Trend-cycles of vegetation dynamics as a tool for land degradation assessment and monitoring

Easdale Marcos Horacio, Fariña C., Hara Sofía María, Pérez León N., Umaña F., Tittonell Pablo, Bruzzone Octavio A.. 2019. Trend-cycles of vegetation dynamics as a tool for land degradation assessment and monitoring. Ecological Indicators, 107:105545, 10 p.

Quartile : Q1, Sujet : ENVIRONMENTAL SCIENCES

Résumé : The use of time series of Normalized Difference Vegetation Index (NDVI), obtained from satellite sensors has become frequent in studies for land degradation assessment and monitoring. Linear trends of NDVI are usually considered as indicators of vegetation dynamics and widely used as proxies for land degradation. Yet, long-term trends of NDVI often exhibit unidirectional (monotonic) but also cyclic (non-monotonic) dynamics, including mid-term oscillations, both of which are poorly captured by linear trends. Trend-cycle is a time series analysis that represents a smoothed version of a seasonally adjusted time series, which provides information on long-term movements while including changes in direction underlying the series. We assessed NDVI trend-cycles in Patagonia (Argentina) as proxies for land dynamics, integrating trend and medium-term cycles (>4 years). We used MODIS images between years 2000 and mid-2018; trend-cycles were analysed using the Basis Pursuit method. We observed that trend-cycles explained a significant portion of total temporal variability (reaching almost 20%), from which most patterns were explained by non-monotonic behaviour. We identified five major patterns in vegetation dynamics: decreasing (0.1% of area), increasing (0.6%), recovery (48.8%), relapsing (36.8%) and no trend-cycle (13.8%). Contrary to what is generally seen in the literature, monotonic patterns and particularly decreasing trend-cycles were marginally recorded in the last 18 years of NDVI records in Patagonia. Instead, the greater proportion of the area was classified as initial or advanced recovery and initial relapsing patterns, which refer to phases of a cyclic behaviour. We call for the need to revisit the conceptualization of land degradation assessment by means of remote sensing, and to critically review the ability of linear trends to reflect vegetation dynamics. Finally, we discuss the potential use of trend-cycle as a tool to monitor land dynamics and progress towards land degradation neutrality.

Mots-clés Agrovoc : télédétection, utilisation des terres, analyse de séries chronologiques, indice de végétation, neutralité en matière de dégradation des terres, imagerie par satellite

Mots-clés géographiques Agrovoc : Argentine

Mots-clés libres : NDVI trends, Desertification, Dryland, Monitoring systems, Wavelet

Champ stratégique Cirad : CTS 2 (2019-) - Transitions agroécologiques

Agences de financement hors UE : Instituto Nacional de Tecnología Agropecuaria, Ministerio de Ciencia, Tecnología e Innovación

Auteurs et affiliations

• Easdale Marcos Horacio, Instituto de Investigaciones Forestales y Agropecuarias Bariloche (ARG) - auteur correspondant
• Fariña C., Instituto de Investigaciones Forestales y Agropecuarias Bariloche (ARG)
• Hara Sofía María, Instituto de Investigaciones Forestales y Agropecuarias Bariloche (ARG)
• Pérez León N., Instituto de Investigaciones Forestales y Agropecuarias Bariloche (ARG)
• Umaña F., INTA (ARG)
• Tittonell Pablo, CONICET (ARG)
• Bruzzone Octavio A., Instituto de Investigaciones Forestales y Agropecuarias Bariloche (ARG)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/603567/)

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