Aboveground Biomass Estimation in Short Rotation Forest Plantations in Northern Greece Using ESA’s Sentinel Medium-High Resolution Multispectral and Radar Imaging Missions

Abstract

Plantations of fast-growing forest species such as black locust (Robinia Pseudoacacia) can contribute to energy transformation, mitigate industrial pollution, and restore degraded, marginal land. In this study, the synergistic use of Sentinel-2 and Sentinel-1 time series data is explored for modeling aboveground biomass (AGB) in black locust short-rotation plantations in northeastern Greece. Optimal modeling dates and EO sensor data are also identified through the analysis. Random forest (RF) models were originally developed using monthly Sentinel-2 spectral indices, while, progressively, monthly Sentinel-1 bands were incorporated in the statistical analysis. The highest accuracy was observed for the models generated using Sentinel-2 August composites (R2 = 0.52). The inclusion of Sentinel-1 bands in the spectral indices’ models had a negligible effect on modeling accuracy during the leaf-on period. The correlation and comparative performance of the spectral indices in terms of pairwise correlation with AGB varied among the phenophases of the forest plantations. Overall, the field-measured AGB in the forest plantations plots presented a higher correlation with the optical Sentinel-2 images. The synergy of Sentinel-1 and Sentinel-2 data proved to be a non-efficient approach for improving forest biomass RF models throughout the year within the geographical and environmental context of our study.

Comparison of Juvenile, Drought Tolerant Black Locust (Robinia pseudoacacia L.) Clones with Regard to Plant Physiology and Growth Characteristics in Eastern Hungary: Early Evaluation

“…The clone with the best height growth, 'NK2', produced 10% of its height increment between September and November, despite the fact, that during the growing season droughty periods occurred, which caused water shortage problems on the sandy soil. Similar to the results of Theofanous et al [81], the maximum values of height increments for the clones studied coincided with the NDVI values.…”

Assessing Black Locust Biomass Accumulation in Restoration Plantations

“…For samples smaller than 5 cm or rotten ones in decay class 5, only one horizontal measurement was taken by a caliper. The woody debris volume was estimated using the formula of the truncated cone and for the conversion of volume into dry biomass, the wood density reduction according to decay classes [30] was used.…”

“…AGB estimation over a domain is based on a combination of ground reference measurements such as classical field-data (forest inventory data) and the harvest of selected trees that are subsequently oven-dried and weighed for deriving accurate estimation of above ground biomass [28,29]. In some cases, however, auxiliary variables derived from satellite-based products (including LIght Detection And Ranging (LIDAR) technology) are used to render more precise spatial estimation of AGB over the desired domain [30][31][32]. Ground reference measurements can provide accurate estimates for the calibration and validation of global satellite-based AGB models.…”

Technology and Data Fusion Methods to Enhance Site-Specific Crop Monitoring

“…Studies showed that the fusion of SAR with optical sensor data improves AGB estimation, as optical data offset the saturation impact. Therefore, AGB monitoring has improved as a result of the latest developments in satellite systems [236][237][238][239]. However, the SAR works for a particular range of AGB, and beyond this range, the system provides coarse data [240].…”