Vegetation Response Research Articles

Normal Difference Vegetation Index Simulation and Driving Analysis of the Tibetan Plateau Based on Deep Learning Algorithms

Global climate warming has profoundly affected terrestrial ecosystems. The Tibetan Plateau (TP) is an ecologically vulnerable region that emerged as an ideal place for investigating the mechanisms of vegetation response to climate change. In this study, we constructed an annual synthetic NDVI dataset with 500 m resolution based on MOD13A1 products from 2000 to 2021, which were extracted by the Google Earth Engine (GEE) and processed by the Kalman filter. Furthermore, considering topographic and climatic factors, a thorough analysis was conducted to ascertain the causes and effects of the NDVI’s spatiotemporal variations on the TP. The main findings are: (1) The vegetation coverage on the TP has been growing slowly over the past 22 years at a rate of 0.0134/10a, with a notable heterogeneity due to its topography and climate conditions. (2) During the study period, the TP generally showed a “warming and humidification” trend. The influence of human activities on vegetation growth has exhibited a favorable trajectory, with a notable acceleration observed since 2011. (3) The primary factor influencing NDVI in the southeastern and western regions of the TP was the increasing temperature. Conversely, vegetation in the northeastern and central regions was mostly regulated by precipitation. (4) Combined with the principal component analysis, a PCA-CNN-LSTM (PCL) model demonstrated significant superiority in modeling NDVI sequences on the Tibetan Plateau. Understanding the results of this paper is important for the sustainable development and the formulation of ecological policies on the Tibetan Plateau.

The spatial variation of hydrological conditions and their impact on wetland vegetation in connected floodplain wetlands: Dongting Lake Basin.

Wetland vegetation plays a crucial role in wetland conservation policy formulation and global climate change research. This study analyzed remotely sensed images of West Dongting Lake (DTL) Wetland from 1994 to 2020. This wetland is one of the most important wetlands in the world. At the pixel scale, we applied the histogram comparison approach, the range variability analysis (RVA) method, and the structural equation model (SEM) to quantify spatial changes in the hydrological conditions of wetland lakes and the ecological effects of environmental factors (precipitation, temperature, nutrients, water coverage) on vegetation. We propose a climate (C) - hydrological status (S) - vegetation response (R) (CSR) framework to elucidate the propagation relationships between climate, hydrology, and wetland vegetation conditions. The study found that the hydrological degradation promotes the succession of vegetation into the lake, and the distribution is concentrated in the northern Yangtze River inflow area. And the extent of hydrological changes in the West DTL region reached 34.5% during the flood period. In addition, the post-dam period showed a high degree of hydro-ecological failure, accounting for 65% of the total. Within the wetland area, there was a significant negative correlation between water coverage nutrient levels and bare vegetation within the lake area. Nutrient levels were also significantly negatively correlated with wetland vegetation conditions. Rainfall and temperature influence wetland vegetation by affecting the condition of the water body. This research provides valuable insights into managing wetland water resources and ecological restoration under the influence of climate change and human activities and provides a basis for decision-making.

Vegetation responses to snow cover removal and rainfall reduction in subalpine grasslands: Insights from a 4-year field experiment in the Spanish Pyrenees

ABSTRACT Reduced precipitation as well as warming may result in less snow accumulation in seasonally snow-covered areas, leading to lower minimum soil temperatures and more frequent and severe soil frosts. Therefore, plant stress is increased not only by drought in warmer months, but also by increased exposure to frost in cooler periods. We conducted a 4-year field experiment to evaluate the effects of diminished snowpack accumulation (through snow removal) and rainfall reduction (through rain-out shelters) on aboveground plant productivity, diversity and species composition of two subalpine grassland plant communities from the central region of the Spanish Pyrenees. We found that the snow removal treatment decreased minimum soil temperature by 0.5°C. Plant diversity decreased by 16 percent, although this effect was only observed in one of the grasslands studied. Aboveground primary productivity seemed to be unaffected. In contrast, we found that the rainfall reduction treatment negatively affected aboveground productivity of leguminous forb species, yet no effect on plant diversity was observed. Both treatments were important drivers of changes in plant species composition. Overall, our results suggest that the resilience of subalpine grasslands to snow cover removal and rainfall reduction treatments may depend on the specific community composition and dominant plant groups.

Human colonisation and vegetation response to Late Pleistocene to mid-Holocene climate variability in Northern Iberia based on a multiproxy analysis of the Atxurra cave-fill

Atxurra Cave (Berriatua, Northern Spain) contains an important Magdalenian archaeological assemblage comprising evidence of ephemeral occupation in the lower cave level and a unique assemblage of rock art. With the aim of understanding the palaeoenvironmental conditions and the nature of the human occupation, detailed micromorphological, mineralogical, palynological and anthracological analyses were undertaken near the entrance of the cave. The lower part of the excavated sequence comprises almost unfossiliferous silty units deposited over a thick speleothem deposit, which alternates with a sandy-silt matrix-supported microfacies dated about 33.4 kyr B.P. Palynological assemblage in this unit suggest regional vegetation was formed by montane pines, junipers and broadleaved elements like birch and hazel. Overlying units of brown clayey material, dated to ca. 19.7–18.4 kyr B.P., contain evidence of a Gravettian occupation with Noailles burins, and a palynoflora indicative of localized conifers with a dense herbaceous steppe understory, in an arid and cold climate. At ca. 15.5–14.5 kyr B.P. there is a return to meso-thermophilous tree and shrub taxa within a warmer and humid climate background, which may have favored the regional development of the Magdalenian culture. The uppermost unit, dated ca. 7.7–7 kyr B.P., reveals postglacial expansion of a mixed Atlantic forest with no signals of anthropization before the start of the Neolithic.

Early response of understory vegetation to the mass dieback of Norway spruce in the European lowland temperate forest

Spruce-dominated forests are commonly exposed to disturbances associated with mass occurrences of bark beetles. The dieback of trees triggers many physical and chemical processes in the ecosystem resulting in rapid changes in the vegetation of the lower forest layers. We aimed to determine the response of non-tree understory vegetation to the mass dieback of Norway spruce (Picea abies) in the first years after the disturbance caused by the European spruce bark beetle (Ips typographus) outbreak. Our study area was the Białowieża Biosphere Reserve covering the Polish part of the emblematic Białowieża Forest, in total 597 ​km2. The main data source comprised 3,900 phytosociological relevés (combined spring and summer campaigns) collected from 1,300 systematically distributed forest sites in 2016–2018 – the peak years of the bark beetle outbreak. We found that the understory responded immediately to mass spruce dieback, with the most pronounced changes observed in the year of the disturbance and the subsequent year. Shade-tolerant forest species declined in the initial years following the mass spruce dieback, while hemicryptophytes, therophytes, light-demanding species associated with non-forest semi-natural communities, as well as water-demanding forest species, expanded. Oxalis acetosella, the most common understory species in the Białowieża Forest, showed a distinct fluctuation pattern, with strong short-term expansion right after spruce dieback, followed by a gradual decline over the next 3–4 years to a cover level 5 percentage points lower than before the disturbance. Thus, our study revealed that mass spruce dieback selectively affects individual herb species, and their responses can be directional and non-directional (fluctuation). Furthermore, we demonstrated that the mass dieback of spruce temporarily increases plant species diversity (α-diversity).

Inferring vegetation response to drought at multiscale from long-term satellite imagery and meteorological data in Afghanistan

Drought caused by climate change has significantly increased vegetation vulnerability in Afghanistan during the last decades. This paper investigates vegetation response to drought at multiple scales across the country based on historical data from 1980 to 2020. It explores the multiscale relationships between drought as indicated by the grid-based standardised precipitation evapotranspiration index (SPEI) and vegetation condition as represented by the satellite-derived vegetation anomaly index (VAI). It also examines the links of dominant land cover with drought and their implications for agriculture. We assess the spatiotemporal correlations by integrating TerraClimate grids with timeseries data sourced from NOAA AVHRR (National Oceanic and Atmospheric Administration Advanced Very High-Resolution Radiometer), MODIS (Moderate Resolution Imaging Spectroradiometer) images and ESA CCI (European Space Agency Climate Change Initiative) land cover maps. We evaluated the effect of cumulative drought on predominant land covers. Our results show years 2000–2001 and 2017–2018 as the driest in the last four decades, and vegetation substantially correlated to drought with spatial and temporal variations across Afghanistan. The most sensitive vegetation response months are June to July and the most significant cumulative drought impacts on vegetation are 6 to 8 months. The predominant land covers more prone to negative effects under severe drought are (in order) shrubland, rainfed cropland, grassland, trees, and irrigated cropland. These findings suggest the sensitivity of vegetation to drought that future national scale drought management should be focused on. This study also demonstrates the usefulness of open-access data to researchers and planners in data-poor countries.

Investigating the Strength and Variability of El Niño–Southern Oscillation Teleconnections to Hydroclimate and Maize Yields in Southern and East Africa

Abstract The state of the El Niño–Southern Oscillation (ENSO) is critical for seasonal climate forecasts, but recent events diverged substantially from expectations in many regions, including sub-Saharan Africa where seasonal forecasts are critical tools for addressing food security. Here, we evaluate 39 years (1982–2020) of data on hydroclimate, leaf area index, and maize yields to investigate the strength of ENSO teleconnections in southern and East Africa. Teleconnections to precipitation, soil moisture, and leaf area index are generally stronger during ENSO phases that cause drought conditions (El Niño in southern Africa and La Niña in East Africa), with seasonality that aligns well with the maize growing seasons. Within maize growing areas, however, ENSO teleconnections to hydroclimate and vegetation are generally weaker compared to the broader geographic regions, especially in East Africa. There is also little evidence that the magnitude of the ENSO event affects the hydroclimate or vegetation response in these maize regions. Maize yields in Kenya, Malawi, South Africa, and Zimbabwe all correlate significantly with hydroclimate and leaf area index, with South Africa and Zimbabwe showing the strongest and most consistent yield responses to ENSO events. Our results highlight the chain of causality from El Niño and La Niña forcing of regional anomalies in hydroclimate to vegetation health and maize yields in southern and East Africa. The large spread across individual ENSO events, however, underscores the limitations of this climate mode for seasonal climate prediction in the region, and the importance of finding additional sources of skill for improving climate and yield forecasts.

The fingerprint of tropospheric ozone on broadleaved forest vegetation in Europe

Tropospheric ozone (O3) increased globally in the 20th century, contributes to climate change and can have adverse effects on terrestrial ecosystems. The response of forest vegetation to ozone is modulated by species- and site-specific factors and visible foliar symptoms (VFS) are the only direct evidence of ozone effects on vegetation. VFS have been observed and reproduced under (semi-) controlled conditions and their field assessment has been largely harmonized in Europe. We analyzed ozone concentration and VFS data as measured at (respectively) 118 and 91 intensive monitoring sites of the International Co-Operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) spanning over five European biogeographic regions from 2005 to 2018. Average values for VFS were calculated accounting for the number of species present and their observed frequency. Spatial and temporal variation of ozone concentrations, VFS, and their relationships across Europe were then investigated by applying Generalized Linear Mixed Models (GLMMs) and combined GLMMs. Ozone concentrations exceeded 40 ppb on 37.3 % of the sites and were significantly higher (p < 0.05) in the Alpine and the Mediterranean regions. Over the 2005–2018 period there was a substantial stagnation of ozone concentrations with a tendency towards decreasing values in the Alpine-Boreal sites and increasing values in the Atlantic sites. Ozone left a “fingerprint” in terms of VFS on 38 % of the observed broadleaved woody species across Europe, with no significant difference among biogeographic regions. Overall, and again with the exception of an increase at the Atlantic sites, the frequency of VFS remained unchanged or has been slightly declining over the investigated period. We found positive relationship between ozone concentrations and VFS across Europe (p < 0.05), while their temporal trends (both insignificant) were not related. The species with the highest frequency of VFS were those classified as sensitive species under controlled/semi-controlled experimental conditions. Frequency of VFS tends to be modulated by vegetation traits such as specific leaf area and leaf thickness (p < 0.10). Our results showed that, although ozone levels suggested a North-to-South gradient of increasing potential risk to vegetation with hot spots in the Alps and in the Mediterranean, VFS observed on the actual species assemblage at the sites modifies this picture. According to frequency of VFS, ozone risk for vegetation may be higher in parts of the Alpine and Continental Europe than in the Mediterranean region.

The impact of drying on the structure and photosynthesis of boreal peatland vegetation

Boreal peatlands harbour large stores of carbon as peat below their surfaces. Climate change is expected to cause drying in northern peatlands, which will in turn impact the carbon balance of these ecosystems that is maintained by high water tables and the hydrologically sensitive plants growing there. This study aims to quantify how vegetation will be structured (I) and photosynthesize (II, III) in a future climate as emulated by long-term water level drawdown (WLD). To do this, changes in the vegetation and its photosynthesis after WLD are linked, and the response of Sphagnum mosses to periodic drought is investigated. Field measurements were done at a long-term WLD field experiment that contained a rich (mesotrophic) fen, a poor (oligotrophic) fen and a bog (ombrotrophic) site. Measurements included vegetation surveys from existing permanent sample plots and leaf-level carbon dioxide exchange measurements. For an experiment in controlled conditions peatland surface cores from this field experiment were transported to a greenhouse where the photosynthesis of lawn Sphagna during and after an experimental periodic drought was measured. The field study revealed that the response of peatland vegetation to WLD depend on peatland type. The species composition in the rich fen was the most impacted by WLD, while the bog vegetation demonstrated stability. Similarly, large increases in photosynthesis occurred following WLD on the vascular plant-covered rich fen, while changes were negligible on the Sphagnum-carpeted bog. The vegetation on the two fens shifted from an open sedge-, or sedge and Sphagnum-dominated ecosystem, to a tree-dominated ecosystem. Canopy development following WLD further accelerated vegetation changes by shading and sheltering the understorey vegetation. Vascular plants were the most likely to increase productivity from WLD as they are best suited to utilize the nutrients made available by peat mineralization, while Sphagnum moss photosynthesis was impacted little. The greenhouse study revealed that lawn Sphagnum mosses exposed to long-term WLD were more vulnerable to drought compared to those from wet sites. Large capitula typical to fen Sphagnum species appeared to be beneficial for surviving periodic drought. This work demonstrated that climate change as emulated by long-term WLD will have a large impact on the vegetation composition of northern peatlands and increase photosynthetic function of these ecosystems, fens in particular. To better predict climate feedbacks from these changes, carbon dynamics including peatland vegetation dynamics should be updated in global process models. Future research to better understand the tipping point of different peatland types after WLD in different climatic regions will help us to predict changes in these diverse and globally important systems.

Warm Early Summer Compensated Reduction in Photosynthesis Caused by 2022 Late Summer Extreme Drought Over the Tibetan Plateau

AbstractThe Tibetan Plateau (TP) is ecologically delicate, its vegetation highly sensitive to climate variations. In 2022, China endured an unprecedented compound drought‐heatwave, escalating TP's August temperature to a record high since 2000. This study examined this event's impact on TP's photosynthesis using multi‐source satellite‐based products. We demonstrated persistent high temperatures from April to August 2022, accompanied by shifting soil water (SW). Initially moist from April to June, the soil turned notably dry, hitting its lowest point in August. Consequently, early summer witnessed a substantial enhancement in gross primary productivity (GPP) and near‐infrared reflectance of vegetation (NIRv) predominantly due to high temperatures, except for reduction in the eastern and southeastern TP. June recorded the largest positive GPP anomaly since 2000. As summer progressed, severe drought, not high temperatures, dominated, causing obvious negative anomalies in GPP and NIRv, especially in August, concentrated in the central and southwestern TP. Separating the growing season into May–June–July (MJJ) and August–September (AS) revealed a clear contrast. Enhancement in photosynthesis during MJJ compensated the decline in AS, making average positive GPP and weak negative NIRv anomalies in the entire growing season. Specifically, MJJ saw GPP magnitudes of 5.724 TgC mo−1 in FluxSat, 9.491 TgC mo−1 in GPP v2.2 and OCO‐2‐based Solar‐induced chlorophyll fluorescence (GOSIF), and 0.004 in NIRv. Conversely, AS experienced a decline: −4.802 TgC mo−1 in FluxSat, −2.837 TgC mo−1 in GOSIF GPP, and −0.006 in NIRv. This delicate balance underscores the intricate interplay between early growth conditions, subsequent environmental stressors, and vegetation's adaptive responses.

Mapping soil suitability using phenological information derived from MODIS time series data in a semi-arid region: A case study of Khouribga, Morocco

To address the increasing global demand for food, it is crucial to implement sustainable agricultural practices, which include effective soil management techniques for enhancing productivity and environmental conditions. In this regard, a study was conducted to assess the efficacy of utilizing phenological metrics derived from satellite data in order to map and identify suitable agricultural soil within a semi-arid region. Two distinct methodologies were compared: one based on physicochemical soil parameters and the other utilizing the phenological response of vegetation through the application of the Normalized Difference Vegetation Index (NDVI) Modis-time series. The study findings indicated that the NDVI-based approach successfully identified a specific class of soil suitability for agriculture (referred to as S1) that could not be effectively mapped using the multi-criteria analysis (MCAD) method relying on soil physicochemical parameters. This S1 class of soil suitability accounted for approximately 5 % of the total study area. These outcomes suggest that phenological-based approaches offer greater potential for spatio-temporal monitoring of soil suitability status compared to MCAD, which heavily relies on discrete observations and necessitates frequent updates of soil parameters. The approach developed to map the soil-suitability is a valuable tool for sustainable agricultural development, and it can play an effective role in ensuring food security and conducting a land agriculture assessment.

Water content estimation of conifer needles using leaf-level hyperspectral data.

Water is a crucial component for plant growth and survival. Accurately estimating and simulating plant water content can help us promptly monitor the physiological status and stress response of vegetation. In this study, we constructed water loss curves for three types of conifers with morphologically different needles, then evaluated the applicability of 12 commonly used water indices, and finally explored leaf water content estimation from hyperspectral data for needles with various morphology. The results showed that the rate of water loss of Olgan larch is approximately 8 times higher than that of Chinese fir pine and 21 times that of Korean pine. The reflectance changes were most significant in the near infrared region (NIR, 780-1300 nm) and the short-wave infrared region (SWIR, 1300-2500 nm). The water sensitive bands for conifer needles were mainly concentrated in the SWIR region. The water indices were suitable for estimating the water content of a single type of conifer needles. The partial least squares regression (PLSR) model is effective for the water content estimation of all three morphologies of conifer needles, demonstrating that the hyperspectral PLSR model is a promising tool for estimating needles water content.

Declining coupling between vegetation and drought over the past three decades

AbstractDroughts have been implicated as the main driver behind recent vegetation die‐off and are projected to drive greater mortality under future climate change. Understanding the coupling relationship between vegetation and drought has been of great global interest. Currently, the coupling relationship between vegetation and drought is mainly evaluated by correlation coefficients or regression slopes. However, the optimal drought timescale of vegetation response to drought, as a key indicator reflecting vegetation sensitivity to drought, has largely been ignored. Here, we apply the optimal drought timescale identification method to examine the change in coupling between vegetation and drought over the past three decades (1982–2015) with long‐term satellite‐derived Normalized Difference Vegetation Index and Standardized Precipitation‐Evapotranspiration Index data. We find substantial increasing response of vegetation to drought timescales globally, and the correlation coefficient between vegetation and drought under optimal drought timescale overall declines between 1982 and 2015. This decrease in vegetation–drought coupling is mainly observed in regions with water deficit, although its initial correlation is relatively high. However, vegetation in water‐surplus regions, with low coupling in earlier stages, is prone to show an increasing trend. The observed changes may be driven by the increasing trend of atmospheric CO2. Our findings highlight more pressing drought risk in water‐surplus regions than in water‐deficit regions, which advances our understanding of the long‐term vegetation–drought relationship and provides essential insights for mapping future vegetation sensitivity to drought under changing climate conditions.

Hillslope and vegetation response to postglacial warming at Bear Meadows Bog, Pennsylvania, USA

AbstractConnecting changes in erosion and vegetation is necessary for predicting topographic and ecologic change in thawing permafrost landscapes. Formerly periglacial landscapes serve as potential analogs for understanding modern permafrost landscape change, yet compared to paleoenvironmental records at these sites, less is known about concurrent geomorphic processes, particularly their rates and relationships to climate change. Here, we target sediments preserved in a central Appalachian peat bog to reconstruct sedimentation across the last deglacial warming. We use ground-penetrating radar and geochemistry of cored bog sediments to quantify sedimentation timing, style, and provenance. Using 14C dating of sedimentary and geochemical shifts, we connect depositional changes to global climate and local vegetation change. We show that deglacial warming promoted deep soil disturbances via solifluction at ca. 14 ka. In contrast, relatively wetter conditions from ca. 10–9 ka promoted shallow disturbance of hillslopes via slopewash, which corresponds to a time of vegetation change. Our results highlight climate-modulated erosion depth and processes in periglacial and post-periglacial landscapes. The existence of similar erosion and vegetation records preserved regionally implies these dynamics were pervasive across unglaciated Appalachian highlands, aiding in reconstructing erosion responses to warming at a resolution with implications for predicting high-latitude landscape responses to disturbance.

Palynological records from glacial lakes, northern Priokhotye (western Beringia)

Palynological analyzes of sediments from glacial lakes in Northern Priokhot'ye provide the first continuous records of regional vegetation responses to climate change at the end of the Pleistocene and during the Holocene. The pollen stratigraphy from these coastal sites is like that described for more northern regions of Western Beringia. Herb dominated tundra with Poaceae-forb meadows characterized the Late Pleistocene and was replaced c. 12,100 cal BP by Betula shrub tundra and then by shrub Betula-Alnus tundra. In the Middle Holocene (c. 8900-4700 cal BP), Larix-Betula platyphylla forests with an undergrowth of Pinus pumila, shrub Betula, and Alnus became widespread. Pinus pumila also formed a high shrub tundra zone above altitudinal treeline. Finds of Betula platyphylla macrofossils suggest that summer temperatures were 2–4 °C warmer than today between c. 7700 and 6700 cal BP. Variations in Pinus pollen percentages during the Middle and Late Holocene suggest changes in altitudinal treeline related to intervals of relatively cooler or warmer climates. The timing of the postglacial thermal maximum and possible shifts in altitudinal treeline suggest paleoclimatic patterns that are more like southern areas of the Russian Far East than northern regions of Western Beringia. A Late Holocene tephra was found for the first time in the lake sediments and peat exposures of Northern Priokhotye. The most likely source of this important chronostratigraphic horizon is the Shiveluch volcanic eruption (Kamchatka Peninsula) dated to 2500–2600 BP (2580–2730 cal BP).

Foredune‐forming grass and plant diversity show contrasting responses along the southeastern United States coast after hurricane disturbance

AbstractAimsLatitudinal gradients in plant communities are well studied, yet how these fundamental ecological patterns influence ecosystem recovery after extreme weather events remains largely unknown. In coastal foredunes, we investigated how the cover of a key dune‐building grass (Uniola paniculata), vegetation diversity and vegetation cover vary along a short latitudinal gradient during recovery from hurricane disturbance.LocationSoutheastern USA.MethodsWe surveyed 24 sites, from central Florida to north Georgia (&gt;400 km), four times over 18 months. General linear mixed‐effect models were used to unravel patterns of vegetation responses across latitude.ResultsVegetation properties showed countervailing patterns across the latitudinal gradient. While vegetation richness, functional diversity and total cover generally declined, Uniola cover increased with increasing latitude. Further, the latitude–richness relationship strengthened while the latitude–functional diversity relationship was invariant with increasing time since the hurricane disturbance. Meanwhile, the latitude–Uniola association was seasonally dependent and strongest in the summer. Latitude also influenced diversity–cover relationships: vegetation cover was positively related to species richness at lower latitudes, while it was positively associated with functional diversity only at northern sites. We found no relationship between species richness or functional diversity and increases in cover between time steps; however, recruitment of new species and functional groups was associated with increases in vegetation cover between time steps at northern sites.ConclusionsOur study highlights the temporal dynamism and contrasting patterns along latitudinal gradients exhibited by key engineering species and overall plant diversity in foredunes — a crucial line of coastal protection — exposed to hurricane disturbances. These results suggest a need for greater integration of latitudinal and diversity effects into our understanding of coastal dune resilience. They also highlight the potential benefits of enhancing dune plant biodiversity, particularly in areas where the dune‐building grasses that are classically employed in restoration (e.g., Uniola) are unfavoured, to accelerate the re‐establishment of well‐vegetated dunes.

Wildlife activity patterns and encroaching woody vegetation response to bush thinning on farmlands in north-central Namibia

The Namibian savannah ecosystem has experienced considerable anthropogenic pressures, which have resulted in the disruption of key ecological processes, and consequently, the proliferation of a dense vegetation structure, commonly known as bush encroachment. Approximately 45 million hectares of land have been affected, which has caused a significant decline in the grazing capacity, poor economic returns for the farmers, and loss of suitable wildlife habitat. Restoration thinning, a method that involves the selective removal of excess trees/shrubs, has been applied to counteract the negative effects associated with this phenomenon. This thesis aimed to assess the effect of thinning on (a) the activity patterns of local ungulates and predators, (b) the encroaching woody vegetation in terms of (i) regeneration, and (ii) structure, abundance, and habitat sighting lines, in a savannah habitat in the north-central region. Generalised linear mixed-effects models (GLMM) and linear mixed-effects models (LME) were used for statistical analysis. Results showed that thinned areas had overall greater wildlife activity. Thinned areas also had reduced tree/shrub abundance, which was significant for the mature height classes. Natural regeneration was rapid in thinned areas, where the abundance of young cohorts was 34% greater than non-thinned areas. In the thinned areas, red umbrella thorn (Vachellia reficiens) was significantly reduced but umbrella thorn (Vachellia tortilis) numbers increased. Tree/shrub densities in the thinned areas fell within the commonly accepted range for a 400 mm rainfall area (600–750 tree equivalents (TE) ha–1). Thinning significantly modified the dense thornbush to an open vegetation structure with a low woody canopy cover that favours grass growth and provides greater sighting lines for open savannah wildlife. This thesis demonstrated that thinning was effective in controlling bush encroachment and could be used as a method to restore other affected areas. However, periodic post-thinning management is recommended to control the established samplings.

The complex relationship between precipitation and productivity in drylands

Abstract Drylands provide multiple essential services to human society, and dryland vegetation is one of the foundations of these services. There is a paradox, however, in the vegetation productivity–precipitation relationship in drylands. Although water is the most limiting resource in these systems, a strong relationship between precipitation and productivity does not always occur. Such a paradox affects our understanding of dryland vegetation dynamics and hinders our capacity to predict dryland vegetation responses under future climates. In this perspective, we examine the possible causes of the dryland precipitation–productivity paradox. We argue that the underlying reasons depend on the location and scale of the study. Sometimes multiple factors may interact, resulting in a less significant relationship between vegetation growth and water availability. This means that when we observe a poor correlation between vegetation growth and water availability, there are potentially missing sources of water input or a lack of consideration of other important processes. The paradox could also be related to the inaccurate measurement of vegetation productivity and water availability indicators. Incorporating these complexities into predictive models will help us better understand the complex relationship between water availability and dryland ecosystem processes and improve our ability to predict how these ecosystems will respond to the multiple facets of climate change.

Mixed-Grass Vegetation Response to an Extreme Wildfire Event

Mixed-Grass Vegetation Response to an Extreme Wildfire Event

Global Patterns and Ecological Effects of Drought Intensification: A Multiscale Analysis

This study delineates the criteria for identifying different types of droughts based on root zone soil moisture deficits, categorizing them into sudden, general, and creeping droughts. By employing an adapted version of the drought detection method proposed by Yuan et al., drought events were analyzed across 26 IPCC-SREX regions using historical soil moisture data. Our findings demonstrate that sudden droughts, which entail a rapid decline in soil moisture, predominantly occur in climatic hotspots and have shown an increasing trend over the past four decades, particularly in Central Europe and South Asia. The research also explores the seasonality of droughts, noting that flash droughts typically align with the growing season, while creep droughts often commence later in the year, potentially affecting vegetation growth in subsequent seasons. The ecological impact assessment, based on the Normalized Difference Vegetation Index (NDVI), reveals a lag in vegetation response to rapid water stress, with a marked decline in health by the end of the drought onset phase. These results underscore the varying ecological responses to drought intensification and contribute to a better understanding of their global patterns and impacts.