Continental Gradient Research Articles

Transboundary Aquifer Management Across the Americas: Hydro-Diplomacy as an Accelerator of Adaptive Groundwater Governance Amid Climate Change Challenges

The management of transboundary aquifers across the Americas faces significant challenges, especially as climate change and population growth intensify groundwater stress. Groundwater use has increased to support domestic, industrial, and agricultural demands but has been extracted through unregulated withdrawals, leading to the severe degradation of aquifer health and transboundary frictions. This study focuses on how hydro-diplomacy can accelerate the adaptive governance of shared groundwater resources in three key regions: Canada–USA, USA–Mexico, and Mexico–Guatemala–Belize. We utilized a mixed methodology by integrating a transect approach, borrowed from ecology, into the field of geopolitics. To compare the hydro-diplomatic relations and groundwater governance across a continental gradient in the Americas, we conducted a literature review and employed the TWINS conflict–cooperation matrix to evaluate governance frameworks and hydro-diplomatic interactions across time. Our findings demonstrate that hydro-diplomacy plays a pivotal role in expediting agreements, fostering transboundary data sharing, and supporting participatory governance models. In particular, the presence of supranational bodies such as the International Joint Commission (IJC) between Canada and the USA has been effective in maintaining long-term collaboration through social learning and technical cooperation. Meanwhile, in regions like Mexico–Guatemala–Belize, the absence of robust institutions has hindered progress, with limited financial and knowledge-sharing networks. This study highlights the need for improved cross-border cooperation mechanisms and the establishment of common monitoring protocols to better manage aquifer resources under the pressures of climate change. The results support the development of more adaptive transboundary groundwater management strategies aligned with Sustainable Development Goal (SDG) 6.5.2 and call for broader geopolitical cooperation to address the complexities of groundwater governance.

In pursuit of change: Divergent temporal shifts in climate sensitivity of Norway spruce along an elevational and continentality gradient in the Carpathians

Across much of Europe, climate change has caused a major dieback of Norway spruce (Picea abies L.), an economically important tree species. However, the southeasternmost fringe of this tree species – the Eastern Carpathians – has not yet suffered large-scale dieback. Studying temporal shifts of climate sensitivity (TSCS) over time may elucidate the degree to which Norway spruce may be vulnerable to climate-change induced decline in upcoming decades. Under this framework, we analyzed a regional tree-ring network comprising >3000 trees, with the aim of quantifying TSCS since 1950. We mathematically defined TSCS as the slope parameter of the regression of climate sensitivity (the correlation coefficient) over time. Given the often-observed contrasting shift of climate sensitivity at low versus high elevations, we were particularly interested in studying potentially divergent TSCS along elevational and spatial gradients. Our analyses revealed several indications of TSCS for Norway spruce in the Eastern Carpathians. First, at high elevations (>1100 m a.s.l.), we found that the positive link between summer temperature and spruce growth decreased significantly over the study period. In turn, these trees, over time, featured an increasing positive relationship with late winter temperatures. At low elevations (<800 m a.s.l.), the signal of positive summer Standardised Precipitation-Evapotranspiration Index (SPEI) correlation became more frequent among sites towards 2021, while the strength of the positive winter SPEI correlation from the previous growing season weakened. Our results revealed that TSCS was driven significantly by an elevational climate gradient and a longitudinal continentality gradient. Overall, our findings indicate that Norway spruce is increasingly affected by water limitations under climate change at low elevations, highlighting a potentially rising risk of decline of this species in the Eastern Carpathians.

Cenozoic stable isotope constraints on the Eurasian continental interior hydroclimate response to high CO2

The response of the terrestrial hydrologic cycle to higher atmospheric CO2 remains poorly constrained, largely due to difficulty in predicting how land surface processes may modify individual hydroclimate parameters such as precipitation (P), evapotranspiration (ET), and runoff (q). To interrogate how the terrestrial hydrologic cycle may change with warming and higher CO2, we utilize the Cenozoic geologic record of terrestrial stable oxygen isotopes (δ18O) as recorded in authigenic minerals, which reflect precipitation δ18O (δ18Op). Values of δ18Op are sensitive to changes in terrestrial hydroclimate, including to the ratio of P/ET and to precipitable water. In short, decreasing P/ET or higher precipitable water produces shallower δ18Op gradients inland, whereas increasing P/ET or lower precipitable water results in steeper δ18Op continental gradients. We compile nearly 15,000 samples of authigenic carbonate and tooth enamel across Eurasia—the largest continental landmass—that span the Cenozoic Era to reconstruct the past spatial distribution and zonal (i.e. east-to-west) gradients of δ18Op. We find that, in epochs with higher CO2, zonal δ18Op gradients increase, suggesting an increase in P/ET across Eurasia despite the expected increase in precipitable water in greenhouse climates. We compare these results to δ18Op gradients simulated by an isotope-enabled climate model (iCESM) forced with both pre-industrial (PI) and 4xPI CO2 mixing ratios. Simulated δ18Op gradients shallow as CO2 rises, in contrast to the reconstructed δ18Op gradients. This data-model mismatch suggests either that Earth system feedbacks not represented in our iCESM simulations, such as changes in Northern Hemisphere ice extent and vegetation, may have fundamentally changed Northern Hemisphere hydroclimate or that land-surface processes under high CO2 climates may be mis-represented in iCESM.

The Relationship between Land Surface Temperature and Air Temperature in the Douro Demarcated Region, Portugal

Climatic studies of agricultural regions normally use gauge-based air temperature datasets, which are produced with interpolation methods. The informative quality of these datasets varies depending on the density of the weather stations in a particular region. A way to overcome this limitation is to use the land surface temperature calculated from satellite imagery. To show this, the MODIS land surface temperature was compared with the PTHRES gridded dataset for air temperature in the Douro Demarcated Region (Portugal) between the years 2002 and 2020. The MODIS land surface temperature was able to detect a more pronounced maritime–continental gradient, a higher lapse rate, and thermal inversions in valley areas in winter. This information could prove to be crucial for farmers looking to adapt their practices and crops to extreme events, such as heat waves or heavy frost. However, the use of land surface temperature in climate studies should consider the differences in air temperature, which, on some occasions and locations, can be up to ten degrees in the summer.

Bayesian parameter estimation in glacier mass-balance modelling using observations with distinct temporal resolutions and uncertainties

Abstract Empirical glacier mass-balance models are commonly used in assessments of glacier and runoff evolution. Recent satellite-borne geodetic mass-balance observations of global coverage facilitate large-scale model calibration that previously relied on sparse in situ observations of glacier mass change. Geodetic observations constitute temporally aggregated mass-balance signals with significant uncertainty, raising questions about the role of observations with different temporal resolutions and uncertainties in constraining model parameters. We employ a Bayesian approach and demonstrate the sensitivity of parameter values to commonly used mass-balance observations of seasonal, annual and decadal resolution with uncertainties characteristic to in situ and satellite-borne observations. For glaciers along a continentality gradient in Norway, the use of annual mass balances results in around 20% lower magnitude of modelled ablation and accumulation (1960–2020), compared to employing seasonal balances. Decadal mass balance also underestimates magnitudes of ablation and accumulation, but parameter values are strongly influenced by the prior distribution. The datasets yield similar estimates of annual mass balance with different margins of uncertainty. Decadal observations are afflicted with considerable uncertainty in mass-balance sensitivity due to high parameter uncertainty. Our results highlight the importance of seasonal observations when model applications require accurate magnitudes of ablation, e.g. to estimate meltwater runoff.

Flora of Northeast Asia.

As a component of the MAP project, the study of the flora in Northeast Asia (comprising Japan, South Korea, North Korea, Northeast China, and Mongolia) convincingly underscores the indispensability of precise and comprehensive diversity data for flora research. Due to variations in the description of flora across different countries in Northeast Asia, it is essential to update our understanding of the region's overall flora using the latest high-quality diversity data. This study employed the most recently published authoritative data from various countries to conduct a statistical analysis of 225 families, 1782 genera, and 10,514 native vascular species and infraspecific taxa in Northeast Asia. Furthermore, species distribution data were incorporated to delineate three gradients in the overall distribution pattern of plant diversity in Northeast Asia. Specifically, Japan (excluding Hokkaido) emerged as the most prolific hotspot for species, followed by the Korean Peninsula and the coastal areas of Northeast China as the second richest hotspots. Conversely, Hokkaido, inland Northeast China, and Mongolia constituted species barren spots. The formation of the diversity gradients is primarily attributed to the effects of latitude and continental gradients, with altitude and topographic factors within the gradients modulating the distribution of species.

Spatio-temporal analysis of North African forest cover dynamics using time series of vegetation indices – case of the Maamora forest (Morocco)

North African forest areas play several roles and functions and represent a heritage of great economic and ecological importance. As a result of global changes, that act independently or synergistically, these areas are currently undergoing a pronounced degradation and their productivity is decreasing due to several factors. This work aims to characterize spatio-temporal dynamics of vegetation within the Maamora forest. This forest is considered as the most extensive cork oak woodland in the world and is divided, from west to east, into five cantons A, B, C, D and E. The data, extracted between 2000–2021 from MODIS NDVI/EVI images of 250 m, were analyzed using statistical parameters with the Pettitt homogeneity and the Mann-Kendall trend tests, with their seasonal and spatial components, in order to better consider the vegetation distribution of this forest. Results show a clear temporal and spatial (inter-canton) variability of vegetation intensity, unrelated to the continental gradient. In fact, recorded mean values in cantons C and E are significantly higher than those of cantons B and D respectively. This is confirmed by both regressive and progressive trends, which were identified respectively from the months of March 2012 and October 2008, in the data series of cantons B and E successively. Spatially, the regressive dynamic remains generalized and affects more than 26.7% of the Maamora’s total area with extreme rates (46.1% and 14.0%) recorded respectively by the two aforementioned cantons. Similarly, all the stand types in canton B show the highest regressive rates, especially the cork oak regeneration strata (75.4%) and the bare lands (86.1%), which may explain the positive tendencies identified by the related series during the fall season. However, the cantons C and E record the lowest rates, respectively, for natural stands of cork oak and artificial plantations. These results highlight also the absence of a causal relationship between the contrasting vegetation dynamics of the Maamora and the climatic conditions, expressed here by the continental gradient. However, they do highlight the effects of other factors, particularly those of a technical nature.

Modelling the response of urban lichens to broad-scale changes in air pollution and climate

To create more resilient cities, it is important that we understand the effects of the global change drivers in cities. Biodiversity-based ecological indicators (EIs) can be used for this, as biodiversity is the basis of ecosystem structure, composition, and function. In previous studies, lichens have been used as EIs to monitor the effects of global change drivers in an urban context, but only in single-city studies. Thus, we currently do not understand how lichens are affected by drivers that work on a broader scale. Therefore, our aim was to quantify the variance in lichen biodiversity-based metrics (taxonomic and trait-based) that can be explained by environmental drivers working on a broad spatial scale, in an urban context where local drivers are superimposed. To this end, we performed an unprecedented effort to sample epiphytic lichens in 219 green spaces across a continental gradient from Portugal to Estonia. Twenty-six broad-scale drivers were retrieved, including air pollution and bio-climatic variables, and their dimensionality reduced by means of a principal component analysis (PCA). Thirty-eight lichen metrics were then modelled against the scores of the first two axes of each PCA, and their variance partitioned into pollution and climate components. For the first time, we determined that 15% of the metric variance was explained by broad-scale drivers, with broad-scale air pollution showing more importance than climate across the majority of metrics. Taxonomic metrics were better explained by air pollution, as expected, while climate did not surpass air pollution in any of the trait-based metric groups. Consequently, 85% of the metric variance was shown to occur at the local scale. This suggests that further work is necessary to decipher the effects of climate change. Furthermore, although drivers working within cities are prevailing, both spatial scales must be considered simultaneously if we are to use lichens as EIs in cities at continental to global scales.

Ecological homogenization of soil properties in the American residential macrosystem

AbstractThe conversion of native ecosystems to residential ecosystems dominated by lawns has been a prevailing land‐use change in the United States over the past 70 years. Similar development patterns and management of residential ecosystems cause many characteristics of residential ecosystems to be more similar to each other across broad continental gradients than that of former native ecosystems. For instance, similar lawn management by irrigation and fertilizer applications has the potential to influence soil carbon (C) and nitrogen (N) pools and processes. We evaluated the mean and variability of total soil C and N stocks, potential net N mineralization and nitrification, soil nitrite (NO2−)/nitrate (NO3−) and ammonium (NH4+) pools, microbial biomass C and N content, microbial respiration, bulk density, soil pH, and moisture content in residential lawns and native ecosystems in six metropolitan areas across a broad climatic gradient in the United States: Baltimore, MD (BAL); Boston, MA (BOS); Los Angeles, CA (LAX); Miami, FL (MIA); Minneapolis–St. Paul, MN (MSP); and Phoenix, AZ (PHX). We observed evidence of higher N cycling in lawn soils, including significant increases in soil NO2−/NO3−, microbial N pools, and potential net nitrification, and significant decreases in NH4+pools. Self‐reported yard fertilizer application in the previous year was linked with increased NO2−/ NO3−content and decreases in total soil N and C content. Self‐reported irrigation in the previous year was associated with decreases in potential net mineralization and potential net nitrification and with increases in bulk density and pH. Residential topsoil had higher total soil C than native topsoil, and microbial biomass C was markedly higher in residential topsoil in the two driest cities (LAX and PHX). Coefficients of variation for most biogeochemical metrics were higher in native soils than in residential soils across all cities, suggesting that residential development homogenizes soil properties and processes at the continental scale.

Синтаксономический обзор мезофитных широколиственных лесов союза Aceri campestris–Quercion roboris Bulokhov et Solomeshch in Bulokhov et Semenishchenkov 2015 Юго-Запада России

Mesophilous broad-leaved forests predominating in south-western part of Russia were included in alliance Aceri campestris–Quercion roboris Bulokhov et Solomeshch in Bulokhov et Semenishchenkov 2015, association Fraxino excelsioris–Quercetum roboris Bulokhov et Solomeshch 2003 and three geographic subassociations. The subassociation F. e.–Q. r. typicum Bulokhov et Solomeshch 2003 in Bulokhov et Semenishchenkov 2015 unites communities occurring mainly in the broad-leaved forests zone of the Central Russian Upland. The subassociation F. e.–Q. r. stellarietosum nemori Semenishchenkov et al. 2015 occurs in the northern part of the association range in the zone of broad-leaved forests and close to the southeastern border of the hemiboreal subzone. Mesophilous broad-leaved forests occurring in the forest-steppe zone of the Central Russian Upland were included in the subass. F. e.–Q. r. crataegetosum curvisepalae Semenishchenkov in Bulokhov et Semenishchenkov 2015. The geographical distribution of the syntaxa is related to the climate continentality gradient — from the subass F. e.–Q. r. crataegetosum curvisepalae (the largest continentality indices) to the subass. F. e.–Q. r. stellarietosum nemori (the smallest continentality indices). The associations Aceri campestris–Tilietum cordatae Zaugolnova et Braslavskaya 2003 (nom. inv.) from the Kaluga and Tula Regions (Zaugolnova, Braslavskaya, 2003) and Aceri campestris–Quercetum roboris (nom. inv.) (var. Acer tataricum) described from the Voronezh Region (Starodubtseva, Khanina, 2009) were included in the association Fraxino excelsioris–Quercetum roboris after comparative syntxonomical analysis. On the basis of a comparative analysis, diagnostic combinations of subassociations were compiled, consisting of species with constancy above 20 % and values of the statistical φ-coefficient for selections above 20: F. e.–Q. r. stellarietosum nemori — Carex sylvatica (5059.9), Equisetum hyemale (2842.3), Galeobdolon luteum (10087.4), Matteucia struthiopteris (4257.7), Ranunculus cassubicus (5857.9), Stellaria nemorum (3349.6); F. e.–Q. r. crataegetosum curvisepalae — Acer tataricum (5362.0), Crataegus rhipidophylla (5964.0), Poa nemoralis (2736.9), Pyrus pyraster (3840.8), Scilla siberica (4558.4), Viola odorata (3440.5). Analysis of the differentiaal table of mesophilous broad-leaved and spruce-broad-leaved forests syntaxa made it possible to conclude that associations previously (Onyshchenko, 2009) assigned in Ukraine to alliance Scillo sibericae–Quercion roboris have a high floristic similarity with the syntaxa of Aceri campestris–Quercion roboris from the South-West of Russia, especially in the forest-steppe part of its range. Selections of three subassociations of the association Mercurialo perennis–Quercetum roboris from Ukraine floristically close to the syntaxa of alliance Querco roboris–Tilion cordatae from the South-West of Russia. In the dendrogram of cluster analysis, the compared syntaxa are grouped into two blocks corresponding to the rank of alliances: Aceri campestris–Quercion roboris and Querco roboris–Tilion cordatae. Based on the review, the authors believe that the «Hierarchical floristic classification system…» (Mucina et al., 2016) may be amended in terms of recognizing the syntaxonomical independence of the alliance Aceri campestris–Quercion roboris and its geographical interpretation. Derivative communities disturbed by humans in the place of mesophylous broad-leaved forests are classified as anthropogenic variants and non-rank «communities» named after the dominant species: Betula pendula, Populus tremula, Tilia cordata. Forests with a poor floristic composition, in which the diagnostic species of association and subassociation drop out of the coenoflora are classified as inops variants. They are characterized by a noticeable decrease in the average floristic saturation in comparison with typical communities. Derivative forests with a predominance of Betula pendula have a higher species richness in comparison with aspen or linden forests, as well as typical phytocoenoses of the association.

Features of biodiversity of the Uchursky landscape nature reserve (Ayano-Maiskoye district of Khabarovsk Territory)

It was revealed that the botanical and geographical feature of the vegetation cover of the Uchursky complex nature reserve is its position in the zone of convergence of the continental and monsoon climates, claimed by sharply contrasting phlorogenetic elements of the vegetation cover. The gradient of continentality - oceanicity in the vegetation cover is quite clearly traced between the eastern and western macroslopes of the mountain systems of the Uchur River basin. A complex history of the formation of the territory, the height difference from 1,000 to 2,000 meters, the variety of rocks created the conditions for the existence of floristic complexes of different ecology and origin. In this regard, on the territory of the nature reserve, an overlap of the marginal zones of plants ranges of oceanic and continental origin was found, which defines the richness of the region’s biodiversity, but makes both species and communities unstable. The uniqueness of the flora of the Geran Ridge was revealed, with the main core formed by species of non-Angarid origin, concentrated on the weathering crust of the basic rocks. The participation of alpinogenic, arctic and arctic-alpine species is noted. The pine-larch forests, which are unique in their species composition, are found on the outcrops of carbonate rocks on the right bank of the Uchur River, opposite the mouth of the Lyalmi River and in the Uchur-Ulkan interfluve. In this area, there are 79 species of endemic highland species of North Asia. The Red Book of Khabarovsk Territory includes 37 species of vascular plants, 4 species of lichens and 1 representative of the kingdom of mushrooms.

Vegetation Recovery Patterns in Burned Areas Assessed with Landsat 8 OLI Imagery and Environmental Biophysical Data

Vegetation recovery after the large wildfires that occurred in central Portugal in 2017 is assessed in the present study. These wildfires had catastrophic consequences, among which were human losses and a vast extent of forest devastation. Landsat 8 OLI images were used to obtain the land use and cover (LUC) classification and to determine the Normalized Burned Ratio index (NBR) for different times. NBR results were used to determine the difference between the NBR (dNBR) before the fire (pre-fire) and after the fire (post-fire), and the results obtained were cross-checked with the LUC. The dNBR results were cross-referenced with biophysical data to identify the characteristics of the most important burned areas in need of vegetative recovery. The results showed the spatial differentiation in vegetation recovery, highlighting different factors in this process, in particular the type of vegetation (the predominant species and bank of seeds available), the biophysical characteristics of burned areas (for example, the soil type in burned areas), the continentality gradient, and the climate conditions. The vegetation recovery was differentiated by time according to the species present in the burned areas pre-fire. In general, shrubland recovery was faster than that of tree species, and the recovery was more marked for species that were regenerated by the rhizomes after fire. The recovery process was also influenced by the season in the study area. It was more efficient in the spring and at the beginning of the summer, highlighting the importance of optimal conditions needed for vegetation regeneration, such as the temperature and precipitation (soil humidity and water availability for growing plants). The results of this research are important to forest planning: the definition of the strategies for the ecosystems’ recovery, the adoption of preventive measures to avoid the occurrence of large wildfires, the modification of anthropogenic practices, etc.

ВЛИЯНИЕ ФАКТОРОВ ОКРУЖАЮЩЕЙ СРЕДЫ НА ПОПУЛЯЦИОННО- ГЕНЕТИЧЕСКУЮ СТРУКТУРУ ДУБА ЧЕРЕШЧАТОГО (QUERCUS ROBUR L.) В БЕЛАРУСИ

Pedunculate oak (Quercus robur L.) is one of the main forest forming species in the Republic of Belarus. 18 allelic variants were identified by means of microsatellite loci analysis, which are grouped into 17 different combinations (haplotypes). Twelve of them are rare (the total frequency of occurrence is 15 %) and five are widespread (the proportion of occurrence varies from 7 to 48 %). The last of the named groups includes haplotypes No. 1 (μdt189, μdt3123, μdt4142, μcd494, μcd574, μkk4109), No. 2 (μdt190, μdt3120, μdt4141, μcd495, μcd574, μkk4109), No. 3 (μdt189, μdt3120, μdt4141, μcd494, μcd575, μkk4109), No. 8 (μdt189, μdt3121, μdt4142, μcd494, μcd574, μkk4109). It was found that the geographical distribution of the dominant haplotypes from west to east (along the gradient of climate continentality increasing) has the following order No. 8 – No. 7 – No. 3 – No. 1 – No. 2. It was revealed that haplotype No. 3 is predominantly found in oak forests growing on hills. Haplotype No. 8 prones to form forest stands in depressions, while haplotypes No. 1, No. 2 and No. 7 mainly occupied middle relief elements. The actually observed and theoretically expected frequencies of occurrence in different types of oak forests are close to each other only in the case of haplotype No. 2. For haplotypes No. 1 and No. 8 opposite tendencies of distribution were revealed. In those forest types where for haplotype No. 1 there was an increase in the actual frequency of occurrence compared to the expected one, for haplotype No. 8 there was opposite situation. The reverse trend was also true for this pare of haplotypes. The second pair for which opposite tendencies of distribution were also revealed is haplotypes No. 3 and No. 7.

Microbial communities are associated with indicators of soil surface condition across a continental gradient

Soil microbes support multiple ecosystem functions in woody biomes and are regulated by both plant communities and soil properties. While most microbes reside in the uppermost soil layer, we have a poor understanding of how the condition of the soil surface affects soil microbes across different woody biomes. This knowledge is important because it could provide a cost-effective means of predicting the extent to which different soil surface types could be useful predictors of microbial communities in soil health monitoring programs. We collected data on soil bacterial and fungal communities, and 13 soil surface indicators and grazing intensity at 173 sites in eastern Australia along a climatic gradient (humid to arid) varying in tree cover. Our aim was to investigate potential relationships among the condition of the soil surface and soil microbes in forests and non-forests using linear regressions, correlations and structural equation modelling. We found that both bacterial and fungal richness were closely associated with measures of soil surface condition, particularly in forests. Greater microbial diversity was related to enhanced plant structure and richness, and lower litter characteristics in both ecosystems. In forests, these relationships were enhanced by higher temperatures or suppressed by greater tree richness. Bacterial and fungal communities responded differently to changes in soil surface attributes in forests, with winners (e.g., Proteobacteria) and losers (e.g., Cyanobacteria) among bacterial phyla, but consistent responses across fungal phyla. Our study provides empirical evidence of significant relationships among microbes and indicators of soil surface condition. This finding advances our understanding of plant-soil interactions, and indicates the possibility of using field-based soil surface attributes as potential cost-effective, practical, yet informative indicators to monitor changes in microbial richness and composition in forests and non-forests (open woodlands, shrublands).

The current climatic trends and meteorological conditions of the fire dangerous situation formation in the Ural-Caspian region

Weather-climatic conditions are one of the leading factors forming fire dangerous satiations in the arid and semi-arid regions. Intra-continental position of the Ural-Caspian area promotes to reveal the diversity of climatic conditions and estimate the current trends in terms of the latitudinal-zonal change of landscapes and an increase of gradient of continentality. Results of analysis of the principal weather-climatic conditions – temperature, air precipitation, hydrothermal terms, wind regime, insolation) are summarized in the paper. Also, we identified spatio-temporal peculiarities of their long-time and current dynamics. The received results were analyzed in the aspect of the formation of fire dangerous situations in different landscapes of the examined region. Long-term archives on heat anomalies FIRMS served as principal data on grass fires. We have detected and confirmed that the most significant trends of the regional climate change are: a) growing air temperature occurring everywhere in frost-free seasons of a year; b) the cyclic dynamics of precipitation with the modern trend to aridization; c) annual distribution of rainfall; d) intensification of anomality of principal climatic parameters with the display of contrasting waves of heat and cold. All these tendencies directly (fire dangerous weather situations) or indirectly (productivity and a state of the vegetation cover) form the dynamics of grass fires. Nevertheless, the role of separate meteorological indicators and weather-climatic conditions, on the whole, are not often statistically significant in wildfires’ development. It is conditioned by the more substantial role of an anthropogenic factor that, in its turn, combines stochastic and purposeful agricultural sources of fires’ emergence.

Belowground consequences of converting broadleaf to conifer forest: Comparing the fine root systems of European beech and Scots pine

Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world’s largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species’ fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees’ susceptibility to climate-warming and drought.

Variability in climate-growth reaction of Robinia pseudoacacia in Eastern Europe indicates potential for acclimatisation to future climate

As a consequence of native tree species decline and distribution range contraction in Europe, acclimation of the non-native tree species at the edge of their distribution is gaining importance. Although non-native tree species may provide sustainable ecosystem services, as a potentially invasive species they may be a threat to local ecosystems as well. In Europe, black locust (Robinia pseudoacacia) a non-native species, seems to meet the condition of acclimation as a multi-generational process. The acclimatization, however, may have consequences not only for growth performance but also for the species' invasive potential. This study investigates the spatiotemporal pattern of secondary growth and climate sensitivity among six black locust stands along continentality gradient in Eastern Europe with the respect to bioclimatic conditions of the species distribution in Europe.Despite comparable bioclimatic conditions, climate sensitivity of black locust stands is highly variable, both temporally and spatially. The winter and spring temperatures are a key climatic driver of the growth pattern in southern and western Poland. Growth response to previous winter and current summer precipitation distinguished stands in western and eastern Poland. A significant increase in the mean annual temperature during the last 70 years likely triggered temporal instability of the black locusts’ climate signal. In general, drought conditions were found to be the main limiting factor at the edge sites within the black locust gradient. Thus, the climate sensitivity of black locust stands reflects rather site-specific microclimatic conditions then bioclimatically-based clustering pattern. Despite climate-related limiting factors, black locust seems to be characterized by high potential for acclimatization to Eastern European climatic conditions, suggesting high invasive potential. Thus, the replacement of native species by black locust or the conversion of local habitats into monocultures for biomass production should not be recommended, while species management should follow proactive measures to reduce the risk of uncontrolled spread of the species. Divergent growth reaction of black locust stands implies high plasticity of secondary growth and thus high probability of acclimatization to future climate. Given the expected range expansion to the East in Europe, we call for expanding dendroclimatic studies to the areas of future species expansion in order to test its climatic and edaphic limitations. This seems to be crucial for formulating non-native species management strategies in line with sustainable forestry, preventing the uncontrolled expansion of the species that threatens vulnerable habitats.

Ecosystem Processes Show Uniform Sensitivity to Winter Soil Temperature Change Across a Gradient from Central to Cold Marginal Stands of a Major Temperate Forest Tree

The magnitude and frequency of soil frost events might increase in northern temperate regions in response to climate warming due to reduced insulation caused by declining snow cover. In temperate deciduous forests, increased soil frost severity can hamper tree growth and increase the mortality of fine roots, soil fauna and microorganisms, thus altering carbon and nutrient cycling. From single-site studies, however, it is unclear how the sensitivities of these responses change along continental gradients from regions with low to high snowfall. We conducted a gradient design snow cover and soil temperature manipulation experiment across a range of lowland beech forest sites to assess the site-specific sensitivity of tree growth and biogeochemical cycling to soil cooling. Even mild and inconsistent soil frost affected tree increment, germination, litter decomposition and the retention of added 15N. However, the sensitivity of response (treatment effect size per degree of warming or cooling) was not related to prevailing winter climate and snow cover conditions. Our results support that it may be valid to scale these responses to simulated winter climate change up from local studies to regional scales. This upscaling, however, needs to account for the fact that cold regions with historically high snowfall may experience increasingly harsh soil frost conditions, whereas in warmer regions with historically low snowfall, soil frost may diminish. Thus, despite the uniform biotic sensitivity of response, there may be opposing directions of winter climate change effects on temperate forests along continental temperature gradients due to different trends of winter soil temperature.

Is Alaska’s Yukon–Kuskokwim Delta Greening or Browning? Resolving Mixed Signals of Tundra Vegetation Dynamics and Drivers in the Maritime Arctic

AbstractAlaska’s Yukon–Kuskokwim Delta (YKD) is among the Arctic’s warmest, most biologically productive regions, but regional decline of the normalized difference vegetation index (NDVI) has been a striking feature of spaceborne Advanced High Resolution Radiometer (AVHRR) observations since 1982. This contrast with “greening” prevalent elsewhere in the low Arctic raises questions concerning climatic and biophysical drivers of tundra productivity along maritime–continental gradients. We compared NDVI time series from AVHRR, the Moderate Resolution Imaging Spectroradiometer (MODIS), and Landsat for 2000–19 and identified trend drivers with reference to sea ice and climate datasets, ecosystem and disturbance mapping, field measurements of vegetation, and knowledge exchange with YKD elders. All time series showed increasing maximum NDVI; however, whereas MODIS and Landsat trends were very similar, AVHRR-observed trends were weaker and had dissimilar spatial patterns. The AVHRR and MODIS records for time-integrated NDVI were dramatically different; AVHRR indicated weak declines, whereas MODIS indicated strong increases throughout the YKD. Disagreement largely arose from observations during shoulder seasons, when there is partial snow cover and very high cloud frequency. Nonetheless, both records shared strong correlations with spring sea ice extent and summer warmth. Multiple lines of evidence indicate that, despite frequent disturbances and high interannual variability in spring sea ice and summer warmth, tundra productivity is increasing on the YKD. Although climatic drivers of tundra productivity were similar to more continental parts of the Arctic, our intercomparison highlights sources of uncertainty in maritime areas like the YKD that currently, or soon will, challenge historical concepts of “what is Arctic.”

The fertile island effect varies with aridity and plant patch type across an extensive continental gradient

Perennial plants play important roles in maintaining ecosystem functions by forming fertile islands beneath their canopies. Little is known about how the fertile island effect varies among different patch types and across climatic gradients, or what drives the strength of its effect. We assessed biotic (plants, biocrusts, litter) and abiotic (soil infiltrability, labile carbon, enzymes) fertile island effects beneath three plant patch types (tree, shrub and grass patches), and collected data on biotic (canopy size, grazing intensity) and abiotic (soil texture, electrical conductivity and pH) drivers at 150 sites along an extensive aridity gradient in eastern Australia. The fertile island effect was generally apparent beneath trees, shrubs and grasses, with biotic (plants) and abiotic (soils) attributes regulated differently by plant canopy size. The fertile island effect intensified with increasing aridity, with the greatest litter and soil resources accumulated beneath trees. Our study provides evidence of the fertile island effect across the whole spectrum of the aridity gradient, with the effect depending on the target attribute and plant patch type. Forecasted increases in aridity will likely strengthen the fertile island effect beneath trees, reinforcing the importance of trees in drier environments to support critical ecosystem functions and services.