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/BM patterns-processes
(3) Improved range management planning by characterizing spatiotemporal 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 (LCNCA), 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.
Semi-structured interviews are currently being administered to targeted stakeholder groups which includes producers, governmental employees, non-governmental land managers, and members in academia. The interview contains both closed- and open-ended questions concerning participants’ knowledge of issues relevant to this study. Focal topics include (i) shrub encroachment and its environmental impacts, and (2) brush management and motives/desires for engaging in this management tool with respect to ecosystem services (Appendix 1). Images of rangelands with differing shrub cover (Image 1) are used to ascertain participants’ preferred degree of shrub cover and the level of shrub cover at which they would consider implementing brush management. Participants are also being asked to review a list of ecosystem services relevant to rangelands and rank them based on their social preference. To date, 10 participants have been interviewed accounting for half of the total anticipated interviews for this study. It is projected that semi-structured interviews will be fully completed by the end of August 2019. At the end of this section (Appx. 1) questions being used in the semi-structured interview is provided.
To administer interviews to a broader audience, an online survey component is being added. The online survey is being developed from insights gathered from the semi-structured interviews that have been conducted to date. This survey will utilize a Best-Worst Scaling methodology (Louviere et al. 2015) and photos to gauge social demands for ecosystem services on rangelands. The targeted audience for this survey is the Cienega Watershed Partnership and the Altar Valley Conservation Alliance. Both organizations have been contacted and have agreed to participate. This online survey tool is currently being constructed within Qualtrics and is slated to be distributed at the beginning of September 2019.
Objective 2: Characterize spatial and temporal dynamics of shrub cover on both shrub-encroached and managed sites with contrasting soils, topography, and management histories.
Aerial images for the years 1936, 1975, 1996, 2007 and 2017 have been obtained, georeferenced, and resampled to 1-m spatial resolution. Shrub cover maps were generated for the entirety of the 42,000-acre Las Cienegas study site using Iterative Self-Organizing (ISO) Cluster Unsupervised Classification tool in a GIS. Post-processing steps followed which used Region grouping and zonal geometry ArcGIS tools to correct misclassification and omissions (Fig. 1).
Once classified, spatial layers for soil type [from SSURGO (Soil Survey Geographic Database)] and elevation (DEM 30-m) were obtained. Shrub cover (%) for each year was assessed with respect to (i) the 17 soil types on the site, (ii) their elevation (which range from 1219-1647 m) and their aspect (derived from the DEM).
Spatial data layers are currently being analyzed using the FRAGSTATS spatial analysis program to quantify shrub patch density, size variance, and distance between patches (Euclidean nearest neighbor). Changes in these variables are being assessed in relation to the above mentioned soil types and topography (elevation and slope aspect). Additionally, areas within the LCNCA that have undergone past brush management actions are being identified and digitized to quantify treatment longevity (e.g. rates and dynamics of the reestablishment of shrub cover). These analyses will yield information on shrub encroachment rates and patterns and rates and patterns of shrub recovery following brush management (Fig. 2) which will help guide management with respect to when, where, and how often to conduct brush management meet desired conservation goals.
Objective 3: Model Spatiotemporal Ecosystem Service Capacity
With the completion of shrub cover layers for created in Objective 2, modeling of spatial temporal ecosystem services can begin. Modeling is slated to being during the start of the 2019-2020 academic year.
Shrub cover at the 0.5 ha scale varied greatly across the study site (Fig. 1) with total shrub cover across the entire site steadily increasing over the past 81 years (1.6% in 1936, 2.8% in 1974, 4.1% in 1996, 5.8% in 2007 and 6.1% in 2017). Video 1 depicts an animation of this change.
Shrub cover pooled across soil types ranged (but excluding intermittent drainages and areas subject to brush management) from 0.04% to 5.04% in 1936, 0.11% to 9.91% in 1975, 0.18% to 14.20% in 1996, 0.20% to 18.62% in 2007 and 0.26% to 18.48% in 2017 (Fig. 2). Sandy washes, sandy loam, and clayey swales had the highest initial coverage and experienced highest rates of encroachment. All of these soils are located at lower elevations near washes or riparian areas and possess a relatively high sand content. Clay loam upland; limy slopes and loamy bottoms not only had the lowest initial shrub coverage but also experienced lowest levels of subsequent encroachment. These areas are mostly concentrated at the southern end of the study site at higher elevations and possess a clay content (> 20%) higher than that of other settings. Of the soil types not located near washes or riparian areas, loamy uplands saw the largest increase in shrub cover, going from 1.22% in 1936 to 8.15% in 2017.
Elevation influenced both shrub canopy cover and rates of encroachment (Fig. 3). A threshold appears to exist around 1400 m with areas below this elevation having shrub cover ≥ 8% and areas above 1400 m having ≤ 4% cover. Rates of encroachment were also found to be more suppressed in areas > 1400m with these areas experiencing an initial encroachment between 1936 to 1975 and then leveling off (with the exception of areas between 1410-1457 m having a steady increase in shrub cover). In contrast, areas <1400 m had higher initial canopy cover and all underwent high rates of encroachment until 2007. Slope aspect was also found to influence encroachment rates (Fig. 4). East-facing slopes were found to support highest levels of canopy cover (8.30%) while southwest-facing slopes were found to have the lowest levels of shrub cover (2.85%).
Landscape metrics are currently being analyzed using FRAGSTATS are in progress. Metrics have been run for most of the Loamy Bottom sections on the study site and are show in Fig. 5. Preliminary results for this ecological site show patch density of shrubs going from 4.6 patches/hectare in 1936 to 60.6 patches/hectare in 2007. Expectedly, the trend for Euclidean distance to the nearest patches 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.
Areas in LCNCA that have undergone past brush management are currently being mapped and analyzed to assess rates of shrubs re-encroachment. Because aerial imagery is more readily available beginning in the 2000s, additional National Agricultural Imagery Program (NAIP) years are being included. Two examples are outlined below which include a loamy bottom site (Img. 3) and a sandy wash site (Img 4). Both were cleared of shrubs in the 1970’s and in 1975 both had shrub cover < 1%. Re-encroachment rates on these sites varied greatly as the loamy bottom saw shrub canopy cover rise to 2.34% in 2010 at which time re-treatment was implemented bringing cover back down to < 1% by 2017. Re-encroachment occurred much more rapidly on the Sandy wash sites, reaching 18.35% by 2010 and 22.14% by 2017 (Fig. 6). These results will be valuable for land managers as they provide a basis for understanding on how re-encroachment rates are controlled by topo-edaphic factors and estimating when re-treatment may be required for a given management objective.
Educational & Outreach Activities
To date, 10 participants have been directly involved in the study through semi-structured interviews. These participants have ranged from those in academia, government employees, non-government personnel, and land users. Ten more participants are being target for in-person interviews and another 100 for the online survey.
Outreach & Ed. Description
A 30-minute oral presentation was given focusing on the above preliminary results on June 22, 2019 at the Science on the Sonoita Plain Symposium in Elgin, Arizona (http://www.cienega.org/event/sosp-10th-annual-symposium/). This conference was attended by ~50 participants and included scientists, governmental and non-governmental land managers, producers, and interested local citizens. The presentation generated good discussion and interest as many people saw connections of how this work can be applied to ongoing and planned activities in the region (i.e. project focused on mesquite bosque locations and change). Furthermore, a large brush management project is slated to begin late 2019 early 2020 at LCNCA. Participants were interested to see how this research can help better plan best places to treat and when to plan for retreatments.
A poster presentation of Objective 2 results was given on December 4, 2018 at the University of Arizona’s Fall Student Showcase. The poster was presented on behalf of the Arid Lands Resource Sciences program. The showcase had roughly 100 attendees which included other undergraduate and graduate students, post-docs, professors and other university technical staff. Many of the attendees were unaware of the shrub encroachment phenomenon and were interested to learn about the topic.
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. The 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 were mainly non-science majors focusing on business, communication and psychology 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.
From 2017-2019, I attended five conferences and five 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, 2017 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
- Research Insights in Semiarid Ecosystems (RISE) October 20th, 2018 Tucson, Arizona. Organized by Agricultural Research Services and College of Agriculture and Life Sciences University of Arizona. Approximately 100 participants.
- Science on the Sonoita Plain June 22nd, 2019, Elgin, Arizona. Organized by Cienega Watershed Partnership. Approximately 50 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.
- Altar Valley Watershed Workshop March 28th, 2019. Organized by Altar Valley Conservation Alliance. Approximately 35 participants.
- State of the Cienega Watershed May 21tst, 2019 Tucson, Arizona. Organized by Cienega Watershed Partnership. Approximately 50 participants.
- Altar Valley Conservation Alliance Community Meeting May 29th, 2019. Organized by Altar Valley Conservation Alliance. Approximately 50 participants.
I am planning submit abstracts for poster presentations for the following conferences:
- Society of Ecological Restoration Southwest Chapter Annual Conference November 8th-10th, 2019. Tucson, Arizona
- Society for Range Management Annual Meeting February 16th-20th, 2020. Denver, Colorado
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. Final results for both Objectives 1 & 2 and anticipated to be available in the near future and this annual report will be updated when available.
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 two years, I have had the opportunity to participate in the planning process of a broad-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. Spatial layers created from this project have been shared with those planning said treatments in order to help inform them the past history on areas targeted for treatment. 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 various ecosystem services, stakeholder demand for those services, and when, where and how often to re-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.
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.