Summary:

## Evergreen Phenology

The evergreen phenology algorithm in the model is the simplest of the three possible types. It assumes that all carbon and nitrogen allocated for new growth in the current timestep goes immediately to the displayed growth pools (f_cur = 1.0). This means there is no accumulation of carbon or nitrogen in the storage or transfer pools, and the onset growth and background onset growth mechanisms are never invoked for this type.

Litterfall for evergreen types occurs only through the background litterfall mechanism, with a continuous (slow) shedding of foliage and fine roots. The rate of background litterfall (r_bglf) depends on the specified leaf longevity (τ_leaf, in years), as:

r_bglf = 1 / (τ_leaf * 365 * 86400)

This is an area where the model could potentially be improved, as it is known that there are distinct periods of higher and lower leaf litterfall for evergreen needleleaf trees in temperate and boreal zones.