How remote sensing choices influence monitoring and evaluation results of ecological restoration.

Ecological restoration has been recognized worldwide as an effective strategy for combating environmental problems and promoting sustainability. Remote sensing imagery such as obtained from Landsat and Sentinel-2 satellites can provide valuable spatial, spectral, and temporal information to support large-scale monitoring, evaluation and learning of restoration activities. However, choices need to be made when monitoring and evaluating restoration interventions through remote sensing, because of the abundance of data, and diverse methodological analysis options. This study aimed to explore the effect of remote sensing choices related to i) the image reference period, ii) size and distribution of the control sample, and iii) satellite sensor type in a before-after-control-impact (BACI) analysis of ecosystem service provision on restoration evaluation outcomes. We explored the effect of these choices in areas with different vegetation degradation classes. Results showed that different moments of the year for comparison lead to the highest percentage of opposite BACI results, meaning that conclusions of the restoration could change depending on when the evaluation is done. Another choice that showed opposite BACI results where different distribution of controls. There were only small differences when using 20 or 100 controls. All the different results obtained with the evaluated remote sensing-related choices were greater in less degraded areas. However, these areas showed a more stable responses on time. Although the choice of different satellite sensors produced similar trajectories of ecosystem service supply, the estimated supply was higher using Sentinel-2 than with Landsat-8 OLI, denoting the need of harmonizing results using ground data when using more than one image source for the evaluation. Common knowledge and documentation of the effect of key remote sensing-related choices on restoration evaluation results is essential to properly understand, manage and adapt restoration initiatives.