To test for the effects of prolonged reduction of UV radiation in a natural habitat, UV-filtering and UV-transmitting windows were installed over S. caninervis plants in situ. In June 2018, twenty 12.7 cm × 12.7 cm (5” × 5”) UV-filtering windows (Fig. 1B & C), 3.175 mm (1/8 in) thick (OP-3 acrylic, Acrylite, Sanford, ME, USA), were installed over target Syntrichia caninervis cushions at the study site (a voucher specimen, Ekwealor 015, has been deposited in the UC herbarium). The UV-filtering windows transmit ca. 90% of radiation across the visible spectrum with a sharp drop to approximately 0% transmittance between 425 nm and 400 nm (www.sdplastics.com/acryliteliterature/1682ACRYLITEOP3techData.pdf). In a paired design, twenty UV-transmitting, but otherwise identical acrylic windows (Polycast Solacryl SUVT acrylic, Spartech, Maryland Heights, MO, USA) were placed over target cushions located within 1 m of their UV-filtering counterpart (Fig. 1B). These UV-transmitting windows transmit at least 90% across the visible and UV-A/B spectrum and then drop to near 0% transmittance between 275 nm and 250 nm (www.polymerplastics.com/transparents_uvta_sheet.shtml). Both types of windows transmit 90% of photosynthetically active radiation (400 – 700 nm; PAR). Additionally, three pairs of windows were installed for microclimate measurements (see below). All windows were installed using #8-32 threaded nylon legs so that each window was nearly flush with the ground on the south edge and approximately 2.5 cm off the ground on the north edge, creating a ca. 13° angle with the soil surface.