Tamarugo (Prosopis tamarugo Phil.) is an endemic and endangered tree species adapted to the hyper-arid conditions of the Atacama Desert, Northern Chile. Diurnal leaf movements were observed in this Leguminoseae tree species both in the lab and in the field and this had an important effect on canopy reflectance as measured with a radiometer. These movements, common in Leguminoseae species, allow the plants to decrease the direct solar irradiation on the leaves at the hottest time of the day and this way minimize photoinhibition. Since pulvinar movement is triggered by cell water turgor and thus limited for trees under water stress, we hypothesize that the expected changes in canopy spectral reflectance can be detected by remote sensing and used to assess water stress. A 25 years Landsat time series showed a strong seasonal variation in the normalized difference vegetation index (NDVI) with peak values in winter, which was negatively correlated to solar radiation. This seasonal variation of the NDVI could be explained by pulvinar movement. Trees with water stress exhibited significantly less seasonal variation. An analysis of 10 years MODIS time series showed a positive difference between the NDVI in the morning (Terra satellite) and the NDVI at midday (Aqua satellite), which again could be explained by the pulvinar movement. This difference was smaller for trees with water stress. We conclude that this NDVI difference obtained from the MODIS Aqua and Terra satellites has potential to detect early symptoms of water stress for Tamarugo trees at the stand level.
|Publication status||Published - 2014|
|Event||NAEM 2014, Lunteren, The Netherlands - |
Duration: 11 Feb 2014 → 12 Feb 2014
|Conference||NAEM 2014, Lunteren, The Netherlands|
|Period||11/02/14 → 12/02/14|