susp: Models the packing of materials in a suspended layer
In pzylstra/Impact: Fire impact functions for FRaME

Based on a negative exponential function;updates base.params

susp(
  base.params,
  a,
  suspNS = "suspNS",
  Flora,
  growth,
  default.species.params,
  age,
  density = 300
)

`base.params`	Parameter input table
`a`	The number of the record to be modelled
`suspNS`	Name of the fuel in the suspended layer
`Flora`	A dataframe with the fields: record - a unique, consecutively numbered identifier per site species - the name of the species, which will call trait data from 'default.species.params' moisture - the moisture content of the species in whole numbers (eg 1 for 100 stratum - numeric value from 1 to 4, counting from lowest stratum comp - base, he, ht, top & w - canopy dimensions for that species (m). he and ht are optional clump - mean ratio of clump diameter to crown diameter openness - ratio of gap to clump size
`growth`	A dataframe with the six fields: species - Name of the species consistent with other tables max - Maximum plant height (m) rate - A constant describing the rate of growth for a Chapman Richards function aQ - First constant in a quadratic equation bQ - Second constant in a quadratic equation cQ - Third constant in a quadratic equation aLin - First constant in a linear equation bLin - Second constant in a linear equation Function prioritises growth equations from left to right
`default.species.params`	Leaf traits database
`age`	The number of years since last fire
`density`	Wood density (kg/m3)