Development of native plant materials & restoration methods to mitigate accelerated soil erosion in the pinyon-juniper woodlands of Bandelier National Monument

Allen, Craig

Pinyon-juniper woodlands cover 19, 000, 000 hectares in the western Un~ ted States. The initiation of intensive grazing by domestic livestock in the late 1800's led to extensive changes in ecosystem structure and function in these pifion-juniper woodlands of the Southwestern United States (Leopold 1924, West and Van Pelt 1987, Evans 1988, Allen 1989). Herbaceous ground cover and litter were greatly reduced, exposing increasing areas of bare soil which led to decreases in infiltration and increases in surface runoff from the typically intense, local, summer rainfall events. Thresholds were exceeded, triggering major increases in soil erosion. The reductions in grassy understories led to widespread establishment of pifion and juniper trees in former savannas and grasslands, due to decreased herbaceous competition with tree seedlings and reductions in fire frequencies. Pinon and juniper trees now dominate dense woodlands, preventing herbaceous plant reestablishment even after the removal of domestic livestock through control of site resources (and possibly allelopaths). In essence, a positive feedback cycle has b13en established over millions of hectares of pifion-juniper woodlands in which accelerated soil erosion and tree dominance work to keep tree interspaces largely barren and subject to further erosion. The pifion-juniper ecosystems which cover 40% of Bandelier National Monument are representative of much of the Southwest as they display the disrupted native plant communities and accelerated soil erosion described above (Allen 1989). A soil survey of the affected pifion-juniper woodland portions of the park estimated soil erosion rates of O. 53 cm/year, or 79. 3 megagrams/ha/year ( 35. 7 tons/acre/year) ( Earth Environmental Consultants 1978). Given total soil depths to bedrock ranging from 15 cm to 1 meter, the extrapolated erosion rate of 53 cm/100 years reflects the clearly unsustainable soil loss observed throughout most of this ecosystem type. In addition, the situation at Bandelier is complicated by the presence of 3000-4000 archeological sites, mostly located on pifion-juniper sites; an ongoing survey has found that over 75% of 1600 inventoried archeological sites are being damaged by erosion (Orcutt 1990). This pre-proposal outlines an approach to develop means to mitigate this serious natural and cultural resource problem which would be widely applicable in the West.