• Neems are in bloom and mango trees fruiting in many parts of India now, but what determines such seasonal changes?
  • At least, in the Sikkim Himalaya temperature, day length and genetic relatedness between species determine when rhododendrons put out their first buds, flowers and fruits.
  • Interest in tree phenology — the timing of biological events such as flowering and fruiting — has increased after climate change has been shown to alter it, especially of plants in high-altitudes.
  • Research in Ecology and Environment studied rhododendron trees in sub-alpine and alpine forests between 3,400-4,230 metres above sea level in Sikkim’s Kyongnosla Alpine Sanctuary.
  • Between 2013 and 2015, the team monitored budding, flowering, fruiting (arrival of first fruits, immature green fruits and mature brown fruits) and fruit dehiscence (splitting open of fruit to release seeds) and the duration of phenology in 320 trees of 10 rhododendron species for every 15 days.
  • But when resources (sunshine as reflected by day length, and temperature) decreased as winter neared, all rhododendrons experienced later phenology events — the arrival of immature green fruits, mature brown fruits and finally, fruit dehiscence — regardless of whether they were closely related or not.
  • Similarly, relatedness did not play a role in phenology of rhododendrons with increasing altitude.
  • Harsher environments at higher elevations — including lower temperatures, heavy snowfall and barren and rockier lands higher up — could be trumping over the species’ common evolutionary history here, write the authors in their study published in Ecosphere.