Educational Module 2
Weather and Microclimate (Soils and Topography)
- Understand the difference between weather and microclimate.
- Explore the sensitivity of seedbed microclimate to soil type, soil depth, slope, aspect and elevation.
- Learn to interpret the mortality index (soil freezing and drought) component of the Restoration Climatology Report.
- Discuss how spatial variability in microclimate might affect or inform: our concepts of ecological resistance and resilience; initial germination and emergence or later phases of plant development; how local site conditions might buffer or mitigate variable-weather effects.
The general importance of climate is acknowledged in most seeding guides in the form of tables that list species and cultivar suitability as a function of mean annual precipitation (Jensen et al., 2001; Lambert 2005; Ogle et al., 2008a, 2008b). The strongest evidence for plant-material suitability for a given climatic region is derived from observation of historical relationships between species and climate, experience-based observation, and long-term assessment of the persistence of planted species (Harris and Dobrowolski, 1986; Shiflet, 1994; Barbour and Billings, 2000; NRCS, 2006). Ecological resilience and resistance to weed invasion have similarly been linked to climatic patterns, specifically those related to mean annual temperature and precipitation as a function of latitude and elevation (Brooks and Chambers, 2011; Chambers et al., 2014a, 2014b, 2016; Miller et al., 2014). Climate, however, is defined as the long-term average of weather, and climatological correlations to vegetation distribution only apply at a relatively coarse spatial scale. Plant community distribution at the local scale, and ecological resilience and resistance to weed invasion at the site level, are also tied to topographic and edaphic patterns across the landscape (Thornton et al., 1997; Zouhar, 2003; Bullied et al., 2012; Reisner et al., 2013; Arkle et al., 2014; Knutson et al., 2014), presumably due to the influence of local site conditions on seedbed microclimate. Hardegree et al. (2013) determined that for a range site in southern Idaho, less than 60% of seedbed favorability for plant establishment was correlated with gross climatic inputs of air temperature and precipitation.
The purpose of this exercise is to provide you with the tools to understand local site variability in soil microclimate as a function of weather inputs, topography and soils. The desired outcome is for you to understand the nature and magnitude of site variability, and how it may effect ecological resilience and resistance to weed invasion. In this exercise, we also introduce and explain the utility of the mortality indices (freezing and drought) that are provided in the Restoration Climatology Report.
Suggested Reading/Viewing Assignments
- Chambers, J.C., B.A. Bradley, C.S. Brown, C. D'Antonio, M.J. Germino, J.B. Grace, S.P. Hardegree, R.F. Miller and D.A. Pyke. 2014a. Resilience to stress and disturbance, and resistance to Bromus tectorum L. invasion in cold desert shrublands of western North America. Ecosystems 17:360-375.
- Hardegree, S.P., R.L. Sheley, S.E. Duke, J.J. James, A.R. Boehm and G.N. Flerchinger. 2016a. Temporal variability in microclimatic conditions for grass germination and emergence in the sagebrush steppe. Rangeland Ecology and Management 69:123-128.
- Webinar on weather variability and forecasting tools for short and long-term restoration planning: https://www.frames.gov/catalog/20013
- Historical daily weather information from the 4-km Gridmet database for the period January 1, 1979 through the current year (Abatzoglou, 2013).
- Seedbed microclimatic simulations from the Simultaneous Heat and Water (SHAW) model for characterizing seedbed microclimate (Flerchinger and Hardegree, 2004; Flerchinger et al., 2012).
- Restoration Climatology Report
Step 1 - Using the Weather and Microclimatic Form (below) pick a location, soil type, and slope and aspect characteristics and download the historical weather file, microclimatic data and a Restoration Climatology Report.
For the microclimatic data, you can either download the 2-cm depth estimates of hourly soil temperature and water potential, or the full soil-profile estimates of temperature, water potential, or volumetric water content. If you are interested in slope, aspect or soil effects, repeat this procedure for several topographic and/or edaphic categories of interest.
Fill out the Weather and Microclimate Form.
Step 2 - Spreadsheet analysis
Open your downloaded files in a spreadsheet application and manipulate the data to explore correlations between weather inputs and seasonal patterns of soil microclimate; investigate soil temperature and moisture patterns as a function of depth; or compare seasonal patterns of soil temperature and water availability as a function of soil type or topography. Identify at least three elements or patterns that you believe would have a significant impact on the relative success of rangeland restoration at your site, or that may be correlated with ecological resilience or resistance to weed invasion.
Step 3 - Download and Evaluate Restoration Climatology Report
From the Restoration Climatology Report, pick 5 random years for analysis and evaluate how topographic position or soil type appears to affect both seedbed microclimatic favorability for establishment, and the temporal density of post-germination/pre-emergence mortality factors of soil freezing and drought.
Step 4 - Synthesis.
Synthesize your new awareness of topographic and soil effects on seedbed microclimate. Select from one of the synthesis/discussion questions below, or generate your own discussion topics. This synthesis is not a simple discussion of the results of your hypothesis testing but should be broader in scope and address how your results inform broader management questions related to restoration planning, policy issues, or adaptive management.
- How do you think you could use this information in planning site-specific restoration at your field location?
- Do soil and topographic variability in microclimate match your expectations for site-specific patterns in resilience and resistance?
- Seed germination is not usually limiting for perennial grass establishment. What about the potential impacts of soil freezing and near-surface drought on post-germination/pre-emergence mortality?
- Resilient plant communities are probably able to access soil resources below the zone exploited by cheatgrass. How do soils and/or topography affect soil water availability below 30 cm?