Quantifying post-restoration changes in hydrology and vegetation composition in subalpine meadows using high-resolution satellite imagery

Wet meadows provide important ecosystem services including groundwater retention, improved downstream water quality, increased soil carbon storage, and habitat for species of concern. Anthropomorphic pressures such as livestock grazing, and development can degrade these systems, often resulting in incised stream channels that decrease groundwater storage capacity and increase rapid runoff and erosion, which in turn result in lower downstream water quality and create conditions that favor drier grassland plant assemblages. Restoring meadows by increasing water residence time and removing stressors can restore ecosystem services; however, monitoring the effects of restoration efforts is a time- and personnel-intensive task. Remote sensing data—here, high-resolution satellite imagery from NAIP and Planet—can be used to track changes in groundwater-dependent vegetation and standing water over multi-year time scales, providing a cost-effective approach to long-term monitoring. Childs Meadow in Tehama County, CA, USA is a 117-hectare meadow complex that has been grazed for over 100 years. Cattle were removed from the lower complex in 2010, and from a restored portion of the upper complex in 2015. The restoration included installation of artificial beaver dams to increase water retention, promote willow growth, and increase native species habitat. Post-restoration, we expected to see an increase in riparian willow coverage and increased surface water area later in the growing season. To quantify these changes, we used a combination of supervised pixel- and object-based classification of aerial imagery to compare 1) willow extent between 2009 and 2018 in both the lower and restored portion of the meadow complex, and 2) surface water extent on a monthly basis in 2015 and 2018 in the restored area. Results suggest these methods can be helpful in quantifying the changes in meadow hydrology post-restoration and thus increase our understanding of the long-term effects of meadow restoration techniques.