Résumé
Vegetation phenology is the study of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and from radiometric data obtained with high accuracy from ground-based measurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the influence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the inflexion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE≤one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series is more likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution.
Auteurs, date et publication :
Auteurs G. Hmimina , E. Dufrêne , J.-Y. Pontailler , N. Delpierre , M. Aubinet , B. Caquet , A. de Grandcourt , B. Burban , C. Flechard , A. Granier , P. Gross , B. Heinesch , B. Longdoz , C. Moureaux , J.-M. Ourcival , S. Rambal , L. Saint André , K. Soudani
Publication : Remote Sensing of Environment
Date : 2013
Volume : 132
Pages : 145–158
Catégorie(s)
#CIRAD #CNRS #FORET Paracou #FORET PuechabonAuteurs, date et publication :
Auteurs A. Bar-Hen , J. Chadø euf , H. Dessard , P. Monestiez
Publication : Statistics and Computing
Date : 2013
Volume : 23
Issue : 3
Pages : 297–309
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Quentin Molto , Vivien Rossi , Lilian Blanc , Robert Freckleton
Publication : Methods in Ecology and Evolution
Date : 2013
Volume : 4
Issue : 2
Pages : 175–183
Catégorie(s)
#CIRAD #FORET ParacouRésumé
entropart is a package for R designed to estimate diversity based on HCDT entropy or similarity-based entropy. It allows calculating species-neutral, phylogenetic and functional entropy and diversity, partitioning them and correcting them for estimation bias.
Auteurs, date et publication :
Auteurs Eric Marcon , Bruno Hérault
Publication : Journal of Statistical Software
Date : 2015
Volume : 67
Issue : 8
Pages : 1–26
Catégorie(s)
#CIRAD #FORET ParacouRésumé
The impact of increases in drought frequency on the Amazon forest's composition, structure and functioning remain uncertain. We used a process‐ and individual‐based ecosystem model (ED2) to quantify the forest's vulnerability to increased drought recurrence. We generated meteorologically realistic, drier‐than‐observed rainfall scenarios for two Amazon forest sites, Paracou (wetter) and Tapajós (drier), to evaluate the impacts of more frequent droughts on forest biomass, structure and composition. The wet site was insensitive to the tested scenarios, whereas at the dry site biomass declined when average rainfall reduction exceeded 15%, due to high mortality of large‐sized evergreen trees. Biomass losses persisted when year‐long drought recurrence was shorter than 2–7 yr, depending upon soil texture and leaf phenology. From the site‐level scenario results, we developed regionally applicable metrics to quantify the Amazon forest's climatological proximity to rainfall regimes likely to cause biomass loss textgreater 20% in 50 yr according to ED2 predictions. Nearly 25% (1.8 million km2) of the Amazon forests could experience frequent droughts and biomass loss if mean annual rainfall or interannual variability changed by 2σ. At least 10% of the high‐emission climate projections (CMIP5/RCP8.5 models) predict critically dry regimes over 25% of the Amazon forest area by 2100.
Auteurs, date et publication :
Auteurs Marcos Longo , Ryan G. Knox , Naomi M. Levine , Luciana F. Alves , Damien Bonal , Plinio B. Camargo , David R. Fitzjarrald , Matthew N. Hayek , Natalia Restrepo-Coupe , Scott R. Saleska , Rodrigo da Silva , Scott C. Stark , Raphael P. Tapajós , Kenia T. Wiedemann , Ke Zhang , Steven C. Wofsy , Paul R. Moorcroft
Publication : New Phytologist
Date : 2018
Catégorie(s)
#CIRAD #FORET ParacouRésumé
1The stoichiometry of resources is increasingly acknowledged as a major control of consumer activity and abundance. Chemical properties of litter, the main source of food for decomposers, are likely to be important drivers of decomposer activity.2Theory predicts a high control of resource stoichiometry on the abundance of consumer organisms that maintain strict homeostasis, due to costs associated with the regulation of nutrient balance in their body tissue. Decomposer efforts in nutrient acquisition should be related to imbalances in resource stoichiometry.3A 21 year old experimental plantation of monospecific plots of trees with leaves of contrasting chemistry was used to test four hypotheses: (i) soil and litter nutrient stoichiometry (C, N, P) are linked; (ii); soil enzyme activity ratios and stoichiometry are linked; (iii) earthworms' tissue stoichiometry does not depend on soil and litter stoichiometry (homeostasis); (iv) earthworm density is dependent upon phosphorus availability, the most limiting nutrient in soils at this site, and, to a lesser extent, to nitrogen availability.4We found (i) no relationship between litter and soil stoichiometry, (ii) microbial activity was linked to soil stoichiometry, (iii) earthworms showed strict homeostasis in their tissue and (iv) earthworm abundance increased with P availability.5We discuss the mechanisms that might lead to these patterns.
Auteurs, date et publication :
Auteurs R. Marichal , J. Mathieu , M.-M. Couteaux , P. Mora , J. Roy , P. Lavelle
Publication : Soil Biology and Biochemistry
Date : 2011
Volume : 43
Issue : 7
Pages : 1528–1535
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Climate change is predicted to increase the occurrence of extreme droughts, which are associated with elevated mortality rates in tropical trees. Drought-induced mortality is thought to occur by two main mechanisms: hydraulic failure or carbon starvation . This chapter focuses on the strategies that plants use to survive these two drought-induced mortality mechanisms and how these mechanisms are distributed among the immense diversity of tropical tree species. The traits that tropical trees may use to survive drought include (1) xylem that is resistant to drought-induced cavitation , (2) high sapwood capacitance that protects xylem from critically low water potentials , (3) drought deciduousness, (4) photosynthetic stems that have the potential to assimilate carbon at greater water-use efficiency than leaves, (5) deep roots, (6) regulation of gas exchange to reduce leaf water loss or to maintain photosynthesis at low leaf water potential and (7) when all else fails, low cuticular conductance from exposed tissues during extended drought. To date, most research has focused on deciduousness, resistant xylem, soil water, gas exchange behavior and sapwood capacitance, whereas little is known about the role of photosynthetic stems or cuticular conductance during extreme extended drought, making these processes a high priority for a complete understanding of tropical tree physiology during drought.
Auteurs, date et publication :
Auteurs Louis S. Santiago , Damien Bonal , Mark E. De Guzman , Eleinis Ávila-Lovera , Guillermo Goldstein , Louis S. Santiago
Date : 2025
Pages : 243-258
Catégorie(s)
#CIRAD #FORET ParacouAuteurs, date et publication :
Auteurs Laëtitia Bréchet , Stéphane Ponton , Tancrède Alméras , Damien Bonal , Daniel Epron
Publication : Plant and Soil
Date : 2011
Volume : 347
Issue : 1-2
Pages : 293–303
Catégorie(s)
#CIRAD #FORET ParacouRésumé
Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrate-induced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 μg g−1 h−1 and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks.
Auteurs, date et publication :
Auteurs Nicolas Fanin , Stephan Hättenschwiler , Sandra Barantal , Heidy Schimann , Nathalie Fromin
Publication : Soil Biology and Biochemistry
Date : 2011
Volume : 43
Issue : 5
Pages : 1014–1022
Catégorie(s)
#CIRAD #FORET ParacouRésumé
In the current global change context, it is urgent to anticipate the fate of tropical forests. This means understanding tree community response to disturbance and the underlying processes. In that respect, we aim here to clarify taxonomic and functional post-disturbance trajectories, and determine the scope of the Intermediate Disturbance Hypothesis (IDH) that remains debated in tropical forests. We analyzed community trajectories following a disturbance gradient from 10 to 60% of above-ground biomass loss in a Neotropical forest over 30 years. We considered trajectories along time of community taxonomic and functional trajectories in terms of richness, evenness, composition, and redundancy. We based on the annual botanical inventories of 75 ha of a Neotropical forest and on large trait datasets comprising seven leaf, stem, and life-history traits. We identified a decoupling between taxonomic composition, differing among communities, and functional composition, similar among communities and convergent in the functional space. The taxonomic diversity followed humped-shaped trajectories along time after disturbance depending on the initial disturbance intensity, which validated the IDH (Intermediate Disturbance Hypothesis). The functional diversity trajectories, however, were homogeneous among plots and dismissed the IDH. We explained this decoupling by the variations in community functional redundancy that mitigated the functional impact of disturbance. Although consistent, the recovery of community composition, diversity, and redundancy remained divergent from the initial state after 30 years. These results acknowledged the need of decades-long cycles without disturbance to ensure community complete recovery.
Auteurs, date et publication :
Auteurs A. Mirabel , B. Hérault , E. Marcon
Publication : Science of The Total Environment
Date : 2020
Volume : 720
Pages : 137397