SRM Symposium Presentations (February 12-16, 2023)

Over the past 40+ years, Dr. Steve Archer and his colleagues have redefined our understanding of rangelands, particularly grassland to shrubland transitions. In observance of his contribution to the profession of rangeland management and the science of ecology, Dr. Archer’s former students organized a symposium at the Society for Range Management Annual Meeting in February of 2023. The theme of the mechanisms and implications of grassland/shrubland dynamics was explored by a series of speakers and a general discussion with the audience, including Steve. This video presents those discussions. Each of the presentation times are noted below the video screen.

Please find the video here.

The importance of understanding seed dispersal and seedling recruitment in arid grassland-shrubland transitions.

Brown, Joel R, USDA NRCS, Jornada Experimental Range, Las Cruces NM
Rutherford, William A, University of Arizona, Tucson AZ
Pierce, Nate, University of Arizona, Tucson AZ

Dr. Steve Archer and colleagues have investigated the ecological processes that initiate grassland to shrubland transitions across multiple arid ecosystems. The investigations have ranged from multi-decadal extensive observations to highly controlled field and glasshouse experiments. The results of this work have not only provided site-specific guidelines for monitoring and treatment implementation/assessment, but taken in total, has led to a re-examination of one of the fundamental principles of rangeland management: competition alone is insufficient to maintain a grassland state by excluding shrubs. The realization that disturbance, managed or natural, is necessary to maintain a grassland across most, if not all, grassland ecosystems is slowly becoming a tenet of successful rangeland management. However, the complexities of temporal variability during planning horizons of adequate length and financial constraints on implementation actions have hindered the ability of managers to use these findings to their advantage. Future research and management should more closely examine how these limitations can be overcome.

Grass-shrub interactions at the core of woody plant encroachment – Contributions to conceptual models, process, and mechanism

Browning, Dawn; USDA-ARS; Jornada Experimental Range; Las Cruces, NM
Katherine Predick; Arizona Sonoran Desert Museum; Tucson, AZ

Steve Archer has inspired and led some of the most effective research to shed light on the mechanisms of shrub proliferation along with evaluation of brush management techniques. The predominant processes driving encroachment for a given location can shift over time. It is through field-based experimental manipulations, modeling and long term observational studies that Dr. Archer has supported directly or indirectly that we understand that there are distinct stages of the shrub encroachment process and in the early stage shrub eradication techniques can be most effective. There are multiple management implications for identifying the predominant drivers (e.g., fire reduction, grazing, or drought) and the stage of shrub encroachment. A few examples include choosing the most relevant restoration practices based on land surface condition and soil type, timing the treatment, and probability of success. The entire body of Dr. Archer’s research legacy contributes directly to practical management implications and has substantially contributed to our best attempts to provide and support numerous ecosystem services including biodiversity, primary and secondary productivity, recreation, carbon storage, and livestock production.

Conceptual frameworks and models for assessing causes, consequences and management of woody plant encroachment

Angerer, Jay, USDA ARS Miles City MT
Brown, Joel, USDA NRCS, Jornada Experimental Range, Las Cruces NM

In grasslands and savannas across the world, woody plants have been increasing in number and size during the last 100 years. Dr. Steve Archer and his collaborators have been at the forefront in conducting research to assess the causes and resulting consequences of this woody plant encroachment. This research has included the development of conceptual models, and use of empirical and simulation models for examining past and potential future trends in the transition from grassland to woodlands, as well as evaluating strategies for managing woody plant encroachment. Early efforts included the use of remote sensing/aerial image analysis, long-term climate data, and simulation modeling for a historical reconstruction of encroachment and assessing effects of rainfall on vegetation state changes. This research produced one of the first conceptual models addressing drivers and processes for transitions between grassland and woody plant states. More recent studies and modeling efforts have examined impacts of woody plant encroachment on soil carbon and how practices implemented for managing woody plants affect ecosystem services. Research and models developed by Archer and his colleagues provides a solid foundation for future improvements to process models for quantification of thresholds and informing adaptive management strategies on lands where woody plants have proliferated.

The implications of woody encroachment on ecosystem patterns and processes

Throop, Heather, Arizona State University, Tempe AZ

Global rangelands have undergone a dramatic increase in woody plant cover over the past 150 years. Dr. Steve Archer and colleagues have advanced our understanding of the ecosystem-level implications of this woody encroachment. This work has used detailed observational and manipulative field studies to document how grassland-to-shrubland transitions have changed spatial and temporal patterns of biogeochemical pools and processes. In addition, modeling efforts have provided critical predictive capacity to understand historical patterns and project patterns under future management scenarios. Importantly, Dr. Archer’s work in this realm has strongly focused on understanding ecosystem patterns in the context of current land management practices, including grazing and brush management. Collectively, this work illustrates that woody encroachment can strongly alter pools and dynamics of carbon and nitrogen cycling. This work provides key information for management decisions, particularly when balancing needs from multiple stakeholders.

Evaluating and Managing Ecosystem Services in Arid Rangelands

Jones, Scott A., University of Arizona, Tucson AZ

Rangelands provide a myriad of ecosystem services, giving them substantial value to socioecological systems. However, many of these rangelands have experienced the proliferation of unpalatable woody plants at the expense of perennial grasses over the past 150 years. These changes can result in alterations to ecosystem structure and functions as well as the provisions and delivery of ecosystem services. Yet our ability to predict ecosystem responses to management aimed at recovering ecosystem services in shrub encroached rangelands is limited or inconsistent at best. More research is needed to help better inform land managers and policymakers so they can make objective, science-based decisions regarding the many trade-offs and competing objectives for the conservation of rangelands. Dr. Steve Archer and colleagues have engaged in several investigations to address this topic which have spanned both spatial and temporal scales. Findings from these efforts can provide a foundation for ongoing research and can help inform land managers on when, where and under what circumstances to employ brush management in order to meet conservation objectives.