Ecological Indicators (Sep 2024)
Chasing success: A review of vegetation indicators used in riparian ecosystem restoration monitoring
Abstract
Land degradation and biodiversity decline are two of the main threats currently faced by humankind. For this reason, ecosystem restoration has become a priority in recent decades. Restoration actions in riparian forests may offer particularly high benefit/effort ratios since riparian zones provide multiple ecosystem services beyond the areas they occupy. As riparian restoration becomes increasingly widespread, it becomes ever more necessary to identify reliable indicators that can efficiently aid in evaluating restoration outcomes. In this study, we review various riparian restoration projects across different contexts. Our specific objectives were to i) review the monitoring methodologies used, ii) identify the most frequently used vegetation indicators applied, and iii) assess the use of such indicators and related sampling methods at different temporal and spatial scales. We systematically reviewed 103 studies published from 1990 to 2022 that monitored riparian vegetation restoration. We found that most of the reviewed studies evaluated restoration outcomes using field sampling (72%). In studies that used remote sensing (RS) data, medium-resolution satellite imagery and aerial RGB imagery were the most frequently used. River reach was the most frequent monitoring extent (53% of studies), while the number of studies decreased as the monitoring scale increased. Most studies monitored short-term changes using field sampling, while remote sensing data was more frequently applied in long-term monitoring. The analysis of studies that applied remote sensing and field data monitoring highlighted that there is no consensus about the best design to combine both methods. Ground cover, species abundance and richness, and regeneration were the most frequently used indicators. In smaller-scale and shorter-term monitoring studies, vegetation composition indicators (e.g., abundance and richness) were more frequently used, while in larger-scale and longer-term monitoring studies, vegetation structure indicators (e.g., ground cover) were more common. A mismatch exists between restoration goals and the indicators applied, suggesting that the development of monitoring routines that can be applied across different contexts is essential for the evaluation and adaptive management of riparian restoration actions. The potential of remote sensing has not yet been fully exploited in riparian restoration evaluation, and studies that incorporate field and remote sensing data in the multiscale evaluation of restoration practices are urgently required.
