Senescence

Senescence mortality provides for an uptick in mortality rates. It is meant to slightly increase the death rate among large adult trees.

Trees killed by this behavior will have a mortality reason code of "natural".

Parameters for this behavior

Parameter name	Description
Senescence Mortality Alpha	Controls the senescence mortality rate.
Senescence Mortality Beta	Controls the senescence mortality rate.
DBH at Onset of Senescence, in cm	DBH at which senescence takes effect.
DBH of Maximum Senescence Mortality Rate, as an integer in cm	The DBH at which maximum mortality occurs. Trees with a DBH greater than this value experience no further increase in the mortality rate.

How it works

All trees to which senescence is applied are evaluated for senescence mortality. In practice, trees below the onset of senescence DBH very rarely die. The probability of death rises with DBH until the DBH of maximum senescence rate is reached, at which point it levels off.

To assess whether a tree will die due to senescence, the following function is evaluated:

where:

m_s is the probability of mortality
α (Senescence Mortality Alpha parameter) and β (Senescence Mortality Beta parameter) control the magnitude of the uptick
DBH is the tree's DBH, in cm
DBH_s is the DBH at Onset of Senescence, in cm parameter

The probability is compared to a random number to determine whether the individual tree will die.

How to apply it

Senescence may be applied to saplings and adults of any species. It cannot be applied to seedlings.