Historical clue formulations

• Transitional region between biomes — 2021-04-07
• Transitional zone between two biomes — 2019-12-26
• Transition area from deciduous to evergreen, e.g. — 2014-04-13
• Environmental transition area — 2014-04-02
• Transitional zone between plant communities — 2013-11-26
• Environmental transition area — 2011-07-09
• Area between forest and prairie, e.g. — 2009-01-10
• Transitional land zone — 2007-02-25
• Transition zone between plant communities — 1996-05-11