Biological events such as bud break and flowering have major implications on population dynamics and ecosystem function. For example, variation in the date of bud break, if measured precisely and continuously, quantifies biological effects of climatic variation. Such ground-based quantification can supplement and validate information acquired from satellite-borne sensors, which cannot resolve data to species or monitor events when clouds are present. Although some validation of plant activity is being acquired with digital cameras and networks of human observers, the spatial coverage is limited because of power or cost limitations. Here we describe a small automatic device that can be placed on a plant to sense the date of bud opening that leads to leaf or flower formation. The device moves beyond the status quo by facilitating continuous monitoring of plant buds at numerous sites. The device consists of an optical fiber that illuminates a target bud with light obtained from an inexpensive light-emitting diode (LED). A second fiber detects reflected light from the LED and guides it to a photodetector where the signal is amplified and then recorded. Changes in the intensity of reflected light indicate changes in bud activity.
Results/Conclusions
Last spring we used the device to measure vegetative bud break on a Douglas fir bud (Psuedotsuga menziesii) and flowering on a garden mum (Dendranthema x grandiflorum). The electronics of the instrument demonstrated effective and continuous recording of bud break and flowering. Both bud break and flowering elicited abrupt changes in the sensor output. This spring we will measure bud break using numerous sensors on different plant species and report our results. We plan to test whether the sensor itself can alter the timing of bud break.