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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 varies 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 winds with gusts 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 11th 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 Summenhumidity 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 Climate Center>Historical Data>Western U S.Climate summaries,NOAA Coop <br /> Stations>Colorado hnp:ttwww.wrcc.dd.edu/summary/Clknsmco.html 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 brief 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 mid-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 years,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 sub-dominant groups,changes in growing season length,responses of cool- <br /> season and warm-season grasses,etc.)is on-going. <br /> Averaged <br /> Frostdree period(days): 129 <br /> Freeze-flee period(days): 150 <br /> Mean annual precipitation(inches): 15.89 <br /> Plaint 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 duration/time controlled grazing strategies,and historical accounts. <br /> The Sandy Bottomland ecological site is characterized by three states:Reference,Shrub,and Eroded State.The Reference State Is <br /> characterized by a dominance of warm-season tallgrasses(sand bluestem,prairie sandreed,and smichgrass) The Shrub State 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 forbs and grasses(sunflower,kochia,Russian thistle,cheatgrass)and early successional plants(sandhill muhly,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 surfed for grazing by domestic <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 /> switchgrass Subdominant grasses include needle and thread.blue grams,little bluestem and western wheatgrass Significant forts and <br /> shrubs are pacific peavine,evening primrose,prairie clovers,leadplant and western sandcherry.Cottonwoods may be present.The potential <br /> vegetation is about 70-85%grasses or grass-like plants,8-15%forbs and 7-15%shrubs. <br /> 9 <br />