Site: Jornada Basin LTER
A sequence of vegetation behind water ponding dikes (15cm high) at the Jornada LTER soon after installation (05-07-75); after 14 years (09-30-89) when monsoon rain storms impacted water collecting area of the dikes and produced runoff for initial plant growth; and 31 years after installation(10-17-06) when the soil moisture reservoir became dependable for producing a significant vegetation cover response.
Rango and Havstad 2009

Desertified shrublands on degraded soils are believed to be very persistent, yet the need for services from these systems has led to numerous attempts to restore them to grassland state, often with little success.

Much of the early restoration research (pre-1970s) at the JRN focused on agronomic approaches for shrub control and grass recovery. Over the decades, numerous trials of various remediation approaches were put into place, including manual, mechanical, or chemical shrub removal, and terracing or other methods to conserve water. While many of these efforts were not successful, several efforts did succeed. Using imagery and ground-based data, JRN researchers found that manipulations can be effective at the landscape scale if treatments are sufficiently large to capture spatial heterogeneity in physical and ecological processes, maintained for long periods of time (decades) to account for climatic variability, and replicated in time and space. This information was used to identify the key factors limiting restoration approaches, including:

1. A scale mis-match between the large-scale processes that drive system dynamics and the fine-scale of restoration treatments

2. A process mis-match where restoration was aimed at processes governing shrub invasion and grass loss, but different processes control grass recovery due to threshold dynamics and positive feedbacks that maintain shrub dominance

3. The spatial context of the system, including initial conditions and landscape position, interacting with dominant processes can overwhelm restoration attempts

4. Insufficient attention to spatial and temporal variability in drivers, in particular water and climate, can either constrain or be used opportunistically to promote grass recovery

JRN researchers are using this knowledge as a basis for multi-scale experiments designed to promote grass recovery in an uncertain future where temperature is expected to continue to increase, but rainfall may increase or decrease.

Long-term grass persistence in remediated areas depends on their ability to survive and increase in density under variable weather conditions, either extended drought periods that favor shrubs or a series of wet years that increases herbaceous vegetation. JRN findings are being used to develop approaches to perennial grass recovery based on an understanding of the role of thresholds, spatial and temporal variability in climatic drivers, and patterns and processes interacting across spatial and temporal scales in driving system responses.

Graph for
Soil water profiles for control, 7.5 cm high dikes, and 15 cm high dikes on the Jornada LTER site. The higher the dike, the greater and more consistent soil water content with depth.
Rango, et al. 2006