Island Trees Have Nowhere to Run From Climate Change
By Marlene Cimons
Kyle Rosenblad was hiking a steep mountain on the island of Maui in the summer of 2015 when he noticed a ruggedly beautiful tree species scattered around the landscape. Curious, and wondering what they were, he took some photographs and showed them to a friend. They were Bermuda cedars, a species native to the island of Bermuda, first planted on Maui in the early 1900s.
"Sometimes, island species are transported by humans outside their native islands — either to a mainland continent or to another island — and manage to survive in the wild there, as the Bermuda cedar has done on Maui," said Rosenblad, a research associate with the Sax Lab at Brown University's department of ecology and evolutionary biology.
He had never been to Bermuda, but suspected its climate was different from Maui's. "Then it hit me: if my suspicion was correct, then this species, by succeeding in Maui's climate, was effectively showing us its biological buffer that might help it survive future climate change," Rosenblad said."However, we still didn't know whether this buffer would be wide enough to accommodate the changes in climate expected to occur on Bermuda."
In other words, the Bermuda cedar could cope with life on Maui, but that doesn't mean it could cope with life in Bermuda later this century.
A Bermuda beach
Existing research shows that island species are less diverse than their cousins on the mainland. That lack of diversity makes them vulnerable to changing conditions. On an island, for instance, every member of a particular tree species might be suited to cool weather, whereas on the mainland, some are suited to the cold, while others are built for the heat. If temperatures rise, at least some of the mainland trees, those built for warm weather, might endure, but the island trees could perish.
"If climate change makes a given island too warm for the species that live there — or too dry or too stormy — then those species will be stuck on their island with nowhere to escape," Rosenblad said.
Rosenblad and his colleagues — Dov Sax, head of the Sax Lab, and doctoral student Daniel Perret — investigated the dangers that climate change poses to island species by studying conifers, a group that includes cedars, firs and pines. "When unique island tree species are given a chance to grow outside their native islands, how much extra climate hardiness do they show?" Rosenblad said. "And will that extra hardiness be sufficient to help them survive predicted future changes in climate?"
Branches of a Bermuda cedar
What they found was troubling. Their work suggests that climate change could push many small island conifers — nearly a quarter of those they studied — into extinction by 2070. The smaller the island the more danger, as trees have nowhere to flee. The larger the island, the more varied the climate, meaning species can relocate to cooler areas. Their research appears in the journal Nature Climate Change.
"Our results took us by surprise," Rosenblad said. "We expect if these species are left to fend for themselves, climate change will eventually drive them extinct."
Species can adapt to new conditions, but climate change will make that difficult. "The rub is that for some species, the amount of hardiness and adaptability they have shown is still not enough to buffer them against the changes in climate that are expected to occur on their native islands," Rosenblad said.
Canary Island pine trees, one of the conifers used in the study
So, while the Bermuda cedar may thrive on Maui, adapting to the future climate of Bermuda "will require an even bigger stretch," he added. He added that while the Bermuda cedar is surviving in many different places, "sadly none of them has a climate that resembles the one that Bermuda is projected to have in 50 years." That being the case, he said, "we still don't have any evidence that it can handle the climatic changes that are expected to occur on its native island."
The scientists urged caution in interpreting the findings, as species might be hardier that the evidence suggests. "However, I still find our results highly concerning," Rosenblad said.
In conducting their study, the researchers relied upon data obtained from global digitized plant specimen collections. Focusing on 55 species of coniferous trees, they cross-referenced information about them with existing worldwide climate statistics to determine the climate conditions, such as temperature and precipitation, at each location where their study species were found, including their native islands and other sites. They then built computer models for each species which told the researchers how the species would fare under different combinations of climatic conditions, including climate conditions projected for their native islands in 50 years.
Norfolk Island pines, one of the conifers used in the study
Researchers said many island tree species likely will require "serious help" withstanding climate change. "Failing to provide this help could have dire consequences, not just for the tree species themselves," he said. Trees perform essential functions, he explained, "like helping to regulate the flows of water and nutrients through the ecosystem."
Researchers called for targeted conservation efforts to avert extinction. Moreover, many of these trees also are culturally significant to island residents, especially the Bermuda cedar.
"It remains an indelible Bermudian cultural symbol," Rosenblad said. "Its wood has long been prized by artisans and builders. There is even a Bermudian wedding tradition, in which the cake is presented carrying a cedar seedling on top, and the couple then plants the seedling together."
He added, " It's important to underscore the beauty of these trees — and help them avoid extinction — so future generations can benefit from all they have to offer."
Reposted with permission from our media associate Nexus Media.
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Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:email@example.com" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
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