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When we import all those magnificent oaks—gracious eastern red oaks, ziggy little pin oaks, stately English oaks—to line our streets and grace our gardens and public places, we’re joining an old tradition. It’s a globalization that dates back to some of the earliest human explorations: we’ve moved taro, breadfruit, and later pineapples throughout Polynesia; coffee between Africa and Asia and South America. 

Chilipepper was moved to Eurasia from the Americas and adopted with such enthusiasm that its dozens of varieties are considered an intrinsic part of cuisines from Italian and Spanish to Hungarian, from Ethiopian and Mozambican to South Indian and Thai, Szechuanese and Filipino. Corn traveled with migrants and traders from Central America to North and South America, and moved to the Eastern Hemisphere where it found employment in every field from European livestock fodder to Southeast Asian dessert topping. (For all I know, it’s a floor wax somewhere.) 

Ornamentals came along too. Tracking their course along human migration routes would be a nice addition to Spencer Wells’ (human) Genographic project. The legend about feral mustard in California is that the Spanish padres scattered them to make a golden, parable-evoking path among the mission outposts, as well as for seasoning. 

In recent history, the Victorians were outstanding examples of beauty-bespelled, novelty-seeking plant hunters. When one of them invented the Wardian case, tender tropicals could be sent for propagation to greenhouses and gardens all over, and so we have araucarias and semitropical palms marking Victorian architecture all around us. 

But oaks are much easier to transport: acorns keep well, and they have enough nutrition to give a seedling tree a good start. They also have nutrition for us—which might account for the fringes of some American oaks’ home ranges—and for other animals. And that latter seems to account for still more aspects of their distribution. 

Glenn Keator, in his book The Life of an Oak: An Intimate Portrait, mentions an interesting fact: 

The distribution of jay species and their diversification coincide closely with the distribution and diversification of oaks. The two areas of the world most noted for their great variety of oaks, Southeast Asia and the highlands of Mexico, are also areas of great jay diversity. 

Oaks are so generous with their acorns that humans that eat them might not have not to plant them often, but I’d bet we extended the ranges of some favored species, like the white oaks, that require less processing to make them palatable. In our area, the first people had familial property rights over the crops of certain trees, and the walk from seafood on the bay shore up to the hills to gather and process acorns was a seasonal village ritual. They built granaries to keep the acorns from sprouting, rotting, or being carried off by furred and feathered neighbors. 

Those neighbors had other ways to store acorns. Acorn woodpeckers famously use “mast trees”—they riddle a tree (or sometimes a pole or building, to people’s alarm) with neat round holes; in each hole they store an acorn, and as the acorns dry and shrink, the birds shuffle them around to other, smaller holes, the very image of flying file clerks. Acorn woodpeckers here live in colonies and the whole gang defends the mast tree. 

Others—notably squirrels and jays—have to resort to earthier methods. They bury, or cache, acorns in the ground, and dig them up later to eat. Jays and their kin (Clark’s nutcrackers, other corvids) exhibit amazing feats of memory, remembering where they’ve stashed hundreds of acorns every year. But no one’s perfect—and anyone can have leftovers. 

Joseph Grinnell, in a 1936 Condor piece quoted in Oaks of California, notes the uphill advance of oak forests, watches jays cache acorns uphill of the trees they came from, and proposes that they, like other birds, squirrels, and woodrats, are agents of dispersal. He concludes that: 

[I]n the long-time interests of the tree species, involving locomotion of the whole forest, there is value received upon this huge rate of production. It is not extravagance, but good investment, for the oaks to provide subsistence for a continuing population of animal species. 

In the case of humans, oaks provide compelling beauty as well as utility—and we oblige them by spreading their populations to our abodes whole continents away.