5 Known limitations

We acknowledge that previous efforts have been made to provide phenology model frameworks (Hänninen & Kramer 2007; Chuine et al. 2013; Brown et al. 2014). Yet, their use and interoperability and scaleability is limited due to platform restrictions or their closed source nature. We recognize that the models as currently presented are by no means an exhaustive list of all model structures found in literature. However, the phenor R package is open source and adding model structures is easy compared to other low level languages (e.g., C / Fortran) and is actively encouraged. We are aware that the phenor R package does not include all possible phenological climatological drivers or phenological calibration/validation data either, although we stress that access to four larger freely available phenological data sources is provided by the phenor R package. Similarly, other sources of climate data, such as the ERA-interim re-analysis data (Dee et al. 2011), could be integrated as long as the described data structure is followed.