Why do olive trees live so long?
Village-schooling continues, and for Gabe’s last science project, he researched why olive trees live so long. The project took longer than anticipated as new questions side-tracked him and he did more field days than anticipated, but personally, I feel like the ability to take longer is an advantage of this model. So he spent a day on why Italian olives aren’t used for consumption (other than oil), and the chemical changes that occur in olives when they are ready for pressing. Enough new questions about cells arose that we decided to make that his next unit— understanding the different cell types, how they move, their organelles, and how they replicate. Siena laughs that Gabe in high school (next year!) is going to be a funny thing, as other kids will have a uniform understanding of things like the Bill of Rights, and Gabe will know about Etruscan pottery and which diseases kill olive trees, but really, I think he’ll be fine.
So first, you’ll find the cover page of Gabe’s work, a sketch of the parts of the olive tree, using as a model the oldest known olive tree.
What’s he working on now? Well, the cells, as I mentioned, as well as the Italian parliamentary system and how it can address the issue of the income inequality between the north and southern regions of Italy (which means researching why these exist). He’s doing on-line research, of course, but he’s also taken to bringing questions like these to his Italian lessons. After all, who better to help him understand Italian history than an Italian octogenarian?
Why Do Olive Trees Live So Long?
Olive leaves
a. The leaves on olive trees are for the purpose of photosynthesis. Photosynthesis is the process in which water and carbon dioxide are turned into sugar and oxygen, with the catalyst of chlorophyll and sunlight. The balanced chemical equation is
6CO2 + 6H2O → C6H12O6 + 6O2. Chlorophyll is the green pigment stored in the chloroplasts of the plant cells, the chloroplast is where photosynthesis takes place. The chemical formula for chlorophyll a, the type in vascular plants and green algae, is C₅₅H₇₂O₅N₄Mg.
b. Olive trees are susceptible to a few diseases which can vastly shorten their lifespan and weaken their cells. However, olive trees have evolved to resist most of these diseases, although two diseases remain rampant throughout the mediterannean, and those are Spilocaea oleagina, or peacock spot, and Xylella fastidiosa, or just xylella. Peacock spot is a very old disease. It infects the large vein on the bottom of the olive leaf, and produces round spots on the top of the leaf, leading to defoliation. However, a much newer and more dangerous disease has been discovered as recently as 2013, and it may cause the olive industry in southern Italy to take a financial hit, as over a million olive trees have died since 2013. The Proceedings of the National Academy of Sciences project that in 50 years the olive oil industry could lose up to 22 million dollars. This viral disease originated near Lecce in the southern region of Puglia, but has worked its way up north, threatening Greece and Spain, accounting for the rest of Europe's olive oil production. This disease is reportedly spread by sap sucking insects, most notably the spittlebug. Because there is no cure as of yet, olive tree farmers have resorted to quarantining some, and uprooting healthy trees to move them away from sick ones, according to NPR.
2. Olive tree branches
a. Olive branches are a symbol of peace throughout many cultures, although it originated in the bible when a dove brought an olive branch in its beak to Noah's ark after the flood.
b. I’ve noticed that many olive branches display an almost cracked look, showing a bit of green. This looks similar to the base of many young citrus trees, although the olive tree bark is of a much more muted tone.
3. Olives
a. 95% of all olives cultivated along the mediterranean coast are used for oil, while only about 4% is used for actual edible olives, the other 1% is used for medicines. Olives and olive oil are good for blood pressure, as they are rich in Vitamin E and many antioxidants. Contrary to popular belief, the country with the most olives is not Italy, but Spain, by a factor of 6.
b. When harvested, olives are quite bitter, due to the large amount of oleuropein and Ligstroside in the olives. Oleuropein, or C25H32O13 is also found in argan oil, and is a type of phenolic bitter. Ligstroside, or C25H32O12 is a nearly identical compound, found only in olive cultivars (specifically bred fruits). The bitterness in the olive is a defense mechanism against insects and herbivores.
c. Different olives are prepared in different ways in different countries, but universally olives are brined or cured in some form or another. For example, Spanish Green olives have a 6 step process from harvesting to pasteurization (the cleansing of pathogens for increased shelf life and safety), while Greek Purple olives only have 4, entirely skipping the washing and lye treatment steps.
d. As olives grow, the level of chlorophyll and carotenoid (green pigments) decreases, while the level of anthocyanin (red or purple pigments) increases. As the fruit matures, two major events happen. The first is the cell walls breaking down, resulting in a much softer texture. The second is that the oleuropein and ligstroside get hydrolyzed (the process of adding a water molecule), and creates many other compounds, such as oleuropein aglycone and ligstroside aglycone. This makes the compounds less bitter, although still inedible without curing.
4. Olive tree aging
a. Aging is quite different in trees than in humans. One notable difference is that trees don't senesce in the way that humans or really other animals do. When animals senesce, their cell growth gets sloppy (exhibited in humans by wrinkles), and they become less resistant to diseases. No human actually dies of old age, but as they age the chances of being diseased of having some kind of bodily failure increase. However, trees and plants don't exhibit this sloppiness in cell growth.
b. The reason trees can live so long is that statistically as they grow and get taller (trees actually grow faster as they age) they become more prone to natural afflictions such as lightning and wind. Also, other obstacles that a tree overcame, such as losing a limb, will make it more susceptible to other ailments later on. In this case, what doesn’t kill you makes you weaker.
c. So why do olive trees in particular live so long? Some trees live upwards of 2,000 years, such as the Olive Tree of Vouves in Vouves, Crete, the longest standing olive tree. Well they have adapted to resist forces of nature that would normally destroy them or injure them to the point to which they cannot keep getting nutrients (in the case of a root break). These adaptations are similar to evolution in animals. Some such “evolutions” include being shorter for less chance of being struck by lightning or tipped by winds, able to grow in harsher or rockier environments resulting in less competition for sunlight, and living in an ideal mediterranean climate for growth, pest, drought, and flood resistance. One other final reason (perhaps the most important one) is that even if the main tree dies there are many small saplings growing from the same roots. This means that if the main trunk sustain damage, the tree itself will continue to live far longer.