Abstracts
Vol. 32, No. 2, May 2000
Are Climate-Tree Growth Relationships Changing in North-Central Idaho, U.S.A.? (pp 111-116)
Franco Biondi
An 861-yr Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) tree-ring chronology has been recently developed for the Salmon River Valley, Challis National Forest, Idaho. Its potential for climatic reconstruction is investigated using monthly instrumental records of precipitation, temperature, and Palmer Drought Severity Index from 1895 to 1995. The temporal stability of climate-tree growth relationships is analyzed by means of evolutionary (backward and forward) and moving response functions. When precipitation and temperature are used as predictors, the strongest (and temporally stable) signal is a negative response to July temperature. Another relevant signal, albeit less temporally consistent, is a positive response to May precipitation. When the Palmer Drought Severity Index is used as an integrated predictor to highlight response to summer moisture stress, the strength of the association with tree growth increases in recent decades. This information can be used to maximize the reliability of dendroclimatic reconstructions, and has important implications for expanding the range of recent studies on altered climate-tree growth relationships during the 20th century.
Boundary Detection in Altitudinal Treeline Ecotones in the Spanish Central Pyrenees (pp 117-126)
J. Julio Camarero, Emilia Gutiérrez, and Marie-Josée Fortin
Spatial identification and description of ecological boundaries is fundamental to better understanding of treeline dynamics. Ecological boundaries across two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones were delineated within the Central Pyrenees (Ordesa and Tessó sites). Boundaries were delineated using an edge detection algorithm for two-dimensional data (lattice-wombling). Tree density, size-structure, growth-form, and estimated age were used to reveal spatial location of boundaries for several size and growth-form tree classes. Overlap statistics were applied to quantify spatial relationships among boundaries determined for different sets of variables. The most significant and consistent boundaries were those for structural variables at the Ordesa site. At this site, the sequential disposition of bigger and unistemmed trees descending across the ecotone produced boundaries for size-structure and growth-form variables. These boundaries were located along an ordered spatial pattern (altitudinal diagonal). At the Tessó site, there were few consistent boundaries, most of which were developed along the slope. Overlap statistics showed that boundaries at the Ordesa site were more spatially related than were those at the Tessó site. This result held when any set of variables was considered. The studied ecotones describe sharp (Ordesa site) and gradual (Tessó site) structural changes in tree populations, related to situations similar to the ecotone and ecocline concepts, respectively. The possible environmental driving factors producing these patterns are the strong winds and reduced snow cover at higher altitudes at the Ordesa site, and snow avalanches at the Tessó site. Boundary detection through time in permanent plots might be a better tool for monitoring climate-change impact in the forest-alpine grassland ecotone than the subjective location of treelines.
Periphyton Dynamics in a Subalpine Mountain Stream During Winter (pp 127-134)
Gregory W. Gustina and James P. Hoffmann
We conducted two experiments to determine the activity of and factors which control periphyton during winter in Stevensville Brook, Vermont. The first experiment during winter/spring 1994 examined the effect of a 300 to 450% difference in light and doubling of flow (low and high light, slow and fast flow) on periphyton chlorophyll a (chl a) and ash-free dry mass (AFDM) from stream rocks and artificial substrata. A second experiment was performed to determine whether periphyton was nitrogen or phosphorus limited. In addition, stream water was sampled during fall/winter 1994/95 for nitrate (NO3), ammonia (NH4), soluble reactive phosphorus (SRP), and total phosphorus (TP) to determine the availability of nutrients in Stevensville Brook. Increases of up to 250% for AFDM and 600% for chl a during the first study indicated robust activity throughout the winter despite low temperatures and light. Flow had a negative effect and sampling date was found to have a significant effect on periphyton biomass (chl a and AFDM) while light was found to influence increases in AFDM on clay tiles only. Water analyses showed that SRP was less than 0.001 mg L-1, NH4 and TP were low and often undetectable, and NO3 remained at about 0.20 mg L-1. Results from the nutrient enrichment experiment showed a significant response of chl a to P but not N and no response of AFDM to enrichment with either N or P. In Stevensville Brook during winter, the algal community, as represented by the chl a concentration, is predominantly controlled by phosphorus concentrations and is influenced to a lesser extent by flow; the periphyton community as a whole, represented by AFDM, is controlled mostly by stream flow and light.
Twentieth-Century Change in the Climate Record for the Front Range, Colorado, U.S.A. (pp 135-146)
Nick Pepin
The long-term climate records of the Mountain Research Station (MRS) at the University of Colorado cover a range of elevations from the lower montane forest zone (~2000-2400 m), through the upper montane forest (~2400 - 2800 m) and subalpine forest (~2800 - 3300 m) to the alpine tundra (>3300 m) on Niwot Ridge, Colorado. Temperature records from all four MRS sites and the additional high plains site of Longmont (1509 m) are analyzed for the period 1952-1997, after extraction of much missing data from the original thermograph charts. The records are adjusted for instrumental changes where necessary and all four records are judged to be homogenous. Contrasting temporal trends are uncovered at the various elevations with warming at middle elevations and absolute cooling above the treeline in the alpine tundra. The resulting increased surface-based lapse rates do not arise from changes in relative frequencies of airflow types as is shown by a synoptic analysis based on objective airflow indices. Lapse rate increases are most systematic for synoptic classes with westerly components and during fall, winter, and spring. Climate at high elevations of the Front Range appears to be responding in an unusual way to global-warming influences.
Simulation of Carbon and Nitrogen Cycling in an Alpine Tundra (pp 147-154)
Alexis H. Conley, Elisabeth A. Holland, T. R. Seastedt, and W. J. Parton
Simulations of an alpine tundra ecosystem using the CENTURY ecosystem model were conducted to test model descriptions of carbon and nitrogen cycling and to explore the alpine ecosystem response to physical and chemical components of global change. The parameterization of the alpine tundra for CENTURY was updated to reflect current knowledge of the site, and sensitivity analyses were conducted. Verification of results from a 6-yr fertilization experiment in the alpine tested the predictive capabilities of the parameterization. Simulations with increased winter precipitation and with the climate predicted under doubled atmospheric carbon dioxide concentrations were then conducted.
Modifications to the parameterization necessary to describe carbon and nitrogen cycling included decreasing the C:N ratios of plant tissues, increasing the amount of nitrogen retranslocated at the end of the growing season, extending the length of the growing season, and lowering the rate of decomposition. The updated parameterization requires 30% greater than observed inputs of net primary productivity to simulate observed levels of total soil carbon suggesting that soil carbon sequestration is not well represented in the model. Carbon and nitrogen cycling showed greatest sensitivity to the length of the growing season and to the temperature regulation of decomposition. Simulation of the nitrogen fertilization experiment resulted in 11% greater productivity than observed empirically, a reasonable verification of the updated parameterization. The major impact from increasing winter precipitation was a 30% increase in the amount of nitrogen in stream flow. Simulation with the climate predicted for a doubling of current carbon dioxide levels reduced production 10% while total soil carbon remained constant. This response was largely controlled by reduced soil moisture during the growing season.
The Influence of Permafrost and Fire upon Carbon Accumulation in High Boreal Peatlands, Northwest Territories, Canada (pp 155-156)
S. D. Robinson and T. R. Moore
Carbon and peat accumulation rates over the past 1200 yr were measured in relation to permafrost aggradation, maturity, ground fires, and degradation in a peatland with discontinuous permafrost near Fort Simpson, N.W.T., Canada. The White River volcanic ash layer, deposited 1200 yr ago, was used as a chronostratigraphic marker to compare peat and carbon accumulation among peat cores collected along transects over a consistent period of time. The aggradation of permafrost results in a change from unfrozen bog to forested peat plateau, and approximate decreases of 50 and 65% in carbon and vertical peat accumulation rates, respectively. Carbon and peat accumulation continue to decrease significantly with both increasing permafrost maturity and the number of ground fires. The transition from peat plateau to collapse bog through internal permafrost degradation results in up to a 72 and 200% increase in carbon and vertical peat accumulation rates, respectively. Permafrost degradation at the margins of a peat plateau can result in the formation of collapse fens, in which vertical peat accumulation increases significantly yet the carbon accumulation rates remain similar to the peat plateau. A warming climate may result in a shift towards higher carbon accumulation rates in peatlands associated with bog vegetation following peat plateau collapse, yet warmer peat temperatures, greater soil aeration, greater rates of peat decomposition, and an increase in burning may provide limits to the increase.
Response of Diatoms and Other Siliceous Indicators to the Developmental History of a Peatland in the Tiksi Forest, Siberia, Russia (pp 176-178)
Kathleen Rühland, John P. Smol, J. P. Paul Jasinski, and Barry G. Warner
Diatoms and other siliceous microfossils were examined from a 386-cm-long peat core, covering the last ca. 7200 yr, from north-central Siberia to gain insights into peatland developmental history, and to explore the potential of diatoms as proxy indicators in arctic peats. Diatom analyses of arctic peatlands are rare, and so one aspect of this study was to examine the sensitivity of diatom taxa in relation to independent paleoindicators already described from this core. Changes in the relative abundances of diatom taxa divided the core into four zones that closely tracked the ontogeny of the peatland from an open water environment (Zone I: benthic, alkaliphilic taxa), followed by fen environments (Zones II and III; epiphytic, acidophilic taxa), and finally to a better-drained, high-centered bog (Zone IV; aerophilic taxa). In addition to the diatom taxa, observations were made on the relative abundances of siliceous protozoan plates, chrysophyte cysts, and phytoliths. Both the diatoms and these other siliceous microfossils appeared to respond to changes in hydrology and moisture, as well as to fire episodes likely triggered by climatic change. This study demonstrates that diatoms and other siliceous microfossils from arctic peat deposits provide an important source of paleoenvironmental information that can strengthen interpretations derived from other commonly used indicators.
Use of Soils to Identify Glacial Deposits of Various Ages East of Glacier National Park, Montana, U.S.A. (pp 179-188)
Eric T. Karlstrom
Degree of soil development increases with age of parent materials in the zone of confluence of continental and alpine piedmont glaciers east of Glacier National Park, Montana. Surficial deposits are assigned to three, possibly four, glacial events on the basis geomorphic and pedologic evidence. Based on over 100 profiles examined, soils in late Wisconsin till and outwash are typically Cryoborolls and Cryochrepts with 0? to 62?cm-thick, brown cambic (Bw) horizons and 50+?cm-thick calcic (Bk) horizons with Stage II to II+ carbonate morphology. Soils in late Illinoian or early Wisconsin sediments are Argiborolls or Argic Cryoborolls with 34? to 92?cm-thick, dark yellowish brown argillic (Bt) horizons and those in Illinoian sediments are strongly developed Paleudolls with 51? to 54?cm-thick, yellowish red argillic horizons. Soils on Number 1 and 2 Bench remnants (considered Pliocene to early Pleistocene in age) are very strongly developed Paleudolls with about 2.5?m-thick, leached, yellowish red argillic horizons. Properties which best reflect relative soil age include thickness of argillic horizon, depth of leaching, depth of oxidation, Harden profile index, Harden rubification index, and clay accumulation index.
Relations between Winter Climate and Ionic Variations in a Seven-meter-deep Snowpack at Okstindan, Norway (pp 73-83)
Peter Raben, Wilfred H. Theakstone, and Kjetil Tørseth
Seven meters of snow accumulated at 1470 m above sea level on the Norwegian glacier Austre Okstindbreen during the 1994-95 winter. Fifty samples, together representing the entire pack, were collected in a continuous column downwards from the surface on 29 April 1995, before the onset of melting. The water-equivalent thickness of each sample was calculated from density measurements. Concentrations of Na+ and non-sea-salt (nss) SO42- in the samples were measured and the ionic loads determined. In an attempt to date some of the stratigraphic variations of ionic concentrations, use was made of precipitation data from the monitoring site Tustervatn (439 m asl), 25 km southwest of the glacier. Synoptic conditions associated with heavy precipitation, extended periods of dry weather, high Na+ loading and high nss SO42- loading were identified. Daily values for precipitation amount, Na+ load and nss SO42- load for the 115 d on which more than 1 mm of precipitation was recorded were recalculated as percentages of the winter totals. Comparison of data from Tustervatn and the 1470 m site indicates that about 2.5 m of the 1470 m snowpack had accumulated by the end of November 1994, 4 m by the middle of January, and 5 m by mid-February.
Retreat of Mediterranean Glaciers since the Little Ice Age: Case Study of Ghiacciaio del Calderone, Central Apennines, Italy (pp 197-201)
Maurizio D'Orefice, Massimo Pecci, Claudio Smiraglia, and Renato Ventura
Ghiacciaio del Calderone is the only glacier in the Italian Apennines and the southernmost glacier in Europe. In this paper, the authors present a tentative synthesis of the evolution of the glacier, with a particular focus on evaluating the variations in area and thickness ranging from the end of the Little Ice Age to the present. The analysis was performed in a GIS environment, using available data for georeferation (mainly from recent topographic maps) and for the reconstruction (from historical documents and old topographic maps) of the variations of the glacier in the last two centuries. The resulting values, reconstructed and/or calculated, covering the period since the end of the Little Ice Age, of about 36 m of ice thickness and of about 59,000 m2 of ice surface area represent the glacier loss by 1990.
Gelifluction: Observations from Large-Scale Laboratory Simulations (pp 202-207)
Charles Harris and Michael C. R. Davies
Despite extensive field studies, progress in understanding gelifluction processes has been limited. Controlled laboratory simulation experiments offer an alternative and potentially extremely effective approach. Such an experiment is described here. It was conducted on a 12° slope formed of two natural soils, one a fine sandy silt derived from slate bedrock, the second a gravelly silty sand derived from mudstone bedrock. Continuous measurements were made of soil temperatures, porewater pressures, frost heave, thaw settlement, and downslope displacements of the soil surface over seven freeze/thaw cycles. Two-dimensional vectors of soil surface movements together with evidence from excavated displacement columns suggest that gelifluction occurred only during thaw consolidation of the upper parts of the soil profile; thawing of the deeper layers caused thaw consolidation but little downslope displacement. Cryogenic processes are shown to cause progressive decreases with depth in void ratio and moisture content and increases in undrained shear strength within the continuous soil matrix that separates ice lenses. Since self-weight stress levels are low, thawing leads to significant shear strain only in the softer, wetter near-surface soil layers.
Responses of Floral Traits and Increase in Female Reproductive Effort to a Simulated Environmental Amelioration in a Hermaphrodite Alpine Dwarf Shrub, Sieversia pentapetala (Rosaceae) (pp 208-211)
Naoya Wada
This report presents empirical data for variations of floral traits and "femaleness" (dry-weight allocation to the female organs) under a simulated environmental amelioration by using open-top chambers (OTCs) in a hermaphrodite alpine dwarf shrub Sieversia pentapetala (L.) Greene, in the Tateyama Range, central Japan. The results showed that gynoecium, peduncle, and flower weight in OTC-manipulated shoots were significantly heavier than those in controls. As a result, "femaleness" showed a significantly higher value in the OTC-manipulated shoots as compared to the controls. Moreover, gynoecium weight was significantly positively correlated with leaf mass (per flowering shoot), while androecium weight was not, suggesting a higher resource requirement for reproduction through the female function. Thus, it was experimentally demonstrated that the gender of S. pentapetala flowers changed from male-biased to female-biased as leaf mass increased under less stressful conditions.
