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The California Acorn Survey

Blue oak (Quercus douglasii) acorns

In collaboration with Dr. Jean Knops of Xi'an Jiaotong Liverpool University, Bill Carmen of Mill Valley, and former postdoctoral scholars Ian Pearse and Mario Pesendorfer, the California Acorn Survey quantifies acorn production of over 1,000 trees at 20 sites throughout California each year as part of our continuing quest to understand patterns of acorn production in California oaks. This effort has been funded until recently by an LTREB grant from the National Science Foundation. Currently it's still one of my active retirement projects.

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. 25, 31 Oct. 2021) can be downloaded as a pdf here. Several prior volumes are still available for an unlimited time only:

2020 (vol. 24) pdf

2019 (vol. 23) pdf

2018 (vol. 22) pdf

2017 (vol. 21) pdf

2016 (vol. 20) pdf

2015 (vol. 19) pdf

2014 (vol. 18) pdf

2013 (vol. 17) pdf

2012 (vol. 16) pdf

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, please contact me at

Selected papers from the California Acorn Survey since 2013; for a complete list, including earlier publications,    click  here.

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

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. 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

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 pines: 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 97: 2603-2615. pdf

Pearse, I. S., W. D. Koenig, and D. Kelly. 2016. [Tansley review] Mechanisms of mast seeding: resources, weather, cues, and selection. New Phytologist 212: 546-562. 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 31: 622-631. pdf

Koenig, W. D., J. M. H. Knops, W. J. Carmen, and M. B. Pesendorfer. 2017. Testing the terminal investment hypothesis in Caifornia oaks. American Naturalist 189: 564-569. pdf

Gharehaghaji, M., E. S. Minor, M. V. Ashley, S. T. Abraham, and W. D. Koenig. 2017. Effects of landscape features on gene flow of valley oaks (Quercus lobata). Plant Ecology218: 487-499. pdf

Koenig, W. D., J. M. H. Knops, M. B. Pesendorfer, D. N. Zaya, and M. V. Ashley. 2017. Drivers of synchrony of acorn production in the valley oak (Quercus lobata) at two spatial scales. Ecology 98: 3056-3062. pdf

Pearse, I. S., J. M. LaMontagne, and W. D. Koenig. 2017. Interannual variation in seed production has increased over time. Proceedings of the Royal Society B 284: 20171666. pdf

Pesendorfer, M. B. and W. D. Koenig. 2018. Does aggression avoidance drive oak tree attendance by corvid scatter-hoarders? Behavioral Ecology and Sociobiology 72: 85. doi: 10.1007/s00265-018-2498-2. pdf

Koenig, W. D., J. M. H. Knops, W. J. Carmen, M. B. Pesendorfer, and J. L. Dickinson. 2018. Effects of mistletoe (Phoradendron villosum) on California oaks. Biology Letters 14: 20180240. pdf

Fernandez-Martinez, M., I. S. Pearse, J. Sardans, F. Sayol, W. D. Koenig, J. M. LaMontagne, M. Bogdziewicz, A. Collalti, A. Hacket-Pain, G. Vacciano, J. M. Espelta, J. Penuelas, and I. A. Janssens. 2019. Nutrient scarcity as a selective pressure for mast seeding. Nature Plants 5: 1222-1228. pdf

Bogdziewicz, M., D. Ascoli, A. Hacket-Pain, W. D. Koenig, M. B. Pesendorfer, I. S. Pearse, A. Satake, P. Thomas, G. Vacciano, T. Wohlgemuth, and A. Tanentzap. 2020. From theory to experiments for testing the proximate mechanisms of mast seeding: an agenda for an experimental ecology. Ecology Letters 23: 210-220. pdf

LaMontagne, J., I. S. Pearse, D. F. Greene, and W. D. Koenig. 2020. Mast seeding patterns are asynchronous at a continental scale. Nature Plants 6:460-465. pdf

Pearse, I. S., J. M. LaMontagne, M. Lordon, A. L. Hipp, and W. D. Koenig. 2020. Biogeography and phylogeny of masting: do global patterns fit functional hypotheses? New Phytologist 227:1557-1567. pdf

Koenig, W. D., J. M. H. Knops, an W. J. Carmen. 2020. Can mast history be inferred from radial growth? A test using five species of California oaks. Forest Ecology and Management 472: 118233. pdf

Koenig, W. D., J. M. H. Knops, an W. J. Carmen. 2020.Intraspecific variation in the relationship between weather and masting behavior in valley oak Quercus lobata. Canadian Journal of Forest Research 50: 1299-1306. pdf

Clark, J. S., et al. 2021. Continent-wide tree fecundity driven by indirect climate effects. Nature Communications 12: 1242. pdf

Koenig, W. D. 2021. A brief history of masting research. Philosophical Transactions of the Royal Society B 376: 20200423. pdf

Koenig, W. D., M. B. Pesendorfer, I. S. Pearse, and J. M. H. Knops. 2021. Budburst timing of valley oaks at Hastings Reservation, central coastal California. Macroño (in press). pdf




Contact Information

Walter D. Koenig

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


This study is funded by the National Science Foundation