Definitions

	Drought Meteorological Biological Sociological
	Drought is a period of water deficit resulting in a negative impact on society (it is a human phenomenon)
	Drought resistance - a generic term applied to tolerance and adaptation; with the exceptions of "hydraulic lift" and boundary layer effects, plants have little ability to resist drying by the atmosphere Drought tolerance - the ability of plants to survive and grow during periods of water deficit Drought adaptation - the ability of plants to modify their function to improve survival and growth during periods of water deficit Drought avoidance - the ability of plants to improve survival and growth by escaping periods of water deficit (e.g. in a dormant state)

Scales of Response

	Community sunny vs shady slopes wet vs dry soils
tall grass prairie, eastern Nebraska Big blue stem, switchgrass, indiangrass		short-grass prairie, western Nebraska Blue grama, needle-and-thread
	Morphological Leaf loss Smaller leaves (reduces the radiation load and transpiring area) Reduced shoot growth Greater absolute and/or relative root growth Leaf senescence and death transpiration (cools the leaf)
	Anatomical and physiological Concentration by dehydration Osmotic adjustment Proline accumulation ABA increase C3 vs C4 metabolism Cell wall elasticity
	Biochemical and molecular Altered enzyme activity (a-amylase) is the result of molecular control Heat shock proteins Multiple genes Water soluble carbohydrates (high sugar grasses)

  Unique aspects of Forages

	Pasture perenniality Anticipated vs unexpected water deficit Dilemma whether or not to continue growth into drought, water loss (ET) µ growth rate (photosynthesis)
	Defoliation Close grazing usually occurs during drought, but impairs recovery from drought Effects of sward height and mass are unclear. Some studies show water conservation with long grass (mulch effect) – some show conservation with short grass (low transpiring surface) - probably a unimodal response confounded by dead matter defoliation reduces root growth
	Dry/severe environment grasslands are usually in the more severe environments
	Endophyte unique to forage grasses
	Quality text 91-92 green:dead ratio Loss of legumes Increased fiber, reduced protein Anti-quality

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