Tree Blog

Quercus engelmanii | Arcadia

There are entire neighborhoods in Arcadia filled with Engelman Oaks which pre-dated neighborhood construction, apparently in the 1950s and 1960s. Suburbia came for Engelman Oak woodland in these communities, with big lawns being the norm, right into the 21st century. Many California tree Oaks are destroyed by lawn watering, as the summer moisture, during a period in which the trees are evolved to experience substantial drought during the summer. Adding water to lawn planted under some native oaks awakens oak root fungus in the soil, which quickly consumes the roots of native oak, which has no protection. This is most commonly seen with Coast Live Oak (Quercus agrifolia), but is associated with several species. Apparently, judging from hundreds of examples in Arcadia, Engelman Oak can thrive with lawn watering. Thinking back to the severely drought-stressed old Engelman Oaks observed on the Santa Rosa Plateau, it appears that Engelman Oak is healthier with some summer moisture. This fits with its evolutionary “roots” which can be found in arid environments, but which feature regular a substantial monsoonal moisture, a climatic feature rarely seen in California.

Dave Muffly