As flowers began to bloom and leaves slowly emerge in the northern hemisphere this time of year, most people are thinking about how they soon get to lose the winter coat and enjoy the warm, spring sunshine. How they can walk outside without the cold stinging their face and how the world soon will be bathed in green again. But for scientists interested in when flowers bloom and the earth returns to its lovely verdant hue, just when spring arrives is a rather interesting question to ask.
The study of the seasonal life cycle changes of plants and animals is called phenology and is a topic we have written about multiple times at PLOS ecology as phenological studies offer some of the most compelling and alarming evidence of how human-induced global climate change is drastically altering our planet. Recent work has shown that spring onset in the Tibetan plateau is occurring on average two weeks earlier now than it did in 1960, with similar patterns also found across China and globally—with the length of growing seasons changing more dramatically closer to the poles. Scientists have been documenting phenological changes for a while, though this research has been greatly improved by changes in how we can observe our earth. Higher-resolution satellites, drones, and aerial observatories have helped to catalyze research by providing heaps of data. However, a few humble old cameras and a dedicated group of scientists have shown a novel way to approach the problem.
This important advance in the study of vegetation phenology has come from the PhenoCam Network—a network of typically tower-mounted cameras that provide near-real time imagery of the surrounding landscape at sites across the United States and southern Canada. The PhenoCam Network recently published a large of 750 site-years of data from over 130 cameras in a data paper in Scientific Data.
The majority of these cameras are located at or near research sites which further increases the utility and impact of the data, as images can be paired with all sorts of other ecological data from cooperating researchers. While satellite based data has been instrumental in studying the earth system, the PhenoCam Network surmounts two key problems with satellite data. One, PhenoCam data are collected at much finer timescales, some at 15 minute intervals for the entire year, in contrast to some satellite data where images are taken every two weeks or so. This greater time resolution provides better means to capture more subtle shifts in phenology, more accurately. PhenoCams also provide “near-surface” remote sensing imagery, which in plain terms means the cameras are close to the ground and you don’t have to worry about clouds and atmospheric effects as you do with satellite data. Importantly, PhenoCam data serves as a bridge between satellite data and other data sources as well.
From this data, measures of both the “greenness” and “redness” of vegetation can be calculated, measures that have been shown to be strong predictors of how an ecosystem is growing, how stressed it is, and how it is responding to changes in climate (e.g. precipitation, temperature). The large spatial distribution of this data, coupled with how often the data are collected, and its public availbility, make this an invaluable resource. The study of vegetation phenology has been growing over the past couple of decades, with over 100 publications on vegetation phenology alone published in 2017—and 25 already in 2018! Long-term datasets such as the PhenoCam network, along with citizen science initiatives like the National Phenology Network, are helping to create impactful research in how our changing climate is changing our world.
Make sure to check out the PhenoCam Image Gallery: https://phenocam.sr.unh.edu/webcam/gallery/