Mosses and lichens that colonize rock barrens are critical for primary soil formation, landscape water storage and ecosystem succession. Mosses and lichens often grow as mats or cushions (referred to as mats) in and above depressions or crevices in the bedrock where moisture availability is greater. Shallow soil deposits covered with mats also provide critical nesting habitat for species-at-risk turtles in the eastern Georgian Bay, Ontario region. However, there is concern that a drying climate will reduce mat productivity due to a reduction in moisture availability, thereby impacting soil formation, landscape hydrology and their suitability as turtle nesting habitat. To better understand how drying may impact moss and lichen mats, we assessed the ecohydrological controls on moisture availability and productivity. Net primary productivity (NPP) was estimated using fine-scale surveys in 2014 and 2024 and complemented with measurements of mat moisture availability at the start and end of the 10-year study period. We found that mat catchment size had a significant impact on moisture availability, but the strength of the relationship was reduced during periods of low soil moisture availability. Catchment size did not have a significant impact on NPP, but there was slightly greater NPP in large catchments, and NPP increased with increasing bedrock depression storage. We suggest that under a changing climate, the overall productivity of moss-dominated rock barrens will decrease with decreasing moisture availability, the relationship between NPP and moss depth will strengthen and mat cover may shift towards more lichen-dominated rock barrens, influencing the availability and function of turtle nesting habitat. Keywords: lichen | moss | net primary productivity | rock barrens | soil moisture | water storage.