Large-scale estimation of xylem phenology in black spruce through remote sensing

There is a growing need for understanding the timing of wood formation in relation to the dynamicsof bud phenology at wide geographical scale. This study analysed the relationships between long-termchronologies of xylem growth and the timing of plant phenology detected by Normalized DifferenceVegetation Index (NDVI) in five permanent stands across the latitudinal distribution of black spruce [Piceamariana (Mill.) BPS] in the boreal forest of Quebec, Canada. Xylogenesis was studied weekly from April toOctober for thirteen years (2002–2014) on anatomical sections derived by wood microcores. The timingof the growing season detected by remote sensing was extracted from MODerate resolution ImagingSpectroradiometer (MODIS) 250 m 16-days NDVI data. The NDVI time-series were fitted using a double-logistic curve. Phenological chronologies from remote sensing and xylem phenology showed a latitudinaltrend. The models correlating the data inferred from satellite sensors and the spring observations ofxylem phenology were significant (p < 0.0001). The length of NDVI growing season and the duration ofxylogenesis showed a close correlation. This study demonstrated that the timing of xylem formationcould be suitably estimated at wide geographical scale using remote sensing data. However, the inter-annual phenological variability remained unexplained, which might limit the application of the modelsonly to the years considered by our chronologies.