Water Availability Is the Main Climate Driver of Neotropical Tree Growth

• Climate models for the coming century predict rainfall reduction in the Amazonian region, including change in water availability for tropical rainforests. Here, we test the extent to which climate variables related to water regime, temperature and irradiance shape the growth trajectories of neotropical trees. • We developed a diameter growth model explicitly designed to work with asynchronous climate and growth data. Growth trajectories of 205 individual trees from 54 neotropical species censused every 2 months over a 4-year period were used to rank 9 climate variables and find the best predictive model. • About 9% of the individual variation in tree growth was imputable to the seasonal variation of climate. Relative extractable water was the main predictor and alone explained more than 60% of the climate effect on tree growth, i.e. 5.4% of the individual variation in tree growth. Furthermore, the global annual tree growth was more dependent on the diameter increment at the onset of the rain season than on the duration of dry season. • The best predictive model included 3 climate variables: relative extractable water, minimum temperature and irradiance. The root mean squared error of prediction (0.035 mm.d–1) was slightly above the mean value of the growth (0.026 mm.d–1). • Amongst climate variables, we highlight the predominant role of water availability in determining seasonal variation in tree growth of neotropical forest trees and the need to include these relationships in forest simulators to test, in silico, the impact of different climate scenarios on the future dynamics of the rainforest

KTC De Marke: twee decennia innovaties voor duurzame melkveehouderij

De Marke, Proefbedrijf voor Melkveehouderij en Milieu bestaat dit jaar 20 jaar. Met militaire precisie is destijds de strategie, opzet en ontwikkeling van dit melkveeproefbedrijf door Frans Aarts, Edo Biewinga en Richard Donker vastgelegd in De Marke-rapport nr. 1: 'Melkveehouderij bij stringente milieunormen'. Nu, 20 jaar later, is er mede door hun aanzet meer bereikt dan we voor mogelijk hielden. Koeien melken met minimale belasting van de omgeving: de melkveehouderij is en blijft een gewaardeerde voedselproducent die schoon werkt in een fraai landschap. Alle reden om hier in 2012 uitgebreid bij stil te staan

A one-dimensional model of water flow in soil-plant systems based on plant architecture

The estimation of root water uptake and water flow in plants is crucial to quantify transpiration and hence the water exchange between land surface and atmosphere. In particular the soil water extraction by plant roots which provides the water supply of plants is a highly dynamic and non-linear process interacting with soil transport processes that are mainly determined by the natural soil variability at different scales. To better consider this root-soil interaction we extended and further developed a finite element tree hydro-dynamics model based on the one-dimensional (1D) porous media equation. This is achieved by including in addition to the explicit three-dimensional (3D) architectural representation of the tree crown a corresponding 3D characterisation of the root system. This 1D xylem water flow model was then coupled to a soil water flow model derived also from the 1D porous media equation. We apply the new model to conduct sensitivity analysis of root water uptake and transpiration dynamics and compare the results to simulation results obtained by using a 3D model of soil water flow and root water uptake. Based on data from lysimeter experiments with young European beech trees (Fagus silvatica L.) is shown, that the model is able to correctly describe transpiration and soil water flow. In conclusion, compared to a fully 3D model the 1D porous media approach provides a computationally efficient alternative, able to reproduce the main mechanisms of plant hydro-dynamics including root water uptake from soil

Multistage accretion and exhumation of the continental crust (Ivrea crustal section, Italy and Switzerland)

The Ivrea crustal section exposes in map view all levels of the southern Alpine continental crust, from ultramafic, mafic, and felsic granulite facies rocks of the deep crust (Ivrea-Verbano Zone), through medium-grade basement rocks (Strona-Ceneri Zone and Val Colla Zone), to unmetamorphosed Permo-Mesozoic sediments. The oldest part of the crustal section is preserved in the medium-grade basement units, which are interpreted to be the overprinted remains of an Ordovician (440-480 Ma) magmatic are or forearc complex. During Variscan subduction this are was tectonically underplated by a Carboniferous accretion-subduction complex(320-355 Ma) containing metasediments and slivers of Rheic oceanic crust presently found in the Ivrea-Verbano Zone. During the late stages of Variscan convergence (290-320 Ma), lithospheric delamination triggered magmatic underplating and lead to polyphase deformation under amphibolite to granulite facies conditions. This was broadly coeval with extensional exhumation and erosion of the Variscan-overprinted Ordovician crust presently exposed in the Strona-Ceneri and Val Colla Zones. Post-Variscan transtensional tectonics (270-290 Ma) were associated with renewed magmatic underplating, mylonitic shearing, and incipient exhumation of the lower crust in the Ivrea-Verbano Zone. This coincided with the formation of elongate basins filled with volcanoclastic sediments in the upper crust. Early Mesozoic, Tethyan rifting of the southern Alpine crust (180-230 Ma) reduced crustal thickness to 10 km or less. In the lower crust, most of this thinning was accommodated by granulite to retrograde greenschist facies mylonitic shearing. The lower crust was exhumed along a large, noncoaxial mylonitic shear zone that was linked to asymmetrical rift basins in the upper crust. The composite structure resulting from this complex evolution is probably typical of thinned, late Variscan continental crust on the passive margins of western Europe. Alpine faulting and folding (20-50 Ma) fragmented the crustal section. The originally deepest levels of the crustal section in the Ivrea-Verbano Zone as well as some segments of the basement-cover contact were steepened, whereas other parts of the crustal section, particularly the Shona-Ceneri Zone, underwent only minor to moderate Alpine rotation

Functional-structural water flow model reveals differences between diffuse- and ring-porous tree species.

A functional-structural (FS) model of tree water flow is applied for single trees in an old-growth temperate broad-leaved forest stand. Roots, stems and branches are represented by connected porous cylinder elements that are divided into the inner heartwood cylinders surrounded by xylem and phloem. Xylem water flow is simulated by applying a non-linear Darcy water flow in porous media driven by the water potential gradient according to the cohesion-tension theory. The flow model is based on physiological input parameters such as the hydraulic conductivity, stomata] response to leaf water potential and root water uptake capability and, thus, can reflect the different properties of the two diffuse-porous tree species Fagus sylvatica and Tilia cordata and the ring-porous species Fraxinus excelsior. The structure of the canopy is obtained by applying an automatic tree skeleton extraction algorithm from point clouds obtained by terrestrial laser scans allowing an explicit representation of the water flow path in the stem and branches. Supported by measurements of stem sap flow, the model reveals differences of the simulated stomatal closure due to low branch xylem water contents between the tree species. The diffuse-porous species reduced the transpiration by the stomatal closure only at hot days with a high potential transpiration. For the ring-porous ash the simulated reduction is much higher with a mean value of all trees over the observation period of 0.72. The model gives insights to the mechanism that lead to the stomatal closure and can spot the axial xylem hydraulic conductance along the flow pathway as the limiting factor of leaf water supply at days with moist soil water conditions