Climate-driven Bark Beetle Outbreaks

breed [trees tree]
breed [beetles beetle]

beetles-own [age]
trees-own [attack pheromone]
globals [dead-trees forest-lost total-dead-trees max-dead-trees max-b-population b-population cut-down-trees]

to setup
  clear-all
  setup-beetles
  setup-trees
  setup-patches

  reset-ticks
end 

to setup-trees
  ask patches
  [if not any? trees-here
    [if random 100 < 80
      [sprout-trees 1
      [set color 54
       set size 1.5 + random-float 1
       set shape "pine"
       set attack 0
       set pheromone 0]
  ]]]
end 

to setup-beetles
  create-beetles Starting-number-of-beetles
  [set color 0
    set size 0.5
    set shape "bark-beetle"
    set age 0
    setxy random-xcor random-ycor
  ]
end 

to setup-patches
  ask patches [set pcolor 37 + random-float 1]
end 

to go

  if ticks >= years [stop]
  ;if not any? beetles [stop]

  move-infest
  attacking
  beetle-mortality
  beetle-flight
  tree-sapling
  tree-grow
  count-dead-trees
  clean-pheromone
  thinning-trees
  forest-management
  tick
end 

to forest-management
  (ifelse
     Cut-down-trees? = "never"
      []

     Cut-down-trees? = "when they are lightly infested"
      [ask trees with [attack > 5]
        [ask beetles-here [die]
         set cut-down-trees cut-down-trees + 1
         die]]

     Cut-down-trees? = "only when they are heavily infested"
      [ask trees with [attack > 35 - (drought-severity * 5)]
        [ask beetles-here [die]
         set cut-down-trees cut-down-trees + 1
         die]]
    )
end 

to thinning-trees
 ask trees with [size >= 1.75]
        [if random 100 < Thinning [set cut-down-trees cut-down-trees + 1 die]]
end 

to clean-pheromone
  ask trees [set pheromone 0]
end 

to  beetle-flight  ;mature beetle flight for new trees
 ask beetles
   [right random 360 forward 1 + random-float 2]
end 

to count-dead-trees

  set total-dead-trees dead-trees
  if total-dead-trees > max-dead-trees
    [set max-dead-trees total-dead-trees]
  set dead-trees 0

  set b-population count beetles
  if b-population > max-b-population
  [set max-b-population b-population]
end 

to tree-sapling
 ask patches
  [if not any? trees-here
    [if random 100 < 5
      [sprout-trees 1
      [set color 54
       set size 1
       set shape "pine"
       set attack 0
       set pheromone 0]]]]
end 

to tree-grow
 ask trees
  [if size <= 2.5
    [set size size + 0.05]]
end 

to beetle-mortality
  ask beetles
  [ if age >= 2 [die]
    if random 100 < 49 - avg-winter-temperature-increase * 2 [die]
  ]
end 

to attacking
  ask trees
  [(ifelse
    attack > 35  - (drought-severity * 5) and attack < 50  - (drought-severity * 5)
      [set color 26]
    attack >= 50  - (drought-severity * 5)
      [set dead-trees dead-trees + 1 set forest-lost forest-lost + 1 die ])]
end 

to move-infest
   ask beetles
  [ifelse any? trees with [pheromone > 0 and attack < 50 - (drought-severity * 5)] in-radius 5           ;if there are trees with pheromone and not fully-occupied in a radius of 5
    [let candidate-trees trees with [pheromone > 0 and attack < 50  - (drought-severity * 5)] in-radius 5      ;if so, let these trees to be the candidate trees
      let my-tree one-of candidate-trees with-max [pheromone]                   ; let one of candidate trees with the max pheromone be my tree
       move-to my-tree                                                          ;infest the tree and reproduce and die
       hatch 2 [set age 0]
        ask my-tree [set attack attack + 2 set pheromone pheromone + 1]

        if random 100 < avg-summer-temperature-increase * 4                     ;effect of rising temperature
           [hatch 2 [set age 0]
            ask my-tree [set attack attack + 2 set pheromone pheromone + 1]]
       die]

    [ifelse any? trees with [size >= 1.75 and pheromone <= 0 ] in-radius 2            ;otherwise, if there are mature non-infested trees in a radius of 2
      [let candidate-trees trees with [size >= 1.75 and pheromone <= 0 ] in-radius 2  ; if so, let these trees to be the candidate trees
       let my-tree one-of candidate-trees                                             ; let one of candidate trees be my tree
        move-to my-tree                                                               ;infest the tree and reproduce and die
        hatch 2 [set age 0]
        ask my-tree [set attack attack + 2 set pheromone pheromone + 1]

        if random 100 < avg-summer-temperature-increase * 4                     ;effect of rising temperature
           [hatch 2 [set age 0]
            ask my-tree [set attack attack + 2 set pheromone pheromone + 1]]
        die]

      [right random 360 forward 1 + random-float 2 set age age + 1]                         ;otherwise, randomly move and increase age
    ]]
end