SHORT COMMUNICATION Digital Images for Plant Phenology Documentation Sanjay Kr. Uniyal 1 • Vikrant Jaryan 1 • Rakesh D. Singh 1 Received: 27 May 2015 / Revised: 11 June 2015 / Accepted: 14 October 2016 Ó The National Academy of Sciences, India 2016 Abstract Plant phenology is a key indicator of changing climatic conditions and, thus, automated documentation of phenology using cameras has recently been advocated. The present study, therefore, aimed at identifying phenological stages in Sapium sebiferum using digital images of a full calendar year. Red, Green and Blue channel information from these images was analyzed. Across the three channels (i.e. R, G, and B) the DN values ranged from a minimum of 71.42 in blue channel (B DN ) to 156.16 in green channel (G DN ). In general, the R DN ,G DN , and B DN values increased till 66 DOY after which there was a steep decline in DN values of R, G, and B channels till 224 DOY. After this, a slight increase in the DN values of all the three channels was observed. The value of Red Fraction ranged between 0.297348281 and 0.352612071. The minimum value for the same was on 3 DOY while the maximum was on 135 DOY. On the other hand, the value of Green Fraction ranged between 0.330045461 and 0.39841947. The values of Green Excess Index (2G-RBi) ranged between -0.009863618 and 0.19525841. It reported minimum value on 42 DOY and the maximum on 139 DOY. Green excess index were found to be reliable indicator of green- ing up in the species. Red Faction was a good indicator of senescence. Photographs provide an ideal tool for docu- menting phenology of a species and can provide inputs for large scale satellite image analyses. Keywords Channel Á Greening Á Himalaya Á Phenology Á Photography Á Sapium Phenology, a science that deals with documentation of temporal patterns of biological events such as leafing, flowering, fruiting, etc. occurring in a species [1] has seen a renewed interest [2]. Owing to the fact that phenology is regulated by climatic conditions, in the contemporary times when climate change is a key global issue, documenting phenology has proved to be amongst the best indicators of changing climatic conditions [3–5]. Changes in temporal patterns of flowering [6, 7] and primary productivity [8, 9] are key phenological implications of changing climatic conditions that have been documented. Changes in primary productivity have been linked to length of the growing season [10, 11] where-in documentation of greening up and senescence are key. Such phenological documentation requires onsite human presence such that temporal patterns are systematically and precisely recorded. This on one hand is labour demanding [12] while restricted in spatial spread on the other. Further, with limitations of field manpower [13] and individual observer biases [2], automated recording of phenology using optical sensors has been advocated [14]. Initiation of global programmes such as budburst (www.budburst.org), national phenology network (https://www.usanpn.org) and many others (http:// mnspruce.ornl.gov) that use images and are testimony to this. Images acquired through satellite are ideal for docu- menting large forest canopies patterns, while images cap- tured using digital camera have been found ideal for species specific phenological documentation [15]. Once captured, these digital images are analyzed for red, green, and blue channel information in the visible range of spectrum and then related to various phenological stages of Electronic supplementary material The online version of this article (doi:10.1007/s40009-016-0517-2) contains supplementary material, which is available to authorized users. & Sanjay Kr. Uniyal suniyal@ihbt.res.in 1 High Altitude Biology Division, CSIR-Institute of Himalayan Bioresource Technology, Palampur, HP 176061, India 123 Natl. Acad. Sci. Lett. DOI 10.1007/s40009-016-0517-2