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Seasonally dry, water-limited regions are often co-dominated by distinct herbaceous and woody plant communities with contrasting ecohydrological properties. We investigated the shape of the above-ground net primary productivity (ANPP) response to annual precipitation (Pa) for adjacent grassland and shrubland ecosystems in Southern California, with the goal of understanding the role of these ecohydrological properties on ecosystem function. Our synthesis of observations and modelling demonstrates grassland and shrubland exhibit distinct ANPP-Pa responses that correspond with characteristics of the long-term Pa distribution and mean water balance fluxes. For annual grassland, no ANPP occurs below a 'precipitation compensation point,' where bare soil evaporation dominates the water balance, and ANPP saturates above the Pa where deep percolation and runoff contribute to the modelled water balance. For shrubs, ANPP increases at a lower and relatively constant rate across the Pa gradient, while deep percolation and runoff account for a smaller fraction of the modelled water balance. We identify precipitation seasonality, root depth, and water stress sensitivity as the main ecosystem properties controlling these responses. Observed ANPP-Pa responses correspond to notably different patterns of rain-use efficiency (RUE). Grass RUE exceeds shrub RUE over a wide range of typical Pa values, whereas grasses and shrubs achieve a similar RUE in particularly dry or wet years. Inter-annual precipitation variability, and the concomitant effect on ANPP, plays a critical role in maintaining the balance of grass and shrub cover and ecosystem-scale productivity across this landscape.

Aim: Changes in dryland ecosystem functioning are threatening the well‐being of human populations worldwide, and land degradation, exacerbated by climate change, contributes to biodiversity loss and puts pressures on sustainable livelihoods. Here, abrupt changes in ecosystem functioning [so‐called turning points (TPs)] were detected using time series of Earth observation data. Hotspot areas of high TP occurrence were identified, observed changes characterized and insights gained on potential drivers for these changes. Location: Arid and semi‐arid regions. Time period: 1982–2015. Methods: We used a time series segmentation technique (breaks for additive season and trend) to detect breakpoints in rain‐use efficiency as a means of analysing changes in ecosystem functioning. A new typology to characterize the detected changes was proposed and evaluated, at regional to local scales, for a set of case studies. Ancillary data on population and drought were used to provide insights on potential drivers of TP occurrence. Results: Turning points in ecosystem functioning were found in 13.6% (c. 2.1 × 106 km2) of global drylands. Turning point hotspots were primarily observed in North America, the Sahel, Central Asia and Australia. In North America, the majority of TPs (62.6%) were characterized by a decreasing trend in ecosystem functioning, whereas for the other regions, a positive reversal in ecosystem functioning was prevalent. Further analysis showed that: (a) both climatic and anthropogenic pressure influenced the occurrence of TPs in North America; (b) Sahelian grasslands were primarily characterized by drought‐induced TPs; and (c) high anthropogenic pressure coincided with the occurrence of TPs in Asia and Australia. Main conclusions: By developing a new typology targeting the categorization of abrupt and gradual changes in ecosystem functioning, we detected and characterized TPs in global drylands. This TP characterization is a first crucial step towards understanding the drivers of change and supporting better decision‐making for ecosystem conservation and management in drylands. [ABSTRACT FROM AUTHOR]

This study compared some attributes of four forages grown in the arid rangelands of Jordan. Three experimental sites were selected, a plot of 0.8 ha was delineated at each site and subdivided into four equal subplots and contour ridges were constructed at all subplots to harness the surface runoff of rainfall. At each site, Atriplex halimus (ATP), Salsola ver miculata (SAL) and barley (BAR) were planted in the ridges in three out of four sub-plots and the fourth sub-plot was left without any intervention to represent natural vegetation (NV) resulting in four treatments: TNV, TNV+ATP, TNV+SAL and TNV+BAR. Biomass production, rain use efficiency of forage production (RUEF), carrying capacity (CC), relative feed value (RFV) and Total Digestible Nutrients (TDN) were monitored in February and April representing early and late spring grazing. The highest fresh and dry weights of forage (240.1 and 131.1 kg ha-1), CC (1.35 SUM ha-1) and RUEF (1.75 kg DM ha-1 mm-1) were observed in TNV+ATP. Planting Atriplex, Salsola or barley negatively affected the forage production of natural vegetation established in the ridges. The socio-economic aspects of production and utilization of TNV+ATP and its impact on rangelands biodiversity should be carefully investigated before out-scaling of this revegetation approach. [ABSTRACT FROM AUTHOR]

The vegetation rain-use efficiency (RUE) represents the ability of an ecosystem to use rainfall and is an important descriptor of ecological functions of terrestrial system. Although studies have been conducted to investigate the impact of droughts on vegetation, we still lack critical understanding of how exactly RUE responds to droughts of different time scales and intensities. Here, we present evidence for a rapid response in RUE, and collapse points of RUE increase trend during droughts by using multi-source meteorological data and satellite-derived vegetation indices. The highest correlation was found consistently between RUE and computed drought index at time scale of 1 month for all biome types and climate regimes. We further discovered that RUE increased significantly with amplification of drought intensity to a maximum RUE, especially for semi-arid and arid biomes. As drought is prolonged, RUE increased till a tipping point was reached across all biomes and climatic conditions, indicating that the long-term droughts weaken the sensitivities of RUE to drought and threaten the resilience of ecosystem. This study comprehensively provides a satellite-based evaluation of RUE response to different drought features. We envisage that the findings would contribute to the development of drought early warning from an ecological perspective and to provide the sustainable environmental management.

Quantifying the ecological patterns of loss of ecosystem function in extreme drought is important to understand the carbon exchange between the land and atmosphere. Rain-use efficiency [RUE; gross primary production (GPP)/precipitation] acts as a typical indicator of ecosystem function. In this study, a novel method based on maximum rain-use efficiency (RUE max ) was developed to detect losses of ecosystem function globally. Three global GPP datasets from the MODIS remote sensing data (MOD17), ground upscaling FLUXNET observations (MPI-BGC), and process-based model simulations (BESS), and a global gridded precipitation product (CRU) were used to develop annual global RUE datasets for 2001–2011. Large, well-known extreme drought events were detected, e.g. 2003 drought in Europe, 2002 and 2011 drought in the U.S., and 2010 drought in Russia. Our results show that extreme drought-induced loss of ecosystem function could impact 0.9% ± 0.1% of earth's vegetated land per year and was mainly distributed in semi-arid regions. The reduced carbon uptake caused by functional loss (0.14 ± 0.03 PgC/yr) could explain >70% of the interannual variation in GPP in drought-affected areas ( p  ≤ 0.001). Our results highlight the impact of ecosystem function loss in semi-arid regions with increasing precipitation variability and dry land expansion expected in the future. [ABSTRACT FROM AUTHOR]

• We detected age-related pattern of forest mortality in the region- and species-level. • Forest dominated by shade-tolerant species shows high drought-induced mortality. • The reverse J-shaped pattern dominated for age-mortality relationship with drought. • Drought-induced forest mortality was mainly driven by temperature in Northeast China. • Precipitation deficit-induced forest mortality was most strongly correlated with age. Given the significantly increasing frequency and intensity of droughts in Northeast China under climate change, it is necessary to understand drought-induced mortality in forest ecosystems. The magnitude of drought-induced forest mortality strongly depends on climate variability and forest age, which are both important driving factors of tree mortality. However, the age-related patterns and climatic driving factors of drought-induced forest mortality at large scales are poorly understood. This study identified the age-related pattern and the key climatic driving factors of drought-induced mortality for 17 dominant tree species in Northeast China using rain-use efficiency (RUE), standardized precipitation evapotranspiration index (SPEI), and tree-list information (species and diameter for every tree). Considering that climate variability and forest age are important factors of drought-induced mortality, species-specific analysis was conducted for describing age-dependent mortality patterns. The results showed that the mean annual rate of the drought-induced mortality of forests in Northeast China was 0.49%, with relatively high mortality rates in the Changbai Mountains and the eastern part of Liaoning Province. The sensitivity of age-dependent mortality patterns to climatic drivers of drought exhibited considerable variability. Resolving the contributions of precipitation deficits and heatwaves on the drought-induced mortality of trees, almost 91.60% of the forest region in Northeast China was found to be primarily affected by heatwaves (temperature anomalies), suggesting the important role of temperature extremes in forest mortality. The findings provide deeper insight into the mechanisms behind the species-specific formation of age-dependent patterns in Northeast China. This study provides a basis for the formulation of drought adaptation measures for forest species across successional stages and highlights the potential of remote sensing indices in identifying the patterns and climatic drivers of large-scale drought-induced forest mortality. [Display omitted] [ABSTRACT FROM AUTHOR]

There is a great deal of debate on the extent, causes, and even the reality of land degradation in the Sahel. Investigations carried out before approximately 2000 using remote sensing data suggest widespread reductions in biological productivity, while studies extending beyond 2000 consistently reveal a net increase in vegetation production, strongly related to the recovery of rainfall following the extreme droughts of the 1970s and 1980s, and thus challenging the notion of widespread, long-term, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends. It is hypothesized that, in addition to rainfall, other meteorological variables and human land use have contributed to vegetation dynamics. Throughout most of the Sahel, the interannual variability in growing season ΣNDVIgs (measured from satellites, used as a proxy of vegetation productivity) was strongly related to rainfall, humidity, and temperature (mean r2 = 0.67), but with rainfall alone was weaker (mean r2 = 0.41). The mean and upper 95th quantile (UQ) rates of change in ΣNDVIgs in response to climate were used to predict potential ΣNDVIgs-that is, the ΣNDVIgs expected in response to climate variability alone, excluding any anthropogenic effects. The differences between predicted and observed ΣNDVIgs were regressed against time to detect any long-term (positive or negative) trends in vegetation productivity. Over most of the Sahel, the trends did not significantly depart from what is expected from the trends in meteorological variables. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by negative, and, in some areas, positive trends. To explore whether the negative trends were human-induced, they were compared with the available data of population density, land use, and land biophysical properties that are known to affect the susceptibility of land to degradation. The spatial variations in the trends of the residuals were partly related to soils and tree cover, but also to several anthropogenic pressures. [ABSTRACT FROM AUTHOR]

The collapse of the Soviet Union in 1991 has been a turning point in the World history that left a unique footprint on the Northern Eurasian ecosystems. Conducting large scale mapping of environmental change and separating between naturogenic and anthropogenic drivers is a difficult endeavor in such highly complex systems. In this research a piece-wise linear regression method was used for breakpoint detection in Rain-Use Efficiency (RUE) time series and a classification of ecosystem response types was produced. Supported by earth observation data, field data, and expert knowledge, this study provides empirical evidence regarding the occurrence of drastic changes in RUE (assessment of the timing, the direction and the significance of these changes) in Northern Eurasian ecosystems between 1982 and 2011. About 36% of the study area (3.4 million km²) showed significant (P < 0.05) trends and/or turning points in RUE during the observation period. A large proportion of detected turning points in RUE occurred around the fall of the Soviet Union in 1991 and in the following years which were attributed to widespread agricultural land abandonment. Our study also showed that recurrent droughts deeply affected vegetation productivity throughout the observation period, with a general worsening of the drought conditions in recent years. Moreover, recent human-induced turning points in ecosystem functioning were detected and attributed to ongoing recultivation and change in irrigation practices in the Volgograd region, and to increased salinization and increased grazing intensity around Lake Balkhash. The ecosystem-state assessment method introduced here proved to be a valuable support that highlighted hotspots of potentially altered ecosystems and allowed for disentangling human from climatic disturbances. [ABSTRACT FROM AUTHOR]

Grazing intensity elicits changes in the composition of plant functional groups in both shortgrass steppe ( SGS) and northern mixed-grass prairie ( NMP) in North America. How these grazing intensity-induced changes control aboveground net primary production ( ANPP) responses to precipitation remains a central open question, especially in light of predicted climate changes. Here, we evaluated effects of four levels (none, light, moderate, and heavy) of long-term (>30 yr) grazing intensity in SGS and NMP on: (1) ANPP; (2) precipitation-use efficiency ( PUE, ANPP : precipitation); and (3) precipitation marginal response ( PMR; slope of a linear regression model between ANPP and precipitation). We advance prior work by examining: (1) the consequences of a range of grazing intensities (more grazed vs. ungrazed); and (2) how grazing-induced changes in ANPP and PUE are related both to shifts in functional group composition and physiological responses within each functional group. Spring (April-June) precipitation, the primary determinant of ANPP, was only 12% higher in NMP than in SGS, yet ANPP and PUE were 25% higher. Doubling grazing intensity in SGS and nearly doubling it in NMP reduced ANPP and PUE by only 24% and 33%, respectively. Increased grazing intensity reduced C3 graminoid biomass and increased C4 grass biomass in both grasslands. Functional group shifts affected PUE through biomass reductions, as PUE was positively associated with the relative abundance of C3 species and negatively with C4 species across both grasslands. At the community level, PMR was similar between grasslands and unaffected by grazing intensity. However, PMR of C3 graminoids in SGS was eightfold higher in the ungrazed treatment than under any grazed level. In NMP, PMR of C3 graminoids was only reduced under heavy grazing intensity. Knowing the ecological consequences of grazing intensity provides valuable information for mitigation and adaptation strategies in response to predicted climate change. For example, moderate grazing (the recommended rate) in SGS would sequester the same amount of aboveground carbon as light grazing because ANPP was nearly the same. In contrast, reductions in grazing intensity in NMP from moderate to light intensity would increase the amount of aboveground carbon sequestrated by 25% because of increased ANPP. [ABSTRACT FROM AUTHOR]

Spatio-temporal patterns of rain-use efficiency (RUE) can explicitly present the steady-state of ecosystem water use and thus ecosystem functioning. The west of Songliao Plain, located along the east fringe of the agro-pasture transitional zone in northern China, is highly sensitive to global change. In this study, satellite-based RUE was calculated using time series SPOT VEGETATION (SPOT-VGT) Normalized Difference Vegetation Index (NDVI) images and precipitation data for the study area from 1999 to 2011. Based on regression model by fitting simple linear regression through the pixel-based time series of RUE in the growing season and calculating the slopes, the change trend of RUE was determined. The grey relational analysis (GRA) method was extended to the spatial scale, and used to select sensitive climate and socio-economic factors that affected RUE variations. The result demonstrated that vegetation RUE increased slightly with an undulating trend, implying the ecosystem function tended to improve between 1999 and 2011. In total, 4.23% of the total area had experienced a significant increase in RUE, whereas 1.29% of the total area presented a significant decrease. Areas showing increased RUE trends mostly coincided with areas of land cover conversions from grassland to forest, shrub to forest and cropland to forest, which suggested a positive linkage with ecological protection policy and projects at national and local levels. Based on the obtained spatial Grey Relation Grade (GRG) values, the pattern of the impact factors clearly showed a spatial heterogeneity. Spatially, sunshine duration, temperature and population density were most closely related to RUE in the west of Songliao Plain between 1999 and 2011. [ABSTRACT FROM AUTHOR]

Successional ecosystems developed spontaneously on agricultural lands cover a substantial area worldwide, particularly in Europe and North America. The functioning of these ecosystems in terms of carbon and water fluxes remains fairly under-investigated. Here, carbon and water exchanges of a spatially heterogeneous tree-shrub-grassland mosaic developed on former semi-dry calcareous grassland in the sub-Mediterranean region of Slovenia were studied. Using eddy covariance, the annual, seasonal and daily dynamics of net ecosystem exchange (NEE) and water vapor exchange were examined, together with their environmental controls during the period August 2008–December 2012. Over this period, the ecosystem appeared to be a carbon sink but the annual carbon fixation had a span of more than four-fold, from 82 to 351 g C m −2 yr −1 . This variability was largely explained by different durations of drought events that occurred during the summer despite the high and relatively evenly distributed rainfall. This is related to the poor ecosystem rain use efficiency, only 0.10–0.35 g C m −2 yr −1 was taken up per mm of rain and the estimated deep water drainage ranged between 44 and 72% of the incoming rain. Drought periods were identified by deriving the critical soil water content (SWC) (here 0.145 m 3 m −3 ) at which evapotranspiration and carbon fluxes started to be limited by water availability. The estimated annual gross primary productivity was shown to be linearly dependent on the duration of the longest annual drought period and not on the drought intensity. Despite a severe drought in the summer of 2012, the ecosystem proved quite resilient to drought stress and restored its carbon uptake after several rain events. As shown by the light response curves, the light dependency of carbon exchange was affected by seasonality and environmental factors, particularly SWC, vapor pressure deficit (VPD) and air temperature (Ta). Interaction between the factors was also observed; negative effect of low SWC was significantly enhanced in the conditions of higher Ta or higher VPD. [ABSTRACT FROM AUTHOR]

Over many decades our understanding of the impacts of intermittent drought in water-limited environments like the West African Sahel has been influenced by a narrative of overgrazing and human-induced desertification. The desertification narrative has persisted in both scientific and popular conception, such that recent regional-scale recovery ("regreening") and local success stories (community-led conservation efforts) in the Sahel, following the severe droughts of the 1970s-1980s, are sometimes ignored. Here we report a study of watershed-scale vegetation dynamics in 260 watersheds, sampled in four regions of Senegal, Mali, and Niger from 1983-2012, using satellite-derived vegetation indices as a proxy for net primary production. In response to earlier controversy, we first examine the shape of the rainfall-net primary production relationship and how it impacts conclusions regarding greening or degradation. We conclude that the choice of functional relationship has little quantitative impact on our ability to infer greening or degradation trends. We then present an approach to analyze changes in long-term (decade-scale) average rain-use efficiency (an indicator of slowly responding vegetation structural changes) relative to changes in interannual-scale rainfall sensitivity (an indicator of landscape ability to respond rapidly to rainfall variability) to infer trends in greening/degradation of the watersheds in our sample regions. The predominance of increasing rain-use efficiency in our data supports earlier reports of a "greening" trend across the Sahel. However, there are strong regional differences in the extent and direction of change, and in the apparent role of changing woody and herbaceous components in driving those temporal trends. [ABSTRACT FROM AUTHOR]

Interannual variation in productivity may be caused by ecosystem structure degradation or recovery or by interannual precipitation fluctuation. A new method for ecosystem assessment was proposed based on the combination of rain-use efficiency (RUE) and normalized difference vegetation index (NDVI). This study aimed to alleviate the effect of precipitation fluctuation on ecosystem productivity. The trend of annual precipitation, annual maximum NDVI, and annual RUE of the study area was first analyzed. The relationship between RUE and precipitation at both temporal and spatial scales was then clarified. Finally, the relationship between the trends of RUE and NDVI was recognized. According to this trend, ecosystem degradation or recovery determined, and the mask of precipitation fluctuation were removed. Results showed that annual RUE varied significantly in space from 1999 to 2008. Annual precipitation displayed a decreasing trend, whereas the annual maximum NDVI presented an increasing trend in most karst ecosystems. RUE presented a remarkable declining trend with annual precipitation at both the temporal and spatial scales ( P < 0.001). At a significant level of 0.2, most karst ecosystems at 16 weather stations were recovering from 1999 to 2008. Ecosystems of Baise, Hechi, and Mengshan stations were in pseudo recovery, whereas those of Laibin and Duan stations were in pseudo degradation because of precipitation fluctuation. At a significant level of 0.05, most karst ecosystems showed non-significant change except four stations were in pseudo recovery. The method of combining RUE and NDVI for ecosystem assessment may remove the mask of precipitation fluctuations and thus improve single NDVI-based method for vegetation analysis. [ABSTRACT FROM AUTHOR]

There is a great deal of debate on the extent, causes, and even the reality of land degradation in the Sahel. Investigations carried out before approximately 2000 using remote sensing data suggest widespread reductions in biological productivity, while studies extending beyond 2000 consistently reveal a net increase in vegetation production, strongly related to the recovery of rainfall following the extreme droughts of the 1970s and 1980s, and thus challenging the notion of widespread, long-term, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends. It is hypothesized that, in addition to rainfall, other meteorological variables and human land use have contributed to vegetation dynamics. Throughout most of the Sahel, the interannual variability in growing season ΣNDVIgs (measured from satellites, used as a proxy of vegetation productivity) was strongly related to rainfall, humidity, and temperature (mean r2 = 0.67), but with rainfall alone was weaker (mean r2 = 0.41). The mean and upper 95th quantile (UQ) rates of change in ΣNDVIgs in response to climate were used to predict potential ΣNDVIgs—that is, the ΣNDVIgs expected in response to climate variability alone, excluding any anthropogenic effects. The differences between predicted and observed ΣNDVIgs were regressed against time to detect any long-term (positive or negative) trends in vegetation productivity. Over most of the Sahel, the trends did not significantly depart from what is expected from the trends in meteorological variables. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by negative, and, in some areas, positive trends. To explore whether the negative trends were human-induced, they were compared with the available data of population density, land use, and land biophysical properties that are known to affect the susceptibility of land to degradation. The spatial variations in the trends of the residuals were partly related to soils and tree cover, but also to several anthropogenic pressures.

Grassland productivity in response to climate change and land use is a global concern. In order to explore the effects of climate change and land use on net primary productivity ( NPP), NPP partitioning [ fBNPP, defined as the fraction of belowground NPP ( BNPP) to NPP], and rain-use efficiency ( RUE) of NPP, we conducted a field experiment with warming (+3 °C), altered precipitation (double and half), and annual clipping in a mixed-grass prairie in Oklahoma, USA since July, 2009. Across the years, warming significantly increased BNPP, fBNPP, and RUEBNPP by an average of 11.6%, 2.8%, and 6.6%, respectively. This indicates that BNPP was more sensitive to warming than aboveground NPP ( ANPP) since warming did not change ANPP and RUEANPP much. Double precipitation stimulated ANPP, BNPP, and NPP but suppressed RUEANPP, RUEBNPP, and RUENPP while half precipitation decreased ANPP, BNPP, and NPP but increased RUEANPP, RUEBNPP, and RUENPP. Clipping interacted with altered precipitation in impacting RUEANPP, RUEBNPP, and RUENPP, suggesting land use could confound the effects of precipitation changes on ecosystem processes. Soil moisture was found to be a main factor in regulating variation in ANPP, BNPP, and NPP while soil temperature was the dominant factor influencing fBNPP. These findings suggest that BNPP is critical point to future research. Additionally, results from single-factor manipulative experiments should be treated with caution due to the non-additive interactive effects of warming with altered precipitation and land use (clipping). [ABSTRACT FROM AUTHOR]

Aims Clarifying the spatiotemporal variations in precipitation-use efficiency (PUE), the ratio of vegetation above-ground productivity to annual precipitation, will advance our understanding of how ecosystems' carbon and water cycles respond to climate change. Our goal is to investigate the variations in PUE at both regional and site scales along a 4500-km climate-related grassland transect. Location The Inner Mongolian Plateau in northern China and the Qinghai-Tibetan Plateau. Methods We collected data on 580 sites from four data sources. The data were acquired through field surveys and long-term in situ observations. We investigated the relationships between precipitation and PUE at both regional and site scales, and we evaluated the effects of the main biotic and climatic factors on PUE at both spatial scales. Results PUE decreased with decreasing mean annual precipitation (MAP), except for a slight rise toward the dry end of the gradient. The maximum PUE showed large site-to-site variation along the transect. Vegetation cover significantly affected the spatial variations in PUE, and this probably accounts for the positive relationship between PUE and MAP. However, there was no significant relationship between inter-annual variations in precipitation or vegetation cover and PUE within given ecosystems along the transect. Conclusions The findings of this research contradict the prevailing view that a convergent maximum PUE exists among diverse ecosystems, as presented in previous reports. Our findings also suggest the action of distinct mechanisms in controlling PUE at different spatial scales. We propose the use of a conceptual model for predicting vegetation productivity at continental and global scales with a sigmoid function, which illustrates an increasing PUE with MAP in arid regions. Our approach may represent an improvement over use of the popular Miami model. [ABSTRACT FROM AUTHOR]

Productivity of semiarid grasslands is primarily limited by seasonal rainfall amount and becomes increasingly limited by nutrient availability under wet conditions. Interactive effects of water and N availability on grassland productivity and parameters related to water use were studied on a grassland site in Inner Mongolia, China, in a 2-factorial experiment with two levels of water (rainfed: 158 mm; irrigated: 839 (N0) and 972 (N1) mm) and N supply (0 or 180 kg N ha−1). RUE was calculated from ANPP and cumulative water supply. Bare soil evaporation (E) was calculated from climatic data and leaf area dynamics, and percolation (D) and transpiration (T) were estimated with HYDRUS-1D. Water-use efficiency (WUE, ANPP / (T + D)) and transpiration efficiency (TE, ANPP / T) were calculated. Resource availability had pronounced effects on the water-use efficiency of semiarid grassland. RUE, WUE, and TE all decreased under irrigated compared to rainfed conditions and were significantly increased with N fertilizer application at both levels of water supply. While the irrigation effect on parameters of water-use efficiency were accordingly reflected in stable carbon isotope signatures, N supply resulted in significantly less negative δ13C-values under rainfed but not irrigated conditions. It is concluded, that spatial or temporal gradients in resource availability have pronounced effects on the water-use efficiency of semiarid grassland. The decrease of water use-efficiency under high water supply was related to differences in TE and not to a relative increase of unproductive water loss. Carbon isotope discrimination was highly correlated with WUE and TE, but can be a poor predictor of RUE. [ABSTRACT FROM AUTHOR]

Native seed needs to be sourced locally yet contain ample genetic variation. A blueprint is developed for assembling and assessing native plant material at one eco-geographical site prior to seed multiplication for restoring degraded drylands of North Africa. To satisfy the ‘local yet ample’ criterion, the feasibility of selecting a limited number of high-yielding genotypes within one starter collection of Cenchrus ciliaris L. in Presaharian Tunisia (100–200 mm annual rainfall) was tested and compared to outcomes with similar work on its ecological complement, Stipa lagascae R. & Sch. Results showed that a limited number of high-yielding genotypes can easily produce quality native seed because of the high genetic diversity of the starter material. Results also showed that there was a high potential to increase the rain-use efficiency of degraded drylands using this seed. Seven ground rules are suggested when building the starter collection: (i) carefully delimit the region for sourcing seed; (ii) work with individual plants; (iii) carefully choose the collection site; (iv) replicate plant material as much as is feasible; (v) match evaluation methods to resource constraints; (vi) wait for conditions of maximum resource availability before culling; and (vii) apply a two-tiered selection strategy. [ABSTRACT FROM AUTHOR]

Land degradation is always with us but its causes, extent and severity are contested. We define land degradation as a long-term decline in ecosystem function and productivity, which may be assessed using long-term, remotely sensed normalized difference vegetation index (NDVI) data. Deviation from the norm may serve as a proxy assessment of land degradation and improvement – if other factors that may be responsible are taken into account. These other factors include rainfall effects which may be assessed by rain-use efficiency, calculated from NDVI and rainfall. Results from the analysis of the 23-year Global Inventory Modeling and Mapping Studies (GIMMS) NDVI data indicate declining rain-use efficiency-adjusted NDVI on ca. 24% of the global land area with degrading areas mainly in Africa south of the equator, South-East Asia and south China, north-central Australia, the Pampas and swaths of the Siberian and north American taiga; 1.5 billion people live in these areas. The results are very different from previous assessments which compounded what is happening now with historical land degradation. Economic appraisal can be undertaken when land degradation is expressed in terms of net primary productivity and the resultant data allow statistical comparison with other variables to reveal possible drivers. [ABSTRACT FROM AUTHOR]

Understanding how the aboveground net primary production (ANPP) of arid and semiarid ecosystems of the world responds to variations in precipitation is crucial for assessing the impacts of climate change on terrestrial ecosystems. Rain-use efficiency (RUE) is an important measure for acquiring this understanding. However, little is known about the response pattern of RUE for the largest contiguous natural grassland region of the world, the Eurasian Steppe. Here we investigated the spatial and temporal patterns of ANPP and RUE and their key driving factors based on a long-term data set from 21 natural arid and semiarid ecosystem sites across the Inner Mongolia steppe region in northern China. Our results showed that, with increasing mean annual precipitation (MAP), (1.) ANPP increased while the interannual variability of ANPP declined, (2) plant species richness increased and the relative abundance of key functional groups shifted predictably, and (3) RUE increased in space across different ecosystems but decreased with increasing annual precipitation within a given ecosystem. These results clearly indicate that the patterns of both ANPP and RUE are scale dependent, and the seemingly conflicting patterns of RUE in space vs. time suggest distinctive underlying mechanisms, involving interactions among precipitation, soil N, and biotic factors. Also, while our results supported the existence of a common maximum RUE, they also indicated that its value could be substantially increased by altering resource availability, such as adding nitrogen. Our findings have important implications for understanding and predicting ecological impacts of global climate change and for management practices in arid and semiarid ecosystems in the Inner Mongolia steppe region and beyond. [ABSTRACT FROM AUTHOR]

In semiarid regions the ratio of annual net primary production to precipitation, rain-use efficiency (RUE), has been used as an index of desertification. In a recent publication ( Hein & de Ridder, 2006 ) it was proposed that an incorrect understanding of the relationship between RUE and rainfall has led to a misinterpretation of the satellite record of desertification in the African Sahel. Here, we examine this suggestion and show that, contrary to Hein and de Ridder's statement, satellite studies of Sahelian RUE have reported increases, decreases, and constant values since 1981. Furthermore, we find that data do not support their proposal that RUE increases with rainfall, even in nondegraded areas. Hence we reject their corollary, that constant RUE is prima facie evidence of desertification. The fundamental difficulty with the use of RUE for detection of desertification remains, that is the difficulty of estimation of the RUE for nondegraded land at a regional scale. [ABSTRACT FROM AUTHOR]

Abstract: Advanced Very High Resolution Radiometer (AVHRR), Normalized Difference Vegetation Index data (NDVI, 1km2, 1985–2003) and modeled net primary production (NPP, 8km2, 1981–2000) data were used to estimate vegetation production in South Africa (SA). The linear relationships of Log e Rainfall with NPP and ΣNDVI were calculated for every pixel. Vegetation production generally had a strong relationship with rainfall over most of SA. Therefore, human-induced land degradation can only be detected if its impacts on vegetation production can be distinguished from the effects of rainfall. Two methods were tested (i) Rain-Use Efficiency (RUE=NPP/Rainfall or ΣNDVI/Rainfall) and (ii) Residual Trends (RESTREND), i.e. negative trends in the differences between the observed ΣNDVI and the ΣNDVI predicted by the rainfall. Degraded areas mapped by the National Land Cover in north-eastern SA had reduced RUE; however, annual RUE had a very strong negative correlation with rainfall and varied greatly between years. Therefore, RUE was not a reliable indicator of degradation. The RESTREND method showed promising results at a national scale and in the Limpopo Province, where negative trends were often associated with degraded areas in communal lands. Both positive and negative residual trends can, however, result from natural ecological processes, e.g. the carryover effects of rainfall in previous years. Thus, the RESTREND method can only identify potential problem areas at a regional scale, while the cause of negative trends has to be determined by local investigations. [Copyright &y& Elsevier]

The impact of human management, in particular livestock grazing, on the vegetation cover of the Sahel is still debated. In a range of studies, satellite images have been used to analyze the development of the Sahelian vegetation cover over time. These studies did not reveal any significant degradation of the Sahel in the last two decades. In this paper, we examine the ecological assumptions underlying the use of satellite imagery to analyze degradation of the Sahel. Specifically, we analyze the variability of the rain-use efficiency (RUE), which is often used as an indicator for the state of the vegetation cover. We detect a fundamental flaw in the way RUE has been handled in most remote sensing studies; they ignored the relation between annual rainfall variation and RUE. Because of the upward trend in annual rainfall that occurred during the 1980s and 1990s, this leads to a bias in the interpretation of the satellite images. In this paper, we show the importance of the variability in RUE for the analysis of remote sensing imagery of semiarid rangelands. Our analysis also shows that it is likely that there has been anthropogenic degradation of the Sahelian vegetation cover in the last two decades. This has important consequences for the debate on the impacts of grazing on semiarid rangelands. Furthermore, the occurrence of anthropogenic degradation is relevant to explain the magnitude of 20th century Sahelian droughts. The analyses also indicate that the population of the Sahel may be more vulnerable for droughts than currently assumed. [ABSTRACT FROM AUTHOR]

Abstract: The impacts of grazing pressure and rainfall variability on rangeland dynamics have been the topic of much debate. Understanding the combined impact of these two factors is crucial for the development of efficient management strategies for rangelands. In this paper, the impacts of grazing and rainfall variability on the dynamics of a Sahelian rangeland in Northern Senegal are examined. Specifically, the paper assesses their combined impact on species composition, above-ground phytomass production and rain-use efficiency (RUE), on the basis of a 10-year (1981–1990) grazing experiment conducted in the Widou-Thiengoly catchment in the Ferlo, Northern Senegal. The experiment included both a high (0.15–0.20TLUha−1, corresponding to current grazing) and a medium (0.10TLUha−1) grazing pressure. It is shown that species composition, above-ground phytomass production and RUE markedly differ for these two grazing regimes—and that the differences are most pronounced in years with low rainfall. In dry years, both above-ground phytomass production and RUE are significantly reduced in the plots subject to a high grazing pressure. Consequently, the impacts of high grazing pressures on the productivity of the Ferlo are hardly noticed during years with normal or above normal rainfall, but the rangeland''s productivity is strongly affected during a drought. The findings have important implications for the management of rangelands; they indicate that high grazing pressures may increase the vulnerability of rangeland ecosystems and local people to droughts. [Copyright &y& Elsevier]

Field experiments were conducted at the University of Jordan Research Station at Al-Muwaqqar village to develop a simple technique for establishing Atriplex seedlings, and to evaluate the browse production under natural precipitation compared with shrubs receiving additional harvested water. Overall survival of the transplants after three growing seasons averaged 67% under strictly rainfed conditions compared to 95% when additional harvested water of 39 mm was applied. Production of grazable browse of 3-year old shrubs averaged 380 and 1151 kg DM (dry matter) ha-1 without and with additional water, respectively. Rain use efficiency averaged 1.14 and 4.48 kg DM ha-1 year-1 mm-1 for strictly rainfed conditions and additional harvested water, respectively. Intensity of cutting had a highly significant effect on the potential of shrub regrowth. Cutting shrubs at a height of 15 and 30 cm above ground level reduced regrowth substantially, whereas cutting at 45 cm enhanced the amount of regrowth. The different cutting intensities had no significant effect on survival of the severed shrubs, which indicates the high tolerance of saltbushes to cutting or browsing. Water-harvesting contour furrows are reasonable for establishing saltbush plantations in low rainfall areas (100–200 mm). Additional harvested water in small amounts from macro-catchements had a substantial effect on shrub survival, biomass production and water use efficiency. [Copyright &y& Elsevier]

During the dormant winter period the semi-arid rangeland areas of South Africa are characterized by unplanned fires, either by lightning or negligence by man. The quantification of the impact of burning in terms of the above- and below-ground phytomass production, rain-use efficiency (RUE), crude protein, root/shoot ratios and plant density of the grass sward was conducted in a semi-arid rangeland over 2 years (2000/2001–2001/2002 growing seasons) following an accidental fire. Fire (head fire) had a significant (p<0.01) influence on plant density. Grass species with larger tufts (Cymbopogon plurinodis and Themeda triandra) suffered the most dieback due to the fire. The initial advantage in quality (crude protein) accompanying the fire does not neutralize the reduction in half of above-ground phytomass production and poor (p<0.01) RUE occurring in the first season following the fire. Burnt rangeland takes at least two full growing seasons to recover in terms of above- and below-ground phytomass production, litter and RUE. Fire lowered (p<0.01) RUE for both growing seasons especially during the first four months. The average RUE was 3.72 and 2.86 kg ha−1 mm−1, respectively, for unburnt and burnt rangeland for the 2 years. Root mass decreased (p<0.01) by 59% over the first 100 mm depth due to fire. More than 80% of the root mass was found in the top 0–300 mm soil layer. The below-ground growth is more sensitive to burning than above-ground growth. Fire reduced the root/shoot ratio from 1.44 to 1.30. These results can serve as scientific guidelines in claims for damages and short-term risk management of semi-arid rangeland after an accidental runaway fire driven by August winds. [Copyright &y& Elsevier]

This study examined the short-term response of rangeland to annual (1993/94 to 1996/97 seasons) application of fertilizer [all combinations of 0; 10; 30 and 50 kgha−1nitrogen (N), with 0 and 10 kgha−1of phosphorus (P)] in terms of aboveground phytomass production, crude protein content, seasonal rain-use efficiency (S-RUE), nutrient use efficiency, botanical composition, basal cover and soil compaction. After 4 years of fertilization, the botanical composition of the high N-fertilized plots changed from a climax to subclimax vegetation.Elionurus muticus showed the greatest decrease in frequency (62%) due to N fertilization. Phosphorus fertilization only, had an insignificant (p>0·05) influence on species composition and basal cover over the 4 years. The production increased (p&les;0·01) with the application of N together with P, compared to applying only N (1074vs. 823 kgha−1). The more fertilizer applied, the more sensitive to drought the climax grasses became. Nitrogen and phosphorus fertilization significantly (p&les;0·01) affected S-RUE. The highest S-RUE of 6·64 kg phytomass ha−1mm−1and 0·23 kg crude protein ha−1mm−1were obtained with fertilizer application of 50 kgN plus 10 kgPha−1. On average over the 4 years, nutrient use efficiency with N+P application for all treatments was lower than without P. The increases in plant production per kg N applied, both with and without P were 28·00 and 29·81 kg respectively. Soil compaction increased with increase in N fertilization. These results confirm the vulnerability of native grasses in dry areas, following change in soil fertility. [Copyright &y& Elsevier]

Sustainable Development Goal (SDG) indicator 15.1.1 proposes to quantify " Forest area as a proportion of total land area " in order to achieve SDG target 15.1. While area under forest cover can provide useful information regarding discrete changes in forest cover, it does not provide any insight on subtle changes within the broad vegetation class, e.g. forest degradation. Continental or national-level studies, mostly utilizing coarse-scale satellite data, are likely to fail in capturing these changes due to the fine spatial and long temporal characteristics of forest degradation. Yet, these long-term changes affect forest structure, composition and function, thus ultimately limiting successful implementation of SDG targets. Using a multi-scale, satellite-based monitoring approach, our goal is to provide an easy-to-implement reporting framework for South Asian forest ecosystems. We systematically analyze freely available remote sensing assets on Google Earth Engine for monitoring degradation and evaluate the potential of multiple satellite data with different spatial resolutions for reporting forest degradation. Taking a broad-brush approach in step 1, we calculate vegetation trends in six south Asian countries (Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka) using the Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) during 2000–2016. We also calculate rainfall trends in these countries using the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) rainfall data, and further calculate Rain-Use Efficiency (RUE) that shows vegetation trends in the context of rainfall variability. In step 2, we focus on two protected area test cases from India and Sri Lanka for evaluating the potential of finer-resolution satellite data compared to MODIS, i.e. Landsat 8, and Sentinel-2 data, for capturing forest degradation signals, which will ultimately contribute towards SDG indicators 15.1.1 and 15.1.2. We find that most countries show a fluctuating trend in vegetation condition over the years, along with localized greening and browning. The Random Forest (RF) classifier utilized in step 2 was able to generate accurate maps (87% and 91% overall accuracy for Indian and Sri Lankan test cases, respectively) of non-intact forest within the protected areas. We find that almost one-third of the Indian test case is degraded forest, even though it shows overall greening as per the broad-brush approach. This finding corroborates our argument that utilizing higher-resolution satellite data (e.g. 10-m) than those normally used for national-level studies will be crucial for reporting SDG indicator 15.2.1: " progress towards sustainable forest management ". • Most south Asian countries witnessed localized greening/browning during 2000–2016. • Coarse-scale satellite data (≥1 km) might not capture subtle forest degradation. • High-resolution data (≤10 m) must be used to assess current forest condition. • A multi-step framework should be employed for accurate reporting of SDG 15. [ABSTRACT FROM AUTHOR]