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September 30. Although these amounts do not represent this specific site, the pattern of precipitation is very close to what was actually received at the site. The pattern of precipitation for 1999 exhibits some very unusual conditions that translate to severe problems for revegetation programs in their initial stages. The overall pattern of precipitation events is similar to the historical patterns for Pueblo, but the amounts received create a very difficult situation for seedling establishment. In late April a region wide precipitation event dropped huge amounts of rain throughout the area. Major flooding occurred throughout the region. Note that in April the total precipitation was 4.42 inches above normal. In a normal April about 0.88 inches of precipitation would be received. The weather station received 5.3 inches in that month. This is 602% of normal. During that last week in April, Pueblo received nearly a third of the average annual precipitation. After that event, the weather turned very dry until July and August when the monsoon arrived. May was above normal by a small amount, but June was very dry with only 15% of normal precipitation. This pattern is almost always disastrous to revegetation programs. The very high precipitation event spanning only a few days induces extremely high germination rates and very high seedling density. If precipitation patterns do not continue at a level that can support that density until the seedling roots can reach sufficient depth to become drought tolerant, extreme moisture competition occurs between the seedlings. This usually results in a seeding failure. Observations of the revegetation program showed extremely high seedling densities in mid-May, no doubt a result of the high quantity of moisture received a couple of weeks earlier. By June some decline in plant density was observed, but seedling density remained unusually high. This was no doubt a result of the slightly wetter than normal May. By July however, virtually no seedlings could be found and few immature plants where seedling density had been high. On the other hand, previously established plants had exhibited dramatic increases in cover and were still in excellent condition. It is not known at the time of this annual report whether this very adverse precipitation pattern has caused a seeding failure of the salty soil revegetation program test, but it appears likely that did occur. It is also possible that more establishment did occur but the plants entered an early dormancy and, in fact, some of the growth is still there. The monsoon peak, however, did not produce any additional growth except in those plants that had become established in previous years. Determination as to whether a failure has occurred cannot be made until mid-May. The positive aspect to this event, however, is that it has been determined that salt tolerant species must be used in these soils. The high germination rate and initial growth clearly showed a pattern not seen when non-salt tolerant species were used. Furthermore, during 1999 the only grasses that expanded in cover were salt tolerant species. Salt intolerant species only expanded where salt affected soils did not exist or other factors kept the salt content at a low level. Furthermore, the high precipitation event in late April undoubtedly leached a large amount of salt out of the soil, creating a more favorable growth environment under more normal conditions. At this time other measures are being considered to create a more uniform establishment environment, including possible irrigation to supplement (not replace) precipitation. A study of normal precipitation patterns is planned to determine if precipitation is characteristically rare during short periods of 6 to 14 days that could be eliminated by supplemental irrigation. Supplemental irrigation would reduce stress on the seedlings during these times, if they exist. Also planted in this experiment was Four-winged Saltbush. This species should be able to grow well on the site. Unfortunately, not a single seedling was seen, even after the large precipitation event. It was then learned that recently it has been determined that this species requires layering to successfully germinate. Layering conditions (exposure to cold temperatures for a prolonged period) did not occur between the time of planting and the start of the growing season. It is likely the layering occurred during Transit Mix of Pueblo 2000 Annual Report M-1977-573 Pueblo West Pit Page 2 of 3