Adapting a mortality model for southeast interior british columbia
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Adapting a Mortality Model for Southeast Interior British Columbia. By - Temesgen H., V. LeMay, and P.L. Marshall University of British Columbia Forest Resources Management Vancouver, BC, V6T 1Z4 The 2001 Western Mensurationists' Meeting Klamath Falls, Oregon June 24-26/2001.

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Adapting a Mortality Model for Southeast Interior British Columbia

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Adapting a Mortality Model for Southeast Interior British Columbia

By - Temesgen H., V. LeMay, and P.L. Marshall

University of British Columbia

Forest Resources Management

Vancouver, BC, V6T 1Z4

The 2001 Western Mensurationists' Meeting

Klamath Falls, Oregon

June 24-26/2001


BC Biogeoclimatic

Ecosystem

Classification units

US Habitat Types

Adapting a GY model

  • The Northern Idaho prognosis variant (NI) has been adapted to the southeast interior of BC, PrognosisBC


Adapting a GY model (cont’d)

  • Different measurement units (metric), basic functions (e.g., volume and taper) and standards

  • Classification of US habitat type to BEC can be subjective

  • Sub-models coefficients and model form may not fit BC data

  • Insufficient ground data for some types of stands


Adapting a GY model

  • Sub-model components:

  • large tree diameter and height growth

  • small tree diameter and height growth

  • small and large tree crown ratio

  • mortality and regeneration

  • others


BACKGROUND

  • Mortality is:

    • an essential attribute of any stand growth projection system

    • frequently expressed as a function of tree size, stand density, individual tree competition, and tree vigor

  • In PrognosisBC, periodic mortality rate is predicted using tree (Ra) and stand based (Rb) mortality functions


BACKGROUND (cont’d)

  • Ra is a logistic function of tree size taken in context of stand structure.

  • Rb operates as a convergence on normal basal area stocking and maximum basal area (BAMAX)

  • Rb isbased on the concept that:

    • for each stand, there is a normal stocking density

    • there is a BAMAX that a site can sustain and this maximum varies

      by site quality


Objectives

  • to adapt a mortality model for southeast interior BC

  • to evaluate selected mortality models for conifers and hardwoods in southeast interior BC


METHODS

  • Three approaches of adapting mortality model were assessed, using BC based PSPs:

    • a multiplier function (Model 1)

    • re-fit the same model form by species/zone combination (Model 2)

    • changing variables (Models 3, 4, and 5)

  • PSPs that were re-measured at 5 to 12 years interval and that consistently included all trees > 2.0 cm were included


METHODS(cont’d)

  • For each PSP, individual tree records were coded, as either live or dead at each measurement period, and variables listed in the mortality models were extracted


METHODS (cont’d)

  • Only species/zone combinations with more than 30 dead trees were selected.

  • To handle the unequal re-measurement periods in the PSP data sets, each model was weighted by the number of years between remeasurement periods.

  • The PSP data set was divided into model (70%) and test data (30%) sets  

  • Observed and predicted number of live and dead trees by species/zone were compared and then a model was selected


RESULTS

  • Noticeable differences were found in the % of correctly classified trees among the five models and the species/zone combinations considered in this study

  • Model 5 had lower Akaike Information Criterion (AIC) and Schwartz Criterion (SC) for most species/zone combinations


Percent of correctly classified trees in the ICH zone, using test data


Number of observed (N_OBS) and predicted (N_Exp) dead trees by species in the ICH zone, using Model 5 on test data


Number of observed (N_obs) and predicted (N_Exp) dead trees by diameter class in the ICH zone, using Model 5 on test data


Percent of correctly classified trees in the IDF zone, using test data


Number of observed (N_OBS) and predicted (N_Exp) dead trees by species in the IDF zone, using Model 5 on test data


Number of observed (N_obs) and predicted (N_Exp) dead trees by diameter class in the IDF zone, using Model 5 on test data


For species/zone combination with little or no data

  • substitution by similar species or BEC zone is suggested.

    FORUSE

    • Bl in IDFICH

    • Cw in IDF ICH

    • E in MSICH

    • Fd in PP IDF


Summary

  • Model 5 predicts mortality of both conifers and hardwoods reasonably well

  • BC based BAMAX values improved the predictive ability of the model

  • Inclusion of eco-physical factors such as slope, aspect, and elevation into the mortality model might increase the predictive ability of the model.


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