Hybrid modelling of plantation crops

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Hybrid modelling of plantation crops

• Euan Mason
• University of Canterbury

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Outline

• Hybrid models
• Current hybrid modelling projects at the School
  of Forestry
• Stand level hybrid growth and yield
• Hybrid initial growth models

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Potential for hybrid models

• Geographic Information Systems
• More known about each site and stand
• Variation in growth pattern from site to site
• Less need for regional models
• Variation in weather from year to year
• Predicting the past
• Variation in monthly climate offers monthly
  predictions
• Climate change may affect growth patterns
• Kyoto protocol
• Carbon storage explicit in some models

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An example hybrid model
3-PG Model (Landsberg Waring 1997)
Allocation varies with fertility
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Application of 3-PG 25-year old experiment
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Potential issues with 3-PG

• Allocation of C is derived from allometry
• Recursiveness, compounded errors
• Over parametarisation
• Fertility is inadequately represented
• Stand and stem geometry are not modelled
• Circularity
• DBH-gtCarbon, Carbon-gtDBH
• Measurement of LAI may partially solve this

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Current HM projects at SoF

• Physiological hybrid Initial Growth Model
• Comparisons between hybrid and traditional G Y
  models
• Modelling effects of nutrition
• Modelling effects of spacing and genotype on
  corewood properties
• National hybrid model for P. radiata
• Modelling clonal stands

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Physiological hybrid IGM
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Comparisons of hybrid models

• Guy Pinjuv, PhD candidate
• Canterbury estate, highly variable sites
• Comparison of a range of hybrids
• Traditional growth and yield
• 3-PG
• Several alternatives in between
• Evaluate fit and utility
• Two types of validation required

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Modelling effects of nutrition

• Horacio Bown, PhD candidate
• Development of fertility modifier for hybrid
  models
• Long-term goal
• Controlled environment
• Field experiments

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Corewood stiffness vs actual stocking clone
J.P. Lasserre
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Modelling clonal stands

• Rajesh Sharma
• What changes are needed when modelling for clonal
  forest management?
• Potential for hybrid modelling to provide
  genotype-specific models
• Large plot clonal experiment - SPBL
• 10 clones, pure and mixed clone blocks
• Planted 1993
• Variation in growth, form, wood quality
• Interchange in dominance
• Competition with self or other genotypes
• Local genotype-dependent individual tree model
• Risk

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National hybrid model for radiata pine

• Postdoctoral Fellow
• Dr Helge Dzierzon
• Can hybrid modelling remove need for regions?
• Are hybrids more effective that traditional
  methods within regions?
• How much local sensitivity do we lose by adopting
  a national hybrid model?
• PSP data from 13 companies
• Monthly weather data from climate stations, with
  local offsets
• Elevation and soils from GIS

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Weather stations used

• Reasonable data coverage from 1960 to 2005
• Stations over all New Zealand
• Data availability for each station is
  heterogeneous

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Landcare Research Soil Layer

• Aim Investigate growth patterns over New Zealand
• Format
• ESRI polygon layer
• 8 Soil Classes (NZSCORD)
• 67 Subclasses (NZSC) covered by PSPs

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Results for MTH using LCR Layer the ultimate
regional approach

• Regression for SC
• MSE2.03
• N 3202
• N classes 26
• Residuals for SC
• From 20955 to 13182

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Results for G using LCR Layer

• Regression of SC
• MSE9.70
• N 3202
• N classes 26
• Residuals for SC
• From 360825 to 302916
• Residuals of Simulation run
• Mean 356021
• Std 9154

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An idea among many

• Time accumulated light
• Use 3-PG type quantum efficiency modifiers to
  accumulate potentially used light
• Use sigmoidal difference equations as usual,
  fitted to PSP data
• Avoids some of 3-PGs problems
• Compounded errors
• Allocation of C
• Overparametarisation
• Lack of stand geometry

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An idea among many

• Estimate genetic components of seasonal
  variations in primary and secondary growth
• Different radiation sums for primary and
  secondary growth

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Seasonal growth in dbh (red), height (yellow) and
3-PG predictions (blue). (Tennent 1986)
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An idea among many

• Climatic variables as well as stocking and
  radiation sum estimates in mortality model
• To what extent can temporal variation in climatic
  influences inform us about influences on crop
  growth and mortality of spatial variation in
  climate?

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An idea among many

• Compatible stand, distribution individual tree
  projection systems
• Models that represent height vs basal area growth
  as functions of site variables
• Models that respond to climatic and local weather
  variation
• Models specific to each site
• Models that naturally provide growth estimates
  within years

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Preliminary Example P. radiata in Central North
Island
Von-Bertalanffy-Richards Daytime temp, VPD
modifiers
Schumacher, daytime temperature modifier
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MTH Results using light sum models - Dzierzon

• Regression example
• MSE 1.40
• N 2146
• Residuals
• From 4427.0 to 4118

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G Results using light sum models - Dzierzon

• Regression Example
• MSE 5.05
• N 2146
• Residuals
• From 57796 to 54822

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Light sum initial growth model Competition for
light in R1835/2
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Future directions

• Two fertile strands for forest modelling research
• Internal qualities of stems
• Physiological hybrids
• The University of Canterbury contributes to both
• Challenge is to bring the two strands together

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Future directions

• Hybrids may obviate a regional approach to growth
  and yield
• Hybrids may provide an alternative or be
  complementary to 300 (500) index/Site index
  approach
• Climatic and silvicultural effects may be more
  easily integrated in hybrid models than in
  traditional G Y models
• Site conditions mediate use of light

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Summary

• Several key studies in hybrid modelling
• Hybrid modelling
• More sensitive to local site conditions
• Seasonal (monthly) predictions
• Reduced need for regions?
• Better estimates of growth since last inventory?
• Carbon sequestration explicit?
• Linkages between mensuration, silviculture and
  physiology