Well‐defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land‐model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid.
1 January 2016 in Agriculture, Ecosystems & Environment
The degradation of ecosystems threatens the provision of ecosystem services and limits human well-being. This systematic literature review evaluates the threats surrounding cultural ecosystem services (CES), namely recreation and landscape aesthetics in European permanent grasslands. We identified underlying causes, direct threats, consequences and suggested solutions for threat mitigation. The most common threats were land-use and management change processes, followed by social attitude, industrial developments and natural threats. However, recreational activities also created negative feedback, affecting the ecosystem, biodiversity and CES, most frequently in the form of various touristic activities. Suggested solutions were most commonly socio-economic and institutional measures to enhance rural communities, as well as improving communication with relevant stakeholders. CES play a crucial role in reconnecting people with nature, and their consequent acknowledgement and incorporation into future ecosystem service frameworks and agri-environmental policy developments are key elements in supporting future sustainable grassland management.
Soil respiration (SR) is a major component of the global carbon cycle and plays a fundamental role in ecosystem feedback to climate change. Empirical modelling is an essential tool for predicting ecosystem responses to environmental change, and also provides important data for calibrating and corroborating process-based models. In this study, we evaluated the performance of three empirical temperature–SR response functions (exponential, Lloyd–Taylor and Gaussian) at seven shrublands located within three climatic regions (Atlantic, Mediterranean and Continental) across Europe. We investigated the performance of SR models by including the interaction between soil moisture and soil temperature. We found that the best fit for the temperature functions depended on the site-specific climatic conditions. Including soil moisture, we identified thresholds in the three different response functions that improved the model fit in all cases. The direct soil moisture effect on SR, however, was weak at the annual time scale. We conclude that the exponential soil temperature function may only be a good predictor for SR in a narrow temperature range, and that extrapolating predictions for future climate based on this function should be treated with caution as modelled outputs may underestimate SR. The addition of soil moisture thresholds improved the model fit at all sites, but had a far greater ecological significance in the wet Atlantic shrubland where a fundamental change in the soil CO2 efflux would likely have an impact on the whole carbon budget.
Multi-species grasslands are reservoirs of biodiversity and provide multiple ecosystem services, including fodder production and carbon sequestration. The provision of these services depends on the control exerted on the biogeochemistry and plant diversity of the system by the interplay of biotic and abiotic factors, e.g., grazing or mowing intensity. Biogeochemical models incorporate a mechanistic view of the functioning of grasslands and provide a sound basis for studying the underlying processes. However, in these models, the simulation of biogeochemical cycles is generally not coupled to simulation of plant species dynamics, which leads to considerable uncertainty about the quality of predictions. Ecological models, on the other hand, do account for biodiversity with approaches adopted from plant demography, but without linking the dynamics of plant species to the biogeochemical processes occurring at the community level, and this hampers the models’ capacity to assess resilience against abiotic stresses such as drought and nutrient limitation. While setting out the state-of-the-art developments of biogeochemical and ecological modelling, we explore and highlight the role of plant diversity in the regulation of the ecosystem processes underlying the ecosystems services provided by multi-species grasslands. An extensive literature and model survey was carried out with an emphasis on technically advanced models reconciling biogeochemistry and biodiversity, which are readily applicable to managed grasslands in temperate latitudes. We propose a roadmap of promising developments in modelling.
Soil respiration, the main ecosystem process that produces carbon dioxide into the atmosphere, is sensitive to extreme climatic events. The immediate, usually negative effect of droughts on soil respiration has often been observed, but the recovery of soil respiration following drought is rarely documented. Soil respiration can be reduced beyond the drought year if drought‐induced changes suppress soil activity. Alternatively, reduction in soil respiration may be overcompensated in the subsequent years due to increased substrate input and soil moisture, resulting from plant dieback during drought. In addition, post‐drought weather patterns may also affect the recovery of soil respiration. In a full‐factorial grassland experiment, we combined an extreme (5 months) summer drought in 2014 with four levels of post‐drought precipitation regimes, including severe (2 months) droughts, moderate (1 month) droughts, ambient weather, and water addition (four large rain events) in summers of 2015 and 2016. We measured soil respiration monthly between May and November, from 2013 to 2016. The extreme drought had an immediate strong negative effect, decreasing soil respiration by 50.8% in 2014 compared to the control plots, and it had a negative legacy effect in 2015 (14.5% reduction), but not in 2016. This legacy effect was unaffected by the post‐drought precipitation regime. Moderate drought decreased soil respiration by 12.1% and 18.6%, while severe drought decreased soil respiration by 18.3% and 27.3% in 2015 and 2016, respectively, while water addition had no effect. Since soil water content in extreme drought plots recovered by 2015, we hypothesize that changes in soil biota and reduced root activity are responsible for extreme drought's long‐term negative effects. Overall, our results highlight that extreme droughts may have negative effects on soil respiration well beyond the event, and thus the full effect on carbon cycling may be much larger than what is estimated solely based on the immediate effects.