The mystery of the centuries-old oaks of Baja California Sur (and the secret to saving them from extinction)
They descend from ancestors who lived more than 50 millions of years and have faced all kinds of challenges.
But today they are still standing, only in one place on the planet.
In the Sierra La Laguna, in the state of Baja California Sur, in northwestern Mexico, is home to the only population of a species of oak known as encino arroyero.
” They are survivors, those trees are heroes “, Silvia Álvarez Clare, Costa Rican ecologist and director of the Global Program told BBC Mundo of Trees of the Morton Arboretum, a botanical garden and conservation center in Illinois, United States.
Mexico is the country with the greatest wealth of oak species in the world and many of them are threatened.
In the case of the stream oak, whose scientific name is Quercus brandegeei, the largest p The problem is that the species is not regenerating.
It is possible to find centenary trees, but there are no seedlings or “baby oaks” born from acorns, as oak seeds are called.
They are like “ a community of pensioners of encino brook, because we have not been able to find juveniles”, Álvarez Clare describes. “And in a healthy population of trees there are a lot of young individuals.”
A project promoted by the Morton Arboretum, together with Mexican scientists and local communities, seeks not only to solve the mystery of the oaks centenarians but to save this iconic and precious species from extinction.
Global but vulnerable
“In the world it is estimated that there are between 300 Y 600 species of oaks or oaks”, told BBC Mundo Maricela Rodríguez, Mexican botanist specialized in oaks and coordinator for Mexico and Central America of the Global Consortium for Oak Conservancy (GCCO).
Some scientists conservatively manage “a figure of 435 species, of which 168 are located in Mexico. That is, more than 37% meet in this part of the world”, he stated. Rodríguez.
“Other sites with a high richness of oak species are Southeast Asia, which is home to 140 species, while the United States reports 91 species”.
The Red List of Oaks, a study published in 2020 by the Morton Arboretum and the International Union for Conservation of Nature (IUCN), notes that at least a third of the oak species are in danger.
And about others 99 species there is not even enough information.
“I find it incredible. They are such rare, new or unknown species that we don’t even know if they are threatened or not,” said Álvarez Clare.
In In the case of Mexico, the Red List estimates that 30 of the oak species of the country are in danger of extinction. And one of the most threatened is the stream oak.
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A refuge in Mexico
How did this species of oak survive only at the end of the Baja California peninsula?
“Since its appearance about 55 million years, in the late Paleocene, the genus Quercus, which brings together all the species of oaks, has survived many biological and physical changes”, Rodríguez explained.
“Since then, climatic changes have caused population movements, expansions and decreases in their distribution, both latitudinally and altitudewise.”
Among the stones on the banks of the streams, the stream oaks found a sanctuary.
The closest relative of the stream oak is a species of oak called Quercus fusiformis, which is found in Texas, Oklahoma and northeastern Mexico.
“The creek oak probably had a more wide and took refuge like other species in the Sierra La Laguna; everything indicates that it is a relict species “, Mexican ecologist Aurora Breceda, a scientist at the Northwest Biological Research Center (Cibnor), who is part of the project.
The “relict species” subsist in their last strongholds and are true relics of the past.
Álvarez Clare affirmed that currently “there is only that relic of the historical distribution of stream oak that we calculate must have a total of less than 5, individuals, very restricted to only the shores of streams”.
Scientists believe that the species failed to adapt to changes that over millions of years created an almost desert climate in this region.
The habitat is so dry that many streams only fill with water from winter rains or intense hurricanes that create currents as powerful as ephemeral.
It is in the humidity of the sandy soil banks, on the banks of the streams of the Sierra La Laguna, that the stream oak found its refuge.
These oaks have ancestors that emerged ago 55 millions of years.
A haven and a resource
Quercus brandegeei is considered a key species for the ecosystem and is highly valued by the local population.
The stream oaks “are beautiful”, pointed out Aurora Breceda.
“Here in Baja California Sur, an area of scarce plant cover such as thickets arid, you have these huge trees”.
“A stream oak can measure 20 meters tall and have cups of 30 square meter. They are like a backwater”.
In the Sierra La Laguna reserve, cattle circulate freely.
Most of these scattered populations of oaks are found within the perimeter of the Sierra La Laguna Biosphere Reserve.
Biosphere reserves are spaces distinguished by UNESCO where biological conservation coexists with the cultural and economic development of local populations.
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The stream oak coexists in its home with humans and their cattle, which are allowed to roam the area freely .
Many locals report having lived with this species for generations.
“I remember my grandmother who used the acorns to make oil, tortillas,” said Rogelio Rosas López, owner of the Rancho Ecológico El Refugio. His grandmother recalled that with the seeds she also made atole, a pre-Hispanic drink consumed in Mesoamerica.
“And she would take us and pinch us because we had to gather sacks of acorns to give them to the pigs” .
The acorns of the stream oak are food for pigs and goats, as well as wild animals. Occasionally, if there is a fallen tree, the wood is used.
“ Much would be lost for the ecosystem if the oaks were not there, mainly the shade. We wouldn’t enjoy such a beautiful landscape,” assured Juan Refugio Manríquez Rosas, another member of the community.
“People would lose the best almonds or acorns, and everything from birds to raccoons and squirrels”.
Manríquez Rosas also reports that the flower honey of this oak, “a virgin honey of natural flowers” , is highly valued and has become a source of income for him.
The cows they are thrown in the shade of oaks and can crush seedlings.
The biggest enigma
Nobody knows exactly how old oaks are streams of the Sierra La Laguna.
“It really is a great mystery. We think they are definitely over a hundred years old. But they may have a hundreds“, Álvarez Clare pointed out.
It is expected that this year a team of scientists who are experts in dendrochronology, the science of dating trees, will reveal this mystery.
But the The greatest enigma is the absence of juveniles, something that has attracted the attention of local inhabitants for a long time.
“My grandfather used to say that there were many more trees,” said José Abelino Cota, owner of a land in the Sierra La Laguna. “It is very rare to see a new tree. I don’t know what it is due to”.
Explaining this lack of regeneration is vital.
Although oaks can sometimes reproduce asexually, producing underground stems with shoots that give rise to new individuals, this form of reproduction does not protect the future of the species.
It only creates clones of the same tree, without the genetic variability necessary to respond to drastic environmental changes or new diseases.
Only sexual reproduction, with small trees born from acorns, can save the stream oak.
The stream oaks can reach up to 20 meters of height.
In search of answers
Scientists explored several hypotheses to explain the lack of regeneration.
The first was the impact of climate change, which according to Álvarez Clare has caused “the dry season to be drier and hotter, and that the rains are more unpredictable in this area of Baja California Sur”.
The second hypothesis was the lack of viability of the acorns.
But a study at Cibnor showed the opposite.
“We collected seeds from various localities. At Cibnor we measured them, did their morphological study and put them to germinate. And they have a very high germination rate, more than 90% germinates”, affirmed Breceda.
The third hypothesis, according to Álvarez Clare, was the conflict with the cattle of the ranchers.
“We think that the cows are definitely a problem for the oak because they love to be in the shade and crush the seedlings”, he stated.
“And also the pigs eat the acorns”.
Biologist Daniel Wblesther Pérez Morales at Cibnor, during the study that demonstrated the high rate of germination of acorns.
For the ecologist of the Morton Arboretum, the mystery of the lack of regeneration of the stream oak continues and “has only been partially resolved“.
Scientists agree on the impact of livestock, but the consequences of climate change raise many questions.
“Climate change is indeed a problem, but how much and to what magnitude is something we are still not sure about”, he clarified.
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For Breceda, the big problem could be the changes in the temporal patterns of both rainfall and temperatures.
“We really don’t know if the effects of climate change could be causing variations in these seasonal patterns, which could be affecting the species. We do not know, a special study is required”.
Silvia Álvarez Clare collecting acorns (before they are devoured by the pigs).
“Let’s save the enino arroyero”
Although the precise impact of climate change on acorn germination is unknown, there is one thing that the project’s experts are certain about: the way to save these oaks lies in the hands of the community members themselves.
“The ranchers have a double function, they are part of the problem, but they are our only solution if we want to save the stream oak“, affirmed Álvarez Clare .
The scientists’ response has been to establish a tree care and adoption program with ranchers and other residents called “Save the andnino arroyero“.
The project is part of the Global Trees Campaign (Global Tree Campaign), an initiative to save the world’s threatened trees coordinated by the Botanic Gardens Conservation Association International (BGCI).
Abelino Cota is one of the members of the community who has planted stream oaks.
The idea is that local people plant, care for and “adopt” seedlings, becoming into guardians of the species, Mexican biologist and researcher Daniel Wblesther Pérez Morales, who leads the work with the communities, explained to BBC Mundo.
The residents will in turn benefit from the acorns and the other multiple services provided by these trees.
“I established We created a community nursery and propagated seedlings to plant new stream oak trees in the region,” said Pérez Morales.
The collected acorns cannot be stored in seed banks. As in the case of other species, the seeds of the stream oak do not tolerate being dehydrated and the best way to preserve them is for them to germinate and be planted.
So far they have been planted near 500 new trees with the help of the inhabitants of the communities.
“We plan to plant about 1,200 new oaks in the region. We will plant within the fences of the ranches to ensure that each oak is growing protected and well cared for,” added Pérez Morales.
“We will also plant outside the ranches in areas where there is less pressure from part of the predators. And with the help of the municipal authorities, we will plant in public spaces, where each planted tree has protection, care and its growth can be monitored.”
“An exchange of knowledge”
A workshop on the initiative “Save the encino arroyero” met at the end of 774 in the town of San Dionisio to scientists, local authorities, ranchers and other members of the community.
“It was a workshop where we co-constructed knowledge“, pointed out Breceda.
“Because it is not that the ‘wise’ scientists ‘ They are going to tell the local people what to do with something that has been theirs for hundreds of years, that grew with these trees”.
Scientists at the workshop in San Dionisio, including Daniel W. Pérez Mor ales (second from right), Silvia Álvarez Clare (seated, second from left) and Aurora Breceda (seated, last from right).
The workshop was, according to Pérez Morales, “an exchange of knowledge”. Local people know better than anyone the best places to plant. And they know that without their help, in an increasingly dry and unpredictable climate, it will be very difficult for the oak to survive.
“It is important that we ranchers give ourselves the task of taking care of these spaces, of watering the trees until they are at least two years old,” said Rogelio Rosas López.
It is planned that in 2022 more workshops are held and the first Festival del Encino Arroyero is held in San Dionisio.
The idea is also to promote other activities that are a source of income, including ecotourism and artisanal products such as mango jelly or damiana drink, another local plant.
Clinging to life
The stream oak project shows how complex, and adapted to each case, is the task of saving endangered species.
“The work has not been easy since the results of these efforts are not immediate and it must be understood that they will be seen over longer periods. However, we are on the right track”, concluded Pérez Morales.
“If this species disappears it disappears from the face of the universe known”, said Breceda.
Noelia Álvarez de Román, director of conservation for Latin America and the Caribbean of the BGCI, told BBC Mundo that “the conservation project for Quercus brandegeei has resulted in important advances in knowledge of the species and its threats, dissemination of the importance of its conservation and increased capacities of local collaborators”.
Aurora Breceda summarizes what is at stake as follows: “If this species disappears, it disappears from the face of the known universe.”
“And on the other hand we lose the possibility of sustainable resources for the rural populations of the south, for which I have enormous respect and admiration”.
Silvia Álvarez Clare never ceases to be amazed that “currents, storms, hurricanes, droughts happen to these oaks and they are still clinging there, producing their acorns, providing shade, cleaning the air, giving life“.
“Really when I am next to one of those trees, I touch the trunk and say, thank you!”
“The creek oaks have been there much longer than us,” said the ecologist of the Morton Arboretum.
“And we want to guarantee that they are there for our children and our grandchildren, that they can have the shade of that wonderful tree that our grandparents had”.
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