Series Of Vegetation Research Articles

The local cooling potential of land restoration in Africa

Land restoration is becoming increasingly popular as a climate change mitigation and adaptation measure. It is suggested that resulting vegetation changes can impact the local surface temperature through biophysical processes such as albedo warming and evaporative cooling. Yet, the potential effect of land restoration on the local surface temperature in Africa remains uncertain. In this study, we use Terra MODIS time series of vegetation, albedo, and land surface temperature to determine vegetation-temperature relationships at a continental scale. We show that vegetation-albedo and vegetation-temperature relationships do not only vary spatially across Africa but also temporally over different time scales, with strong cooling effects in semi-arid environments. Furthermore, we predict that land restoration can decrease local land surface temperature by around 0.2 Kelvin on average. This study gives a more detailed insight into where future land restoration provides additional positive climate impacts, and where land restoration may instead warm the local environment.

Exploring the driving forces of potential marsh wetlands formation and distribution in the Qilian Mountains of Qinghai, China

The formation and distribution of marsh wetlands are influenced by both climate changes and human activities. Quantifying the driving factors of marsh wetlands is essential for understanding the sustainable utilization of wetland ecosystems. The current study simulated the potential marsh wetlands’ spatial distribution in the Qilian Mountains of Qinghai (QMQ) by a random forest (RF) model with a series of environmental indicators, including climate, vegetation, soil, topography, and human activity factors in 2020. Simultaneously, a structural equation modeling (SEM) was utilized to explore driving factors of formation and distribution of marsh wetlands. Results showed that: (1) The potential marsh wetlands area was determined to be 2502.01 km2 in the QMQ, mainly distributed in the watershed source and along the river. (2) Normalized difference vegetation index (NDVI), normalized difference water index (NDWI), digital elevation model (DEM), fraction vegetation coverage (FVC), and ground surface temperature (GST) were the most critical factors in marsh wetland simulation, with the relative importance index of 11.14 %, 9.70 %, 9.07 %, 8.39 %, and 6.50 %, respectively. (3) The topography acted on the potential marsh wetlands’ distribution by influencing the nutrient input function of potential marsh wetlands (indirect effect 0.28). The climate was the fundamental factor that directly controls the distribution of potential marsh wetlands (direct effect 0.44), and vegetation had a total effect of 0.24. The current study may provide information for policy decisions on wetland conservation and restoration.

New plant communities to define the southern boundary of the European Atlantic Province in mainland Portugal

This study identifies and analyzes the plant communities that allow the definition of the geographic limits between Temperate and Mediterranean macrobioclimates, for the center of Portuguese mainland. The altitude of Serra da Estrela, Açor and Lousã, combined with the increase in atmospheric humidity, allows the presence of vegetation typical of a Temperate macrobioclimate. Thus, based on the phytosociological methodology, floristic relevés were carried out in order to identify the series of vegetation existing in these territories. Through these relevés carried out, four new plant associations were identified: Cytisetum grandifloro-striati ass. nova, Scrophulario grandiflorae-Sambucetum nigrae ass. nova, Pruno lusitanicae-Coryletum avellanae ass. nova that lives in the submediterranean bioclimatic variant, mesotemperate humid to hyper-humid. A new association namely Genisto falcatae-Quercetum broteroanae ass. nova with two subassociations were also identified. Based on the vegetation distribution, new biogeographic limits are proposed. Thus, it was intended to identify the southern limits of the European Atlantic Province (Atlantic Orolusitania Subrovince) based on the vegetation cover, namely the distinction between the Estrela Sierran District and a new Biogeographical District, the Alvo-Gardunhense.

Floristic Survey of Deedwana Tehsil, District Nagaur, Rajasthan

Abstract: The present research paper presents a comprehensive floristic study of Deedwana Tehsil, District Nagaur, Rajasthan, aimed at documenting the plant diversity and understanding its ecological significance. The study involved extensive field surveys, specimen collections, and interviews with local experts to identify and classify the plant species within the region. The results revealed a diverse and unique assemblage of plant species in Deedwana Tehsil, representing various vegetation types and habitats. The enumeration of identified plant species showcased a rich floral diversity, including both native and exotic species. A total of 331 species of angiospermic plants belonging to 218 genera and 65 families were recorded including four series of natural vegetation in Deedwana tehsil: 1. Acacia nilotica-Maytenus emarginata-Balanites aegyptiaca series 2. Prosopis cineraria-Crotalaria burhia-Leptadaenia pyrotechnica series. 3. Prosopis cineraria- Capparis decidua-Tephrosia purpuria series and 4. Suaeda fruticosa-Cressa cretica–Heliotropium curassavicum series. (Quereishi, 2018). The study also provide information about the traditional uses of plants by local communities, providing insights into their cultural significance and medicinal applications. Traditional knowledge holders and local healers shared valuable information about medicinal plant practices, adding to the understanding of the region's traditional healthcare systems. The study also analyzed the major threats faced by the flora of Deedwana Tehsil, such as habitat loss, overgrazing, climate change, and unsustainable resource extraction. These findings highlighted the urgent need for conservation and sustainable management initiatives to protect the region's botanical wealth

A generalized framework for drought monitoring across Central European grassland gradients with Sentinel-2 time series

Fractional cover time series of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and soil from remote sensing provide essential detail to understand how grasslands are affected by recent and future drought periods in the 21st century. In this regard, Sentinel-2A/B offer frequent large-area observations, which have not yet been fully exploited for a spatially continuous drought monitoring of highly dynamic Central European grasslands. In this study, we developed a generalized drought monitoring framework for Central European grasslands linking Sentinel-2 data, field survey information, and spectral unmixing. We first implemented a consistent and repeatable strategy to obtain a grassland spectral library supported by the Europe-wide Land Use/Cover Area frame statistical Survey (LUCAS) and multitemporal Sentinel-2 data. Our library captured the spectral variability of PV, NPV, and soil cover from 12 grassland areas distributed along typical environmental and land use gradients of Central Europe. We trained a generalized regression-based unmixing model with synthetic data generated from the spectral library and compared fractional cover estimates to a multitemporal reference dataset. PV, NPV, and soil were estimated with good accuracy, achieving MAEs of 6.54%, 13.7%, and 12.2%, respectively. Local unmixing models trained on area-specific library subsets were overall outperformed by the generalized model highlighting the value of a comprehensive grassland library for generalized spectral unmixing. Based on fractional cover time series from 2017 to 2021, we calculated time series of the grassland-specific Normalized Difference Fraction Index (NDFI) capturing proportions of NPV and soil relative to PV. Comparison of annual growing season drought metrics derived from the NDFI to annual meteorological drought statistics from the Standardized Precipitation Evapotranspiration Index (SPEI) as well as the Soil Moisture Index (SMI) revealed widespread drought impacts on grasslands during the persistent drought period in Central Europe from 2018 to 2020. While impacts on grasslands overall closely followed meteorological and soil drought conditions, regionally varying drought metrics underline that local to regional environmental and hydrological conditions shaped the drought response of Central European grasslands. Our study emphasizes the value of combining Sentinel-2 data, field survey information, and spectral unmixing to enable drought monitoring across grassland gradients of Central Europe with Sentinel-2 time series.

Opposite eco-hydrological processes in flood and drought years caused comparable anomaly in dry-season canopy growth over southern Amazon

While the influences of droughts on Amazon rainforest have been extensively examined, little attention was paid to the extremely wet years characterized by low radiation which may limit the rainforest growth. Here, based on a series of satellite-observed vegetation and hydro-meteorological products, we found a two-stage canopy growth anomaly in the record-breaking wet year 2009, i.e. negative anomalies during April–July followed by positive ones during August–November. Our analysis suggests that, in April–July, low radiation associated with above-average rainfall and cloud cover was the most likely cause for negative anomalies in the canopy growth. In August–November, the rainfall and cloud cover were close to the average, but the solar radiation reaching the land surface was considerably above the average. This was because the atmospheric aerosols were extremely low, resulting from reduced biomass burning activities under the wet conditions. Large-scale positive anomalies in the canopy growth were observed during this 4 month period, mainly driven by the above-average radiation. During the severe drought year 2005, the forest canopy growth also experienced a two-stage process, but in the opposite order from the one in 2009. In April–July, enhanced canopy growth was observed in response to the above-average radiation. With the drought progress and soil water depletion, the canopy senescence was observed during the drought peak in August–November. Interestingly, if we examined the regional canopy growth anomaly during the typical dry season (i.e. July–September), both years showed similarly negative anomalies, but resulting from opposite eco-hydrological processes. This study identifies the explanation for the negative anomalies in the dry-season canopy growth over southern Amazon rainforest in both flood and drought years, and also underscores the necessity to separate different hydro-meteorological stages to better understand vegetation responses to extreme events.

A new association of relict maquis with Ptilostemon greuteri (Oleo-Ceratonion, Quercetea ilicis), located in a circumscribed area of north-western Sicily

This paper illustrates the results of a survey aimed at deepening available knowledge on the ecology of Ptilostemon greuteri (Asteraceae), a very rare palaeoendemic and relict nano-phanerophyte discovered about 15 years ago on Monte Inici, near Castellammare del Golfo (province of Trapani, north-western Sicily). Two plant communities characterised by P. greuteri are described in detail; they occur in the locus classicus and in a second, recently discovered stand, which is also very localised and threatened by fire. The field investigations revealed that the sites where the species grows are very similar from the ecological point of view; in fact, both of them are located on the steep slopes of deep gullies, benefitting from constantly cool and shady microclimatic conditions, and allowed to a) better identify the currently preferred habitat (ledges, screes at the base of cliffs), b) analyse from a floristic and phytosociological point of view the maquis communities where P. greuteri grows as co-dominant or dominant species, referable to the class Quercetea ilicis, c) to identify the syndynamic role that these coenoses play within the series and microgeoseries of local vegetation. As far as syntaxonomy is concerned, the Malvo olbiae-Ptilostemonetum greuteri ass. nova is described, a basiphilous, thermophilous and shade-tolerant maquis framed in the Oleo-Ceratonion alliance. Moreover, two subassociations are described: 1) typicum subass. nova, corresponding to a pioneer maquis community prevailing on the coarse, loose and mobile debris located along the slopes at the base of rock cliffs, where P. greuteri is clearly dominant and shows a nano-phanerophytic habitus, and 2) euphorbietosum bivonae subass. nova, a primary aspect found of the ledges of carbonate cliffs, where the species can play either a dominant or co-dominant role with other elements of the maquis (Euphorbia bivonae, Chamaerops humilis, etc.), sometimes showing a slightly smaller size.

Geobotanical field activities for learning landscape interpretation concepts and methods for university students

The landscapes of various areas of southern Spain are studied, for this we rely on the methodology previously established by other researchers, through which a complete diagnosis of a territory is reached, since the series and geoseries of vegetation are revealed. Being a study of natural reality, the abstract character presented by concepts such as sigmetum, sinassociation, series, geoserie, climatófilo, edafoxerofilo, catena; it is perfectly clarified to the student, which makes the student progress efficiently, coming to the fore the acquisition of practical knowledge compared to theoretical ones. For this reason practical teaching acquires preponderance, since it not only provides knowledge, but also development of cognitive and psychomotor skills, which are essential in the acquisition of skills and development of the individual's personality.

Влияние нанокомпозиций на основе производных легких фуллеренов на культурные растения в благоприятных и стрессовых условиях среды их обитания

The relevance of the new forms of ecologically safe, stable in composition, in functional activity, biodegradable preparations development with a complex positive effect on plants remains high and the presented work is devoted to acquaintance with the generalized results of interdisciplinary studies for the effect on the system of soil (soil substitute) - cultivated plants by nanocompositions created based on carbon (water-soluble polyhydroxylated, carboxylated and amino acid derivatives of fullerene C60) nanostructures with additions of microelements in certain concentration ratios. Based on the previously identified concentration ranges of the tested fullerene derivatives with a positive effect on plants when treating their seeds, introducing them into the soil, other root habitats and foliar exposure, their compositions with salts of microelements were developed and in a series of vegetation and field experiments under controlled favorable conditions and when modeling oxidative stress caused by UV-B irradiation, deficiency of soil moisture, deficiency of nutrients, phytopathogens, as well as in the natural conditions of the Leningrad region, the main mechanisms of positive impact (regulatory on vital systems, adaptogenic, immunomodulatory, protective) of the created nanocompositions on plants and the prospects of their application in plant growing are shown.

Influence of nanocompositions based on light fullerene derivatives on cultural plants under favorable and stress conditions of their habitat

The relevance of the new forms of ecologically safe, stable in composition, in functional activity, biodegradable preparations development with a complex positive effect on plants remains high and the presented work is devoted to acquaintance with the generalized results of interdisciplinary studies for the effect on the system of soil (soil substitute) - cultivated plants by nanocompositions created based on carbon (water-soluble polyhydroxylated, carboxylated and amino acid derivatives of fullerene C60) nanostructures with additions of trace elements in certain concentration ratios. Based on the previously identified concentration ranges of the tested fullerene derivatives with a positive effect on plants when treating their seeds, introducing them into the soil, other root habitats and foliar exposure, their compositions with salts of trace elements were developed and in a series of vegetation and field experiments under controlled favorable conditions and when modeling oxidative stress caused by UV-B irradiation, deficiency of soil moisture, deficiency of nutrients, phytopathogens, as well as in the natural conditions of the Leningrad region, the main mechanisms of positive impact (regulatory on vital systems, adaptogenic, immunomodulatory, protective) of the created nanocompositions on plants and the prospects of their application in plant growing are shown. Keywords: nanocompositions, water-soluble fullerenes C60, polyhydroxylated C60, carboxylated C60, amino acid derivatives C60, soil (soil substitute) --- plant system, production process, abiotic stresses, resistance.

Quantifying drought effects in Central European grasslands through regression-based unmixing of intra-annual Sentinel-2 time series

Severe droughts caused unprecedented impacts on grasslands in Central Europe in 2018 and 2019. Yet, spatially varying drought impacts on grasslands remain poorly understood as they are driven by complex interactions of environmental conditions and land management. Sentinel-2 time series offer untapped potential for improving grassland monitoring during droughts with the required spatial and temporal detail. In this study, we quantified drought effects in a major Central European grassland region from 2017 to 2020 using a regression-based unmixing framework. The Sentinel-2-based intra-annual time series of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and soil fractional cover provide easily interpretable quantities relevant for understanding drought effects on grasslands. Fractional cover estimates from Sentinel-2 matched in-situ conditions observed during field visits. The comparison to a multitemporal reference dataset showed the best agreement for PV cover (MAE = 7.2%). Agreement was lower for soil and NPV, but we observed positive relationships between fractional cover from Sentinel-2 and the reference data with MAE = 10.1% and MAE = 15.4% for soil and NPV, respectively. Based on the fractional cover estimates, we derived a Normalized Difference Fraction Index (NDFI) time series contrasting NPV and soil cover relative to PV. In line with meteorological and soil moisture drought indices, and with the Normalized Difference Vegetation Index (NDVI), NDFI time series showed the most severe drought impacts in 2018, followed by less severe, but persisting effects in 2019. Drought-specific metrics from NDFI time series revealed a high spatial variability of onset, duration, impact, and end of drought effects on grasslands. Evaluating drought metrics on different soil types, we found that grasslands on less productive, sandy Cambisols were strongly affected by the drought in 2018 and 2019. In comparison, grasslands on Gleysols and Histosols were less severely impacted suggesting a higher drought resistance of these grasslands. Our study emphasizes that the high temporal and spatial detail of Sentinel-2 time series is mandatory for capturing relevant vegetation dynamics in Central European lowland grasslands under drought.

Long-term dynamics of aquatic vegetation and the state of ecosystems of soda lakes in southeastern Transbaikalia

The cyclical nature of long-term changes in the annual amounts of atmospheric precipitation in Transbaikalia controls most of the processes in ecosystems. The paper briefly describes the long-term vegetation dynamics of soda lakes in the southeast of Transbaikal territory. These dynamics are driven by changes in abiotic parameters of the lakes, mainly water salinity and pH values. When the values of these indicators increase, the perennial succession series of vegetation of higher plants is as following: Helophytes + Neustophytes + Hydatophytes → Helophytes + Hydatophytes → Helophytes. The succession series of macrophytic algae is as following: Stigeoclonium sp. or Spirogyra sp. → Cladophora fracta + Charophyta → Enteromorpha intestinalis.

A palaeovegetation and diatom record of tropical montane forest fire, vegetation and hydroseral changes on Mount Kenya from 27,000–16,500 cal yr BP

Fire is an important ecological disturbance in moist tropical forests influencing vegetation composition and structure. Contemporary and historical records of forest fires in mountain forests of Kenya are limited to the past decades and have a strong anthropogenic influence for ignition patterns and fire suppression activities. Palaeoenvironmental geoarchives provide the temporal depth to investigate long-term (multidecadal-to-millennial) changes in fire activity. Here we use a sediment record from the Rumuiku wetland, located in a volcanic crater on the eastern flank of Mount Kenya that was radiocarbon dated and analysed for diatom, pollen and charcoal subfossils to produce a highly resolved time series of local hydroclimatic change, vegetation, and fire; respectively. This study focuses on the time during and following the global Last Glacial Maximum, a time of rapid warming and changing regional hydroclimate with relatively stable atmospheric CO2 and not yet intensive anthropogenic modification of ecosystems. Charcoal and pollen data support associated changes in vegetation-fire centred around 21,500 cal yr BP when Afromontane forests with predominant abundances of Juniperus, Podocarpus and other montane forest trees changed to Hagenia-dominated forests that are relatively more open and adapted to burn more frequently but with less intense fires.These transitions in ecosystem composition, distribution and structure support the important role of fire in driving and maintaining forest composition in the watershed and contributing to the spatial complexity of forests around the mountain. These changes in composition, structure and biomass occurred during a time of rapid Late Pleistocene climate warming, regional hydroclimatic drying, and slowly rising atmospheric CO2 from 27,000 to 16,500 cal yr BP, during and following the conditions of the global Last Glacial Maximum. Temperature, hydroclimate and atmospheric CO2 are well-known drivers of montane vegetation change in the tropics and the role of fire is shown here to be a contributing driver to the spatial heterogeneity of forest patches at long time scales. Vegetation modelling at spatial scales relevant to land management and conservation should include retrospective evidence of the range of drivers of ecological disturbance regimes.

Does hot and dry equal more wildfire? Contrasting short‐ and long‐term climate effects on fire in the Sierra Nevada, CA

AbstractClimate and wildfire are closely linked. Climate regulates wildfire directly over short timescales through its effect on fuel aridity and indirectly over long timescales through vegetation productivity and the structure and abundance of fuels. Prediction of future wildfire regimes in a changing climate often uses empirical studies that presume current relationships between short‐term climate variables and wildfire activity will be stationary in the future. This is problematic because landscape‐scale wildfire dynamics exhibit non‐stationarity, with both positive and negative feedback loops that operate at different temporal and spatial scales. This requires that such feedbacks are accommodated in a model framework from which wildfire dynamics are emergent rather than pre‐specified. We use a new model, RHESSys‐WMFire, that integrates ecohydrology with fire spread and effects to simulate a 60‐yr time series of vegetation, fuel development, and wildfire in a 6572‐ha watershed in the Southern Sierra Nevada, USA, with a factorial design of increased temperature and severe drought. All climate scenarios had an initial pulse of elevated area burned associated with high temperature, low precipitation, and high fine fuel loading. There were positive correlations between annual area burned and mean annual maximum temperature and negative correlations with annual precipitation, consistent with understood direct effects of climate on wildfire in this system. Decreased vegetation productivity and increased fine fuel decomposition were predicted with increased temperature, resulting in long‐term reduced fine fuels and area burned relative to baseline. Repeated extreme drought increased area burned relative to baseline and over the long‐term had substantially reduced overstory biomass. Overstory biomass was resilient to repeat wildfire under baseline climate. The model system predicts that the short‐term direct effects of climate on wildfire can differ from long‐term indirect effects such that the simple maxim hotter/drier equals more wildfire can be both true and false, depending on scale.

Canopy Adjustment and Improved Cloud Detection for Remotely Sensed Snow Cover Mapping

AbstractMaps of snow cover serve as early indicators for hydrologic forecasts and as inputs to hydrologic models that inform water management strategies. Advances in snow cover mapping have led to increasing accuracy, but unsatisfactory treatment of vegetation's interference when mapping snow has led to maps that have limited utility for water forecasting. Vegetation affects snow mapping because ground surfaces not visible to the satellite produce uncertainty as to whether the ground is snow covered. At nadir, the forest canopy obscures the satellite view below the canopy. At oblique viewing angles, the forest floor is obscured by both the canopy and the projection of tree profiles onto the forest floor. We present a canopy correction method based on Moderate Resolution Imaging Spectroradiometer satellite imagery validated with field observations that mitigates geometric and georegistration issues associated with changing satellite acquisition angles in forested areas. The largest effect from a variable viewing zenith angle on the viewable gap fraction in forested areas occurs in moderately forested areas with 30–40% tree canopy coverage. Cloud cover frequently causes errors in snow identification, with some clouds identified as snow and some snow identified as cloud. A snow‐cloud identification method utilizes a time series of fractional vegetation and rock land‐surface data to flag snow‐cloud identification errors and improve snow‐map accuracy reducing bias by 20% over previous methods. Together, these contributions to snow‐mapping techniques could advance hydrologic forecasting in forested, snow‐dominated basins that comprise an estimated one fifth of Northern Hemisphere snow‐covered areas.

Vegetation Phenology Influenced by Rapid Urbanization of The Yangtze Delta Region

Impacts of urbanization and climate change on ecosystems are widely studied, but these drivers of change are often difficult to isolate from each other and interactions are complicated. Ecosystem responses to each of these drivers are perhaps most clearly seen in phenology changes due to global climate change (warming climate) and urbanization (heat island effect). The phenology of vegetation can influence many important ecological processes, including primary production, evapotranspiration, and plant fitness. Therefore, evaluating the interacting effects of urbanization and climate change on vegetation phenology has the potential to provide information about the long-term impact of global change. Using remotely sensed time series of vegetation on the Yangtze River Delta in China, this study evaluated the impacts of rapid urbanization and climate change on vegetation phenology along an urban to rural gradient over time. Phenology markers were extracted annually from an 18-year time series by fitting the asymmetric Gaussian function model. Thermal remote sensing acquired at daytime and nighttime was used to explore the relationship between land surface temperature and vegetation phenology. On average, the spring phenology marker was 9.6 days earlier and the autumn marker was 6.63 days later in urban areas compared with rural areas. The spring phenology of urban areas advanced and the autumn phenology delayed over time. Across space and time, warmer spring daytime and nighttime land surface temperatures were related to earlier spring, while autumn daytime and nighttime land surface temperatures were related to later autumn phenology. These results suggest that urbanization, through surface warming, compounds the effect of climate change on vegetation phenology.

Land surface phenology and greenness in Alpine grasslands driven by seasonal snow and meteorological factors

Snow accumulation and melt have multiple impacts on Land Surface Phenology (LSP) and greenness in Alpine grasslands. Our understanding of these impacts and their interactions with meteorological factors are still limited. In this study, we investigate this topic by analyzing LSP dynamics together with potential drivers, using satellite imagery and other data sources. LSP (start and end of season) and greenness metrics were extracted from time series of vegetation and leaf area index. As explanatory variables we used snow accumulation, snow cover melt date and meteorological factors. We tested for inter-annual co-variation of LSP and greenness metrics with seasonal snow and meteorological metrics across elevations and for four sub-regions of natural grasslands in the Swiss Alps over the period 2003–2014. We found strong positive correlations of snow cover melt date and snow accumulation with the start of season, especially at higher elevation. Autumn temperature was found to be important at the end of season below 2000 m above sea level (m asl), while autumn precipitation was relevant above 2000 m asl, indicating climatic growth limiting factors to be elevation dependent. The effects of snow and meteorological factors on greenness revealed that this metric tends to be influenced by temperatures at high elevations, and by snow melt date at low elevations. Given the high sensitivity of alpine grassland ecosystems, these results suggest that alpine grasslands may be particularly affected by future changes in seasonal snow, to varying degree depending on elevation.

Estimating and understanding crop yields with explainable deep learning in the Indian Wheat Belt

Forecasting crop yields is becoming increasingly important under the current context in which food security needs to be ensured despite the challenges brought by climate change, an expanding world population accompanied by rising incomes, increasing soil erosion, and decreasing water resources. Temperature, radiation, water availability and other environmental conditions influence crop growth, development, and final grain yield in a complex nonlinear manner. Machine learning (ML) techniques, and deep learning (DL) methods in particular, can account for such nonlinear relations between yield and its covariates. However, they typically lack transparency and interpretability, since the way the predictions are derived is not directly evident. Yet, in the context of yield forecasting, understanding which are the underlying factors behind both a predicted loss or gain is of great relevance. Here, we explore how to benefit from the increased predictive performance of DL methods while maintaining the ability to interpret how the models achieve their results. To do so, we applied a deep neural network to multivariate time series of vegetation and meteorological data to estimate the wheat yield in the Indian Wheat Belt. Then, we visualized and analyzed the features and yield drivers learned by the model with the use of regression activation maps. The DL model outperformed other tested models (ridge regression and random forest) and facilitated the interpretation of variables and processes that lead to yield variability. The learned features were mostly related to the length of the growing season, and temperature and light conditions during this time. For example, our results showed that high yields in 2012 were associated with low temperatures accompanied by sunny conditions during the growing period. The proposed methodology can be used for other crops and regions in order to facilitate application of DL models in agriculture.

Environmental evaluation of MODIS-derived land units

A land stratification of the French territory had been previously performed based on time series of vegetation and texture indices. This stratification led to 300 radiometrically homogenous regions that were considered as land units (LUs). In this paper, we present a quantitative analysis of the LUs, with the aim of testing if these LUs are linked to landscape. In this sense, an evaluation of their thematic meaning in terms of environmental variables and land cover was performed. In order to achieve this, we first conducted a statistical analysis at national scale using a set of environmental variables and land cover by means of Moran’s autocorrelation index and Spearman rank correlation index. Second, to analyze the quality of the boundaries between neighboring LUs, we developed a method based on the Spearman rank correlation index calculated on test areas across the boundaries. The first analyses showed that the most explanatory variables of the LUs were land cover, topography and parent material. The boundaries analysis was applied at a regional scale (Pyrenean region), and showed that 89% of the boundaries were well explained by the land cover compositions. The results obtained support the hypothesis that time series of broad resolution remote-sensing images can capture landscape identities and produce LUs maps that have an environmental and land occupation sense.

Ground- and satellite-based evidence of the biophysical mechanisms behind the greening Sahel.

After a dry period with prolonged droughts in the 1970s and 1980s, recent scientific outcome suggests that the decades of abnormally dry conditions in the Sahel have been reversed by positive anomalies in rainfall. Various remote sensing studies observed a positive trend in vegetation greenness over the last decades which is known as the re-greening of the Sahel. However, little investment has been made in including long-term ground-based data collections to evaluate and better understand the biophysical mechanisms behind these findings. Thus, deductions on a possible increment in biomass remain speculative. Our aim is to bridge these gaps and give specifics on the biophysical background factors of the re-greening Sahel. Therefore, a trend analysis was applied on long time series (1987-2013) of satellite-based vegetation and rainfall data, as well as on ground-observations of leaf biomass of woody species, herb biomass, and woody species abundance in different ecosystems located in the Sahel zone of Senegal. We found that the positive trend observed in satellite vegetation time series (+36%) is caused by an increment of in situ measured biomass (+34%), which is highly controlled by precipitation (+40%). Whereas herb biomass shows large inter-annual fluctuations rather than a clear trend, leaf biomass of woody species has doubled within 27years (+103%). This increase in woody biomass did not reflect on biodiversity with 11 of 16 woody species declining in abundance over the period. We conclude that the observed greening in the Senegalese Sahel is primarily related to an increasing tree cover that caused satellite-driven vegetation indices to increase with rainfall reversal.