropospheric layer, the concentration of ozone increases with an increase in the concentration of nitrogen dioxide.

The impact of climate change on the agriculture and the economy of Southern Gaul: New perspectives of agent-based modelling.

What impact did the Roman Climate Optimum (RCO) and the Late Antique Little Ice Age (LALIA) have on the rise and fall of the Roman Empire? Our article presents an agent-based modelling (ABM) approach developed to evaluate the impact of climate change on the profitability of vineyards, olive groves, and grain farms in Southern Gaul, which were the main source of wealth in the roman period. This ABM simulates an agroecosystem model which processes potential agricultural yield values from paleoclimatic data. The model calculates the revenues made by agricultural exploitations from the sale of crops whose annual volumes vary according to climate and market prices. The potential profits made by the different agricultural exploitations are calculated by deducting from the income the operating and transportation costs. We conclude that the warm and wet climate of the Roman period may have had an extremely beneficial effect on the profitability of wine and olive farms between the 2nd century BCE and the 3rd century CE, but a more modest effect on grain production. Subsequently, there is a significant decrease in the potential profitability of farms during the Late Antique Little Ice Age (4th-7th century CE). Comparing the results of our model with archaeological data enables us to discuss the impact of these climatic fluctuations on the agricultural and economic growth, and then their subsequent recession in Southern Gaul from the beginning to the end of antiquity.

DISTRIBUTION AND VARIATION OF NET PRIMARY PRODUCTIVITY IN FORESTLAND AND GRASSLAND OF CHINA

Net primary productivity (NPP) can characterize the state and service functions of terrestrial ecosystems and reflect the responses of plants to climate fluctuations and human disturbances. Many studies have analysed changes in NPP and its influencing factors in some parts of China, but few studies have made in-depth comparisons between different regions, decades, and land cover types across China. Based on uniform NPP products and land cover data, the distribution, difference and variation of NPP in forestland and grassland in China were investigated with GIS spatial analysis and least-squares regression methods, and results indicated that average NPP increased gradually from northwest to southeast, and the regions with average NPP of 1-200 gC m-2 yr-1 occupied the largest proportion. During 1981–2018, the regions where decadal average NPP increased were larger than those where NPP decreased, and the areas with inter-decadal difference of 1-50 gC m-2 yr-1 were the largest. In different land cover types or regions, NPP generally exhibited a rapid rising trend in the 1990s and a slow or declining trend in the 2000s. Annual NPP increased at a rate of 13.2 gC m-2 decade-1 in the entire study area during 1981–2018, and the NPP in forestland and grassland increased at a speed of 15.6 and 11.1 gC m-2 decade-1, respectively. Spatially, NPP increased at a rate of 1-100 gC m-2 decade-1 in most areas, and the increasing trend was statistically significant in Qinghai-Tibetan Plateau, most of Northwest China and eastern Northeast China. The area with a significant increase in NPP over the past 38 years accounted for 21.0% of the total study area. Our results highlight the consistent and upward variation of NPP in general, but there are some distinctions among different land cover types and different regions of China, and higher quality datasets and more reliable methods should be fully explored in further studies. Keywords: Net primary productivity, spatial distribution, linear trend, forestland and grassland, China.