Revegetation Projects Research Articles

Response of two riparian woody plants to Phytophthora species and drought

Disease combined with drought poses an important threat to plant survival, often compromising success in the restoration of riparian forests. Thus, understanding how biotic and abiotic stressors may affect plant survival and growth performance can greatly increase the success of ecosystem management strategies. The purpose of this study was to understand how two plant species, often used together in restoration of riparian ecosystems but with different ecological preferences, would respond to infection by each of two Phytophthora species in Mediterranean-climate regions, in the absence or presence of a simulated drought. Saplings of the drought resistant species Frangula californica, and of the riparian species Alnus rhombifolia were each inoculated in a greenhouse experiment with one of two Phytophthora species and exposed to two watering regimes. Saplings were allocated to six treatments, combining three levels of pathogen inoculation (no inoculation, inoculation with Phytophthora cactorum and inoculation with Phytophthora crassamura), and two watering regimes (well-watered and drought). The response of A. rhombifolia and F. californica saplings was assessed through the observation of health metrics and morphological parameters. Results showed that both P. cactorum and P. crassamura are important pathogens of A. rhombifolia and F. californica. As expected, drought conditions were the main cause of decline and mortality in A. rhombifolia saplings, while water availability was a facilitator of P. cactorum infection in F. californica saplings. We observed two seemingly contrasting results in A. rhombifolia saplings: infection by Phytophthora spp. decreased survival in well-watered plants, while the opposite was recorded for saplings under drought conditions whose survival increased in Phytophthora-inoculated treatments. Saplings of F. californica were able to cope with drought conditions, even when infected by Phytophthora species and water availability increased root infection and decreased sapling survival. We conclude that the continued use of F. californica and A. rhombifolia in sites infested by Phytophthora species can be beneficial in restoration, if appropriate management actions are adopted. Such actions include avoiding the planting of F. californica saplings in areas subjected to water accumulation, and ensuring that A. rhombifolia is planted in areas where drought stress is minimal and where Phytophthora species are possibly absent. We also emphasize the importance of ensuring that plant stock used in revegetation projects is not infected by Phytophthora species, and that biotic and abiotic risks are assessed prior to restoration actions.

Drought and water-use efficiency are dominant environmental factors affecting greenness in the Yellow River Basin, China

Revegetation is accelerating globally because of its benefits in terms of ecosystem restoration, desertification prevention, and warming mitigation. The Yellow River Basin (YRB), as an ecological barrier in northern China, has implemented revegetation projects (such as the ‘Grain for Green’ program) for over two decades. However, a consensus on whether a significant change in greenness has been achieved and to what extent have environmental factors contributed to this change, as well as their importance ranking, is lacking. Leaf area index (LAI) is a critical indicator for estimating global greenness and projecting the dynamics of climate change. Herein, we apply four methods (Geodetector, random forest, multiple linear regression, and structural equation models) to explore the contribution of different environmental factors to greenness using the LAI in the YRB. We found that greenness has been increasing (greening over 67.22% (p < 0.05; 47.7%) of the YRB) with great spatial heterogeneity in the entire basin since 2000. Specifically, the greening process differed with elevation and slope. Temperature vegetation dryness index (TVDI) and water-use efficiency (WUE) dominated the greening; however, the three subregions evaluated revealed differing performance. In the upstream region, LAI increased by 0.031 y−1. The primary positive factors of greening change were WUE and the annual highest value of daily minimum temperature; the negative factors were TVDI and the highest number of consecutive days when precipitation <1 mm. In the midstream region, LAI increased by 0.025 y−1; greenness was mainly affected by the negative interaction of TVDI and the positive interaction of WUE. Annual maximum consecutive 5-day precipitation and annual count when daily minimum temperature < 0 °C had a great indirect impact on greenness, mainly through TVDI and WUE. In the downstream region, LAI increased by 0.045 y−1, and the main driving factors were the annual lowest value of daily minimum temperature with a negative influence and the annual lowest value of daily maximum temperature with a positive influence. In addition, we found that the effect of the interaction of any two driving factors on greenness was greater than or equal to the single effect of a driving factor. This study concludes that drought and WUE are important predictors to evaluate the greenness in arid and semi-arid regions. We emphasise that the selection and assessment of greenness factors should follow a scientific and rigorous process rather than experience, and increased attention should be paid to the interaction of multiple factors. Furthermore, the perspective of system analysis will deepen our understanding of vegetation change in a vulnerable ecosystem.

Re-vegetation Improves Soil Quality by Decreasing Soil Conductivity and Altering Soil Microbial Communities: A Case Study of an Opencast Coal Mine in the Helan Mountains.

Microbial communities constitute a diverse genetic resource pool in the soil and are key indicators of soil health and quality. How re-vegetation affects soil microbial diversity and community composition at the dump of an opencast coal mine is largely unknown. Using high-throughput sequencing, we performed a comparative study of the bacterial and fungal communities from non-vegetated (bare land) soil and from areas re-vegetated by Astragalus laxmannii, Halogeton arachnoideus, and Artemisia desertorum at an opencast coal mine in the Helan Mountains in western China. These results indicated that re-vegetation significantly reduced soil conductivity. The soils re-vegetated by all three plant species showed greater richness of bacterial species than the bare land, and soils re-vegetated with A. desertorum and A. laxmannii showed significantly greater richness of fungal species than bare land. The bacterial and fungal β-diversity values differed significantly between vegetated and non-vegetated soil, and these differences were more pronounced for bacterial communities than for fungal communities. Re-vegetation significantly increased the relative abundances of Proteobacteria and Bacteroidota and decreased the relative abundance of Chloroflexi. The decreasing soil conductivity that occurred with re-vegetation was found to be an important environmental determinant of the soil microbial community. This study provides evidence that re-vegetation may enhance soil quality via decreasing soil conductivity and altering the soil microbial community, and A. laxmannii was found to be a more effective species than H. arachnoideus or A. desertorum with respect to decreasing soil conductivity and altering the soil microbial communities in the Opencast Coal Mine arid region. This work may provide a helpful guideline for selection of plant species for re-vegetation projects.

Regeneration with or without seedling management: Serra do Mar slope, São Sebastião/SP

The survival of forest communities is based on the seedling bank, since the greater the diversity, the greater the probability of heterospecific replacements. This work aimed to verify, through the species composition, if there is natural regeneration of the clearing with and without management and if it is possible that the clearing regeneration occurs without the management. The study site covered a clearing and a fragment of the Atlantic Forest Biome, in the municipality of São Sebastião/SP, north coast of the state of São Paulo. Ten subplots of 0.5 m x 1.0 m were installed randomly in 8 transects of 2.0 m x 50.0 m, with and without seedling management, where the set of seedlings with up to 20 cm was sampled. At the end of the study, 266 individuals were found, grouped into 38 families and 5 life forms (arboreal, shrub, herbaceous, epiphyte and liana), later classified into: 45 species (60.81%), 23 genera (31.08%) and 6 families (8.10%). Myrtaceae and Rubiaceae stood out as the most species-rich families, with 8 and 6 species, respectively. In the clearing, 22.2% of the sampled species were found, while 77.8% belonged to the forest. The difference between the number of species in the clearing and in the forest fragment suggests that the invasive species Melinis minutiflora and Scleria plusiophylla can hinder the establishment of seeds, preventing the germination of native species. Therefore, for the clearing regeneration process to occur faster, human intervention is necessary in the management of invasive species. Accordingly, the elaboration of a revegetation project withmonitoring and evaluation of the area of study was emphasized.

Different biomass production and soil water patterns between natural and artificial vegetation along an environmental gradient on the Loess Plateau

Loess Plateau (LP) is a vulnerable and climate-sensitive ecoregion. With the implementation of “Grain for Green” project (GGP), the vegetation cover has largely improved, while the contradiction between overconsumption of soil water and sustainability of restored vegetation is increasingly prominent, and further threatening the ecosystem sustainability and socioeconomic development. Understanding the different responses of relations of biomass production and soil water regimes between natural and artificial vegetation along environmental gradient will be crucial for sustainability of restored vegetation on the LP. Here, aboveground biomass (AGB) and soil water content (SWC) of natural and artificial vegetation were measured in steppe, forest-steppe and forest zone from 2008 to 2017 on the Yanhe River catchment. The results showed that artificial vegetation consumed more soil water than natural vegetation in steppe and forest-steppe zone, while it did not over consume soil water in forest zone. The AGB of natural vegetation in forest zone was significantly higher than that in steppe and forest-steppe zone. Steppe zone had serious overload of artificial vegetation (overload ratio: 5.35), while no overload occurred in forest zone. So, we suggest a cessation of artificial vegetation expansion in steppe zone. In steppe zone, planting artificial vegetation increased competition intensity between AGB and SWC, and the relative benefit tended to be AGB, their competition intensity was the highest. In forest zone, the trade-off relationship between AGB and SWC had no significant difference between natural and artificial vegetation, and the competition intensity between the AGB and SWC was the weakest. Optimal vegetation restoration approach would maintain the balance between vegetation restoration and soil water. To obtain social and ecological sustainability on the LP, vegetation suitability and suitable management along different environmental gradients should be considered and identified in the future revegetation project.

Coping with changing plant–plant interactions in restoration ecology: Effect of species, site, and individual variation

AbstractQuestionNurse–beneficiary plant interactions are often used to restore degraded habitats. However, whether and how shifts in plant–plant interactions along the facilitation–competition continuum alter revegetation success has been seldom considered. To test whether and how shifts in plant–plant interactions (due to woody species identity, study site, early life stage, and individual nurse) might alter plant recruitment and thus the success of revegetation projects, we chose a system comprising the Mediterranean dwarf palm (Chamaerops humilis) and seven common woody plant species.LocationTwo human‐degraded sites within Doñana National Park (southwestern Spain).MethodsWe carried out several well‐replicated field experiments to compare plant performance (seed survival, seedling emergence, seedling survival, seedling recruitment) in the presence and absence of Chamaerops humilis.ResultsChamaerops humilis had marked effects on the performance of woody species that, however, changed among life stages. Depending on woody species identity, seed survival was up to 193 times greater in adjacent open spaces than beneath Chamaerops humilis. Conversely, seedling survival and recruitment were up to 19 times greater beneath Chamaerops humilis than in open spaces. Importantly, none of the studied woody species showed greater accumulated recruitment in open spaces than beneath Chamaerops humilis. Interestingly, we found strong inter‐individual palm variation in the sign and strength of their effect on woody plant performance.ConclusionsWe found strong seed–seedling conflicts the strength of which was species‐specific. The strong inter‐individual palm variation depicts a facilitation–competition continuum with important implications for restoration. We propose several management recommendations across different hierarchical levels (i.e., from individuals to communities) that may increase plant recruitment and therefore the success of revegetation projects. Our results are particularly relevant for restoring arid, semi‐arid and alpine landscapes worldwide where the nurse–beneficiary plant interactions are critical to ameliorating stressful conditions.

Sowing Mixtures of Native Plant Species: Are There Any Differences between Hydroseeding and Regular Seeding?

Hydroseeding is a convenient, low-cost way to plant seeds. Traditionally, fast-growing commercial species that are cheap to obtain are preferred in hydroseeding, while native species have limited use. Nowadays, the use of native species is often desired in revegetation projects. However, there is a paucity of information about hydroseeding native species in Northern areas of Europe. Therefore, we aimed to determine whether hydroseeding has any effects on native plant cover formation, species richness and abundance, the development of plant morphological features, or aboveground biomass. A total of 40 native plant species in Lithuania were sowed using hydroseeding and regular seeding. The experimental plots were assessed for two years. The results show a relatively small and short positive effect of hydroseeding on plant cover formation. No significant differences were found in species richness between the sowing treatments. However, a comparison of species composition revealed significant differences between the sowing treatments that were more associated with species abundance than species diversity. Hydroseeding was favoured by legume species, such as Onobrychis viciifolia, Ononis arvensis, Lotus corniculatus, and Trifolium medium, while Festuca rubra favoured the regular seeding treatment. Overall, our findings emphasize that legume species that display more competitive growth traits should be included in the seed mixture in lower proportions when hydroseeding is applied.

Quantifying the supply-demand balance of ecosystem services and identifying its spatial determinants: A case study of ecosystem restoration hotspot in Southwest China

Ecosystem conservation and restoration are the primary practices for enhancing ecosystem services (ESs) and achieving sustainable development goals. However, inappropriate land use interventions and revegetation projects may lead to an imbalance between the supply and demand of ESs. This study applied the ES matrix approach and spatial panel models to quantify the supply–demand balance of ESs in the southwest karst region and to identify their spatial determinants and spillover effects. The overall patterns for landscape metrics between 1980 and 2015 remained relatively stable, while landscape fragmentation and population growth weakened the ES supply capacity but increased the demand, which caused an imbalance (i.e. the demand exceeded the supply), particularly in the surrounding areas of the urban agglomerations. Population density and individual landscape metrics were significantly associated with ES balance (p < 0.01) and were identified as the dominant spatial determinants. Additionally, the spillover effects of determinants also influenced ES balance patterns, which should be considered in integrated landscape planning and ecosystem management to coordinate collaborations from local and adjacent regions to mitigate ES imbalance. Excessive reclamation and urbanisation temporarily improved grain provision and economic profits, respectively, but caused an imbalance in ESs and threatened ecological security. Additionally, excessive conservation practices ignored economic costs and the livelihood of residents, which threatened food security and exacerbated poverty. Therefore, a balance between the contrasting targets should be maintained through the lens of ES balance to reconcile ecosystem conservation and socioeconomic development. This study provides a complete and feasible perspective to examine and optimise human interventions, with the aim of achieving win-win goals.

Correlation assessment of NDVI and land use dynamics with water resources for the southern margin of Mu Us Sandy Land, China.

To prevent desertification, countries worldwide have made diversified efforts, and vegetation restoration has been demonstrated to be an effective approach. However, in regard to sandy land with limited water resources, measures such as revegetation may lead to an increased drought risk. Despite confirmed sand utilization achievements, many controversies remain regarding the advantages of desert greening, especially considering water scarcity. Therefore, the long-run and causal relationships between sandy land, water consumption, and vegetation coverage are necessarily explored. Choosing the southern margin of the Mu Us Sandy Land as the study area, this study explored the interactions between sandy land, water consumption, and normalized difference vegetation index (NDVI) of 2000-2018 with the vector autoregression (VAR) model approach. In the study area, various revegetation projects have been implemented, resulting in a notable reduction in the sandy land area. In addition, the NDVI increased from 0.196 in 2000 to 0.371 in 2018, an increase of 89.3%. The results indicated that there exist long-term stable equilibrium and causal relationships existed between water consumption and sandy land and NDVI. NDVI enhancement is relatively the direct factor that causes the increase of water consumption. It could be inferred that the implemented revegetation measures may rely on a large water consumption amount, which may further aggravate water shortages and ecological damage issues. More scientific and stronger effective water resource management measures should be locally implemented to achieve a balance between water resources and revegetation.

Combined effects of multiple factors on spatiotemporally varied soil moisture in China’s Loess Plateau

Identifying the factors controlling spatiotemporally varied soil moisture (SM) is fundamental for water resources management, but the combined effects of multiple factors across multiple timescales have been rarely considered. The objective of this study is to identify the factor(s) individually or simultaneously controlling SM in China’s Loess Plateau, a region with arid climate experiencing substantial vegetation change because of a revegetation project implemented in 1999. With SM product derived from Global Land Evaporation Amsterdam Model Version 3.0a, we investigated large-scale SM dynamics for surface soil (0–10 cm) and root zone (10–250 cm) for 1982–2015, and considered environmental factors at the regional scale (e.g. precipitation PCP, mean temperature TMP, potential evapotranspiration PET, normalized difference vegetation index NDVI, land use types, elevation, slope gradient, clay fraction, and reference bulk density) and at the global scale (e.g. El Niño/Southern Oscillation ENSO, Pacific Decadal Oscillation PDO, North Atlantic Oscillation NAO, and Arctic Oscillation AO). Spatially, the mean SM in both surface and deep layers decreases with a gradient from the southeast to the northwest. Temporally, SM tends to decrease in the southeast while increases in the northwest, implying a pattern of “wet gets drier, dry gets wetter”. Individually, PET and ENSO are the most important regional and global factors controlling SM, respectively. Simultaneously, PET, PCP, and NDVI have combined effects, while the global factors exhibit no combined effects. The regional and global factors both influence SM at a scale of 8–16 months across the whole study period. In addition, the effects of regional factors exhibit at the scale of 32–64 months but tend to disappear after 1999. The global factors have smaller impacts than regional factors, but they tend to indirectly influence SM through perturbing regional climate. The identified factors highlight the complicated changes and controlling factors of SM, which provides important information for land use management and water resources management. The employed methods are effective in identifying the combined effects of multiple factors and can be extrapolated to other regions.

Cultivars of popular restoration grass developed for drought do not have higher drought resistance and do not differ in drought‐related traits from other accessions

Numerous functional traits have been identified as key contributors to plant performance under drought. However, many of these traits, specifically root traits, are rarely considered in the development of native plant cultivars. In this study, we assessed whether cultivars of the perennial grass Elymus trachycaulus (Slender wheatgrass) developed for drought differ in (a) drought resistance (i.e. a plant's ability to maintain aboveground biomass productivity under water deficit), (b) aboveground and belowground traits, and (c) trait responses to drought from other accessions (i.e. other cultivars, wild accessions). We also evaluated trait plasticity, assessed whether multivariate trait relationships varied between control and drought conditions, and determined which suites of traits are related to drought resistance. We worked with seedlings at two developmental stages to assess whether patterns vary ontogenetically. E. trachycaulus cultivars developed for drought did not differ from other accessions in drought resistance or traits related to drought‐coping strategies. The effects of drought and accession on drought resistance, traits, and trait plasticity varied by developmental stage, but relationships among traits varied little between the two developmental stages. A primary axis of functional variation related to resource acquisition (plant height, root length, root tips) was consistently associated with drought resistance. However, which secondary axes were related to drought resistance varied by developmental stage and moisture condition. Our results suggest that traits and performance of commonly used cultivars ought to be reexamined to determine whether they are actually the best candidates for revegetation projects in specific contexts.

Sustainable and cost-effective vegetation restoration framework under climate change

Although potential natural vegetation (PNV) information can be used as references in revegetation projects, previous studies have largely ignored the sustainability and cost-effectiveness of revegetation in light of climate change and funding requirements. To address these issues, this study proposes a sustainable and cost-effective vegetation restoration framework based on the growing potential index (GPI, i.e., normalized gross primary productivity) of the PNV type, mitigating adverse effects of climate change. The framework is simulated with a dynamic vegetation model using China’s Loess Plateau (LP) as a case study. The results show that: (1) Among the PNV types, temperate steppe occupied 73.2% of the LP, followed by temperate deciduous broad-leaved forest with 22.3% and temperate evergreen coniferous forest with 3.9%. Several conversions occurred among the PNV types from current to future periods, implying that future climate change will strongly disturb PNV patterns. (2) The GPI of PNV type during 2001–2020 displayed distinct spatial heterogeneity within its pattern; although the GPI of PNV type during 2081–2100 had similar spatial variation to GPI during 2001–2020, spatial statistic information of GPI during 2001–2020 and 2081–2100 showed large differences, suggesting that the growth status of PNV type will be largely affected by future climate change. (3) To mitigate the effects of climate change on vegetation restoration, a PNV pattern undisturbed by climate change from 2021 to 2100 was identified, accounting for 77.8–68.76%, which can be considered as a reference to ensure sustainability. The GPI of the undisturbed PNV types showed a progressive decrease from southeast to northwest and from low to high altitudes. Our results can be used to plan sustainable and cost-effective revegetation projects especially for areas with high growing potential for undisturbed PNV types and may provide insights into other ecological restoration projects globally.

Revegetation projects significantly improved ecosystem service values in the agro-pastoral ecotone of northern China in recent 20 years

Revegetation is a conventional approach used for ecological protection and restoration projects, especially in the agro-pastoral ecotone of northern China (AENC). However, for this ecologically vulnerable area, the changes in land use and ecosystem service values (ESV) resulting from revegetation projects have received little attention and have not been fully elucidated. In this study, based on a rapid valuation tool–the benefit transfer method modified by the biomass factor (net primary productivity, NPP)–we assessed the ESV of the AENC at multiple-time scales by designing land scenarios related to local revegetation projects. The results showed that forestland expansion (+697 thousand ha) and grassland shrinkage (−650 thousand ha) dominated the land use change in the AENC in 2000–2018 and indirectly resulted in a net increase of US$8.18 billion in total ESV, in which revegetation projects generated nearly 1.5 million ha of new vegetated land and a corresponding US$6.86 billion in ESV (83.83% of the total increase). For future revegetation, the returning-farmland-to-forestland scenario exhibited a greater potential with increases of 5.66 million ha of forestland and US$65.20 billion in ESV to be provided. Overall, revegetation projects improved the ESV of the AENC in the last two decades because of the pronounced expansion in forestland of high ESV at the expense of the reductions in farmland and grassland, and this trend will be led continually by the Grain for Green Project in the future through the rapid assessment based on the modified benefit transfer method. Specifically, more investments and attention must be directed to the protection and restoration of grassland and wetland ecosystems.

The Use of Very-High-Resolution Aerial Imagery to Estimate the Structure and Distribution of the Rhanterium epapposum Community for Long-Term Monitoring in Desert Ecosystems.

The rapid assessment and monitoring of native desert plants are essential in restoration and revegetation projects to track the changes in vegetation patterns in terms of vegetation coverage and structure. This work investigated advanced vegetation monitoring methods utilizing UAVs and remote sensing techniques at the Al Abdali protected site in Kuwait. The study examined the effectiveness of using UAV techniques to assess the structure of desert plants. We specifically examined the use of very-high-resolution aerial imagery to estimate the vegetation structure of Rhanterium epapposum (perennial desert shrub), assess the vegetation cover density changes in desert plants after rainfall events, and investigate the relationship between the distribution of perennial shrub structure and vegetation cover density of annual plants. The images were classified using supervised classification techniques (the SVM method) to assess the changes in desert plants after extreme rainfall events. A digital terrain model (DTM) and a digital surface model (DSM) were also generated to estimate the maximum shrub heights. The classified imagery results show that a significant increase in vegetation coverage occurred in the annual plants after rainfall events. The results also show a reasonable correlation between the shrub heights estimated using UAVs and the ground-truth measurements (R2 = 0.66, p < 0.01). The shrub heights were higher in the high-cover-density plots, with coverage >30% and an average height of 77 cm. However, in the medium-cover-density (MD) plots, the coverage was <30%, and the average height was 52 cm. Our study suggests that utilizing UAVs can provide several advantages to critically support future ecological studies and revegetation and restoration programs in desert ecosystems.

Better left alone: Trying to control pasture grasses in untended rainforest plantings incurs multiple costs and delivers few benefits

AbstractRainforest revegetation projects often deliver suboptimal outcomes due to the recolonization of invasive pasture grasses, but little is known about the effects of grass reinvasion on the survival and growth of established saplings. Even less is known about the costs and benefits of controlling pasture grasses once they have reinvaded.To address these knowledge gaps, we implemented a split‐plot grass control experiment in a 2‐year old subtropical rainforest restoration planting in South East Queensland, Australia, that was reinvaded by the exotic pasture grassChloris gayana.Grass removal involved brush cutting around saplings, spraying herbicide and then laying 1 m2jute matting. The costs of implementing the treatment were recorded, and the survival, growth and physiological stress of treated and control saplings were monitored for 1 year.Non‐target herbicide application reduced survival by 6.5% in treated saplings, affecting mainly smaller plants that were below the grass canopy at the onset of the experiment. Beyond this direct herbicide effect, smaller treated saplings were also more stressed (lower chlorophyll fluorescence) and had substantially lower survival after 1 year than untreated saplings of the same size. There was limited evidence that removing grass increased growth rates, even for saplings that were already taller than the grass canopy at the start of the experiment.While the growth benefits of controlling grass may become more apparent with time, our results suggest that grass removal is not an effective management strategy in untended plantings due to the heightened risk of sapling mortality, coupled with the considerable labour and material costs.

Satellite observed cooling effects from re-vegetation on the Mongolian Plateau

During the past decades, a series of new policies and ecological projects have been implemented to mitigate land degradation on the Mongolian Plateau. However, climatic effects from re-vegetation still remain largely unknown. In this paper, we investigate local land surface temperature response to re-vegetation changes by comparing between locations with forest or grassland gains and their nearby unchanged land units based on satellite observations. Our results demonstrate that reforestation in humid regions and grassland cover gains in arid regions result in annual net cooling effect, but temperature response to reforestation shows asymmetric diurnal (daytime cooling but nighttime warming) and seasonal (summer cooling but winter warming during daytime) cycle. Local cooling effect of transition land cover is enhanced with continuous restoration of vegetation. The underlying process is mainly controlled by biophysical effects from surface albedo and evapotranspiration. Increased albedo associated with snow cover in winter significantly contributes to the cooling effect of grassland, and evapotranspiration along with increase in precipitation amplifies interannual temperature differences especially in summer. This study reminds that rational land use policy should be formulated carefully to realize potential climatic benefits from re-vegetation projects.

Maternal source affects seed germination of a rare Arabian desert species (Astragalus sieberi)

Understanding variation of seed germination in wild populations can assist restoration projects through improved seed source selection. Recruitment of artificially distributed seed can be improved by selecting for suitable dormancy and germination characteristics. We investigated seed germination and emergence responses of three Astragalus sieberi DC. (Fabaceae) populations (Abdali, Liya, and Salmi) to in situ storage for five months at depths of 0 and 5 cm, pre-sowing hydration for 12 and 24 hours, and chemical scarification with concentrated sulfuric acid for 5, 10, and 15 min. The germination percentage was low for freshly collected seed (&lt;3%) from Abdali and Salmi, though in situ storage partially enhanced germination. Pre-sowing hydration did not affect seedling emergence, but acid scarification effectively broke seed dormancy. The longest scarification treatment of 15 min produced the greatest seedling emergence, though populations responded differently. Our results indicate that selection of maternal, native seed sources can improve revegetation projects in desert areas. Knowledge of inter-population variation can improve the understanding of the mechanisms regulating seed germination, thus optimizing restoration projects by selecting optimal seed sources.

Integrating vegetation suitability in sustainable revegetation for the Loess Plateau, China

Revegetation is accelerating globally due to its benefits for ecosystem restoration, desertification prevention, and climate change mitigation. The Loess Plateau has suffered serious erosion in the past decades, and revegetation projects, such as those under the ‘Grain for Green’ program, have been conducted for soil erosion prevention. The irrational distribution of artificial plantations had negative consequences, including vegetation degradation, soil drying, and decreases in streamflow. Determining the suitable plant species is critical in guiding the design of revegetation programs and may help delimit the suitable boundaries for artificial plantations. In this study, we used an eco-hydrological model to quantify the suitability of two typical revegetation species (Robinia pseudoacacia and Stipa bungeana) using a developed vegetation suitability equation, which estimates the water use/water stress trade-off. The results showed that R. pseudoacacia was more sensitive to water stress than S. bungeana. The water use of both species varied along the precipitation gradient, and S. bungeana generally had a higher water use than R. pseudoacacia. Suitable areas for R. pseudoacacia were mainly located in the northeastern part of the plateau. By overlaying the suitable boundaries for R. pseudoacacia on the current land cover, we found that the area of forests distributed in unsuitable regions reached 7.31% of the entire Loess Plateau. Converting forests beyond the suitable boundary to grasslands would increase the water yield (0.51%–12.23%) and slightly decrease the soil retention capacity (0.01%–0.08%), resulting in a ‘win-win’ situation for sustainable plant-soil ecosystems and soil-water conservations. Additionally, the suitable area of R. pseudoacacia is predicted to shrink under projected future drying trends. In conclusion, vegetation suitability in the future planning and design of revegetation projects should be considered to effectively tackle the impacts of environmental degradation and climate change in the Loess Plateau.

Not vegetation itself but mis-revegetation reduces water resources

Increasing greening of planet Earth to slow down the rise of atmospheric CO2 concentrations is certainly desirable; however, its consequences on water resources are less affirmative and thus are a matter of wide concern. China, as the largest and most successful country of the world in terms of artificial revegetation, is naturally the focus of the concerns and warnings. Based on previous studies, we analyzed the mechanism for the effects of climate and watershed characteristics on water resources, explained various hydrological results and phenomena, and considered the ways in which water consumption by artificial revegetation projects can be reduced. Moreover, some guidelines are suggested for artificial revegetation at watershed scale with consideration of water resource sustainability. The findings of this study highlight the need for more top-down approaches when studying the mechanism of “forest and water”.

Estimation of carbon stock in urban parks: Biophysical parameters, thresholds, reliability, and sampling load by plant type

At present scarce information is available on what biophysical parameters of plants are important to what kind of vegetation carbon stock, and what thresholds should be adopted in sampling different types of plants, and what species/plants store carbon most efficiently. The answer to these questions is significant as it dictates the reliability of the carbon stock estimate and estimation cost, and can guide the design of efficient urban green infrastructure. This study aims to assess the carbon storage capacities of plants, their biophysical parameters important to the carbon stock by plant type, and the influence of parameter thresholds on carbon estimate and sampling load. In total, 1,681 woody plants were surveyed in 20 plots in Auckland parks and reserves. Trees (51%), shrubs (22%), and ferns (27%) co-existed spatially, and stored 115.30, 2.05, and 5.94 Mg C, respectively, at a ratio of 19.4:0.3:1. On average, a tree, shrub, and fern/palm stored 138.09 ± 333.7, 5.59 ± 6.0, and 13.36 ± 15.5 kg C per plant. The top five carbon-contributing tree species were exotic pines (29.1%), kauri (9.8%), rimu (3.8%), kahikatea (2.9%), and matai (2.1%). Matai should be the choice in revegetation projects to maximise carbon stock given its unparalleled carbon contribution index (17.2). Stem length was totally ineffective in indicating plant carbon, followed by canopy area. Diameter at breast height (DBH) was a better indicator of tree and shrub carbon . Total vegetation carbon would be underestimated by 3.7% if a DBH threshold of ≥10 cm were adopted for trees, and ≥14 cm for shrubs and ferns, all causing the carbon stock of the respective plant type to be underestimated by about 1.60 Mg C. However, these thresholds would reduce the overall sampling load by 47.2%. The established relationship between DBH and cumulative carbon allows calibration of the estimated carbon in accordance with the DBH threshold adopted in sampling different plants. Whether the amount of calibration still holds true in other types of urban plants requires further study.