Summary: Shrub expansion in northern Chihuahuan Desert grasslands: spatial patterns and biophysical constraints
Darroc Goolsby1,3, Brandon Bestelmeyer1,3,4, Steve Archer2,3
1 New Mexico State University; 2 University of Arizona; 3Jornada LTER; 4USDA/ARS
Among the greatest contemporary threats to the structure, function and biological diversity of desert grassland and shrub savanna ecosystems is the
displacement of mesophytic grasses by xerophytic woody plants. Information needed by land managers falls into two categories: (i) how to prevent
shrub encroachment; and (ii) how to restore grasslands once shrub encroachment has occurred. Managers need to anticipate which landscapes are
most susceptible to shrub encroachment and which are most likely to be restored once shrub encroachment has occurred. Information currently
available from traditional inventory and monitoring programs and small-scale, short-term field experiments is not sufficient to make these predictions.
In order to develop a predictive understanding of shrub encroachment and grassland restorability, we are quantifying long-term, large-scale rates and
patterns of shrub encroachment with the dual goals of :
(i) identifying the biophysical properties of grasslands that put them at risk to woody plant invasion; and
(ii) characterizing the properties of shrub-invaded grasslands that make them suitable candidates for restoration.
Here, we have focused on the first goal and asked:
· What soil characteristics are correlated with the occurrence of persistent grass patches (i.e., those that are uninvaded by shrubs)?
· Can an understanding of historic spatial patterns of shrub expansion help us predict future landscape change?
Assembling Spatial and Plot Data
Site: Jornada Basin Long-Term Ecological Research site near Las Cruces, NM.
Land cover of a 11,700 ha area was digitized from aerial photography (1942) and a
Quickbird satellite image (2003) using a combination of hand digitization and image-