Abstract
Annual grasslands are an essential component of oak savanna ecosystems as the primary source of fodder for livestock and wildlife. Drought resistance adaptation has led them to complete their life cycle before serious soil and plant water deficits develop, resulting in a close link between grass phenology and soil water dynamics. In this work, these links were explored using a combination of terrestrial photography, satellite imagery and hydrological ground measurements. We obtained key phenological parameters of the grass cycle from terrestrial camera data using the Green Chromatic Coordinate (GCCc) index. These parameters were compared with those provided by time-series of vegetation indices (VI) obtained from Sentinel-2 (S2) satellites and time-series of abiotic variables, which defined the hydrology of the system. The results showed that the phenological parameters estimated by the S2 Normalized Difference Vegetation Index (NDVI) (r = 0.83, p < 0.001) and soil moisture (SM) (r = 0.75, p < 0.001) presented the best agreement with ground-derived observations compared to those provided by other vegetation indices and abiotic variables. The study of NDVI and SM dynamics, that was extended over four growing seasons (July 2015–May 2019), showed that the seasonality of both variables was highly synchronized, with the best agreements at the beginning and at the end of the dry seasons. However, stage changes were estimated first by SM, followed by NDVI, with a delay of between 3 and 10 days. These results support the use of a multi-approach method to monitor the phenology and the influence of the soil moisture dynamic under the study conditions.
Highlights
Monitoring the phenology of Mediterranean ecosystems is key to adequately assessing the impacts of global warming on different time scales, identifying pre-critical states in the framework of early warning decision-making systems, and establishing adaptation planning and management in the medium- to long-term time horizons
Annual grasslands are an essential component of this system as the primary source of fodder for livestock, and is the main economic activity in these areas, and contains a high richness of vascular plants supporting a wide diversity of habitats [5]
The two hydrological years of study period A are an example of Mediterranean climate variability (Figure 2), and of phenology variability
Summary
Monitoring the phenology of Mediterranean ecosystems is key to adequately assessing the impacts of global warming on different time scales, identifying pre-critical states in the framework of early warning decision-making systems, and establishing adaptation planning and management in the medium- to long-term time horizons. The holm oak savanna ecosystem of the Iberian Peninsula (known as dehesa in Spain and montado in Portugal) is an ancient system emerging as the only productive and sustainable structure able to deal with the combination of low soil fertility and the high variability of the Mediterranean climate [1]. This landscape is formed by a low density of holm oak trees, an understory of grasslands and, occasionally, shrubs and crops of cereals and legumes. This results in a close link between grass phenology and soil water dynamics
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
