Germination, growth, blooming, and leaf drop – these and other cyclical phenomena in the life cycle of plants are the subject of the scientific term known as phenology. Such recurring events are determined by plants' genes, and they are correlated to specific seasons through environmental conditions such as temperature, precipitation, and light. Global climate changes have a significant impact on the phenology of many plants, and consequently on their composition and functioning, as well as on the ecosystem services they provide to humankind.
In recent decades, climate change has been occurring relatively faster on our planet than was typical in the past. Just since the start of the millennium, we in Israel have observed the desiccation and death of oak trees, of natural and planted pines, and of other species, all of which may be attributed to climate change. Phenological changes in plants are rapid, apparently their first response to climatic changes. Stress in trees, for instance, can be seen as a result of prolonged periods of drought. Hence the importance of continuous and consistent phenological monitoring, which is considered the primary means to reveal such early warning signs.
To carry out this kind of tracking and analysis of the impact of climate change on the life cycle of trees, a new scientific project has been launched at Ramat Hanadiv using a multi-spectral digital camera installed at the top of the research tower. The camera photographs the vegetation daily at frequencies across the electromagnetic spectrum, capturing information from a range of wave lengths invisible to the human eye. It is focused on common oaks, phillyrea, Aleppo pines, spiny broom, and prickly burnet, growing together densely at the north-facing slope of Hanadiv wadi.
In order to explore the performance of a multispectral camera and assess a year-around phenological cycle, continuous daily data from both multispectral camera and conventional RGB camera will be gathered in the Ramat Hanadiv site. Multispectral images will be geometrically corrected and two indices will be calculated (NDVI and Red Edge). From daily RGB images two simple indices will be calculated; normalized “brightness” and ‘‘greenness’’ index (Richardson et al., 2007, 2009). Physiological measurements will be carried out every two month on 24 selected trees (six individuals of each of the four dominant species). In this framework water potential (Ψl) at predawn and midday, stomatal conductance (gs) and chlorophyll content measurements will be performed in order to correlate the spectral indices and these biophysical measurements. In addition, several phenological observations, such as leaves senescence, fruit and young leaves emergence, bud burst, and flowering will be performed.
The camera takes three images per day: at 11:00, 12:00 and 13:00 in five different spectral bands: green (550 nm), red (670 nm), two red edge bands (740 & 780 nm) and NIR (860 nm). Spatial resolution varies with the distance from the camera (5 cm-15 cm per pixel). The data is transformed to our lab in the same day.
The research is a joint venture between Ramat Hanadiv, Prof. Arnon Karnieli and the Remote Sensing Laboratory team of Ben Gurion University's Institutes for Desert Research