2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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1 • • • Introduction BUILDING A FOUNDATION FOR DIVERSITY: TOPDRESSING VARIABILITY FOR DISTINCT PLANT COMMUNITIES Bruce Buchanan, Tim Ramsey and Douglas Romig' In the mid 1960's a reclamation decision was made at Navajo Mine to either save topsoil or use irrigation for the establishment of vegetation. Everyone knew that mine dirt was all the same and that water would make anything grow so, irrigation won. By the early 1970's, the need for topsoil became evident and so a few new terms were added to the mines vocabulary- topdressing stockpile, seed bed preparation, and mulch. Irrigation continued at BHP and is still used today at our Navajo and San Juan Mine operations. The reclamation at the La Plata Mine (LPM) operation is all dry land. My earliest experiences in mine land reclamation began in 1975. The objective was to protect the soil and produce cover and biomass. The only post mine land use (PMLU) was livestock grazing and plant diversity was something we measured in inches and pounds. As we have tried to better understand plant diversity we found, like everyone else, production and diversity are opposites. At Navajo and San Juan Mines pure stands of Alkali Sacaton are the most productive. They were easy to establish with irrigation, especially on long smooth slopes with uniform applications of topdressing. Shrubs became established in areas where the topsoil was thin or the landscape was concave and water collected. The deep pockets of topsoil might produce stands of Indian Ricegrass or Galleta. But it was easier and generally less expensive to keep things uniform. If we had diversity, it was in the seed mix. Eight grasses, six forbs, two shrubs -and a partridge in a pear tree. At one time we even seeded by the pound. A pound of this with a pound of that. No wonder Alkali Sacaton was successful. Over the years plant diversity, of sorts, was being created - mostly by doing things that would not be approved. Especially in our mistakes. Today we see plant diversity associated with variation in some of the following: Topsoil depth Spoil quality Irrigation schedules- timing and amount Seed mix Seeding rate Time of seeding Double Wedge Study Genetic source of seed Slope grade and aspect Slope shape- convex vs. concave Use of amendments Application of direct haul topdressing In 1991, LPM included a program to more carefully document the factors influencing diversity. Attention was directed to two factors; topsoil depth and spoil quality. The objective was to evaluate the effects of topsoil depth and spoil quality on plant response measured by cover, production and diversity. The hypothesis was that plant response would be different for different soil depths. La Plata Mine is located 20 miles north of Farmington, NM. The annual precipitation averages 12 inches (30 cm) per year at an elevation of 6100 ft. The dominant native plant communities are a mix of sagebrush grasslands and pirlon and juniper forests. The landforms are steeply sloping questas dissected by deep valley fill. Soils are typically shallow with occasional deep alluvial fill. The overburden is composed of sandstone, siltstone and claystone. The rock formation is described as the Kirtland shale. Study Design & Purpose: In 1991, a study to evaluate topdressing depth and spoil quality was designed by overlapping a topdressing wedge and a spoil wedge -the result was a double wedge plot with the purpose of monitoring plant response to various combinations of topdressing depth and spoil quality. Previous studies have shown a significant interaction between topdressing depth, spoil quality and plant response. Generally, high plant productivity can be established with thin applications of topsoil if high spoil quality is used 1 Bruce Buchanan, Buchanan Consultants Ltd., Farmington, NM; Tim Ramsey, San Juan Coal Co. - La Plata Mine, La Plata, NM; Douglas Romig, NM Mining and Minerals Div., Santa Fe, NM.