Showing papers by "University of New Hampshire published in 1993"

Global climate change and terrestrial net primary production

Abstract: A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric CO2 concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of CO2 doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by CO2, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.

Tropical Deforestation and Habitat Fragmentation in the Amazon: Satellite Data from 1978 to 1988

Abstract: Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.

Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event

Abstract: THE warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate, the best-known of which is the Younger Dryas event1. Despite much study of the causes of this event and the mechanisms by which it ended, many questions remain unresolved1. Oxygen isotope data from Greenland ice cores2–4 suggest that the Younger Dryas ended abruptly, over a period of about 50 years; dust concentrations2,4 in these cores show an even more rapid transition (≲20 years). This extremely short timescale places severe constraints on the mechanisms underlying the transition. But dust concentrations can reflect subtle changes in atmospheric circulation, which need not be associated with a large change in climate. Here we present results from a new Greenland ice core (GISP2) showing that snow accumulation doubled rapidly from the Younger Dryas event to the subsequent Preboreal interval, possibly in one to three years. We also find that the accumulation-rate change from the Oldest Dryas to the Bo11ing/Allerod warm period was large and abrupt. The extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the North Atlantic climate system.

Red edge spectral measurements from sugar maple leaves

Abstract: Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll data and high spectral resolution spectrometer laboratory reflectance data were acquired for multiple collections of single detached sugar maple leaves variously affected by the insect over the 1988 growing season. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various samples and populations of leaves. These included differences in the red edge inflection point (REIP), a ratio of reflectance at 740-720 nm (RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D705). All three red edge parameters were highly correlated with variation in total chlorophyll content. Other spectral measures, including the Normalized Difference Vegetation Index (NDVI) and the Simple Vegetation Index Ratio (VI), also varied among populations and over the growing season, but did not correlate well with total chlorophyll content. Leaf stacking studies on light and dark backgrounds indicated REIP, RE3/RE2 and D715/D705 to be much less influenced by differences in green leaf biomass and background condition than either NDVI or VI.

The ‘flickering switch’ of late Pleistocene climate change

Abstract: POLAR ice contains a unique record of past climate variations; previous Greenland ice cores have documented relatively warm ‘interstadial’ periods during the last glaciation and short (centuryscale) returns to colder conditions during the glacial to interglacial warming (see, for example, ref. 1). These climate features have also been observed to varying degrees in ocean sediment cores2–4 and terrestrial pollen and insect records5–7. Here we report electrical conductivity measurements from a new Greenland ice core, which confirm these previous observations, and also reveal a hitherto unrecognized mode of rapid climate variation. Fluctuations in ice conductivity on the scales of <5–20 years reflect rapid oscillations in the dust content of the atmosphere. This ‘flickering’ between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation.

Instrument description and performance of the Imaging Gamma-Ray Telescope COMPTEL aboard the Compton Gamma-Ray Observatory

Abstract: The imaging Compton telescope COMPTEL is one of the four instruments on board the Compton Gamma-Ray Observatory (GRO), which was launched on 1991 April 5 by the space shuttle Atlantis into an Earth orbit of 450 km altitude. COMPTEL is exploring the 1-30 MeV energy range with an angular resolution (1σ) between 1° and 2° within a large field of view of about 1 steradian. Its energy resolution (8.8% FWHM at 1.27 MeV) makes it a powerful gamma-ray line spectrometer. Its effective area (for on-axis incidence) varies between 10 and 50 cm 2 depending on energy and event selections. Within a 14 day observation period COMPTEL is able to detect sources which are about 20 times weaker than the Crab. The measurement principle of COMPTEL also allows the measurements of solar neutrons

Effect of a lowered water table on nitrous oxide fluxes from northern peatlands

Abstract: NORTHERN peatlands contain 20–30% of the total organic nitrogen and carbon in the world's soils1,2, and thus they apparently have the potential to exert a significant influence on the global atmospheric budget of the greenhouse gases carbon dioxide, methane and nitrous oxide (N2O). In the drier, warmer summer conditions predicted at high latitudes by some climate models3,4 as a result of greenhouse-gas forcing, northern peatlands would become drier, increasing the rate of mineralization of organic matter1,5 and of the microbial processes that produce N2O. These regions might therefore be expected to exert a strong feedback on climate. But whereas methane emissions have been well studied6,7, little is known about the effect on N2O fluxes of changes in the level of peatland water tables. Here we present a comparison of present-day N2O fluxes from virgin peatlands in Finland with those from sites in the same regions that were drained by ditching 30 and 50 years ago. The lowered water table had no effect on N2O emissions from nutrient-poor peat but enhanced those from nutrient-rich peat. We estimate that equivalent drying caused by climate change would increase the total emissions of N2O from northern peatlands by 0.03–0.1 teragrams of nitrogen per year, which is just 0.3–1% of the present global annual emissions. Thus northern peatlands are unlikely to exert a significant climate feedback from N2O emissions.

The atmosphere during the younger dryas.

Abstract: One of the most dramatic climate change events observed in marine and ice core records is the Younger Dryas, a return to near-glacial conditions that punctuated the last deglaciation. High-resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the arctic atmosphere at this time. This record shows that both the onset and the termination of the Younger Dryas occurred within 10 to 20 years and that massive, frequent, and short-term (decadal or less) changes in atmospheric composition occurred throughout this event. Changes in atmospheric composition are attributable to changes in the size of the polar atmospheric cell and resultant changes in source regions and to the growth and decay of continental biogenic source regions.

Yeast Sugar Transporters

Abstract: Transport of sugars is a fundamental property of all eukaryotic cells. Of particular importance is the uptake of glucose, a preferred carbon and energy source. The rate of glucose utilization in yeast is often dictated by the activity and concentration of glucose transporters in the plasma membrane. Given the importance of transport as a site of control of glycolytic flux, the regulation of glucose transporters is necessarily complex. The molecular analysis of these transporters in Saccharomyces has revealed the existence of a multigene family of sugar carriers. Recent data have raised the question of the actual role of all of these proteins in sugar catabolism, as some appear to be lowly expressed, and point mutations of these genes may confer pleiotropic phenotypes, inconsistent with a simple role as catabolic transporters. The transporters themselves appear to be intimately involved in the process of sensing glucose, a model for which there is growing support.

Primary structure and biological activity of a third gonadotropin-releasing hormone from lamprey brain.

Abstract: Previous studies have led to the identification of two molecular forms of GnRH (GnRH-I and II) in the brain of the sea lamprey, Petromyzon marinus. From analysis of these two forms, the primary structure of GnRH-I and the amino acid composition of GnRH-II were determined. We have now isolated a third molecular form of GnRH (GnRH-III) from the brain of this species that is different from GnRH-I and -II. The primary structure of GnRH-III is pGlu-His-Trp-Ser-His-Asp-Trp-Lys- Pro-Gly-NH2. A synthetic decapeptide with this amino acid sequence was chromatographically identical to natural GnRH-III. Intraperitoneal injection of synthetic lamprey GnRH-III (0.1 microgram/g) produced a significant (P < 0.05) elevation of plasma progesterone (31% over basal values) in female lampreys that was comparable to that produced by the same dose of lamprey GnRH-I (36% over basal). The elevation in plasma estradiol produced by lamprey GnRH-III (244% over basal) was significantly (P < 0.05) less than the elevation produced by G...

Response of Early Successional Vertebrates to Historic Changes in Land Use

Abstract: Unlike other regions of North America, forested habitats in New England bave increased substantially in the past 100 years. The proportion of land in New Hampshire covered by forests was 47% in 1880 and 87% in 1980. This increase was largely the result of a region-wide abandonment of farms and the subsequent colonization of these lands by second-growth forests. I examined the sequence of farm abandonment, forest colonization and forest maturation that occurred in New Hampshire in relation to changes in the abundance and distribution of a group of forest mammals and birds that have undergone substantial declines. A modeled pattern of secondary succession resulted in the availability of approximately 195,000 ha of early seral habitats (10–25 years after abandonment) from 1905 to 1940. These habitats then mutured into closed-canopy forests by about 1960. Concurrent to the loss of early successional habitats, populations of New England cottontails (Sylvilagus transitionalis) decreased from an apparent continuous distribution throughout 60% of New Hampshire to fragmented populations that occupy less than 20% of the state Bobacts (Felis rufus) responded functionally (S. transitionalis in diet: 1951–1954 = 43%, 1961–1964 = 10%) and numerically (mean annual harvest of bobcats: 1951–1954 = 350, 1965–1969 = 36) to changes in cottontail abundance. Eighteen of 26 species of migratory passerines that nest in the forests of northern New England also declined during the period their populations were monitored (1934–1987). Eight (44%) of the species that declined are associated with early successional habitats, and these species consistently exhibited population declines during the 1950s. The reduction of early successional species may be extended in space and time by current land uses that fragment and isolate patches of habitat. Ownership patterns of forest lands in New England (excluding Maine) reveal 88% private ownership with an average holding of 10 ha. This suggests that large tracts of early successional habitats will be restricted to industrial and state/national forests. Although even-aged management of a portion of these forests may be prerceived as incompatible with area-sensitive and interior species, clustering of clearcuts and maintaining large tracts of mature habitats could sustain diverse populations of forest vertebrates. Resumen: A diferencia de otras regiones en Norte America, los habitats boscosos en Nueva Inglattera se han incrementado substancialmente en los ultimos 100 anos. La proporcion de tierra cubierta por bosques en New Hampshire fue del 47 % en 1880 y del 87% en 1980. Este incremento fue, en gran medida, el resultado de un abandono a nivel regional de granjas y la subsecuente colonizacion de estas tierras por un crecimiento secundario de bosques. Yo examine la secuencia del abandono de las granjas, la colonizacion de los bosques y la maduracion de los bosques que ha ocurrido en New Hampshire en relacion con los cambios en la abundancia y distribucion de un grupo de mamiferos y pajaros que han sufrido declinaciones substanciales. Un patron modelado de sucesion secundaria resulto en la disponibilidad de aproximadamente 195,000 ha de habitats serales tempranos (10–25 anos despues del abandono) entre 1905 y 1940. Subsecuentemente, hacia 1960, estos habitats, maduraron hacia bosques de canopeo cerrado. Conjuntamente con la pardida de habitats sucesionales tempranos, las poblaciones de conejos (Sylvilagus transitionalis) de Nueva Inglaterra decrecieron de una distribucion aparentemente continua a traves del 60% de New Hampshire, a una poblacion fragmentada que ocupa < 20% del estado. Los “bobcats” (Felis rufus) respondieron funcionalmente (S. transitionalis en dieta; 1951–54 = 43% versus 1961–64 = 10%) y numericamente (media anual de la captura de Linces: 1951–54 = 350, 1965–69 = 36) a cambios en la abundancia de conejos. Dieciocho de las 26 especies de paserinidos migratorios que anidan en los bosques del norte de Nueva Inglaterra tambien declinaron durante el periodo en que la poblacion fue monitoreada (1934–87). Ocho (44%) de las especies que declinaron estan asociadas con habitats sucesionales tempranos, y estas especies consistentemente exhibieron declinaciones durante los anos 50. La reduccion de especies sucesionales tempranas puede ser extendida (en espacio y tiempo) por los usos actuales de la tierra que fragmentan y aislan los patches de habitat. Los patrones de tenencia de tierra de bosques en Nueva Inglaterra (excluyendo Maine, 88% en manos privadas con una media de tenencia de 10 ha) sugieren que grandes extensiones de habitats sucesionales tempranos van a estar restringidos a usos industriales y reservas estatales/nacionales. Aunque un manejo con stands de la misma edad de porciones de estos bosques puede ser percibido como incompatible con especies sensibles al area y con especies interiores, el agrupamiento de areas taladas y el mantenimiento de grandes extensiones de habitats maduros pueden sustentar poblaciones diversas de vertebrados del bosque.

Assessing the role of fine roots in carbon and nutrient cycling

Abstract: Fine roots remain one of the most difficult and important areas to study in terrestrial ecosystems. Recent investigations have focused on carbon and nitrogen balances to assess their dynamics in natural systems. The results of these new, system-level, budgeting approaches together with those of the more conventional biomass measurement methods may provide valuable insight into fine root carbon and nutrient cycling dynamics. These findings, in turn, may facilitate a more holistic understanding of ecosystem structure and function, which is critical for the assessment and prediction of disturbances to terrestrial systems.

Toward a more accurate time scale for the human mitochondrial DNA tree

Abstract: Several estimates of the time of occurrence of the most recent common mitochondrial DNA (mtDNA) ancestor of modern humans have been made. Estimates derived from noncoding regions based on a model that classifies sites into two categories (variable and invariable) have been consistently older than those derived from the third positions of codons. This discrepancy can be attributed to a violation of the assumption of rate homogeneity among variable sites when analyzing the noncoding regions. Additional data from the partial control region sequences allow us to take into account some of this further heterogeneity. By assigning the sites to three classes (highly variable, moderately variable, and invariable) and by assuming that the last common mtDNA ancestor of humans and chimpanzees lived 4 million years ago, the most recent common mtDNA ancestor of humans is estimated to have occurred 211,000 ±111,000 years ago (±1 SE), consistent with the estimate, 101,000 ± 52,000 years, made from third positions of codons and also with those proposed previously. We used the same technique to estimate when a putative expansion of modern humans out of Africa took place and estimated a time of 89,000 ± 69,000 years ago. Even though the standard errors of these estimates are large, they allow us to reject the multiregional hypothesis of modern human origin.

Model of magnetosheath plasma in the magnetosphere: Cusp and mantle particles at low‐altitudes

Abstract: A model of plasma transport in the open magnetic field region of the dayside magnetosphere has been used to investigate the source regions and the distribution of solar wind plasma in the magnetospheric cusp and mantle. This model includes the variation in the magnetosheath properties as the plasma accelerates away from the subsolar point, the variation in the transport of magnetosheath plasma across the magnetopause as the orientation of the magnetic field line evolves following reconnection, and the transport of the magnetosheath plasma within the magnetosphere. The authors' model results are compared with low-altitude spacecraft data from a crossing of the cusp and mantle. They find qualitative and quantitative agreement between the model results and the data. This agreement suggests that the zeroth-order processes included in the model are sufficient to reproduce the commonly observed particle distributions in the low-altitude cusp and mantle regions. 16 refs., 2 figs.

“Feminine style” and political judgment in the rhetoric of Ann Richards

Abstract: This essay argues for a revised perspective of the theory of “feminine style” developed by Karlyn Kohrs Campbell to explain the characteristics of historical feminist rhetorical action. Using a cas...

Sexually inactive marriages

Abstract: A sample of 6,029 married persons from the National Survey of Families and Households was analyzed to determine the correlates of sexual inactivity in marriage and to see if sexually inactive marriages were less happy and stable than those with sexual activity. Sixteen percent of the marriages in this sample had been sexually inactive during the month prior to the interview. A logistic regression analysis showed unhappiness with the marital relationship, increased likelihood of separation, lack of shared activity, few arguments over sex, lack of physical violence, increased age, fewer children, the presence of preschoolers, and poor health all to be significant correlates of sexually inactive marriage. Significant differences existed between males and females, such as the presence of relationship violence being associated with sexual activity only for females, and the presence of preschoolers and poor health associated with sexual inactivity only for males. These findings suggest that although sexually in...

Productivity response of climax temperate forests to elevated temperature and carbon dioxide: a north american comparison between two global models

Abstract: We assess the appropriateness of using regression- and process-based approaches for predicting biogeochemical responses of ecosystems to global change. We applied a regression-based model, the Osnabruck Model (OBM), and a process-based model, the Terrestrial Ecosystem Model (TEM), to the historical range of temperate forests in North America in a factorial experiment with three levels of temperature (+0 °C, +2 °C, and +5 °C) and two levels of CO2 (350 ppmv and 700 ppmv) at a spatial resolution of 0.5° latitude by 0.5° longitude. For contemporary climate (+0 °C, 350 ppmv), OBM and TEM estimate the total net primary productivity (NPP) for temperate forests in North America to be 2.250 and 2.602 × 1015 g C ⋅ yr−1, respectively. Although the continental predictions for contemporary climate are similar, the responses of NPP to altered climates qualitatively differ; at +0 °C and 700 ppmv CO2, OBM and TEM predict median increases in NPP of 12.5% and 2.5%, respectively. The response of NPP to elevated temperature agrees most between the models in northern areas of moist temperate forest, but disagrees in southern areas and in regions of dry temperate forest. In all regions, the response to CO2 is qualitatively different between the models. These differences occur, in part, because TEM includes known feedbacks between temperature and ecosystem processes that affect N availability, photosynthesis, respiration, and soil moisture. Also, it may not be appropriate to extrapolate regression-based models for climatic conditions that are not now experienced by ecosystems. The results of this study suggest that the process-based approach is able to progress beyond the limitations of the regression-based approach for predicting biogeochemical responses to global change.

Determinants of social support among gay men: the context of AIDS

Abstract: In this study, the determinants of social support are examined among a probability sample of gay men residing in San Francisco. Using two waves of data (collected in 1985 and 1987), cross-sectional and longitudinal analyses focused on the effects of five sets of factors (demographic, community integration/network, AIDS-related loss, individual, and health) on satisfaction with three types of support (emotional, informational, and practical). Personal acceptance of one's gay identity and talking to family members about AIDS showed the strongest positive associations with concurrent measures of support and changes in support satisfaction over the two-year period. Conversely, depression and number of HIV symptoms were negatively associated with cross-sectional support and support changes. Family knowledge of respondents' homosexuality interacted with HIV symptoms, such that knowledge was negatively associated with support among those experiencing greater numbers of HIV symptoms. Findings suggest that those most in need of support may be the least satisfied with the support they receive. Family appear to have the potential to be particularly helpful or especially harmful to gay men trying to cope with the AIDS crisis.

Modulation of cellular polyamines in tobacco by transfer and expression of mouse ornithine decarboxylase cDNA.

Abstract: In an attempt to modulate the metabolism of polyamines in plants, Agrobacterium tumefaciens strains were produced which contained either a full-length or a 3′-truncated mouse ornithine decarboxylase (ODC) cDNA under the control of the cauliflower mosaic virus 35S promoter. Plants of Nicotiana tabacum cv. Xanthi were used for transformation with these two strains of Agrobacterium. Transformations were confirmed by Southern hybridization and amplification by polymerase chain reaction. Two plants containing the full-length cDNA (ODC-12 and ODC-30) and two containing the truncated cDNA (12701-2 and 12701-31) were selected for further experiments. Northern blot analysis indicated that transcription was occurring and western blot analysis detected a polypeptide of ca. 50 kDa that was unique to the plants transformed with truncated ODC cDNA. In order to distinguish between the native and the mouse ODC in the transformed tissues, enzyme activity was assayed at pH optima for the two enzymes, i.e. pH 8.2 and 6.8, respectively. Substantially higher levels of ODC activity were seen at pH 6.8 (optimum for mouse ODC) in the transformants as compared to the controls. This ODC activity was inhibited by α-difluoromethylornithine and anti-mouse ODC antisera in a manner consistent with that reported for the mouse ODC. Analysis of cellular polyamines showed significantly elevated levels (4–12-fold) of putrescine in callus derived from transformed plant tissues as compared to the controls. The modulation of polyamine biosynthesis in plants by these techniques should allow us to further analyze the role of these ubiquitous compounds in plant growth and development.

Everyday forms of employee resistance

Abstract: Drawing on empirical material collected from over 250 individuals employed in a variety of short-term positions, this article examines how temporary employees pursue grievances against their employing organizations. The findings indicate that temporary employees generally respond to offensive behavior on the part of their employers in nonaggressive ways. Gossip, toleration, and resignation are popular, while occasionally grievances are expressed by theft, sabotage, or noncooperation. Collective responses, formal complaints, and legal action are rare. These restrained responses are traced not to the severity of injustices but to the social environment associated with temporary employment, where workers are loosely tied to their organizations and one another. This research may help explain the decline of organized resistance in the contemporary workplace.

Resonant behaviour of MHD waves on magnetic flux tubes. IV: Total resonant absorption and MHD radiating eigenmodes

Abstract: Resonant absorption of MHD waves on a nonuniform flux tube is investigated as a driven problem for a 1D cylindrical equilibrium. The variation of the fractional absorption is studied as a function of the frequency and its relation to the eigenvalue problem of the MHD radiating eigenmodes of the nonuniform flux tube is established. The optimal frequencies producing maximal fractional absorption are determined and the condition for total absorption is obtained. This condition defines an impedance matching and is fulfilled for an equilibrium that is fine tuned with respect to the incoming wave. The variation of the spatial wave solutions with respect to the frequency is explained as due to the variation of the real and imaginary parts of the dispersion relation of the MHD radiating eigenmodes with respect to the real driving frequency.

Habitat structure, conspecific presence and spatial variation in the recruitment of a temperate reef fish

Abstract: Pronounced spatial variation in recruitment occurs in many marine invertebrate and fish populations and is thought to be critical to the demography of these species. In this study I examined the importance of habitat structure and the presence of conspecific residents to spatial variation in larval settlement and recruitment in a temperate fish Tautogolabrus adspersus. I define settlement as the movement of individuals from the water column to the benthic habitat, while I refer to recruitment as numbers of individuals surviving some arbitrary period of time after settlement. Experiments in which standard habitats were stocked with conspecifics showed that resident conspecifics were not an important factor contributing to small-scale variability in recruitment. Further correlative analyses demonstrated that large-scale variation in recruitment could not be explained by variability in older age classes. By contrast, manipulations of macroalgal structure within a kelp bed demonstrated that recruitment was significantly higher in habitats with a dense understory of foliose and filamentous algae than in habitats with only crustose algae. Understory algae varied in their pattern of disperison among sites, and the dispersion of fish matched that of the plants. In order to determine the effects of differences in patterns of algal dispersion on the demography of associated T. adspersus populations, I used experimental habitat units to manipulate patterns of dispersion. Settlement was significantly greater to randomly placed versus clumped habitats; however, no differences in recruitment between random and clumped habitats were detected. Because recruitment is a function of the numbers of settlers minus the subsequent loss of settlers, rates of mortality or migration must have been higher in the randomly placed habitats. These results are counter to the current paradigm for reef fishes which suggests that larval settlement is the crucial demographic process producing variability in population abundance. In this experiment patterns of settlement were modified by varying the patch structure of the habitat.

Regional distribution of monsoon and desert dust signals recorded in Asian glaciers

Abstract: Short-term (6 months to 17 years) glaciochemical records have been collected from glacier basins throughout the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled predominantly by the influx of dust from the arid and semi-arid regions in central Asia. The glaciochemical data suggests that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the southeastern Tibetan Plateau, are the ones most likely to contain longer-term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long-range transport of Asian dust.