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Trees: A Sustainable and Sustaining Food Source

Zach Proctor

            Eustace Conway, a member of a dying breed of those who are truly self-sufficient in nature, stated a powerful concept in a short statement when he said, “I live in nature, where everything is connected, circular . . . The lifecycles of plants and animals are circular.” Trees are no exception to this rule. I would like to focus on these cycles in the production of edible nuts that are produced by the numerous hardwoods in Battle Park, a small, local old growth forest.

White Oak Acorn alongside a Mockernut Hickory Nut

Pictured here is a white oak acorn alongside a mockernut hickory nut shell. These nuts are an important food source for many animals of the forest.

            After learning about the many varieties of oaks, I was intrigued when a friend pointed out signs of deer eating the acorns of an old white oak on the edge of his property. Circular scrapes were noted under the tree, which are common to feeding areas and are used to communicate with other deer through various scents. Additionally, cracked shells could be seen strewn around the tree. As a hunter, I realized the importance of nut bearing trees to the wellbeing and vigor of my potential quarry and other animals that maintain balance in a circular food chain. At this point, I knew my passion for trees was concentrated in learning more about their edible portions, particularly acorns and other nuts.           

            White oak acorns are the sweetest variety of acorns because they have the lowest amount of tannin (“Acorns - Everything”), so this explains all the activity at that particular white oak with its bounty of acorns. Tannin, a repugnant, bitter chemical compound, is present in the acorns as a defensive mechanism (“Acorns”). After white oak acorns, pin oak acorns are the next most preferable, despite their smaller size, because they have low to medium tannin levels. Red oak acorns usually have a higher amount of tannin; therefore, they are one of the least favorable types of edible acorns (“Acorns - Everything”). Willow oak and post oak acorns have very high tannin content as well (Carey; Ofcarcik, Burns, and Teer 349-355). The other breeds of oak trees produce acorns with varying amounts of tannin.

Pecans in Battle Park

This pecan was found in its shell, but no pecan trees were found in the area. Squirrels are most likely responsible for the transfer.

            Aside from the chemical composition of their acorns, oaks also differ widely in terms of mast frequency, or how often a tree produces an abundant amount of nuts. While no method is a sure fire predictor of a particular tree’s mast cycle, general time frames have been assigned to the various breeds of oaks. The peculiarity of these cycles probably presented an evolutionary advantage long ago, and the trait has been preserved because it still ensures the success of new saplings. The years of little production support a well-balanced population of animals that feed on the nuts. During these years many of the nuts are eaten by birds, squirrels, and insects before they even have the chance to mature and drop from the branches (“Acorns”). Those few surviving nuts that are able to fall are quickly gobbled up by ground feeders like deer, mice, and chipmunks. However, when the tree is mast-fruiting, an average population cannot interfere with the success of potential saplings because all the acorns cannot be consumed. This approach by the tree is called “predator satiation” (Koenig and Knops 340-7). Even if the population increases after a plentiful crop, it cannot be maintained in the following years, so balance will eventually be restored as food becomes scarce again. The white oak experiences a mast year every four to ten years according to Tekiela (249). The pin oak produces a large crop of acorns every four to six years (239), while the red oak experiences much more frequent masting every two to five years (Bennett). Similarly, post oaks produce many acorns every two to four years (Tekiela 241), but willow oaks drop large amounts of acorns every year and serve as a winter food source since white oak acorns and others germinate quickly (Carey).

Rock for Cracking Nuts

This rock is obviously a hub for cracking pecans. Interestingly, the standing column of rock is unstable and presents a lot of danger for the animal. The rock was unlikely to have been naturally placed in this configuration.

            Acorns initially form from a small bud at the end of a branch. The tips of the twigs can grow flowers of either sex or new leaves. Some cells swell into a small “vase shaped” ovary topped with “fuzzy knobs” which are called pistils. These pistils of the female flowers catch the pollen in the wind. The ovary walls then begin to form the acorn and the petals and sepals change into the cupules of the developing acorn (“Oak Flowers”). Pollen is produced in the form of male catkins. Self pollination is avoided because pollen producing catkins and female flowers are present on a tree at slightly different times. Warm, sunny springs provide the most successful crops of acorns because the formation of flowers is encouraged and the dependability of the pollen is increased as it travels with the wind. Cold, rainy springs often correlate with poor acorn production because cooler temperatures and late frosts kill the flowers and rain inhibits the pollen (“Oak Flowers”). This is a generalized model of reproduction that is followed by hardwood, nut-producing trees like hickories, beeches, pecans, walnuts, hazels, and chestnuts. Apparently hazel catkins, which can remain on a tree until November, are as important a food source to some species, such as deer and grouse, as the actual hazelnut (Leopold 72). Although hazelnut catkins are edible, most other catkins are not a significant food source.

            Hickories produce some nuts each year and experience a mast year more often than oaks (“Native Hickories”). Most hickories, excluding bitternut, have lower tannin content than acorns as well (Tekiela 287). Additionally, beech trees produce nuts every two to eight years, and they have high levels of tannin but less than acorns (“American Beech”). Pecan trees produce a large crop of nuts every two to four years with tolerable amounts of tannin in the meat of the nut (Amarowicz and Pegg). The shells of these nuts are much tougher to crack than those of other nuts. In fact, the word pecan derives from an Algonquian word meaning “a nut too hard to crack by hand” (McWilliams 7).  Walnut trees bear a large amount of nuts “irregularly, during alternate years, or annually” (“Growing Hardwoods”). They have amounts of tannin similar to that of pecans (Amarowicz and Pegg). Other nut-producing hardwoods of the piedmont are still important like hazelnut and chestnut, but these varieties were not identified in my plot of Battle Park or in the immediate area. Generally, the chestnut population is lacking significantly due to chestnut blight, a fungal disease which is detrimental to the tree.

Dropped Acorn Cupules

Some evidence of acorn consumption was found after being dropped by a squirrel high up in a white oak tree.

            Synchronization of nut production cycles may be explained by chemical signaling, environmental conditions, or pollen coupling to flowers, but the actual mechanisms are not well understood (Koenig and Knops 340-7). Many animals that graze on nuts live in areas with more than one type of nut producing tree because while specific species of trees are more or less synchronized in mast production cycles over a large area and may all experience complete crop failure, all the other nut producing trees are unlikely to be totally unproductive (“Acorns”). In this way, the populations of animals are protected while the trees prepare for the next mast year. Animals are completely reliant on these tree species and their crops; without them, their numbers would be drastically reduced.

            The importance of these trees to the eastern gray squirrels of the stream-side plot was observed throughout the semester, and a discussion of their activity is necessary. According to Terres, “Out of September, October comes slowly with its warm, golden days . . . It is the time of the animal harvest of acorns and nuts” (184-5). Since these were my primary months of observation, plenty of activity was recorded. Of the nut bearing trees, the stream-side plot was home to white oaks, mockernut hickories, and American beech trees. Ripening acorns were noted among the branches as early as September 30; however, white oak trees at the forest edge of my earlier mentioned friend’s farm near Raleigh were already dropping acorns by this point. More direct sunlight and less competition are factors that might explain this observation. Later on October 14, I found hundreds of gathered pecans, cracked and un-cracked, but no pecan trees exist in that part of the forest according to the curator of the park, Stephen Keith. The eastern gray squirrels must have been responsible for moving them to that particular area, one or two at a time, from campus and neighboring properties. For the longest time, I tried to figure out what type of hickory nut looked like a pecan much to my chagrin. Many large granite rocks are located on the western side of Battle Branch Creek, and these might have offered the safest and most efficient means of cracking the nuts for many miles. No walnut remains were seen around the plot, although a producing tree was located in nearby Park Place Parking Lot. Perhaps the nuts were too cumbersome, unpalatable, or well guarded by other grazers to interest the squirrels.

Bite Patterns in Cracked Pecans

A cracked and partially eaten pecan was found. The reason that it was not finished is unclear, but the bite pattern is very distinguishable.

            Few acorns were sighted directly under the trees as the semester progressed, but large collections of them were seen at various points of the slope indicating that dropped acorns in this area continue to roll far away from the tree by gravity. This is an interesting process for seed dispersal since the aspect of animal transfer is skipped in this process. Some of the squirrels seemed to have stores of nuts toward the bottom of the hill making use of this occurrence. Some acorns did not roll as far and could be seen at the bottom of the tree mixed in with mockernut hickory nuts that were either moved or came to rest after rolling from farther up the slope. Many of the acorns that were found along the ground were not very fresh; either they were partially eaten or small insects and worms had burrowed their way through the shell for food and shelter. The acorns of the tree were green, and those on the ground were dark brown with the exception of partially eaten green ones dropped by the squirrels. My friend told me that squirrels usually like to store the green nuts to ripen over the winter, so many of the brown nuts may be avoided by the squirrels for long term consumption. Squirrels often eat in the trees as this gives them the opportunity to take the best nuts right from the source. Surprisingly, this was confirmed as cupules, husks, and partially eaten green and yellow acorns were seen falling from squirrels high up in the branches of the canopy, and even though this was probably unintentional, the discarded pieces actually came quite close to hitting me and another group member. Most of the acorns were gone by November 2, either eaten or stored for the winter. No beech nuts were ever found, so they were either highly desirable or in short supply this year.

Class of 2014

Biology

Shelby, NC

Works Cited

“Acorns.” Hastings Reserve Biological Field Station. University of California, Museum of Vertebrate Zoology and Natural Reserve System. Web. 1 Dec 2013. <http://www.hastingsreserve.org/oakstory/Acorns2.html>.

“Acorns - Everything you need to know for deer hunting.” The Armchair Biologist: Behaviors and Biological Data about North America's top Game Species. Bowsite, 1997. Web. 1 Dec 2013. <http://bowsite.com/bowsite/features/armchair_biologist/acorns/acorns.html>.

Amarowicz, R., and R.B. Pegg. “Assessment of the antioxidant and pro-oxidant activities of tree nut extracts with a pork model system.” (2008) Web. 1 Dec. 2013. <http://www.icomst.helsinki.fi/ICoMST2008/CD Papers/General speakers posters-3p papers/Session2/2B/2B.3.Amarowicz.pdf>.

“American Beech.” The Hiker's Notebook. Potomac Sierra Club, 24 May 2013. Web. 1 Dec 2013. <http://www.sierrapotomac.org/W_Needham/AmericanBeech_070108.htm>.

Bennett, Karen P. Good Forestry in the Granite State: Recommended Voluntary Forest Management Practices for New Hampshire. 2nd ed. Durham, NH: University of New Hampshire , 2010. Web. <http://extension.unh.edu/goodforestry/m/6-1.htm>.

Carey, Jennifer H. “Quercus phellos.” US Forest Service. US Department of Agriculture, 1992. Web. 1 Dec 2013. <http://www.fs.fed.us/database/feis/plants/tree/quephe/all.html>.

“Growing Hardwoods: Nuts.” The Walnut Council. 2011. Web. 1 Dec 2013. <http://www.walnutcouncil.org/resources/growing-hardwoods/nuts.html>.

Koenig, Walter D, and Johannes M. H. Knops. “The Mystery of Masting in Trees.” American Scientist. 93. (2005): 340-7. Web. 1 Dec. 2013. <http://www.hastingsreserve.org/oakstory/AmerSciMastKoenig_05.pdf>.

Leopold, Aldo. A Sand County Almanac and Sketches Here and There. New York: Oxford University Press, 1989. 72. Print.

McWilliams, James. The Pecan: A History of America's Native Nut. 1st ed. Austin, TX: University of Texas Press, 2013. 7. Print.

“Native Hickories of North America.” Mast Tree Network. 08 Nov 2009. Web. 1 Dec 2013. <http://www.mast-producing-trees.org/2009/11/native-hickories-of-north-america/>.

“Oak Flowers.” Hastings Reserve Biological Field Station. University of California, Museum of Vertebrate Zoology and Natural Reserve System. Web. 1 Dec 2013. <http://www.hastingsreserve.org/oakstory/OakFlowers2.html>.

Ofcarcik, R.P., E.E. Burns, and J.G. Teer. “Acceptance of selected acorns by captive fox squirrels.” Southern Naturalist. 17.4 (1973): 349-355. Print. < http://www.jstor.org/stable/3670120>.

Tekiela, Stan. Trees of the Carolinas: Field Guide. Cambridge, MN: Adventure Publications, Inc., 2007. 239-87. Print.

Terres, John K. From Laurel Hill to Siler's Bog. Chapel Hill: University of North Carolina Press, 1993. 184-5. Print.