Fragmentation Effects on Soil Aggregate Stability in a Patchy Arid Grassland

Abstract

Soil aggregate stability (AS) has been promoted as a primary indicator of soil-surface function and a key metric in state-and-transition models. There are few studies, however, that relate indices of AS to the process of grassland degradation. In a Chihuahuan Desert rangeland, we measured variation in AS across vegetated-bare patch boundaries within six plot types reflecting a hypothesized fragmentation/transition sequence. We also examined wetting front depth and pH along this sequence. We found that AS exhibited consistent and interpretable variation across the patch boundaries of the different plot types. Average AS was highest in grass patches adjacent to small to medium-sized (0.5-1.5 m) bare patches and was low in grass patches adjacent to large (> 3 m) bare patches. AS of bare ground was also lowest when bare patches in continuous grassland were large and when bare ground formed an interconnected matrix. Wetting depth after a large storm decreased and pH increased along the fragmentation sequence. The results suggest that AS has interpretable relationships with grassland fragmentation and transitions among states. Careful attention to patchiness within states and stratification, however, is important and simple classifications of strata, such as ‘‘bare interspace’’ and ‘‘plant,’’ may not be sufficient to document variation in soil function.

Surface soil physical and hydrological characteristics in Bromus tectorum L. (cheatgrass) versus Artemisia tridentata Nutt. (big sagebrush) habitat

“…Across AT sites we noted that under the drip line of AT it was more common to find bare patches of soil then in BT areas. Somewhat similar results were found by Bestelmeyer et al (2006) working in arid grasslands of the Chihuahuan Desert where higher aggregates stabilities were seen in grass patch areas compared to bare areas.…”

Soil and Plant Property Differences Across a Chronosequence of Humid-Temperate Tallgrass Prairie Restorations

“…However, WSA in the native prairie were more uniform among aggregate size classes than in any of the restorations. Bestelmeyer et al (2006) attempted to use aggregate stability (AS) as an index of grassland degradation in Chihuahuan Desert rangeland of New Mexico because it related to ecosystem fragmentation and reported that AS differed among size combinations of vegetatedbare patch assemblages. However, to our knowledge, no such studies have been conducted investigating the effects of tallgrass prairie restoration and/or restoration age on soil AS under the edaphic and climatic conditions that are unique to the Ozark Highlands because, at least in part, of the extremely limited and highly fragmented nature of the present tallgrass prairies, whether restorations or remnants, in the region.…”

Using Resilience and Resistance Concepts to Manage Persistent Threats to Sagebrush Ecosystems and Greater Sage-grouse

“…This agrees with Archer (1989) who suggested that changes to natural disturbance regimes might cause increases in woody plants. Bestelmeyer et al (2006) showed that as the size of bare patches increased, aggregate stability decreased. Shaver (2010b) showed that the results of herbicide treatment on these treated plots, although long lasting, were beginning to decline.…”