Droughts and Downpours: Resolving the disconnect between rainfall manipulation experiments and terrestrial ecosystem models

The biological responses to precipitation within the terrestrial components of Earth system models, or land surface models (LSMs), are mechanistically simple and poorly constrained, leaving projections of terrestrial ecosystem functioning and feedbacks to climate change uncertain. A number of field experiments have been conducted or are underway to test how changing precipitation will affect terrestrial ecosystems. Results from these experiments have the potential to vastly improve modeled processes. However, the transformation of experimental results into model improvements still represents a grand challenge. Here we review the current state of precipitation manipulation experiments and the precipitation responses of biological processes in LSMs to explore how these experiments can help improve model realism. First, we discuss contemporary precipitation projections and then review the structure and function of current-generation LSMs. We then examine different experimental designs and discuss basic variables that, if measured, would increase a field experiment's usefulness in a modeling context. Next, we compare biological processes commonly measured in the field with their model analogs and find that, in many cases, the way these processes are measured in the field is not compatible with the way they are represented in LSMs, an effect that hinders model development. We then discuss the challenge of scaling from the plot to the globe. Finally, we provide a series of recommendations aimed to improve the connectivity between experiments and LSMs and conclude that studies designed from the perspective of researchers in both communities will provide the greatest benefit to the broader global change community

Potential implications of climate change for Rooibos (A. linearis) production and distribution in the greater Cederberg region, South Africa

Includes bibliographical referencesWild plants assist in supporting human livelihoods worldwide, both within traditional systems of medicine, and as economically useful plants. Indigenous to the Fynbos biome in the north-western part of the Western Cape, South Africa is the leguminous shrub, A. linearis (rooibos), which is extensively used as ethnomedicine by local communities, while also commercially grown and exported for the herbal tea market. Being a range-restricted species, climate change poses a threat to wild plants and their dependent communities, as well as the sustainability of the rooibos industry. Climate mediated impacts on rooibos are mostly substantiated by anecdotal evidence from commercial growers and local communities and have traditionally been insufficiently addressed. This study integrates predictive modelling and empirical data to provide important insights into rooibos' plant physiological functioning in the presence of climatic and environmental constraints. The aim is to determine whether there is evidence of climate change over the rooibos distribution area, how these climate anomalies are expected to affect the species distribution and to perform experimental studies by testing plant physiological functioning of A. linearis under changing climate conditions. Analysis of climate parameters important for rooibos production (rainfall frequency and intensity, temperature extremes and wind speed) have shown that plants will experience a shorter period of water availability during winter, and prolonged exposure to summer conditions (high temperatures and water stress) in the coming decades. Under these conditions, climate envelope modelling suggests that wild and cultivated rooibos types are at risk to lose between 49.8% and 88.7% in the extent of the bio-climatically suitable localities, most notably along the western and northern periphery of the rooibos production area by 2070. Plant physiological responses (growth analysis, gas exchange parameters and leaf carbon and nitrogen isotope ratios) to the assessed climate anomalies were measured in experimental studies at glasshouse and field scale. Specific adaptation mechanisms (increasing water use efficiency, developing a higher level of sclerophylly and altering the allocation of plant reserves) which helped seedlings to survive short term drought in the glasshouse were not able to offset more severe conditions in field settings. Finally, a comparison of wild and cultivated tea has shown an apparent adaptive advantage of wild tea to tolerate increased aridity with greater water economy, and more reliance on biological nitrogen fixation for N nutrition, indicating a potentially less severe scenario of range contraction for wild types than initially indicated. This study provides a more robust prediction of rooibos plant responses to climate change factors to enable more effective adaptive planning and conservation management in a changing climate

Whitepaper: Understanding land-atmosphere interactions through tower-based flux and continuous atmospheric boundary layer measurements

Executive summary ● Target audience: AmeriFlux community, AmeriFlux Science Steering Committee & Department of Energy (DOE) program managers [ARM/ASR (atmosphere), TES (surface), and SBR (subsurface)] ● Problem statement: The atmospheric boundary layer mediates the exchange of energy and matter between the land surface and the free troposphere integrating a range of physical, chemical, and biological processes. However, continuous atmospheric boundary layer observations at AmeriFlux sites are still scarce. How can adding measurements of the atmospheric boundary layer enhance the scientific value of the AmeriFlux network? ● Research opportunities: We highlight four key opportunities to integrate tower-based flux measurements with continuous, long-term atmospheric boundary layer measurements: (1) to interpret surface flux and atmospheric boundary layer exchange dynamics at flux tower sites, (2) to support regionalscale modeling and upscaling of surface fluxes to continental scales, (3) to validate land-atmosphere coupling in Earth system models, and (4) to support flux footprint modelling, the interpretation of surface fluxes in heterogeneous terrain, and quality control of eddy covariance flux measurements. ● Recommended actions: Adding a suite of atmospheric boundary layer measurements to eddy covariance flux tower sites would allow the Earth science community to address new emerging research questions, to better interpret ongoing flux tower measurements, and would present novel opportunities for collaboration between AmeriFlux scientists and atmospheric and remote sensing scientists. We therefore recommend that (1) a set of instrumentation for continuous atmospheric boundary layer observations be added to a subset of AmeriFlux sites spanning a range of ecosystem types and climate zones, that (2) funding agencies (e.g., Department of Energy, NASA) solicit research on land-atmosphere processes where the benefits of fully integrated atmospheric boundary layer observations can add value to key scientific questions, and that (3) the AmeriFlux Management Project acquires loaner instrumentation for atmospheric boundary layer observations for use in experiments and short-term duration campaigns

Global Analysis, Interpretation and Modelling: An Earth Systems Modelling Program

The Goal of the GAIM is: To advance the study of the coupled dynamics of the Earth system using as tools both data and models; to develop a strategy for the rapid development, evaluation, and application of comprehensive prognostic models of the Global Biogeochemical Subsystem which could eventually be linked with models of the Physical-Climate Subsystem; to propose, promote, and facilitate experiments with existing models or by linking subcomponent models, especially those associated with IGBP Core Projects and with WCRP efforts. Such experiments would be focused upon resolving interface issues and questions associated with developing an understanding of the prognostic behavior of key processes; to clarify key scientific issues facing the development of Global Biogeochemical Models and the coupling of these models to General Circulation Models; to assist the Intergovernmental Panel on Climate Change (IPCC) process by conducting timely studies that focus upon elucidating important unresolved scientific issues associated with the changing biogeochemical cycles of the planet and upon the role of the biosphere in the physical-climate subsystem, particularly its role in the global hydrological cycle; and to advise the SC-IGBP on progress in developing comprehensive Global Biogeochemical Models and to maintain scientific liaison with the WCRP Steering Group on Global Climate Modelling

The decadal state of the terrestrial carbon cycle: global retrievals of terrestrial carbon allocation, pools and residence times

The terrestrial carbon cycle is currently the least constrained component of the global carbon budget. Large uncertainties stem from a poor understanding of plant carbon allocation, stocks, residence times, and carbon use efficiency. Imposing observational constraints on the terrestrial carbon cycle and its processes is, therefore, necessary to better understand its current state and predict its future state. We combine a diagnostic ecosystem carbon model with satellite observations of leaf area and biomass (where and when available) and soil carbon data to retrieve the first global estimates, to our knowledge, of carbon cycle state and process variables at a 1° × 1° resolution; retrieved variables are independent from the plant functional type and steady-state paradigms. Our results reveal global emergent relationships in the spatial distribution of key carbon cycle states and processes. Live biomass and dead organic carbon residence times exhibit contrasting spatial features (r = 0.3). Allocation to structural carbon is highest in the wet tropics (85–88%) in contrast to higher latitudes (73–82%), where allocation shifts toward photosynthetic carbon. Carbon use efficiency is lowest (0.42–0.44) in the wet tropics. We find an emergent global correlation between retrievals of leaf mass per leaf area and leaf lifespan (r = 0.64–0.80) that matches independent trait studies. We show that conventional land cover types cannot adequately describe the spatial variability of key carbon states and processes (multiple correlation median = 0.41). This mismatch has strong implications for the prediction of terrestrial carbon dynamics, which are currently based on globally applied parameters linked to land cover or plant functional types

Shortgrass Steppe LTER VI: examining ecosystem persistence and responses to global change, 2010-2014 proposal

Includes bibliographical references.The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.The Shortgrass Steppe Long-term Ecological Research (SGS-LTER) program focuses on how grassland ecosystems function and persist or change in the face of global change. Our conceptual framework asserts that climate, physiography, grazing, fire and landuse, operating over different spatial and temporal scales, are the dominant determinants of the structure, function, and persistence of the SGS. Using the shortgrass steppe (SGS) ecosystem of the North American Great Plains as a model, we seek to (1) identify the ecological attributes of grasslands that historically have resulted in their persistence and (2) understand these attributes in ways that will allow us to identify area of vulnerability and better forecast the future of grasslands in the face of global change. Given its geographic extent and history, the SGS encapsulates many of the features of a system driven by social-ecological interactions and the vulnerabilities of semiarid grasslands to global change. Our overarching question is: How will structure and function of the SGS respond to expected changes in climate, management, and land-use, and what will be the consequences