Grassland Restoration and Climate Change: Altar Valley, Arizona Case Study By Anne Gondor CAPSTONE RESEARCH PAPER Submitted in partial fulfillment of the requirements for the degree MASTER OF NATURAL RESOURCES Department of Forest Ecosystems and Society College of Forestry OREGON STATE UNIVERSITY Corvallis, Oregon January 2020 Approved by: Abstract The Altar Valley is an important working landscape that supports biodiversity and vulnerable species in Pima County, Arizona (Huckelberry 2000). This semi-desert grassland, alluvial valley and 713,807-acre watershed composed of 39 subbasins serves as an aquifer to a portion of southwestern Tucson. This region of Southern Arizona has been identified by an Arizona State Climate Summary in the 4th National Assessment as being highly vulnerable due to predicted high variability and decreases of greater than 20% springtime precipitation (Frankson et al. 2017). Other efforts have identified the area with a forecasted climate stress index of high sensitivity including recommendations to promote ecosystem adaptive capacity by enhancing resilience through “maintaining connectivity, using aggressive prevention and control of invasive plant species and grassland restoration of woodland invasion sites” (Comer 2012, page 77). These predicted climate change impacts have the potential to impact the ability of restoration projects to reach desired future conditions goals. In addition, climate variables related to species survival may shift spatially and temporally in the future. Thus, current restoration decisions and species selection become more important in preparation for a potentially shifting future landscape condition as a result of climate change. Restoration efforts may inadvertently promote locally non-climate-adapted species. Recent literature have demonstrated how climate change impacts from variability of precipitation and changes in soil moisture have impacted grass abundance (Bodner and Robles 2017; Gremer et al. 2015). A recent paper by Cang et al. (2016) found that niche rates of grass species may not keep up with the projected rate of climate change (Cang, Wilson, and Wiens 2016). Studies such as these point to the need to slow water and increase soil moisture as much as possible on the landscape. They also suggest a need to 2 understand how grasses and other plant species may respond to climate change, so that restoration efforts can be more successful. Altar Valley Conservation Alliance (AVCA) and Pima County (PC) are prioritizing watershed restoration at the subbasin level based on hydrologic modeling. This research may help prioritize restoration locations focused specifically on restoring native grass species in potentially more climate resilient locations. Eight recent papers will help identify additional environmental variables and approaches (Godfree et al. 2011; Fehmi et al. 2014; Gremer et al. 2015; Cang, Wilson, and Wiens 2016; G. S. Bodner and Robles 2017; Munson and Long 2017; Kane et al. 2017; Hulvey et al. 2017). Evaluating potential climate change impacts to species distributions or habitat suitability using a model such as Maxent is an important tool for conservation of biodiversity (Guisan et al. 2013). Global circulation models (GCM), extreme scenario (RCP 8.5) from the ClimateNA dataset (Wang et al. 2016) were used with Maxent, to model potential habitat suitability for 25 grass species. The suitable habitat probabilities results of the grouped C3 and C4 grass species are somewhat mixed depending on time period and GCM. Results suggest that potential habitat suitability probabilities shift to zero probability in some lower elevation locations of the AV by 2050. The main recommendation is to consider climate change projections to inform species selections for revegetation of restoration locations. Two next steps could be to conduct climate change scenario planning (Caves et al. 2013; Star et al. 2016) and develop a comprehensive seed plan specific to Altar Valley (Buckley et al. 2016) that also highlights grass seed provenances from lower elevations within the Sonoran Desert ecoregion not just the Madrean Archipelago Ecoregion. 3 TABLE OF CONTENTS 1.0 Introduction ........................................................................................................................ 6 1.1 Goals and Objectives of this Case Study ........................................................................... 9 2.0 Altar Valley Background Information ............................................................................. 12 2.1 Macroecology: Ecoregions, Vegetation Pattern, Soils, Hydrology, Climate and Disturbance ...................................................................................................................... 14 2.2 Current and Legacy Land Management Impacts on Landscape Condition ..................... 20 2.3 Current Watershed-scale Collaborative Conservation in the Altar Valley ...................... 26 3.0 Methods and Results ........................................................................................................ 29 3.1 Species Distribution Modeling ........................................................................................ 29 3.2 Species Selection Process ................................................................................................ 30 3.3 Climatic Data Selection Process ...................................................................................... 32 3.4 Environmental Predictor Variables (EPV) Selection Process ......................................... 37 3.5 Model dynamics and parameters settings ........................................................................ 41 4.0 Model Results .................................................................................................................. 43 5.0 Conclusion: Restoration Sustainability Under Climate Change ...................................... 46 6.0 References ........................................................................................................................ 52 Appendix 1: Maxent Rarefied Species Occurrence Inputs .................................................... 61 Appendix 2: Climate Data Altar Valley ................................................................................ 62 Appendix 3: Species Habitat Suitability Probability by Climate Scenario. .......................... 64 Appendix 4: C3 and C4 Habitat Suitability Scenarios by Elevation ..................................... 65 4 LIST OF FIGURES AND TABLES Figure 1.1.0 Case Study Area ................................................................................................ 13 Figure 1.2.0 Altar Valley Land Management ........................................................................ 14 Figure 1.3.0 Ecoregions, AV Case Study and Maxent Extents……………………………..15 Figure 1.4.0 Vegetation of the Altar Valley ........................... Error! Bookmark not defined. Figure 2.1.0 Sustainability web modified from Monger and Bestelmeyer 2006 ................... 20 Figure 2.2.0 Buenos Aires National Wildlife Refuge view to Baboquivari Peak demonstrates mesquite woody plant encroachment (WPE) 2018. ......................................... 22 Table 3.1 Species list………………………………………………………………………..31 Figure 3.2.1 Precipitation summary for Arivaca, Arizona. ................................................... 34 Figure 3.2.3 Historic to projected Arivaca, AZ 30-year average annual precipitation (mm) and Jan-June average precipitation (mm). ......... Error! Bookmark not defined. Figure 3.2.4 Monthly precipitation Arivaca, AZ historic: 1981-2010 from PRISM data and 2041-2070 Ensemble and IPSL-CM5A from ClimateNA. .............................. 36 Table 3.2 Environmental Predictor Variables List………………………………………….40 Figure 4.0.0 A-J. Summarized Maxent Results by Functional Group and Climate Scenario Time Period.. .................................................................................................... 45 Figure 5.0.0 Drought monitoring for Arizona 2000-2019. Source: Dought.gov 2019. .. Error! Bookmark not defined. Figure 5.1.0 Palmer Drought Severity Index for Arizona 1981-2010 ................................... 48 Table 5.0. Past Climate Analog for Projected Future Climate (RCP 8.5) for Altar Valley...50 5 Grassland Restoration and Climate Change: Altar Valley, Arizona Case Study 1.0 Introduction Climate change will challenge natural resource users to respond through innovative thinking and collaborative action versus our conventional response norms and perceptions gained through decades of “stable” climate. This case study attempts to help inform the adaptive management and restoration response to a shifting climate in a working grassland landscape that human use has had influence on for hundreds to thousands of years. Native grass species in the Altar Valley, Arizona have been evolving in this arid landscape with variable rainfall, interspersed with decades of drought conditions. However, what is their full range of adaptive capacity? Are they at the limit of their adaptive capacity? Many studies have developed species distribution models (SDMs) as potential predictive responses to climate change for longer lived tree species (Rehfeldt et al. 2012; 2015; Notaro, Mauss, and Williams 2012). There are not many developed for grasses (Kane et al. 2017). It is more difficult to model shorter lived perennials or annuals. Their lifespans are shorter than the 30 year historic climate data used in models. Many also have physiological