"One of the most visible effects of the downturn in the economy is the near freeze in private new construction, creating a sea of vacant lots—5299 in San Francisco, to be precise, adding up to approximately 250 acres. Learn about proposals for a network of temporary parks at 399 Fremont Street, which would provide a common refuge for people, birds and butterflies using the vocabulary of the construction site. With landscape architects Sarah Kuehl and Adam Greenspan of Peter Walker + Partners and architects Owen Kennerly and Sarina Bowen of Kennerly Architecture & Planning."