Evaluating potential groundwater recharge in the unsteady state for deep-rooted afforestation in deep loess deposits

Groundwater recharge reduces due to high transpiration from shallow-rooted to deep-rooted afforestation. However, reaching a steady state in recharge process is challenging and no methods are available for assessing potential groundwater recharge under unsteady state. Hence, this study developed a new method to quantify groundwater recharge in the unsteady state by (1) calculating the water age (A₂) at maximum root depth (D₂) for deep-rooted afforestation using the chloride accumulative age method; (2) determining the soil depth (D₁) corresponding to A₂ under shallow-rooted vegetation using the multi-year average pore water velocity multiplied by A₂; (3) calculating the reduction in groundwater recharge (∆R) from shallow- to deep-rooted afforestation as the depth difference multiplied by the average water content between D₁ and D₂, divided by stand age. The average groundwater recharge for deep-rooted afforestation is equal to the average annual groundwater recharge under shallow-rooted vegetation minus ∆R. Soil cores with >25 m soil profiles below four land-use types of Hippophae rhamnoides Linn. (H. rhamnoides), Platycladus orientalis (L.) Franco (P. orientalis), Robinia pseudoacacia L. (R. pseudoacacia), and grassland were collected to measure soil water content, root distribution, and chloride and tritium contents. The results revealed that: (1) maximum root depths were 11.0 ± 0.5, 20.2 ± 1.2, and 22.6 ± 0.8 m, with soil water deficits of 373.48, 823.65, and 1847.92 mm under H. rhamnoides, P. orientalis, and R. pseudoacacia, respectively; (2) groundwater recharge following land-use change has not reached a steady state; (3) an average annual groundwater recharge was 89.12 mm yr^-1 under grassland, amounting to 16 % of the average annual precipitation; deep-rooted afforestation did not significantly differ, with 83.55, 84.91, and 85.65 mm yr^-1 under H. rhamnoides, P. orientalis, and R. pseudoacacia, respectively. This study contributes to a rational assessment of groundwater resources under unsteady state during land-use change.

Understanding deforestation impacts on soil erosion rates using 137Cs, 239+240Pu, and 210Pbex and soil physicochemical properties in western Iran

To investigate the effects of converting forests into vineyards typical to Zarivar Lake watershed, Iran, which occurred mainly in the 1970s and 80s, on soil erosion,137Cs and 210Pbex, being mid-and-long-term soil loss tracers, were applied. In Chernobyl-contaminated areas like those found in some parts of Europe and Asia, the proportion of 137Cs Chernobyl fallout needs to be determined to convert 137Cs inventories into soil erosion rates. To do so, Pu radioisotopes were applied for the first time in Iran. The soil samples were gathered from two adjacent, almost similar hillslopes under natural forest (slope length: 250 m; slope gradient: 20%) and rainfed vineyard (slope length: 200 m; slope gradient: 17%). 137Cs/239+240Pu ratios indicated that 49.8 ± 10.0% of 137Cs originated from Chernobyl. The net soil erosion rates derived by 137Cs, and 210Pbex approaches were 5.0 ± 1.1 and 5.9 ± 2.9 Mg ha-1 yr-1 in the forested hillslope, and 25.9 ± 5.7 and 32.5 ± 14.5 Mg ha-1 yr-1 in the vineyard hillslope, respectively. Both 137Cs and 210Pbex highlighted that deforestation increased soil erosion by around five times. Moreover, the impacts of deforestation on soil physicochemical properties were investigated in surface and subsurface soils. Compared to forested hillslope, soil organic carbon stock in the upper 40 cm of the vineyard reduced by 14 Mg C ha-1 (29%), 8 Mg C ha-1 of which was removed by erosion within 35 years, and the remaining have likely been lost via emissions (6 Mg C ha-1). The vineyard topsoil experienced the most dramatic drops in percolation stability (PS), sealing index, and organic matter by about 55, 51, and 49%, respectively. Among all measured physicochemical properties, PS showed the greatest sensitivity to land-use change. Overall, the present study's findings confirmed that deforestation for agricultural purposes triggered soil loss, deteriorated soil quality and possibly contributed to the reduction of the lake's water quality and climate change.

Reconciling climate action with the need for biodiversity protection, restoration and rehabilitation

Globally, we are faced with a climate crisis that requires urgent transition to a low-carbon economy. Simultaneously, the biodiversity crisis demands equally urgent action to prevent further species loss and promote restoration and rehabilitation of ecosystems. Climate action itself must prevent further pressures on biodiversity and options for synergistic gains for both climate and biodiversity change mitigation and adaptation need to be explored and implemented. Here, we review the key potential impacts of climate mitigation measures in energy and land-use on biodiversity, including the development of renewable energy such as offshore and onshore wind, solar, and bioenergy. We also assess the potential impacts of climate action driven afforestation and native habitat rehabilitation and restoration. We apply our findings to Ireland as a unique case-study as the government develops a coordinated response to climate and biodiversity change through declaration of a joint climate and biodiversity emergency and inclusion of biodiversity in key climate change legislation and the national Climate Action Plan. However, acknowledgement of these intertwined crises is only a first step; implementation of synergistic solutions requires careful planning. We demonstrate how synergy between climate and biodiversity action can be gained through explicit consideration of the effects of climate change mitigation strategies, such as energy infrastructure development and land-use change, on biodiversity. We identify several potential "win-win" strategies for both climate mitigation and biodiversity conservation. For Ireland, these include increasing offshore wind capacity, rehabilitating natural areas surrounding onshore wind turbines, and limiting the development of solar photovoltaics to the built environment. Ultimately, climate mitigation should be implemented in a "Right Action, Right Place" framework to maximise positive biodiversity benefits. This review provides one of the first examples of how national climate actions can be implemented in a biodiversity-conscious way to initiate discussion about synergistic solutions for both climate and biodiversity.

Soil type determines the magnitude of soil fertility changes by forest-to-pasture conversion in Western Amazonia

The deforestation of tropical forests raises environmental concerns worldwide. Removing the pristine forest impacts the soil, consequently affecting the environmental services it provides. Within this context, the main goal of this study was to determine how the conversion of the tropical rainforest to pasture affects soil fertility across an extended range of soil heterogeneity, including different soil types. We sampled 13 sites, among forests, recent pastures (≤7-year-old), and old pastures (≥10-year-old), on Acrisols, Ferralsols, Plinthosols, and Luvisols, across a ± 800 km geographical range in the Western Brazilian Amazon. Soils were classified taxonomically, and their superficial layer's chemical and physical properties (0-10 cm) were analyzed. Furthermore, we tested the sensibility of Actinobacteria and Proteobacteria to detect changes in these soil properties based on their ecological habitat. An inter-regional gradient of soil fertility was observed, and the sampling sites were clustered mostly by soil type and associated land use than by spatial distance. The Sum of bases, Ca + Mg, base saturation, Al saturation, and pH were consistently affected by land use, increasing after conversion to pasture, at different degrees and with a more pronounced effect on oxidic soils. The Sum of bases was the only property that increased significantly among the study sites (R_adj = 0.860, p < 0.001), being able to detect the effect of anthropic land use on a larger coverage of soil types. Finally, the Actinobacteria:Proteobacteria ratio was also sensitive to the impact of forest-to-pasture conversion, with a higher ratio observed in pasture systems, and it was positively correlated with soil pH (rho = 0.469, p < 0.001). Our results consistently show that the forest-to-pasture conversion leads to strong alterations in the soil environment, with varying intensities depending on soil type.

Mangrove microbial community recovery and their role in early stages of forest recolonization within shrimp ponds

Shrimp farming is blooming worldwide, posing a severe threat to mangroves and its multiple goods and ecosystem services. Several studies reported the impacts of aquaculture on mangrove biotic communities, including microbiomes. However, little is known about how mangrove soil microbiomes would change in response to mangrove forest recolonization. Using genome-resolved metagenomics, we compared the soil microbiome of mangrove forests (both with and without the direct influence of shrimp farming effluents) with active shrimp farms and mangroves under a recolonization process. We found that the structure and composition of active shrimp farms microbial communities differ from the control mangrove forests, mangroves under the impact of the shrimp farming effluents, and mangroves under recolonization. Shrimp farming ponds microbiomes have lower microbial diversity and are dominated by halophilic microorganisms, presenting high abundance of multiple antibiotic resistance genes. On the other hand, control mangrove forests, impacted mangroves (exposed to the shrimp farming effluents), and recolonization ponds were more diverse, with a higher abundance of genes related to carbon mobilization. Our data also indicated that the microbiome is recovering in the mangrove recolonization ponds, performing vital metabolic functions and functionally resembling microbiomes found in those soils of neighboring control mangrove forests. Despite highlighting the damage caused by the habitat changes in mangrove soil microbiome community and functioning, our study sheds light on these systems incredible recovery capacity. Our study shows the importance of natural mangrove forest recovery, enhancing ecosystem services by the soil microbial communities even in a very early development stage of mangrove forest, thus encouraging mangrove conservation and restoration efforts worldwide.

Coastal wetland conversion to aquaculture pond reduced soil P availability by altering P fractions, phosphatase activity, and associated microbial properties

Reclamation and conversion of wetlands strongly affect nutrient cycling and ecosystem functions, while little attention has been paid to the effects of converting coastal wetland to aquaculture on the cycling and balance of soil phosphorus (P). Herein, we investigated soil P fractions, alkaline phosphatase (ALP) activity, and associated microbial properties following coastal wetland conversion in subtropical China. Soil P availability (especially resin-P) concentration and ALP activity in wetland were significantly higher than those in pond. The conversion of coastal wetlands to aquaculture significantly reduced the abundance and diversity of bacterial phoD genes and altered their community structure. The lower phosphatase activity and associated microbial properties after wetland conversion suggested a weaker capacity of microbes to transform organic P (Po) to inorganic P (Pi), consistent with the low P availability but the high Po:Pi ratio in pond. Structural equation modeling indicated that the conversion of the wetland to the pond decreased ALP activity and P availability by affecting soil variables such as bulk density, pH, the carbon: nitrogen ratio, and/or moisture. It was concluded that wetland conversion to pond reduced soil P availability and phosphatase activity, altered the abundance, diversity and community composition of the phoD gene, and ultimately affected coastal P cycles and balances. Moreover, an extended corollary is that the smaller amounts of variation in soil total P and lower labile P concentrations in pond than in wetland suggest that large amounts of P (introduced in feed and not harvested in shrimp) are "lost" from the system. Thus, aquaculture ponds might serve as a source of P for the surrounding environment. More investigations focusing on the P biogeochemical cycle and its potential impacts on adjacent ocean environments at regional and global scales is urgently needed, which could contribute to better management of coastal land uses.

Anthropogenic degradation alter surface soil biogeochemical pools and microbial communities in an Andean temperate forest

Soil microbial communities regulate a myriad of critical biogeochemical functions in forest ecosystems. Anthropogenic disturbances in natural forests could drive major shifts in plant and microbial communities resulting in substantial biogeochemical alterations. We evaluated the effect of anthropogenic disturbances in the soils of Andean temperate forests with different levels of degradation: i) mature forest (MF), ii) secondary forest (SF), iii) degraded forest (DF), and iv) deforested site converted into a prairie (DP). We quantified total soil carbon, nitrogen and phosphorous (TC, TN, and TP), and available nutrient stocks. The soil microbial community structure (i.e., composition, diversity, and abundance) was assessed under each condition from amplicon sequence variants (ASVs) obtained via NGS-Illumina sequencing and subsequent microbiome analysis. There were no significant differences in TC, TN, and TP across the forested states (MF, SF, DF). The deforested site condition presented significantly higher soil TC, TN, and TP and the lowest C:N, C:P, and N:P ratios. The DP soil microbiome was significantly more diverse in bacteria (D' = 0.47 ± 0.04); and fungi (H' = 5.11 ± 0.33). The bacterial microbiome was dominated by Proteobacteria (45.35 ± 0.89 %), Acidobacteria (20.73 ± 1.48 %), Actinobacteria (12.59 ± 0.34 %), and Bacteroidetes (7.32 ± 0.36 %) phyla in all sites. The soil fungal community was dominated by the phyla Ascomycota (42.11 ± 0.95 %), Mortierellomycota (28.74 ± 2.25 %), Basidiomycota (24.61 ± 0.52), and Mucoromycota (2.06 ± 0.43 %). Yet, there were significant differences at the genus level across conditions. Forest to prairie conversion facilitated the introduction of exotic bacterial and fungal taxa associated with agricultural activities and livestock grazing (∼50 % of DP core microbiome composed of unique ASVs). For example, the ammonia-oxidizing bacteria community emerged as a dominant group in the DP soils, along with a reduction in the ectomycorrhizal fungi community. The surface soil microbial community was surprisingly resistant to forest degradation and did not show a clear succession along the degradation gradient, but it was strongly altered after deforestation.

Microbial diversity and abundance in loamy sandy soil under renaturalization of former arable land

The abundance and taxonomic diversity of different physiological groups of bacteria and fungi and yeasts in the fields of the long-term experiment of renaturalization of infertile arable soils were studied. The experiment involved four land conversion methods: conversion of arable land to cultivated meadow, soil and forest, leaving the experimental area of arable land. With these studies, we have begun to fill research gaps related to the taxonomic and functional diversity of soil microorganisms. The greatest changes in the abundance of cultivable organotrophic, diazotrophic and nitrifying bacteria were found to be observed in those areas where anthropogenic activities took place, i.e. in the cultivated field and in the cultural grassland. The abundance of bacteria was relatively lower and that of fungi was higher in the soil and in the cultivated area. It was also found that the higher jumps in the abundance of diazotrophs and nitrifiers during the respective stages of vegetation were caused by the applied agrotechnical measures and the cultivation of the respective plants. The abundance of cultivable bacteria was up to 10⁵, and the number of fungi was 10³ CFU in 1 g of dry soil. The taxonomic structure was determined by Next Generation Sequencing. The taxonomic groups of Actino- and Proteobacteria had the highest abundance. The highest number of fungal OTU was distinguished by Ascomycota fungi (37-42% of the total number of fungi). Comparing the taxonomic structure of all studied samples, the area planted with pines stands out, where an increase in the taxonomic group of Basidiomycota fungi (up to 24%) is observed at the expense of Ascomycota fungi. In order to have a balanced, fully rich soil, efforts must be made to maintain a stable structure of microbial communities, which can only be achieved through targeted research.

Environmental implications of agricultural abandonment on Fe cycling: Insight from iron forms and stable isotope composition in karst soil, southwest China

Land-use change influences the fate of nutrient elements, including iron (Fe), and then threaten soil security. In this study, Fe forms and stable isotope composition (δ⁵⁶Fe) in soils were investigated to identify the variations in the processes of Fe cycling during agricultural abandonment in a karst region of Southwest China. Soil δ⁵⁶Fe compositions varied from -0.05‰-0.02‰ in croplands, 0.05‰-0.12‰ in abandoned croplands, to 0.30‰-0.80‰ in the native vegetation lands. In the croplands, Fe oxidation-precipitation process is considered as the main contributor to Fe migration and isotope fractionation, leading to a relatively enrichment of heavier Fe isotope in deeper soil layer. In the abandoned croplands and native vegetation lands, Fe isotope in the organic-rich layer (0-10 cm) was significantly lighter than that in subsurface layer (20-30 cm), mainly due to the recovery of soil organic carbon (SOC) and macro-aggregate after cropland abandonment. Moreover, the eluviation process mainly caused a decrease in soil Fe contents and enrichment of heavy Fe isotope in deeper soils (below 40 cm). The positive correlation between oxidized Fe and SOC contents suggested the accumulation of mobile Fe in soils after agricultural abandonment, which is beneficial for Fe uptake and assimilation by plants. This study suggests that agricultural abandonment significantly reduce soil Fe leaching loss and improve plant Fe supply by SOC accumulation in surface soil, which gives an environmental implication for the management of soil nutrients.

Response of soil respiration to changes in soil temperature and water table level in drained and restored peatlands of the southeastern United States

BACKGROUND

Extensive drainage of peatlands in the southeastern United States coastal plain for the purposes of agriculture and timber harvesting has led to large releases of soil carbon as carbon dioxide (CO₂) due to enhanced peat decomposition. Growth in mechanisms that provide financial incentives for reducing emissions from land use and land-use change could increase funding for hydrological restoration that reduces peat CO₂ emissions from these ecosystems. Measuring soil respiration and physical drivers across a range of site characteristics and land use histories is valuable for understanding how CO₂ emissions from peat decomposition may respond to raising water table levels. We combined measurements of total soil respiration, depth to water table from soil surface, and soil temperature from drained and restored peatlands at three locations in eastern North Carolina and one location in southeastern Virginia to investigate relationships among total soil respiration and physical drivers, and to develop models relating total soil respiration to parameters that can be easily measured and monitored in the field.

RESULTS

Total soil respiration increased with deeper water tables and warmer soil temperatures in both drained and hydrologically restored peatlands. Variation in soil respiration was more strongly linked to soil temperature at drained (R² = 0.57, p < 0.0001) than restored sites (R² = 0.28, p < 0.0001).

CONCLUSIONS

The results suggest that drainage amplifies the impact of warming temperatures on peat decomposition. Proxy measurements for estimation of CO₂ emissions from peat decomposition represent a considerable cost reduction compared to direct soil flux measurements for land managers contemplating the potential climate impact of restoring drained peatland sites. Research can help to increase understanding of factors influencing variation in soil respiration in addition to physical variables such as depth to water table and soil temperature.

Spatial optimization of ecological ditches for non-point source pollutants under urban growth scenarios

Non-point source (NPS) pollution is regarded as the major threat to water quality worldwide, and ecological ditches (EDs) are considered an important and widely used method to collect and move NPS pollutants from fields to downstream water bodies. However, few studies have been conducted to optimize the spatial locations of EDs, particularly when the watershed experiences urbanization and rapid land-use changes. As land-use patterns change the spatial distribution of NPS loads, this study used a cellular automata-Markov method to simulate future land-use changes in a typical agricultural watershed. Three scenarios are included as follows: historical trend, rapid urbanization, and ecological protection scenarios. The spatial distributions of particulate phosphorus loads were simulated using the revised universal soil loss equation and sediment transport distribution model. The results suggested that the total particulate phosphorus (TP) load in the Zhuxi watershed decreased by 10,555.2 kg from 2000 to 2020, primarily because the quality and quantity of forests in Zhuxi County improved over the last 20 years. The TP load in Zhuxi watershed would be 2588.49, 2639.15, and 2553.32 kg in 2040 in historical trend, rapid urbanization, and ecological protection scenarios, respectively, compared with 2308.1 kg in 2020. This indicated that urban expansion increases the TP load, and the faster the expansion rate, the more the TP load. Consequently, the optimal locations of EDs were determined based on the intercepted loads and the period during which they existed during land-use changes. The results suggested that rapid urbanization would consequently reduce the space available for building EDs and also increase the cost of building EDs to control the NPS pollution in the watershed.

Anthropogenic land use and urbanization alter the dynamics and increase the export of dissolved carbon in an urbanized river system

Greenhouse gas emissions from urban rivers play a crucial role in global carbon (C) cycling, this is tightly linked to dissolved C in rivers but research gaps remain. The effects of urbanization and anthropogenic land-use change on riverine dissolved carbon dynamics were investigated in a temperate river, the River Kelvin in UK. The river was constantly a source of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere (excess concentration of CH₄ ranged from 13 to 4441 nM, and excess concentration of CO₂ ranged from 2.6 to 230.6 μM), and dissolved C concentrations show significant spatiotemporal variations (p < 0.05), reflecting a variety of proximal sources and controls. For example, the concentration variation of dissolved CH₄ and dissolved CO₂ were heavily controlled by the proximity of coal mine infrastructure in the tributary near the river head (~ 2 km) but were more likely controlled by adjacent landfills in the midstream section of the rivers main channel. Concentration and isotopic evidence revealed an important anthropogenic control on the riverine export of CO₂ and dissolved organic carbon (DOC). However, dissolved inorganic carbon (DIC) input via groundwater at the catchment scale primarily controlled the dynamics of riverine DIC. Furthermore, the positive relationship between the isotopic composition of DIC and CO₂ (r = 0.79, p < 0.01) indicates the DIC pool was at times also significantly influenced by soil respiratory CO₂. Both DIC and DOC showed a weak but significant correlation with the proportion of urban/suburban land use, suggesting increased dissolved C export resulting from urbanization. This research elucidates a series of potentially key effects anthropogenic activities and land-use practices can have on riverine C dynamics and highlights the need for future consideration of the direct effects urbanization has on riverine C dynamics.

On the use of Earth Observation to support estimates of national greenhouse gas emissions and sinks for the Global stocktake process: lessons learned from ESA-CCI RECCAP2

The Global Stocktake (GST), implemented by the Paris Agreement, requires rapid developments in the capabilities to quantify annual greenhouse gas (GHG) emissions and removals consistently from the global to the national scale and improvements to national GHG inventories. In particular, new capabilities are needed for accurate attribution of sources and sinks and their trends to natural and anthropogenic processes. On the one hand, this is still a major challenge as national GHG inventories follow globally harmonized methodologies based on the guidelines established by the Intergovernmental Panel on Climate Change, but these can be implemented differently for individual countries. Moreover, in many countries the capability to systematically produce detailed and annually updated GHG inventories is still lacking. On the other hand, spatially-explicit datasets quantifying sources and sinks of carbon dioxide, methane and nitrous oxide emissions from Earth Observations (EO) are still limited by many sources of uncertainty. While national GHG inventories follow diverse methodologies depending on the availability of activity data in the different countries, the proposed comparison with EO-based estimates can help improve our understanding of the comparability of the estimates published by the different countries. Indeed, EO networks and satellite platforms have seen a massive expansion in the past decade, now covering a wide range of essential climate variables and offering high potential to improve the quantification of global and regional GHG budgets and advance process understanding. Yet, there is no EO data that quantifies greenhouse gas fluxes directly, rather there are observations of variables or proxies that can be transformed into fluxes using models. Here, we report results and lessons from the ESA-CCI RECCAP2 project, whose goal was to engage with National Inventory Agencies to improve understanding about the methods used by each community to estimate sources and sinks of GHGs and to evaluate the potential for satellite and in-situ EO to improve national GHG estimates. Based on this dialogue and recent studies, we discuss the potential of EO approaches to provide estimates of GHG budgets that can be compared with those of national GHG inventories. We outline a roadmap for implementation of an EO carbon-monitoring program that can contribute to the Paris Agreement.

The carbon emissions related to the land-use changes from 2000 to 2015 in Shenzhen, China: Implication for exploring low-carbon development in megacities

Megacities exploit enormous amounts of lands from outside of the city boundary. However, there is a large knowledge gap in the impact of socioeconomic activities associated land-use changes on carbon emissions of megacities during the urbanization. In the current work, we combined the material-flow analysis, environmental extended input-output model, and land matrix data to construct a hybrid network framework. Such a framework was used to estimate the carbon emissions driving from trade between sectors and associated land use changes during 2000-2015 in Shenzhen, China. Results indicated that the total carbon emissions of Shenzhen had a growth rate of 262.7% from 2000 to 2010 and a declining rate of 17.6% from 2010 to 2015. This pattern is associated with large declining rates in the overall energy and carbon intensities by 53.8% and 63.2% during the period of 2000-2015. Meanwhile, embodied carbon emissions of Shenzhen kept rising by approximately twofold, accompanied by the increasing trends in the land-use related carbon emissions both inside and outside of city boundary. The land uses per unit GDP showed a dramatical decline by 85.7% and with a large contribution of the transportation and industrial land, and this caused a gradual increase in overall land-use related emissions with average growth rate of 7.1%. In addition, the land-use change related carbon emissions of the transportation and industrial land had a cumulative growth of 85%. As for the embodied land-use related carbon emissions, the dominated contributor was the Agriculture sector which drove an average of 0.13 MtC yr^-1 emissions via importing agricultural products from outside of Shenzhen. This study provides a scientific foundation for corporately mitigate carbon emissions between megacities and their surrounding regions.

How can process-based modeling improve peat CO2 and N2O emission factors for oil palm plantations?

Oil palm plantations on peat and associated drainage generate sizeable GHG emissions. Current IPCC default emission factors (EF) for oil palm on organic soil are based on a very limited number of observations from young plantations, thereby resulting in large uncertainties in emissions estimates. To explore the potential of process-based modeling to refine oil palm peat CO₂ and N₂O EFs, we simulated peat GHG emissions and biogeophysical variables over 30 years in plantations of Central Kalimantan, Indonesia. The DNDC model simulated well the magnitude of C inputs (litterfall and root mortality) and dynamics of annual heterotrophic respiration and peat decomposition N₂O fluxes. The modeled peat onsite CO₂-C EF was lower than the IPCC default (11 Mg C ha^-1 yr^-1) and decreased from 7.7 ± 0.4 Mg C ha^-1 yr^-1 in the first decade to 3.0 ± 0.2 and 1.8 ± 0.3 Mg C ha^-1 yr^-1 in the second and third decades of the rotation. The modeled N₂O-N EF from peat decomposition was higher than the IPCC default (1.2 kg N ha^-1 yr^-1) and increased from 3.5 ± 0.3 kg N ha^-1 yr^-1 in the first decade to 4.7-4.6 ± 0.5 kg N ha^-1 yr^-1 in the following ones. Modeled fertilizer-induced N₂O emissions were minimal and much less than 1.6% of N inputs recommended by the IPCC in wet climates regardless of soil type. Temporal variations in EFs were strongly linked to soil C:N ratio and soil mineral N content for CO₂ and fertilizer-induced N₂O emissions, and to precipitation, water table level and soil NH₄⁺ content for peat decomposition N₂O emissions. These results suggest that current IPCC EFs for oil palm on organic soil could over-estimate peat onsite CO₂ emissions and underestimate peat decomposition N₂O emissions and that temporal variation in emissions should be considered for further improvement of EFs.

Future land-use competition constrains natural climate solutions

Natural climate solutions (NCS) are an essential complement to climate mitigation and have been increasingly incorporated into international mitigation strategies. Yet, with the ongoing population growth, allocating natural areas for NCS may compete with other socioeconomic priorities, especially urban development and food security. Here, we projected the impacts of land-use competition incurred by cropland and urban expansion on the climate mitigation potential of NCS. We mapped the areas available for implementing 9 key NCS strategies and estimated their climate change mitigation potential. Then, we overlaid these areas with future cropland and urban expansion maps projected under three Shared Socioeconomic Pathway (SSP) scenarios (2020-2100) and calculated the resulting mitigation potential loss of each selected NCS strategy. Our results estimate a substantial reduction, 0.3-2.8 GtCO₂ yr^-1 or 4-39 %, in NCS mitigation potential, of which cropland expansion for fulfilling future food demand is the primary cause. This impact is particularly severe in the tropics where NCS hold the most abundant mitigation potential. Our findings highlight immediate actions prioritized to tropical areas are important to best realize NCS and are key to developing realistic and sustainable climate policies.

Dynamic of land use, landscape, and their impact on ecological quality in the northern sand-prevention belt of China

Changes in land use and landscapes have a direct impact on the regional eco-environment. It is of great importance to understand the change pattern of land use, landscapes, and their mechanism on the ecological quality, especially ecologically fragile areas. The northern sand-prevention belt (NSPB) is an important ecologically fragile area in China, which has a large influence on the ecological security of the entire country. Based on the land use data of the NSPB in 2000, 2010, and 2018, we studied the spatio-temporal characteristics of land-use change and change in landscape patterns. The ecological quality represented by the remote sensing-based desertification index (RSDI) was calculated using satellite images. The effects of land use and landscape patterns on RSDI were analyzed by geographic detector and geographically weighted regression. Important results include the following: (1) Land-use change in the study area was high during 2000-2010 but slower in 2010-2018. Grassland was the largest land-use type in the NSPB, and varied greatly in terms of total change and spatial location. The major change was the conversion between dense and moderate grass, with 64,860 km² of dense grass turning into moderate grass, and 48,505 km² changing the other way. (2) Among the four landscape metrics, patch density, area-weighted mean fractal dimension, and edge density increased, whereas the aggregation index decreased, which indicated that the landscape was developing towards heterogeneity, fragmentation, complexity, and aggregation. Spatially, the landscape metrics presented a strip distribution in the east of the NSPB. (3) The effects of various land-use types on ecological quality, from high to low, were unused land, woodland, dense grass, cropland, moderate grass, built-up land, sparse grass, and waterbody. The areas where the ecological quality was greatly affected by the landscape patterns were concentrated in the agro-pastoral ecotone and the forest-steppe ecotone. The results of this study reveal the trends of land use and landscape patterns in the NSPB over 18 years and can help to understand their mechanism on ecological quality, which is of significance for the management of this area.

Increased soil moisture intensifies the impacts of forest-to-pasture conversion on methane emissions and methane-cycling communities in the Eastern Amazon

Climatic changes are altering precipitation patterns in the Amazon and may influence soil methane (CH₄) fluxes due to the differential responses of methanogenic and methanotrophic microorganisms. However, it remains unclear if these climate feedbacks can amplify land-use-related impacts on the CH₄ cycle. To better predict the responses of soil CH₄-cycling microorganisms and emissions under altered moisture levels in the Eastern Brazilian Amazon, we performed a 30-day microcosm experiment manipulating the moisture content (original moisture; 60%, 80%, and 100% of field capacity - FC) of forest and pasture soils. Gas samples were collected periodically for gas chromatography analysis, and methanogenic archaeal and methanotrophic bacterial communities were assessed using quantitative PCR and metagenomics. Positive and negative daily CH₄ fluxes were observed for forest and pasture, indicating that these soils can act as both CH₄ sources and sinks. Cumulative emissions and the abundance of methanogenesis-related genes and taxonomic groups were affected by land use, moisture, and their interaction. Pasture soils at 100% FC had the highest abundance of methanogens and CH₄ emissions, 22 times higher than forest soils under the same treatment. Higher ratios of methanogens to methanotrophs were found in pasture than in forest soils, even at field capacity conditions. Land use and moisture were significant factors influencing the composition of methanogenic and methanotrophic communities. The diversity and evenness of methanogens did not change throughout the experiment. In contrast, methanotrophs exhibited the highest diversity and evenness in pasture soils at 100% FC. Taken together, our results suggest that increased moisture exacerbates soil CH₄ emissions and microbial responses driven by land-use change in the Amazon. This is the first report on the microbial CH₄ cycle in Amazonian upland soils that combined one-month gas measurements with advanced molecular methods.

Ecological risk assessment models for simulating impacts of land use and landscape pattern on ecosystem services

Rapid urbanization involves the expansion of construction land, which changes the land use and landscape pattern in watersheds. Moreover, it degrades ecosystem services and habitat quality, thus creating adverse ecological impacts such as the diffusion of non-point source (NPS) pollution. Therefore, it is urgent to investigate the adverse effects and potential ecological risks caused by variations in land use due to territory development and urbanization. Houxi Basin is a typical Chinese southeastern coastal watershed in the process of urbanization, and the ecological risk from 2011 to 2019 is here assessed. Based on ecosystem vulnerability and the interference with the ecosystem, we evaluated the risk of degradation of habitat services provided by terrestrial ecosystems due to changes in landscape patterns. In addition, the export coefficient model is employed to build an exposure-response relationship between land use and NPS pollution to investigate the risk of degrading water-purification services provided by aquatic ecosystems. The results show that the risks of degrading habitat-provision services increase slightly but for water-purification services increases rapidly. Alternatively, the integrated optimization scenario of key areas for 2030 reduces the risk of pollution diffusion and the landscape risk by 4.27% and 10.25%, respectively, compared with the business-as-usual scenario. In summary, reasonable planning of land-use types and spatial layout is conducive to reducing ecological risks. Other conclusions can be drawn: the combined replacement of forest and grassland more effectively inhibits pollution diffusion than does replacing only forest or only grassland. Optimizing areas with high land-use impact coefficients inhibits pollution diffusion more effectively than does optimizing areas with high export coefficients. Lastly, instead of increasing the area of green land, adjusting its spatial layout proves to be more effective in lowering the ecological risk to water-purification and habitat-provision services.

Integrated model for land-use transformation analysis based on multi-layer perception neural network and agent-based model

The efficacy of land-use changes on aquatic ecosystems has been extensively studied in recent decades. Water resource management needs to understand the relationship between land-use change patterns and water quality, especially in urban areas. Hence, recognizing spatial-temporal changes in land use is required for sustainable development and proper water resource management. This research has developed an integrated model based on agent-based model (ABM) and multi-layer perceptron (MLP) neural network technique to predict the future land-use transformation tested on the North Ahvaz watershed, Iran. Random forest-supervised classification technique was applied to derive the land-use maps using Landsat 1989, 2004, and 2019 images in the Google Earth Engine (GEE) platform. The overall accuracy of classified land-use images was 0.82, 0.81, and 0.84, respectively, with the kappa coefficient of 0.74, 0.72, and 0.78. Land-use change analysis and generating transition potential maps were carried out in land change modeler (LCM) through MLP based on seven driving factors. Then, the land-use map for 2019 (for validation) and 2040 was simulated using the transition potential map and an agent-based approach. The ABM scenario was farmers' and urban landowners' decisions to convert undeveloped and unprotected lands to residential lands. The results showed that residential areas and pasture lands would grow by 67.96 km² and 64.63 km², and agricultural and barren lands would degrade about 84.19 km² and 47.98 km² during 2019-2040, respectively. Predicting land-use change through the integrated MLP-ABM model may be used to evaluate the effects of land-use change coming out of human decision-making.

Changes in the core species of the ant-plant network of oak forest converted to grassland: replacement of its ant functional groups

Land-use change in terrestrial environments is one of the main threats to biodiversity. The study of ant-plant networks has increased our knowledge of the diversity of interactions and structure of these communities; however, little is known about how land-use change affects ant-plant networks. Here we determine whether the change in land use, from native oak forest to induced grassland, affected the network properties of ant-plant networks in a temperate forest in Mexico. We hypothesize that the disturbed vegetation will be more nested and generalized due to the addition of generalist species to the network. The oak forest network comprises 47 plant species and 11 ant species, while the induced grassland network has 35 and 13, respectively. Floral nectar was the resource used most intensely by the ants in both vegetation types. The ant-plant network of the induced grassland was significantly more nested and generalist than that of the oak forest; however, none of the networks were nested when considering the frequency of interaction. In both vegetation types, the ants were more specialized than the plants, and niche overlap was low. This could be related to the dominant species present in each type of vegetation: Prenolepis imparis in the oak forest and Camponotus rubrithorax in the grassland. The central core of cold climate ant species in the oak forest was replaced by a central core of subordinate Camponotini and tropical specialists in the induced grassland. These results suggest that the increase in nestedness and generalization in the grassland may be related to the loss of the cold climate specialists from the core of the oak forest network. Our findings provide evidence that land-use change increases the level of generalization in the ant-plant interaction networks of temperate forests.

Effects of vegetation succession on soil organic carbon fractions and stability in a karst valley area, Southwest China

A series of complex organic fractions with different physical and chemical properties make up soil organic carbon (SOC), which plays a vital role in climate change and the global carbon cycle. Different SOC fractions have different stability and respond differently to vegetation succession. This research was carried out to assess the impacts of vegetation succession on SOC dynamics in the Qingmuguan karst valley area, southwest China. Soil samples were collected from four typical vegetation succession stages, including farmland, grassland, shrubland, and forest. The total SOC content and four oxidizable SOC fractions were measured. Results showed that the total SOC content and storage under farmland were highest, followed by forest and shrubland, and the grassland had the lowest total SOC content and storage. The SOC sequestration potential under different vegetation types in the study area was grassland (26.32 Mg C ha^-1) > shrubland (9.64 Mg C ha^-1). All SOC content, storage, and fractions showed a decrease with the increase of soil depth over the 0-50 cm in the study area. The four SOC fractions under forest at topsoil (0-10 cm) were higher than that under the other vegetation types. Compared with the other land uses, the farmland had the highest stable oxidizable SOC fractions (F3 and F4) at the 10-50-cm depth, while the shrubland had the highest active oxidizable SOC fractions (F1 and F2). In terms of the lability index of SOC, shrubland was the largest, followed by grassland and forest, and farmland was the smallest. These results provide essential information about SOC fractions and stability changes resulting from changes of vegetation types in a karst valley area of southwest China. It also supplements our understanding of soil carbon sequestration in vegetation succession.

Seizing resilience windows to foster passive recovery in the forest-water interface in Amazonian lands

Forest regeneration has increased in many tropical abandoned lands and current restoration commitments in this region aim to restore over 1,400,000 km² of degraded land by 2030. Although regenerating forests recover biomass, biodiversity, and processes with time, the recovery trajectories may be uncertain due to past disturbances. Currently, there is a lack of knowledge to sustain the effectiveness of passive regeneration for the recovery of riparian forests and the adjacent waterbodies in the tropics, which may compromise the outcomes of ongoing and future tropical riparian restoration programs. We evaluated the drivers of riparian forest structural recovery and how this relates to stream conditions in 12 abandoned pasturelands in eastern Brazilian Amazonia. These pasturelands range across regeneration age (pasture (PA) - 0 to 4 years; young regeneration (YR) - 8 to 12 years; old regeneration (OR) - 18 to 22 years) and years of past land-use (PA - 23.25 average years of past land-use, YR - 18.25, OR - 7). We compared the conditions of these sites to 4 reference sites with conserved forests (REF, >100 years), where there was no recorded pasture use in the past. Short-term responses of forests and streams to passive regeneration indicated high ecosystem resilience after low to intermediate past land-use intensity, reflected in the improvement of stream ecosystems. Such high resilience is possibly attributable to low- to intermediate-intensity pasture-related disturbances, remaining forest matrix, and residual structures (e.g. roots, sprouts, and in-stream wood) observed in the area. Our results suggest a recovery by 12 to 20 years for riparian forests of this region. However, areas degraded by intensive land-use apparently showed delayed recovery. We conclude that seizing resilience windows (defined here as the period when ecosystems retain high potential resilience) is essential to foster passive recovery of riparian forests and streams more cost-effectively in the tropics.

Anthropogenic legacies shaping the present composition of demarcation trees in a temperate upland field landscape in Japan

BACKGROUND

Isolated trees are often planted in agricultural landscapes around the world, but their planting background often remains unclear. In this study, we examined the history of demarcation trees in Ibaraki Prefecture in eastern Japan by using land dispute records mainly from the early modern period (from 1600 to 1868), the Rapid Survey Map (RSM) drawn in the late nineteenth century, demarcation tree records from 2011, and interviews of the local residents.

METHODS

We reviewed 39 documents on land disputes to examine the temporal and spatial usage of demarcation tree species in the early modern period. The association between the present distribution of 1486 individuals of six demarcation tree species and past land use in the RSM were analyzed with Fisher's exact test and residual analysis. In addition, we conducted interviews with 48 farmers, most of whom were over 60 years old.

RESULTS

The demarcation plants in vast communal lands and village boundaries in the early modern period were mostly visually prominent tall trees, usually pines. In contrast, smaller trees were planted for demarcation in small-scale areas of forests and farmlands. Although Pourthiaea villosa (Thunb.) DC. Has been planted since the mid-eighteenth century, its planting seems to have accelerated as communal forests were divided mainly in the Meiji period (from 1868 to 1912). The present dominant state of Deutzia crenata Siebold et Zucc. in older farmlands and its ritual use, history of upland field development in the Kanto region, and ancient demarcation use in central Japan indicate its original use may date back to the medieval (from 1185 to 1600) or ancient ritsuryo period (from the seventh century to 1185). Tea (Camellia sinensis (L.) Kuntze) and mulberry (Morus spp.) individuals were considered as early modern or modern crop remnants. Results from the map-based analysis and interviews clarified the recent increase in the use of Euonymus japonicus Thunb. and Celtis sinensis Pers. for demarcation.

CONCLUSIONS

Chronologically dynamic anthropogenic legacies have shaped the present agricultural landscape with different demarcation tree species. A better understanding of the dynamic transformation of vegetation under human influence adds to the historical heritage value of the landscape and should motivate its conservation.

Land-use-mediated inconsistency of changes in the provision and delivery of soil erosion control services at the watershed scale

Soil erosion control services (SECSs) are the benefits delivered to people derived from preventing the negative impacts of soil erosion, such as avoiding the loss in soil productivity and preventing the damage to infrastructures such as dams and roads. SECS is derived from the functions of the ecosystems and is delivered to people through physical processes and social activities. The land-use change (LUC) reshapes the SECSs supply capacity, the SECS flow over the landscape, and the related benefit people received. Numerous studies have revealed how LUC shapes the SECSs supply capacity. However, the SECSs flow to local communities, and the LUC-derived SECS flow dynamics remain unclear. This study quantified the SECSs delivered to local communities following a land-use-specific cascade mechanism and using the WATEM/SEDEM framework. The effects of on-site soil erosion and sediment delivery over the watershed were combined. The cultivated lands were considered as the conveyers of SECSs. The study revealed the inconsistency of temporal change in SECS provision and the actual SECSs delivery to local communities. The results illustrated the increased capacity for soil erosion prevention and sediment flow reduction and a consequent increase in SECS supply capacity. However, the total amount of actual SECSs delivered to the local communities was declined due to the land-use change featured in reduced cropland area. The results imply that changes in SECS provision capacity cannot directly indicate the changes in SECS delivery to local communities. Though the modeled SECSs did not cover all SECSs in this region, this study highlights the effectiveness of the land-use-specific cascade framework in describing the delivery of SECSs and the importance of addressing the delivery processes of ecosystem services from ecosystem to people.