The condition of each tree was estimated using the NDVI index (Natural Deviation Vegetation Index), which is a well-tested index for estimating tree condition and has a high correlation with chlorophyl levels in the leaves.
For each tree we examined the NDVI values for the center of the canopy. For each tree species we examined the distribution of the NDVI values and categorized the into three categories: Average – trees with NDVI values within 1 standard deviation from the specie average; High – trees with NDVI values higher than 1 standard deviation from the specie average; Low – trees with NDVI values lower than 1 standard deviation from the specie average.
The garden area was divided into 25 sections according to the irrigation scheme of the garden. For each section we examined the percentage of Low trees within the section and determined the status of the section.