Expansion Of Vegetation Research Articles

Contributions of Vegetation Greening and Climate Change to Evapotranspiration Trend after Large-Scale Vegetation Restoration on the Loess Plateau, China

Since the early 2000s, the vegetation cover of the Loess Plateau (LP) has increased significantly, which has been fully recorded. However, the effects on relevant eco-hydrological processes are still unclear. Here, we made an investigation on the changes of actual evapotranspiration (ETa) during 2000–2018 and connected them with vegetation greening and climate change in the LP, based on the remote sensing data with correlation and attribution analysis. Results identified that the average annual ETa on the LP exhibited an obvious increasing trend with the value of 9.11 mm yr−1, and the annual ETa trend was dominated by the changes of ETa in the third quarter (July, August, and September). The future trend of ETa was predicted by the Hurst exponent. Partial correlation analysis indicated that annual ETa variations in 87.8% regions of the LP were controlled by vegetation greening. Multiple regression analysis suggested that the relative contributions of potential evapotranspiration (ETp), precipitation, and normalized difference vegetation index (NDVI), to the trend of ETa were 5.7%, −26.3%, and 61.4%, separately. Vegetation greening has a close relationship with the Grain for Green (GFG) project and acts as an essential driver for the long-term development trend of water consumption on the LP. In this research, the potential conflicts of water demanding between the natural ecosystem and social-economic system in the LP were highlighted, which were caused by the fast vegetation expansion.

Using Standardized Time Series Land Cover Maps to Monitor the SDG Indicator “Mountain Green Cover Index” and Assess Its Sensitivity to Vegetation Dynamics

SDG indicators are instrumental for the monitoring of countries’ progress towards sustainability goals as set out by the UN Agenda 2030. Earth observation data can facilitate such monitoring and reporting processes, thanks to their intrinsic characteristics of spatial extensive coverage, high spatial, spectral, and temporal resolution, and low costs. EO data can hence be used to regularly assess specific SDG indicators over very large areas, and to extract statistics at any given subnational level. The Food and Agriculture Organization of the United Nations (FAO) is the custodian agency for 21 out of the 231 SDG indicators. To fulfill this responsibility, it has invested in EO data from the outset, among others, by developing a new SDG indicator directly monitored with EO data: SDG indicator 15.4.2, the Mountain Green Cover Index (MGCI), for which the FAO produced initial baseline estimates in 2017. The MGCI is a very important indicator, allowing the monitoring of the health of mountain ecosystems. The initial FAO methodology involved visual interpretation of land cover types at sample locations defined by a global regular grid that was superimposed on satellite images. While this solution allowed the FAO to establish a first global MGCI baseline and produce MGCI estimates for the large majority of countries, several reporting countries raised concerns regarding: (i) the objectivity of the method; (ii) the difficulty in validating FAO estimates; (iii) the limited involvement of countries in estimating the MGCI; and (iv) the indicator’s limited capacity to account for forest encroachment due to agricultural expansion as well as the undesired expansion of green vegetation in mountain areas, resulting from the effect of global warming. To address such concerns, in 2020, the FAO introduced a new data collection approach that directly measures the indicator through a quantitative analysis of standardized land cover maps (European Space Agency Climate Change Initiative Land Cover maps—ESA CCI-LC). In so doing, this new approach addresses the first three of the four issues, while it also provides stronger grounds to develop a solution for the fourth issue—a solution that the FAO plans to present to the Interagency and Expert Group on SDG Indicators (IAEG-SDG) at its autumn 2021 session. This study (i) describes the new approach to estimate the MGCI indicator using ESA’s CCI-LC and products, (ii) assesses the accuracy of the new approach; (iii) reviews the limitations of the current SDG indicator definition to monitor progress towards SDG 15.4; and (iv) reflects on possible further adjustments of the indicator methodology in order to address them.

Plant community composition alters moisture and temperature sensitivity of soil respiration in semi-arid shrubland.

Soil respiration (Rs) is the second largest carbon (C) flux to the atmosphere and our understanding of how Rs and its components shift with plant-community composition remains an important question. We used high-frequency soil respiration measurements and root exclusion to evaluate how Rs, autotrophic respiration (Ra) and heterotrophic respiration (Rh) vary between a semi-arid perennial shrub community and annual invasive community. Over two growing seasons, total Rs was 40% higher under annual vegetation compared to shrubs. Partitioning revealed consistently higher Ra under annual vegetation which accounted for most of the difference in Rs. Under annual vegetation, Ra increased soon after the first rain events and remained high despite cooling temperatures while shrub Ra increased only when soil temperature began to warm up. The Rh rates were similar between vegetation types when daily soil temperatures were lower than 20°C. As soil temperatures increased and soil moisture dropped below 10%, Rh was consistently higher under annual vegetation than shrubs. Seasonal dynamics of Rs and Rh were best modeled with an interaction term between soil moisture and temperature with significantly different model parameters for each vegetation type. Differences in the timing and magnitude of Rs and Ra between vegetation types are consistent with phenological differences between shrubs and annuals. Under annuals, larger Rh at high temperatures suggests that expansion of annual vegetation and future hotter and drier conditions could lead to greater C losses from this semi-arid shrub system.

Urban expansion and enhanced flood risk in Africa: The example of Lagos

ABSTRACT The world is increasingly characterised by uncertainty, complexity and rapid change while vulnerability to potential disasters is equally increasing. The situation is more dire in countries where governments are unable to manage land use and development in rapidly growing towns and cities. Lagos, a major city in Nigeria, is notorious for flooding, owing to its being lowland, and this is compounded by inadequate planning and uncoordinated physical development. A systematic study of urban expansion in Lagos was done using Landsat ETM, OLI and Google Earth imageries for 2000, 2013 and 2019 to analyse land use and land cover change, and pattern of encroachment of physical development into vegetation cover and flood plains in Lagos. The comparison of the three Land Use Land Cover Change (LU/LC) schemes, indicates that built-up areas accounted for about 50.0% of land use in Lagos in 2019. The increase is almost thrice the extent recorded in the year 2000. As the pace of growth quickens, new structures deplete vegetation and fuels lateral expansion into marginal land. Adherence to land use planning regulation, vertical expansion and flood-plain-buy-back were recommended as strategies to mitigate flood risk.

Late Pleistocene-Holocene diatomites from the coastal plain of southern Brazil: Paleoenvironmental implications

The southern Brazilian coastal area harbors one of the largest wetland systems of South America, important for its plant and animal biodiversity and ecosystems services provided for human populations. As an attempt to understand the development of those wetlands, samples from a diatom ooze and indurated diatomites found in the coastal plain of the state of Rio Grande do Sul were analyzed. The fragmented state of the frustules found in the samples allowed identification of most diatoms only to the genus level, nevertheless the assemblages are represented by 16 genera reported today in freshwater bodies in the studied region. The identified taxa include the planktonic Aulacoseira and Cyclotella and several benthic genera, mostly Eunotia, Pinnularia and Rhopalodia. The diatomites consist mostly of corroded irregular-shaped silica grains from frustules dissolved by alkaline water, but five diatom genera were identified. These diatomites accumulated in ephemeral ponds developed on loess sediments in dry environments and seasonal climate between the latest Pleistocene and Middle Holocene. The diatom ooze and associated organic-rich silty sediments accumulated in shallow lakes with abundant catchment vegetation and considerable dissolved organic carbon, and contain fragmented but slightly dissolved frustules as a result of hydrodynamics and low pH, and also megascleres of Porifera, cysts of Chrysophyceae, and abundant phytoliths of Poaceae. The sediment underlying the diatom ooze was dated as of 4.6–4.4 cal 14C ka BP and contains a diatom assemblage dominated by benthic epiphytic and acidophilous forms such as Eunotia, Pinnularia, and Gomphonema. The ooze and sediment overlying it contain an assemblage dominated by the planktonic Aulacoseira and Cyclotella, indicating ≥1 m-deep water column subject to moderate wind-driven hydrodynamics and variable water table. This succession shows that the development of the modern wetlands during the Middle Holocene, accompanied by the expansion of vegetation, resulted from a combination of high sea-level and increased rainfall and productivity driven by the wetter and warmer climate of the Holocene Hypsithermal, although the dense accumulation of frustules in the diatom ooze suggests a drier episode around ~4 ka BP. The results show that diatom assemblges preserved as diatomites can be used to understand the origins and response of the southern Brazilian wetlands to environmental changes, which may help address the extent of anthropogenic influence and response to future climate change, thereby contributing for the conservation and management of the coastal ecosystems.

Paleoenvironmental reconstruction of the headwaters of the preto river, Minas Gerais state, Brazil, through siliceous bioindicators

The Preto River, located in the municipality of São Gonçalo do Rio Preto (Minas Gerais, Brazil), is one of the few perennial watercourses in the semi-arid region of northeastern Minas Gerais and is essential for the socio-environmental dynamics of the region. Its headwaters are located in the Southern Espinhaço Mountain Range, which is characterized by predominantly quartzite lithologies that form a relief with dissected altimetric variations interspersed with planation surfaces, where the climate is high-altitude tropical. The soils are poorly developed and small fragments of forest, together with phytophysiognomies of the Cerrado Biome such as wet grasslands (Campo limpo úmido), colonize the peatland ecosystems. The aim of this study is to contribute to the paleoenvironmental reconstruction of the headwaters of the River Preto, using sliliceous bioindicators associated with other indicators (multi-proxy analysis). It was possible to infer that there was no change in phytophysiognomies from around 23,330 cal years BP to the present. However, there were 4 periods with oscillations between a cooler, drier environment in the Late Pleistocene, which gradually became warmer and more humid in the Late Holocene. Period 1 (Late Pleistocene) corresponds to the interval from before 23,300 to 13,500 cal years BP, in which the low tree density index (D/P) indicates vegetation similar to the current. Period 2 (end of the Late Pleistocene) corresponds to the period between 13,500 and 11,700 cal years BP. The increase in the D/P index indicates a small expansion of tree vegetation, albeit with the continued predominance of open vegetation. The appearance of Arecaceae characteristic phytoliths, associated with the drop in the climate index (Ic%), indicates an increase in temperature in relation to the previous phase. Period 3 (Pleistocene to Holocene transition) corresponds to the period from 11,700 to 10,000 cal years BP. It is a little colder and drier than the previous period, as observed from the increase in the climate index (Ic%). This period includes the Younger Dryas event, which was colder and drier than currently and had a global influence. Period 4 (Holocene) corresponds to the last 10,000 cal years BP. During this period there was no change in vegetation cover, the D/P and Pa/P indexes remain low, and there is a tendency towards a gradual increase in temperature. The use of siliceous bioindicators associated with other proxies and the regional and global events that occurred during the Quaternary in the analyzed sediments enabled the observation that, at least in the last 23,300 cal years BP, there have been no changes in the local vegetation cover. However, there were small expansion episodes or decreases in the density of tree and Arecaceae cover, as well as a tendency towards increased temperature and humidity in the Upper Holocene. The results proved to be useful for paleoenvironmental research and highlighted how peatland ecosystems are fundamental for understanding the evolution of the landscape and for reconstructing the environmental history of the Cerrado biome.

Shrub decline and expansion of wetland vegetation revealed by very high resolution land cover change detection in the Siberian lowland tundra

Vegetation change, permafrost degradation and their interactions affect greenhouse gas fluxes, hydrology and surface energy balance in Arctic ecosystems. The Arctic shows an overall “greening” trend (i.e. increased plant biomass and productivity) attributed to expansion of shrub vegetation. However, Arctic shrub dynamics show strong spatial variability and locally “browning” may be observed. Mechanistic understanding of greening and browning trends is necessary to accurately assess the response of Arctic vegetation to a changing climate. In this context, the Siberian Arctic is an understudied region. Between 2010 and 2019, increased browning (as derived from the MODIS Enhanced Vegetation Index) was observed in the Eastern Siberian Indigirka Lowlands. To support interpretation of local greening and browning dynamics, we quantified changes in land cover and transition probabilities in a representative tundra site in the Indigirka Lowlands using a timeseries of three very high resolution (VHR) (0.5 m) satellite images acquired between 2010 and 2019. Using spatiotemporal Potts model regularization, we substantially reduced classification errors related to optical and phenological inconsistencies in the image material. VHR images show that recent browning was associated with declines in shrub, lichen and tussock vegetation and increases in open water, sedge and especially Sphagnum vegetation. Observed formation and expansion of small open water bodies in shrub dominated vegetation suggests abrupt thaw of ice-rich permafrost. Transitions from open water to sedge and Sphagnum, indicate aquatic succession upon disturbance. The overall shift towards open water and wetland vegetation suggests a wetting trend, likely associated with permafrost degradation. Landsat data confirmed widespread expansion of surface water throughout the Indigirka Lowlands. However, the increase in the area of small water bodies observed in VHR data was not visible in Landsat-derived surface water data, which suggests that VHR data is essential for early detection of small-scale disturbances and associated vegetation change in permafrost ecosystems.

Feedback between vegetation, flow, and deposition: A study of artificial vegetation patch development

Laboratory experiments examined how the hydrodynamic interaction between neighboring patches of model vegetation impacted deposition and the potential for patch expansion. The evolution of the vegetated region was modeled experimentally by introducing new artificial vegetation into regions of enhanced deposition. The study began with a pair of side-by-side, circular patches, each of diameter D = 10.5 cm, constructed from circular cylinders (d = 3.2 mm) that extended through the flow depth. The interaction between the patches generated a zone of enhanced deposition on the centerline between the patches, and this zone had a much greater longitudinal extent than the region of enhanced deposition formed behind an individual patch. This suggested that the interaction between patches could enhance streamwise growth. In addition, deposition on the centerline eventually led to the merger of the two adjacent patches, a mechanism for lateral patch growth. Finally, regions of diminished velocity on the outside edge of the patch pair were observed to enhance deposition over a lateral distance of 0.5D. These observations of lateral growth stand in contrast to previous descriptions of vegetation-flow interaction that emphasize negative feedbacks for lateral growth and positive feedbacks only for streamwise growth. Although lateral growth was observed, the tendency for enhanced deposition (growth) extended much farther in the streamwise direction (40D) than in the lateral direction (0.5D), such that vegetation expansion was dominated by streamwise growth.

Soil predictors are crucial for modelling vegetation distribution and its responses to climate change

Bioclimatic envelope models have been extensively used to predict the vegetation dynamics in response to climate changes. However, they are prone to the uncertainties arising from General Circulation Models (GCMs), classification algorithms and predictors, with low-resolution results and little detail at the regional level. Novel research has focused on the improvement of these models through a combination of climate and soil predictors to enhance ecological consistency. In this framework, we aimed to apply a joint edaphoclimatic envelope to predict the current and future vegetation distribution in the semiarid region of Brazil, which encompasses several classes of vegetation in response to the significant environmental heterogeneity. We employed a variety of machine learning algorithms and GCMs under RCP 4.5 and 8.5 scenarios of Coupled Model Intercomparison Project Phase 5 (CMIP5), in 1 km resolution. The combination of climate and soil predictors resulted in higher detail at landscape-scale and better distinction of vegetations with overlapping climatic niches. In forecasts, soil predictors imposed a buffer effect on vegetation dynamics as they reduced shifts driven solely by climatic drift. Our results with the edaphoclimatic approach pointed to an expansion of the dry Caatinga vegetation, ranging from an average of 16% to 24% on RCP 4.5 and RCP8.5 scenarios, respectively. The shift in environmental suitability from forest to open and dry vegetation implies a major loss to biodiversity, as well as compromising the provision of ecosystem services important for maintaining the economy and livelihoods of the world's largest semiarid population. Predicting the most susceptible regions to future climate change is the first step in developing strategies to mitigate impacts in these areas.

Palynological evidence of Middle Pleistocene palaeoenvironmental changes from the ‘Buca dell’Onice’ flowstone (Alpi Apuane, Central Italy)

AbstractBuca dell’Onice di Monte Girello is a small cave located in the Alpi Apuane (central Italy). It preserves an exceptionally thick flowstone deposited intermittently during the Middle Pleistocene. Two main depositional cycles, separated by a physical discontinuity, have been recognised and described. This discontinuity and the top surface of the flowstone attest to two main phases of interrupted growth related to palaeoenvironmental and palaeoclimate changes. Pilot palynological investigations support the existence of such changes. Despite the high number of barren pollen samples and the overall very low concentration of pollen grains per gram of sediment, palynology furnishes some interesting insights especially regarding floral composition, vegetation cover and local to regional climate. The pollen record also contributes to the definition of the stratigraphic distribution of taxa no longer growing in this area (i.e. Carya and Picea). According to the pollen assemblage characteristic of arboreal vegetation cover, the flowstone was deposited predominantly during humid phases under both warm and cool climate conditions (interglacials/interstadials and at the end of interglacials). The warm and cool phases correspond, respectively, to increases of mixed thermophilous forest taxa and montane arboreal taxa. On the other hand, the pollen record does not show the major expansion of open vegetation associated with the coldest and driest conditions, which apparently fall at the main middle discontinuity and at the top interruption of the flowstone. Previous data permit changes in precipitation to be identified as one of the major limiting factors for the growth of this flowstone, probably in a period including MISs 13‐10. The more significant lithological features of the flowstone as well as the vegetal and climate signatures suggest that its development principally represents a response to global events including teleconnections active between the Mediterranean and the Atlantic circulation, with minor contribution from local factors.

Rapid soil and vegetation changes at regional scale in continental Antarctica

Antarctica is the last pristine environment on Earth, its biota being adapted to the harsh and extreme polar climate. Until now, soil formation and vegetation development in continental Antarctica were considered very slow due to the extreme conditions of this polar desert. Since the austral summer 2002/2003, a long-term monitoring network of the terrestrial ecosystems (soils, vegetation, active layer thickness) has been established at Victoria Land (VL) across a > 500 km latitudinal gradient of coastal sites (73°–77°S). In only one decade large ecosystem changes were detected. Climate was characterized by a significant increase of thawing degree days in northern VL and of autumn air temperature. No extreme climatic events (such as hot spells) where detected in the study period. Soil chemistry suffered large quantitative changes, clearly indicating rapid pedogenetic processes. In most soils the upper layers exhibited a strong alkalinization (pH increases up to 3 units) and increases in conductivity, anions and cations (in particular of SO4 and Na). The largest changes were observed in soils with low vegetation cover. Statistically significant differences in soil chemistry were detected between soils with high and low vegetation cover, the former showing lower pH, conductivity, Na and Cl. Most plots exhibited changes of total cover, species richness and floristic composition, with vegetation expansion in soils with low vegetation cover and the largest increase recorded at Apostrophe Island (northern VL). Principal Component Analysis (PCA) identified the main trend of vegetation change, with a shift from lower to higher cover and a secondary trend of change associated with a gradient of water availability, consistent with an increase in water instead of snow. Redundancy analysis (RDA) identified the trend of change in soil chemistry with increases in pH, conductivity, anions and cations associated with the concomitant decrease in C, N, NO3, PO4. The RDA confirmed that soil changes were associated with a gradient of vegetation change (from low to high cover) as well as of water availability, as already indirectly outlined by the PCA. Field manipulation experiments carried out at five locations of the network between 73°S and 77°S, simulating increases of precipitation from snow or water additions didn’t induce changes in soil pH, indicating that pulse events of snow accumulation or melting could not trigger persistent soil pH changes. These data allow hypothesize the occurrence of a main ecosystem change occurring at regional scale at Victoria Land. The slight air warming and its consequences on soil chemistry and vegetation, further highlight the sensitivity of the fragile Antarctic ecosystems to the consequences of even small changes in climate.

Late Holocene climate and land-use history in the Mongolian Altai Mountains: Combined evidence from palynological, macro-charcoal and tree-ring analyses

The Mongolian Altai is an ecologically sensitive region in Central Asia where changes in climate and anthropogenic activities have a strong impact on the forest-steppe vegetation. We combine high-resolution data (pollen, non-pollen palynomorphs (NPP), charcoal) of two new sedimentological archives from the Altai Tavan Bogd National Park with dendrochronological analyses on Larix sibirica trees to study climatic changes and human landscape interactions over the last 1,350 cal yr BP. Multi-proxy palaeoenvironmental reconstructions show that the present landscape is a result of both short- and long-term climatic variations and of locally different land use. Combined evidence suggests that in the period from 1,350 to 670 cal yr BP western Mongolia was impacted by a rather cold and dry climate, followed by an episode of improved warmer and wetter climatic conditions from 670 to 400 cal yr BP. From around 400 to 200 cal yr BP, the Little Ice Age influenced the forest-steppe vegetation in the area, favoring an expansion of steppe vegetation. Over the last 70 years, climatic conditions were characterized by markedly high summer temperatures. NPP data reveal periods of increased grazing activities in the forests especially during unfavorable climatic periods. During the late 20th century, a decreasing deposition of coprophilous fungal spores with a simultaneous slight decrease of Larix sibirica forest suggest that economic timber harvesting seemed to be of more significance for forest degradation than pastural activities.

Varying snow and vegetation signatures of surface-albedo feedback on the Northern Hemisphere land warming

Changes in snow and vegetation cover associated with global warming can modify surface albedo (the reflected amount of radiative energy from the sun), therefore modulating the rise of surface temperature that is primarily caused by anthropogenic greenhouse-gases emission. This introduces a series of potential feedbacks to regional warming with positive (negative) feedbacks enhancing (reducing) temperature increase by augmenting (decreasing) the absorption of short-wave radiation. So far our knowledge on the importance and magnitude of these feedbacks has been hampered by the limited availability of relatively long records of continuous satellite observations. Here we exploit a 31 year (1982–2012) high-frequency observational record of land data to quantify the strength of the surface-albedo feedback on land warming modulated by snow and vegetation during the recent historical period. To distinguish snow and vegetation contributions to this feedback, we examine temporal composites of satellite data in three different Northern Hemisphere domains. The analysis reveals and quantifies markedly different signatures of the surface-albedo feedback. A large positive surface-albedo feedback of +0.87 (CI 95%: 0.68, 1.05) absorbed solar radiation per degree of temperature increase is estimated in the domain where snow dominates. On the other hand the surface-albedo feedback becomes predominantly negative where vegetation dominates: it is largely negative (−0.91 (−0.81, −1.03) ) in the domain with vegetation dominating, while it is moderately negative (−0.57 (−0.40, −0.72) ) where both vegetation and snow are significantly present. Snow cover reduction consistently provides a positive feedback on warming. In contrast, vegetation expansion can produce either positive or negative feedbacks in different regions and seasons, depending on whether the underlying surface being replaced has higher (e.g. snow) or lower (e.g. dark soils) albedo than vegetation. This work provides fundamental knowledge to model and predict how the surface-albedo feedback will evolve and affect the rate of regional temperature rise in the future.

Spatial heterogeneity of vegetation extent and the response to water level fluctuations and micro-topography in Poyang Lake, China

Wetland vegetation dynamics are vital but difficult to understand due to complex impact factors and their spatial heterogeneities. Poyang Lake, the largest freshwater lake in China, is well-known for its ecological importance as a floodplain wetland. However, heterogeneity in vegetation extent and its response to water regimes across different geomorphic units of Poyang Lake remain unclear to date. To address this gap, Landsat images acquired during dry seasons from 1987 to 2018 were selected to explore vegetation extent and its response to water level fluctuations across multiple elevation bands and four wetland types, namely Riparian Wetland (RW), Delta Wetland (DW), Dish-shaped Wetland (DSW), and Fan-shaped wetland (FSW). Results show that vegetation extent in lower elevation bands of the four wetland types increased remarkably with an average increase rate of 0.53 km2/year between 2003 and 2018 compared to −0.17 km2/year−1 during 1987 to 2002. Hydrological variables indicating high-flow events negatively affected vegetation extent in DSW while variables indicating low-flow events appear to be positive for vegetation extent in RW, DW, and FSW. Over-long floods as happened in 2016 has caused fatal damage to vegetation extent in DSW. In addition, extreme droughts in recent years caused by the Three Gorges Dam promoted significant (p < 0.05) vegetation expansion in lower elevation bands of RW, DW, and FSW, but a deterioration of vegetation extent in higher elevation bands, making Poyang Lake at risk of shrinkage and degradation. Human impacts on the evolution Poyang Lake system have caused wide concern, which also contribute to the proposal of Poyang Lake water control structure. Heterogeneity in vegetation extent and their response to water regimes across Poyang Lake provide precise spatial information for restoration efforts of the wetland ecosystem.

Eutrophication management in a Great Lakes wetland: examination of the existence of alternative ecological states

AbstractThe degradation and loss of ecologically important wetlands has been a topical issue in the Great Lakes region, where 60–80% of the coastal wetlands have been lost since the 1800s. The present modeling study aims to guide the restoration efforts in Cootes Paradise marsh, one of the most degraded shallow wetlands in Southern Ontario. We use a process‐based eutrophication model designed to reproduce the biotic competition among multiple phytoplankton and macrophyte functional groups. Our primary focus is to offer guidelines for wetland restoration by characterizing the ecophysiological processes of the autotrophic assemblage, such as the nutrient uptake from the water column and/or the sediment pore waters, the relative ability to harvest light and fuel photosynthesis, and temperature control of the algal/macrophyte growth and basal metabolism. We predict that the additional reduction of external phosphorus loading in Cootes Paradise could induce an abrupt, non‐linear shift from the current turbid phytoplankton‐dominated state to a desirable clear macrophyte‐dominated state. The emergence of this critical (or tipping) point, where the shift to another ecological state may occur, can be accelerated by the presence of a thriving macrophyte community with an enhanced ability to sequester phosphorus. However, it may also be delayed by the presence of a suite of biogeochemical mechanisms (often referred to as “feedback loops”), such as the remobilization of legacy P due to sediment diagenetic processes, wind resuspension, bioturbation, hydraulic loading from local tributaries, water‐level fluctuations, and the leachable P pool of dead plant material that can be returned into the water column through senescence. Our study identifies the restoration actions required to minimize the likelihood of prolonged hysteresis and to facilitate a shift to a desirable ecological state in the foreseeable future. The areal expansion of aquatic vegetation will not only lead to the establishment of a thriving meadow and emergent vegetation community, but may also pave the way for submerged macrophytes through a suite of synergistic mechanisms. Additional point‐source loading reductions will facilitate the transition to an alternative stable clear macrophyte‐dominated state, but could also consolidate the future resilience of the marsh.

Quantifying of surface urban cool island in arid environments case study: Isfahan metropolis

The cities that are built on the arid biomes with the hot and dry climates can adjust the temperature (oasis effect) and create the urban cool island (UCI) during the day. As the background climate of the Isfahan metropolis is warm and dry, we can expect an UCI during the day. The MODIS land cover product data were used to distinguish between the urban and nonurban areas. The MODIS/Terra/LST data from 2000 to 2016 were then used for day-time view to examine the UCI. In the next step, the UCI intensity index was calculated by the spatial correlation representative pixel method for the city and the background. This study showed that due to the passage of the Zayandehrood river from the middle of the city and the expansion of vegetation in the urban environment, the metropolitan area of Isfahan is 3.5° cooler than the suburban barren lands during the day. The UCI intensity index has been intensified over the last few years and has fallen below − 4.5°. The studies have shown that the UCI intensity index is weakened during the cold months and intensified in the warm months of the year. The seasonal changes in UCI intensity in the metropolitan area of Isfahan can be related to the high variability of vegetation throughout the year.

Acceleration of vegetation dynamics in hydrologically connected wetlands caused by dam operation

AbstractThe dynamic responses of wetlands to upstream water conservancy projects are becoming increasingly crucial for watershed management. Poyang Lake is a dynamic wetland system of critical ecological importance and connected with the Yangtze river. However, in the context of disturbed water regime in Poyang Lake resulting from human activities and climate change, the responses of vegetation dynamics to the Three Gorges Dam (TGD) have not been investigated. We addressed this knowledge gap by using daily water level data and Landsat images from 1987 to 2018. Landsat images were acquired between October and December to ensure similar phenological conditions. Object‐oriented Artificial Neural Network Regression for wetland classification was developed based on abundant training and validation samples. Interactions between vegetation coverage and water regimes pre and post the operation of the TGD were compared using classification and regression trees and the random forest model. Since the implementation of the TGD in 2003, Poyang Lake has become drier, especially during the dry season. A more rapid plant growth rate was observed post TGD (44.74 km2 year−1) compared to that of the entire study period (12.9 km2 year−1). Average water level for the antecedent 20 days most significantly affected vegetation before 2003, whereas average water level for the antecedent 5 or 10 days was more important after 2003. The impoundment of the TGD after the flood season accelerated the drawdown processes of Poyang Lake, and the rapidly exposed wetlands accelerated vegetation expansion during the dry seasons, resulting in shrinkage and degradation of the lake area. This study deepens our knowledge of the influences of newly developed dams on lakes and rivers.

Assessment of the current situation of lake siltation and swamping in the Jiuzhaigou World Natural Heritage Site after the earthquake

地震及其伴生地貌过程破坏山体植被和土壤，产生的松散物源进入湖泊可能会带来泥沙淤积与沼泽化的风险.为探明九寨沟8.8大地震后湖泊淤积与沼泽化现状，以及松散物源的影响，本研究选取九寨沟景区内4个淤积与沼泽化程度不同的湖泊，进行了实地勘查，采用植被指标为主、促淤效应为辅的沼泽化综合评价方法进行现状评价；同时，结合无人机获取的湖泊周边环境和受灾程度信息，探讨了地震后伴生地貌过程及产物对九寨沟湖泊淤积与沼泽化的影响.结果表明：（1）四个湖泊的沼泽化发展模式均是由岸边向湖心推进.（2）各湖淤积与沼泽化程度空间分布特征存在差异，按发展程度从高到低依次表现为：五花海沼泽化程度最高，西北侧处于沼泽化后期（沼泽化指标值为[3，4]）；镜海次之，局部处于沼泽化盛期（沼泽化指标值为[1.5，3]）；犀牛海再次，仅出入水口处于沼泽化前期（沼泽化指标值为[1.5，2.5]）；箭竹海最低，整体处于沼泽化前期（沼泽化指标值为[0，1.5]）.（3）松散物源输入造成湖岸淤积程度增加、促进水生植被扩张，是造成九寨沟湖泊淤积和沼泽化发展的重要原因.管理者需重点关注小微湖泊、出入水口、受灾点的沼泽化发展情况.;The earthquake and its associated geomorphic processes destroy mountain vegetation and soil. The loose material may bring the risk of siltation and swamping after entering the lake. To investigate the current situation of lake siltation and swamping in Jiuzhaigou after the earthquake as well as the impact of the loose materials, this study selected four lakes in Jiuzhaigou scenic area with different siltation and swamping and then conducted the field surveys. The comprehensive evaluation method of swamping was adopted to evaluate the current situation utilizing vegetation indicators as the main principle and siltation promotion effect as the subsidiary principle. Meanwhile, the unmanned aerial vehicle was used to acquire the information of the surrounding environment as well as the damage degree of the lake and the impact of loose material from seismic damage on the siltation and swamping of Jiuzhaigou lakes were further discussed. The results show that:(1) The swamping development model of the four lakes all evolved from the shore to the center of the lake. (2) The spatial distribution characteristics of siltation and swamping degree of various lakes are different, and the degree of development from high to low is shown as follows:Lake Colorful has the highest swamping degree with the northwest side being in the late stage of swamping (index value[3, 4]). Lake Mirror ranks the second with part of it having a high level of swamping (index value[1.5, 3]). The next is Lake Rhino with only the inlet and outlet of the lake being in the early stage of swamping (index value[1.5, 2.5]). Last is the Lake Arrow Bamboo with an overall swamping degree being in the early stage (index value[0, 1.5]). (3) The large amount of loose material caused by seismic damage increases the siltation of the lakeshore and promotes the expansion of aquatic vegetation, which is the main reason for the development of siltation and swamping of Jiuzhaigou lakes. Managers in charge should focus on the development of swamping on small lakes, inlets, outlets, and disaster-stricken spots.

Riparian Vegetation Expansion Due to the Change of Rainfall Pattern and Water Level in the River

Riparian Vegetation Expansion Due to the Change of Rainfall Pattern and Water Level in the River

Imprint of Climate Change on Pan-Arctic Marine Vegetation

The Arctic climate is changing rapidly. The warming and resultant longer open water periods suggest a potential for expansion of marine vegetation along the vast Arctic coastline. We compiled and reviewed the scattered time series on Arctic marine vegetation and explored trends for macroalgae and eelgrass (Zostera marina). We identified a total of 38 sites, distributed between Arctic coastal regions in Alaska, Canada, Greenland, Iceland, Norway/Svalbard, and Russia, having time series extending into the 21st Century. The majority of these exhibited increase in abundance, productivity or species richness, and/or expansion of geographical distribution limits, several time series showed no significant trend. Only four time series displayed a negative trend, largely due to urchin grazing or increased turbidity. Overall, the observations support with medium confidence (i.e., 5–8 in 10 chance of being correct, adopting the IPCC confidence scale) the prediction that macrophytes are expanding in the Arctic. Species distribution modeling was challenged by limited observations and lack of information on substrate, but suggested a current (2000–2017) potential pan-Arctic brown macroalgal distribution area of 655,111 km2(140,433 km2intertidal, 514,679 km2subtidal), representing an increase of about 45% for subtidal- and 8% for intertidal macroalgae since 1940–1950, and associated polar migration rates averaging 18–23 km decade–1. Adjusting the potential macroalgal distribution area by the fraction of shores represented by cliffs halves the estimate (340,658 km2). Warming and reduced sea ice cover along the Arctic coastlines are expected to stimulate further expansion of marine vegetation from boreal latitudes. The changes likely affect the functioning of coastal Arctic ecosystems because of the vegetation’s roles as habitat, and for carbon and nutrient cycling and storage. We encourage a pan-Arctic science- and management agenda to incorporate marine vegetation into a coherent understanding of Arctic changes by quantifying distribution and status beyond the scattered studies now available to develop sustainable management strategies for these important ecosystems.