physiological

The development rate of plants and invertebrate animals often depends on amount of heat received while the ambient temperature is between minimum and maximum thresholds.

The number of degree-days is a commonly used statistic related to the development of plants and invertebrates. Degree-days, DD, is given by:
 

DD = ∫ Tt.dt

• T is temperature in degrees Celsius (could be Fahrenheit)
• t is time in days.

degree-days is then ^oC days or ^oF days.