Many rangelands have experienced encroachment of shrubs in concert with the loss of native grasses. Efforts to combat this phenomenon include a variety of ‘brush management’ practices (BM) usually aimed at restoring forage production – but are seldom economically viable from that standpoint. However, encroachment also affect numerous other ecosystem services (ES). A broader evaluation of the impacts of shrub encroachment and BM on ES would enable: (i) more accurate assessments of the utility of BM and (ii) development of guidelines for determining when, where and under what circumstances to use BM to promote desired ES. Shrub encroachment/BM influences on ES are locally constrained by soils, topography, disturbance, and management, but no conceptual framework integrating these factors with ES exists. This project aims to take a holistic approach to the shrub encroachment phenomenon, how it has altered ES capacities and the ability of BM to promote desired services.
Outcomes will include:
(1) Understanding of producer demands for ES on shrub-encroached landscapes
(2) Enhanced knowledge of shrub encroachment/BMpatterns-processes
(3) Improved range management planning by characterizing spatio temporal changes in ES on rangelands
(4) Identification of ES trade-offs/synergies associated with shrub encroachment/BM in rangeland environments, and
(5) A decision-support framework giving stakeholders a workflow for evaluating ES and associated tradeoffs/synergies.
To achieve these outcomes, I will quantify rates/patterns of shrub cover change across the Las Cienegas National Conservation Area, a working rangeland, with contrasting soils, topography, and management histories in order to set baseline levels of ES and identify their change over time. I will then model how future shrub encroachment/BM actions will impact capacities of stakeholder-desired ES across a working rangeland. Outreach will include disseminating results through local annual workshops, Cooperative Extension programs, K-12 educational materials for local communities, and through peer-reviewed journals.
The overarching goal of this research is to take a holistic approach to the shrub encroachment phenomenon, how it has altered ES capacities and the ability of brush management to promote desired services.
Specific objectives are to:
(1) Identify and weigh producers’ demands for rangeland ES through semi-structured interviews and surveys.
(2) Characterize spatial and temporal dynamics of shrub cover on both shrub-encroached and managed sites with contrasting soils, topography, and management histories.
(3) Model Spatiotemporal Ecosystem Service Capacity
- Using land cover classifications from (2), assign values for ES based upon field data and relevant peer-reviewed literature, and assess spatiotemporal changes in them.
- Using statistical analysis, evaluate relationships between multiple ES to identify possible trade-offs and synergies.
(4) Using ES values and assessments of trade-offs and synergies, develop a decision-support framework for evaluating shrub encroachment-brush management interrelationships.
Objective 1: Identify and weigh producers’ demands for rangeland ES.
A semi-structured interview has been developed and was submitted for review and approved by the Institutional Review Board (IRB) at the University of Arizona in July 2018. This interview contains both closed- and open-ended questions concerning participants’ knowledge relevant to this study. Topics include shrub encroachment, its environmental impacts, brush management and motives/desires for engaging in this management tool with regards to ecosystem services. Images of rangelands with differing shrub cover are also included to ascertain participants’ preferred percent shrub cover and why in terms of ecosystem services.
A preliminary list of participants has been drafted. The list includes producers, governmental employees, and non-governmental land managers. Upon approval by the IRB, participants will be contacted and interviews will begin. Information gleaned from these semi-structured interviews will be used to construct a broader online survey to be distributed to a wider audience.
Objective 2: Characterize spatial and temporal dynamics of shrub cover on both shrub-encroached and managed sites with contrasting soils, topography, and management histories.
Classification of shrub cover change over time at Las Cienegas National Conservation Area is currently taking place. Aerial imagery (black and white) from 1936, 1946, 1968, 1975, 1988, 1996, 2007 and 2017 have been sampled to a common resolution of 1 meter and classified using the Iso Cluster Unsupervised Classification tool within the ArcGIS platform. This was followed by post-processing steps using the Regional Grouping and Zonal Geometry ArcGIS tool to correct mis-classifications and omissions (Fig. 1).
Once classified, spatial layers will be analyzed using the FRAGSTATS: Spatial Analysis Program to quantify changes in shrub cover, patch density, patch size variance, and Euclidean nearest neighbor. Changes in these variables will be assessed in relation to soil type [using data from SSURGO (Soil Survey Geographic Database), topography (slope aspect, inclination from digital elevation models) and brush management history. These analyses will yield information on shrub encroachment rates and patterns and rates and patterns shrub recovery following brush management (Fig. 2).
To date approximately 11,500 acres of the 42,000-acre study site have been classified for each of the selected years and landscape metrics have been analyzed with FRAGSTATS (Fig. 3). Shrub cover (%) for each of the soil types within the classified area have been calculated (Fig. 4). Preliminary results show a steady increase in shrub cover over the past 81 years from 2.8% in 1936 to 14.3% in 2017 with patch density of shrubs going from 4.6 shrubs/hectare to 60.6 shrubs/hectare. Expectedly, the trend for Euclidean distance to the nearest shrub neighbor inversely followed patch density. Preliminary results for variance in patch size show pulses of size variance. This could be caused by small shrub recruitment which temporarily increases patch size variability until these patches mature and fill in decreasing size variability.
Preliminary results regarding changes in shrub cover by soil type indicate that sandy soils had highest initial shrub cover, underwent highest rates of encroachment early on and may be approaching a maximum cover steady-state. This is contrasted by clayey soils which have experienced slower rates of encroachment, but are still experiencing upward trends in cover change. These results will become clearer as the entire study site is classified. Furthermore, once classification is complete, data on slope aspect and inclination will be included in the analysis to see how topography influences shrub cover metrics. Landscapes receiving past brush management will then be analyzed to quantify rates and patterns of shrub re-establishment. Final results for these will be included in next year’s report.
Educational & Outreach Activities
To date, no participants have been formally involved in this study. This will change in the near future as the semi-structured interview for this study passes the IRB review and interviews are conducted.
Outreach & Ed. Description
A poster presentation of preliminary results for Objective 2 was given on June 2, 2018 at the Science on the Sonoita Plain Symposium in Elgin, Arizona. This conference was attended by ~75 participants and included scientists, governmental and non-governmental land managers, producers, and interested local citizens. The poster was well received and a number of attendees exchanged information in order to be updated on final results as they become available.
Aspects of this research was also presented in Spring of 2018 to roughly 150 undergraduate students enrolled in a general science course (Global Change 170) at the University of Arizona during a section on global change and its impacts on the Southwest. Students enrolled in this course are mainly non-science majors focusing on business, communication and phycology degrees. A number of students expressed interest in this project and if given again in the future, a site visit may be included to those interested.
During the past year, I attended three conferences and two workshops in Arizona (listed below). These events provided great networking opportunities in which I was able to explain my research and methodology and interact with relevant stakeholders who I am hoping to interview for Objective 1.
- Research Insights in Semiarid Ecosystems (RISE) October 21st, 2018 Tucson, Arizona. Organized by Agricultural Research Services and College of Agriculture and Life Sciences University of Arizona. Approximately 100 participants.
- Madrean Conference May 14th-18th, 2018 Tucson, Arizona. Organized by Sky Island Alliance. Approximately 500 participants.
- Science on the Sonoita Plain June 2nd, 2018, Elgin, Arizona. Organized by Audubon Society. Approximately 75 participants
- State of the Cienega Watershed March 6th, 2018 Tucson, Arizona. Organized by Cienega Watershed Partnership. Approximately 50 participants.
- Altar Valley Brush Management Workshop April 19th, 2018 Arivaca, Arizona. Organized by Altar Valley Conservation Alliance. Approximately 75 participants.
A preliminary website has been created for this project (https://cals.arizona.edu/research/archer/es_changes.html). As results become available the site will be updated. This site will also nest other products of this research such as fact sheets, published manuscripts, and other outreach materials.
The results and final outreach for this project are still in preparation. These materials will be included in the final assessment once results and the education and outreach activities are completed.
Working on this project has increased both my knowledge of extension activities as well as the importance of good outreach practices which target a variety of stakeholders. Over the past year, I have had the opportunity to participate in the planning process of a large scale brush management project focused in Southern Arizona. I was asked to participate because it is anticipated that my project can help shed light on where to treat to achieve desired conservation objectives and when re-treatment can be expected. Seeing the number of stakeholders who are participating in this planning (i.e. both governmental and non-governmental land managers, producers, hunters and community members) has shed light on the complexity of sustainability issues and why a variety of stakeholders are vital for the success and longevity of conservation actions.
Once analysis for this project is completed, we will have a better understanding of the rates/dynamics of the shrub encroachment phenomenon, how it has impacted services, and when, where and how often to treat to meet desired conservation goals. This will not only benefit the above mentioned planning process but other producers and land managers across the west dealing with encroachment.