### 2.20.4.3. 14.4.3 Stress-Deciduous: Long Growing Season[¶](#stress-deciduous-long-growing-season "Permalink to this headline")

Under conditions when the stress-deciduous conditions triggering offset are not met for one year or longer, the stress-deciduous algorithm shifts toward the evergreen behavior. This can happen in cases where a stress-deciduous vegetation type is assigned in a climate where suitably strong stresses occur less frequently than once per year. This condition is evaluated by tracking the number of days since the beginning of the most recent onset period (\\({n}\_{days\\\_active}\\), d). At the end of an offset period \\({n}\_{days\\\_active}\\) is reset to 0. A long growing season control variable (_LGS_, range 0 to 1) is calculated as:

(2.20.71)[¶](#equation-20-71 "Permalink to this equation")\\\[\\begin{split}LGS=\\left\\{\\begin{array}{l} {0\\qquad \\qquad \\qquad {\\rm for\\; }n\_{days\\\_ active} <365} \\\\ {\\left({n\_{days\\\_ active} \\mathord{\\left/ {\\vphantom {n\_{days\\\_ active} 365}} \\right.} 365} \\right)-1\\qquad {\\rm for\\; }365\\le n\_{days\\\_ active} <730} \\\\ {1\\qquad \\qquad \\qquad {\\rm for\\; }n\_{days\\\_ active} \\ge 730} \\end{array}\\right. .\\end{split}\\\]

The rate coefficient for background litterfall (\\({r}\_{bglf}\\), s\-1) is calculated as a function of _LGS_:

(2.20.72)[¶](#equation-20-72 "Permalink to this equation")\\\[r\_{bglf} =\\frac{LGS}{\\tau \_{leaf} \\cdot 365\\cdot 86400}\\\]

where \\({\\tau}\_{leaf}\\) is the leaf longevity. The result is a shift to continuous litterfall as \\({n}\_{days\\\_active}\\) increases from 365 to 730. When a new offset period is triggered \\({r}\_{bglf}\\) is set to 0.

The rate coefficient for background onset growth from the transfer pools ( \\({r}\_{bgtr}\\), s\-1) also depends on _LGS_, as:

(2.20.73)[¶](#equation-20-73 "Permalink to this equation")\\\[r\_{bgtr} =\\frac{LGS}{365\\cdot 86400} .\\\]

On each timestep with \\({r}\_{bgtr}\\) \\(\\neq\\) 0, carbon fluxes from storage to transfer pools are calculated as:

(2.20.74)[¶](#equation-20-74 "Permalink to this equation")\\\[CF\_{leaf\\\_ stor,leaf\\\_ xfer} =CS\_{leaf\\\_ stor} r\_{bgtr}\\\]

(2.20.75)[¶](#equation-20-75 "Permalink to this equation")\\\[CF\_{froot\\\_ stor,froot\\\_ xfer} =CS\_{froot\\\_ stor} r\_{bgtr}\\\]

(2.20.76)[¶](#equation-20-76 "Permalink to this equation")\\\[CF\_{livestem\\\_ stor,livestem\\\_ xfer} =CS\_{livestem\\\_ stor} r\_{bgtr}\\\]

(2.20.77)[¶](#equation-20-77 "Permalink to this equation")\\\[CF\_{deadstem\\\_ stor,deadstem\\\_ xfer} =CS\_{deadstem\\\_ stor} r\_{bgtr}\\\]

(2.20.78)[¶](#equation-20-78 "Permalink to this equation")\\\[CF\_{livecroot\\\_ stor,livecroot\\\_ xfer} =CS\_{livecroot\\\_ stor} r\_{bgtr}\\\]

(2.20.79)[¶](#equation-20-79 "Permalink to this equation")\\\[CF\_{deadcroot\\\_ stor,deadcroot\\\_ xfer} =CS\_{deadcroot\\\_ stor} r\_{bgtr} ,\\\]

with corresponding nitrogen fluxes:

(2.20.80)[¶](#equation-20-80 "Permalink to this equation")\\\[NF\_{leaf\\\_ stor,leaf\\\_ xfer} =NS\_{leaf\\\_ stor} r\_{bgtr}\\\]

(2.20.81)[¶](#equation-20-81 "Permalink to this equation")\\\[NF\_{froot\\\_ stor,froot\\\_ xfer} =NS\_{froot\\\_ stor} r\_{bgtr}\\\]

(2.20.82)[¶](#equation-20-82 "Permalink to this equation")\\\[NF\_{livestem\\\_ stor,livestem\\\_ xfer} =NS\_{livestem\\\_ stor} r\_{bgtr}\\\]

(2.20.83)[¶](#equation-20-83 "Permalink to this equation")\\\[NF\_{deadstem\\\_ stor,deadstem\\\_ xfer} =NS\_{deadstem\\\_ stor} r\_{bgtr}\\\]

(2.20.84)[¶](#equation-20-84 "Permalink to this equation")\\\[NF\_{livecroot\\\_ stor,livecroot\\\_ xfer} =NS\_{livecroot\\\_ stor} r\_{bgtr}\\\]

(2.20.85)[¶](#equation-20-85 "Permalink to this equation")\\\[NF\_{deadcroot\\\_ stor,deadcroot\\\_ xfer} =NS\_{deadcroot\\\_ stor} r\_{bgtr} .\\\]

The result, in conjunction with the treatment of background onset growth, is a shift to continuous transfer from storage to display pools at a rate that would result in complete turnover of the storage pools in one year at steady state, once _LGS_ reaches 1 (i.e. after two years without stress-deciduous offset conditions). If and when conditions cause stress-deciduous triggering again, \\({r}\_{bgtr}\\) is rest to 0.

