PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Soil carbon patterns in a semiarid pinyon-juniper woodland.
Reiley, David*,1, Breshears, Dave2, Zedler, Paul 1, Ebinger, Mike2, Meyer, Clif2, 1 University of Wisconsin-Madison, Madison, WI, USA2 Los Alamos National Laboratory, Los Alamos, NM, USA
ABSTRACT- Pinyon-juniper-grassland complexes cover 60 million acres of the American west. An increase in tree and shrub components has been noted worldwide in the last century along the grassland-shrubland-woodland continuum. This woody encroachment may contribute to the missing sink of carbon noted in various evaluations of global carbon cycles. In Northern New Mexico, pinyon-juniper (PJ) woodland encroachment into grasslands creates patchy landscapes with sparse herbaceous cover between tree clusters. To evaluate soil carbon storage we measured total carbon % in a PJ stand in Los Alamos, New Mexico. A total of 180 cores and 1071 samples of 5 or 10 cm depth increments were obtained and analyzed. We found that soil carbon was greater on a percentage basis under tree canopies than grass patches or bare soil in intercanopy areas and, as we generally expected, was greater in the upper few centimeters of soil than at depth. We hypothesize the observed pattern is due to litter inputs into the upper few centimeters of soil where trees provide greater inputs, grasses somewhat less, and bare soils less still. However, surface soils often have bulk densities that are low compared to samples taken at depth. Comparisons using % carbon may be overstating the actual differences in the carbon stored within soils. We used a local bulk density evaluation to estimate carbon storage on a mass/volume basis. Despite the lighter soils in the highest carbon containing fractions (canopy and grass soils at the surface), our analysis of soil carbon on a mass/volume basis lead to substantially the same conclusions. Our results suggest that management of PJ for carbon sequestration will require careful consideration of patch dynamics and the interplay with potential disturbances that may be common at different stages of woodland development such as erosion or crown fire.
Key words: semiarid, soil carbon, resource management