References of "Delpierre, N"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailForest summer albedo is sensitive to species and thinning: How should we account for this in Earth system models?
Otto, J.; Berveiller, D.; Bréon, F.-M. et al

in Biogeosciences (2014), 11(8), 2411-2427

Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we ... [more ▼]

Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we develop an approach that could be implemented in Earth system models. A stand-level forest gap model is combined with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning on summertime canopy albedo. This approach reveals which parameter has the largest affect on summer canopy albedo: we examined the effects of three forest species (pine, beech, oak) and four thinning strategies with a constant forest floor albedo (light to intense thinning regimes) and five different solar zenith angles at five different sites (40° N 9° E-60° N 9° E). During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning. These trends continue until the end of the rotation, where thinning explains up to 50% of the variance in near-infrared albedo and up to 70% of the variance in visible canopy albedo. <br><br> The absolute summertime canopy albedo of all species ranges from 0.03 to 0.06 (visible) and 0.20 to 0.28 (near-infrared); thus the albedo needs to be parameterised at species level. In addition, Earth system models need to account for forest management in such a way that structural changes in the canopy are described by changes in leaf area index and crown volume (maximum change of 0.02 visible and 0.05 near-infrared albedo) and that the expression of albedo depends on the solar zenith angle (maximum change of 0.02 visible and 0.05 near-infrared albedo). Earth system models taking into account these parameters would not only be able to examine the spatial effects of forest management but also the total effects of forest management on climate. © 2014 Author(s). [less ▲]

Detailed reference viewed: 17 (2 ULg)
Full Text
Peer Reviewed
See detailSpatial variability of soil CO 2 efflux linked to soil parameters and ecosystem characteristics in a temperate beech forest
Ngao, J.; Epron, D.; Delpierre, N. et al

in Agricultural and Forest Meteorology (2012), 154-155

The aim of this study was to determine the amplitude and the driving factors of the spatial variability in soil CO 2 efflux in a young European beech forest. Soil CO 2 efflux was measured in 2003 and 2004 ... [more ▼]

The aim of this study was to determine the amplitude and the driving factors of the spatial variability in soil CO 2 efflux in a young European beech forest. Soil CO 2 efflux was measured in 2003 and 2004 in seven beech plots differing in terms of soil type and leaf area index. After eliminating temporal fluctuations due to soil temperature and soil water content, standardized soil CO 2 efflux varied significantly among plots over a large range given the homogeneity of the land cover type. Correlation analyses revealed that this spatial variability could not be explained by root biomass, litter C content, soil C contents, stand basal area or stem density. Conversely, very significant correlations were found with topsoil bulk density, superficial soil C/N ratio, and leaf area index. Multiple regression analysis led to a model relating standardized soil CO 2 efflux to C/N ratio and topsoil bulk density, thus explaining 87% of observed inter-plot spatial variability. This study highlighted the need to consider spatially varying soil factors such as C/N ratio and bulk density when experimental schemes are elaborated to estimate mean soil CO 2 efflux at forest scale. © 2011 Elsevier B.V. [less ▲]

Full Text
Peer Reviewed
See detailGround-based Network of NDVI measurements for tracking temporal dynamics of canopy structure and vegetation phenology in different biomes
Soudani, K.; Hmimina, K.; Delpierre, N. et al

in Remote Sensing of Environment (2012), 123

Detailed reference viewed: 86 (5 ULg)
Full Text
Peer Reviewed
See detailDetecting the critical periods that underpin interannual fluctuations in the carbon balance of European forests
Le Maire, G.; Delpierre, N.; Jung, M. et al

in Journal of Geophysical Research: Biogeosciences (2010), 115(4),

The interannual variability of CO<inf>2</inf> exchange by forest ecosystems in Europe was analyzed at site and regional scales by identifying critical periods that contributed to interannual flux ... [more ▼]

The interannual variability of CO<inf>2</inf> exchange by forest ecosystems in Europe was analyzed at site and regional scales by identifying critical periods that contributed to interannual flux anomalies. Critical periods were defined as periods in which monthly and annual flux anomalies were correlated. The analysis was first conducted at seven European forest flux tower sites with contrasting species and climatic conditions. Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE), a generic process-based model, represented fairly well most features of the critical period patterns and their climate drivers at the site scale. Simulations at the scale of European forests were performed with ORCHIDEE integrated at a 0.25° spatial resolution. The spatial and temporal distributions of critical periods for canopy photosynthesis, ecosystem respiration, and net ecosystem exchange (NEE) as well as their underlying climate drivers were analyzed. The interannual variability in gross primary productivity (GPP) was explained by critical periods during spring and summer months. In contrast, the interannual variability in total ecosystem respiration (TER) was explained by critical periods occurring throughout the year. A latitudinal contrast between southern and northern Europe was observed in the distributions of critical periods for GPP and TER. The critical periods were positively controlled by temperature in northern Europe and by soil water availability in southern Europe. More importantly, the latitudinal transition between temperature-driven and water-driven critical periods for GPP varied from early spring to late summer. Such a distinct seasonal regime of critical periods was less clearly defined for TER and NEE. Overall, the critical periods associated with NEE variations and their meteorological drivers followed those associated with GPP. Copyright © 2010 by the American Geophysical Union. [less ▲]

Detailed reference viewed: 7 (1 ULg)
Full Text
Peer Reviewed
See detailExceptional Carbon Uptake In European Forests During The Warm Spring Of 2007: A Data-Model Analysis
Delpierre, N.; Soudani, K.; Kostner, B. et al

in Global Change Biology (2009), 15(6), 1455-1474

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature ... [more ▼]

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006-winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44 degrees to 62 degrees N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m(-2) anomaly compared with the decadal mean over the January-May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m(-2) anomaly over 5 months), leading to higher net uptake than the long-term mean at all sites (+12 to +79 gC m(-2) anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process-based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation. [less ▲]

Detailed reference viewed: 54 (20 ULg)