Spectral response of forest disturbances induced by beaver caused floods: A case study in Estonia using Sentinel-2 MSI image time series

Beavers are known as ecosystem engineers and the habitats that they create can change the landscape greatly. When a new beaver colony establishes itself by building dams, digging canals and burrows and felling trees, the resulting changes are often large enough to be studied with medium resolution earth observation sensors like Sentinel-2 MSI. In this study we compare the spectral signatures of 405 sample areas disturbed by beaver-induced flooding with 261 healthy forest sample areas surrounding the area. We used 28 Sentinel-2 MSI multispectral images from years 2015 to 2018 over the southern part of Estonia in Military Grid Reference System map tile T35VME. In summer the average pixel values for areas that are affected by beavers show the largest differences in reflectance values for shortwave infrared (SWIR) and the visible parts of the spectrum compared to areas that are not affected by beavers. Some smaller differences are present also in the near-infrared (NIR) parts of the spectrum, but sometimes they are not significant according to p-values, being over the 0.05 threshold, of the t-test. In autumn and spring, when deciduous trees do not have their leaves and ground vegetation is not thriving, the differences in visible parts of the spectrum disappear. Multispectral vegetation indices, like the Normalized Difference Vegetation Index (NDVI) and others, also show clear differences in the beaver-disturbed forests and surrounding healthy forests throughout all vegetation phenology stages. Keywords: beavers; flood disturbance; phenology; forest damage; habitat change; Sentinel-2 MSI