17 June, 2001
Plant day on the tundra.
Erika and I went out with Bob Hollister this AM to learn and practice plant identification. Bob, from U. of Michigan, is completing his PhD thesis with data gathered here at various sites around Barrow for the past few years. He is extremely knowledgeable about the tundra's vegetation and helped us out with names and characteristics.
The tundra ecosystem is characterized by short, fast growing, cold tolerant plants, which survive on a limited water supply. The Arctic tundra is really a "polar desert" and the vegetation here is well adapted to the rigors of extreme temperatures, a short growing season (8 weeks), shallow, nutrient poor soil and limited amounts of water. Most of the northern arctic region receives approximately 10-cm. of precipitation per year, mostly in the form of snow. When the snow melts, during the spring and summer months, the tundra turns into marshes and flooded areas but the permafrost layer prevents the water from infiltrating deep below the surface. This layer (permafrost) is what causes the surface pools to form and prevents the surface melt water from draining away.
Only 5% of arctic plants biomass is found above ground with the remaining 95% below the surface, consisting of roots and rhizomes (root stocks which grow horizontally under ground sending shoots up) thus giving the false impression that the plants are small and scant. Plant photosynthesis, or growth, occurs very slowly here, as does decomposition due to extremely low temperatures. Dead material from last season's plants accumulates but does not breakdown so what you see on first looking out on the tundra is a thick carpet of brown grasses. One has to look under this, on your hands and knees, to get a real picture of what is growing here.
Most plants of the tundra have been thought of as a major sink (absorber) of CO2 from the atmosphere. Carbon is taken in by the plants during photosynthesis, growth phase, and O2 is released. This carbon is stored in the growing tissues as well as the dead matter and in the soil, which is mostly peat. Below the surface, roots and rhizomes also are growing and the CO2 / O2 gas exchange is occurring underground. In the winter when the permafrost extends to the surface, this gas exchange cannot take place because the pore spacesin the soil are filled with frozen water. In the summer when the permafrost prevents water drainage, liquid water fills in the pore spaces and gas exchanges are also stopped. It is not just cold temperatures inhibiting photosynthesis from occurring but also, and sometimes more importantly, the thaw depth, which controls gas exchange, hence plant growth in the tundra. Soil moisture is an important variable when study vegetation here.
Most of the year soil bacteria and other decomposing agents are not very active due to the low temperatures and permafrost depth, so the life cycle of plants on the tundra progresses at a slow pace, over tens and somtimes hundreds of years, rather than seasonally as in more temperate or tropical regions.
The nutrients, in the form of minerals, which plants need to grow, are also in short supply. When vegetation breaks down slowly as it does in the north, the cycling of plant nutrients, especially nitrogen, is also delayed thus limiting the growth cycle of new plant life. With all these factors effecting growth one can begin to understand how fragile the ecosystem is.
The main groups of plants that successfully exist here are rushes, sedges, grasses, mosses, liverworts, fungi and a small number of flowering, vascular plants. Each has developed adaptations that enable them to survive. One adaptation they have evolved is connected to their physiology. Chemical processes have developed which enable the plants here to continue to grow even in cold weather. There are times in the growth period when the temperature, especially with wind blowing, drops below freezing. With such a short growing season the plants cannot afford to loose hours or days going dormant. These chemicals keep the plants photosynthesizing rather that going dormant. A short growing season also has provided for the development of more adaptations. Many of the plants leaves are green all year or at least semi-green. Thus the plants don't waste any time at the onset of their growing season developing new green leaves in order to start photosynthesizing but start the growth process at the moment the sunlight hits them. Most arctic plants are perennials, plants existing for more then one growing season. They are able to progress through their stages in spurts and carry on the following year where they left off the previous year. There are a few annuals here and their life cycles are stretched over two years, one year to flower and the next to set seed.
The tundra landscape provides a number of different microclimates. Some plants are suited to grow on the tops of ridges where it is windy, cold and dry, other plants are suited to grow in between hummocks where they are protected from wind but have more water available, and depending on the direction the plant is facing different water and soil conditions exist. This increases the number of different species the tundra can support.
One thing that all plants here have to adapt to is the nutrient poor soil. Some plants have devised ways to catch dust parcticles floating in the wind to help them increase their nutrient levels. Larger leaves and furry edges and stems aid in this endeavor.
The pictures below are a small sample of the plants I have come across and am able to identify. I will be adding to these as the season progresses. The buttercups pictured a few days ago are some of the first wildflowers to appear early in the season. As I see more I will include them for you. ---------------------------------------------------------------------------------------- ----------------
Read A Naturalist's Guide to the Arctic by E. C. Pielou , University of Chicago Press, 1994. This book is a great comprehensive introduction to the many plants, animals, insects, landforms and processes occurring in the Arctic tundra. Much of the above information was taken from this book.
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