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Shrub (Prosopis velutina) encroachment in a semidesert grassland: spatialtemporal changes in soil organic

Summary: Shrub (Prosopis velutina) encroachment in a semidesert
grassland: spatial­temporal changes in soil organic
carbon and nitrogen pools
H E AT H E R L . T H R O O P * and S T E V E N R . A R C H E R w
*Department of Biology, New Mexico State University, MSC 3AF, Las Cruces, NM 88003, USA, wSchool of Natural Resources,
University of Arizona, Tucson, AZ 85721-0043, USA
Recent trends of increasing woody vegetation in arid and semiarid ecosystems may
contribute substantially to the North American C sink. There is considerable uncertainty,
however, in the extent to which woody encroachment alters dryland soil organic carbon
(SOC) and total nitrogen (TN) pools. To date, studies assessing SOC and TN response to
woody plant proliferation have not explicitly assessed the variability caused by shrub
age or size and subcanopy spatial gradients. These factors were quantified via spatially
intensive soil sampling around Prosopis velutina shrubs in a semidesert grassland, using
shrub size as a proxy for age. We found that bulk density increased with distance from
the bole (Po0.005) and decreased with increasing shrub size (P 5 0.056), while both SOC
and TN increased with shrub size and decreased with distance from the bole (Po0.001
for both). Significant (and predictable) spatial variation in bulk density suggests that use
of generic values would generate unreliable estimates of SOC and TN mass, and
subcanopy SOC pools could be overestimated by nearly 30% if intercanopy bulk density


Source: Archer, Steven R. - Savanna/Woodland Ecology Lab., School of Natural Resources and the Environment, University of Arizona


Collections: Environmental Sciences and Ecology