932 resultados para Vegetation succession
Resumo:
Principal coordinates analysis and multiple regression analysis were used to determine the environmental factors associated with the decline in phytoplankton production during and after the 1977 drought for the San Francisco Bay-Delta Estuary. Physical, chemical and biological data were collected semimonthly or monthly during the spring-summer between 1973 and 1982 from 15 sampling sites located throughout the Bay-Delta. A decline in phytoplankton community diversity and density during the 1977 drought and subsequent years (1978 through 1981) was described using principal coordinates analysis. The best multiple regression which described the changes in phytoplankton community succession contained the variables water temperature, wind velocity and ortho-phosphate concentration. Together these variables accounted for 61 percent of the variation in the phytoplankton community among years described by principal coordinates analysis. An increase in water temperature, wind velocity and ortho-phosphate concentration within the Bay-Delta, beginning in June 1976 and continuing through 1981, was demonstrated using weighted moving averages. From the strong association between phytoplankton community succession and climatic variables it was hypothesized that the decline in phytoplankton production during and after the 1977 drought was associated with climatic changes within the northeast Pacific.
Resumo:
EXTRACT (SEE PDF FOR FULL ABSTRACT): Sediment traps placed in the profundal region of Elk Lake, north central Minnesota during the 1979 spring and 1983-84 fall and spring seasons monitored seasonal diatom production for two climatically distinctive periods.
Resumo:
The effect of decreasing frost frequency on desert vegetation was documented in Grand Canyon by replication of historical photographs. Although views by numerous photographers of Grand Canyon have been examined, 400 Robert Brewster Stanton and Franklin A. Nims views taken in the winter of 1889-1890 provide the best information on recent plant distribution. In Grand Canyon, where grazing is limited by the rugged topography, vegetation dynamics are controlled by climate and by demographic processes such as seed productivity, recruitment, longevity and mortality. The replicated photographs show distribution and abundance of several species were limited by severe frost before 1889. Two of these, brittlebush (Encelia farinosa) and barrel cactus (Ferocactus cylindraceus), have clearly expanded their ranges up-canyon and have increased their densities at sites where they were present in 1890. In 1890, brittlebush was present in warm microhabitats that provided refugia from frost damage. Views showing desert vegetation in 1923 indicate that Encelia expanded rapidly to near its current distribution between 1890 and 1923, whereas the expansion of Ferocactus occurred more slowly. The higher frequency of frost was probably related to an anomalous increase in winter storms between 1878 (and possibly 1862) and 1891 in the southwestern United States.
Resumo:
A normalized difference vegetation index (NDVI) has been produced and archived on a 1 latitude by 1 longitude grid between 55S and 75N. The many sources of data errors in the NDVI include cloud contamination, scan angle biases, changes in solar zenith angle, and sensor degradation. Week-to-week variability, primarily caused by cloud contamination and scan angle biases, can be minimized by temporally filtering the data. Orbital drift and sensor degradation introduces interannual variability into the dataset. These trends make the usefulness of a long-term climatology uncertain and limit the usefulness of the NDVI. Elimination of these problems should produce an index that can be used for climate monitoring.
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31491CNKNapHP;( 0~10 cm)Ca0( 20-30 cm40-50 cm);2;3CR-S;C-CNC-CR-SC-SR-SR-W-Bs-VBs-V-4C- SC-CNK; SSR-R-CR-SNaCa0pH550 mm (6 13C)( Artemisia scoparia)( Lespedeza davurica);(Stipabungeana)(Artemisia gmelinii)(Artemisia giraldii); ( Bothriochloa ischaemun)-26.890.66-26.240.48, -26.210.49, -26.861.09, -27.610.39-15 .811. 79;2.360.63%2.380.29%2.00.29%2.00.25%1.500.37% 1.240.19% 13C5 13C 13C; 13C 13C -19744%22%20%14%; 197104881028t.y-l104881028y-119995244051y-119995.3199914 %100059%;100041%1147.2234RMB.yr-146%27%14%13%
Resumo:
EXTRACT (SEE PDF FOR FULL ABSTRACT): Large-scale changes in the growth and decay of land plants can be deduced from trends in the concentration of atmospherics [sic] carbon dioxide, after removing signals in the recorded data caused by oceanic and industrial disturbances to the concentration.
