Photo: Miguel Viera/Flickr
We recently learned how, as global average temperatures continue to rise, marine animals are migrating towards the poles in search of a habitat that they're used to—as scientists have predicted they would. Now, scientists from the University of Arizona have, for the first time, documented that mountain plants in the Southwest are too shifting where they grow, in response to today's warmer and drier conditions.
Since 1949, the mean annual temperature in the Tucson Basin has increase by 0.25°C per decade. By the end of this century, the Southwest is expected to warm by an additional 3-6°C.
The changes are easy to see, according to the report: "Even a casual observer could recognize the changes in plant elevation boundaries since the...surveys of 50 yeas ago, without so much as stopping the car as they drive up the Catalina highway. Large and conspicuous plants such as alligator juniper [pictured above], bracken fern, beargrass, and sotol simply do not begin to appear...until much higher elevations.
Photo: Wikipedia
Researchers looked at 50 years of data on the 27 most-catalogued types of plants that grow on Mount Lemmon, located outside of Tucson, and found that 75 percent of them have "moved their range significantly upslope." Some are now first spotted at elevations 1,000 feet higher than they were in 1963.
Interestingly, of the species examined in the study, 60 percent of them now grow in a more restricted elevation band than they used to. That is, they start at a higher elevation, but don't extend further up the mountain than before. Only four now grow higher than they used to, and eight actually have decreased their upper elevation, according to the report. Four of the species are now found at a greater range of elevations than they were previously—two expanding lower and higher, one up-mountain, and one slightly down-mountain.
Beyond confirming the hypothesis that plants will move higher in elevation due to climate change, the main takeaway from the research, the authors say, comes from the observation that the plants are all reacting differently. They aren't moving together as an ecological community, but rather moving independently, creating a new mix of plants at any given elevation.
As for the future implications of these migrating plants, the outlook is dire. "If climate continues to warm as the climate models predict," study lead author Richard Brusca said, "the subalpine mixed conifer forests on the tops on the mountains, and the animals dependent on them, could be pushed right off the top and disappear."