Climate Effects on Vertical Forest Phenology of Fagus sylvatica L., Sensed by Sentinel-2, Time Lapse Camera, and Visual Ground Observations

authored by

Lars Uphus, Marvin Lüpke, Ye Yuan, Caryl Benjamin, Jana Englmeier, Ute Fricke, Cristina Ganuza, Michael Schwindl, Johannes Uhler, Annette Menzel

Abstract

Contemporary climate change leads to earlier spring phenological events in Europe. In forests, in which overstory strongly regulates the microclimate beneath, it is not clear if further change equally shifts the timing of leaf unfolding for the over-and understory of main deciduous forest species, such as Fagus sylvatica L. (European beech). Furthermore, it is not known yet how this vertical phenological (mis)match—the phenological difference between overstory and under-story—affects the remotely sensed satellite signal. To investigate this, we disentangled the start of season (SOS) of overstory F.sylvatica foliage from understory F. sylvatica foliage in forests, within nine quadrants of 5.8 × 5.8 km, stratified over a temperature gradient of 2.5 °C in Bavaria, southeast Germany, in the spring seasons of 2019 and 2020 using time lapse cameras and visual ground ob-servations. We explained SOS dates and vertical phenological (mis)match by canopy temperature and compared these to Sentinel-2 derived SOS in response to canopy temperature. We found that overstory SOS advanced with higher mean April canopy temperature (visual ground observations: −2.86 days per °C; cameras: −2.57 days per °C). However, understory SOS was not significantly af-fected by canopy temperature. This led to an increase of vertical phenological mismatch with increased canopy temperature (visual ground observations: +3.90 days per °C; cameras: +2.52 days per °C). These results matched Sentinel-2-derived SOS responses, as pixels of higher canopy height advanced more by increased canopy temperature than pixels of lower canopy height. The results may indicate that, with further climate change, spring phenology of F. sylvatica overstory will ad-vance more than F. sylvatica understory, leading to increased vertical phenological mismatch in temperate deciduous forests. This may have major ecological effects, but also methodological conse-quences for the field of remote sensing, as what the signal senses highly depends on the pixel mean canopy height and the vertical (mis)match.

External Organisation(s)

Julius Maximilian University of Würzburg
Technical University of Munich (TUM)

Type

Article

Journal

Remote sensing

Volume

13

ISSN

2072-4292

Publication date

05.10.2021

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

General Earth and Planetary Sciences

Sustainable Development Goals

SDG 13 - Climate Action

Electronic version(s)

https://doi.org/10.3390/rs13193982 (Access: Open)