Examining multi-scale dynamics of drylands amid multi-year wet and dry periods using imagery

Authors: HEINTZMAN, LUCAS - Orise Fellow; Peters, Debra; Savoy, Heather; RAMIREZ, GEOVANY - New Mexico State University

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2021
Publication Date: 8/6/2021
Citation: Heintzman, L., Peters, D.C., Savoy, H.M., Ramirez, G. 2021. Examining multi-scale dynamics of drylands amid multi-year wet and dry periods using imagery. Ecological Society of America Abstracts.

Interpretive Summary:

Technical Abstract: Our objective was to examine changes in patch- and landscape-scale vegetation dynamics for ecosystems representing the Chihuahuan Desert (upland grasslands, creosotebush shrublands, mesquite shrublands, and tarbush shrublands) during multi-year wet and dry periods. Twelve locations were selected that were distributed across the Jornada USDA-Long Term Ecological Research site in southern New Mexico, USA. Since 1989, these locations have been field-surveyed annually (via 49 1m2 quadrats per site) and used for validation of the imagery. We categorized vegetation into four functional groups (shrubs, grasses, forbs/subshrubs, and bare soil). We assessed landscape patterns from aerial imagery in 2005, 2009, 2011, 2014, 2016, and 2018 using unsupervised classification for each category. These years were chosen as they encompassed periods of regional shifts in hydrological regime (wet year: 2005; dry years: 2009, 2011; average years: 2014, 2016; 2018) and featured data availability that captured our study extent. When compared with quadrat-based information, our imagery based classification results were congruent with respect to functional group dominance at a ~60% rate. This rate increased to ~70% when presence/absence was assessed. At the patch scale: our preliminary results indicated levels of vegetative dynamism with highly variable changes in landscape metrics for composition, configuration, and connectivity through time. However vegetative changes were often subtle, and frequently did not correspond to field-based estimates due to multiple species assemblages inducing spectral mixing, and soil background masking effects. Our patch-based observations emphasize the influence of wet-dry periods on dryland ecosystem structural properties and their potential corresponding vegetative lag effects across scales. Moreover, our observations at both the patch- and landscape-scale highlight the importance of expanding landscape connectivity theory beyond traditional two-dimensional applications.