Introduction and Site Description 49 



The brown lemming is the dominant consumer; their numbers 

 increase from less than 1 ha"' to nearly 200 ha"' every 2 to 5 years. In 

 "lemming high" years their impact on the vegetation is startling; they 

 reproduce beneath the snow cover and completely cut all standing plants 

 during the winter. Their consumption of the annual primary production 

 varies from 40% to 0.1% but on the average they consume a higher 

 percentage than any other grazer community on earth. No single factor 

 has been found to control the lemming population cycles. Instead, control 

 may occur by a combination of year-to-year variation in the nutrient 

 content of plants, of the amount of protection by the snow, and of 

 predation. 



The lemming cycles also produce a cycle in abundance of their 

 predators, the pomarine jaegers, snowy owls, short-eared owls, least 

 weasels, ermines, and arctic foxes. The large birds eat four to seven 

 lemmings per day and breed only when lemmings are abundant. 



The common smaller birds (seven species of shorebirds and two 

 buntings) arrive in the first days of the spring melt and begin to breed at 

 once (80-100 pairs km"^). They eat mostly insects such as larvae and 

 adults of craneflies and midges. About 30% of adult insects and 1% of 

 larvae are harvested. 



On the tundra, about 60% of the weight of plant material disappears 

 within 3 years of death. Half of this loss occurs in the first year. After the 

 first year, the loss is the sum of two exponential decay rates, one of 49% 

 yr"' for rapidly metabolized compounds and one of 11% yr"' for 

 recalcitrant compounds. Factors controlling the decomposition rate 

 include the duration of freezing, the low pH, the low O2 concentrations in 

 the soil, the low amounts of available N and P, and the low temperatures. 



Soil respiration is another way to measure decomposition. Over an 85- 

 day summer period, the evolution of CO2-C from meadow soils (159 g C 

 m""^) matched the net primary production. Most of the respiration is by 

 microbes. Bacterial numbers, 10® or 10'° (g dry weight)"' are similar to 

 temperate soils. The amount of fungal mycelia (g dry weight)"' is 200 to 

 270 m but this is only a third to a quarter the biomass of the bacteria. 



The major soil invertebrates are nematodes, annelid worms, mites, 

 springtails, and dipteran larvae. Their total biomass is 1.3-5.1 g dry wt 

 m'^ or about the same amount as the microbes. Enchytraeid worms 

 dominate (50-75% of biomass). Most of the animals are found in the top 

 2.5 cm (aerobic layer). The cranefiies and worms have long life cycles (up 

 to 4 years). Thus, although the biomass is high, the productivity is low. 



Despite the high average rate of lemming grazing, most of the energy 

 passes through the soil saprovores and microbivores. There is so much 

 organic matter in the soil (22 to 45 kg m "^ to a depth of 20 cm), that the 

 total primary production for 1 year is only 0.25 to 2% of the total. Because 

 of this large quantity of soil organic matter, the small changes each year 

 can not be measured and it is impossible to discover whether the soil 

 systems are gaining or losing organic matter. Two hypotheses have been 



