What’s next? Assisted Migration The diversity of oak trees is astounding, and their genetic lineages are mysterious, complex, and so fun to investigate. Mexico is said to be the home of the highest diversity of oak species on the planet. These trees are somewhat different in form from the northern deciduous varieties that have evolve to handle less light, and colder winters, yet these Mexican species are also at home in high elevations that receive temperatures that are common in Zone 7 gardens (0 degrees F). The Mexican oak diversity reaches north into the south west United States, reaching through the expanse of sky islands from southern AZ north up into Utah and Oregon. The boundary between native and non-native oaks becomes harder and harder to differentiate when we really grasp the population spread of species like Quercus chrysolepis, which spreads from WA to OR to southern CA to eastern AZ in my personal observation. With the Oak’s proclivity to hybridize, it becomes even harder to distinguish local from non-local genetics. And perhaps Q. Oblongifolia is actually the same tree as Q. Engelmannii, an evergreen blue oak native to Southern California….

The blend of cold tolerance and desert sun tolerance of the Mexican and Arizona oaks makes these species particularly useful and enticing when considering our tasks for designing landscapes for climate change mitigation and adaptation, along with assisted migration. It is clear that the world’s climates are transformng rapidly, and ecologies are bound to evolve. Insects, birds, animals, and humans will all fall into the category of climate refugee in areas that are hit hard by drought, flood, and fires. As restoration ecologists and contractors, we are put to the task of maintaining the stability of our ecosystems by stabilizing the water cycle, and anticipating the patterns of change by selecting particular species that are appropriate to replace diminishing populations of climate change victim species. While the native Oregon White Oak still stand strong in Oregon ecologies, its range has been diminished by up to 97 percent of its original populations. Western oaks of all sorts hold the power to feed and host a wide range of the local fauna and insects. These drought adapted Arizona species, that are already familiar with growing along side our native understories of snowberry, Oregon grape, honeysuckle, ferns, ceanothus, manzanitas,  grasses, and wild flowers, etc, hold an interesting potential role of stabilizing our ecosystems amidst climate catastrophe. And if by some miracle humanity can wake up to the global situation and make amends to our systemic impact to create a balanced ecosystem, our biggest problem is to be surrounded by the diversity of beautiful species that make fantastic urban trees with the benefit of supporting local populations of insects and animals. Oaks are a true win-win!


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