Phenology is the study of periodic plant life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation). So you can measure date of emergence of leaves and flowers, date of last appearance, etc. Because many such phenomena are very sensitive to small variations in climate, especially to temperature, phenological records can be a useful proxy for temperature in historical climatology.

See:

Proc Natl Acad Sci U S A. 2007 Jan 23; 104(4): 1278–1282.

Published online 2007 Jan 12. doi:  10.1073/pnas.0608379104

PMCID: PMC1783115

Evolution

Rapid evolution of flowering time by an annual plant in response to a climate fluctuation

Remote Sensing Based Detection of Crop Phenology for Agricultural Zones in China Using a New Threshold Method..PDF enclosed

A crop phenology detection method using time-series MODIS data..PDF enclosed

Dear Abdenour Kheloufi

Phenological changes we observe and study for long field experiments on cereals crops by optical methods. Informative parameters are indices of NDVI and CV NDVI and their relationships in temporal and spatial scales.  

            Such an approach for detection phenological marks  is less precise than traditional methods. But it allows you to receive important additional information about the status of the plants quickly and with higher accuracy throughout their life cycle. 

Application of different stress models makes it possible to detect and identify specific and nonspecific responses of plants on changing weather conditions.

Sharing both methods provides a synergistic effect in obtaining qualitatively new information. This information is important for the identification of the optimal technologies of cultivation and development of new algorithms for processing remote sensing data.

I wish you success Dr. Vladimir Surin

Thank you all of you

Dear Abdenour Kheloufi,

It might be worth looking at this ...

Article CropPhenology: An R package for extracting crop phenology fr...

http://cropphenology.wixsite.com/package

Cheers!

Thank u Araya

Thank you all of you for your consideration and answers