### 2.17.1.2. Growth Respiration[¶](#growth-respiration "Permalink to this headline")

Growth respiration is calculated as a factor of 0.11 times the total carbon allocation to new growth (\\(CF\_{growth}\\), after allocating carbon for N acquisition, Chapter [2.18](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/FUN/CLM50_Tech_Note_FUN.html#rst-fun).) on a given timestep, based on construction costs for a range of woody and non-woody tissues, with estimates of the growth respiration flux revised downswards following (Atkin et al. 2017). For new carbon and nitrogen allocation that enters storage pools for subsequent display, it is not clear what fraction of the associated growth respiration should occur at the time of initial allocation, and what fraction should occur later, at the time of display of new growth from storage. Eddy covariance estimates of carbon fluxes in forest ecosystems suggest that the growth respiration associated with transfer of allocated carbon and nitrogen from storage into displayed tissue is not significant (Churkina et al., 2003), and so it is assumed in CLM that all of the growth respiration cost is incurred at the time of initial allocation, regardless of the fraction of allocation that is displayed immediately (i.e. regardless of the value of \\(f\_{cur}\\), section 13.5). This behavior is parameterized in such a way that if future research suggests that some fraction of the growth respiration cost should be incurred at the time of display from storage, a simple parameter modification will effect the change. [1](#id3)

[1](#id2)

Parameter \\(\\text{grpnow}\\) in routines CNGResp and CNAllocation, currently set to 1.0, could be changed to a smaller value to transfer some portion (1 - \\(\\text{grpnow}\\) ) of the growth respiration forward in time to occur at the time of growth display from storage.
