Abandoning land transforms biodiversity

Collapse and recovery of livestock systems shape fire regimes on the Eurasian steppe: a review of ecosystem and biodiversity implications

Shifts in fire regimes can trigger rapid changes in ecosystem functioning and biodiversity. We synthesize evidence for patterns, causes and consequences of recent change in fire regimes across the Eurasian steppes, a neglected global fire hotspot. Political and economic turmoil following the break-up of the Soviet Union in 1991 triggered abrupt land abandonment over millions of hectares and a collapse of livestock populations. The build-up of vegetation as fuel, rural depopulation and deteriorating fire control led to a rapid increase in fire size, area burned and fire frequency. Fire regimes were also driven by drought, but likely only after fuel had accumulated. Increased fire disturbance resulted in grass encroachment, vegetation homogenization and decreasing plant species diversity. Feedback loops due to the high grass flammability were likely. Direct and carry-on effects on birds, keystone small mammals and insects were largely negative. Nutrient cycling and carbon balance changed, but these changes have yet to be quantified. The regime of large and frequent fires persisted until ca 2010 but shifted back to a more grazing-controlled regime as livestock populations recovered, reinforced by increasing precipitation. Key future research topics include the effects of future climate change, changing pyrodiversity and pyric herbivory on ecosystem resilience. Ongoing steppe restoration and rewilding efforts, and integrated fire management will benefit from a better understanding of fire regimes.This article is part of the theme issue 'Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks'.

Beyond retreat: Land-seascape legacies of change and continuation

Planned retreat is an increasingly common climate adaptation approach. Whilst effective at reducing exposure to unacceptable risks, it is subject to significant resistance. In response, research has focussed on risk, governance and justice, but there has been less attention on spatial perspectives, including how spaces are reconfigured and the resultant land-seascape legacies. We identify 161 cases of planned retreat and develop a typology to analyse land use change in origin sites worldwide. In many cases, we find land transfer from private to public ownership, and restoration of land and environmental relations, to a complete failure to consider spatial legacies. The research stresses the importance of moving beyond planned retreat as risk management to consider longer-term spatial relations. Consequently, we argue, the definition and practice of 'planned retreat' must include early planning for the values, uses and reconfigurations of origin sites, extending the bounds of reimagination beyond 'retreat' and beyond the site.

Ecological Connectivity for Reptiles in Agroecosystems: A Case Study with Olive Groves in Liguria (Northwestern Italy)

Agricultural expansion and intensification are major drivers of biodiversity loss, particularly through habitat fragmentation. In the Mediterranean region, traditional farming systems like olive groves have historically supported biodiversity by creating heterogeneous landscapes. This study evaluates the role of olive groves in maintaining ecological connectivity for reptiles in Liguria, Italy. Using a dataset of 5211 georeferenced reptile records and habitat suitability models, we constructed taxon-specific resistance maps and applied circuit theory to model landscape-scale connectivity. We addressed three key questions: (1) Do olive groves act as barriers to reptile movement? (2) Do olive groves provide connectivity levels comparable to those of natural habitats? (3) Do olive groves serve as corridors connecting protected areas? Our results indicate that olive groves do not impede reptile movement, with normalized current flow (NCF) values close to 1, similar to those of natural habitats. Additionally, olive groves frequently intersect with least-cost paths between protected areas, highlighting their role as connectivity corridors. These findings underscore the conservation value of traditional olive groves in fragmented landscapes. By integrating these agroecosystems into regional conservation strategies, we can enhance biodiversity while supporting sustainable agriculture. This study provides critical insights for land management practices that balance ecological and agricultural priorities.

Revealing the distribution and change of abandoned cropland in Ukraine based on dual period change detection method

Since the outbreak of the Russia-Ukraine conflict in 2022, Ukraine has experienced different types of abandoned cropland, such as unused and unattended cropland, as a result of war damage, agricultural infrastructure destruction, and refugee outflows. Common methods for detecting abandoned cropland have difficulty effectively identifying and distinguishing these different types. This study proposes a Dual-period Change Detection method to reveal the spatial distribution and changes of different types of abandoned cropland in Ukraine, which can aid in agricultural assessments and international assistance in conflict-affected areas. The method mainly utilizes time-series NDVI data to fit the crop curves corresponding to cropland on a pixel-by-pixel basis, and then establishes discrimination rules for different types of abandoned cropland based on the crop curves, so as to detect unused cropland in the pre-conflict period (2015-2021) as well as unused cropland and unattended cropland in the post-conflict period (2022-2023). Finally, the detection results are validated and accuracy assessed using medium and high resolution spatiotemporal remote sensing imagery interpretation. The results show that the overall accuracy of the abandoned cropland extraction in Ukraine ranges from 83 to 96% during the study period. Before the conflict, the national average unused rate was 1.6%, with the lowest in 2021 and the highest in 2018. In 2022, the unused cropland area was approximately twice the average unused area before the conflict, and it was widely distributed, with the area of unattended cropland reaching 462,000 hectares, mainly in the eastern part of Ukraine. In 2023, compared to 2022, the unused cropland area decreased by 67.8%, while unattended cropland increased by 116.7%. Both types of abandoned cropland exhibited spatial clustering, with major clusters identified in the Crimea region, Kherson Oblast, Zaporizhzhia Oblast, and Donetsk Oblast.

Sensitive shrubland and unique urbanization patterns: the key to understanding emerging towns growth in arid regions

The urbanization process is complex and lengthy, typically resulting in dual changes in the socioeconomic structure and ecological environment. However, in the context of arid environments and initial urbanization, emerging towns undergo evolutionary processes different from those of traditional cities. This study focuses on a typical town, analyzing its growth under the combined effects of arid conditions and incipient urbanization. The results reveal a unique urbanization trajectory in the hinterland of southern Xinjiang: transitioning from refined agricultural planting to shrubland and bare land dominated by natural factors and then to impervious surfaces. While the pattern was complex, the direction of transition was clear. Using the town's establishment in 2014 as a critical node for urbanization initiation, shrubland emerged as the most sensitive land type, with a proportional increase by a factor of 2.6 from 2010 to 2015. This was driven by the abandonment of cultivated land, which decreased by 11.3% during the study period, with 78% of the newly added shrubland area converted from cropland. By applying the Markov model together with the InVEST model, the study predicted urban land-use transition patterns over the next 5 years and revealed that urbanization primarily exacerbates the instability of water yield in the surrounding region. This study uniquely addresses the gap in understanding the impacts of the urbanization process of emerging towns in arid regions and its associated ecological processes. A detailed investigation of such urbanization is crucial to mitigating issues like disorderly land use and promoting the sustainable development of small and medium-sized towns.

Large, but Dispersal-Limited Populations of the Marsh Fritillary Euphydryas aurinia Persist on Abandoned Military Training Areas Three Decades After the End of the Cold War

Military training areas can host important biodiversity, due to the preservation of diverse, nutrient-poor historical cultural landscapes and an insect-friendly disturbance regime. In Europe, many training areas were abandoned after the end of the cold war in 1991 and the withdrawal of the Allied and Soviet forces. Many of these are now protected areas, and current management strategies vary from rewilding to active habitat management such as grazing or mowing. In a capture-release-recapture approach, marking 2418 individuals, we assessed the population size and movement patterns of the dry ecotype of the Marsh Fritillary Euphydryas aurinia Rottemburg 1775 on three former military training areas in Germany that varied in size and management (natural succession, mowing, and sheep-/goat grazing). Euphydryas aurinia is a rare and declining butterfly species listed in Annex II of the European Union Habitats Directive. Jolly-Seber models revealed a large population of ca. 19,000 individuals on the largest study site and a smaller population at a second site, whereas recapture rates were too low to predict the population size reliably at a third site. Population densities were 190-194 butterflies ha-1 at the unmanaged, large site and 56-71 butterflies ha-1 at a smaller site grazed with sheep. Thirty-nine percent of the recapture events occurred within the same 1-ha-study plot. The average minimum flight distance between the study plots was 313 m for males and 328 m for females. The maximum lifetime flight distance was 1237 m within 3 days. No dispersal was detected between study sites. Thirty years after cessation of the military use, the large former training site still held what likely is one of the largest populations of the species dry ecotype in Central Europe, including in areas where management ceased already in 1991. This suggests remarkable persistence of the species in areas without regular management, contrary to current opinion. However, regular flight distances seem not to be sufficient to connect the isolated habitat patches. It remains unknown how long the large population at the abandoned military area will persist without active habitat management. Careful, but active habitat management and restoration of habitat connectivity should thus be considered.

Invasibility framework to predict the early colonization of alien Sonneratia in mangrove: Implications for coastal area management

Invasibility, or an ecosystem's susceptibility to invasion, plays a critical role in managing biological invasions but is challenging to quantify due to its dependence on specific ecosystem variables. This limitation restricts the practical application of this concept in the control of alien species. This study aims to simplify invasibility into measurable components and develop an applicable framework to predict early colonization of alien plants within the coastal mangrove ecosystem. We used the unchanneled path length (UPL), a widely applied hydrological connectivity-related indicator, to assess the accessibility of the mangrove. The enhanced vegetation index (EVI), positively correlated with above-ground biomass, was used to evaluate the potential competitive intensity. Firstly, building on existing studies, we developed a four-quadrant concept model integrating the effects of EVI and UPL on the early colonization of the alien species Sonneratia apetala. Our results revealed significant differences in EVI and UPL values between colonized and uncolonized areas, with colonized regions displaying markedly lower values (P < 0.001). Additionally, logistic regression showed a significant negative association between the probability of successful colonization by S. apetala and both indicators (P < 0.001). These results validate the effectiveness of our conceptual model. Furtherly, we identified four key niche opportunities for exotic species in mangrove: mudflats outside the mangrove forest, tidal creeks, canopy gaps, and unmanaged abandoned aquaculture ponds. Overall, this study provides important insight into the ecological processes of alien S. apetala colonization and practical information for management of coastal areas susceptible to invasion. Additionally, it presents a case study on the practical application of the concept of invasibility in the management of alien species.

The exposure of the world's mountains to global change drivers

Global change affects mountain areas at different levels, with some mountains being more exposed to change in climate or environmental conditions and others acting as local refugia. We quantified the exposure of the world's mountains to three drivers of change, climate, land use, and human population density, using two spatial-temporal metrics (velocity and magnitude of change). We estimated the acceleration of change for these drivers by comparing past (1975-2005) vs. future (2020-2050) exposure, and we also compared exposure in lowlands vs. mountains. We found Africa's tropical mountains facing the highest future exposure to multiple drivers of change, thus requiring targeted adaptation and mitigation strategies to preserve biodiversity. European and North America's mountains, in contrast, experience more limited exposure to global change and could act as local refugia for biodiversity. This knowledge can be used to prioritize local-scale interventions and planning long-term monitoring to reduce the risks faced by mountain biodiversity.

Effects of human depopulation and warming climate on bird populations in Japan

Quantifying biodiversity trends in economically developed countries, where depopulation, associated secondary succession, and climate warming are ongoing, provides insights for global biodiversity conservation in the 21st century. However, few studies have assessed the impacts of secondary succession and climate warming on species' population trends at a national scale. We estimated the population trends of common breeding bird species in Japan and examined the associations between the overall population trend and species traits with the nationwide bird count data on 47 species collected from 2009 to 2020. The overall population trend varied among species. Four species populations increased moderately, 18 were stable, and 11 declined moderately. Population trends for 13 species were uncertain. The difference in overall trends among the species was associated with their habitat group and temperature niche. Species with relatively low-temperature niches experienced more pronounced declines. Multispecies indicators showed a moderate increase in forest specialists and moderate declines in forest generalists (species that use both forests and open habitats) and open-habitat specialists. Forest generalists and open-habitat specialists also declined more rapidly at sites with more abandoned farmland. All species groups showed an accelerated decline or decelerated increase after 2015. These results suggest that common breeding birds in Japan are facing deteriorating trends as a result of nationwide changes in land use and climate. Future land-use planning and policies should consider the benefits of passive rewilding for forest specialists and active restoration measures (e.g., low-intensive forestry and agriculture) for nonforest specialists to effectively conserve biodiversity in the era of human depopulation and climate warming.

From invasive species stand to species-rich grassland: Long-term changes in plant species composition during Solidago invaded site restoration

Biological invasions degrade ecosystems, negatively affecting human well-being and biodiversity. Restoration of invaded agricultural ecosystems is among specific goals of European Union Biodiversity Strategy. Successful restoration of invaded lands is a long-term process that requires monitoring to assess the effects of interventions. Here, we present the results of a long-term experiment (8 years) on restoration of semi-natural grassland on abandoned arable field overgrown by invasive Solidago species (S. gigantea and S. canadensis). We examined effect of different invaders removal methods (rototilling, turf stripping, herbicide application) and seed application practices (commercial seed mixture, fresh hay) on changes in species composition and taxonomic diversity of restored vegetation. Our results showed a positive effect of grassland restoration on taxonomic diversity and species composition, manifested by a decrease in Solidago cover and an increase in cover and richness of target graminoids and forbs characteristic of grassland. The seed source had a longer lasting and still observable effect on the vegetation composition than the Solidago removal treatments, which ceased to differ significantly in their influence after the first few years. Applying fresh hay as a seed source increased the cover of grassland species such as Arrhenatherum elatius and Poa pratensis. For commercial seed mixture, we observed the high cover of Lolium perenne and Schedonorus pratensis (introduced with seed mixture) at the beginning and the slow decrease along the experiment course. The most striking effect was the fresh hay with herbicide application, which resulted in the lowest Solidago cover and the highest cover of target graminoids. Nonetheless, with years the non-chemical methods, including no treatment, gives comparable to herbicide effectiveness of restoration. Overall, during the experiment, alpha diversity increased, while beta and gamma diversity reached a species maximum in the third year, and then decreased. In conclusion, this study gives guidance to successful restoration of species-rich grasslands on sites invaded by Solidago. It should be emphasised that short-term effect differ considerably from long-term outputs, especially highlighting the importance of seed source, as well as effectiveness of environmentally friendly methods such as regular mowing to control the invader.

Divergent ecological responses to typhoon disturbance revealed via landscape-scale acoustic monitoring

Climate change is increasing the frequency, intensity, and duration of extreme weather events across the globe. Understanding the capacity for ecological communities to withstand and recover from such events is critical. Typhoons are extreme weather events that are expected to broadly homogenize ecological dynamics through structural damage to vegetation and longer-term effects of salinization. Given their unpredictable nature, monitoring ecological responses to typhoons is challenging, particularly for mobile animals such as birds. Here, we report spatially variable ecological responses to typhoons across terrestrial landscapes. Using a high temporal resolution passive acoustic monitoring network across 24 sites on the subtropical island of Okinawa, Japan, we found that typhoons elicit divergent ecological responses among Okinawa's diverse terrestrial habitats, as indicated by increased spatial variability of biological sound production (biophony) and individual species detections. This suggests that soniferous communities are capable of a diversity of different responses to typhoons. That is, spatial insurance effects among local ecological communities provide resilience to typhoons at the landscape scale. Even though site-level typhoon impacts on soundscapes and bird detections were not particularly strong, monitoring at scale with high temporal resolution across a broad spatial extent nevertheless enabled detection of spatial heterogeneity in typhoon responses. Further, species-level responses mirrored those of acoustic indices, underscoring the utility of such indices for revealing insight into fundamental questions concerning disturbance and stability. Our findings demonstrate the significant potential of landscape-scale acoustic sensor networks to capture the understudied ecological impacts of unpredictable extreme weather events.

Echoes of the past: Agricultural legacies shape the successional dynamics of protected semi-natural dry grasslands

European semi-natural dry grasslands are among the most endangered terrestrial ecosystems, being recognised as habitats of community interest by the EU Habitats Directive. The occurrence and preservation of these habitats depend on a combination of anthropogenic and natural factors, although little is known regarding the role of past land-use changes. Here, we investigated the role of time since cultivation abandonment as a major driver of grassland successional dynamics in the Mediterranean agro-pastoral system of Alta Murgia, southern Italy. By integrating cartographic information on the past agricultural land-use with the main abiotic constraints (patch area, slope and aspect), we used generalised additive mixed models to test for the probability of occurrence of current grassland habitat types along time since cultivation abandonment (10 to 200 years). Our results disclosed the successional sequence of grassland plant communities since crop abandonment in the study area, highlighting that the distribution of semi-natural grassland communities largely depends on land use history besides current environmental patterns. Among the habitat types protected under the EU Habitats Directive, we highlighted that xero-thermic communities may represent an intermediate step of grassland succession after cultivation abandonment, while more mesic perennial communities indicate a late successional stage. These successional dynamics are further modulated by mesoclimatic conditions associated with slope and aspect, especially in case of long-standing pastures that were not historically affected by agricultural transformations. Our findings can contribute to a deeper understanding of dynamics relevant to spontaneous vegetation recovery in open environments, which is a prerequisite for setting up effective grassland conservation and restoration actions. Furthermore, our results underline the value of integrating historical maps and current information for the assessment of habitat conservation status.

The neglected role of abandoned cropland in supporting both food security and climate change mitigation

Despite the looming land scarcity for agriculture, cropland abandonment is widespread globally. Abandoned cropland can be reused to support food security and climate change mitigation. Here, we investigate the potentials and trade-offs of using global abandoned cropland for recultivation and restoring forests by natural regrowth, with spatially-explicit modelling and scenario analysis. We identify 101 Mha of abandoned cropland between 1992 and 2020, with a capability of concurrently delivering 29 to 363 Peta-calories yr-1 of food production potential and 290 to 1,066 MtCO2 yr-1 of net climate change mitigation potential, depending on land-use suitability and land allocation strategies. We also show that applying spatial prioritization is key to maximizing the achievable potentials of abandoned cropland and demonstrate other possible approaches to further increase these potentials. Our findings offer timely insights into the potentials of abandoned cropland and can inform sustainable land management to buttress food security and climate goals.