Browsing by Author "Hajek, Ernst R."

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    Growing seasons in Chile: Observation and prediction
    (1979) Hajek, Ernst R.; Gutierrez, J. R.
    Temperature data for 42 Chilean locations were analysed and heat sums calculated (for base 5 C and 10 C). Also, the length, starting and ending dates of the growing seasons were obtained. Temperature values normally found in Chilean climatological records, i.e. monthly and annual means, were related with temperature accumulations. In Chile it is possible to predict the accumulation of temperature from the annual mean temperature (r=0.995, P<.001, for base 5 C and r=0.984, P<.001, for base 10 C) or from the mean monthly temperature of January. In this latter case, a good adjustment with an exponential curve is found (r=0.76, P<0.001, base 5 C; r=0.78, P<0.001, base 10 C). For Chile, temperature courses along the year were approximated by using a harmonic analysis. No significant differences were observed between predicted and observed values. By integrating these equations as a function of time, it is possible to determine both the accumulation of temperature and the length of growing seasons for different threshold temperatures. A significant relationship was found between these variables and the latitude, and gradients were also obtained. Differences exist between littoral and continental stations in the extension of growing seasons and the accumulation of temperatures.
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    Seasonality of conception in human populations in Chile
    (1981) Hajek, Ernst R.; Gutiérrez, Julio R.; Espinosa, G.
    Seasonality of conceptions in human populations in Chile was studied for a period of 30 years (1945 1974). Clear seasonal conception courses exist in the country, exception made of the northern and southern extremes. Seasonal flux is concentrated mainly in January, but also secondary increases in April and June were observed. Along the 30-year period a general pattern of decreasing seasonality is observed. Conception is significantly related to temperature and photoperiod in this country, the maximum rates of conceptions being observed in coincidence with the maximum temperatures and photoperiods. Nonclimatic factors which may be affecting seasonality of conceptions are also discussed.
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    Seasonality of mortality in human populations of Chile as related to a climatic gradient
    (1984) Hajek, Ernst R.; Gutiérrez, Julio R.; Espinosa, G. A.
    Mortality of human populations in Chile was studied from a latitudinal and seasonal perspective, and related to climate and main diseases. Approximately 3 mill. deaths were analyzed. Seasonality considered along a latitudinal and climatic gradient is almost absent in the northern portion of the country, in the central part peaks are evident in summer, at latitudes 40 S in winter and at 45 S in winter and spring. Seasonality along the years of analysis shows a different behaviour for the different zones of the country and no unique pattern is evident. A clear relationship between the air enthalpy and seasonality of mortality is detected. Circulatory diseases appear as the most important causes of deaths, exception made of latitude 40 where respiratory diseases are the significant causes of deaths. Age groups below one and above 65 years are mostly affected.
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    Temperature effect on autochory inColliguaya odorifera (Euphorbiaceae)
    (1980) Giliberto, J.; Gutiérrez, Julio R.; Hajek, Ernst R.
    Colliguaya odorifera Mol. is the only species of the Chilean matorral which shows an active dispersion of its seeds (autochory). This mechanism is dependent on daily variation of temperatures. Other climatic variables (air humidity of vapor pressure deficit) appear as not having direct influences on seed dispersal.