Palm trees may be headed north to plant their roots in areas that have long been too cold for them, a recent study suggests.
An international team of researchers analyzed the relationship between temperature and the spread of palm trees across the globe. They wanted to determine how shifting climate zones will redistribute the plants, which is key for understanding how our ecosystems and landscapes will change over time.
They chose palm trees in particular because of their inability to survive in frigid temperatures.
“Palms are therefore sensitive indicators of changing climates, both in the remote geological past and in the present day,” study co-author and Brandon University researcher David Greenwood said in a release.
Though palm trees typically aren’t built for cold weather, a 2007 study conducted in the Swiss Alps found palm trees in the foothills of the mountains. It determined that the trees spread because frost isn’t as common as it once was.
“Our results strongly suggest that the expansion of palms into (semi‐)natural forests is driven by changes in winter temperature and growing season length and not by delayed population expansion,” wrote the scientists. “This implies that this rapid expansion is likely to continue in the future under a warming climate.”
According to the current study, palm trees’ distribution relies on the average temperature of a region’s coldest month. In order for the trees to survive, temperatures have to be above 36 degrees Fahrenheit.
As climate zones begin to move north, plant habitats might migrate with them.
“As an example, this means that at present, Washington D.C. is just a little too cold (34 degrees in January) for palms to successfully propagate in the wild, but that you can expect range expansion in the coming decades as average winter temperatures warm up,” study co-author and Lamont-Doherty Earth Observatory researcher Tammy Reichgelt said in the release.
The scientists also discovered that the palms’ evolutionary heritage also plays a role in their ability to tolerate different temperatures.
“If you find a palm fossil and can determine its affinity to a modern subgroup of the palm family, you can, using our data, determine the temperature of the climate of when that palm was growing,” explained Reichgelt.
When reconstructing previous climates, the presence of palm trees usually indicated warmer conditions. However, Reichgelt said fossils of the trees dating back more than 50 million years were found in the Antarctic, which suggests the region’s climate at that time was “near-tropical.”
Palms’ ability to withstand certain cold temperatures also differs across their organs and life stages, according to the study.
“Seedlings, in particular, (are) less tolerant of subzero temperatures than adult plants, limiting successful establishment of populations while permitting adult palms to survive in cultivation outside their natural ranges,” wrote the scientists.
Greenwood told Earther that parts of the north and areas close to Canada are nearing winter climates that could allow cold-tolerant plants to survive.
“In all of these areas, palms in people’s gardens are flowering and setting fruit, which means the temperatures are now warm enough for that step in their reproduction,” he said. “A little bit more warming will see their seedlings survive winters.”