Determination of Leaf Area Index, Total Foliar N, and Normalized Difference Vegetation Index for Arctic Ecosystems Dominated by Cassiope tetragona
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Leaf area index (LAI) and total foliar nitrogen (TFN) are important canopy characteristics and crucial variables needed to simulate photosynthesis and ecosystem CO(2) fluxes. Although plant communities dominated by Cassiope tetragona are widespread in the Arctic, LAI and TFN for this vegetation type have not been accurately quantified. We address this knowledge gap by (i) direct measurements of LAI and TFN for C tetragona, and (ii) determining TFN-LAI and LAI-normalized difference vegetation index (NDVI) relationships for typical C tetragona tundras in the subarctic (Sweden) and High Arctic (Greenland and Svalbard). Leaves of C tetragona are 2-6 mm long and closely appressed to their stems forming parallelepiped shoots. We determined the LAI of C tetragona by measuring the area of the leaves while still attached to the stem, then doubling the resulting one-sided area. TFN was determined from leaf N and biomass. The LAI-NDVI and TFN-LAI relationships showed high correlation and can be used to estimate indirectly LAI and TFN. The LAI-NDVI relationship for C tetragona vegetation differed from a generic LAI-NDVI relationship for arctic tundra, whereas the TFN-LAI relationship did not. Overall, the LAI of C tetragona tundra ranged from 0.4 to 1.1 m(2) m(-2) and TFN from 1.4 to 1.7 g N m(-2).