Jornada Basin LTER (JRN-LTER-VI, 2012-2018) Outcomes report

1. Intellectual Merit

The Jornada Basin long-term ecological research site (JRN-LTER) is a temperate dryland in southern New Mexico, representative of many arid and semi-arid ecosystems (drylands) in the southwest USA and globally.  The JRN, like many drylands, has experienced dramatic changes in vegetation structure and ecosystem function over the past century. These changes, manifested as conversion of perennial grasslands to landscapes dominated by unpalatable, xerophytic shrubs (shrub encroachment), are often accompanied by increases in soil erosion, reduced productivity and declining biodiversity. Because drylands occupy >40% of the Earth’s land surface, these state changes have important consequences for the provisioning of goods and services to the >1 billion people living in these landscapes.

In LTER-VI (2012-2018), we developed a conceptual framework focused on alternative stable states in the context of grassland and shrubland transitions. Notably, we demonstrated that shrub encroachment can be explained as the outcome of positive feedback mechanisms relating to bare soil connectivity, operating within heterogeneous spatial (soil and geomorphology) and temporal (climate and management) contexts.  We expanded our research to examine alternative transition types observed at the Jornada, including from shrublands back toward perennial grassland, between shrublands dominated by different shrub species, and between grasslands or shrublands toward novel ecosystems driven by climate change and invasive plant species. For each transition type, we quantified patterns of change in the landscape and initiated mechanistic studies of those dynamics.

A major outcome of JRN-LTER-VI was the development of bare soil connectivity concepts and metrics, now used in drylands globally. Connectivity controls redistribution of soil, water, nutrients and seeds, and is central to plant-soil feedbacks at multiple scales, including wind and water erosion-deposition processes.  Our research demonstrated that increasing bare soil connectivity associated with drought and grazing, can further suppress grasses, while providing opportunities for shrub establishment. We showed that shrub encroached grassland can recover over ~20 year time-frames if ungrazed, but only when remnant grass cover exceeds a 3% threshold. We also found that a multi-year wet period triggered perennial grass recovery through demographic processes correlated with summer rainfall during the current growing season, seed production during two previous growing seasons, and the number of consecutive prior wet years.

Shrub encroachment did not reduce average biomass of desert rodents, important consumers that can potentially reduce cover of perennial grasses.  However, wet periods produced irruptions of rodents (one year later) especially on shrubby sites (Figure 1), while biomass was higher on unencroached grasslands following droughts.

Long-term climate change experiments (increased precipitation variability with constant mean) indicate that future increases in precipitation variability will reduce grass production. However, shrub production increases with rainfall variability, partially ameliorating the negative effect on overall primary production (Figure 2).

Hydrological observations enhanced understanding of watershed processes related to channel infiltration, evapotranspiration, and runoff (Figure 3).  A new conceptual model, and a distributed hydrological model, showed the importance of channel infiltration promoting groundwater recharge. Both increasing storm size and woody plant encroachment were identified as potentially increasing future groundwater recharge.

We developed a trans-disciplinary approach, based on human guided machine-learning and big data analyses, to integrate patterns and processes at local scales to landscape, regional and continental scales.  The approach was successful in explaining historic patterns of vegetation during the 1930s Dust Bowl and current patterns in animal disease across the Western US.  

2. Broader Impacts

The JRN-LTER continues to publish high-impact research in leading ecological and inter-disciplinary journals, including influential articles in Nature, Science, Ecology, PNAS and other journals.   Peer-reviewed articles totaled 216 during the 2012-2018 period (average 36/year; Figure 4).

More than 110,000 K-12 students (~18,700/y) participated in science education programs associated with JRN-LTER-VI, including full-day field trips, classroom and schoolyard lessons (Figure 5). Separately, more than 2,000 children (~345/y) participated in data-centered learning as part of our innovative Desert Data Jam program.  The Data Jam approach has been adopted as a model for K-12 outreach and engagement by several other LTER sites.  We provided teacher professional development to >3,700 teachers (~621/y), supported graduate student training through >40 graduate research fellowships (~7/y), and hosted family education events for more than 3,300 individuals (~562/y). We also published One Day in the Desert, Jornada's contribution to the LTER Children's Book Series.

NSF highlighted JRN-LTER hydrological research (https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=296120&org=NSF&from=news).  We continued outreach to Federal and other natural resource managers through co-leadership of the Interpreting and Managing Indicators of Rangeland Health (IIRH) course, and as part of BLM Assessment, Inventory and Monitoring (AIM) trainings. The training manual for the IIRH course now includes updated sections on landscape connectivity informed by JRN research. JRN results are communicated through global outreach and trainings associated with the Land-Potential Knowledge System, which is experiencing exponential growth in use (see https://landpotential.org).

Last Modified: 01/03/2020
Modified by: Niall P Hanan