Opened 10 months ago

Closed 9 months ago

#640 closed defect (fixed)

Revisit the initial planting density in stomate_prescribe

Reported by: luyssaert Owned by: gmarie
Priority: critical Milestone: IPSLCM6.v2
Component: Biogeochemical processes Version:
Keywords: Cc:

Description

For FG2 with LIMIT_WEST=8, LIMIT_NORTH=48, LIMIT_SOUTH=46 and LIMIT_EAST=10 the combination between stand density and diameter (thus the RDI) is higher than RDI_target_upper. This implies that the last day of the year the stand will be thinned to reach RDI_target_lower. Because we start with very small trees now, this RDI_target_lower can be so small that there is not enough LAI to grow properly. Note that the RDI_target_xxx are calculated from yield tables which do not account for very small trees.

Elements of a possible solution:
(1) use forest_managed(ipts,j) to chose how the initial stand density will be calculated. The current approach with start_by_grad seems pretty robust for unmanaged stands (FM1) that have to follow self-thinning. Applying the same approach to managed stands (FM2) may be problematic in cases because the initial density results in an RDI above RDI_target_upper.
(2) the initial diameter of the trees should be independent of the FM strategy but the initial number of individuals could differ between FM1 and FM2 (as is typically the case in reality). FM1 could make use of the start_by_grad = y, FM2 could make use of start_by_grad = n.
(3) Right now there is no reason to revise start_by_grad = y
(4) If start_by_grad = n, in stomate_prescribe.f90 RDI_target_xxx should be calculated and used to calculate the initial density. One proposal is to select the initial stand density such that the stand RDI equals RDI_target_upper. In that case in sapiens_forestry.f90 thinnings should be abandoned as long as RDI_target_lower is less than a threshold (i.e. 20). The risk is that there won't be any mortality in the first years resulting a too slow diameter growth and hence a too slow change in the RDI_targets. There are several ways to ensure this does not happen: as long as the calculated RDI_target_lower is less than 20, it could be overwritten by RDI_target_upper-0.01. That way we will have to kill some trees every year. This mortality will stimulate the growth of the remaining trees resulting in higher RDI's.

Change History (4)

comment:1 Changed 10 months ago by gmarie

  • Resolution set to fixed
  • Status changed from new to closed

comment:2 Changed 10 months ago by luyssaert

  • Resolution fixed deleted
  • Status changed from closed to reopened

comment:3 Changed 9 months ago by luyssaert

  • Owner changed from somebody to gmarie
  • Status changed from reopened to assigned

comment:4 Changed 9 months ago by gmarie

  • Resolution set to fixed
  • Status changed from assigned to closed

Changes committed in r6437

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