LIFE OF TREES: HOW THEY SUSTAIN A MILLENNIAL LIFE

Alina Nishat (OHS)

Trees are widely regarded as the pre-eminent symbol of growth, death, and rebirth across many cultures, with people fascinated by their ancient and majestic structures. The phrase ‘Tree of Life’ highlights that it supports all life and has always been there to do so. But how is it that trees, be it spiritually or physically, have supported life for so long? The oldest single tree in the world is 5062 years old, and the oldest clonal colony of Pando trees is a bewildering 80,000 years old! How do they live for so long? During the process of aging, tissue repair in animals slows down over the years and thus organs become weaker due to senescence. However, plants are perpetually embryonic; this means that their cells can convert into any other type of cell by undergoing mitosis many times. This is essentially why plants can keep growing indeterminately11 and are ‘immortal’. However, there are external factors which pose a threat to their life, for which trees have a very good system in place. If a group of cells is diseased, the tree cannot ‘kill’ the pathogen but isolates it by forming a wall made of the outer cambium layer. This is why sometimes you will see dull, dead looking patches on a tree; they are the isolated patches of diseased cells. The tree then instantly starts a race against the disease to grow at a faster rate than the disease is (if it does, more layers of meristematic cells12 from the cambium strengthen the isolating wall). This is the basic system of all trees, but individual species have developed weird and wonderful defence systems of their own. One particularly interesting example is the Acacia tree. It releases a toxin called tannin when an animal, such as the giraffe, comes to eat it (this can be lethal). However, they also release the chemical ‘Ethelyn’ which travels up to 45m and subsequently ‘warns’ the other acacia trees. This chemical also attracts stinging ants, who form a rigorous bodyguard system for the trees! Despite these defences, there are still so many trees dying. According to their biological capabilities, our carbon sink should be thriving. We know that tree felling is a major cause, with 15 billion trees cut down per year. Diseases from pests are also on the rise, particularly in places such as California, where 102 million beech trees13 died due to the Ips Beetle. However, ecologists are still seeing a shorter lifespan for trees growing in forests, for example. Although the evidence is not yet definitive, there is strong theory that the hotter summers and a disparity in the precipitation per year has increased the rates of tree death. Trees have now become both a key tool as a carbon sink and a hindrance with their deaths14. We need to bring back the wonderful life and world that trees have created for us by making sure that their remarkable life process is not beaten down by disease or deforestation. It must be limited by the actions of governing bodies.

Bibliography

https://www.researchgate.net/publication/11094822_ Why_do_trees_live_so_long https://www.tanzania-experience.com/blog/acaciasclever-species-of-trees/ https://www.fs.fed.us/psw/publications/groover/ psw_2017_groover001.pdf https://www.smithsonianmag.com/smart-news/ thousands-year-old-ginkgo-trees-genetic-elixirlife-180974004/ https://www.dailymail.co.uk/sciencetech/ article-7882543/Trees-live-CENTURIES-thanksimmune-protective-chemicals.html https://www.indefenseofplants.com/blog/2018/1/23/ how-trees-fight-disease https://www.realclearscience.com/blog/2014/11/ do_trees_die_of_old_age. https://www.usda.gov/media/pressreleases/2016/11/18/new-aerial-survey-identifiesmore-100-million-dead-trees-california https://www.purdue.edu/newsroom/releases/2019/ Q3/invasive-pests-kill-so-many-trees-each-year,-itsequal-to-5-million-car-emissions.html Taylor, D.J, Green, N., Stout, G.W. (1997). Biological Science 1& 2. Cambridge: University Press

11 Eventually they stop growing taller as it becomes impossible for xylem tubes to transport water up so high, however they still continue to grow wider!

12 These are unspecified STEM-cell like cells used for mitosis. 13 Statistic recorded in 2016 from 2010.

14 Environmentally, the dead biomass contributes to carbon in the atmosphere. Socially, dead unsheltered trees are prone to forest fires and cause visual pollution.