Hi-sAFe: a 3D agroforestry model for integrating dynamic tree–crop interactions

Agroforestry, the intentional integration of trees with crops and/or livestock, can lead to multiple economic and ecological benefits compared to trees and crops/livestock grown separately. Field experimentation has been the primary approach to understanding the tree–crop interactions inherent in agroforestry. However, the number of field experiments has been limited by slow tree maturation and difficulty in obtaining consistent funding. Models have the potential to overcome these hurdles and rapidly advance understanding of agroforestry systems. Hi-sAFe is a mechanistic, biophysical model designed to explore the interactions within agroforestry systems that mix trees with crops. The model couples the pre-existing STICS crop model to a new tree model that includes several plasticity mechanisms responsive to tree–tree and tree–crop competition for light, water, and nitrogen. Monoculture crop and tree systems can also be simulated, enabling calculation of the land equivalent ratio. The model’s 3D and spatially explicit form is key for accurately representing many competition and facilitation processes. Hi-sAFe is a novel tool for exploring agroforestry designs (e.g., tree spacing, crop type, tree row orientation), management strategies (e.g., thinning, branch pruning, root pruning, fertilization, irrigation), and responses to environmental variation (e.g., latitude, climate change, soil depth, soil structure and fertility, fluctuating water table). By improving our understanding of the complex interactions within agroforestry systems, Hi-sAFe can ultimately facilitate adoption of agroforestry as a sustainable land-use practice

Comparisons of observed and modelled lake δ18O variability

With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Simple models for light competition within agroforestry discontinuous tree stands: are leaf clumpiness and light interception by woody parts relevant factors?

Contact: [email protected] audiencePredicting the temporal and spatial variability of radiation intensity under wide-spaced tree stands is required for many applied issues in savannah-like ecosystems, orchards, agroforestry and urban forestry systems. Numerous authors have advocated the use of simple light interception models that approximate the crown shape with ellipsoids. They have suggested taking into account leaf clumping to improve the efficiency of these simple models, but this was never assessed. We tested this hypothesis together with the impact of including predictions of light interception by woody parts (trunks, branches). We calibrated and evaluated the model using cross-validation across eight walnut trees with field measurements of radiation intensity and spatial heterogeneity using hemispherical photographs. Leafless trees were efficiently modelled using Wood Area Density (WAD, m(2)m(-3)) for branches and an opaque cone for the trunk. We introduced a clumping parameter (mu) but this proved inefficient, clumping being highly variable amongst trees. This results from the limitations of representing the crown as an ellipsoid, a procedure too coarse to be improved by using a clumping parameter. The model proved efficient to predict the light pattern around an average tree, but was not fit for simulating the variability of individual trees. We finally discuss practical recommendations for modelling light competition in integrated agroforestry models simply

A field assessment of the actual final land equivalent ratio of a temperate agrofoestry system.

International audienceThe land equivalent ratio (LER) of an agroforestry system (AFS) is a measure of the advantage of mixing species for production. LERs of annual crop mixtures are easy to measure, as each growing season provides an estimate. LERs of perennial AFS are more difficult to measure or predict. The long-term growth of the tree component must be measured, and the productivity of the intercrops must be monitored for a long time, until crop production is no longer profitable. Several pitfalls of LER calculation must also be avoided, and require data for sole crop and sole tree plots that are very often missing in many experimental designs. This explains why almost no measured LERs of AFS have been published to date. We monitored a poplar-cereal AFS from tree plantation in 1996 until tree harvest in 2008 in southern France. This allowed us to measure the actual value of the final LER of the system. This is probably the first field measurement of an agroforestry LER in Europe and in the temperate zone. Four systems were monitored, differing by tree row orientation and poplar clones. The average LER is very high compared to previously published estimates of LERs in temperate AFS. Using simulation models of the system, we tried to separate the impacts of various factors in explaining such high productivities of tree-crop mixtures. Three factors appear to be essential: phenology lags between tree and crop components, plasticity of the root systems of the tree component in response to the competition by the crop component, and the availability of a deep resource of water that is within reach of the trees’ rooting system. Such productivity data are at odds with many predictions of the value of temperate AFS, and could be a stimulus for the adoption of AFS throughout Europ

Assessing the importance of phenological lags between trees and crops in temperate agroforestry systems with a process-based interaction model

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Cereal productivity in the shade, a key to the success of temperate agroforestry systems

International audienceCereal varieties were selected in full sun conditions, and models of crop productivity were also designed and validated for full sun conditions. Both may therefore not be adapted to agroforestry cultivation and simulation, respectively. Durum wheat productivity was monitored in agroforestry systems with deciduous broadleaved tree species during the last ten years in southern France. Dedicated experiments with artificial shade were also set up to control light availability. Yield components (plant density, number of tillers, number of ears, grains per ear, grain weight, protein content of the grains and qualitative parameters) were measured in both full light and reduced light conditions. Beyond a threshold of 70% radiation during the flowering and grain filling stages, the cereal yield was not decreased by the shade. For heavier shade conditions, the cereal yield was significantly reduced. A crop model (STICS) was used to simulate the crop productivity in both full light and shaded conditions. Leaf area indexes were not much reduced by deciduous tree shade, as most the leaf growth was finished before significant shade occurred on the plot. The main impact of the shade was on the fertility of the ears. The grain weight was not modified, while the protein content was significantly increased in shaded conditions. The protein yield per hectare was therefore not much reduced by the shade, even when the dry matter grain yield was significantly reduced. Some processes were not correctly simulated in the shade such as crop temperature and soil temperature, and improvements of the crop model are suggested. The optimization of temperate agroforestry systems would require the selection of cereal varieties less sensitive to a deficit of radiation at flowering, and the genetic variability of cereals should be explored for this new criterio

What explanations for the surprising productivity of temperate agroforestry systems as measured by their Land Equivalent Ratio?

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