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Fish stocking and harvest regulations are frequently used to maintain or enhance freshwater recreational fisheries and contribute to fish conservation. However, their relative effectiveness has rarely been systematically evaluated using quantitative models that account for key size- and density-dependent ecological processes and adaptive responses of anglers. We present an integrated model of freshwater recreational fisheries where the population dynamics of two model species affect the effort dynamics of recreational anglers. With this model, we examined how stocking various fish densities and sizes (fry, fingerlings, and adults) performed relative to minimum-length limits using a variety of biological, social, and economic performance measures, while evaluating trade-offs. Four key findings are highlighted. First, stocking often augmented the exploited fish population, but size- and density-dependent bottlenecks limited the number of fry and fingerlings surviving to a catchable size in self-sustaining populations. The greatest enhancement of the catchable fish population occurred when large fish that escaped early bottlenecks were stocked, but this came at the cost of wild-stock replacement, thereby demonstrating a fundamental trade-off between fisheries benefits and conservation. Second, the relative performance of stocking naturally reproducing populations was largely independent of habitat quality and was generally low. Third, stocking was only economically advisable when natural reproduction was impaired or absent, stocking rates were low, and enough anglers benefitted from stocking to offset the associated costs. Fourth, in self-sustaining fish populations, minimum-length limits generally outperformed stocking when judged against a range of biological, social and economic objectives. By contrast, stocking in culture-based fisheries often generated substantial benefits. Collectively, our study demonstrates that size- and density-dependent processes, and broadly the degree of natural recruitment, drive the biological, social, and economic outcomes of popular management actions in recreational fisheries. To evaluate these outcomes and the resulting trade-offs, integrated fisheries-management models that explicitly consider the feedbacks among ecological and social processes are needed.

Background and aimsUnderstanding the effects of livestock grazing on the ecosystem biomass and soil nitrogen processes of grassland ecosystems is critical to improving knowledge on the mechanisms underlying grassland degradation and accurately assessing the influence of grazing management on grassland functions.MethodsWe examined the interannual patterns of ecosystem biomass and soil nitrogen mineralization in response to cattle grazing in a Chinese meadow steppe. The soil core incubation method was employed for soil N transfer estimation, whilst the fumigation extraction method, a modified Baermann funnel method and harvest method were used for various measurements of ecosystem biomass parameters.ResultsWe found that cattle grazing caused consistent significant increases in soil temperature, irrespective of the stocking rate and year, whereas significant effects on soil moisture and edaphic properties were observed only in individual years and/or at specific stocking rates. Consistent positive effects at moderate stocking rates were observed for aboveground net primary production and soil nematode biomass in all study years. The across stocking rate pattern of N mineralization in response to cattle stocking appeared to be year-specific, although negative effects were found in most cases. In contrast, the interannual pattern of N mineralization was determined principally by the interannual patterns in precipitation and soil moisture and was much less affected by cattle grazing.ConclusionsSoil N mineralization in this meadow steppe was affected by cattle grazing via two major mechanisms, i.e., its effects on the aboveground net primary production (ANPP) and thus the quantity of plant litter input into the soil and its effects on soil temperature and moisture. Overall, our study spanned the longest consecutive years with the broadest range of stocking rates thus far of its kind, which revealed for the first time that the soil nitrogen mineralization pattern with respect to stocking rate was year-specific. Our findings have important implications for adaptive management and sustainable utilization of Chinese grasslands.

Increasing atmospheric [CO₂] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO₂ (eCO₂) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7-yr study examining effects of CO₂ enrichment (to 600 ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on in vitro dry matter digestibility (IVDMD) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO₂ substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO₂ reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO₂ was related both to reduced [N] and increased acid detergent fiber (ADF) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO₂ increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO₂ may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality

Changes in the spatiotemporal pattern of vegetation alter the structure and function of landscapes, consequently affecting biodiversity and ecological processes. Distinguishing human-induced vegetation changes from those driven by environmental variations is critically important for ecological understanding and management of landscapes. The main objectives of this study were to detect human-induced vegetation changes and evaluate the impacts of land use policies in the Xilingol grassland region of Inner Mongolia, using the NDVI-based residual trend (RESTREND) method. Our results show that human activity (livestock grazing) was the primary driver for the observed vegetation changes during the period of 1981–2006. Specifically, vegetation became increasingly degraded from the early 1980s when the land use policy—the Household Production Responsibility System—led to soaring stocking rates for about two decades. Since 2000, new institutional arrangements for grassland restoration and conservation helped curb and even reverse the increasing trend in stocking rates, resulting in large-scale vegetation improvements in the region. These results suggest that most of the degraded grasslands in the Xilingol region can recover through ecologically sound land use policies or institutional arrangements that keep stocking rates under control. Our study has also demonstrated that the RESTREND method is a useful tool to help identify human-induced vegetation changes in arid and semiarid landscapes where plant cover and production are highly coupled with precipitation. To effectively use the method, however, one needs to carefully deal with the problems of heterogeneity and scale in space and time, both of which may lead to erroneous results and misleading interpretations.

Livestock grazing at low stocking rates is widely recommended to maintain grassland biodiversity. However, empirical evidence of grazing‐intensity effects on plant diversity is contradictory. Explicitly considering the small‐scale heterogeneity of short, frequently grazed and tall, rarely grazed patches typical of low‐input grazing systems may be crucial to the understanding of paddock‐scale grazing effects. We studied three patch types (short, intermediate, tall) within an unfertilised long‐term cattle grazing experiment in Lower Saxony, Germany, comparing three paddock‐scale grazing intensities. We analysed soil nutrient concentrations and recorded vegetation composition at a total of 135 plots. We determined species richness, Simpson diversity, Simpson evenness and beta diversity of individual plots (plot scale) and patch types within paddocks (patch scale). To quantify paddock‐scale diversity, we resampled plot‐scale species composition across a gradient of relative proportions of short and tall patches within a paddock. Patch type, not paddock‐scale grazing intensity, was the main driver of plant diversity at both plot and patch scale. Short patches were more diverse than tall patches, but the effect was not strongly mediated by the lower soil nutrient concentrations in the short patches. By contrast, both patch type and grazing intensity affected vegetation composition at plot and patch scale. Beta‐diversity within and between patch types was independent of grazing intensity; consequently, paddock‐scale diversity was determined by the relative proportion of short versus tall patches. Higher alpha diversity of short patches compared to tall patches was more important than beta diversity between the two patch types in shaping paddock‐scale diversity. Consequently, with increasing short‐patch proportion, paddock‐scale diversity increased. Synthesis and applications. Our study identifies the grazing‐induced patch structure as the most important driver of plant diversity across different grazing intensities in low‐input, that is, unfertilised and continuously stocked, pastures. To optimise grazing management for biodiversity, understanding plant‐diversity responses to grazing at the patch scale is indispensable. Our results suggest that, in unfertilised, continuously stocked European pastures, trade‐offs between biodiversity and agronomic production may be small, as short patches, whose proportion increases with stocking rate, also had the highest plant diversity. Our study identifies the grazing‐induced patch structure as the most important driver of plant diversity across different grazing intensities in low‐input, that is, unfertilised and continuously stocked, pastures. To optimise grazing management for biodiversity, understanding plant‐diversity responses to grazing at the patch scale is indispensable. Our results suggest that, in unfertilised, continuously stocked European pastures, trade‐offs between biodiversity and agronomic production may be small, as short patches, whose proportion increases with stocking rate, also had the highest plant diversity.

AimsLivestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate.MethodsIn situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique.ResultsWe found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools.ConclusionsIn this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate.

To investigate the effects of stocking rates on nitrification activity and active nitrifying communities in a typical steppe grazing system, we conducted a laboratory incubation study using soil from a 10-year-old grassland gradient grazing experiment with sheep. A combination of molecular methods, such as DNA-based stable-isotope probing (DNA-SIP), real-time quantitative PCR, and high-throughput sequencing, was used to identify changes of nitrification activity and active nitrifying communities under different stocking rates (0 (SR0), 3 (SR3), 6 (SR6), and 9 (SR9) sheep per ha). The nitrification activity of soils was significantly increased by light grazing (SR3), while it was significantly decreased by heavy grazing (SR9). Nitrososphaera viennensis lineage of ammonia-oxidizing archaea (AOA) functionally predominated over ammonia-oxidizing bacteria (AOB) in nitrification in the SR3 soil, while the Nitrosospira cluster 3 of AOB was the major player in the SR9 soil. Therefore, stocking rates altered the distribution of active nitrifying communities by affecting soil chemical and physical conditions.

Livestock grazing has degraded many arid and semi‐arid rangelands around the world, and the drier climate predicted by climate change scenarios may amplify these effects and even lead to catastrophic vegetation shifts. We assess the long‐term effects (1900–2100) of grazing and rainfall on various aspects of vegetation structure including the grass‐shrub balance, the maintenance of spatial vegetation patterns, and the decline or recovery of palatable grasses (e.g. Poa ligularis) on a cover and/or density basis. We used the eco‐hydrological and individual‐based simulation model DINVEG for this purpose, which describes the spatiotemporal dynamics of Patagonian grass‐shrub steppes based on six decades of field research (1955–2018). Rainfall and grazing affected the simulated vegetation structure in different ways. Total plant cover was mostly influenced by rainfall, but the cover of palatable grasses was mostly influenced by stocking rate. Dry conditions and low stocking rates (122 mm/year and <0.2 sheep/ha) favoured grasses over shrubs, whereas shrub encroachment occurred only in the high rainfall scenario combined with high stocking rates (181 mm/year and >0.2 sheep/ha). High stocking rates and/or drier conditions caused only gradual shifts in spatial vegetation patterns, but maintained the observed positive association for grasses around shrubs. In contrast, shrub encroachment was associated with repulsion between grasses and shrubs and the formation of shrub clusters into a matrix of scattered less palatable grasses. Plant compositional changes occurred through grass species replacement (e.g. P. ligularis is replaced by Pappostipa humilis) and the associated hysteresis effect of palatable grass species: model simulations suggest that 2–3 decades of heavy and year‐long continuous grazing can drive palatable grasses to close to extinction, whereas natural recovery of degraded steppes may take 100 years or longer. Synthesis and applications. Desertification and climate change challenge grazing management in semi‐arid rangelands, especially in already degraded ecosystems. Management that alternates between years of grazing and resting was effective to maintain the cover of palatable grasses, but this allowed for only very slow recovery of degraded steppes. While drier climate and grazing may not change the overall spatial patterns of vegetation, our results are rather pessimistic regarding the short‐term recovery of palatable grasses. This will require increasing complexity in ecosystem restoration efforts, combined with interventions such as sowing, watering, reseeding or major changes in land use. Resumen El pastoreo doméstico ha degradado muchos pastizales áridos y semiáridos en todo el mundo, y el clima más seco predicho por los escenarios de cambio climático puede amplificar estos efectos e incluso conducir a cambios catastróficos en la vegetación. Evaluamos los efectos a largo plazo (1900–2100) del pastoreo y de la lluvia para varios aspectos de la estructura de la vegetación, incluyendo el balance entre pastos y arbustos, el mantenimiento de los patrones espaciales y la disminución o recuperación de pastos palatables (e.g. Poa ligularis) en base a cambios en la cobertura y/o densidad. Para ello se utilizó el modelo de simulación eco‐hidrológico basado en individuos DINVEG, que describe la dinámica espacio temporal de las estepas graminoso‐arbustivas de la Patagonia en base a seis décadas de investigación de campo (1955–2018). Las precipitaciones y el pastoreo afectaron la estructura de la vegetación simulada en modos distintos. La cobertura total estuvo influenciada principalmente por las lluvias, pero la cobertura de pastos palatables fue influenciada principalmente por la carga ganadera. El escenario climático seco y la baja carga ganadera (122 mm/año y < 0,2 ovejas·ha‐1) favorecieron a los pastos frente a los arbustos, mientras que la invasión de arbustos solo se produjo en el escenario húmedo combinado con altas cargas ganaderas (181 mm/año y > 0,2 ovejas·ha‐1). Las altas cargas ganaderas y/o las condiciones secas causaron sólo cambios graduales en los patrones espaciales de la vegetación, pero mantuvieron las asociaciones positivas de los pastos alrededor de los arbustos. En cambio, la invasión de arbustos se asoció con la repulsión entre pastos y arbustos y la formación de isletas de arbustos en una matriz de pastos no palatables esparcidos. Los cambios en la composición florística se produjeron a través del reemplazo de especies de gramíneas (e.g. P. ligularis es reemplazada por Pappostipa humilis) y el efecto de histéresis observado en las especies de pastos palatables: las simulaciones sugieren que 2–3 décadas de pastoreo con altas cargas durante todo el año pueden llevar a los pastos palatables a una situación cercana a la extinción, mientras que la recuperación natural de las estepas degradadas puede llevar 100 años o más. Síntesis y aplicaciones. La desertificación y el cambio climático desafían al manejo del pastoreo en los pastizales semiáridos, especialmente en ecosistemas ya degradados. El manejo rotativo del pastoreo donde alternan períodos de descanso fue efectivo para mantener la cobertura de pastos palatables, pero sólo permitió una recuperación muy lenta de las estepas degradadas. Mientras que el clima seco y el pastoreo pueden no cambiar los patrones espaciales generales de la vegetación, nuestros resultados son bastante pesimistas con respecto a la recuperación a corto plazo de los pastos palatables. Esto requerirá de esfuerzos más complejos para la restauración de estos ecosistemas, combinados con intervenciones como la siembra, el riego, la resiembra o cambios drásticos en el uso de la tierra. Desertification and climate change challenge grazing management in semi‐arid rangelands, especially in already degraded ecosystems. Management that alternates between years of grazing and resting was effective to maintain the cover of palatable grasses, but this allowed for only very slow recovery of degraded steppes. While drier climate and grazing may not change the overall spatial patterns of vegetation, our results are rather pessimistic regarding the short‐term recovery of palatable grasses. This will require increasing complexity in ecosystem restoration efforts, combined with interventions such as sowing, watering, reseeding or major changes in land use.

Developing an optimal grazing strategy for livestock in spatially heterogeneous vegetation is essential for the animal production. An agent-based model (ABM) is a spatial explicit simulation modelling that predicts the internal state of livestock (e.g., metabolic energy) and external environment (e.g., plant biomass) that influence livestock movement through space. In this study, we used an ABM to predict the effects of various spatial grazing patterns of Mongolian livestock on intake energy. In the ABM, sheep acted as the agent and, vegetation was represented by the environment. The environment (approximately 8 × 8 km) was divided into 976 grid cells; the plant parameters in each cell, such as species composition, biomass, nutrition value and palatability, were measured. The movement pattern of Mongolian sheep is either voluntary or controlled by herders. The voluntary movement pattern was determined by GPS-tracking the actual movement of sheep. For the herder-controlled movement of sheep, we simulated three types of herder strategies by moving the sheep to a neighboring cell with the maximum or relative (probabilistic) high values of (1) biomass or (2) palatability or (3) nutrition of grass on the model. The metabolizable energy intake of sheep was estimated by determining the intake mass × metabolizable energy content of plant × palatability in each cell. The final energy intake of sheep were estimated after 2 months of simulation in summer at three different stocking rates. The energy intake of the freely grazing sheep was intermediate or less than that of the sheep controlled by herders in the maximum and probabilistic movement pattern of the agent, respectively. The biomass-oriented movement strategy was the best grazing strategy. Moreover, the grazing distribution resulting from the application of biomass-oriented movement strategy was spatially dispersed even the stock density was doubled. The best grazing strategy for animal production and grazing distribution is the semi-arid Mongolian grassland would be that herders move their sheep to patches with the most abundant plant biomass.

Background Assessing the relationships between spatial and temporal structures and functions of plant communities is an effective way to understand the changing dynamics of plant communities in specific environments. In this study, we investigated the response of structural and functional stabilities of plant communities to stocking rate in the desert steppe over a 16-year grazing period as the research background. Methods We used classical statistical methods to investigate the quantitative characteristics of plant communities over time (2014–2019) and space (2017–2019) at four stocking rates (control, CK, 0 sheep·ha –1 ·month –1 ; light grazing, LG, 0.15 sheep·ha –1 ·month –1 ; moderate grazing, MG, 0.30 sheep·ha –1 ·month –1 ; heavy grazing, HG, 0.45 sheep·ha –1 ·month –1 ) in the Stipa breviflora desert steppe of Inner Mongolia. We then examined the relationship between structural and functional stability of plant communities. Results On the spatial scale, the structural stability of plant community was the highest in the LG treatment and the lowest in the MG treatment. The functional stability of plant community was the highest in the MG treatment and the lowest in the HG treatment. On the temporal scale, the structural stability of plant community was the highest in the MG treatment and the lowest in the LG treatment. The functional stability of plant community was the highest in the LG treatment and the lowest in the HG treatment. Affected by the stocking rate, the structural stability of plant community fluctuated more widely on the spatial scale and its functional stability varied more widely on the temporal scale. Nonetheless, the functional stability of the plant community is more responsive to the stocking rate. Conclusions Our findings suggest that influenced by the disturbance of stocking rate, the structural stability of plant community is more significant than the functional stability in the desert grassland ecosystem, which lays a solid foundation for the study of ecosystem stability.