Caracterización de la fenología de Fagus sylvatica L. en poblaciones mediterráneas del Sistema Central español mediante datos Landsat OLI/ETM+ y Sentinel-2A/B

[EN] The Spanish Central Range hosts some of the southernmost populations of Fagus sylvatica L. (European beech). Recent cartography indicates that these populations are expanding, going up-streams and gaining ground to oak forests of Quercus pyrenaica 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.[ES] Algunas de las poblaciones más meridionales de Fagus sylvatica L. (haya) se encuentran en el Sistema Central español. La cartografía reciente de estas poblaciones indica que están expandiéndose a lo largo de arroyos y ganando terreno a robledales de Quercus pyrenaica Willd., brezales, y pinares. Conocer la fenología espectral de estos hayedos mediterráneos de montaña, cuya apertura de hojas se adelanta a la de otras formaciones vegetales permitiría inferir su dinámica reciente y modelizar su comportamiento frente a futuras oscilaciones climáticas. Se utilizaron 211 imágenes Landsat OLI/ETM+ adquiridas entre abril 2013-diciembre 2019 y 217 imágenes Sentinel-2A/B adquiridas entre abril 2017-diciembre 2019 para caracterizar la fenología espectral de hayedos y otras cinco formaciones vegetales en 108000 ha. Se calcularon y analizaron índices de vegetación: Normalized Difference Vegetation Index (NDVI) y Tasseled Cap Angle (TCA) con datos Landsat, NDVI y Enhanced Vegetation Index (EVI) con Sentinel-2. Se extrajeron las series temporales de estos índices en píxeles muestra para analizar mediante software TIMESAT, ajustando modelos Savitzky-Golay y función logística, y describiendo paramétricamente la fenología espectral: inicio, fin, y duración de temporada, así como momento y valor máximo del índice. Las series NDVI de Landsat y Sentinel-2 representaron una duración similar de la temporada fenológica (214 y 211 días para el periodo común de análisis, 2017-2019), aunque inicio y fin no coincidieron. Comparando con las curvas NDVI homólogas, la temporada TCA comenzó y alcanzó el pico máximo antes, y la temporada EVI fue más corta. Los valores máximos de NDVI en las series Sentinel-2 fueron más altos que los de Landsat. Los hayedos comenzaron la temporada fenológica de media 21 días antes que los robledales. El análisis conjunto de datos de la constelación virtual Landsat/Sentinel-2 y la calibración con observaciones de campo permitirá conocer mejor la fenología a escala de paisaje.This work was funded by the Spanish Ministry of Science, Innovation and University through projects: AGL2013-46028-R “Forest manage-ment facing the change in forest ecosystems dynamics: a multiscale approach (SCALyFOR)” and AGL201676769-C2-1-R “Influence of nat-ural disturbance regimes and management on forests dynamics, structure and carbon balance (FORESTCHANGE)”. 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Don't Thrash: How to Cache Your Hash on Flash

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