This document describes the measurement of ancillary vegetation variables at ICOS ecosystem stations in forests. These variables are Green Area Index (GAI), Aboveground Biomass (AGB), and litter biomass. In summary, they are measured for the following aims and with the following methods: - GAI is measured to explain seasonal variation in ecosystem-atmosphere fluxes and is measured indirectly with Digital Hemispherical Photography (DHP) or a linear ceptometer. The choice of method depends on the GAI (seasonal max GAI6 m² m-2 requires ceptometer), however the choice of method should be discussed between the station PI and the ETC. The sensor type should be kept constant over time. - AGB is measured to estimate Aboveground Net Primary Productivity (ANPP) and lateral carbon flow through harvest. AGB is measured by measuring diameter at breast height (DBH), stem height and allometric relations for overstorey vegetation and destructive measurements for understorey vegetation. - Litter biomass is measured to correct the yearly ANPP estimated from AGB and is measured with litter traps at the Class 1 stations. This document is structured in four different sections with the aim to facilitate the use and application: - Measurements: in this section the sensors, setup and methods to correctly collect the data and info are described. It includes sub-sections on sensors characteristics, practical indication for the setup/collection, info on the sampling design and guidelines for the installation/sampling also respect to other sensors/measurements - Maintenance: in this section all the maintenance and calibration guidelines are described, including the general timeline. - Submission: it is the section related to the data preparation and submission to the ETC. It includes the list of all the parameters, the correct formatting and the way to submit them to the database. It is linked to the BADM system needed to submit the metadata and not continuous measurements - Processing: this section is for internal use of the ETC and describes the processing applied to the single variable/info/sample submitted. It is important to remind that the exact application of the protocol at site level is also discussed with ETC in order to find agreed solutions for specific cases. If a specific part is relevant only for a specific ecosystem or station Class this is also reported in the document.