## 2.20.5. Litterfall Fluxes Merged to the Column Level[¶](#litterfall-fluxes-merged-to-the-column-level "Permalink to this headline")
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CLM uses three litter pools, defined on the basis of commonly measured chemical fractionation of fresh litter into labile (LIT1 = hot water and alcohol soluble fraction), cellulose/hemicellulose (LIT2 = acid soluble fraction) and remaining material, referred to here for convenience as lignin (LIT3 = acid insoluble fraction) (Aber et al., 1990; Taylor et al., 1989). While multiple plant functional types can coexist on a single CLM soil column, each soil column includes a single instance of the litter pools. Fluxes entering the litter pools due to litterfall are calculated using a weighted average of the fluxes originating at the PFT level. Carbon fluxes are calculated as:

(2.20.86)[¶](#equation-20-86 "Permalink to this equation")\\\[CF\_{leaf,lit1} =\\sum \_{p=0}^{npfts}CF\_{leaf,litter} f\_{lab\\\_ leaf,p} wcol\_{p}\\\]

(2.20.87)[¶](#equation-20-87 "Permalink to this equation")\\\[CF\_{leaf,lit2} =\\sum \_{p=0}^{npfts}CF\_{leaf,litter} f\_{cel\\\_ leaf,p} wcol\_{p}\\\]

(2.20.88)[¶](#equation-20-88 "Permalink to this equation")\\\[CF\_{leaf,lit3} =\\sum \_{p=0}^{npfts}CF\_{leaf,litter} f\_{lig\\\_ leaf,p} wcol\_{p}\\\]

(2.20.89)[¶](#equation-20-89 "Permalink to this equation")\\\[CF\_{froot,lit1} =\\sum \_{p=0}^{npfts}CF\_{froot,litter} f\_{lab\\\_ froot,p} wcol\_{p}\\\]

(2.20.90)[¶](#equation-20-90 "Permalink to this equation")\\\[CF\_{froot,lit2} =\\sum \_{p=0}^{npfts}CF\_{froot,litter} f\_{cel\\\_ froot,p} wcol\_{p}\\\]

(2.20.91)[¶](#equation-20-91 "Permalink to this equation")\\\[CF\_{froot,lit3} =\\sum \_{p=0}^{npfts}CF\_{froot,litter} f\_{lig\\\_ froot,p} wcol\_{p} ,\\\]

where \\({f}\_{lab\\\_leaf,p}\\), \\({f}\_{cel\\\_leaf,p}\\), and \\({f}\_{lig\\\_leaf,p}\\) are the labile, cellulose/hemicellulose, and lignin fractions of leaf litter for PFT _p_, \\({f}\_{lab\\\_froot,p}\\), \\({f}\_{cel\\\_froot,p}\\), and \\({f}\_{lig\\\_froot,p}\\) are the labile, cellulose/hemicellulose, and lignin fractions of fine root litter for PFT _p_, \\({wtcol}\_{p}\\) is the weight relative to the column for PFT _p_, and _p_ is an index through the plant functional types occurring on a column. Nitrogen fluxes to the litter pools are assumed to follow the C:N of the senescent tissue, and so are distributed using the same fractions used for carbon fluxes:

(2.20.92)[¶](#equation-20-92 "Permalink to this equation")\\\[NF\_{leaf,lit1} =\\sum \_{p=0}^{npfts}NF\_{leaf,litter} f\_{lab\\\_ leaf,p} wcol\_{p}\\\]

(2.20.93)[¶](#equation-20-93 "Permalink to this equation")\\\[NF\_{leaf,lit2} =\\sum \_{p=0}^{npfts}NF\_{leaf,litter} f\_{cel\\\_ leaf,p} wcol\_{p}\\\]

(2.20.94)[¶](#equation-20-94 "Permalink to this equation")\\\[NF\_{leaf,lit3} =\\sum \_{p=0}^{npfts}NF\_{leaf,litter} f\_{lig\\\_ leaf,p} wcol\_{p}\\\]

(2.20.95)[¶](#equation-20-95 "Permalink to this equation")\\\[NF\_{froot,lit1} =\\sum \_{p=0}^{npfts}NF\_{froot,litter} f\_{lab\\\_ froot,p} wcol\_{p}\\\]

(2.20.96)[¶](#equation-20-96 "Permalink to this equation")\\\[NF\_{froot,lit2} =\\sum \_{p=0}^{npfts}NF\_{froot,litter} f\_{cel\\\_ froot,p} wcol\_{p}\\\]

(2.20.97)[¶](#equation-20-97 "Permalink to this equation")\\\[NF\_{froot,lit3} =\\sum \_{p=0}^{npfts}NF\_{froot,litter} f\_{lig\\\_ froot,p} wcol\_{p} .\\\]
