Abstract
Semi-natural grasslands are perennial ecosystems and an important part of agricultural landscapes that are threatened by urbanization and agricultural intensification. However, implementing national grassland conservation policies remains challenging because their inventory, based on short-term observation, rarely discriminate semi-natural permanent from temporary grasslands. This study aims to map grassland frequency at a national scale over a long period using Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m satellite time-series. A three-step method was applied to the entire area of metropolitan France (543,940 km²). First, land-use and land-cover maps—including grasslands—were produced for each year from 2006–2017 using the random forest classification of MOD13Q1 and MYD13Q1 products, which were calibrated and validated using field observations. Second, grassland frequency from 2006–2017 was calculated by combining the 12 annual maps. Third, sub-pixel analysis was performed using a reference layer with 20 m spatial resolution to quantify percentages of land-use and land-cover classes within MODIS pixels classified as grassland. Results indicate that grasslands were accurately modeled from 2006–2017 (F1-score 0.89–0.93). Nonetheless, modeling accuracy varied among biogeographical regions, with F1-score values that were very high for Continental (0.94 ± 0.01) and Atlantic (0.90 ± 0.02) regions, high for Alpine regions (0.86 ± 0.04) but moderate for Mediterranean regions (0.62 ± 0.10). The grassland frequency map for 2006–2017 at 250 m spatial resolution provides an unprecedented view of stable grassland patterns in agricultural areas compared to existing national and European GIS layers. Sub-pixel analysis showed that areas modeled as grasslands corresponded to grassland-dominant areas (60%–94%). This unique long-term and national monitoring of grasslands generates new opportunities for semi-natural grassland inventorying and agro-ecological management.
Highlights
Grasslands are one of the most extensive terrestrial ecosystems on Earth and a source of food for livestock [1]
Semi-natural grasslands efficiently support ecosystem services such as biodiversity maintenance [4], water resources [5], carbon storage and forage supply [6]. They are often related to agricultural systems with high nature value [7] but are threatened by urbanization and agricultural intensification [6]. In this context, inventorying and monitoring semi-natural grasslands is a major objective for conservation, in particular within the framework of European programs and legislation such as the European Union (EU) Rural Development Program, Habitat Directive [8], Water Framework Directive [9], Common Agricultural Policy (CAP) [10] and land use and forestry regulation for 2021–2030 [11]
The modeling accuracy of the grassland class differed by biogeographical region, with an excellent mean F1-score for the Continental (0.94 ± 0.01) and Atlantic (0.90 ± 0.02) regions, a very good score for the Alpine (0.86 ± 0.04) region and a moderate score (0.62 ± 0.10) for the Mediterranean region
Summary
Grasslands are one of the most extensive terrestrial ecosystems on Earth and a source of food for livestock [1]. Permanent grasslands that are not part of crop rotations can be defined as “land on which vegetation is composed of perennial or self-seeding annual forage species which may persist indefinitely” [2] They include semi-natural grasslands, which are defined as a “managed ecosystem dominated by indigenous or naturally occurring grasses and other herbaceous species” [2]. Semi-natural grasslands efficiently support ecosystem services such as biodiversity maintenance [4], water resources [5], carbon storage and forage supply [6] They are often related to agricultural systems with high nature value [7] but are threatened by urbanization and agricultural intensification [6]. The lack of a comprehensive, inter-annual and parcel-scale map of semi-natural grasslands makes their conservation challenging [12,13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
