Quantifying vegetation change and spatial-temporal extent of cadaver decomposition islands in the Artic tundra of Svalbard

By Stijn Sombekke

Abstract
Cadaver decomposition islands (CDI) are localized hotspots of high nutrient soil left behind by cadavers that decomposed and leached organic materials of high nitrogen, phosphorus and carbon content into the soil. The surge of nutrients released is known to affect the local vegetation communities by changing the species composition and increasing the biomass. The nutrient surge could be of particularly large influence on nutrient limited habitats, like Artic tundra, where nutrient turnover is low. This study aims to analyse the average spatio-temporal pattern of CDI vegetation response with (multi)spectral UAV imagery in the nutrient poor Artic tundra of Svalbard. The study used vegetation indices calculated from RGB (i.e. GLI & MGRV) and multispectral (i.e. NDVI & NDSI) UAV imagery captured of 69 Svalbard reindeer (Rangifer tarandus platyrhynchus) as indicators of vegetation cover and chlorophyll absorption. In addition, this study also aimed to analyse the effect of UAV altitude on the measured vegetation response for optimization purposes of future studies. Lastly, this study aimed to investigate what effect reindeer sex and age range, vegetation cover and slope steepness has on the vegetation response. Generalized Additive Model (GAM) prediction plots were used to model the measured vegetation response over distance from cadaver centre. This study found an average decrease in vegetation response measured in the first 0.5 m from the cadaver centre, after which a strong increase and peak in positive vegetation response was measured at 0.8 m. The increase in vegetation response was found up to 3.2 m. The largest peak in vegetation response was measured around two years after reindeers death. The increase in vegetation response was measurable up to approximately 8 years after reindeers death. UAV flight altitude was found to reduce the measured vegetation response in size and distance due to linear spectral mixing. The presence of a hillslope was found to increase the total positive vegetation response downslope, yet steeper slopes were found to reduce the total positive vegetation response due to the rugged terrains with limited root depths at steeper slopes. Fractional vegetation cover was found to increase the size of vegetation decrease at the cadaver centre. There was no significant difference found between reindeer sex and age range. Cadaver scattering was found to significantly reduce the positive vegetation response measured, as it indicates cadaver scavenging that reduced the amount of cadaveric material to enter the soil. The displacement of cadaveric material could potentially create multiple CDI’s.