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Ecosystem properties of semiarid savanna grassland in West Africa and its relationship with environmental variability

Tagesson, Torbern; Fensholt, Rasmus; Guiro, Idrissa; Rasmussen, Mads Olander; Huber, Silvia; Mbow, Cheikh; Garcia, Monica; Horion, Stephanie; Sandholt, Inge and Holm-Rasmussen, Bo, et al. (2015) In Global Change Biology 21(1). p.250-264
Abstract
The Dahra field site in Senegal, West Africa, was established in 2002 to monitor ecosystem properties of semiarid savanna grassland and their responses to climatic and environmental change. This article describes the environment and the ecosystem properties of the site using a unique set of in situ data. The studied variables include hydroclimatic variables, species composition, albedo, normalized difference vegetation index (NDVI), hyperspectral characteristics (350-1800nm), surface reflectance anisotropy, brightness temperature, fraction of absorbed photosynthetic active radiation (FAPAR), biomass, vegetation water content, and land-atmosphere exchanges of carbon (NEE) and energy. The Dahra field site experiences a typical Sahelian... (More)
The Dahra field site in Senegal, West Africa, was established in 2002 to monitor ecosystem properties of semiarid savanna grassland and their responses to climatic and environmental change. This article describes the environment and the ecosystem properties of the site using a unique set of in situ data. The studied variables include hydroclimatic variables, species composition, albedo, normalized difference vegetation index (NDVI), hyperspectral characteristics (350-1800nm), surface reflectance anisotropy, brightness temperature, fraction of absorbed photosynthetic active radiation (FAPAR), biomass, vegetation water content, and land-atmosphere exchanges of carbon (NEE) and energy. The Dahra field site experiences a typical Sahelian climate and is covered by coexisting trees (similar to 3% canopy cover) and grass species, characterizing large parts of the Sahel. This makes the site suitable for investigating relationships between ecosystem properties and hydroclimatic variables for semiarid savanna ecosystems of the region. There were strong interannual, seasonal and diurnal dynamics in NEE, with high values of similar to-7.5g Cm(-2)day(-1) during the peak of the growing season. We found neither browning nor greening NDVI trends from 2002 to 2012. Interannual variation in species composition was strongly related to rainfall distribution. NDVI and FAPAR were strongly related to species composition, especially for years dominated by the species Zornia glochidiata. This influence was not observed in interannual variation in biomass and vegetation productivity, thus challenging dryland productivity models based on remote sensing. Surface reflectance anisotropy (350-1800nm) at the peak of the growing season varied strongly depending on wavelength and viewing angle thereby having implications for the design of remotely sensed spectral vegetation indices covering different wavelength regions. The presented time series of in situ data have great potential for dryland dynamics studies, global climate change related research and evaluation and parameterization of remote sensing products and dynamic vegetation models. (Less)
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published
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keywords
dryland, eddy covariance, evapotranspiration, latent heat flux, net, ecosystem exchange, Sahel, savanna, sensible heat flux
in
Global Change Biology
volume
21
issue
1
pages
250 - 264
publisher
Wiley-Blackwell
external identifiers
  • wos:000346698100024
  • scopus:84916941267
ISSN
1354-1013
DOI
10.1111/gcb.12734
language
English
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yes
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036ceb5d-fa5b-4116-a8a5-f968ee07cb56 (old id 5085155)
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2015-02-26 11:52:53
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2017-09-10 03:27:34
@article{036ceb5d-fa5b-4116-a8a5-f968ee07cb56,
  abstract     = {The Dahra field site in Senegal, West Africa, was established in 2002 to monitor ecosystem properties of semiarid savanna grassland and their responses to climatic and environmental change. This article describes the environment and the ecosystem properties of the site using a unique set of in situ data. The studied variables include hydroclimatic variables, species composition, albedo, normalized difference vegetation index (NDVI), hyperspectral characteristics (350-1800nm), surface reflectance anisotropy, brightness temperature, fraction of absorbed photosynthetic active radiation (FAPAR), biomass, vegetation water content, and land-atmosphere exchanges of carbon (NEE) and energy. The Dahra field site experiences a typical Sahelian climate and is covered by coexisting trees (similar to 3% canopy cover) and grass species, characterizing large parts of the Sahel. This makes the site suitable for investigating relationships between ecosystem properties and hydroclimatic variables for semiarid savanna ecosystems of the region. There were strong interannual, seasonal and diurnal dynamics in NEE, with high values of similar to-7.5g Cm(-2)day(-1) during the peak of the growing season. We found neither browning nor greening NDVI trends from 2002 to 2012. Interannual variation in species composition was strongly related to rainfall distribution. NDVI and FAPAR were strongly related to species composition, especially for years dominated by the species Zornia glochidiata. This influence was not observed in interannual variation in biomass and vegetation productivity, thus challenging dryland productivity models based on remote sensing. Surface reflectance anisotropy (350-1800nm) at the peak of the growing season varied strongly depending on wavelength and viewing angle thereby having implications for the design of remotely sensed spectral vegetation indices covering different wavelength regions. The presented time series of in situ data have great potential for dryland dynamics studies, global climate change related research and evaluation and parameterization of remote sensing products and dynamic vegetation models.},
  author       = {Tagesson, Torbern and Fensholt, Rasmus and Guiro, Idrissa and Rasmussen, Mads Olander and Huber, Silvia and Mbow, Cheikh and Garcia, Monica and Horion, Stephanie and Sandholt, Inge and Holm-Rasmussen, Bo and Goettsche, Frank M. and Ridler, Marc-Etienne and Boke-Olén, Niklas and Olsen, Jorgen Lundegard and Ehammer, Andrea and Madsen, Mathias and Olesen, Folke S. and Ardö, Jonas},
  issn         = {1354-1013},
  keyword      = {dryland,eddy covariance,evapotranspiration,latent heat flux,net,ecosystem exchange,Sahel,savanna,sensible heat flux},
  language     = {eng},
  number       = {1},
  pages        = {250--264},
  publisher    = {Wiley-Blackwell},
  series       = {Global Change Biology},
  title        = {Ecosystem properties of semiarid savanna grassland in West Africa and its relationship with environmental variability},
  url          = {http://dx.doi.org/10.1111/gcb.12734},
  volume       = {21},
  year         = {2015},
}