Philip C. Miller

An Arctic ecosystem : the coastal tundra at Barrow, Alaska

Direct financial support of the Biome-wide program was derived from three major sources: the National Science Foundation, the State of Alaska and the petroleum industry through the University of Alaska. The NSF funding was under the joint sponsorship of the U. S. Arctic Research Program (Division of Polar Programs) and the U. S. International Biological Program (Ecosystem Analysis). The Army Research Office and the Department of Energy (previously AEC and ERDA) both contributed funded projects to the Program. Industry support was provided through unrestricted grants from: Atlantic Richfield Company, Alyeska Pipeline Service Company, BP Alaska, Inc. Cities Service Company, Exxon Company, USA (Humble Oil and Refining Company), Gulf Oil Corporation , Marathon Oil Company, Mobil Oil Company, Prudhoe Bay Environmental Subcommittee of the Alaska Oil and Gas Association, Shell Oil Company, Standard Oil Company of California, Standard Oil (Indiana) Foundation Inc., and Sun Oil Company.

Simulating carbon accumulation in northern ecosystems

A model of the carbon balance in arctic and boreal forests has been developed to estimate the effects of higher carbon diox ide levels in the atmosphere on northern ecosystems. The model predicts that northern ecosystems should accumulate 5-10% of the carbon added to the atmosphere each year. Ac cumulation rates should increase by 2-8 times by year 2020 depending on the availability of nutrients. The rates of change in several processes are only estimates. The predictions are subject to large errors because of the complexity of ecosys tems interactions and the absence of data on the long-term ef fects of higher temperature and atmospheric CO2 levels. More differentiation of plant types, more feedback interactions, and more stochastic variations could improve the model. How ever, the results show that carbon accumulation in northern ecosystems is a significant fraction of the terrestrial carbon flux. The response of these systems is therefore important in predicting global carbon balance.

Competition for nitrogen in a tussock tundra ecosystem

SummaryThe objective was to measure the competition for nitrogen among vascular plants, mosses, and soil microbes along a continuum of nitrogen availability, induced by carbon and nitrogen amendments, in a tussock tundra ecosystem.15N was used as a tracer. Vascular plants showed an increasing15N recovery with increasing time and with increasing nitrogen availability; the latter suggests that nitrogen was limiting vascular plant growth. Green mosses took up15N initially, but showed no significant trends with either treatment or time. There was a higher15N recovery in the soil insoluble compartment for the carbon-amended treatment than in the nitrogen-amended treatments; this suggested that carbon as an energy source limited microbial activity. After two months, the relative15N recovery fell in the order: soil microbes (≈79%)>vascular plants (≈16%) >green mosses (≈2%).

Water Relations of Selected Plant Species in the Alpine Tundra, Colorado

The purpose of this study was to measure some aspects of the water relations of selected plant species in the alpine tundra, Colarado, in order to assess the possible role of water limitation on primary production. Leaf water potentials were measured in Kobresia myosuroides, Geum rossii, Bistorta bistortoides, Deschampsia caespitosa, and Caltha leptosepela. Leaf resistances to water loss were measured in Bistorta and Caltha. Measurements were made at dawn and midday throughout the season and several times through selected days in plants along a moisture gradient. Leaf resistance was related to leaf water potential, light, and temperature. Leaf water potentials decreased throughout the season and were higher on the wetter site. Minimum water potentials of the species in the order listed above were —40, —23, —17, —31, and —17 bars. Minimum leaf resistances of Bistorta and Caltha were 0.8 and 1.6 s.cm—1, respectively, and were lower on the wetter site. Both Bistorta and Caltha on the wet meadow showed partial midday stomatal closure, but Bistorta on the dry meadow did not At —16 bars leaf resistance increased abruptly in Caltha, but was still low in Bistorta. Leaf resistances were low at incident solar radiation levels of 0.2 ly ° min—1 and at temperatures near 20°C. Leaf resistances increased with temperatures below 15°C. Root resistances for Bistorta were 0.9 x 104 s ° cm—1 ° bar—1 at the dry site and 0.8 x 104 at the wet site, and for Caltha were 0.6 x 104 s ° cm—1 ° bar—1 at the wet site. The changing daily pattern of leaf water potential and leaf resistance is shown to be related to the diurnal environmental pattern, to root resistances, and to the relationships between leaf resistance and leaf water potential and between leaf water potential and leaf relative saturation deficit.

A PRELIMINARY MODEL OF PROCESSES AFFECTING PRIMARY PRODUCTION IN THE ARCTIC TUNDRA

A preliminary model of physical processes affecting primary production in the arctic tundra was developed from the energy budget equation for single leaves, equations expressing the radiation and wind profiles in the canopy, and a simplified concept of the allocation of photosynthetic material to stems and leaves. The model was validated with data for 1965 and 1970 from Point Barrow, Alaska. For both years, calculated net production increased as leaf area increased in spite of decreasing solar radiation through the growing season, except for a drop in net production when temperatures rose in August 1965. Production of Dupontia fischeri was lower in a mixed sward than in a pure sward. Production increased with decreased standing dead material, increased leaf area index, increased solar radiation, and increased air temperatures up to 5 to 10?C. Production was not affected by infrared radiation from the sky or from the ground.

Soil Moisture Relations in the Southern California Chaparral

Contrary to previous studies of vegetation cover and environment, soil moisture was greater on a south—facing slope than on the opposite north—facing slope in southern California chaparral. Vegetation cover on the north—facing slope (mixed chaparral) was greater than the cover on the south—facing slope (Adenostoma chaparall). Precipitation on the two slopes was the same. The soil moisture profiles were analyzed to estimate soil moisture losses due to subsurface drainage, surface evaporation, and transpiration. Subsurface drainage was greater on the south—facing slope. Evaporation was greater on the south—facing slope, but transpiration was greater on the north—facing slope. The greater vegetation cover and drier soils on the north—facing slope are probably related to the drought—resistant nature of vegetation in this mediterranean climate. See full-text article at JSTOR

The influence of annual precipitation, topography, and vegetative cover on soil moisture and summer drought in southern California

SummaryThe influence of annual precipitation and vegetation cover on soil moisture and on the length of the summer drought was estimated quantitatively using 9 years of soil moisture data collected at Echo Valley in southern California. The measurements support the conclusions that in the semi-arid mediterranean climate a soil drought will occur regardless of vegetation cover and annual precipitation, but the length of the drought is greatly dependent on soil depth and rockiness. Evergreen species which can survive this drought tend to accentuate the drought, especially in deep soil levels, by developing a canopy with a large transpiring surface.

WATER RELATIONS OF PLANT SPECIES IN THE WET COASTAL TUNDRA AT BARROW, ALASKA

Various aspects of the water relations of six species (Arctophila fulva, Dupontia fischeri, Carex aquatilis, Eriophorum angustifolium, Potentilla hyparctica, and Salix pulchra) characteristic of the wet, coastal tundra near Barrow, Alaska, were measured during the summers of 1972 and 1973 to examine the hypothesis that water stress may increase stomatal resistance and inhibit photosynthesis. A simulation model of internal water status was constructed to examine this hypothesis. The slopes of the leaf water potential vs. relative saturation deficit (RSD) curves were between -0.6 and 1.8 bars RSD-1. The minimum leaf resistances were between 1 and 3 sec cm-1 for all species but A. fulva which was 6 sec cm-1. The relation

Comparative field water relations of four co-occurring chaparral shrub species

SummaryThe seasonal course of water relations was measured in the field in Adenostoma fasciculatum, Quercus dumosa, Ceanothus greggii, and Arctostaphylos glauca, four prominent members of the southern California chaparral vegetation. Ceanothus greggii and A. glauca developed similar seasonal patterns of minimum leaf water potentials, as estimated by xylem pressure measurements, which were much less negative than A. fasciculatum and Q. dumosa growing in close proximity on the same pole-facing slope site. Adenostoma fasciculatum on an adjacent equator-facing slope developed more negative water potentials than did A. fasciculatum on the pole-facing slope.Leaf conductance differed between species, and by leaf age class and slope exposure within a species. The greatest differences were measured between leaf age classes in A. fasciculatum on the pole-facing slope, with new leaves showing the greatest conductances early in the season. The same trend was measured in A. fasciculatum on the equator-facing slope, but the differences were less between leaf age classes and diminished earlier in the season than in A. fasciculatum on the pole-facing slope. The analysis of daily hysteresis in the leaf conductance-water potential relation suggests that early in the season when water is available, stomatal behavior is simultaneously governed by a complex of environmental factors, while late in the season stomatal behavior becomes increasingly dominated by tissue water status.

Tests of Solar Radiation Models in Three Forest Canopies

Several models expressing the decrease of solar radiation in vegetation canopies have been proposed. The models are similar in (1) including a method of projecting the shadow of one more leaves onto a horizontal plane and (2) including a method of relating the projected shadow to the decrease of solar radiation. The models differ in the equations used and in the assumptions made. The models used the binomial, the Poisson, or some modification of the binomial to relate the projected shadow to the radiation at different levels. When the models were tested against the percentage of sunlit area at different levels in the canopy, the best fitting models was one proposed in this paper in which the shadow of the leaf is projected as a shadow of a cone and the binomial is used to express the decrease of radiation. Negative exponential models usually overestimated the percentage of sun. Including the shadow cast by twigs and branches in the prediction improved the agreement between the observed and the expected pe...