Lars Eklundh

Leaf area index (LAI) of boreal ecosystems were estimated with optical instruments at the Laxemar and the Forsmark investigation areas in Sweden. The aim was to study the relationship between LAI and the normalized difference vegetation index (NDVI) from Landsat-5 and SPOT and evaluate the applicability of the MODIS (Moderate Resolution Imaging Spectroradiometer) LAI product for small boreal regions. Relationships between ground-estimated LAI and NDVI were significant for coniferous, deciduous and mixed forest sites in Laxemar. For Forsmark, effective LAI was correlated to NDVI for all sites. LAI estimated from NDVI was also used for evaluating accuracy of the MODIS LAI product. The comparison showed no correlation between MODIS LAI and NDVI-based LAI in Forsmark whereas there was in Laxemar. MODIS LAI was on average 2.28 higher than NDVI-based LAI and it also showed larger scatter. Scale issues were the main explanation to high MODIS LAI, since the heterogeneous landscapes with open areas (given a value of zero in the NDVI estimates) was seen as forest in the large pixels of the MODIS LAI product. Therefore, we do not recommend using the MODIS LAI product in small boreal regional landscapes, such as the Forsmark and Laxemar investigation areas.