Microclimate refugia: Comparing modeled to empirical near-surface temperatures on rangeland

Authors: Srygley, Robert; Dixon, Jacob; LORCH, PATRICK - Sierra Research Labratories

Submitted to: Geographies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2023
Publication Date: 5/11/2023
Citation: Srygley, R.B., Dixon, J.I., Lorch, P.D. 2023. Microclimate refugia: Comparing modeled to empirical near-surface temperatures on rangeland. Geographies. 3:344-358. https://doi.org/10.3390/geographies3020018.
DOI: https://doi.org/10.3390/geographies3020018

Interpretive Summary: Topography influences incident sunlight creating differences in ambient temperature that affect growth, reproduction and survival of organisms. That these microhabitats provide refuges for animals to shuttle between to regulate temperature and avoid thermally stressful environments is well established. Microclimate diversity might influence insect population expansion and extinction. Specifically, it has been hypothesized that Mormon crickets persist in topographically heterogeneous regions, like mountain ridges, from which they reinvade relatively homogeneous valley floors. Climate data collected at weather stations has been scaled to temperatures at heights above and below ground with physical models. We measured temperatures at 2.5 cm above and below ground at 50 sites on rangeland in Utah and compare the data to that modeled at each of the locations with slope and aspect measured at the sites. We found that empirical and modeled air temperatures differed greatly, and although soil temperatures differed less it was still substantial (on average, 12.9°C for air temperature and 7.6°C for soil). Additions to the model of topographic shading and soil parameters for each location did not improve the fit with the empirical data. A hybrid model for air temperature that incorporated surface soil temperature when snow depth exceeded 2.5 cm improved the fit with the empirical data significantly. These results have improved our ability to model microclimates at biologically relevant heights above ground. Additional work is needed to bring modeled microclimates closer to the long-term measures of near surface temperatures. This research is essential for extrapolating local temperatures to topographically-dependent microhabitats that might provide refuges from extreme climatic events.

Technical Abstract: Microhabitats can provide thermal niches that affect geographic range shifts of species as the climate changes and provide refuges for pest and beneficial insect populations in agricultural regions. The spatial distribution of microhabitats is influenced by topography that can influence local extinction and recolonization by animal populations. Scaling local temperature-dependent processes to a regional scale of population expansion, and contraction requires the validation of biophysical models of near surface temperatures. We measured temperature at 2.5 cm above and below ground at 25 sites in each of the two regions: southern and northern Utah, USA. Using NichMapR version 3.2.0, we modeled the temperature at these same sites with local slopes and aspects for four years for the former and eight years for the latter region. Empirical and modeled air temperatures differed by 7.4 °C, on average, and soil temperatures differed less (4.4 °C, on average). Site-specific additions of hill shading at 25 m distance or soil parameters did not improve the agreement of the empirical and modeled temperatures. A hybrid model for air temperature that incorporated soil temperature at 0 cm depth when snow depth exceeded 3 cm resulted in an average improvement of 8% that was as great as 31%. Understanding biological processes at the regional scale and in projected future climates will continue to require biophysical modeling. To achieve the widest applications possible, biophysical models such as NichMapR need to be validated with empirical data from as wide a variety of altitudes, latitudes, soil types, and topographies wherein organisms currently inhabit and where their ranges might expand to in the future.