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See detailAboveground biomass mapping of African forest mosaics using canopy texture analysis: toward a regional approach.
Bastin, Jean-François ULg; Barbier, Nicolas; Couteron, Pierre et al

in Ecological Applications (2014), 24(8), 1984-2001

In the context of the reduction of greenhouse gas emissions caused by deforestation and forest degradation (the REDD+ program), optical very high resolution (VHR) satellite images provide an opportunity ... [more ▼]

In the context of the reduction of greenhouse gas emissions caused by deforestation and forest degradation (the REDD+ program), optical very high resolution (VHR) satellite images provide an opportunity to characterize forest canopy structure and to quantify aboveground biomass (AGB) at less expense than methods based on airborne remote sensing data. Among the methods for processing these VHR images, Fourier textural ordination (FOTO) presents a good potential to detect forest canopy structural heterogeneity and therefore to predict AGB variations. Notably, the method does not saturate at intermediate AGB values as do pixelwise processing of available space borne optical and radar signals. However, a regional scale application requires to overcome two difficulties: (i) instrumental effects due to variations in sun-scene-sensor geometry or sensor-specific responses that preclude the use of wide arrays of images acquired under heterogeneous conditions and (ii) forest structural diversity including monodominant or open canopy forests, which are of particular importance in Central Africa. In this study, we demonstrate the feasibility of a rigorous regional study of canopy texture by harmonizing FOTO indices of images acquired from two different sensors (Geoeye-1 and QuickBird-2) and different sun-scene-sensor geometries and by calibrating a piecewise biomass inversion model using 26 inventory plots (1 ha) sampled across very heterogeneous forest types. A good agreement was found between observed and predicted AGB (RSE=15%; R²=0.85; p-value<0.001) across a wide range of AGB levels from 26 Mg/ha to 460 Mg/ha, and was confirmed by cross validation. A high-resolution biomass map (100 m pixels) was produced for a 400 km² area, and predictions obtained from both imagery sources were consistent with each other (r=0.86; slope=1.03; intercept=12.01 Mg/ha). These results highlight the horizontal structure of forest canopy as a powerful descriptor of the entire forest stand structure and heterogeneity. In particular, we show that quantitative metrics resulting from such textural analysis offer new opportunities to characterize the spatial and temporal variation of the structure of dense forests and may complement the toolbox used by tropical forest ecologists, managers or REDD+ national monitoring, reporting and verification bodies. [less ▲]

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See detailEddy Covariance Co2 Flux Measurements In Nocturnal Conditions: An Analysis Of The Problem
Aubinet, Marc ULg

in Ecological Applications (2008), 18(6),

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See detailLandscape-level thresholds and newt conservation
Denoël, Mathieu ULg; Ficetola, G. Francesco

in Ecological Applications (2007), 17(1), 302-309

Ecological thresholds are defined as points or zones at which a rapid change occurs from one ecological condition to another. The existence of thresholds in species - habitat relationships has important ... [more ▼]

Ecological thresholds are defined as points or zones at which a rapid change occurs from one ecological condition to another. The existence of thresholds in species - habitat relationships has important implications for management, but the lack of concordance across studies and the wide range of methods used make generalizations difficult. We used two different statistical methods to test for the existence of thresholds for both individual species and the whole community, using three newt species as models. Based on a sample of 371 ponds, we found significant thresholds for both landscape configuration and composition. These were for the relationships between distance to forest and occurrence of Triturus alpestris and T. helveticus, and forest and crop cover and T. helveticus. Variability in the location of thresholds observed for the different species in this study caution against their use at the community level. Future studies should be based on the identification and assessment of thresholds for targeted species. Thresholds can be a useful concept from which tools may be developed to focus conservation effort for threatened species and their habitats. [less ▲]

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See detailAn artificial neural network analysis of factors controlling ecosystem metabolism in the coastal ocean
Rochelle Newall, Emma J.; Winter, Christian; Barrón, Cristina et al

in Ecological Applications (2007), 17(5), 185196

Knowing the metabolic balance of an ecosystem is of utmost importance in determining whether the system is a net source or net sink of carbon dioxide to the atmosphere. However, obtaining these estimates ... [more ▼]

Knowing the metabolic balance of an ecosystem is of utmost importance in determining whether the system is a net source or net sink of carbon dioxide to the atmosphere. However, obtaining these estimates often demands significant amounts of time and manpower. Here we present a simplified way to obtain an estimation of ecosystem metabolism. We used artificial neural networks (ANNs) to develop a mathematical model of the gross primary production to community respiration ratio (GPP:CR) based on input variables derived from three widely contrasting European coastal ecosystems (Scheldt Estuary, Randers Fjord, and Bay of Palma). Although very large gradients of nutrient concentration, light penetration, and organic-matter concentration exist across the sites, the factors that best predict the GPP:CR ratio are sampling depth, dissolved organic carbon (DOC) concentration, and temperature. We propose that, at least in coastal ecosystems, metabolic balance can be predicted relatively easily from these three predictive factors. An important conclusion of this work is that ANNs can provide a robust tool for the determination of ecosystem metabolism in coastal ecosystems. [less ▲]

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