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Impact of Climate Change on Vegetation Phenology Using Multi-Channel Photography

Alex Stein

The term ‘phenology’ is used to describe the seasonal repetition of phenomena during a plant’s lifecycle, such as germination, growth, leaf budding, flowering and leaf fall. These phenomena are affected by the genetics of the different plant species and are directed to certain seasons by environmental conditions such as temperature, water and light. Global climate change has a crucial impact on the phenology of many plant species, and as a result, on the composition, function and services provided by ecosystems to humans.

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In recent decades, climate change has taken place at a relatively rapid rate to that which characterised the earth in the past – in the last decade in Israel we have witnessed desiccation and mortality of oaks, native and planted pines and other species, which can be linked to climate change. Since changes in plant phenology are rapid and probably are the plants’ first response to climate change, it is very important to monitor them routinely and continuously. For example, phenological monitoring should be the first to reveal signs of stress in trees, stemming from consecutive drought years. During 2014–15, remote sensing data were collected as part of a scientific study aiming to monitor the impact of climate change on plants’ lifecycles – vitality, leaf budding, leaf fall and flowering, in order to obtain an early

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warning about desiccation and mortality of the vegetation. Monitoring was performed by daily photography with a multi-channel digital camera (that provides information at a number of wavelengths), installed at the top of a tower, as well as with a regular digital camera. The two cameras provide photographs around midday, where the digital camera photographs within

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the visible spectrum only, while the multispectral camera photographs at five different wavelengths in the visible and near-infra red ranges.

From the remote sensing data we can calculate indices that represent the physiological and phenological state of the vegetation in the region, such as the normalised difference vegetation (NDVI) index , based on the

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multispectral camera data. In parallel, from the digital camera data we can calculate relatively simple indices based on the values of the digital numbers (DN) in the visible spectrum only.

During the first research year (April 2014 – April 2015), physiological measurements (water potential, stomatal conductivity and chlorophyll content) were performed every two months on 24 representative trees and shrubs, in order to link the spectral indices to the biophysical measurements.

As part of the analysis of the multispectral camera data, annual time series of NDVI were constructed for each of the monitored trees and for the entire study area. These time series presented characteristic phenological patterns for evergreen Mediterranean tree species, with higher NDVI values during spring. The physiological measurements that were performed in parallel during this year showed a physiological response of the trees to the seasonal water deficit, expressed by a decrease in the values of water potential and limited stomatal opening, mainly during summer. Similarly, examination of the correlation between NDVI values and leaf chlorophyll content showed that the relationship between these indices is not significant, probably due to the methodological difficulty in appropriately representing the entire tree canopy during the sampling season.

A follow-up study will focus on analysing additional spectral indices from the cameras operating in the field, in combination with phenological observations in the study area as a tool for understanding and explaining the processes observed using remote sensing technology.

The study took place in collaboration with Prof. Arnon Karnieli and the staff of the Remote Sensing Laboratory of the Institutes for Desert Studies at Ben-Gurion University of the Negev.

Of further interest...

Accessibility

Memorial Gardens Main Entrance

The main entrance to the Memorial Gardens – located next to the Visitors Pavilion. In the entrance plaza are temporary exhibitions on a range of subjects promoted by Ramat Hanadiv

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Sustainability

The Footprint Garden

The term ‘ecological footprint’ is taking shape in the western part of the Visitors Pavilion. A large gardening plot shaped like a foot lies in the middle of the area, with the heel pointing north, and the five toes, as one unit – to the south.

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Dining Here

Dining-The Picnic Site

The picnic area is located near the secondary parking lot. You are welcome to spend time there before or after your tour of the Gardens.

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The Footprint Garden

The term ‘ecological footprint’ is taking shape in the western part of the Visitors Pavilion. A large gardening plot shaped like a foot lies in the middle of the area, with the heel pointing north, and the five toes, as one unit – to the south.

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Within the foot and outside of it is a colorful mixture of vegetation that attracts butterflies: nectar in the flowers, and leaves as a place for laying eggs and as food for the larvae (caterpillars). Besides the enjoyment and beauty provided by the butterflies, they are used as a biological indicator that reflects changes occurring within ecosystems.
Fringed rue, for example, is a medicinal plant with a controversial fragrance among humans; however for the Old World swallowtail it is a safe refuge for rearing its larvae. It turns out that most of the plants in the crucifer family are used as hosts for the Large white, while during a shortage, leaves of the garden nasturtium will suffice. But don’t worry, the larvae won’t start nibbling leaves in the nearby shrubbery. Even scutch grass, considered by most to be a ‘weed’, is the preferred host for one butterfly: the female Large wall brown lays her eggs on it.
The Footprint Garden also includes plants that attract birds, such as: Buddleia (butterfly bush), Hibiscus and Lantana, which breathe life into the garden.
The Footprint Garden strives to show visitors the importance of a range of organisms, both large and small, each one with its role in the overall web of life. Besides conservation of biodiversity, the garden conveys an important social message of integrating different people into the community. The garden is cared for by the green fingers of people with disabilities, who are part of the gardening staff at Ramat Hanadiv.
As a technological complement, the plumbing of the geothermic cooling system was dug beneath this garden, and the pipes may be seen through a window to the soil’s depths.
All of these carry an important message for the future:

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Our actions today determine the ecological stamp we leave for future generations; it’s best that we leave colorful, carefree footprints of flowers and butterflies…

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