linden leaves carpeting the great lawn in the botanical garden (Dec. 16, 2010)
Walking in the park yesterday, I noticed brilliant flashes of fall color still decorating the park . . . in mid December! Are these trees confused?! It’s so late! Then I had a revelation: these flames of color throughout the park are all species from far away places where the climate is very different. Here, in San Francisco, we normally wouldn’t have such brilliant displays of fall color. Maybe some russet grasses but nothing like the flaming golds and oranges that we get from Lindens (Tilia cordata), which originate in Europe or Tulip Trees (Liriodendron tulipifera), which are native to the eastern U.S. or Ginkgos (Ginkgo biloba), which probably originated in China but are no longer found in the wild at all.
We import fall color here, like we put artificial snow on our lawns at Christmas. Golden Gate Park is an exotic stage set and these trees put on a show for us each fall. It’s an extended run some years, because they are, indeed, somewhat confused. The climate here is not what they are programmed for; can’t rely on a cold snap every year in October, to signal that it’s time to turn. But this year we did have a cold snap, in late November, and they got the message. A stellar production this year!
tulip tree near the conservatory of flowers (Dec. 16, 2010)
gingko on Martin Luther King Jr. Drive (Dec. 16, 2010)
golden gate park: views from the thicket 
Thanks for this tribute to the non-native trees of San Francisco which bring us a little color in the fall and early winter when we would not otherwise have any. There were few native trees in San Francisco in places sheltered from the salty wind and most are evergreen.