Losing the small, fragile flora may have impacts on water sources worldwide
Alpine plants, fragile and adapted to live in a limited ecosystem, may be the canary in the coal mine of climate change.
Alpine plants face a number of threats: Recreation (trampling and disturbance via hiking, mountain biking and snowmobiling), construction and mining.
The leading threat to alpine plants, however, is climate change.
"Which is, of course, the threat that is the hardest to combat," said Emily Griffoul, a conservation scientist at Betty Ford Alpine Gardens, the highest-elevation botanic gardens in North America.
The alpine zone has "a really strict definition, which is everything above tree line," Griffoul said.
In Colorado, that line is drawn around 11,500 feet, but it varies around the world depending on temperature -- in warmer locations near the equator, the tree line might fall around 13,000 feet.
This is because trees need to do a lot of photosynthesis to grow, and photosynthesis is not as efficient at temperatures below 40 degrees Fahrenheit. In locations with fewer days above that temperature -- a shorter growing season, "you're just not going to get the volume of tissue that you need to build something like a tree," Griffoul said.
Within just a six-week growing season in Colorado, alpine plants need to produce flowers, produce pollen, get pollinated, produce seed, ripen the seed and then release the seed.
The alpine environment also has high UV radiation and high, desiccating winds, both of which make it challenging to sustain life.
But plants that live in alpine zones have developed adaptations that allow them to grow under these conditions.
For one, alpine plants grow slowly over a long period, making them tiny but long-lasting.
"They might only be putting on a little bit of tissue each season, but they're still going to grow for a long time," Griffoul said.
Another adaptation some alpine plants adopt is to preform their buds. Then, when the weather warms enough to put out leaves and flowers, the plants can start photosynthesizing immediately and take advantage of any pollinators that might be out.
Alpine plants will also often have big flowers compared to the size of the rest of the plant.
"It's almost cartoonishly funny, where you'll have like a really small plant, really short, small leaves, and then just giant flowers," Griffoul said. "It's really beautiful and really cool."
Some alpine plants also have adapted to sport fuzz, which looks similar to hair, which functions as sun protection and breaks up the drying winds, preventing moisture loss.
Many alpine plants also have a long taproot, the dominant root from which all others grow, both anchoring the plant against wind and shifting snow and allowing it to access water buried deep in the soil.
For plants living in environments with short, cold growing seasons, any variation in climate is significant. Even just a handful of days on either end can expand the six-week growing season by a quarter.
"We know that alpine environments across the globe are warming faster than other terrestrial ecosystems," Griffoul said.
Warmer temperatures sound, in theory, like a good thing for plants. But alpine plants are already adapted to their harsh environment. "If that environment changes, what are they going to do?" Griffoul said.
Obligate alpine plants can only grow under the harsh alpine conditions. As temperatures warm and growing seasons lengthen, these plants will migrate upward, toward conditions they know. But there is only so far up these species can travel before they run out of room.
Other alpine plants may be able to adapt to gentler growing conditions.
"They actually do great. They often get much bigger, much quicker. They flower earlier, sometimes they'll have a second flowering," Griffoul said.
But these plants will often be outcompeted by their better-adapted cousins.
"The reason that alpine plants don't live below tree line, even when they obviously could and could thrive below tree line, is because of competition," Griffoul said.
Plants that live below tree line tend to grow faster, allocate resources more quickly, germinate more quickly and have more efficient reproductive systems. As the alpine warms, these plants will move up, using their better-adapted skills to outcompete the alpine plants for water and space.
With climate change, precipitation levels will also change. The fluctuating precipitation that accompanies climate change can significantly impact alpine plants' seed production. In a dry year, some alpine plants will make no seeds at all.
An additional climate change-related cause for concern is the potential for tropic asynchrony. While plants rely primarily on temperature to decide when to flower, pollinators often rely on both sunlight and temperature.
If the weather becomes warmer earlier in the year, plants may flower before there are any pollinators around, because the same date each year will have the same amount of sunlight but could have a dramatically different temperature.
"That can be especially devastating in an ecosystem where the growing season is so incredibly short," Griffoul said. "There aren't that many days available to do any of this pollination and fertilization."
The first argument for the importance of preserving alpine plants is their intrinsic value. "This is part of our natural heritage," Griffoul said.
But the plants are also a crucial part of the water system. "Plants and the water cycle are inextricably intertwined," Griffoul said.
Alpine environments and high-elevation environments serve as a water source for a significant percentage of the human population. Around 2 billion people worldwide depend on snow melt or glaciers for their water. "Changing any of these patterns in water availability matters to people," Griffoul said.
Lower elevation plants tend to be bigger and grow faster than alpine plants, with higher rates of transpiration, or using and releasing water into the atmosphere. The amount of water that ends up downstream is based on how much transpiration is happening at the top of the mountain, where snowmelt begins.
As alpine communities change to favor lower-elevation plants, the amount of water available for downstream users will likely be reduced.
While the timeline at which climate change impacts on the alpine will concretely occur is unknown, Griffoul said she has already seen one lower elevation species creeping its way into the alpine: Willow shrubs. Unlike their alpine cousins, which are mat-like and measure a couple of centimeters tall, the shrubs will use more water and create shade that steals sunlight from the smaller alpine plants.