Phenological characterization of Fagus sylvatica L. in Mediterranean populations of the Spanish Central Range with Landsat OLI/ETM+ and Sentinel-2A/B

Abstract

<jats:p>&lt;p&gt;The Spanish Central Range hosts some of the southernmost populations of &lt;em&gt;Fagus sylvatica&lt;/em&gt; L. (European beech). Recent cartography indicates that these populations are expanding, going up-streams and gaining ground to oak forests of &lt;em&gt;Quercus pyrenaica &lt;/em&gt;Willd., heather-lands, and pine plantations. Understanding the spectral phenology of European beech populations—which leaf flush occurs earlier than other vegetation formations—in this Mediterranean mountain range will provide insights of the species recent dynamics, and will enable modelling its performance under future climate oscillations. Intra-annual series of 211 Landsat OLI/ETM+ images, acquired between April 2013-December 2019, and 217 Sentinel-2A/B images, acquired between April 2017-December 2019, were employed to characterize the spectral phenology of European beech populations and five other vegetation types for comparison in an area of 108000 ha. Vegetation indices (VI) including the Normalized Difference Vegetation Index (NDVI) and Tasseled Cap Angle (TCA) from Landsat, and the NDVI and Enhanced Vegetation Index (EVI) from Sentinel-2 were retrieved from sample pixels. The temporal series of these VI were modelled with Savitzky-Golay and double logistic functions, and assessed with TIMESAT software, enabling the parametric characterization of European beech spectral phenology in the area with the start, length, and end of season, as well as peak time and value. The length of beech phenological season was similar when portrayed by Landsat and Sentinel-2 NDVI time series (214 and 211 days on average for the common period 2017-2019) although start and end differed. Compared with NDVI counterparts the TCA season started and peaked later, and the EVI season was shorter. Sentinel-2 NDVI peaked higher than Landsat NDVI. The European beech had an earlier (21 days on average) start of season than competing oak forests. Joint analysis of data from the virtual constellation Landsat/ Sentinel-2 and calibration with field observations may enable more detailed knowledge of phenological traits at the landscape scale.&lt;em&gt;&lt;/em&gt;&lt;/p&gt;</jats:p>

Espectrofenología con datos Sentinel 2: definición de curvas de referencia para la caracterización de ecosistemas forestales

“…La definición de variables y métricas espectrofenológicas permite convertir las series de datos procedentes de fuentes de observación remota en indicadores del funcionamiento ecológico, abriendo nuevas vías a la obtención de resultados de predicción y seguimiento complementarios a los datos de referencia recogidos en terreno con criterio experto, difíciles de conseguir y a menudo limitantes por su disponibilidad espaciotemporal. En los últimos años, son varios los trabajos que han utilizado la LSP para definir información referente a la fenología de la vegetación (Helman 2018;Caparros-Santiago y Rodríguez-Galiano 2020;Gómez et al 2020) y detección de cambios (Zhu 2017;Rubio-Cuadrado et al 2021), a partir de series temporales de índices de vegetación procedentes de imágenes satelitales y sensores aerotransportados. No obstante, a pesar de la actual disponibilidad de datos y las posibilidades de la LSP como herramienta de monitoreo ambiental, muy pocos estudios han evaluado la definición matemática de curvas tipo para hábitats o especies forestales a escala regional.…”