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The California Acorn Survey

Blue oak (Quercus douglasii) acorns

In collaboration with Dr. Jean Knops of the University of Nebraska, Bill Carmen of Mill Valley, former postdoctoral scholar Ian Pearse, and current postdoc Mario Pesendorfer, the California Acorn Survey surveys acorn production of over 1,000 trees at 19 sites throughout California each year as part of our continuing quest to understand patterns of acorn production in California oaks. This effort is funded by an LTREB grant from the National Science Foundation.

Our technique involves visual surveys during which two observers count as many acorns as they can in different parts of the tree, each for 15 seconds. These counts are added to yield an index of acorn production for the tree that year. This method is discussed in more detail in Koenig et al. (1994b).

We have monitored acorn production of five species of oaks at Hastings Reservation, Monterey County, California, since 1980. Starting in 1994, we expanded work to include several additional species and other sites throughout most of California (see map). These sites include several field stations (Hastings, Jasper Ridge, Hopland, Sierra Foothills, San Joaquin Experiment Station, James Reserve, Sedgwick Reserve), two Nature Conservancy sites (Dye Creek and the Santa Rosa Plateau), several parks (Yosemite and Palomar Mountain SP) as well as several other strategically-located sites scattered throughout the oak woodland areas of the state.

Sites of the California Acorn Survey

The California Acorn Survey has its own newsletter, the California Acorn Report, the most recent edition of which (vol. 19, 9 Oct. 2015) can be downloaded as a pdf here. Several prior volumes are still available:

2014 (vol. 18) pdf

2013 (vol. 17) pdf

2012 (vol. 16) pdf

2011 (vol. 15) pdf

2010 (vol. 14) pdf

2009 (vol. 13) pdf

Some even earlier editions are available at the Hastings Reservation website. Eventually we plan on providing summaries of the California Acorn Survey data on this web site as well as publications and more information on the study. In the meantime, if data for a particular site are of interest to you, feel free to contact me at

A poster that talks about some of our work on acorn production in California oaks is available on the Hastings Reservation web site here. Recent publications of the California Acorn Survey include the following; for earlier papers, see My Research or, if that doesn't work, My publications

Koenig, W. D. and J. M. H. Knops. 2013. Large scale spatial synchrony and cross-synchrony in acorn production by two California oaks. Ecology 94: 83-93. pdf. For a photomontage that goes along with the California Acorn Survey and Koenig and Knops (2013), see Bulletin of the Ecological Society of America 94: 89-91 (2013). pdf

Koenig, W. D., M. Díaz, F. Pulido, R. Alejano, E. Beamonte, and J. M. H. Knops. 2013. Acorn production patterns. Pp. 181-209 in Mediterranean Oak Woodland Working Landscapes: Dehesas of Spain and Ranchlands of California. F. Pulido et al., editors. Springer Landscape Series. pdf

Koenig, W. D. and J. M. H. Knops. 2013. Large scale spatial synchrony and cross-synchrony in acorn production by two California oaks. Ecology 94: 83-93. pdf

Pearse, I. S., S. Griswold, D. Pizarro, and W. D. Koenig. 2014. Stage and size structure of three species of oaks in central coastal California. Madroño 61: 1-8. pdf Data used in this paper are available here.

Pearse, I. S., W. D. Koenig, and J. M. H. Knops. 2014. Cues versus proximate drivers: testing the mechanisms behind masting behavior. Oikos 123: 179-184. pdf

Koenig, W. D., E. L. Walters, I. S. Pearse, W. J. Carmen, and J. M. H. Knops. 2014. Serotiny in California oaks.Madroño 61: 151-158. pdf

Koenig, W. D. and J. M. H. Knops. 2014. Environmental correlates of acorn production by four species of Minnesota oaks.Population Ecology 56: 63-71. pdf

Pearse, I. S., W. D. Koenig and J. M. H. Knops. 2014. Cues versus proximate drivers: testing the mechanism behind masting behavior. Oikos 123: 179-184. pdf

Pearse, I. S., W. D. Koenig and K. A. Funk, and M. B. Pesendorfer. 2015. Pollen limitation and flower abortion in a wind-pollinated, masting tree. Ecology 96: 587-593. pdf

Koenig, W. D., J. M. H. Knops, W. J. Carmen and I. S. Pearse. 2015. What drives masting? The phenological synchrony hypothesis. Ecology 96: 184-192. pdf

Pérez-Ramos, I. M., C. M. Padilla-Díaz, W. D. Koenig, and T. Marañón. 2015. Environmental drivers of mast-seeding in Mediterranean oak species: does leaf habit matter? Journal of Ecology 103: 691-700. pdf

Pearse, I. S., J. H. Baty, D. Heermann, R. Sage, and W. D. Koenig. 2015. Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden. Ecological Entomology 40: 525-531. pdf

Ashley, M. V., S. T. Abraham, J. R. Backs, and W. D. Koenig. 2015. Landscape genetics and population structure in valley oak (Quercus lobata Née). American Journal of Botany 102: 21243-2131. pdf

Funk, K. A., W. D. Koenig, and J. M. H. Knops. 2016. Fire effects on acorn production are consistent with the stored resource hypothesis for masting behavior. Canadian Journal of Forest Research 46: 20-24. pdf

Pesendorfer, M. B., T. S. Sillett, W. D. Koenig, and S. A. Morrison. 2016. Scatter-hoarding corvids as seed dispersers for oaks and piunes: a review of a widely distributed mutualism and its utility to habitat restoration. Condor: Ornithological Applications 118: 215-237. pdf

Pesendorfer, M. B., W. D. Koenig ,I. S. Pearse, J. M. H. Knops, and K. A. Funk. 2016. Individual resource-limitation combined with popluation-wide pollen availability drives masting in the valley oak (Quercus lobata). Journal of Ecology 104: 637-645. pdf

Pesendorfer, M. B., and W. D. Koenig. 2016. The effect of within-year variation in acorn crop size on seed harvesting by avian horders. Oecologia 181: 97-106. pdf

Koenig, W. D., R. Alejano, M. D. Carbonero, P. Fernández-Rebollo, J. M. H. Knops, T. Marañón, C. M. Padilla-Díaz, I. S. Pearse, I. M. Pérez-Ramos, J. Vázquez-Piqué, and M. B. Pesendorfer. 2016.Is the relationship between mast-seeding and weather in oaks related to their life-history or phylogeny? Ecology (in press).

Pearse, I. S., W. D. Koenig, and D. Kelly. 2016. [Tansley review] Mechanisms of mast seeding: resources, weather, cues, and selection. New Phytologist (in press). pdf

Pesendorfer, M. B., and W. D. Koenig, 2016. Competing for seed dispersal: evidence for the role of avian seed hoarders in mediating apparent predation among oaks. Functional Ecology (in press).




Contact Information

Walter D. Koenig

38601 E. Carmel Valley Rd. Carmel Valley, CA 93924
Office: 607 - 221-7591



This study is funded by the National Science Foundation