There are so many ways to bring natural environments into the urban fabric, from formal parklands and freeway lids, to pocket parks and sidewalk plantings. Then there's the more radical interventions to create connective spaces that are literally formed out of thin air to knit the fabric of pedestrian life into those hard, urban spaces. New York's High Line is a great example.
Urban forestry and watershed restoration are excellent tools that can be used to restore degraded urban land. In the case of Los Angeles, there's plenty of "thrown away" industrial and commercial land that can be used to implement regenerative design that provides the spaces necessary for natural processes to restore themselves. A very ambitious project is currently underway, the restoration of the LA River.