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N Deposition, Invasive Species and Impacts on Biodiversity in Southern California

N Deposition, Invasive Species and Impacts on Biodiversity in Southern California. Edith B. Allen Department of Botany and Plant Sciences University of California, Riverside. Four major vegetation types are subject to N deposition in southern California

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N Deposition, Invasive Species and Impacts on Biodiversity in Southern California

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  1. N Deposition, Invasive Species and Impacts on Biodiversity in Southern California Edith B. Allen Department of Botany and Plant Sciences University of California, Riverside

  2. Four major vegetation types are subject to N deposition in southern California • Coastal sage scrub and desert scrub are subject to vegetation type conversion by exotic annual grasses. • Mixed coniferous forest and chaparral are relatively stable.

  3. Levels of increasing N deposition required to increase invasive species and fire frequency in different vegetation types

  4. What are critical loads for N deposition that promote vegetation type conversion in coastal sage scrub (28-35 cm precipitation, 30 kg ha-1yr-1 N deposition) vs. Mojave desert scrub (< 25 cm, > 8 kg ha-1yr-1 )?

  5. Soil N gradient from north to south in the Riverside-Perris Plain

  6. Box Springs Mt. with high N deposition dominated by exotic annual grassesLopez Canyon with low N deposition dominated by native forbs and shrubs

  7. % cover and biomass of grasses following the 1993 fire and N fertilization (60 kg/ha/yr). The threshold for fire is 0.5-1.0 t/ha of fine grass fuel.

  8. % cover of exotic and native forbs following the 1993 fire and N fertilization.

  9. Air pollution at Key’s View, JOTR Dec. 04 Schismus barbata and Brassica tournefortii invasion at Snow Creek following fire

  10. Exotic grass biomass following two years of N fertilization at four sites at Joshua Tree National Park, 2004

  11. Elevated exotic grass biomass above the threshold value of 0.5-1.0 T/ha is most likely responsible for the high incidence of fire in the areas of CSS affected by N deposition. Even in the absence of fire, after a decade of N deposition at 60 kg/ha/yr exotic grasses increased and native species declined. In arid regions N will accumulate in soil, so critical loads are determined by a combination of time X level of N inputs.

  12. Number of plant species in each lifeform in 3 ha plots at seven sites along a N deposition gradient with varying concentrations of soil N (mg/kg)

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