Digital cameras have been used in phenological observations for their high accuracy and low labor cost. To accurately estimate the dates of phenological events from digital images, both the greenness and redness indices are needed.

Prof. Zhang Yiping and his research team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted studies in Ailaoshan Mountain Nature Reserve (24°32′N, 101°01′E, 2476 masl) and Menglun Nature Reserve of Xishuangbanna (21°55′N, 101°15′E, 750 masl) in Yunnan Province, southwestern China.

They used images of three species (two from Ailaoshan evergreen broad-leaved forest and one from Xishuangbanna tropical seasonal rain forest) to estimate phenological events of leaf development and senescence. They employed both the greenness and redness indices.

Their objectives were to: 1) evaluate the accuracy of the timing of phenological events from the two color indices, 2) compare it among the three tree species, and 3) reveal the effects of climatic factors on phenological events based on the color indices.

Their study found that the redness index was more accurate when estimating leaf senescence. The greenness index was more accurate for estimating leaf development events. Variations of the color indices (red fractionor green fraction) during periods of phenological events were well correlated with climatic factors and showed a time lag of around 10 days.

 The study entitled “Using digital cameras for comparative phenological monitoring in an evergreen broad-leaved forest and a seasonal rain forest” has been published in Ecological Informatics, http://dx.doi.org/10.1016/j.ecoinf.2012.03.001