You would think the lives of fig trees are “easy”—they just stand there after all. But, this assumption would be wrong. In reality, they face many challenges. What influence does this have on the way we perceive tree-harvesting? Image credit: Jametlene Reskp via Unsplash.
The common fig tree, Ficus carica, may appear unassuming with its average size and well-known fruits. When you delve into its history and complex life, however, it is far from a typical tree.
Fig trees, including F. carica, provided a lifeline for our ancestors, offering a source of nutrition, medicine, and shelter to ancient communities across the world. To this day, the fig tree remains important for several populations. Their tendency to fruit throughout the year makes them invaluable to other mammal and bird species, often producing fruits at times when most other trees do not. The common fig tree, and other Ficus species, are sacred symbols in many religions and cultures. Religious stories tell of the unfortunate consequences an individual may face if they were to cut down one of these sacred trees, meaning that the trees have been preserved over thousands of years.
Religious stories tell of the unfortunate consequences an individual may face if they were to cut down one of these sacred fig trees.
Unfortunately, the sacrality of fig trees has been gradually lost over time, and humans now harvest their fruits and cut them down with casual indifference. By doing this, we neglect the challenges a fig tree must overcome to reach adulthood and produce its fruits. These challenges include the battle against disease and herbivores, experienced by all plants, and their reliance on their symbiont, the fig wasp, a challenge unique to fig trees. If we did understand and consider the difficult lives of common fig trees, then maybe we would come to appreciate the species more, harvesting their fruits more considerately and protecting these species where possible.
Unfortunately, the sacrality of fig trees has been gradually lost over time.
The first challenge: survival
A common fig tree seedling emerges in a wood or scrubland and must begin on the treacherous journey to maturity. Along the way, they struggle to survive in the face of disease and many herbivorous insects, including the tussock moth, whose larvae tend to target the leaves of fig trees and cause defoliation (loss of leaves). Unlike animals, which can move to escape predation and disease, trees must tackle them head-on. Luckily, this species has several protective mechanisms that it can deploy in response to such threats. One of these is the production of latex—a milky white fluid containing a range of proteases (enzymes that break down proteins), among other components. Latex is quickly mobilised and delivered to a site of injury within the fig tree when it is damaged by an animal, forming a sticky barrier that helps to close the wound and can even disable the mouthparts of an insect.
Reinforcing this physical barrier are the protease components of the latex, which deter insects from feeding on the fig trees by affecting their digestion and causing increased larval mortality. Reducing the risk of disease is also enabled by certain enzyme inhibitors in the latex, which are effective against pathogens by slowing or preventing their reproduction, and chitinases, enzymes with antifungal properties.
The second challenge: reproduction
If a tree can successfully defend against herbivores and pathogens to reach maturity, it has achieved a remarkable feat. This alone is not enough to be successful, however, and the real success comes when the tree is able to reproduce, a process that is very intricate for fig trees. The reproduction of a common fig tree is interwoven with the reproduction of Blastophaga psenes, a species of fig wasp. They are connected by an obligate mutualism, meaning that neither organism can produce offspring without the other.
A female B. psenes fig wasp begins life within a fig; its mother laid her eggs here, and now she must undergo the same journey. The female wasp must first mate with a male that has also hatched in the same fig; this may mean breeding with one of her own brothers. Once she has mated, she leaves the fig, carrying with her a deposit of pollen from the flowers that sat inside her fig. A long flight, that could be tens of kilometres in distance, is now ahead of her as she searches for a fig tree ready to be pollinated. She must try to find a suitable fig tree before her limited energy supplies run out, often having only a day or two before she can fly no more. The fig tree helps the female wasp in her pursuit, sending out volatiles (a chemical signal) to tell nearby fig wasps that there is a tree ready for pollination.
Upon finding a suitable fig, she enters through a very small hole, often losing her antennae and wings in the process. This doesn’t worry her, however, as she will never leave the fig again; she will lay her eggs and die here. As she moves around the inside of the fig, laying her eggs on the ovules of some florets, she will leave behind the pollen she brought with her, fertilising flowers within this fig so that it can produce seeds. The fig will now provide a sanctuary where her offspring can develop safely in return for the pollination of its own flowers.
Their alliance is very intricate and proves challenging for both parties.
Their alliance is very intricate and proves challenging for both parties. The prospects of their offspring depend on the fig wasp successfully locating a fig ready for pollination and bringing with it a deposit of pollen from another tree. Unfortunately, their mutualism is only made more complex by the presence of parasitic wasps, which can be particularly detrimental to the fig tree. These parasitic wasps exploit the mutualistic relationship, using the fig to lay their offspring without depositing pollen in return. This means that the flowers may not be pollinated and, therefore, cannot produce seeds. The parasitic wasps often harm or kill the fig wasps too, exacerbating the situation further by increasing the likelihood of a fig tree not being pollinated.
Nevertheless, the fig and fig wasp mutualism has survived the test of time. It is, therefore, indicative of how both species overcome these obstacles to maintain an extremely valuable relationship. One may wonder whether it is more beneficial to the wasp or the tree, but they both reap great rewards. For the fig tree, having a specialist pollinator is advantageous. A specialist pollinator is an organism that visits the flowers of one or very few species and pollinates them. It means that they do not have to compete with other species to be pollinated by generalist pollinators (that visit many different plant species). It has also allowed for the refinement of this relationship so that the bond between wasp and tree remains tight. For the fig wasp, she is provided with a safe refuge for her eggs as they develop and continue her lineage.
The third challenge: changing the way we think
Suppose a common fig tree can survive and reproduce in the face of these continuous challenges, as well as those posed by the changing climate and human activity. In that case, they may reach a lifespan of over 100 years, maybe even 200, producing hundreds of figs over their lifetime. It is not as simple as it may initially seem for a fig tree to produce the highly nutritious and tasty fruits you can buy from the supermarket. The heavy investment of time and energy into making them reflects the value of figs and their seeds to a fig tree and begins to shed light on the reasons why we, too, should value the trees that we so often exploit and readily harvest. Possibly only when we remove ourselves from the lives of the common fig tree, considering the challenges of life from their perspective, may we begin to appreciate the process of producing figs, their value, and the trees that spend their lives producing them in the face of herbivory, disease, and parasites.
It is, therefore, more important than ever that we try to re-establish a healthy relationship between humans and these trees.
The fig production industry continues to grow due to the importance of figs as a dietary supplement for humans, particularly as they are one of the highest sources of calcium and fibres in plants. For this reason, figs will continue to be commercially valuable and in high demand. It is, therefore, more important than ever that we try to re-establish a healthy relationship between humans and these trees, harvesting them with more consideration and protecting them from being cut down. By creating this balance, figs can still provide huge nutritional benefits, but the species, and possibly its sacrality, can be protected for many more years to come.