Assessment of Rangeland Condition in a Dryland System Using UAV-Based Multispectral Imagery

Dry savannahs are water-limited and under increasing anthropogenic pressure. Thus, considering climate change and the unprecedented pace and scale of rangeland deterioration, we need methods for assessing the status of such rangelands that are easy to apply, yield reliable and repeatable results that can be applied over large spatial scales. Global and local scale monitoring of rangelands through satellite data and labour-intensive field measurements respectively, are limited in accurately assessing the spatiotemporal heterogeneity of vegetation dynamics to provide crucial information that detects degradation in its early stages. Fortunately, newly emerging techniques such as unmanned aerial vehicles (UAVs), associated miniaturized sensors and improving digital photogrammetric software allow us to transcend these limitations. Yet, they have not been extensively calibrated with rangeland functional attributes. In our study, we fill this gap by testing the relationship between UAV-acquired multispectral imagery and field data collected in discrete sample plots in a Namibian dryland savannah along a degradation gradient. The first results are based on a supervised classifier performed on the very high resolution multispectral imagery to distinguish between rangeland functional attributes, with a relatively good match to the field observations. Integrating UAV-based observations to improve rangeland monitoring could greatly assist in climate-adapted rangeland management

The Importance of Soil Seed Bank Dynamics as Potential Indicators of Desertification Tipping Point

Soil seed banks play a major role in the vegetation dynamics of drylands, where annual rainfall is unpredictable and plants depend on a persistent stage (seeds) to survive over the dry season. The purpose of the study is to understand the behaviour of the rangeland system in terms of soil seed bank dynamics before, during and after crossing the “so called” DTP and to determine whether different management systems plays a role in accelerating the desertification process. Through the use of the Space for Time Substitution Approach the study analysed spatial grazing gradients (gradients radiating from water points) to predict how soil seed banks would respond to long term grazing scenarios. Soil seed bank samples were collected along grazing gradients under two management systems (commercial and communal), processed through seedling emergence method and analysed with SPSS statistical package. Though our results indicated larger soil seed bank under the commercial management system, the seed bank size did not differ significantly along both commercial and communal grazing gradients. Commercially managed sites had a larger seed bank of perennial grasses compared to communal sites. Some of which increased gradually with increasing grazing intensity (Eragrostis trichophora), while other decreased with the increase in grazing intensity (Eragrostis rigidior and Eragrostis pallens). Further testing of other seed processes is still ongoing and will be completed in the 1st quota of 2022. Based on the first results soil seed bank size might not be a good indicator of DTP but rather seed bank life form composition as well as species composition of perennial grasses might serve as good indicators of DTP

Towards Early Warning Signals for Desertification

Dryland ecosystems cover a large share of the world’s terrestrial surface. Deficiency and spatio-temporal variability of precipitation as well as low vegetation growth rates make dry rangelands prone to degradation, especially under changing climate and intensified land use. Degradation often occurs gradually but sometimes, a sudden and surprising shift from a healthy to a degraded rangeland can be observed, where perennial grasses are lost, and bare soil is exposed. If such changes are sudden and irreversible, they are coined a tipping point. Due to their abrupt appearance, it is a great challenge to discover early warning signals that precede the regime shifts. Theory predicts that variance and autocorrelation in state conditions could be used as early warning signals. However, these theoretical assumptions have rarely been tested in real ecosystems. Here, we use a data-based approach to contribute to filling this research gap using desertification processes in a semi-arid rangeland as a case study. In order to test the applicability of theoretical early warning signals for tipping points, we looked at a dataset from Widou, Senegal, that includes annual observations of rainfall, grazing intensity and primary production from 1981 – 2007. We analysed productivity-based metrics, such as rain use efficiency, in order to detect patterns that may precede a shift between alternate stable states. Strong signals of a regime shift were detected that were expressed in a sudden alteration of species composition and general decline of productivity after a drought. However, we did not find any changes in the theoretically proposed parameters that may reflect early warning signals for a critical transition, i.e. the regime shift was essentially unpredictable. We suggest that while the theory around tipping points and early recognition thereof may be robust, the applicability of theoretical concepts to the real world may be challenging

Evaluating grazing response strategies in winter annuals : A multi-trait approach

Plants minimize fitness losses through grazing by three fundamental strategies: tolerance, avoidance and escape. Annual species have been traditionally assumed to escape grazing through their short life cycle and seed dormancy; however, their grazing response strategies remain almost unexplored. How traits and their coordination affect species' grazing responses, and whether the generalized grazing model, which posits convergent filtering by grazing and drought, is applicable to this ecologically and economically important species group thus remain unclear. We used a trait-based approach to evaluate grazing response strategies of winter annuals from the Middle East. Across 23 species, we examined the coordination of 16 traits hypothesized to be relevant for grazing responses, and linked them to species' fecundity responses, as proxy for fitness responses, to simulated grazing in controlled conditions, to species' abundance responses to grazing in the field and to species' distribution along a large-scale rainfall gradient. Winter annuals exhibited both grazing escape and to a lesser extent tolerance indicated by (a) independent coordination of escape and tolerance traits, and (b) maintenance of higher fecundity in species with more pronounced escape or tolerance traits under simulated grazing. In the natural habitat, species with a more pronounced escape but not tolerance strategy maintained higher abundance under grazing in dry habitats, indicating convergent favouring of escape by both grazing and drought. However, this finding at the local scale was not mirrored by a strategy shift along a large-scale rainfall gradient. Synthesis. The convergent favouring of escape traits by grazing and drought in annuals is consistent with the generalized grazing model. This model, which has been developed for perennials based on the avoidance strategy, can thus be extended to annuals based on escape, a finding that should facilitate projecting consequences of global change in drylands dominated by annuals. © 2021 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Societ

Evaluating grazing response strategies in winter annuals : A multi-trait approach

Plants minimize fitness losses through grazing by three fundamental strategies: tolerance, avoidance and escape. Annual species have been traditionally assumed to escape grazing through their short life cycle and seed dormancy; however, their grazing response strategies remain almost unexplored. How traits and their coordination affect species' grazing responses, and whether the generalized grazing model, which posits convergent filtering by grazing and drought, is applicable to this ecologically and economically important species group thus remain unclear. We used a trait-based approach to evaluate grazing response strategies of winter annuals from the Middle East. Across 23 species, we examined the coordination of 16 traits hypothesized to be relevant for grazing responses, and linked them to species' fecundity responses, as proxy for fitness responses, to simulated grazing in controlled conditions, to species' abundance responses to grazing in the field and to species' distribution along a large-scale rainfall gradient. Winter annuals exhibited both grazing escape and to a lesser extent tolerance indicated by (a) independent coordination of escape and tolerance traits, and (b) maintenance of higher fecundity in species with more pronounced escape or tolerance traits under simulated grazing. In the natural habitat, species with a more pronounced escape but not tolerance strategy maintained higher abundance under grazing in dry habitats, indicating convergent favouring of escape by both grazing and drought. However, this finding at the local scale was not mirrored by a strategy shift along a large-scale rainfall gradient. Synthesis. The convergent favouring of escape traits by grazing and drought in annuals is consistent with the generalized grazing model. This model, which has been developed for perennials based on the avoidance strategy, can thus be extended to annuals based on escape, a finding that should facilitate projecting consequences of global change in drylands dominated by annuals. © 2021 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Societ

GLOWA JR Atlas: Results of the GLOWA Jordan River Project.

Bitte die ZIP-Datei downloaden und auf Ihrem Computer entzippen und dann bei Windows-Betriebssystemen auf atlas.exe drücken. Bei Linux-Systemen machen Sie bitte die Datei start.sh ausführbar und rufen diese auf. In der Datei user_manual.pdf finden Sie Hinweise zur Nutzung des Atlas.Please download the ZIP-file and extract it on your computer. On windows operation systems click on atlas.exe. On Linux operation systems make the file start.sh executable and select it. The file user_manual.pdf is the instruction manual for using the atlas.The GLOWA Jordan River (GLOWA JR) Atlas is an end-user geographical information system (GIS). It presents the spatial results of the GLOWA JR project and helps to visualize, organize, and analyze them. The geographical scope of the atlas is Israel, Jordan and Palestine. It includes maps about climate change and its impact on water and land resources, including ecosystems, as well as information about the impact of global change on ecosystem services, land use and agriculture. Moreover it includes maps about the potential of rainwater harvesting, managed aquifer recharge and irrigation with treated wastewater

An Integrated Framework to Study Ecological Tipping Points in Social-Ecological Systems

Sudden regime shifts or tipping points pose a major threat to various ecosystems and people\u27s livelihoods worldwide. However, tipping points are still hard to predict and often occur without warning. To avoid dramatic social-ecological consequences, it is crucial to understand tipping point behaviour and to identify early warning indicators. Previous studies have hardly implemented an integrated social-ecological approach, which has led to a fragmented understanding and oversimplification of tipping point phenomena. Against this background, we present a systemic research framework that harmonizes ecological and social perspectives to gain a mechanistic understanding of tipping point behaviour. We utilize a social-ecological systems (SES) approach to identify drivers, consequences, and feasible preventive strategies. Our proposed framework consists of a retrospective, a comparative and a prospective perspective; each of them utilizes interdisciplinary studies in both sub systems at multiple scales. The research framework was developed by the members of NamTip, an inter- and transdisciplinary research project aiming to understand and manage desertification tipping points in Namibia’s semi-arid rangelands. The NamTip project represents a practical implementation of the research framework, that uses an integrated, social-ecological study design combining the threefold approach with dynamic modelling. This includes analyses of time-series and archival data, experimental and observational studies, as well as scenario development and exploration of decision-making with local farmers. After the initial practical implementation and with our ongoing evaluation, we are convinced that such an ambitious and complex framework will guide the way to a profound understanding of tipping point phenomena and feasible management options

Spatial pattern and neighbour effects on Helianthemum squamatum seedlings in a Mediterranean gypsum community

Question: Do, in a semi-arid gypsum environment, neighbours condition the spatial patterns of emergence, survival and height of Helianthemum squamatum seedlings ? Location: Vicinity of Chinchón, province of Madrid, Spain (40°11'N, 3° 35'W, 550 m a.s.l.) Methods: We evaluated the effects of neighbours on the survival and growth of naturally emerging Helianthemum seedlings in a semi-arid area during a two-year period. We followed a two-fold approach based on the use of neighbour models for seedling survival and growth and spatial point pattern analyses for seedling emergence, taking into account the germination date. Results: Seedlings appeared clumped in the vicinity of mature Helianthemum individuals. The neighbour models fitted showed that interactions with neighbours were extremely important for the survival and growth of Helianthemum seedlings. These models also suggest that the effects of neighbours on these variables vary with changes in spatial scale and in the abiotic conditions. Some species exerted negative or positive effects on Helianthemum seedlings only at certain spatial scales, and others exerted negative or positive effects at earlier stages of seedling development, but none later and vice versa. Conclusions: We suggest that the observed patterns are mainly influenced by small-scale modifications in soil conditions and microclimate created by neighbours, which change in time and space