Social media contains enormous amounts of data about people, our everyday lives, and our interactions with our surroundings. As a byproduct, it also contains a vast trove of information about the natural world. In a new study published in Flora, we show how social media can be used for “incidental citizen science”. From photos posted to a social site, we mapped countrywide patterns in nature over a decade in relatively fine detail. Our case study was the annual spread of cherry blossom flowering across Japan, where millions of people view the blooming each year in a cultural event called “hanami”. The flowering spreads across Japan in a wave (“sakura zensen” or 桜前線) following the warmth of the arriving spring season.
Many flowering plants, including the cherry blossoms of Japan, require insect pollination. To reproduce, plant flowers bloom at optimal times to receive visits from insects like bees. Temperature is an important mechanism for plants to trigger this flowering. Previous research has highlighted how climate change may create mismatches in space or time between the blooming of plants and the emergence of pollinating insects. It has been difficult for researchers to map the extent of this problem in detail, as its study requires simultaneous data collection over large areas. The use of citizen science images deliberately, or incidentally, uploaded to social network sites enables big data solutions.
We collected images from Japan uploaded to Flickr between 2008 and 2018 that were tagged by users as “cherry blossoms”. We used computer vision techniques to analyse these images, and to provide sets of keywords describing their image content. Next, we automatically filtered out images appearing to contain content that the computer vision algorithms determined didn’t match our targeted cherry blossoms. For instance, many contained images of autumn leaves, another popular ecological event to view in Japan. The locations and timestamps of the remaining cherry blossom images were then used to generate marks on a map of Japan showing the seasonal wave of sakura blossoms, and to estimate peak bloom times each year in different cities. Our study using social network site images was validated against the detailed information published by the Japan National Tourism Organization.
