At the base of a narrow, windy road off Avenue 45 in Mount Washington is a hidden pocket of nature called Rainbow Canyon. It's home to a hearty grove of California black walnut trees, a stream that comes and goes with the rain, chopped-up tree trunks deliberately placed for seating — and since last year, several "test plots" aiming to repair these quiet, damaged acres to vibrancy while taking account of our changing climate and urban environments.

Growing inside these plots are varieties of plants, including hummingbird sage and big saltbush — grouped together for a given experiment and separated by low wood fences.

"Walnuts drop chemicals through their leaf litter into the ground below them to control competition," says Alex Robinson, with L.A. nonprofit Test Plot .

On a rece

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