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The three Workman Creek watersheds were instrumented to determine the hydrology of mixed conifer forests and to determine the changes in streamflow and sedimentation as a result of manipulating the forest vegetation. A small riparian cut on North Fork did not increase water yields. A selection timber harvest, improvement cut, and fire which removed 45% of the basal area on South Fork increased yields slightly. In contrast, converting 32.4 ha (80 acres) of moist site forest to grass significantly increased water yields on the 100.4-ha (248 acre) North Fork watershed. Water yields were increased even more after 40.5 ha (100 acres) of dry site pine forest were converted to grass. An increase of 69 mm (2.70 in.), or 84%, of expected runoff resulted from the combined treatment. Clearing 83% of the South Fork watershed preparatory to planting ponderosa pine significantly increased water yields by 93 mm (3.67 in.), or by 111%. INTRODUCTIONMixed conifer stands cover approximately 121,500 ha (300,000 acres) in Arizona. They are an important source of water. Under Arizona conditions, water yielded as streamflow is usually a small percent of the precipitation, around 10-15% for mixed conifer sites. This report summarizes the changes in water yields resulting from the most recent treatments applied at WorkmanCreek. DESCRIPTION OF WORKMAN CREEK WATERSHEDS General CharacteristicsThe Workman Creek experimental watersheds are located within the Salt River drainage in central Arizona, about 48 airline km (30 mi) north of Globe. They are part of the Sierra Ancha experimental forest. The three watersheds (Figure 1), North Fork with 100.4 ha (248 acres), Middle Fork with 210.9 ha (521 acres), and South Fork with 128.7 ha (318 acres), drain into Salome Creek and then into Roosevelt Reservoir. Perennial streamflow has been measured continuously since gaging stations were established in 1938. Climate The Workman Creek climate is characterized by cold moist winters, dry warm springs, and hot moist summers [Pase and Johnson, 1968]. There are two distinct rainy seasons. Annual precipitation measured at the recording rain gage in Middle Fork of Workman Creek has averaged (with standard error) 835 + 41 mm (32.89 + 1.60 in.) from 1938 through 1973. Highest annual precipitation, 1,547 mm (60.92 in.), occurred during the 1972-1973 water year (October-September), following the lowest annual precipitation, 428 mm (16.85 in.), during the 1971-1972 water year. Precipitation during the eight winter months, October-May, has averaged 559 + 42 mm (22.01 + 1.64 in.), or 67%, of the annual total. Summer precipitation has averaged 276 + 16 mm (10.88 + 0.61 in.). Annual temperatures at the Workman Creek climatic station averaged about 8.9øC (48øF), varying from -0.6øC (31øF) in January to 18.3øC (65øF) during July and August. Geology and Soils The Workman Creek watersheds are underlain by Dripping Springs quartzite that has been intruded by diabase and basalt Copyright ¸ 1976 by the American Geophysical Union. plugs and sills. Troy sandstone outcrops are ...

The diversity of uncultured Frankia populations in root nodules of Alnus oblongifolia trees geographically isolated on mountaintops of central Arizona was analyzed by comparative sequence analyses of nifH gene fragments. Sequences were retrieved from Frankia populations in nodules of four trees from each of three mountaintops (n ‫؍‬ 162) and their levels of diversity compared using spatial genetic clustering methods and single-nucleotide or 1, 3, or 5% sequence divergence thresholds. With the single-nucleotide threshold level, 45 different sequences with significant differences between the mountaintops were retrieved, with the southern site partitioning in a separate population from the two other sites. Some of these sequences were identical in nodules from different mountaintops and to those of strains isolated from around the world. A high level of diversity that resulted in the assignment of 14 clusters of sequences was also found on the 1% divergence level. Single-nucleotide and 1% divergence levels thus demonstrate microdiversity of frankiae in root nodules of A. oblongifolia trees and suggest a partitioning of diversity by site. At the 3 and 5% divergence levels, however, diversity was reduced to three clusters or one cluster, respectively, with no differentiation by mountaintop. Only at the 5% threshold level do all Frankia strains previously assigned to one genomic group cluster together.

Snow falling in high‐elevation forests is an important source of water for much of the arid Southwest. Snowpack conditions in Arizona and New Mexico differ from those in more northern regions, because of the variability in annual accumulations and the intermittent melting throughout the winter season. Snow management research in Arizona and New Mexico over the past 25 years has indicated the possibilities of increasing snowmelt water yields through forest management activities. The effects of management can be predicted from forest inventory data. Other research has resulted in the development of snow‐runoff forecasting procedures and computer simulation models of forest snowpack dynamics, as well as increasing the general knowledge of snow hydrology.