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Industry or inter-species mutualism? Cork trees & humans

When we think of domesticated birds, servile, passive poultry come to mind, yet our pre-Neolithic ancestors may have collaborated with animals and plants (including birds) without entirely domesticating them.

To illustrate our point, let’s consider an ancient foraging activity, “hunting” for wild honey. Honey collection is an activity so ancient that it predates, by far, the domestication of honeybees, a more recent event first documented in ancient Egypt.

Foraging activities like honey hunting aren’t only immemorial, but we may have improved our “honey hunting” with the help of birds, which in return could get their own grubs and beeswax reward, as some current anthropological evidence suggests.

Humans perfected the domestication of several species of plants and animals during the first Neolithic revolutions 12,000 years ago. But what about most of the human prehistory? Before the arrival of agriculture and animal domestication, hunter-gatherers had already established mutualistic relationships with animals and plants that remained wild, although they evolved in close relation with humans.

Our lost relationship with wild animals (and trees)

In a mountain valley cave near the town of Bicorp (Valencia), on Spain’s Mediterranean coast, archeologists found, amid other schematic Iberian paintings from the region’s Mesolithic period around 8,000 years ago, a painting depicting a honey seeker. The human figure is climbing a tree to get to a round honeycomb amid flying bees while carrying a basket and seems ready to collect the sweet bounty.

This remote portrait of ancient casual “honey hunting” appears among other depicted everyday survival activities, from foraging to the hunting of megafauna. Still, the evidence of human impact in shaping the landscape of regions like Iberia before Romanization is spotty and depends on the interpretation of archeological remainings, despite the efforts of structural anthropology to underline the cultural relations that link current or recent landscapes and cultures with their ancient versions.

When we think of ancient ecological interaction with trees in thriving ecosystems, such as cooperation or symbiosis between different species, we consider the vital ecosystem cycle guaranteed by the subterranean collaboration that reinforces fungi and trees’ root systems, thanks to their connection with immense networks of mycorrhiza. The colonization of land by plants relied on this ancient relationship.

“Man of Bicorp”: human figure gathers honey from a beehive as depicted on an 8000-year-old cave painting near Valencia, Spain

Yet trees have also benefited from their relationship with pollinizers (birds, insects) and even mammals. But we don’t seem to be ready to include ourselves in this group of mammals engaging in biological mutualism with plants way before plants’ domestication in agricultural societies: large portions of the Amazon rainforest are the result —a new hypothesis states—of millennia of human impact (and management): rather than a pristine wilderness “untouched” by man, the Amazon itself is the outcome of thousands of years of forest gardening, as the fertile soil of human origin “terra preta” shows, a consequence of big-scale slash-and-char agriculture.

The education of the honeyguide

On the other side of the Atlantic, there’s evidence that pre-Roman peoples inhabiting long stretches of southwestern Europe such as the Tartesians, as well as pre-Celtic and Celtic tribes such as Lusitanians and Vettones, used the renewable bark of Quercus suber, the cork trees native of the region before the advent of the neolithic revolution. In this part of the world, forest management took a different route, and the trees and vegetation that thrived, such as Quercus suber, did so due to their resilience and valuable properties.

Ancient use of the cork tree suggests an intentional landscape transformation to harvest its bark; in exchange, the tree benefited from the proliferation of its habitat across the arid areas of the southwestern Iberian Peninsula. There is evidence of early use of cork as floats for fishing nets, sandals, plugs for jugs and barrels, insulation against rain and fire, and beehives.

For the sake of keeping this story’s sweetness: archeological remains found in the Caucasus region show honey remains in clay vessels dating back at least five millennia, though our predilection for the sweet substance may not have evolved as a purely human activity, after all. For at least thousands of years, humans developed early collaborations such as the ones observed with honeyguides (birds helping humans to get to beehives), other bird species (peregrine falcons, eagles), and mammals (canids, felines, tarpan horses) for hunting or as a method of controlling pests with the rise of husbandry.

Such honey vessels could have been like those depicted in the hands of the anthropomorphic figure in the Mesolithic painting from Valencia. Yet it could have been made of a lighter, sturdier, more flexible, and fire-resistant local material: cork. As of today, there’s no archeological evidence of the use of cork (or other plant-based, heavily biodegradable materials) containers in pre-Neolithic Iberia.

A very special bark

An ancient renewable material, cork has attracted attention as a material with a promising future way beyond its traditional applications in the wine and construction industries. Some of these applications don’t follow industrial or high-tech narratives but develop relationships resembling biological mutualism: instead of developing monocultures of raw materials, cork oak forests are drought-tolerant and have insulation properties adapted to the southern Iberian Peninsula, including a heavy, light bark that produces a fire-retardant natural coat, protecting the tree (or any cork-clad human-made surface, like ancient Iberian beehives) from fire.

The ancient relationship between humans and Quercus suber tree species may not be considered early agricultural domestication nor an ancient, prehistoric version of silviculture, though it may have equally benefited the species, which expanded across the European southwest and local tribes.

Traditional cork beehive, used across the Westen half of Iberian Peninsula: this one comes from Olivenza, an Extremaduran town in the border between Badajoz province and Portuguese Extremadura

If recent studies associate the early domestication of dogs with hunting strategies across human groups surviving the Ice Age across Eurasia, there’s living evidence of our ancient relationship with birds to master foraging techniques and benefit all parts involved.

Unlike early agricultural societies, which developed cultural ways to increase mutualism with wild animals and plants to reach domestication to the point of transforming the species, hunter-gatherers practiced loosened strategies to guarantee abundance in their environment, using tools such as fire or inter-species collaboration, for example, spread the availability of wild edible tubers in Australasia or develop semi-domestication and husbandry of reindeer, bison, aurochs, and other species in Eurasia and the Americas.

But, when this relationship evolved with plants (or fish, insects, etc.) instead of the highly symbolic megafauna, the bonds created for the mutual benefit of participants may be considered arbitrary. If it wasn’t domesticated, we seem to assume, it lacks any relationship with any human culture worth exploring. Hence biological mutualism with humans, a more subtle relationship between our species and “undomesticated” species, may explain, at least in part, the lack of scientific interest in biological mutualism between humans and other species.

Us and the perceived “wilderness”

Until 12,000 years ago, all humans practiced hunting-gathering: hunting, fishing, and looking for wild vegetation and nutrients like honey has been the main reality of our species until recently, and, despite having lost most of the knowledge regarding ancient survival strategies, we live in the false dichotomy that our surrounding world is either heavily shaped by human action since the neolithic, or a part of “the wilderness.” Yet archeological evidence suggests that regions we associate with primeval landscapes, such as the Amazon Basin, are in part a byproduct of ancient human action.

The Hadza, a surviving tribe of hunter-gatherers living around Tanzania’s lake Eyasi, abandoning traditional methods due to a growing relationship with modernity, includes a minority still living off foraging and little prey, their diet consisting of a mix of tubers, meat, fruit, and a relatively big amount of wild honey, explains anthropologist Frank W. Marlowe.

We may think collecting wild honey is a tricky, if not nearly impossible, the main source of calories; not to the last human groups using birds to find honeycombs. To collect wild honey, the Hadza must find wild hives located out of reach in towering trees such as baobabs. To do so, they have developed a mutualistic relationship with a small local bird that serves as a “honeyguide.” Honeyguides like grubs and beeswax, so when the Hadza look for honey, they whistle a special tune that will attract members of that bird species.

Following the honeybird, they wait for it to land near a beehive. Then it’s time for the Hadza group to smoke out the bees and get to the honey. The honeyguide watches the process and waits patiently for the moment when he can gather the remaining beeswax. The relationship between the remaining local traditional gatherers and honeyguides is so fruitful to Hadzas that, according to Yale’s biological anthropologist Brian Wood, between 8 and 10 percent of their diet depends on the collaboration with the bird species.

Foraging collaborations

Hadzas’ relationship with honeyguides is complex and doesn’t depend on a series of predetermined interactions but evolves depending on the context: sometimes, Hadzas will bury part of a honeycomb to prevent a bird from getting a disproportionate bounty of grubs or wax to guarantee that their partner will be up for the foraging collaboration the next day. The tribe’s mythology includes stories and songs in which their traditional bird guide behaves as a trickster, demanding special abilities from the human side of the relationship that can only replicate if the bird stays hungry enough to persevere the next day.

The alliance between the Hadza and the honeyguide isn’t equitable mutualism, but a skillful manipulation that could be considered, to some extent, certain domestication, or according to a description of such asymmetrical mutualism by Brian Wood in a paper he published in 2014, it consists of “an act by partner A that causes partner B to alter its behavior in a way that is beneficial to A and marginally costly to B.”

The observed mutualist relation among the Hadzas and honeyguides was once a broader foraging strategy documented across sub-Saharan Africa, though it could have traveled with human populations to other world regions, adapted to other climates, animal species, and mutualism relationships.

Mutualism refers to an interaction between two or more species where each of them has some sort of benefit, unlike situations that have evolved to the point that a relationship benefits only one partner (parasitism) or either habitat transformation or extinction forces one partner to either abandon the old mutualist practice or switch species or develop an autonomy that is a consequence of the extinct relationship.

Floating Gauls invading Rome

Across regions in Western Eurasia and Northern Africa, the Mesolithic (or the long transition between hunter-gatherer cultures and the Neolithic Revolution) saw the development of pottery, construction techniques, better tools, and more elaborated ornaments. Could the use of cork have expanded then? Roman chroniclers mention the use of cork for beehives, but such applications could have begun much, much earlier.

Early Mediterranean civilizations, from Phoenicians to Greeks and Romans, used cork to keep their bottles sealed; Iberians and Celts were probably doing so at the same moment, if not earlier. After barely escaping from a falling tree, Horace celebrated:

“Corticum abstrictum pice demovebit amphorae… (Pull the cork, set in pitch, from the bottle)”

The process was lost with the fall of Rome, then perfected again in the 1600s by French Benedictine monks. Yet other uses of cork were widely shared across Europe and the Mediterranean in Antiquity. In A.D. 100, Plutarch wrote about the siege of Rome by the Gauls in 400 B.C. The invading tribes used a curious rapid deployment technology to cross the Tiber River: men used cork buoys to ease the last dangerous obstacle they had found before reaching their bounty.

Iberian Lynx

Pliny described the bark of Quercus suber in his Natural History, A.D. 77:

“The cork oak is a small tree, and its acorns are bad in quality and few in number; its only useful product is its bark which is extremely thick and which, when cut, grows again.”

If cork oaks are making a comeback, it’s because of their multifaceted nature and characteristics: they sustain healthy, diverse forests that are proven more resilient to droughts, fires, and extreme temperature events than the monocrop species that were presented as alternatives decades ago, such as Douglass pine trees and eucalyptus forests to feed the local paper factories in Portugal and Galicia (northwest Spain).

Cork beehives on Iberian fields

Unlike forest monocrops, planted in substitution of more diverse forests and more prone to wildfires, cork trees remain relevant not only to the local ecosystems they reinforce but stay useful to local human communities by providing an average of 15 cork harvests from the moment they become mature at 25 years, to the moment they slow their bark regeneration capabilities at 150 years of life. Cork extraction is a cultural process that involves intergenerational human planning: the time in between extractions is close to a decade: its timing seems to fit mentalities at odds with contemporary society.

Cork has a long past, but it’s also a living part of rural Iberia. As a kid, we’d travel every summer several hundred kilometers from Barcelona to a forgotten corner in the very rural Sistema Central, a mountain range dividing the Meseta, a highland region that elevates the Iberian Peninsula’s interior, between the two main rivers flowing westward, the Douro and the Tagus.

I still remember visiting some fields in which old farmers kept what seemed bare tree stumps on the side of fields. Later, I learned they were cylindrical beehives made of local cork because of the material’s low heat conduction, among other properties. I remember asking why they had such a shape so similar to tree stumps, and the answer included my question within: traditional cork beehives were assembled out of already two rounded bark sheets of the tree joined together, using cork to cover the top and bottom, secured with long wooden nails made of local shrubs.

Old mutualistic relations between local cultures and species such as cork trees could inspire future applications and habitat improvements based on the proliferation of forests rich in Quercus suber (ideal habitat of the endangered Iberian lynx and the use of their renewable bark, whose quality improves after their original bark is extracted).

Restorative projects

Like rubber trees and maples, among other tree species that provide a sought-after product and can also remain a fundamental part of healthy forests in their natural habitat, cork is making a comeback in southwestern Europe: its forests provide natural protection against fire hazards near villages and reinforce the health of local forests affected by eucalyptus plantations, especially pervasive in rural Portugal as they provided a quick income and little maintenance requirements to small land owners.

Take, for example, Pedro Pedrosa’s volunteer work to protect the small Central Portugal village of Ferraria de São João from the increased fire hazard that represents the nearby eucalyptus plantations: with the help of neighbors in town, the Pedrosas have expanded the already existing perimeter of cork trees between the village’s meadows and the nearby hills. His effort is an important part of a project of rural restoration that also involves attracting young families committed to rural life in the era of remote work.

Yet mentalities are evolving, and newer generations are beginning to warm to the idea of helping with the expansion of habitats that are also “slow” industries yielding fruits across spans comprising several generations. During the 150-year cork harvest lifespan of Quercus suber, landscapes can experience dramatic evolutions. Maybe for the better this time.

A Portuguese saying captions the mentality shift:

Quem pensa em si planta um eucalipto.
Quem pensa nos filhos planta um pinheiro.
Quem pensa nos netos planta um sobreiro.

Who thinks of himself plants a eucalyptus.
Who thinks of his children plants a pine tree.
Who thinks of his grandchildren plants a cork tree.