Spring in urban Southern California is … well, the word “unnatural” comes to mind, but it’s prudent to avoid provocation. Safer words might be “novel” or “anachronistic” or “cosmopolitan.”

Spring in Southern California is novel. Like last year, we are enjoying a quite cosmopolitan season of growth.

The proper place to say this is at a VIP luncheon, wearing a blousy floral number. At heart, though, these are just euphemistic ways of saying that SoCal spring is … unnatural.

What is unnatural about our urban spring? Like its human population, most street trees and plants sprinkled throughout the yards of Southern California did not originate here. In fact, they are from climate regions quite unlike our own: they evolved in temperate or tropical areas and follow cycles of growth appropriate to those regions. Many of these species are waking up right now, at the end of our rainy season, in the spring. Since the rains will soon stop, they are undoubtedly grateful for our ever-present irrigation systems.


A recent metastudy of plant diversity in Los Angeles counted 907 species across selected sample plots (around 700 plots total). In residential yard samples, the study reported that the vast majority were cosmopolitan ornamentals with only a measly 4% native to our region! Although providing only a partial picture, the study gives us a glimpse of the vast diversity of non-native plants across Los Angeles – a diversity at least equal to two-thirds of the native plants reported to have existed in the region!

City-wide, the majority of our cultivated plants originate in Eurasia and Africa with only 5% of all species originating in the Mediterranean Basin. This last statistic is a bit of a surprise, since both California and the Mediterranean enjoy wet mild winters and dry summers. In other words, Mediterranean plants are particularly well-adapted to our region and it shows: consider the utter banality of restaurant olive trees in Los Angeles County!


Although a lot of our urban plant diversity is a legacy of colonialism, some of it is just a natural consequence of human migration.

The paperwhite narcissus, just recently finished blooming in Southern California, came here by an unusually circuitous route: originally from the Mediterranean, paperwhites were brought to China over a 1000 years ago where they became part of the iconography of Lunar New Year. They were then imported into the Western United States by Chinese immigrants during the waning days of American colonization. Since they are Mediterranean bulbs, they are in growth during our wet winter, following displaced cycles in a climate that is more compatible than their home has been for the past 1000 years!

Chief among the cosmopolitan street trees in Los Angeles, to my mind, is the crape myrtle (Lagerstroemia sp.). Along my former street, the roots of these common trees oozed to fill the city strip like liquid, forming pools of bizarre polished wood. Other common novelties in Los Angeles County include the sidewalk-destroyer Ficus benjamina, magnolias, evergreen pears, jacarandas and assorted citrus. Many of these plants are found at Arlington Garden as well – the Washington navel oranges are blooming right now with a heady aroma. Our jacarandas should be blooming by the end of the month. 

A particularly beautiful novel species in Los Angeles’ urban landscape is the purple-and-white wisteria vine (Wisteria sinensis). It was first introduced to Europe by the (colonial and villainous) East India Company. The species originates from temperate China and, as a temperate cosmopolitan, defoliates during the winter. The vine at Arlington is now dripping with enormous flower spikes. While glorious, it is no comparison to the one-acre specimen (weighing an estimated 250 tons) in nearby Sierra Madre. The so-called “Sierra Madre Wisteria” is perhaps the world’s largest blossoming plant but sadly accessible to the public only one day a year. 


Spring bird migration season in Southern California is now underway. Many bird species are currently moving south-to-north across Los Angeles County to reach thawing northern regions. Migration usually happens at nighttime, and a vast multitude of birds will pass through the region under cover of darkness. Ever wonder why you typically don’t see large migrations? It’s because they’re functionally imperceptible in the night sky. Their swift little shadows fly back up against the stars.

It is possible to track the migrants, however, along their nightly pilgrimage. One method is radar: on just one night this month (Friday, April 12th) the bird migration tracker BirdCast used radar blips to estimate that 307,700 birds crossed Los Angeles county. This is more than twice the human population of Pasadena — aloft and invisible on a single night. 

Species currently passing through the county include the Band-tailed Pigeon, various hummingbird species, Cedar Waxwing, Yellow-rumped Warbler, and many, many passerines – “passerine” denoting a bird that perches.


In Los Angeles County, there is a population of around 3000 red-crowned parrots (also called “Mexican red-headed parrots”) that are thriving in the urban treescape. If you live in the right neighborhood, you have probably heard them thundering overhead in a riot of flapping, squawking, and explosive screeching. These successful birds use Los Angeles and Pasadena’s tropical plants as forage and shelter. The species is endangered in its native habitat in eastern Mexico, and the feral population in Los Angeles is thought to be roughly equal in size! Some day, our local population may provide a source of birds to be reintroduced back into their native habitat.


I made a big show of using the word “unnatural” at the start of this letter, but there’s a sense, of course, in which Spring in Southern California is completely natural. After all, human beings are natural, and here we are in our local megalopolis, doing more-or-less natural human sorts of things – planting stuff that we think is attractive, cultivating fruit with significance to us, and being motivated by what other people are doing. It’s all totally natural. What is unnatural isn’t what we are doing but the environment we have created: an ecosystem unlike any other and one which we do not fully understand. Spring in Los Angeles County provides a good illustration of how unusual this place is. What other rare or interesting creatures besides the parrots are we supporting with our residential water regimes? What native birds use our non-native plantings? How do specific street trees affect human and animal health? And – a question particularly relevant since Earth Day is today – how is climate change affecting all this? 

* image of Yellow-rumped warbler courtesy of Rhododendrites, CC BY-SA 4.0 via Wikimedia Commons

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