Grassland Dynamics Research Articles

Responses of carbon dynamics to grazing exclusion in natural alpine grassland ecosystems on the QingZang Plateau.

In the context of "Carbon Emissions Peak" and "Carbon Neutrality", grazing exclusion (GE) has been applied widely to rehabilitate degraded grasslands and increase carbon sequestration. However, on the QingZang Plateau (QZP), the impacts of GE on the carbon dynamics of alpine grasslands are poorly understood, particularly at a regional scale. To fill this knowledge gap, we evaluated the responses of carbon sequestration to GE in different alpine grasslands across QZP by using meta-analysis. The effects of GE on ecosystem carbon fractions were dependent on GE duration, grassland types and climate factors. Specifically, our results indicated that GE had more obviously positive effects on carbon stock across the alpine meadow than the alpine steppe. However, when considering different GE duration, the longer duration of GE was more effective for increasing ecosystem carbon sequestration (R 2 = 0.52, P<0.0001) in the alpine steppe. Our results further demonstrated that annual mean precipitation (AMP) and temperature (AMT) began to dominate ecosystem carbon sequestration after three years of GE duration across the alpine meadow; and AMP was an important climate factor limiting ecosystem carbon sequestration (R 2 = 0.34, P<0.01) in the alpine steppe. In terms of plant carbon fraction, GE generated continuous positive effect (P<0.05) on aboveground biomass with the increased GE duration in the alpine meadow, while this positive effect disappeared after the 8th year of GE duration. And no positive effects were found on belowground biomass in the 11th year in alpine steppe. For soil organic carbon (SOC), there existed periodic fluctuations (increased and then decreased) on SOC in response to GE. For microbial biomass carbon, there were no obvious trends in response to GE duration. In general, we highlighted that the responses of different carbon fractions (plant-soil-microbe) to GE were non-uniform at spatial and temporal scales, thereby we should adopt different carbon management practices for sustainable development of different grasslands.

Intermediate snowpack melt-out dates guarantee the highest seasonal grasslands greening in the Pyrenees

In mountain areas, the phenology and productivity of grassland are closely related to snow dynamics. However, the influence that snow melt timing has on grassland growing still needs further attention for a full understanding, particularly at high spatial resolution. Aiming to reduce this knowledge gap, this work exploits 1 m resolution snow depth and Normalized Difference Vegetation Index observations acquired with an Unmanned Aerial Vehicle at a sub-alpine site in the Pyrenees. During two snow seasons (2019–2020 and 2020–2021), 14 NDVI and 17 snow depth distributions were acquired over 48 ha. Despite the snow dynamics being different in the two seasons, the response of grasslands greening to snow melt-out exhibited a very similar pattern in both. The NDVI temporal evolution in areas with distinct melt-out dates reveals that sectors where the melt-out date occurs in late April or early May (optimum melt-out) reach the maximum vegetation productivity. Zones with an earlier or a later melt-out rarely reach peak NDVI values. The results obtained in this study area, suggest that knowledge about snow depth distribution is not needed to understand NDVI grassland dynamics. The analysis did not reveal a clear link between the spatial variability in snow duration and the diversity and richness of grassland communities within the study area.

Retrieval of High-Resolution Vegetation Optical Depth from Sentinel-1 Data over a Grassland Region in the Heihe River Basin

Vegetation optical depth (VOD), as a microwave-based estimate of vegetation water and biomass content, is increasingly used to study the impact of global climate and environmental changes on vegetation. However, current global operational VOD products have a coarse spatial resolution (~25 km), which limits their use for agriculture management and vegetation dynamics monitoring at regional scales (1–5 km). This study aims to retrieve high-resolution VOD from the C-band Sentinel-1 backscatter data over a grassland of the Heihe River Basin in northwestern China. The proposed approach used an analytical solution of a simplified Water Cloud Model (WCM), constrained by given soil moisture estimates, to invert VOD over grassland with 1 km spatial resolution during the 2018–2020 period. Our results showed that the VOD estimates exhibited large spatial variability and strong seasonal variations. Furthermore, the dynamics of VOD estimates agreed well with optical vegetation indices, i.e., the mean temporal correlations with normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and leaf area index (LAI) were 0.76, 0.75, and 0.75, respectively, suggesting that the VOD retrievals could precisely capture the dynamics of grassland.

Predicting spring green-up across diverse North American grasslands

Vegetation phenology influences many ecosystem and climate processes, such as carbon uptake and energy and water cycles. Thus, understanding drivers of vegetation phenology is crucial for predicting current and future impacts of climate change on ecological systems. Existing models can accurately predict the date of spring green-up in temperate forests but tend to perform poorly in grassland systems. We hypothesize this is because most do not incorporate water availability, a primary limiting factor for grassland plants. In this study, we used long-term datasets of digital imagery from the PhenoCam Network of 43 diverse North American grassland sites (195 site-years) to test existing spring phenology models, as well as develop several new models that incorporate precipitation or soil moisture (53 models). Most of the new models performed substantially better, with the best model requiring sufficient accumulated precipitation followed by warm temperatures to trigger spring onset (root mean square error, RMSE, between predicted and observed dates = 16.0 days). Importantly, the best model performed well across all grassland types using a single set of parameters, from temperate to arid grasslands. Since plants are adapted to their local climates, model performance was further improved when parameters were independently optimized for four separate climate regions (RMSE = 10.4 days). Therefore, both sufficient precipitation and temperature are required for grassland green-up, but optimal thresholds vary by region. Running the top model with projected climate data (representative concentration pathway 8.5) suggests that, depending on the climate region, spring onset will occur up to 12 days earlier within 100 years in temperature-limited sites, but the trend is unclear for precipitation-limited sites (3.5 ± 8.0 days later). This new phenology model improves our ability to understand and predict grassland dynamics, with implications for both current and future ecosystem processes related to carbon and water cycling.

Livestock production land and conservation areas play a complementary role in the conservation of a critically endangered grassland bird

AbstractIn many parts of the world, livestock production and biodiversity conservation are important land uses of native grasslands in agricultural landscapes. Approaches to managing grasslands typically differ between production farms and conservation areas as they have different goals. Such differences may have consequent effects on the spatial and temporal habitat suitability for grassland fauna. In semi‐arid grasslands of south‐eastern Australia, the critically endangered Plains‐wanderer (Pedionomus torquatus) is a grassland habitat‐specialist bird that can occur on land managed for livestock production and conservation, but it is unclear if, and when, habitat suitability is affected in each land‐use type.Here, we investigate how land‐use type (livestock production, conservation) and rainfall (preceding accumulated rainfall) affect habitat suitability for the Plains‐wanderer using 11 years of bird occurrence and remotely sensed habitat structure data.We found habitat suitability for the Plains‐wanderer was driven by an interaction between land use and rainfall, with conservation areas supporting larger areas of preferred habitat structure during dry periods but less during wet periods. By contrast, Plains‐wanderers were more likely to occur on livestock production farms during wet periods. We speculate this is because higher grazing pressure on livestock production farms was able to limit biomass accumulation and, hence, maintain more areas of preferred habitat structure.Our findings show that land used for livestock production can complement conservation areas by providing preferred habitat for the Plains‐wanderer during climatic periods that promote grass growth. Furthermore, we highlight that land use and climate are important temporal drivers of grassland dynamics, and approaches to biodiversity conservation should consider how patterns of habitat suitability may shift across landscapes over time. Strategic, landscape‐scale planning and effective agri‐environmental initiatives will be critical to the future of grassland birds such as the Plains‐wanderer.

Evaluating the Impact of Dynamic Changes in Grasslands on the Critical Ecosystem Service Value of Yanchi County in China from 2000 to 2015

Grasslands are the basis for sustainable development in the northern farming-pastoral transition zone of China, with functions of human production, living, and ecology. Large-scale human activities inevitably lead to significant changes in grasslands, resulting in significant impacts on ecosystem services. To this end, we quantitatively estimated the ecosystem services value in each positive succession process (the improvement in the coverage or area of grasslands) and negative succession process (the degradation in the coverage or area of grasslands). The results indicated that (1) grasslands showed an improving trend from 2000 to 2015. The grassland improvement from low to high coverage dominated the positive succession process. Grassland degradation from high to low coverage dominated the negative succession process. (2) The total ecosystem services value increased by 25,294.87 × 104 yuan from 2000 to 2015. The grassland improvement from low to high coverage was the most important process that led to the increase in ecosystem service value. The degradation between grasslands and non-grasslands was the key process that led to the decrement in ecosystem services value. (3) The impact of grassland dynamics on the regional ecosystem service value showed significant spatial heterogeneity at the town scale. The results will provide some implications for the sustainable development of grassland ecosystem services to improve human well-being.

Elevational pattern of soil organic carbon release in a Tibetan alpine grassland: Consequence of quality but not quantity of initial soil organic carbon

Soil organic carbon (SOC) dynamics along elevational gradients are highly uncertain due to our limited knowledge of the underlying mechanisms that determine SOC release. By combining field investigation and laboratory aerobic incubation with multiple soil analytical approaches, we explored the determinants of SOC release along an elevational gradient (3200–4200 m) in the Tibetan alpine grassland. We illustrated that the SOC quantity (i.e., the initial standing SOC stock) and SOC quality (i.e., chemical recalcitrance, physico-chemical protection and biological recalcitrant fraction) increased gradually with elevation, reaching a maximum value at the middle altitude (∼3600 m), while an opposite unimodal distribution pattern was observed in CO2–C release. Our results also showed that SOC quality explained more variance in CO2–C release than did SOC quantity and soil properties. The proportion of stable SOC fractions in larger initial SOC stocks is higher, especially the recalcitrant SOC pool and mineral-associated OC fractions, which could be the potential mechanism behind high initial SOC stocks leading to lower soil CO2–C release. Collectively, our results provide compelling evidence that SOC quality plays a primary role in the elevational pattern of CO2–C release in Tibetan alpine grassland. Our findings highlight the importance of SOC quality in predicting SOC dynamics in the Tibetan alpine grassland under climate change scenarios.

Something went missing: cessation of Traditional Owner land management and rapid mammalian population collapses in the semi-arid region of the Murray&amp;#x2013;Darling Basin, southeastern Australia

The nineteenth century mass mammal extinctions in the semi-arid zone of the Murray&amp;#x2012;Darling basin, southeastern Australia, are examined in the context of prior traditional land management. A model of grassland dynamics reveals a multi-trophic level productive pulse one to five years post-fire, followed by senescence and increasing flammability. Traditional Owner patch burning of grassland optimized human and mammalian food (including tubers, seeds and fungi) and decreased fire risk. Over at least 40 000 years, the persistence and abundance of fauna responded to this energetically closed self-reinforcing management. In 1830, depopulation (disease, massacres and displacement) effectively ended traditional management, an ecologically traumatic event that extinguished these productivity pulses. Associated mammal populations of c. 20 species collapsed, and all eco-engineering and mycophagous species, such as bilbies, bettongs and bandicoots, rapidly disappeared. Traditional land management increased productivity, habitat heterogeneity and reduced wildfire risk, underpinning mammal abundance. This has remained unrecognized by most mammalogists and land managers. Blaming extinctions predominantly on the additions by Europeans (introduction of ungulates, feral grazers and predators etc.), disastrous as they were, fails to acknowledge the initial cause of rarity, i.e. loss of productivity, habitat and niches when traditional management was subtracted from country. As ecosystems continue to degrade, understanding the primary cause is fundamental to improved management. Although too late for extinct species, respect for, and inclusion of, traditional land management knowledge provides a direction for future land management.

Assessing drivers of intra-seasonal grassland dynamics in a Kenyan savannah using digital repeat photography

Understanding grassland dynamics and their relationship to weather and grazing is critical for pastoralists whose livelihoods depend on grassland productivity. Studies investigating the impacts of climate and human factors on inter-seasonal grassland dynamics have focused mostly on changes to vegetation structure. Yet, quantifying the impact of these on the inter-seasonal dynamics of specific grassland communities is not known. This study uses digital repeat photography to examine how intra-seasonal grassland dynamics of different grassland communities are affected by precipitation, temperature, and grazing in a heterogeneous semi-arid savannah in Kenya. A low-cost digital repeat camera network allowed for fine-scale temporal and spatial variability analysis of grassland dynamics and grazing intensity. Over all grass communities, our results show precipitation driving mainly early-season and in some cases mid-season flushing, temperature driving end-of-season senescence, and grazing influencing mid-season declines. Yet, our study quantifies how these three drivers do not uniformly impact grassland species communities. Specifically, Cynodon and Cynodon/Bothriochloa communities are rapidly and positively associated with precipitation, where mid-season declines in Cynodon communities are associated with grazing and late-season declines in Cynodon/Bothriochloa communities are associated with temperature increases. Setaria communities, on the other hand, have weaker associations with the drivers, with limited positive associations with precipitation and grazing. Kunthii/Digitaria diverse communities had no association with the three drivers. Highly diverse mixed communities were associated with increased precipitation and temperature, as well as lower intensity grazing. Our research sheds light on the complex interactions between plants, animals, and weather. Furthermore, this study also demonstrates the potential of digital repeated photography to inform about fine-scale spatial and temporal patterns of semi-arid grassland vegetation and grazing, with the goal of assisting in the formulations of management practises that better capture the intra-annual variability of highly heterogeneous dryland systems.

Change in Alpine Grassland NPP in Response to Climate Variation and Human Activities in the Yellow River Source Zone from 2000 to 2020

Identifying the relative contributions of climate change and human activities to alpine grassland dynamics is critical for understanding grassland degradation mechanisms. In this study, first, the actual NPP (NPPa) was obtained by MOD17A3. Second, we used the Zhou Guangsheng model to simulate the potential met net primary productivity (NPPp). Finally, the NPP generated by anthropogenic activities (NPPh) was estimated by calculating the difference between NPPp and NPPa. Then, the relative contributions of climate change and human activities to NPP changes in grasslands were quantitatively assessed by analyzing trends in NPPp and NPPa. Thereby, the drivers of NPP change in the Yellow River source grassland were identified. The results showed that the temperature and precipitation in the study area showed a warm-humid climate trend from 2000 to 2020. The NPPp and NPPa increased at a rate of 1.07 g C/m2 and 1.51 g C/m2 per year, respectively, while the NPPh decreased at a rate of 0.46 g C/m2 per year. It can be seen that human activities had a positive effect on the change of NPP in the Yellow River source grassland from the change rate. The relative contribution analysis showed that 55.90% of grassland NPP increased due to climate change, 40.16% of grassland NPP increased due to human activities, and the grassland degradation was not significant. The research results can provide a theoretical basis and technical support for the next step of the Yellow River source grassland ecological protection project.

Impact of mowing frequency and temperature on the production of temperate grasslands: explanations received by an individual‐based model

Grasslands represent an important ecosystem type as they provide numerous ecosystem services. Field studies have shown that temperate grasslands with high diversity can be highly productive. Management and changing environmental conditions can impact the diversity–production relationship. However, the specific mechanisms and role of biodiversity, environmental factors or anthropogenic interventions that lead to changes in production are not well understood. Here, we used the individual‐based grassland model GRASSMIND parameterized for a field biodiversity experiment to analyze changes in the diversity–production relationship when varying the mowing frequency and increasing air temperature. Our results revealed that the positive diversity–production relationship persists with varied mowing frequency and temperature increase, with an increased proportion of herbs in more frequently mown grasslands (from 78% to 85%). Using the model, we further investigated quantitatively how different processes (e.g. plant shading) affect grassland dynamics and production under varied mowing frequencies and air temperature. Although aboveground net primary production (ANPP) decreased in more frequently mown grasslands (20% less ANPP), biomass yields increased due to an even stronger decrease in space‐dependent plant mortality (30% less crowding). Plant mortality (intrinsic and by crowding) caused more biomass losses than caused by shading between plants or by a reduced production due to temperature increase. This study revealed how models, complementary to field experiments, can be used to analyze and quantify the importance of mechanisms and the role of environmental factors in grassland dynamics.

Grassland type and seasonal effects have a bigger influence on plant functional and taxonomical diversity than prairie dog disturbances in semiarid grasslands.

Prairie dogs (Cynomys sp.) are considered keystone species and ecosystem engineers for their grazing and burrowing activities (summarized here as disturbances). As climate changes and its variability increases, the mechanisms underlying organisms' interactions with their habitat will likely shift. Understanding the mediating role of prairie dog disturbance on vegetation structure, and its interaction with environmental conditions through time, will increase knowledge on the risks and vulnerability of grasslands.Here, we compared how plant taxonomical diversity, functional diversity metrics, and community‐weighted trait means (CWM) respond to prairie dog C. mexicanus disturbance across grassland types and seasons (dry and wet) in a priority conservation semiarid grassland of Northeast Mexico.Our findings suggest that functional metrics and CWM analyses responded to interactions between prairie dog disturbance, grassland type and season, whilst species diversity and cover measures were less sensitive to the role of prairie dog disturbance. We found weak evidence that prairie dog disturbance has a negative effect on vegetation structure, except for minimal effects on C4 and graminoid cover, but which depended mainly on season. Grassland type and season explained most of the effects on plant functional and taxonomic diversity as well as CWM traits. Furthermore, we found that leaf area as well as forb and annual cover increased during the wet season, independent of prairie dog disturbance.Our results provide evidence that grassland type and season have a stronger effect than prairie dog disturbance on the vegetation of this short‐grass, water‐restricted grassland ecosystem. We argue that focusing solely on disturbance and grazing effects is misleading, and attention is needed on the relationships between vegetation and environmental conditions which will be critical to understand semiarid grassland dynamics under future climate change conditions in the region.

Leaf N:P stoichiometry overrides the effect of individual nutrient content on insect herbivore population dynamics in a Tibetan alpine grassland

Based on resource availability hypothesis, increasing exogenous nutrient inputs may favour herbivores by improving quality and quantity of host plants. Such plant-herbivore interactions have been demonstrated under nitrogen (N) addition, but less examined in the context of simultaneous inputs of N and phosphorus (P). Here, we conducted a multiple-nutrient addition experiment (Control, N addition alone, P addition alone, both N and P additions) in a Tibetan alpine grassland, to explore how N addition interacts with P to affect the larval density of the grassland caterpillar Gynaephora menyuanensis. We showed that P addition alone did not obviously affect the larval density, but P suppressed N-induced increases in larval density when N and P were simultaneously added. We further found that changes in leaf N:P of host plants induced by nutrient additions regulated larval density more strongly than leaf N or P content. Both increased plant productivity and shifted species composition under nutrient additions contributed less to the larval density. Interactive effects of N and P suggest that the simultaneous inputs of multiple nutrients may boost the carrying capacity of grasslands and reduce the risk of herbivorous insect outbreaks. The work also reveals that the resource availability hypothesis does not well predict the response of insect herbivore to all nutrient inputs, implying the necessity of incorporating N:P stoichiometry in this hypothesis.

Clay fraction properties and grassland management imprint on soil organic matter composition and stability at molecular level

AbstractThe dynamics of soil carbon in grassland are partly determined by soil organic matter (SOM) composition. However, it remains unclear which role grassland management plays in the interplay between SOM composition and carbon dynamics. Using pyrolysis‐field ionization mass spectrometry (Py‐FIMS), we studied the effect of meadow, mown pasture and pasture on the molecular SOM composition in German topsoils. In sandy soils of the Schorfheide‐Chorin region, SOM composition and stability were strongly affected by clay contents and concentrations of crystalline Fe‐oxides. Here, the grassland management type influenced lipid proportions, which accounted for a maximum of 11.1% of the total ion intensity (TII) under mown pasture. In the Hainich‐Dün region, SOM composition was mainly related to the SOM decomposition stage (abundance of potentially recalcitrant compounds) but not to minerals. Compound classes of carbohydrates (4.3% TII), phenols and lignin monomers (8.5% TII), N‐containing compounds (2.2% TII) and peptides (4.6% TII) were highest under meadow, while compound classes of lignin dimers (3.4% TII) and lipids (8.1% TII) were highest under pasture. In the Schwäbische Alb region, the proportion of free fatty acids (1.6 to 2.3% TII) was positively related to the C/N ratio (r = 0.86); SOM stability was positively affected by poorly crystalline Fe‐oxide content (r = 0.85). The results suggest that grassland management is affecting SOM composition and stability and thus influence SOM dynamics in grasslands. However, the proportion and composition (Fe‐oxide content) of the soil clay fraction overrode grassland management effects if soil clay/OC ratios were &lt;10.

Plant–microbial linkages regulate soil organic carbon dynamics under phosphorus application in a typical temperate grassland in northern China

Anthropogenic activities have increased ecosystem phosphorus (P) inputs and have affected terrestrial ecosystem carbon (C) cycles. However, the fate of soil organic C (SOC) under P addition remains elusive, and the potential mechanisms underlying plant-microbial linkages mediated SOC formation and decomposition are poorly understood. Here, we conducted a field P fertilization experiment to explore the effects on SOC dynamics in a typical temperate grassland in northern China. P addition increased soil P availability and pH, thereby stimulating plant nutrient uptake and growth, leading to higher C inputs to soils via plant biomass (shoots, litter and roots). However, P addition exacerbated microbial N limitation, altered microbial community composition (with a lower fungal to bacterial ratio), shifted microbial life-history strategies, which transitioned from the K-strategy (Acidobacteria, Chloroflexi, and Verrucomicrobia dominant) to the r- strategy (Proteobacteria, Bacteroidetes, and Firmicutes dominant), and modulated their functional characteristics. All of these factors regulated microbial substrate preferences and changed the C components that undergo decomposition. These changes ultimately accelerated the utilization of active C, hampered passive C decomposition, and helped to create a longer-term stable C sink in the grassland.

Spatiotemporal Dynamics of Grasslands Using Landsat Data in Livestock Micro-Watersheds in Amazonas (NW Peru)

In Peru, grasslands monitoring is essential to support public policies related to the identification, recovery and management of livestock systems. In this study, therefore, we evaluated the spatial dynamics of grasslands in Pomacochas and Ventilla micro-watersheds (Amazonas, NW Peru). To do this, we used Landsat 5, 7 and 8 images and vegetation indices (normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and soil adjusted vegetation index (SAVI). The data were processed in Google Earth Engine (GEE) platform for 1990, 2000, 2010 and 2020 through random forest (RF) classification reaching accuracies above 85%. The application of RF in GEE allowed surface mapping of grasslands with pressures higher than 85%. Interestingly, our results reported the increase of grasslands in both Pomacochas (from 2457.03 ha to 3659.37 ha) and Ventilla (from 1932.38 ha to 4056.26 ha) micro-watersheds during 1990–2020. Effectively, this study aims to provide useful information for territorial planning with potential replicability for other cattle-raising regions of the country. It could further be used to improve grassland management and promote semi-extensive livestock farming.

Long-term effects of sheep-grazing and its removal on vegetation dynamics of British upland grasslands and moorlands; local management cannot overcome large-scale trends

The upland and mountainous regions of northern Europe provide a wide variety of ecosystem services. However, these ecosystem services are highly vulnerable to environmental and land-use change. To ensure their future conservation, it is therefore, essential to understand whether upland plant communities will respond positively or negatively to a range of environmental factors such as grazing pressure and landscape-scale factors such as changes in atmospheric SO2 and NOx deposition. To understand this, here, we describe the long-term trends in four UK upland communities (high-level grassland, intermediate grassland, blanket bog, high-level bog) using four replicated long-term experiments examining the effects of sheep grazing compared to no-sheep grazing in Moor House (from 1954 to 2016). Our results showed that species richness and abundance recovered in grazed plots after 2000, with improvements in species richness and abundance of vascular plants, mosses, and liverworts. Unfortunately, no improvement was found for lichens. Species richness, vascular plants, and mosses recovered the fastest, and much faster than liverworts. There was no evidence of slower recovery of species richness and abundance in plots where sheep grazing was removed. These results are consistent with longitudinal studies suggesting recovery after 2000 as a result of reduced atmospheric deposition. Although trends in diversity and abundance in the grazed and ungrazed plots were not identical, they were not markedly different either. The similar richness and abundance trends in the grazed and ungrazed plots found in each plant community suggest that within-community dynamics may overcome initial differences between the grazing treatments over time. In contrast, differences in richness and abundance among plant communities over time suggest that some landscape-scale trends, such as those caused by a reduction in nutrient inputs, initiate community-dependent recovery.

Detection of Grassland Mowing Events for Germany by Combining Sentinel-1 and Sentinel-2 Time Series

Grasslands cover one-third of the agricultural area in Germany and play an important economic role by providing fodder for livestock. In addition, they fulfill important ecosystem services, such as carbon storage, water purification, and the provision of habitats. These ecosystem services usually depend on the grassland management. In central Europe, grasslands are grazed and/or mown, whereby the management type and intensity vary in space and time. Spatial information on the mowing timing and frequency on larger scales are usually not available but would be required in order to assess the ecosystem services, species composition, and grassland yields. Time series of high-resolution satellite remote sensing data can be used to analyze the temporal and spatial dynamics of grasslands. Within this study, we aim to overcome the drawbacks identified by previous studies, such as optical data availability and the lack of comprehensive reference data, by testing the time series of various Sentinel-2 (S2) and Sentinal-1 (S1) parameters and combinations of them in order to detect mowing events in Germany in 2019. We developed a threshold-based algorithm by using information from a comprehensive reference dataset of heterogeneously managed grassland parcels in Germany, obtained by RGB cameras. The developed approach using the enhanced vegetation index (EVI) derived from S2 led to a successful mowing event detection in Germany (60.3% of mowing events detected, F1-Score = 0.64). However, events shortly before, during, or shortly after cloud gaps were missed and in regions with lower S2 orbit coverage fewer mowing events were detected. Therefore, S1-based backscatter, InSAR, and PolSAR features were investigated during S2 data gaps. From these, the PolSAR entropy detected mowing events most reliably. For a focus region, we tested an integrated approach by combining S2 and S1 parameters. This approach detected additional mowing events, but also led to many false positive events, resulting in a reduction in the F1-Score (from 0.65 of S2 to 0.61 of S2 + S1 for the focus region). According to our analysis, a majority of grasslands in Germany are only mown zero to two times (around 84%) and are probably additionally used for grazing. A small proportion is mown more often than four times (3%). Regions with a generally higher grassland mowing frequency are located in southern, south-eastern, and northern Germany.

Satellite-observed shifts in C3/C4 abundance in Australian grasslands are associated with rainfall patterns

Species composition is a key determinant of grassland ecosystem function and resilience. Climate change is predicted to alter the distribution of cool season (C3) and warm season (C4) grasses, however, the lack of spatial distributions and temporal variations of grass functional type information severely limits our understanding of climate impacts on grasslands. This study classified C3 and C4 grasses per pixel according to the peak of growing season generated from Enhanced Vegetation Index time series. From 2003 to 2017, the C3-C4 composition of Australian rain-fed grasslands and pastures was mapped at 500 m resolution on an annual basis across a wide geographical range (10°S – 45°S), and revealed extreme inter-annual fluctuations. Over the 15-year period, the satellite-derived ratio of C4 to C3 grasses significantly increased (p < 0.05), indicating a long-term shift in community composition that was confirmed with 182,911 Atlas of Living Australia ground observations. The most pronounced changes occurred in mid-latitude transitional areas where C3 and C4 grasses co-dominate. Our climate analysis indicated the inter-annual fluctuations of C4/C3 grass ratios were significantly associated (p < 0.05) with warm/cool season rainfall ratios, and not with temperature or annual rainfall. This suggests that an increase in the warm/cool season rainfall ratio favors C4 grasses and a decrease in the warm/cool season rainfall ratio favors C3 grasses. Our findings reveal spatially-detailed dynamics of grasslands and demonstrate large-scale grassland compositional changes over 15 years. The grass composition maps should help improve ecological forecasting of grass distributions and enable researches on grassland ecosystem responses to climate change that are relevant to both adaptation of rangeland agricultural and fire management practices. Our study should also help predict grass distribution under future climate conditions, and assist in the accurate modelling of global water, carbon, and energy exchanges between the land surface and atmosphere.

Effects of large mammalian herbivory, previous fire, and year of burn on fire behavior in an African savanna

AbstractFire, herbivores, and climatic factors are all major drivers of savanna and grassland dynamics, and they interact in complex ways, which are still in the process of being explored. In particular, herbivores can reduce fire intensity by removal of biomass, and this could be reinforced by herbivores’ attraction to recently burned sites, although grassland resilience may limit the temporal depth of such effects. Fire temperature is the most common fire metric reported for grassland fire, but additional aspects of fire behavior can also be measured. Using a set of controlled, replicated experiments, we examined the effects of year of burn, herbivory by livestock and wildlife, previous burn, and weather history on fire behavior in an African savanna. Multiple measures of fire behavior (minimum fire temperature, flame front speed, fire residence time, maximum flame height, and flame length) in 36 controlled burns were positively intercorrelated. Burns conducted in 2018 were significantly cooler, especially at heights &gt;0.5 m above the ground, than those in 2013, a wetter year with more grass fuel. Grass fuel loads and fire temperatures were reduced by the presence of livestock and wildlife. Our sampling methods did not for the most part reveal expected differences in fire temperatures or other behaviors between the reburned plots and those burned for the first time in 2018, with or without herbivores, suggesting strong postfire resilience in this semiarid savanna rangeland.