## 2.20.2. Evergreen Phenology[¶](#evergreen-phenology "Permalink to this headline")
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The evergreen phenology algorithm is by far the simplest of the three possible types. It is assumed for all evergreen types that all carbon and nitrogen allocated for new growth in the current timestep goes immediately to the displayed growth pools (i.e. f\\({f}\_{cur} = 1.0\\) (Chapter 13)). As such, there is never an accumulation of carbon or nitrogen in the storage or transfer pools, and so the onset growth and background onset growth mechanisms are never invoked for this type. Litterfall is specified to occur only through the background litterfall mechanism – there are no distinct periods of litterfall for evergreen types, but rather a continuous (slow) shedding of foliage and fine roots. This is an obvious area for potential improvements in the model, since it is known, at least for evergreen needleleaf trees in the temperate and boreal zones, that there are distinct periods of higher and lower leaf litterfall (Ferrari, 1999; Gholz et al., 1985). The rate of background litterfall (\\({r}\_{bglf}\\), section 14.1.4) depends on the specified leaf longevity (\\(\\tau\_{leaf}\\), y), as

(2.20.44)[¶](#equation-20-44 "Permalink to this equation")\\\[r\_{bglf} =\\frac{1}{\\tau \_{leaf} \\cdot 365\\cdot 86400} .\\\]

