By Dr. David Wartinbee, for the Redoubt Reporter
The earliest flowers appear at our house in the rock garden. It is perhaps the prettiest garden at our house, and my wife claims it is the easiest to take care of. There are no shortages of rocks in our area and just about every business that sells plants here in Alaska will have a couple species that are appropriate for growing in rocky, well-drained soil. There are rock-garden enthusiasts all over the world, and there is an active and particularly knowledgeable group here in Alaska (visit http://www.args.com for more information).
As a graduate student I spent considerable time in alpine communities of Montana and Wyoming, and I always marveled at the miniature plants that were found way above tree line. They were often very small with seemingly giant flowers. Most interesting to me was that these plants were growing in some of the worst soil possible and in some of the most challenging physical conditions one could imagine.
These plants were exposed to intense, ultraviolet-rich sunshine in the summer months, high winds year-round, frequent dehydrating conditions, freezing conditions almost every night, and then long winters of snow cover and below-zero temperatures. Yet they survived the harsh environment and held onto their precarious foothold among the talus-strewn mountains.
Because of the poorly developed soils and harsh physical conditions, these alpine plants use an array of methods to survive. Most alpine soils have little organic material and usually contain few of the essential minerals, like nitrogen, phosphorous and potassium.
In some cases, the only soil available is wedged into a crack in a rock and that is enough for a tiny plant to prosper. To access the needed minerals, many alpine plants have long taproots that reach down to places where moisture and some basic minerals can be found. Interestingly, these long roots then provide some physical stability to the talus or scree materials of the soil.
Alpine areas are windblown on a nearly continuous basis. Because of abrading wind, alpine plants are always short in stature with many only reaching a few inches above the ground. The only place any plants can grow taller is where they are protected from the wind on the lee side of a rock or boulder. If you find yourself in a windy situation, lie down and notice how much less wind there is closer to the ground. There is a strong selective advantage to being short when you are a plant living at high elevations.
As an example of this wind avoidance, there are woody plants, like birches, azaleas and rhododendrons, in alpine habitats that are only a few inches tall.
Another example of the stunting effect of the wind can be demonstrated with Labrador tea (Ledum groenlandicum). This
plant, with thick, leathery leaves, is commonly found throughout the wetlands of the Kenai Peninsula and is usually 18 to 24 inches in height. When it grows in alpine areas, it may only be a couple inches tall. Taller plants would simply be blown over and broken by strong gusts of wind.
Perhaps one of the most interesting permutations of wind avoidance is the cushion-shaped growth form. Right in the middle of a barren talus slope can sometimes be found what looks like a miniature putting green that is only a few inches in diameter. This mat-shaped mass of individual plants may rise less than an inch above the gravelly soil so the tiny photosynthetic leaves are out of the wind. Several saxifrage species grow in low mats that can cover and hold onto surrounding rocky debris. While some cushion-forming plants produce their flowers right on the smooth cushion surface, others like the Saxifrage send up stiff stems a few inches above the cushion mass with a single flower on top.
Another hardship of living in the alpine is low temperatures. Even during summer months, many alpine areas drop below freezing each night. When water freezes within a cell, ice crystals expand and puncture the plasma membrane, which causes the cell to die. This same process is what happens when skin freezes and we get frostbite.
One way to avoid ice formation is to increase the solutes dissolved within the fluids of plant cells. Some plants increase the internal concentration of salts or form organic molecules like sugars or alcohols within the cells. These extra dissolved molecules cause a lowering of the freezing point, just like antifreeze prevents ice from forming in an automobile radiator. Another way to protect the individual plant cells is to force excess water from the cell and store it in noncellular areas. This lowers the freezing point within the individual cells, and if ice does form in the exuded water, no cellular damage results.
While one might not expect this to be a problem, many alpine areas are quite dry. So, the ability to conserve or store water
is an adaptive advantage. Some alpine plants have special leaves that enable them to store water. Other plants have waxy cuticles on their leathery leaves that prevent water loss. While this may seem more appropriate for desert plants, remember that many alpine communities, like much of Alaska’s Brooks Range, may only receive a dozen inches of rain all year.
Alpine plants reproduce sexually and asexually. The majority are perennial plants and many can survive an entire season without much growth or an opportunity to flower. And many of these plants can easily reproduce from fragmented roots. Members of the genus Sempervivum, sometimes called “mother and chicks,” have the ability to form small clonal structures (chicks) that can separate from the parent plant and begin growth on their own. Sometimes these spherical clones become dislodged, roll away from the parent plant and form a new colony wherever they end up.
Even though asexual reproduction seems to be the most successful means, the variety of flowers produced by alpine plants during sexual reproduction is impressive. Often the showy flowers are disproportionately large compared to the visible leaves. Flies and solitary bumblebees are the most common pollinators for alpine plants, since honeybees do not often venture to the alpine. When seeds are produced, the wind is the obvious means of dispersal.
Because these alpine plants are only able to survive in very specific microclimatic areas, they are essentially isolated from other members of their populations. Additionally, because the mountain ranges where these plants grow are widely separated from one another, there are lots of endemic species. The beautiful blue gentian species we find in Alaska alpine communities are noticeably different from the gentians found in the Rocky Mountains and those found in the European Alps.
The great variety of alpine plants and, of course, their beautiful flowers, make them the darlings of rock-garden enthusiasts of the world. Because they normally thrive in harsh conditions, growing them may be counterintuitive for many gardeners. As an example, the beautiful alpine flower Lewisia rediviva is the state flower of Montana. I found instructions about growing this plant that warn about overwatering or providing soil that is too rich.
If you choose to experiment with rock-garden plants, remember that they are actually alpine plants and prefer well-drained and rocky soil. They can withstand harsh temperatures, they like bright light, they don’t need much fertilizer and they don’t have to be watered very often. This is my kind of gardening!
Now is the time to visit the high country and see these beautiful alpine flowers. There are many local places to get above tree line and many alpine flowers are currently blooming. A few easily accessible areas are Hatcher Pass, most areas along the Denali Highway, and Glen Alps or Flattop Mountain in Anchorage. For those willing to hike a little, there are any number of local trails, like Skyline Trail, that will get you above tree line and surrounded by alpine plants.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.