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INTRODUCTION TO 3-PG PROCESS MODEL

INTRODUCTION TO 3-PG PROCESS MODEL. Joe Landsberg & Dick Waring. WHAT ARE PROCESS-BASED MODELS (PBMs)?. Process-based simulation models describe the

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INTRODUCTION TO 3-PG PROCESS MODEL

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  1. INTRODUCTION TO 3-PG PROCESS MODEL Joe Landsberg & Dick Waring

  2. WHAT ARE PROCESS-BASED MODELS (PBMs)? Process-based simulation models describe the essential features of systems such as forest stands in terms of the (physiological) processes that determine the way the systems behave and respond to change. PBMs can deal with features such as tree form, branching and wood density only through empirical relationships

  3. THE MAJOR PROCESSES GOVERNING FOREST GROWTH Biomass production and distribution:  Interception of solar energy  Conversion of solar energy to biomass (canopy photosynthesis)  The distribution (allocation) of biomass to component parts of trees (determines the patterns of tree growth) Adaptation to adverse/marginal conditions:  Frost tolerance and degree of impact  Drought tolerance  Susceptibility to defoliation

  4. Flow diagram General Process Model of Forest Growth Driving variables

  5. The 3-PG model (Landsberg and Waring, 1997) is a process-based model that provides a tool that can be used to simulate growth and yield of forest stands and the effects of environmental factors on growth. It can also be used as an analytical tool to evaluate the probable effects of altering, by breeding or selection, the physiological processes that govern tree growth

  6. MAIN COMPONENTS OF 3-PG Production of biomass – Based on environmental modification of light use efficiency and constant ratio of NPP to GPP. Biomass partitioning – Affected by growing conditions and tree size. Stem mortality – Based on self-thinning rule. Soil water balance – A single soil layer model with evapo-transpiration determined from Penman-Monteith equation. Stand properties – Determined from biomass pools and assumptions about specific leaf area, branch+bark fraction, and wood density.

  7. INPUTS Weather data: temperature, precipitation, humidity, radiation, subfreezing days Initial biomass:foliage, stems, roots Variables:maximum available soil water, initial stem number, stand age, max. stand age Parameters: canopyphotosynthetic efficiency, & environmental responses canopy leaf properties: area, mass, turnover & allometric equations soil properties: texture, water holding capacity, & fertility index

  8. MONTHLY CALCULATES Leaf area index & foliage mass, leaf fall Specifies extent that climatic variable limits stomatal or canopy conductance Transpiration estimated from Penman-Monteith equation Gross photosynthesis from utilizable PAR multiplied by quantum efficiency Net primary production (PN) as a fixed fraction of gross photosynthesis Fraction of PN allocated to roots, stems, branches, and foliage

  9. ANNUALLY CALCULATES Stemwood production, mass & volume Net production, above & below ground Mortality, natural and through thinning Live & dead stem biomass Leaf and root turnover Autotrophic (plant) respiration Relative constraints of environment

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