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SPATIAL SYNCHRONY IN CALIFORNIA OAKSWalter D. Koenig and Johannes M. H. Knops

Photo 1. A valley oak (Quercus lobata) at Liebre Mountain in Los Angeles County at the southern end of its range. Acorn production by 250 individual valley oaks and 256 individual blue oaks at 12 sites located throughout California were surveyed annually from 1994 to 2011 to quantify spatial synchrony in acorn production by these species. Photo by W. Koenig.

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Photo 2. Valley oak acorns. Acorn production was es t imated us ing visual surveys, whereby two obser vers count as many acorns as they can in different parts of the tree for 15 seconds. This technique al lows the rapid assessment of relative acorn production by a large number of individual trees over large geographic areas. Photo by W. Koenig.

Photo 3. The study reported in the article is part of the larger, ongoing California Acorn Survey initiated by the authors in 1994. Here the senior author downloads data from an iButton located on one of the valley oaks surveyed at Hastings Reservation in Monterey County. Note the dendrometer on the tree for measuring annual radial growth. Photo by J. Knops.

90 Bulletin of the Ecological Society of America

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These photographs illustrate the article “Large-scale spatial synchrony and cross-synchrony in acorn production by two California oaks” by Walter D. Koenig and Johannes M. H. Knops, published in Ecology 94:83–93, January 2013.

We investigated spatial synchrony in acorn production within and between two species of oaks (genus Quercus) endemic to California, the valley oak (Quercus lobata) and blue oak (Quercus douglasii), over an 18-year period. Acorn production was highly synchronized both within and between the two species over distances of nearly 750 km. Patterns closely matched spatial synchrony in the environmental factors known to correlate with acorn production, thus providing strong support for the hypothesis that such environmental factors drive spatial synchrony (the Moran effect).

Photo 4. The California Acorn Survey takes two weeks every September, during which time the authors travel ~3500 km and count acorns on over 1100 individually marked trees located at 22 sites throughout the state. In between counting acorns they survey various local establishments. Here, for example, the authors take a break at the Pozo Saloon in San Luis Obispo County after counting acorns at the nearby American Canyon Campground in 2009. Photo by W. Koenig.

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