High latitude Low temperature, Frenot 2005; Fuentes 2013; Sax Kennedy 1996 et al. et al. extended low 2001; Stohlgren 2005; Schnitzler et al. et al. photosynthetic energy 2007 periods, high seasonal variation in photoperiod
High latitude Low temperature, extended low photosynthetic energy periods, high seasonal variation in photoperiod Frenot et al. 2005; Fuentes et al. 2013; Sax 2001; Stohlgren et al. 2005; Schnitzler et al. 2007 Kennedy 1996