Submitted to: Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2005
Publication Date: 4/15/2006
Citation: Bestelmeyer, B.T., Ward, J.P., Havstad, K.M. 2006. Soil-geomorphic heterogeneity governs patchy vegetation dynamics at an arid ecotone. Ecology. 87(4):963-973. Interpretive Summary: We show that rangeland vegetation change over 60 years occurring on a loamy soil in the Chihuahuan Desert of southern New Mexico is patchy, with patches often smaller than a few meters across. We also show that whether a patch stays vegetated, recovers vegetation, loses vegetation, or stays unvegetated is related closely to inherent soil properties, especially carbonate content of the surface and clay content of the subsoil. Patchiness in these soil properties thus controls how this rangeland has changed Monitoring and mangement needs to take this patch structure into account.
Technical Abstract: Soil properties are well known to affect vegetation, but the role of soil heterogeneity in the patterning of vegetation dynamics is poorly documented. We asked whether the location of an ecotone separating grass-dominated and sparsely-vegetated areas reflected only historical variation in degradation or was related to variation in inherent soil properties. We then asked whether changes in the cover and spatial organization of vegetated and bare patches assessed using repeat aerial photography reflected self-organizing dynamics unrelated to soil variation or the stable patterning of soil variation. We found that the present-day ecotone was related to a shift from more weakly to more strongly developed soils. Parts of the ecotone were stable for over 60 year, but shifts between bare and vegetated states, as well as persistently vegetated and bare states, occurred largely in small (<40 m2) patches throughout the study area. The probability that patches were presently vegetated or bare, as well as the probability that vegetation persisted and/or established over the 60 year period, was negatively related to surface calcium caronate and positively related to subsurface clay content. Thus, only a fraction of the landscape was susceptible to vegetation change and the sparesely-vegetated area likely featured a higher frequency of susceptible soil patches. Patch dynamics and self-organizing processes can be constrained by subtle (and often unrecognized) soil heterogeneity.