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Growth, flowering, and nutrient content of Eriophorum vaginatum were observed an- nually over 4 yr at 34 sites spanning 5.50 latitude and 1050 m elevation in northern and central Alaska. We found a strong correlation between the average number of thawing degree-days during the growing season and the peak-season leaf mass per tiller. However, the results from reciprocal transplant gardens established at five sites suggested the correlation was due more to genetic differences among populations than to direct climatic effects. Other variables showed little correlation with long-term degree-day averages, and leaf N and P concentrations were site specific. A year of high inflorescence density at any site along the latitudinal transect was likely to be a high flowering year at all other sites. However, a year of above-average growth north of the Brooks Range did not always coincide with above-average growth to the south, and vice versa. The greatest year-to-year variation was in inflorescence density; least variation was in leaf mass per tiller and N and P concentrations. We conclude that yearly variation in weather affects plants on a broad regional scale, but specific controls over flowering versus growth differ in their geographic extent.

Changes in land use over the past two centuries have caused a significant release of CO2 to the atmosphere from the terrestrial biota and soils. An analysis of this release is based on amounts of organic carbon within an ecosystem following changes such as harvest of forests; it is also based on rates of changes, such as conversion of forest to agriculture, deduced from agricultural and forestry statistics. A model is used to calculate the net amount of carbon stored or released each year by the biota and soils of 69 regional ecosystems. Some of the changes, such as afforestation, the growth of harvested forests, and buildup of soil organic matter, result in a storage of carbon; others, such as harvest of forests and increase in pasture and agricultural areas, result in a loss of carbon to the atmosphere. According to this analysis, there has been a net release of carbon from terrestrial ecosystems worldwide since at least 1860. Until 1960, the annual release was greater than release of carbon from fossil fuels. The total net release of carbon from terrestrial ecosystems since 1860 is estimated to have been 180 x 1015 g (a range of estimates is 135-228 x 1015 g). The estimated net release of carbon in 1980 was 1.8-4.7 x 1015 g; for the 22 yr since 1958 the release of C was 38-76 x 1015 g. The ranges reflect the differences among various estimates of forest biomass, soil carbon, and agricultural clear- ing. Improvements in the data on the clearing of tropical forests alone would reduce the range of estimates for 1980 by almost 60%. Estimates of the other major terms in the global carbon budget, the atmospheric increase in C02, the fossil fuel release of C02, and the oceanic uptake of C02, are all subject to uncertainties. The combined errors in these estimates are large enough that the global carbon budget appears balanced if the low estimate for the biotic release of carbon given above is used (1.8 x 1015 g released in 1980) with the higher estimates of oceanic uptake. If higher estimates for biotic release are used, then the carbon budget does not balance, and the estimates of oceanic uptake or of other factors require revision.

This chapter describes and compares the seasonal course of mineral nutrients, total nonstructural carbohydrate, and crude fat in plant tissues from Echo Valley and Fundo Santa Laura.

Effects of variable mineral nutrient status on evergreen leaf longevity were investigated in a field fertilization experiment, and by comparison of plants from several sites. The species studied was Ledum palustre spp. decumbens, with a normal leaf life expectancy of 2.06 years and a maximum leaf longevity of 4.5–5.0 years. Most leaf losses took place during the growing season, not during the winter. Fertilization increased leaf production but decreased leaf survivorship. Total number of leaves per stem was unchanged with fertilization. In a comparison among sites, there was a moderate negative correlation between plant N and P concentrations and leaf longevity. These intraspecific responses are similar to known interspecific changes along nutrient gradients, i.e. with high nutrient availability a vegetation should become more “deciduous” and less “evergreen”.

A study of effects of terrestrial biota on the amount of carbon dioxide in the atmosphere suggests that the global net release of carbon due to forest clearing between 1860 and 1980 was between 135 x 10(15) and 228 x 10(15) grams. Between 1.8 x 10(15) and 4.7 x 10(15) grams of carbon were released in 1980, of which nearly 80 percent was due to deforestation, principally in the tropics. The annual release of carbon from the biota and soils exceeded the release from fossil fuels until about 1960. Because the biotic release has been and remains much larger than is commonly assumed, the airborne fraction, usually considered to be about 50 percent of the release from fossil fuels, was probably between 22 and 43 percent of the total carbon released in 1980. The increase in carbon dioxide in the atmosphere is thought by some to be increasing the storage of carbon in the earth's remaining forests sufficiently to offset the release from deforestation. The interpretation of the evidence presented here suggests no such effect; deforestation appears to be the dominant biotic effect on atmospheric carbon dioxide. If deforestation increases in proportion to population, the biotic release of carbon will reach 9 x 10(15) grams per year before forests are exhausted early in the next century. The possibilities for limiting the accumulation of carbon dioxide in the atmosphere through reduction in use of fossil fuels and through management of forests may be greater than is commonly assumed.

Alders (Alnus crispa) in shrub tundra in northern Alaska showed significant regularity of spacing. Removal of neighboring alder shrubs stimulated nutrient accumulation and growth of remaining alders but did not stimulate nutrient accumulation or growth of any other shrub species. This demonstrates that neighboring alders competed with one another and that, when alders were removed, the resources made available were used preferentially by remaining alders rather than by the community in general. Neither patterns of seedling establishment nor patterns of frostrelated features could explain the regular distribution of alder. We suggest that regular patterns of plant distribution are restricted to sites of low-resource availability, because in these habitats (1) there is strong competition for a scarce resource, and (2) there are only one or a few dominant species to compete for these resources in a given canopy height or rooting depth.

(1) Soil characteristics and vegetation were studied in vehicle tracks and adjacent undisturbed tundra along local moisture gradients at four tundra sites in northern Alaska. Vehicle tracks generally had 2 OC higher soil temperatures, deeper thaw, and higher concentrations of available soil phosphate than adjacent undisturbed tundra, but did not differ consistently from controls in soil bulk density, volumetric moisture content, pH, or soil organic content. (2) Vegetation in vehicle tracks had fewer species than controls, reflecting decreased abundance of shrubs, particularly evergreens, and increased dominance by a few species of graminoids. (3) Wet and mesic tracks exhibited a 2to 15-fold increase in above-ground standing crop of nitrogen and phosphorus as a result of increased leaf nutrient concentrations and increased leaf biomass of graminoids, a consequence of increases in both shoot density and shoot weight. (4) We reject our original hypothesis that the known temperature effects upon root growth, nutrient absorption, and organic matter mineralization account for the increased standing crop of biomass and nutrients in vehicle trails. We conclude that other factors, perhaps related to soil water and nutrient movement, are in large part responsible for the increased nutrient status and production of vehicle tracks and exert an important control over growth in undisturbed tundra.

(1) Growth and nutrient relations of Carex aquatilis were examined in the field and in glasshouse-grown plants from five polygon microhabitats in wet meadow tundra at Barrow, Alaska. These habitats can occur within 1 m of each other, and differ greatly in soil moisture, availability of N and P and thaw depth. (2) Field-grown plants from these microhabitats differed between populations in above-ground weight per tiller, leaf-production rate, root:leaf weight ratio, rate of uptake of 32P, and concentration of sugar, N and P in roots and rhizomes. Tissue concentrations of N and P were correlated with corresponding availability in the soil but not with plant size. There was a moderate positive correlation between soil moisture and plant size. (3) Carex aquatilis populations grown in the glasshouse with either no addition or moderate addition of phosphate showed no significant differences in plant size, but large differences in tissue-nutrient concentrations, 32P-uptake kinetics and responsiveness to phosphorus availability. A strong effect of phosphorus stress on nitrogen and potassium metabolism was observed. Responsiveness of 32P-uptake kinetics to changed conditions was inversely related to the degree of responsiveness in growth rate and mineral accumulation in the tissues. (4) These ecotypic differences among populations of Carex aquatilis are remarkable in view of the extreme rarity of reproduction by seed in the field, and the close proximity of the populations.

Deciduous species (graminoids, forbs and deciduous shrubs) completed accumulation of biomass, nitrogen (N) and phosphorus (P) in new leaves and current-year's twigs by midsummer in arctic Alaska, whereas these processes continued throughout the growing season in the same tissue of evergreen shrubs. Nand P-use-efficiency increased from deciduous species to evergreen shrubs to lichens and mosses. Fertilization with N-plus-P had no effect on N-use-efficiency in deciduous leaves but caused a decline in N-useefficiency in evergreen leaves, mosses and lichens. P-use-efficiency declined with nutrient addition in leaves of all growth forms. Approximately half of the maximum pools of leaf N and P were withdrawn from leaves prior to autumn senescence, but this resorption was unaffected by nutrient addition treatment or by growth form. Key-words: Arctic, deciduous, evergreen, growth, nitrogen, phosphorus, resorption, tundra

SUMMARY (1) Life-tables were constructed for vegetative tillers of Eriophorum vaginatum from undisturbed and disturbed tussock tundra in Alaska. Life-tables were also constructed for tillers from tundra that had been fertilized with N, P and K. The life-tables were used to estimate population parameters and to construct constant coefficient matrix models of tiller demography. (2) Tiller survival was lower in disturbed than it was in undisturbed tundra, and daughter tillers were produced sooner. Addition of nutrients (as fertilizer) produced no change in tiller survival and in the age distribution of daughter tiller production in the first year following fertilization. The shapes of the survival curves were intermediate between Deevey Type I and Deevey Type II curves. (3) The generation time for tillers in undisturbed tundra was 5.3 years-about twice as long as in disturbed tundra-while the annual rate of increase of tillers did not differ greatly. Fertilization produced large increases in the annual rate of increase, but the generation time was shortened only slightly. (4) Reproductive values, defined as the expected number of daughter tillers from tillers of a given age relative to the expected number from a tiller aged 0, fell into one of three patterns: (i), decline from maximum value at age 0; (ii), increase from age 0 followed by a monotonic decline; (iii), increase from age 0 followed by a gradual, irregular decline and a plateau in the older age classes. The peak in reproductive value for patterns (ii) and (iii) occurred 2-4 years after the onset of tillering at age 1 or 2 years; this result was attributed to increases in age-specific tillering rate with tiller age. (5) Sensitivity analysis of the matrix models revealed that sensitivity of the annual rate of increase to changes in tillering rate and survival declines with age. The annual rate of increase was equally sensitive to changes in tillering rate and survival from age 0 to age 3. In the older age classes the annual rate of increase was more sensitive to changes in tillering rate than to changes in survival.

The effects of nitrogen-phosphorus-potassium fertilization on primary production and plant biomass were determined for four tussock tundra sites in Alaska. The results generally supported conclusio...