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Climatic Features <br /> Average annual precipitation across the MLRA extent is 14 to 17 inches,and ranges from 13 inches to over 18 inches,depending on location <br /> The.average is 15 inches Precipitation increases from north to south.Mean Annual Air Temperature(MART)is 50`F in the northern part and <br /> increases to 52`F in the southern part.Portions of Morgan and Weld counties(in the northern part)are cooler and drier,the MAAT is 48'F, <br /> and average precipitation is 13 to14 inches per year Two-thirds of the annual precipitation occurs during the growing season from mid-April to <br /> late September Snowfall averages 30 inches per year,area-wide,but vanes by location from 20 to 40 inches per year.Winds are estimated <br /> to average 9 miles per hour annually.Daytime winds are generally stronger than at night,and occasional strong storms may bring periods of <br /> high vonds with yusts to more than 90 mph High intensity afternoon thunderstorms may arise The average length of the freeze-free period <br /> (28'F)is 155 days from April 30th to October to 3rd.The average frost-free period(32'F)is 136 days from May 11 th to September 24th.July <br /> is the hottest month,and December and January are the coldest months.Summer temperatures average 90"F and occasionally exceed <br /> 100'F Summer humidity is low and evaporation is high Winters are characterized with frequent northerly winds,producing severe cold with <br /> temperatures occasionally dropping to-30"F or lower.Blizzard conditions may form quickly For detailed information,visit the Western <br /> Regional Climate Center website Western Regional Climale Center>Histon al Data>Western U 5.Climate summaries.NOAA Coop <br /> Stations>Colorado hftp:Itwww.wrcc,dd.edu/summary/Chmsrnco.htmi Eastern Colorado was strongly affected by extended drought conditions <br /> in the"Dust Bowl'period of the 1930's,with recurrent drought cycles in the 1950s and 1970s Extreme to exceptional drought conditions have <br /> re-visited the area from 2002 to 2012,with beef interludes of near normal to normal precipitation years Long-term effects of these latest <br /> drought events have yet to be determined.Growth of native cool-season plants begin about April 1 and continue to and June.Native warm <br /> season plants begin growth about May 1 and continue to about August 15 Regrowth of cool-season plants occur in September in most years. <br /> depending on moisture.Note.The climate described here is based on historic climate station data in the past 30 to 50 yeam and is averaged <br /> to provide an overview of annual precipitation temperatures,and growing season.Future climate is beyond the scope of this document <br /> However,research to determine the effects of elevated CO2 and/or heating on mixed-grass prairie ecosystems,and how it may relate to <br /> future plant communities(i e.potential shifts in dominant and subdominant groups,changes in growing season length responses of cool- <br /> season and warm-season grasses,etc)is on going <br /> Avera ed <br /> Frost-free period(days): 129 <br /> Freeze-free period(days): 150 <br /> Mean annual precipitation(inches): 15-89 <br /> Plant Communities <br /> Ecological Dynamics of the Site <br /> The information in this ESD.including the state-and-transition model diagram(STM),was developed using archeological and historical data, <br /> professional experience,and scientific studies.The information is representative of a dynamic set of plant communities that represent the <br /> complex interaction of several ecological processes.The plant composition has been determined by study of rangeland relic areas areas <br /> protected from excessive disturbance,seasonal use pastures,short duraWn/time controlled grazing strategies,and historical accounts. <br /> The Sandy Bottermland ecological site is characterized by three slates.Reference.Shrub,and Eroded State.The Reference State is <br /> characterized by a dominance of warm-season tallgrasses(sand bluestem,prairie sandreed,and switchgrass).The Shrub Slate is dominated <br /> by sand sagebrush and a minor component of understory species(sand dropseed.Fendler threeawn) The Eroded State is characterized by <br /> annual(orbs and grasses(sunflower,kochia.Russian thistle cheatgrass)and early successional plants(sandhill rnuhly.sand dropseed. <br /> Fendler threeawn and lemon scurfpea) <br /> Reference Plant Community <br /> This is the interpretive plant community.This plant community evolved with grazing by large herbivores,is well suited for grazing by dormesiia <br /> livestock and can be found on areas that are properly managed with grazing that allows adequate recovery opportunity following each grazing <br /> occurrence during the growing season. <br /> The reference plant community consists chiefly of warm-season tallgrasses.Principle dominants are sand bluestem,prairie sandreed,and <br /> swhchgrass Subdominant grasses include needle and thread,blue grama,little bluestem and western wheatgrass.Significant(orbs and <br /> shrubs are pacific peavine-,evening pnini prairie clovers,leadplant and westem sandcherry Cottonwoods may be present.The potential <br /> vegetation is about 70-85%grasses or grass-like pants.8-15%forbs and 7-15%shrubs. <br /> 9 <br />