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establishes the seeded species and second -year irrigation ensures vegetation stand <br />development and seedling maturity. Irrigation generally was not applied after the <br />second growing season (Porterfield, 1990). Field inspections performed one and two - <br />years after cessation of irrigation typically observed significant decline of seeded <br />grasses, shrubs and forbs, even though the seeded species were genetically adapted to <br />arid conditions. Plants that germinated and developed under irrigated conditions <br />adapted physiologically to this increased moisture regime. "Addiction" to irrigation <br />water resulted in morphological changes to roots, stems and leaves that could not <br />withstand the removal of irrigation. Additionally, seedling density established under <br />irrigated conditions could not be supported under natural conditions (Wertz, G. <br />Personal Communications, 2002). Similar vegetation responses to irrigation and <br />irrigation removal were observed on test plots established in 1998 and 1999 at the Rocky <br />Mountain Arsenal north of Denver, Colorado. <br />If a seed mix is properly designed for a specific cite using native and adapted species, <br />the selected plant species should have the genetic capability to withstand the climatic <br />and environmental conditions that occur during the growing season. Typically, seeds <br />will remain dormant until soil moisture conditions allow germination and <br />establishment. The seeds of many species adapted to arid and semi -arid regions may <br />remain viable and lie dormant in the soil for periods of 5 or more years (Schuman et al., <br />2001). Allowing reconstructed soils to lie fallow before planting permanent seed <br />mixtures may serve to improve seedling germination and establishment, particularly <br />during drought cycles. <br />TIMING OF SEEDING OPERATIONS <br />There are two generally accepted primary periods for conducting planting operations <br />on arid and semi -arid rangelands, including a fall and a spring planting period. When <br />possible and practicable, seeding operations will be conducted during these two general <br />Appendix G 9 07/01/02 <br />