Quantifying the Effects of Moisture Change on the Spectral Signatures (350-2500 nm) of Arctic Mosses, Liverworts, and Lichens

Increasing temperatures have been altering hydrological conditions and leading to ecological regime shifts across the Arctic biome, with influences on terrestrial carbon cycling. However, the sign, extent, and magnitude of change in Arctic terrestrial carbon cycling from warming is still ambiguous, especially in wetlands and peatlands. Non-vascular vegetation (specifically bryophytes and lichens), which can tolerate low light, extreme cold, desiccation, and waterlogged conditions, are dominant vegetation components in high-latitude ecosystems. As such, they have significant ecological roles in moderating soil temperature and moisture, water flow/retention, nutrient availability, and carbon storage. However, despite their importance and dominance in northern ecosystems, they are still severely neglected or inadequately represented in most Earth System Models. Remote sensing, being quick and cost-effective, is a popular tool to monitor inaccessible Arctic environments. While the spectral properties of low-latitude vascular vegetation have been of large focus, few have looked at the spectral responses of (sub-)Arctic mosses, lichens, and liverworts, especially how they change with moisture shifts. Using lab water table depth manipulations to simulate shifts from desiccation (0% moisture) to saturation (100% moisture), this project quantified the effects of moisture change on the hyperspectral signatures (350-2500nm) of Arctic mosses, lichens, and liverworts. Results show that spectral properties vary widely across species and plant types, especially in the VIS and NIR. As moisture was lost, species showed similar patterns in spectral response (primarily in SWIR), with a general increase in reflectance and similar changes in shape; all species developed new peaks and rises in reflectance in SWIR1 and SWIR2 after reaching a certain desiccation point. Furthermore, below 20 to 30% moisture, species eventually became spectrally indistinguishable in the SWIR. Overall, the unique spectral properties in the VIS and NIR can be used to create a “spectral library” to distinguish between some of these non-vascular species; likewise, I show that moisture plays a critical role in the spectral response of these species and, as they get close to desiccation, spectral discrimination in SWIR wavelengths may prove very challenging. This finding may have critical implications for the methods used to map these vegetation types and their unique ecological functions