Thesis defense: 'Is NDVI indicative of shrub abundance, leaf area or both, and what does it tell us about CO2 exchange in moist acidic tundra of Northern Alaska?' April 25

Thursday, April 25, 10 a.m. UAA/APU Consortium Library, Room 302A

Andy Anderson-Smith, M.S. candidate in biological sciences, will defend his thesis, "Is NDVI indicative of shrub abundance, leaf area or both, and what does it tell us about CO2 exchange in moist acidic tundra of Northern Alaska?"

Evidence has accumulated during the last several decades that shrub communities are expanding in the Arctic and Normalized Difference Vegetation Index (NDVI) values, which measure surface greenness, are rising. Several studies have suggested that NDVI increases could be driven by either increasing leaf area or shrub abundance across the Arctic. While it is clear that NDVI varies across vegetation types, it is not clear that increasing NDVI values in moist acidic tundra (MAT), the most extensive vegetation type in arctic Alaska, are driven by increasing shrub abundance. The focus of this research is to determine if rising NDVI values in Northern Alaska indicate increasing shrub abundance and the implications of this shift in community composition on CO2 exchange.

In order to clarify the role of shrub encroachment per se as opposed to other functional groups or leaf area in driving increases in NDVI, researchers measured functional group composition MAT in conjunction with hand-held measures of NDVI, projected leaf area and CO2 exchange to explicitly link spectral properties, shrub and graminoid density, and trace gas feedbacks to atmospheric chemistry. The results show that NDVI is indicative of shrub density (R2=.64), but shows a negative correlation to graminoids and overall leaf area. Furthermore, NDVI is closely correlated with net ecosystem CO2 uptake in MAT.

April Archive