ABSTRACT
Vegetation forms in assemblages that grow under a speciœc range of environmental conditions, characterized as biomes, and thrive when optimal conditions for that particular assemblage occur. However, vegetation is subjected to “stress” when environmental conditions differ signiœcantly from optimal conditions, such as when drought or unfavorable temperatures occur, or insufœcient or excess nutrients are present [4-6]. When stress factors impair physiological function through biochemical mechanisms, this impacts the exchange of carbon, water, and energy between vegetation and the atmosphere. Since nonoptimal conditions are more common than optimal conditions over extensive periods of time, assumptions based on optimal conditions are typically not reasonable, either in interpreting observations or for model retrievals.
