50 years of woody vegetation changes in the Ferlo (Senegal) assessed by high-resolution imagery and field surveys

Dendoncker, Morgane; Brandt, Martin; Rasmussen, Kjeld; Taugourdeau, Simon; Fensholt, Rasmus; Tucker, Compton J.; Vincke, Caroline

doi:10.1007/s10113-020-01724-4

Cited by 16 publications

(17 citation statements)

References 42 publications

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“…For larger trees and favourable illumination and canopy reflectance conditions, it would also be possible to delineate tree crowns manually from HEXAGON: We found the radiometric quality good enough to differentiate between lighter crown and darker shadow in many cases. This is, however, not the case for the CORONA images, as was already observed by Dendoncker et al (2020) and Andersen (2006).…”

Section: Mapping Trees With Hexagon Vs Other Very High Resolution Ima...mentioning

confidence: 60%

“…Compared to the FB dataset, we found tree counts for all dates 34-40% lower in the WB dataset owing, above all, to our inability to visually separate all trees with overlapping crowns growing in clumped-canopy groups: We missed 29% of the field-mapped group trees in the WorldView images. This problem is reported in many studies that quantify treedensity (e.g., Axelsson and Hanan, 2017;Dendoncker et al, 2020). Brandt et al (2020) reported their dryland tree-mapping model to have missed 3.8% of the reference trees due to inclusion in clumped canopies.…”

Section: Mapping Trees With Hexagon Vs Other Very High Resolution Ima...mentioning

confidence: 98%

“…The lower size limit for tree detection differs between studies, since the spatial resolution and radiometric quality of historical AP and VHRS images varies considerably. Some authors found black-and-white AP also suitable for tree-crown delineation (and thus calculation of percentage woody cover; Lahav-Ginott et al, 2001;Moustakas et al, 2006), but this is not feasible with the lower-resolution CORONA VHRS images (Dendoncker et al, 2020). Although various studies use CORONA images for mapping forest-ecosystem changes (e.g., Tappan et al, 2004;Frost and Epstein, 2014;Nita et al, 2018), quantification of woody cover change on the tree level is rarely achieved.…”

Section: Introductionmentioning

confidence: 99%

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Monitoring Dryland Trees With Remote Sensing. Part A: Beyond CORONA—Historical HEXAGON Satellite Imagery as a New Data Source for Mapping Open-Canopy Woodlands on the Tree Level

Marzolff

Kirchhoff

Stephan

et al. 2022

Front. Environ. Sci.

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Monitoring woody cover by remote sensing is considered a key methodology towards sustainable management of trees in dryland forests. However, while modern very high resolution satellite (VHRS) sensors allow woodland mapping at the individual tree level, the historical perspective is often hindered by lack of appropriate image data. In this first study employing the newly accessible historical HEXAGON KH-9 stereo-panoramic camera images for environmental research, we propose their use for mapping trees in open-canopy conditions. The 2–4 feet resolution panchromatic HEXAGON satellite photographs were taken 1971–1986 within the American reconnaissance programs that are better known to the scientific community for their lower-resolution CORONA images. Our aim is to evaluate the potential of combining historical CORONA and HEXAGON with recent WorldView VHRS imagery for retrospective woodland change mapping on the tree level. We mapped all trees on 30 1-ha test sites in open-canopy argan woodlands in Morocco in the field and from the VHRS imagery for estimating changes of tree density and size between 1967/1972 and 2018. Prior to image interpretation, we used simulations based on unmanned aerial system (UAS) imagery for exemplarily examining the role of illumination, viewing geometry and image resolution on the appearance of trees and their shadows in the historical panchromatic images. We show that understanding these parameters is imperative for correct detection and size-estimation of tree crowns. Our results confirm that tree maps derived solely from VHRS image analysis generally underestimate the number of small trees and trees in clumped-canopy groups. Nevertheless, HEXAGON images compare remarkably well with WorldView images and have much higher tree-mapping potential than CORONA. By classifying the trees in three sizes, we were able to measure tree-cover changes on an ordinal scale. Although we found no clear trend of forest degradation or recovery, our argan forest sites show varying patterns of change, which are further analysed in Part B of our study. We conclude that the HEXAGON stereo-panoramic camera images, of which 670,000 worldwide will soon be available, open exciting opportunities for retrospective monitoring of trees in open-canopy conditions and other woody vegetation patterns back into the 1980s and 1970s.

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Section: Mapping Trees With Hexagon Vs Other Very High Resolution Ima...mentioning

confidence: 60%

Section: Mapping Trees With Hexagon Vs Other Very High Resolution Ima...mentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Monitoring Dryland Trees With Remote Sensing. Part A: Beyond CORONA—Historical HEXAGON Satellite Imagery as a New Data Source for Mapping Open-Canopy Woodlands on the Tree Level

Marzolff

Kirchhoff

Stephan

et al. 2022

Front. Environ. Sci.

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“…Des travaux récents combinent à la fois des données satellitaires et des données historiques de relevés botaniques dans le nord du Sénégal. Les variations des communautés ligneuses avant, pendant et après la période de sécheresse sont étudiées (Dendoncker et al, 2020). Ce travail a reposé en partie sur l'utilisation de bases de données historiques de la végétation, en particulier la base Flotrop (Taugourdeau et al, 2019)…”

Section: Changement Des Communautés Des Savanes Sahéliennes Suite Aux...unclassified

Élevages au pâturage et développement durable des territoires méditerranéens et tropicaux

Ickowicz

Moulin

2022

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Les élevages de ruminants au pâturage en zones méditerranéennes et tropicales Contributions potentielles des élevages de ruminants au pâturage aux ODD et controverses Un cadre général pour mener des recherches sur la contribution des élevages au pâturage au développement durable 2. Adaptation aux changements locaux et globaux des systèmes d'élevage au pâturage 1. www.ppzs.org. 2. www.gbif.org/dataset/eb605c7a-a91c-4ab8-a588-85d0ccb2be9e.

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“…Forest and savanna ecosystems in sub-Saharan Africa are characterized by significant changes in land cover and vegetation composition due to agro-pastoral activities and impacts from various other land-use practices (Arakwiye et al, 2021 ; Dendoncker et al, 2020 ; Ellis, 2006 ). In many regions of Sub-Saharan Africa (SSA), charcoal production plays an important role as a driver in environmental change.…”

Section: Introductionmentioning

confidence: 99%

Using an unmanned aerial system to analyse environmental impacts of charcoal production on tropical savanna ecosystems in northwestern Kenya

Petersen

Nüsser

2022

Environ Monit Assess

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In many regions of Sub-Saharan Africa, charcoal plays an important role as energy source but is widely perceived as a major driver of deforestation and forest degradation. This narrative, however, is mostly based on research within primary production regions. Though space-borne remote sensing applications can be useful in monitoring such large-scale production modes, environmental effects of household-level production are less easy to assess. Therefore, the present study employs an unmanned aerial system (UAS) to assess the impact of small-scale charcoal production on the vegetation density in the immediate vicinity of production sites. The UAS data was complemented by field measurements and very high-resolution WordView-2 satellite imagery. This approach revealed only small differences between charcoal production sites and reference plots which were usually evened out after 20–25-m distance to the plot centre using a concentric ring analysis. Results further show that a distinction between different land-use practices is difficult, even with the high spatial resolution provided by a UAS. Thus, more research and new approaches are needed to evaluate the role of small-scale charcoal production in deforestation and forest degradation processes against the background of other human activities. However, to exploit the full potential of UAS for monitoring environmental effects in charcoal producing areas, official regulations need to be clearer and more reliable.

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50 years of woody vegetation changes in the Ferlo (Senegal) assessed by high-resolution imagery and field surveys

Cited by 16 publications

References 42 publications

Monitoring Dryland Trees With Remote Sensing. Part A: Beyond CORONA—Historical HEXAGON Satellite Imagery as a New Data Source for Mapping Open-Canopy Woodlands on the Tree Level

Monitoring Dryland Trees With Remote Sensing. Part A: Beyond CORONA—Historical HEXAGON Satellite Imagery as a New Data Source for Mapping Open-Canopy Woodlands on the Tree Level

Élevages au pâturage et développement durable des territoires méditerranéens et tropicaux

Using an unmanned aerial system to analyse environmental impacts of charcoal production on tropical savanna ecosystems in northwestern Kenya

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