Valéry Gond

Valéry Gond
Cirad - La recherche agronomique pour le développement | CIRAD · Unité Propre de Recherche Biens et Services des Écosystèmes Forestiers Tropicaux: l'Enjeu du Changement Global (BSEF)

Ph.D in Geography

About

243
Publications
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Introduction
I am geographer specialized in remote sensing processing. I worked on European temperate forest and Western African savannas during my PhD (1995) and as a Post-Doc (1996-2000). My researches focused on forest spatial pattern characterization using trees functioning or stand structure. I am involved also in the determination of human impact on forest by determining particular activities (mining, logging, agriculture). I am working in Amazonian, Central Africa and Indonesia.
Additional affiliations
February 1996 - January 1999
University of Antwerp
October 1993 - December 1995

Publications

Publications (243)
Article
Full-text available
African forests within the Congo Basin are generally mapped at a regional scale as broad-leaved evergreen forests, with the main distinction being between terra-firme and swamp forest types. At the same time, commercial forest inventories, as well as national maps, have highlighted a strong spatial heterogeneity of forest types. A detailed vegetati...
Book
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Au niveau mondial, ce sont les écosystèmes des tourbières, ces zones humides dont le sol présente une accumulation de matière organique partiellement décomposée, qui stockent le volume le plus important de carbone terrestre par unité de surface (Rydin and Jeglum 2006 ; Leifeld and Menichetti 2018). Elles couvrent près de 3 % de la surface terr...
Article
The United Nations Decade on Ecosystem restoration (2021¬–2030) lists mangrove ecosystems as a restoration priority. Interest in their conservation has increased recently due to their widespread degradation. Anthropogenic stressors and rehabilitation practices, specifically, have resulted in a significant decline in their species compositions. We i...
Article
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The phenology of tropical forests is tightly related to climate conditions. In the Amazon, the seasonal greening of forests is conditioned by solar radiation and rainfall. Yet, increasing anthropogenic pressures (e.g. logging and wildfires), raise concerns about the impacts of forest degradation on the functioning of forest ecosystems, especially i...
Article
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Le plan France Relance lancé en septembre 2020 prévoit des mesures forestières sur 2 ans, avec un accent sur la reconstitution des peuplements forestiers sinistrés, affaiblis par les sécheresses ou attaqués par les scolytes. Cependant la crise forestière liée au changement climatique est partie pour durer et les efforts sur les connaissances à acqu...
Article
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While forest degradation rates and extent exceed deforestation in the Brazilian Amazon, less attention is given to the factors controlling its spatial distribution. No quantified correlation exists between changes of forest structure due to anthropogenic disturbances and dynamics of land use and cover change occurring at broader spatial levels. Thi...
Article
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Surface water storage in floodplains and wetlands is poorly known from regional to global scales, in spite of its importance in the hydrological and the carbon balances, as the wet areas are an important water compartment which delays water transfer, modifies the sediment transport through sedimentation and erosion processes, and are a source for g...
Article
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A Madagascar, le taux de déforestation est parmi le plus intense des régions tropicales. Pour la préservation des espaces forestiers, l'une des actions fortes des pouvoirs publics ces dernières décennies a été la mise en place d'espaces protégés. La connaissance des dynamiques d'occupation du sol avant et après la mise en place d'un parc permet d'e...
Article
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Quantifying ecological condition, notably the extent of forest degradation is important for understanding and designing measures to protect biodiversity and enhancing the capacity of forests to deliver ecosystem services. Conservation planning, particularly the prioritization of management interventions for forests, is often lacking spatial data on...
Article
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In 2011, the Government of Uzbekistan established the Lower Amu Darya State Biosphere Reserve (LABR). This reserve aims to conserve the Tugay, an endangered riparian forest ecosystem straddling the main rivers of Central Asia’s drylands, which is under extreme anthropogenic pressure. The LABR has reintroduced Bukhara red deer (Cervus hanglu bactria...
Article
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The forests of Central Africa contain some of Earth's few remaining intact forests. These forests are increasingly threatened by infrastructure development, agriculture, and unsustainable extraction of natural resources (e.g. minerals, bushmeat, and timber), all of which is leading to deforestation and forest degradation, particularly defaunation,...
Article
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Assessing land use and land cover (LULC) change is essential for the sustainable 13 management of natural resources, biodiversity conservation, monitoring food security, and research 14 related to climate change and ecology. With increasingly rapid changes in LULC in response to 15 human population growth, a better assessment of land-use changes is...
Article
Remote sensing observations such as NDVI trends can provide important insights into past and present states of land condition. However, they do not directly provide comprehensive information about our representation of land degradation and the processes at work. This study aimed to analyze vegetation productivity underlying factors in order to asse...
Article
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Forests across the world stand at a crossroads where climate and land-use changes are shaping their future. Despite demonstrations of political will and global efforts, forest loss, fragmentation, and degradation continue unabated. No clear evidence exists to suggest that these initiatives are working. A key reason for this apparent ineffectiveness...
Article
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Degraded tropical forests dominate agricultural frontiers and their management is becoming an urgent priority. This calls for a better understanding of the different forest cover states and cost-efficient techniques to quantify the impact of degradation on forest structure. Canopy texture analyses based on Very High Spatial Resolution (VHSR) optical i...
Article
Recently, there has been renewed interest in the ecosystem services of mangroves such as carbon sequestration or coastal protection, and consequently, the development of tools providing an effective and automatic monitoring of the dynamics of mangrove land coverage including rehabilitated or naturally regenerated forest stand is increasingly demand...
Preprint
Full-text available
Measuring forest degradation is important for understanding and designing measures to protect biodiversity and the capacity of forests to deliver ecosystem services. Conservation planning, particularly the prioritization of management interventions for forests, is often lacking spatial data on ecological condition, and it is often overlooked within...
Preprint
Full-text available
Forests across the world stand at the crossroad with climate and land use changes shaping their future. Despite the demonstration of political will and global efforts, forest loss, fragmentation and land degradation continue unabated. No clear evidence exists that these initiatives are working. Why are policies designed to halt deforestation and in...
Article
Full-text available
Forest conservation in human-dominated tropical landscapes ensures provision of major ecosystem services. However, conservation goals are threatened by growing demands for agricultural products. As the expansion of agricultural frontiers continues to exert increasing pressure on forest cover, it is crucial to provide indicators on forest vulnerabil...
Conference Paper
Full-text available
Abstract from a presentation at the 4th World Congress of Agroforestry - held in Montpellier (France) between 20-22 May 2019
Data
VALERI : a network of sites and methodology for the validation of medium spatial resolution land products
Article
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Monitoring forest–agriculture mosaics is crucial for understanding landscape heterogeneity and managing biodiversity. Mapping these mosaics from remotely sensed imagery remains challenging, since ecological gradients from forested to agricultural areas make characterizing vegetation more difficult. The recent synthetic aperture radar (SAR) Sentinel...
Article
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Rainfall thresholds under which forests grow in Central Africa are lower than those of Amazonia and SE Asia. Attention is thus regularly paid to rainfall whose seasonality and interannual variability has been shown to control Central African forests' water balance and photosynthetic activity. Nonetheless, light availability is also recognized as a...
Article
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The issue of invasive plants in Togo (West Africa): contribution of landscape systemic analysis and remote sensing. Description of the subject. Invasive plants are a major threat to natural habitats, agriculture and health worldwide. Certain land uses are known to promote plant invasions. Despite the occurrence of rapid land-use mutations, particul...
Chapter
Rapid population growth and economic change on the tropical islands of Mauritius have led to one of the highest rates of urban build-out in the world. Pressure on many of the island’s natural features and resources increasingly risks further degradation to the environmental services that they provide to the country. Fourteen types of marine and ter...
Presentation
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Biological invasions and changes in land use are two components of global change affecting biodiversity worldwide. Both contemporary and historic land use may influence the spread of invasive plants by altering landscape patterns, soils, and biotic communities. Indeed, invasion within land uses is often associated with the historical legacy of chan...
Conference Paper
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Les conditions d'éclairement prévalant en Afrique Centrale et leur impact potentiel sur les traits et le fonctionnement des forêts ont été peu étudiés. S'appuyant sur des estimations satellitaires horaires de rayonnement solaire incident, et tenant compte des interactions d'échelles entre cycle diurne et cycle saisonnier, nous montrons que le Gabon...
Article
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In the agricultural frontiers of Brazil, the distinction between forested and deforested lands traditionally used to map the state of the Amazon does not reflect the reality of the forest situation. A whole gradient exists for these forests, spanning from well conserved to severely degraded. For decision makers, there is an urgent need to better ch...
Article
Mapping ecosystem services (ES) over large scales is important for environmental monitoring but is often prohibitively expensive and difficult. We test a hybrid, low-cost method of mapping ES indicators over large scales in Pará State, Brazil. Four ES indicators (vegetation carbon stocks, biodiversity index, soil chemical quality index and rates of...
Presentation
Tropical natural ecosystems host a very diverse flora and fauna and are key ecosystems for global climate and biogeochemical regulation. Unfortunately, in West African landscapes, large areas of savanna and forest have been progressively replaced or fragmented by crops. These dynamics promote the spread of many invasive plants representing on the o...
Article
Full-text available
Monitoring and understanding the changes in mangrove ecosystems and their surroundings are required to determine how mangrove ecosystems are constantly changing while influenced by anthropogenic, and natural drivers. Cosistency in high spatial resolution (30 m) satellite and high performance computing facilities are limiting factors to the process,...
Article
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Lorey's height, representative of mean height in uneven-aged forest stands, is a valuable parameter for forest ecosystem management. While in situ measures provide the most precise information, remote-sensing techniques may provide less expensive but denser and more operational alternative of Lorey's height estimation over highly mountainous areas....
Chapter
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Les pays du domaine sahélien sont parmi ceux qui possèdent les taux d'émissions de carbone les plus bas au monde à cause de leur faible niveau de développement industriel. La majorité des émissions nettes de CO2 résulte régionalement de la déforestation et de la dégradation forestière. Mais au-delà de ses faibles émissions de gaz à effet de serre,...
Article
This viewpoint paper presents a reaction to the article by Brandt et al. (2016). It highlights the complexities inherent to the attribution of deforestation impacts to policy interventions when using remote-sensing data. This critique argues that in the context of the Congo a suite of factors (i.e., population density in particular) other than thos...
Article
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Tropical forests of the Guiana Shield are the most affected by gold-mining in South America, experiencing an exponential increase in deforestation since the early 2000's. Using yearly deforestation data encompassing Guyana, Suriname, French Guiana and the Brazilian State of Amapá, we demonstrated a strong relationship between deforestation due to g...
Presentation
Landscapes of the Togodo Protected Area (TPA) in southeastern Togo and its periphery have been under increasing modifications for decades As for the dry savannah and forest ecosystems in West Africa, one of the main factors of this transformation in land cover/ use is the expansion of agricultural systems to meet the demand for food from a growing...
Article
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In the Brazilian Amazon, degraded forests dominate the landscapes on the agricultural frontiers. This region is now facing a major challenge: halting degradation and sustainably managing these forests. Today, degraded forests represent a class of forest in their own right. They can nevertheless play a key role in combating climate change, and can a...
Chapter
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Forests occupy one-third of the planet’s landmass, covering nearly 4 billion hectares. The largest forested areas are located in the boreal and equatorial zones. This current distribution is not fixed, but has continuously changed over time due to the influence of environmental change and anthropogenic impact. One-third of current forested areas ar...
Article
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In the Brazilian Amazon, multiple logging activities are undergoing, involving different actors and interests. They shape a disturbance gradient bound to the intensity and frequency of logging, and forest management techniques. However, until now, few studies have been carried out at the landscape scale taking into account these multiple types of l...
Article
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Tropical forests with a low human population and absence of large-scale deforestation provide unique opportunities to study successful conservation strategies, which should be based on adequate monitoring tools. This study explored the conservation status of a large predator, the jaguar, considered an indicator of the maintenance of how well ecolog...
Data
Sites where implemented surveys of jaguars (bold) and prey (bold and other), with projected geographic coordonates, threats, landscape categories, Human footprint, and abundance of a selected set of prey species. (XLSX)
Article
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In this study, the recently launched Sentinel-2 (S2) optical satellite and the active radar Sentinel-1 (S1) satellite supported by active fire data from the MODIS sensor were used to detect and monitor forest fires in the Congo Basin. In the context of a very strong El Niño event, an unprecedented outbreak of fires was observed during the first mon...
Article
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En Guyane française le phénomène de l’orpaillage illégal a vu le jour au milieu des années 90 et s’amplifie depuis à cause de la hausse des prix de l’or sur le marché international. Couverte à 96% de forêt tropicale humide, la Guyane française est peu accessible et permet aux travailleurs illégaux d’opérer loin des contrôles. La technique d’extract...