. Foresta Uso di terra e streamflow nel centro di Oregon. Le foreste e la silvicoltura Oregon Ochoco Creek Watershed uso multiplo; Gestione di Spartiacque Oregon Ochoco Creek spartiacque; le misurazioni del flusso di Oregon Ochoco Creek spartiacque. Per determinare se la pendenza apparente si rompe in figura 9 si è verificato un caso, test statistici di significatività sono state effettuate mediante metodi di covarianza. I periodi 1942-58 e 1958-65 sono stati testati contro il periodo 1921- 42. Sono state riscontrate differenze per essere altamente significativo4 in entrambi i casi. La differiscono- ence tra il 1942-58 e il 1958-65 periodi è stata trovata essere significativo a th

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. Forest land use and streamflow in central Oregon. Forests and forestry Oregon Ochoco Creek Watershed Multiple use; Watershed management Oregon Ochoco Creek Watershed; Stream measurements Oregon Ochoco Creek Watershed. To determine whether the apparent slope breaks in figure 9 occurred by chance, statistical tests of significance were made by methods of covariance. The periods 1942-58 and 1958-65 were tested against the period 1921- 42. Differences were found to be highly significant4 in both cases. The differ- ence between the 1942-58 and the 1958-65 periods was found to be significant at the 95-percent confidence level. These statistical tests show that increased streamflow subsequent to 1942 did not occur due to chance. They show further that the 1.18 inches average decrease in annual flow after 1958 is a real change. The recognized slope breaks indicate times at which inconsistencies or changes occurred in the relation between pattern and measured flows. The difference in slopes of the lines on either side of the breaks indicates the extent of the change. With reasonable assurance that data collection methods have not changed, the need remains to identify plausible events or physical changes which coincide with slope breaks. Knowing the approximate timing of changes in streamflow relationships, one may analyze the history of Ochoco Creek for causes. However, such analysis is necessarily qualita- tive due to the general character of certain use data. The possibility exists that streamflow relations changed in response to a persistent climatic change. Though annual precipita- tion amounts at Prineville during the period 1922- 65 are essentially a normal distribu- tion, mean annual precipitation during 1943-58 was nearly 2 inches greater than during 1922-42. However, from prediction equations developed for both periods, 5 a streamflow increase of only 0.5 to 0.7 inch would be the expected result of a 2-inch increase in annual precipitation. Significant at the 99-pe

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