Natural Revegetation Research Articles

Anthoxanthum odoratum (Poaceae) as a bioindicator of arbuscular mycorrhizal fungi abundance prior to native revegetation on agricultural soils

ABSTRACT Mycorrhizal fungi, which form symbiotic associations with plant roots, can be critical to the successful establishment of plants. Up to 90% of land plant species form associations with arbuscular mycorrhizal fungi (AMF), which develop fungal structures inside host roots. Common site preparation practices prior to ecological restoration, such as soil disturbance and herbicide application, may lessen the availability of AMF, potentially jeopardising plant establishment. However, the state of the soil microbiome can be difficult to assess directly. This study examines the potential of the widespread pasture grass Anthoxanthum odoratum (Sweet Vernal, Poaceae) as a bioassay of AMF abundance in soils. We present a rapid clearing and staining protocol for visualising AMF structures in the roots of A. odoratum. We then compare % colonisation on roots of naturally established A. odoratum plants collected from undisturbed pastures vs. sprayed and tilled pastures. Roots of A. odoratum collected from sprayed and tilled pastures showed a significantly lower average AMF colonisation at 43.8% compared with 57.6% on roots from undisturbed pastures. However, all plants sourced from the sprayed and tilled pastures still showed some AMF structures. Our results strongly suggest that A. odoratum can be a useful bioindicator of AMF presence and abundance in soils, offering a promising tool for seed-based restoration on retired agricultural land.

Assessment of nutrient differences in detached soil particles between cropland and revegetated abandoned land

AbstractCropland (CRL) abandonment is a worldwide phenomenon of land use change with significant impacts on agro‐ecosystems. This research attempts to deepen the analysis of the positive and negative effects arising by focusing on the changes in soil properties and the amount and composition of soil particles detached after several periods of rainfall and the resulting exported sediment that occurs in abandoned areas with natural revegetation compared to CRL. The study was carried out in an agroforestry catchment with a temperate climate, on which CRL and abandoned land with natural vegetation were compared. The soil was sampled along two representative hillslopes integrating elements of the landscape and land use/land covers. Sediments were collected after seven periods in which flood events were recorded during the period July 2016 to December 2017, using artificial‐lawn mats. Soil and sediment composition (texture, soil organic carbon [SOC] and nutrients [total nitrogen and total phosphorous]) under both land uses were assessed and compared and related to rainfall characteristics using principal component analysis. Nutrient enrichment factors in the sediments compared to soils were also evaluated. The results highlight that after abandonment, SOC increased significantly, reaching contents almost three times higher than in CRL. Consequently, soil erodibility decreased, resulting in substantially lower sediment generation after erosive rainfall events. On average, sediment generation was three times lower in abandoned areas than in CRL, despite their steeper slopes. Soil total nitrogen also increased on abandoned lands, reaching values about twice as high as those in CRL. However, total phosphorous content was almost twice as high in CRL than in abandoned land posing a potential risk for water due to higher erosion rates recorded in CRL. The results confirmed the association of phosphorous with smaller particles and also demonstrated the total phosphorous‐SOC link in abandoned land. Furthermore, the effect of rainfall intensity on phosphorous mobilisation was confirmed, whilst nitrogen losses were mainly related to the total amount of rainfall recorded. In a scenario of increasing extreme precipitation, both total amount and increased precipitation intensity may exacerbate water pollution problems following nutrient loss in cultivated areas. This research contributes to identifying the impacts on agroforestry systems within the current context of converting natural areas into cultivated land, whilst in other regions revegetated natural areas are developed from abandoned agricultural land.

Vertical flow structures on a vegetated immobile bed under wave-current conditions: Laboratory experiments

Natural revegetation alters local hydrodynamic conditions in coastal lagoons. To investigate vertical flow structures in revegetated lagoons, a series of flume experiments are implemented on an immobile bed with Phragmites australis by a certain staggered configuration. Six incident wave heights and five inflow discharges are considered. The experimental results demonstrate that wave dominates turbulent kinetic energy (TKE) distributions under wave-current conditions. Vegetation morphology plays an important role in wave-current-vegetation interactions, which regulates TKE distributions by diminishing wave effects within 70% of water depth especially (0.3 < z/h < 1). The increasing inflow discharge has positive effects on diminishment of wave effects, while the reduction of mean streamwise flow velocity is stable under the present vegetation configuration. Moreover, the practical values of vertical mean flow velocity can be obtained from the empirical equation, which includes wave effects by a quadratic polynomial relationship between the ratio of experimental values to theorical values (U/Up) and the relative wave height H0/h. Furthermore, two relationships are established between the reduction of mean streamwise flow velocity r and z/h, involving a logarithmical relationship in the lower layer (0 < z/h < 0.3), and a cubic polynomial relationship in the upper layer (0.3 < z/h < 0.7).

Divergent changes in particulate and mineral-associated organic carbon under natural revegetation along a soil texture gradient in temperate grasslands of China

The natural revegetation of grasslands can stimulate belowground carbon inputs and facilitate the storage of soil organic carbon (SOC), which is conducive to the restoration of grassland ecosystems. Previous studies have investigated the dynamics of organic carbon (OC) in bulk soil, but paid little attention to OC fractions within aggregates. This study explored the response of OC changes in functionally distinct fractions, namely particulate organic matter (POM) and mineral-associated organic matter (MAOM), to natural restoration through systematic measurements of two grassland vegetation species at three study sites along a soil texture gradient in the Loess Plateau. In naturally restored grasslands, the SOC and OC contents of POM (POM_C) and MAOM (MAOM_C) within bulk soil and aggregates were significantly (p < 0.05) higher relative to bare land, with more effective improvement of POM_C (1.01−6.55 times) than MAOM_C (0.88−4.26 times). Compared to cover type (6.01 %−26.04 %), soil texture explained the variance of OC fractions to a greater extent (56.39 %−88.16 %). Soil texture had a larger contribution to MAOM_C in bulk soil with standardized path coefficients for total effect of 0.78 than POM_C, which had a coefficient of 0.67 (p < 0.05). Moreover, the growth rate of the MAOM_C pool exhibited a gradual decline (p < 0.001), which subsequently approached saturation level despite a persistent increase in total SOC in both bulk soil and aggregates. During soil carbon sequestration, aggregate fractions with relatively smaller particle size reached the MAOM_C saturation more easily than fractions with larger size. The findings of this study highlight the important role of soil texture in determining the saturation level of the MAOM_C pool at the regional scale. In the development of soil carbon sequestration strategies, more attention should be paid to the divergent behaviors of different SOM fractions and their distinct responses to natural restoration at larger spatiotemporal scales.

Erasing anthropogenic disturbance: Natural revegetation of linear features following wildfire, and the implications for woodland caribou (Rangifer tarandus caribou) habitat management.

The federal recovery strategy for woodland caribou identifies wildfires within the last 40 years and anthropogenic disturbance visible at a scale of 1:50,000, including a 500-m buffer, as disturbed. Long-term vegetation recovery on linear features post-fire has not yet been documented. We examined vegetation recovery including stem density and height, hiding cover, and reindeer lichen cover along 40+ year-old legacy linear features in Northern Saskatchewan, in both uplands and lowlands 1–41 years post-fire. We compared these results with burned areas off-lines and unburned lines. On unburned lines in uplands there was minimal recovery, while there was significant recovery of stem count, height and hiding cover on burned lines and burned off-lines. Reindeer lichen cover and thickness remained significantly lower on burned lines and burned off-lines than on unburned lines until the 41-year age group, where there was no longer a significant difference. In lowlands, the stem density and stem height were initially significantly higher on unburned lines than on either burned lines or burned off-lines. After 27–32 years post-fire there was no longer a significant difference in stem densities. Our findings show that fires substantially accelerate natural revegetation and instigate a recovery that is similar on and off disturbance features in both uplands and lowlands. These findings can inform management decisions on restoration planning and calculation of range disturbance metrics. We suggest that the anthropogenic 500-m buffer should be removed post fire, as anthropogenic disturbance is reset, and anthropogenic disturbance should be classified as naturally recovering.

Vegetation responses to large dam removal on the Elwha River, Washington, USA

Large dam removal can trigger changes to physical and biological processes that influence vegetation dynamics in former reservoirs, along river corridors downstream of former dams, and at a river’s terminus in deltas and estuaries. We present the first comprehensive review of vegetation response to major fluvial disturbance caused by the world’s largest dam removal. After being in place for nearly a century, two large dams were removed along the Elwha River, Washington, USA, between 2011 and 2014. The exposure, erosion, transport, and deposition of large volumes of sediment and large wood that were impounded behind the dams created new fluvial surfaces where plant colonization and growth have occurred. In the former reservoirs, dam removal exposed ~290 ha of unvegetated sediment distributed on three main landforms: valley walls, high terraces, and dynamic floodplains. In addition to natural revegetation in the former reservoirs, weed control and seeding and planting of desirable plants influenced vegetation trajectories. In early years following dam removal, ~20.5 Mt of trapped sediment were eroded from the former reservoirs and transported downstream. This sediment pulse, in combination with transport of large wood, led to channel widening, an increase in gravel bars, and floodplain deposition. The primary vegetation responses along the river corridor were a reduction in vegetated area associated with channel widening, plant establishment on new gravel bars, increased hydrochory, and altered plant community composition on gravel bars and floodplains. Plant species diversity increased in some river segments. In the delta, sediment deposition led to the creation of ~26.8 ha of new land surfaces and altered the distribution and dynamics of intertidal water bodies. Vegetation colonized ~16.4 ha of new surfaces: mixed pioneer vegetation colonized supratidal beach, river bars, and river mouth bars, and emergent marsh vegetation colonized intertidal aquatic habitats. In addition to the sediment-dominated processes that have created opportunities for plant colonization and growth, biological processes such as restored hydrochory and anadromous fish passage with associated delivery of marine-derived nutrients may influence vegetation dynamics over time. Rapid changes to landforms and vegetation growth were related to the large sediment pulse in the early years following dam removal, and the rate of change is expected to attenuate as the system adjusts to natural flow and sediment regimes.

Combining isotopic and elemental tracers for enhanced sediment source partitioning in complex catchments

Sediment fingerprinting quantifies soil erosion processes by tracing sediment origins in water bodies. In this regard, several types of tracers have been used to discriminate different sediment sources. Stable isotopic composition of fatty acids is associated with land use/vegetation cover, while elemental composition is related to different mineralogy. Isotopic tracers are characterised by their isotopic ratio and total content, requiring specific fingerprinting models. Consequently, this has led to few studies combining elemental and isotopic tracers.In this context, our analysis explores merging isotopic and elemental tracers to identify sediment sources in an ungauged Mediterranean mountain catchment. This catchment features consistent lithology, seasonal streams, and a history of land use changes, shifting from rangelands to croplands for increased agricultural production and later reverting to natural revegetation due to mid-20th-century land abandonment. Achieving effective source discrimination in these intricate landscapes remains a significant challenge, emphasising the need for diverse tracer integration.To explore this possibility, we collected composite source samples from three distinct land uses: cropland, Mediterranean forest, and pine forest, as well as two geomorphic features: highly disturbed areas such as exposed subsoil and channel banks. By considering these diverse sampling locations, we aim to capture the variability in sediment sources within the catchment. Our dataset spans one full hydrological year, allowing us to analyse sediment dynamics throughout different seasons and hydrological events.First, the Conservative Balance (CB) method was applied to integrate isotopic ratio and total content of each fatty acid into a single weighted tracer. Combining the weighted fatty acid (WFA) with elemental composition tracers significantly enhanced source discrimination, underlining the utility of employing diverse tracers for challenging source discrimination.The apportionment results revealed that agriculture, channel banks, and subsoils were the primary contributors, accounting for an average contribution of 29%, 39%, and 30% across most seasons. In contrast, sediment sources characterised by more permanent vegetation cover and minimal human influence, such as pine afforestation and Mediterranean forest, exhibited negligible contributions. The findings indicate the substantial impact of agricultural practices in Mediterranean agroecosystems, especially during storm events, on catchment hydrodynamics and sediment export. Additionally, despite their limited coverage, degraded areas significantly contributed to overall sediment dynamics through severe soil loss.By unravelling the hydrological implications of these sediment sources, our study provides valuable insights into the interplay between land use, hydrological processes, and sediment dynamics in Mediterranean mountain catchments.

Can natural undisturbed revegetation restores soil organic carbon to levels under native climax vegetation under tropical semiarid climate?

AbstractLand‐use change has driven soil carbon stock losses in ecosystems worldwide. Implementing agricultural crops and exploiting forest resources trigger the breakdown of soil aggregates, thus exposing organic matter to microbial decomposition and enhancing carbon dioxide emissions, especially in biomes more susceptible to climate extremes as in the tropical semiarid regions. This study was based on the hypothesis that the undisturbed soil from the dry forest (Caatinga biome under natural revegetation in Brazilian semiarid) would have an improvement in the mass of macroaggregates and recover more than 50% of the soil C stock within 10 years. Thus, a field experiment was conducted to investigate soils from the Caatinga biome under native vegetation, “cowpea cropping” for over 30 years, and soil under natural revegetation for over 10 years, after conventional soil cultivation of maize and cowpea, to determine soil and soil‐aggregates carbon stocks and to estimate the recovery rate of these stocks. The proportional mass of aggregates of different sizes and the total stock of particulate organic carbon (POC) were also quantified. The results showed that soil under preserved native vegetation of dry forest Caatinga biome had higher total soil C stock (50.9 Mg ha−1) than that under cowpea cropping (23.2 Mg ha−1) and natural revegetation (45.1 Mg ha−1). The proportional mass of large macroaggregates was higher in soil under native vegetation for all depths. However, soil under cowpea cropping had lower C stocks in macroaggregates, and recovered roughly 63% of the original C stocks, while revegetation recovered 78% of the stock in 10 years. Although the conventional management system for cowpea monoculture aggravated losses in soil carbon stock by more than 50% of the original C stocks, dry forest under natural revegetation recovered 79% of this stock and almost 100% of POC stock in 10 years (~12 Mg ha−1). Furthermore, soil under undisturbed Caatinga dry forest achieved C stock levels equivalent to that of the global average range for semiarid tropical environments. The high recovery rate of C stock in forest soil under natural revegetation indicates the resilience potential of organisms responsible for structural protection of aggregates and the encapsulated soil organic matter content.

Effects of post-abandonment management on surface runoff in a Mediterranean mid-mountain basin

Mid-mountain catchments across the Mediterranean basin undergone a decrease in runoff and sediment yield during the second half of the 20th century mainly due to forest cover increase following rural abandonment together with a transition to drier climatic conditions. During last decades, land use and land cover (LULC) management of these areas has become a target of environmental policy makers and stakeholders to ensure the sustainability of ecosystem services. In some areas, an active management through the reduction of vegetation density or by human afforestation has been applied, while others undergone a natural process of revegetation. In this context, assessing the contribution of different LULC management on runoff is fundamental for addressing water management and soil loss at the catchment and regional scales. Within this background, the aim of this work is to analyse the relative effects of LULC management techniques on hydrological connectivity and water yield in a Mediterranean mid-mountain basin. To pursue this objective, we applied hydrological connectivity (IC index) and ecohydrological (RHESSys) models to different sub-basins of the Leza River catchment (Iberian System, Spain), representative of three different scenarios: (i) natural revegetation; (ii) human afforestation; and (iii) shrub clearing. Results shows how hydrological connectivity tends to decrease when vegetation cover increases (i.e., natural revegetation and human afforestation) while tend to increase when shrub clearing take place. Runoff coefficient followed a similar pattern, decreasing in basins where vegetation increases and decreasing where there was vegetation clearing. Important differences were observed in terms of the distribution of connectivity changes, their location in relation to the outlet and the effects on surface runoff. Studies of this type are necessary to know the response of the Mediterranean basins to different types of management with the aim of adopting sustainable management measures to guarantee surface water resources in a context of Global Change.

A review of natural and managed revegetation responses in two de-watered reservoirs after large dam removals on the Elwha River, Washington, USA

Large dam removals are increasing in frequency and the response of natural and managed revegetation is a critical consideration for managed restoration of dewatered reservoir landscapes post dam removal. The removal of two large dams on the Elwha River in 2011-2014 provides insight into reservoir revegetation. We review literature and datasets from 2012 through 2018, 1-6 years since reservoir dewatering, to compare pre-dam removal predictions on the Elwha to post-dam removal of natural revegetation, managed revegetation effects and invasive non-native vegetation response. Pre-dam removal hypotheses about natural revegetation did not predict species performance on reservoir sediments, seed rain patterns, or seed bank response. Sediment texture and landform affected multiple aspects of revegetation, including vegetation cover, species richness, woody stem densities and species composition. Reservoir drawdown timing influenced species composition and seedling densities. Predictions about managed revegetation effects were mixed. Planting trees and shrubs did not accelerate woody cover but did increase species richness. Seeding reduced non-native vegetation frequency and species richness, had no effect on vegetation cover on fine sediments, but increased vegetation cover on coarse sediments. Planting trees and shrubs during drawdown appeared to result in higher survival rates compared to plantings installed 1+ years post drawdown. Seeding Lupinus rivularis (riverbank lupine) on coarse sediments was successful and increased foliar nitrogen in planted conifers. Invasive non-native vegetation was correctly predicted to be more abundant in the Aldwell reservoir but did not preclude native species establishment in either reservoir, likely due to rapid establishment of native species and robust management that occurred before, during and after dam removal.

Modelling opportunities of potential European abandoned farmland to contribute to environmental policy targets

Farmland abandonment is a major proximate driver of landscape change in European rural areas and is often followed by natural revegetation. In certain conditions, it might be preferable to prevent or reverse farmland abandonment or manage these areas towards active restoration (i.e., guided rewilding with wild or domesticated animals). These alternative responses to farmland abandonment lead to context-dependent impacts, which can potentially contribute to European Green Deal objectives for environment and rural areas. While previous studies analysed direct impacts of abandonment, there is little insight into how alternative ways of managing abandoned farmland can best contribute to environmental policy goals, and what type of management is preferred where. To assess opportunities in these areas, we compared three abandonment trajectories: natural revegetation, active restoration with rewilding, and extensive re-farming. We analysed the potential positive and negative environmental and cultural impacts of developing these management strategies in all farmland locations that could potentially be abandoned across Europe. Mapping and quantification of the benefits and risks associated with different management responses to abandonment indicate a large spatial variation across regions. While natural revegetation can support high benefits for carbon sequestration and erosion reduction, it is also linked to more frequent trade-offs than re-farming and rewilding. However, there is a very strong spatial variation in these trade-offs. It is worthwhile to focus on areas with the largest gains and fewest trade-offs when targeting investments for prevention of abandonment or rewilding. Our maps can help inform interventions in abandoned farmland to maximise the potential contributions of these lands to the European Green Deal environmental and rural policy targets.

Total Bacteria and Fungi in Gold-Mine Tailing in Buru of Indonesia after Three-Year Natural Revegetation

The concern of agricultural environment damage due to amalgamation process of gold mining in Indonesia is increased. Gold mine tailing deposition in agricultural land pose a serious problem about the mercury (Hg) accumulation in soil. The objective of this study was to verify the population of heterotroph-aerobic bacteria and filamentous fungi in the tailing deposit grown with pioneer plants in comparison to both population in bare tailing after three-year revegetation. Moreover, the research was conducted to analyze the different of acidity (pH) and electrical conductivity (EC) of both sites. The study area was performed in artisanal and small-scale gold mining in Waelo village of Buru Regency, Maluku Province. The bacterial and fungal population in tailing that is naturally grown by sedges and grasses were lower than that in bare tailing without vegetation. In general, the bacterial and fungal count of tailing with vegetation was 9.3 and 4.3. while in bare tailing were 8.49 and 3.79. The acidity of both locations was not different but the pH was strongly acid ranged from 3.52-4.29. The EC was lower (21.61) in the tailing with vegetation compared to bare tailing without vegetation (58.94). This study suggested that the fungal and bacterial population as well as pH were increased after revegetation that benefit plant growth.

How do acid or alkaline soil environments affect soil organic carbon stocks in a post-abandonment secondary succession process in Mediterranean mountain areas?

Farmland abandonment has become one of the most important land use and land cover (LULC) changes threatening mountain areas in the Mediterranean. The concomitant natural revegetation process brings with it a series of ecosystem services and disservices for these marginal areas. Secondary succession can improve soil environment properties; however, its effects can be influenced by the specific characteristics of the site (topography, climate, vegetation, etc.). Thus, the main objective of this research was to study how soil quality and carbon sequestration are affected by post-abandonment secondary succession depending on the environment (delimited from the bedrock and the typical vegetation communities of the area. Soil sampling was carried out in a representative area of the Mediterranean mid-mountains (Leza Valley, Spain) for two soil environments (acid and alkaline), at different depths (0–40 cm) and in 5 stages of the abandonment process: cropland (CRL); shrubland (SH); bushland (BS); young forest (YF); and old forest (OF). Soil physico-chemical parameters were analysed and data analysis carried out with the following results: (i) significant differences were detected between environments for most LULCs; (ii) LULC, depth and soil environment significantly affected most of the soil variables studied; (iii) alkaline soil environments showed a progressive increase of soil organic carbon (SOC) and total nitrogen (N) stocks as the revegetation process and age of abandonment advanced (from 101.16 Mg ha−1 SOC (CRL) to 181.68 Mg ha−1 SOC (OF); (iv) in acid soil environments, the highest stocks were observed in the YF (161.56 Mg ha−1 SOC) with an irregular evolution pattern.Our study showed that secondary succession can improve soil quality and SOC sequestration. However, factors such as soil environment may be of great importance in selecting the best post-abandonment management strategy in a bid to gain recovery of ecosystem services and mitigate the effects of Global Change.

Natural revegetation has dominated annual runoff reduction since the Grain for Green Program began in the Jing River Basin, Northwest China

The Grain for Green Program (GFGP) has successfully increased the vegetation cover in northern China over the last two decades through large-scale natural and artificial revegetation approaches. Unfortunately, an obvious runoff reduction has been observed in many basins, especially on the semiarid Loess Plateau. Past studies generally attributed this runoff reduction to the artificial revegetation of the GFGP, i.e., the land cover type change from cropland to forest, since there was no significant annual precipitation decrease. Such cognition has led to widespread concern about the hydrological effects of the GFGP. In fact, in addition to artificial revegetation, natural revegetation relies on natural processes of vegetation succession without land cover type changes directed by humans. Therefore, it is necessary to separate and quantify the contributions of natural and artificial revegetation to runoff reduction to assess the GFGP and optimize revegetation in the future. In this study, the contributions of natural and artificial revegetation to annual runoff change after the implementation of the GFGP were quantified in fifteen subbasins of the Jing River Basin in the central Loess Plateau. The mean annual runoff of the Jing River Basin decreased by 11.8 mm after the GFGP, although the climate (precipitation and potential evapotranspiration) inversely increased the mean annual runoff by 6.6 mm. This is due to that the direct effect of climate change was much less than the ecohydrological effect of revegetation on runoff reduction, i.e., the revegetation caused the mean annual runoff reduction of 18.4 mm. Natural revegetation (50.5% of basin area) was the dominant reason for runoff reduction rather than artificial revegetation (9% of basin area). The natural revegetated area with vegetation quality improvement, i.e., an NDVI increase without land cover type change, contributed to a runoff reduction of 15.5 mm, accounting for 131.1% of the total runoff reduction after the GFGP, and the grassland of natural revegetation was the main vegetation type, with runoff reductions of 9.8 mm. However, artificial revegetation by area increase and quality improvement, i.e., NDVI increase, contributed to a runoff reduction of 8.4 mm, accounting for 49.6% of the total runoff reduction. These results demonstrated that the GFGP needs to be properly adjusted, i.e., natural revegetated areas should be opened in a timely manner and properly utilized, and improving vegetation quality improvement rather than increasing vegetation area would be a priority management measure in artificial revegetated areas.

Revegetation-induced changes in vegetation diversity improve soil properties of gully heads

Revegetation is among the most efficient methods to improve gully headcut erosion. However, the influencing mechanism of revegetation on the soil properties of the gully head (GHSP) is still unclear. Thus, this study hypothesized that the variations in the GHSP were influenced by vegetation diversity during nature revegetation, and the influence pathways were mainly root traits, aboveground dry biomass (ADB), and vegetation coverage (VC). We studied six grassland communities of the gully head with different natural revegetation ages. The findings showed that the GHSP were improved during 22-year revegetation. The interaction effect of vegetation diversity, roots, aboveground dry biomass, and vegetation coverage on the GHSP was 43 %. In addition, vegetation diversity significantly explained >70.3 % of the changes in the root traits, ADB, and VC of the gully head (P < 0.05). Therefore, we combined vegetation diversity, roots, ADB, and VC to establish the path model to explain the GHSP changes, and the goodness of fit of the model was 82.3 %. The results showed that the model explained 96.1 % of the variation in the GHSP, and the vegetation diversity of the gully head affected the GHSP through roots, ADB, and VC. Therefore, during nature revegetation, vegetation diversity dominates the improvement of the GHSP, which has important significance for designing an optimal vegetation restoration strategy to control gully erosion.

Drivers of growth and establishment of the invasive plant Rumex acetosella within Andean fallow systems

Intensification of crop rotations and associated agricultural practices are reducing the capacity of traditional fallows to restore soil fertility and provide forage in Andean cropping systems. While the implementation of improved fallows offers great promise to enhance forage provision and maintain soil productivity, effects of these practices on the establishment of problematic weeds, including non-native plant species, remain poorly understood. To address this knowledge gap, we studied: i) how biotic and abiotic environmental factors influence the establishment and productivity of weeds in traditional fallows; and ii) to what extent improved fallows can help control weedy vegetation in smallholder rotations of the high Andes. Specifically, in this research, we focused on the invasive plant species Rumex acetosella L., which is a common concern of farmers throughout the central Peruvian Andes. We leveraged a multi-site, participatory research trial established in 2017 across eight communities in the region to understand the main drivers of R. acetosella presence and productivity. We used a total of 82 sites, each with paired treatments of traditional fallow (control with natural revegetation) and improved fallow (seeded with Vicia sativa L. and Avena sativa L.). Prior to treatment establishment we measured soil texture, pH, soil organic matter content as well as exchangeable macro-nutrients. Vegetation data was recorded in each treatment and divided into four categories: 1) A. sativa, 2) V. sativa, 3) R. acetosella, and 4) other weeds, and weighed to determine the relative biomass contribution of each. From these data, we calculated an index for R. acetosella pressure, weed pressure, and forage productivity. Our findings indicate that improved fallows greatly suppress weedy vegetation relative to unmanaged controls, including the invasive R. acetosella. Multivariate analyses suggested that R. acetosella abundance was associated with the presence of other non-planted weeds and predictors of soil fertility. The mean R. acetosella index in improved fallows was significantly lower compared to traditional fallows. We found R. acetosella biomass to be greater at lower productivity sites, i.e., those at higher elevations with cooler climates and sites with less fertile soils. Our findings indicate that if the fallow portion of a rotation is kept productive via adequate soil fertility inputs, the biomass of weeds, including the alien R. acetosella, is dramatically reduced.

How do land use and land cover changes after farmland abandonment affect soil properties and soil nutrients in Mediterranean mountain agroecosystems?

Mediterranean mountains are sensitive agroecosystems that have suffered intense land use and land cover changes (LULCC) during the last century. From the middle of the twentieth century, most of the cultivated lands in Mediterranean mountains were abandoned, allowing the recovery of vegetation (through natural revegetation and afforestation programmes). To examine the effects of farmland abandonment, secondary succession (natural revegetation) and afforestation, an intensive soil sampling was carried out in the Araguás catchment (Central Spanish Pyrenees) including sparsely vegetated areas (badlands), grasslands, shrublands and afforested sites. LULCC were mapped, and soil physico-chemical properties were analysed in reference sites (unaltered areas during the last centuries) and in the different land uses. Likewise, the soil organic carbon (SOC) content in the bulk soils and in the fractions separated by density fractionation have been studied. This study evidenced that farmland abandonment led to a mosaic landscape with different land use and land covers. Results show that LULCC significantly affect soil physico-chemical properties (soil texture, stoniness, pH, SOC, total carbon, CorgN ratio, bulk density and field capacity). Significant differences were observed between secondary and afforested sites following farmland abandonment. Afforestation triggered higher SOC than shrubland sites (natural revegetation) (1.4 and 1.1% respectively), suggesting a slower process of organic matter accumulation after farmland abandonment in the natural revegetation compared to afforestation. The significant role of grassland sites for enhancing the accumulation of SOC has been also confirmed. The results showed also significant differences in the relative contribution of each organic fraction to the bulk SOC: the amount of labile fraction (free and occluded labile fractions) is significantly higher in afforested and shrubland sites (58.1 and 51.2% respectively) than in grassland sites (36.8%). Understanding the effects of LULCC on soil properties and SOC dynamics is essential when planning post-land management practices after farmland abandonment.

Investigating the recovery in ecosystem functions and multifunctionality after 10 years of natural revegetation on fly ash technosol

Technogenic soil (technosol) developed from coal fly ash (FA) landfilling has been considered a critical environmental problem worldwide. Drought-tolerant plants often naturally grow on FA technosol. However, the impact of these natural revegetations on the recovery of multiple ecosystem functions (multifunctionality) remains largely unexplored and poorly understood. Here we assessed the response of multifunctionality, including nutrient cycling (i.e., carbon, nitrogen, and phosphorus), carbon storage, glomalin-related soil protein (GRSP), plant productivity, microbial biomass carbon (MBC), microbial processes (soil enzyme activities), and soil chemical properties (pH and electrical conductivity; EC) to FA technosol ten years' natural revegetation with different multipurpose species in Indo-Gangetic plain, and identified the key factors regulating ecosystem multifunctionality during reclamation. We evaluated four dominant revegetated species: Prosopis juliflora, Saccharum spontaneum, Ipomoea carnea, and Cynodon dactylon. We found that natural revegetation initiated the recovery of ecosystem multifunctionality on technosol, with greater recovery under higher biomass-producing species (P. juliflora and S. spontaneum) than lower biomass-producing ones (I. carnea and C. dactylon). The individual functions (11 of the total 16 variables) at higher functionality (70 % threshold) also exhibited this pattern among revegetated stands. Multivariate analyses revealed that most of the variables (except EC) significantly correlated with multifunctionality, indicating the capability of multifunctionality to consider the tradeoff between individual functions. We further performed structural equation modeling (SEM) to detect the effect of vegetation, pH, nutrients, and microbial activity (MBC and microbial processes) on ecosystem multifunctionality. Our SEM model predicted 98 % of the variation in multifunctionality and confirmed that the indirect effect of vegetation mediated by microbial activity is more important for multifunctionality than their direct effect. Collectively, our results demonstrate that FA technosol revegetation with high biomass-producing multipurpose species promotes ecosystem multifunctionality and emphasizes the significance of microbial activity in the recovery and maintenance of ecosystem attributes.

Potential of land-based climate change mitigation strategies on abandoned cropland

Natural revegetation, afforestation, and lignocellulosic crops for bioenergy, possibly coupled with a developing technology like carbon capture and storage, are the most common land-based climate change mitigation options. However, they can compete for land and threaten food security or nature conservation. Using abandoned cropland for their deployment can minimize these risks, but associated potentials are unclear. Here, we compare alternative land-based mitigation options by integrating historical and future (up to 2050) abandoned cropland with site-specific biomass yields and life-cycle emissions. Considering natural revegetation in biodiversity priority areas and different measures in the remaining land can achieve a mitigation potential of 0.8–4.0 GtCO2-equivalents yr−1 (2–11% of 2021 global CO2 emissions). Afforestation generally provides larger climate benefits than bioenergy, but bioenergy with carbon capture and storage delivers the highest mitigation in most locations. Overall, these results offer refined estimates of mitigation potentials from abandoned cropland and highlight opportunities for context-specific mitigation measures.

Removing invasive giant reed reshapes desert riparian butterfly and bird communities

AbstractGiant reed (Arundo donax) is a prevalent invasive plant in desert riparian ecosystems that threatens wildlife habitat. From 2008 to 2018, under a United States–Mexico partnership, prescribed burns and herbicide applications were used to remove giant reed and promote native revegetation along the Rio Grande—Río Bravo floodplain in west Texas, USA, and Mexico. Our goal was to explore the effects of the removal efforts on butterfly and bird communities and their habitat along the United States portion of the Rio Grande—Río Bravo floodplain in Big Bend National Park, Texas. During spring and summer, 2016–2017, we surveyed butterflies, birds, and their habitat using ground‐collected and remotely sensed data. Using a variety of generalized linear and N‐mixture modeling routines and multivariate analyses, we found that the initial giant reed removal efforts removed key components of riparian habitat leading to reduced butterfly and bird communities. Within several years following management, giant reed levels remained low, while riparian habitat conditions and butterfly and bird communities largely rebounded, including many disturbance‐sensitive butterfly species and riparian‐associated bird species. Butterflies were most consistently associated with forb and grass cover, and birds with a remotely sensed index of greenness (the normalized difference vegetation index), several vegetation cover types, and habitat heterogeneity, habitat elements that were most common in locations that had the longest time to recover following management actions. Our results suggest that prescribed burns and herbicide applications, when used following protocols to minimize risk to wildlife, can limit the spread of giant reed in desert riparian systems and introduce habitat conditions that support diverse and abundant butterfly and bird communities.