PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Long-term influence of Maasai settlement sites on plant nitrogen and carbon isotopes.

PHILLIPS, SUSAN¹, SANFORD, ROBERT², REID, ROBIN³, BELNAP, JAYNE¹, ^{1 2 3}

ABSTRACT- In East African savannas where plant production and distribution are limited by low water and nitrogen availability, the highly concentrated dung and urine inputs associated with pastoralist corrals have been shown to influence soil resources. To assess the manner and duration of the effect of abandoned Maasai settlement sites (bomas) and associated corrals on plant nutrient and water dynamics, we surveyed 14 sites that had been abandoned for 1 month to 149 years. The leaves of mature Seriococcomopsis pallida, a perennial C₃ shrub growing both on and off bomas, were analyzed for nitrogen and carbon isotopic content and C:N ratios. Leaf ¹⁵N values from plants growing at least 150 m outside of bomas varied little with boma age, and were significantly lower than those growing on bomas of all ages. For plants in bomas, leaf 15N varied considerably with boma age, and reflected changes in nitrogen source. The ¹³C values from open grown leaves were lower than those for leaves from young and old bomas; this pattern was reversed for 25-60 yr old bomas. Although dung heaps are known to increase water availability, leading to more positive ¹³C values, we propose that our results are more strongly influenced by nutrient release from soil microbial activity. Finally, leaf C:N ratios are consistently lower inside bomas, suggesting that nitrogen availability is improved for at least 150 years after abandonment.

KEY WORDS: pastoralism, nutrient hotspots, dung, east african savanna