Masterarbeit

Leaf coloration along an elevational gradient on the Island of La Réunion - Exploring the possibilities of field sampling and remote sensing -

Esther Baumann (01/2017-09/2017)

Betreuer: Carl Beierkuhnlein

Color was and still is fascinating mankind for centuries. In ecology, a broad variety of studies are present, concerning the distinct differences in coloration of different organisms, animals and plants alike. However, the matter of leaf coloration is somewhat neglected: while studies concerning the color of flowers are found more often, leaf coloration per se triggers not much interest. Mainly studies focus on the chemical reasons that are manifested in color changes or the agricultural value of leaf colors expressing, for example, the maturity of the crop or indicate malnutrition. But leaf coloration itself is a morphological and physical property of a plant, which can react to biotic and abiotic drivers. There are studies exploring the possibility of leaf coloration acting as camouflage or repellent against herbivores. And there are as well studies, hinting at different leaf colors as a product of differences in environmental conditions. One prominent gradient to test the plants reaction on changing conditions is the elevational gradient. Incorporation changes of many different abiotic conditions, it can be seen as a proxy for overall harsher environmental condition. However, the topic of changing leaf coloration as a reaction of an altered physical environment is not well researched. This study therefore aimed at detecting patterns of leaf coloration changes along an elevational gradient and subsequently gaining further knowledge about adaptive strategies of plants. The study was conducted in the subalpine shrubland of La Réunion, an oceanic island of volcanic origin located in the Indian Ocean. Colors were measured according to the Munsell Color System. Additionally, Sentinel 2 images were utilized to relate the sampled field data with a dataset derived via remote sensing. Plots were located along a gradient between roughly 2000 and 2900 m.a.s.l. and leaf coloration as well as growth height, species specific cover and leaf area were recorded and analyzed. Results evidently show an overall increasing leaf color brightness with altitude. However, the patterns seemed to be heavily influenced by few dominant species rather than a change in species composition. The combination of the field data and the satellite images in the form of calculated Vegetation Indices turned out to be problematic: despite several significant relationships found, their reliability is questionable. The direct comparison of the field data and the remote sensing data, translated in a common color space, showed very clearly, that both color assessment systems are not picturing the same reality, most likely due to their fundamental difference in how they measure color.