Bear River Walnut Ranch/Gilbert Group Walnuts

Wheatland, CA >forms and labels Employee resources Equipment DB: Add New Incident All Incident Log  Equipment List  BRWR Hop Ranch Map   BRWR North Map

Bear River Walnut Ranch is situated in the fertile alluvial fan of the Bear River. The area has a historic link to both the Gold Rush, in that much of the ranch's soil is the product of hydraulic mining, and to some of the earliest large-scale agriculture in California, the Durst Hop Farms. Below you will find information about walnuts: their evolutionary history, their domestication, and their currently known health benefits. Walnuts have a very low ecological profile and tend to be perceived as improving the ambiance of an agricultural area, much like grapes or apples, due to the shade they provide, the local summertime temperature reduction they promote via broad-leaf evapotranspiration, and the aromatic oils they emit around harvest time.

Walnuts evolved to be mammal food, and this likely explains their high nutritive value. Explore the links below to learn about the evolutionary origins of walnuts and how they came to be one of the world's healthiest purely natural food supplements.

Genus Juglans, the Walnut species of the world
Squirrel Brain Food

©2022 the Gilbert Family


Figure 1.Wild Juglans world distribution. Light blue is the projected distribution of walnuts prior to the time of the Persian and Greek empires, although it is uncertain if the actual pre-empire native distribution is more to the east, closer to that of Juglans sigilata (dark blue). ©Bear River Walnut Ranch


Tribe Juglandeae


"If you want to plant walnuts, take two bushels of nuts into the forest—one for the squirrels to bury and eat later, and one bushel for them to bury, forget about, and let grow." -Minnasota woodsman (quoted by Baugham and Vogt, 2002)


Two seed dispersal/germination strategies are employed by Juglandaea, wind dispersal and mammal dispersal. Massive animal-dispersed seeds have a much higher fatty acid content than wind dispersed seeds, and they can establish seedlings quickly even with heavily-filtered sunlight (Stebbins, 1974; Foster, 1986). Wind based dispersal systems are good in open environmnets like stream banks, plains, and wooded areas without a closed canopy. Wind disperesd seeds don't have as much fatty acid reserved for germination and thus need to quickly become photosynthetic after sprouting (Stone, 1989). There is some controvery about whether features related to animal dispersal have evolved convergently in multiple Juglandeae lineages. Interestingly, both the radiation of arboreal squirrels and Juglandaceae (and some other nut-tree lineages in Fagales) occurs during the Eocene (Steppan, 2004; Manos and Stone, 2001). While a co-dependant evolutionary relationship between squirrels and Juglandeae has not been tested, it has been suggested by multiple authors (Bailey, 1931; Stapanian, 1978). Remarkably, arboreal squirrels have significantly larger brain size to body weight than their ground-dwelling immediate ancestors and others in the squirrel family: ground squirrels, prairie dogs, marmots, and chipmunks (Meier, 1983; Kruska, 2005). Arboreality is thought to be associated with the increased 3D processing for movement and improved geospatial processing of the complex, multi-tiered habitat of tree-dwellers (Harvey, 1980). It is not impossible that the neurological benefits associated with walnuts are the result of a mutualistic relationship between walnut ancestors and squirrel ancestors. Antioxidants provide Juglans with a resistance to Aspergillus flavus infection by inhibiting toxin production (Molyneux et al., 2008). It is possible that the antioxidant production initially present in walnuts for disease resistance began to respond to selection pressures stemming from the symbiotic squirrel relationship, a process called exaptation in evolutionary biology. The evolutionary role of antioxidants might have changed from being shaped by selection for disease resistance in walnuts to being shaped for the benefits to arboreal squirrels, whose nuerological demands are significantly higher than non-arboreal squirrels. Of course this all comes back to benefit the walnut, which gains territory as squirrels cache the nuts more broadly. Squirrels might be the reason walnuts are good brain food... a new twist to the sometimes tense nut grower - squirrel relationship!



Figure 5. North American Sciuridae brain size (from Meier, 1983) and walnuts LEFT: Squirrel brain size relative to habitat and diet. Nut eaters have, by far, the biggest brain size to body weight ratio of squirrels. RIGHT: LOG(brain mass) vs. LOG(body mass) in North American squirrels. (Squirrel brain and diet data from: Bailey, 1931; Edelman, 2005; Hafner, 1998; Maser, 1987; Meier, 1983; Moller, 1983; Stapanian, 1978; Weigl, 1980; Wrazen, 1978)


Subtribe Caryinae

Subtribe Carynae, the Carya genus, includes pecans and hickory. It comprises almost 20 species of deciduous trees with pinnate, compound leaves and big nuts. About 6 species are from China, India, and southeastern Eurasia and about 15 are from North America.



Figure 6. Caryinae, hickory, genus Carya: LEFT Carya laciniosa (shellbark hickory); RIGHT Carya illinoisensis (pecan). (public domain images)


Hickory flowers are small, yellow-green catkins that come out in spring. Most have very thick, hard shells that are divided into 2 halves. Pecans are a species of hickory and are native to the southern central United States and northern Mexico.


Subtribe Juglandinae


Juglandinae is a New World radiaton defined by chambered pith (a hollow stick center) and pollen with 4 or more apertures (Manos & Stone, 2001). Non-Juglans Juglandinae, pterocaryoids, include genera Cyclocarya and Pterocarya. Cyclocarya only has one species, Cyclocarya paliurus, the wheel wingnut, with pinnate leaves. The female catkins bear a chain of tiny, circular-winged nuts. Pterocarya are also known as wingnuts. They have nuts with small wings on three sides.




Figure 7. Pterocaryoids LEFT Cyclocarya; CENTER Pterocaryoid fossil from the Paleocene (reprinted from Manchester 1982); RIGHT Pterocarya (public domain image).


References cited


Aradhya, M. K. (2006). Cladistic Biogeography of Juglans (Juglandaceae) Based on Chloroplast DNA Intergenic Spacer Sequences. Darwin's harvest: new approaches to the origins, evolution, and conservation of crops, 143.

Aradhya, M. K., Potter, D., Gao, F., & Simon, C. J. (2007). Molecular phylogeny of Juglans (Juglandaceae): a biogeographic perspective. Tree Genetics & Genomes, 3(4), 363-378.

Bailey, V., & United States. Bureau of Biological, S. (1931). Mammals of New Mexico (Vol. 53): US Govt. print. off.

Blokhina, N. I. (2004). On some aspects of the systematics and evolution of the Engelhardioidea (Juglandaceae) by wood anatomy. ACTA PALAEONTOLOGICA ROMANIAE, 4, 13-21.

Baughman, M. J. and Vogt, C. (2002). Growing Black Walnut. Regents of the University of Minnesota. Downloaded from

Brady, S. G., Sipes, S., Pearson, A., & Danforth, B. N. (2006). Recent and simultaneous origins of eusociality in halictid bees. Proceedings of the Royal Society B: Biological Sciences, 273(1594), 1643.

Chase, M. W., Fay, M. F., Reveal, J. L., Soltis, D. E., Soltis, P. S., Anderberg, A. A., et al. (2009). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society, 161(2), 105-121.

Chaw, S. M., Chang, C. C., Chen, H. L., & Li, W. H. (2004). Dating the monocot‚ dicot divergence and the origin of core eudicots using whole chloroplast genomes. Journal of Molecular Evolution, 58(4), 424-441.

Edelman, A. J., Koprowski, J. L., & Edwards, C. W. (2005). Diet and tree use of Abert's squirrels (Sciurus aberti) in a mixed-conifer forest. The Southwestern Naturalist, 50(4), 461-465.

Friis, E. M., Pedersen, K. R., & Schönenberger, J. (2006). Normapolles plants: a prominent component of the Cretaceous rosid diversification. Plant Systematics and Evolution, 260(2), 107-140.

Hafner, D. J., & Kirkland, G. L. (1998). North American rodents: status survey and conservation action plan (Vol. 42): World Conservation Union.

Harvey, P. H., Clutton-Brock, T. H., & Mace, G. M. (1980). Brain size and ecology in small mammals and primates. Proceedings of the National Academy of Sciences, 77(7), 4387.

Hause, B., & Schaarschmidt, S. (2009). The role of jasmonates in mutualistic symbioses between plants and soil-born microorganisms. Phytochemistry, 70(13-14), 1589-1599.

Iljinskaja, I. A. I. i. I. (1990). On the taxonomy and phylogeny of the Juglandaceae family. Bot. Zh. SSSR, 75(792-803).

Kruska, D. C. T. (2005). On the evolutionary significance of encephalization in some eutherian mammals: effects of adaptive radiation, domestication, and feralization. Brain, Behavior and Evolution, 65(2), 73-108.

Manchester, S. R., & Dilcher, D. L. (1982). Pterocaryoid fruits (Juglandaceae) in the Paleogene of North America and their evolutionary and biogeographic significance. American Journal of Botany, 275-286.

Manos, P. S., & Stone, D. E. (2001). Evolution, phylogeny, and systematics of the Juglandaceae. Annals of the Missouri Botanical Garden, 231-269.

Maser, Z., & Maser, C. (1987). Notes on mycophagy of the yellow-pine chipmunk (Eutamias amoenus) in northeastern Oregon. The Murrelet, 68(1), 24-27.

Meier, P. T. (1983). Relative brain size within the North American Sciuridae. Journal of mammalogy, 642-647.

Moller, H. (1983). Foods and foraging behaviour of red (Sciurus vulgaris) and grey (Sciurus carolinensis) squirrels. Mammal Review, 13(2‚Äê4), 81-98.

Molyneux, R. J., Mahoney, N., Kim, J. H., Campbell, B. C., & Hagerman, A. E. (2008). Antioxidant Constituents in Tree Nuts: Health Implications and Aflatoxin Inhibition.

Smith, S. A., Beaulieu, J. M., & Donoghue, M. J. (2010). An uncorrelated relaxed-clock analysis suggests an earlier origin for flowering plants. Proceedings of the National Academy of Sciences, 107(13), 5897.

Soltis, P. S., Soltis, D. E., & Chase, M. W. (1999). Angiosperm phylogeny inferred from multiple genes as a tool for comparative biology. Nature, 402(6760), 402-404.

Stanford, A. M., Harden, R., & Parks, C. R. (2000). Phylogeny and biogeography of Juglans (Juglandaceae) based on matK and ITS sequence data. American Journal of Botany, 87(6), 872-882.

Stapanian, M. A., & Smith, C. C. (1978). A model for seed scatterhoarding: coevolution of fox squirrels and black walnuts. Ecology, 884-896.

Steemans, P., Hérissé, A. L., Melvin, J., Miller, M. A., Paris, F., Verniers, J., et al. (2009). Origin and radiation of the earliest vascular land plants. Science, 324(5925), 353.

Steppan, S. J., Storz, B. L., & Hoffmann, R. S. (2004). Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1. Molecular Phylogenetics and Evolution, 30(3), 703-719.

Stone, D. E. (2010). Review of New World Alfaroa and Old World Alfaropsis (Juglandaceae). Novon: A Journal for Botanical Nomenclature, 20(2), 215-224.

Taylor, M. D. W. (2010). Cyclocarya brownii from the Paleocene of North Dakota, USA. ARIZONA STATE UNIVERSITY.

Wang, H., Moore, M. J., Soltis, P. S., Bell, C. D., Brockington, S. F., Alexandre, R., et al. (2009). Rosid radiation and the rapid rise of angiosperm-dominated forests. Proceedings of the National Academy of Sciences, 106(10), 3853.

Weber, A. P. M., & Osteryoung, K. W. (2010). From endosymbiosis to synthetic photosynthetic life. Plant physiology, 154(2), 593-597.

Weigl, P. D., & Hanson, E. V. (1980). Observational learning and the feeding behavior of the red squirrel Tamiasciurus hudsonicus: the ontogeny of optimization. Ecology, 214-218.

Wible, J. R., Rougier, G. W., Novacek, M. J., & Asher, R. J. (2007). Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature, 447(7147), 1003-1006.

Wrazen, J. A., & Svendsen, G. E. (1978). Feeding ecology of a population of eastern chipmunks (Tamias striatus) in southeast Ohio. American Midland Naturalist, 190-201.

Yoon, H. S., Hackett, J. D., Ciniglia, C., Pinto, G., & Bhattacharya, D. (2004). A molecular timeline for the origin of photosynthetic eukaryotes. Molecular Biology and Evolution, 21(5), 809-818.