text:
Forest - A Simulated Ecosystem
NOTE
This problem was taken from this reddit thread (spoiler alert!), and I have adjusted it to make it fit with this site's format. All credit goes to reddit user "Coder_d00d".
In this problem, we will simulate a forest.
For this simulated forest we will be dealing with 3 aspects.

Trees which can be a Sapling, Tree or Elder Tree.
Lumberjacks (He
chops down down trees, he eats his lunch and goes to the Lava-try)
Bears (He mauls the lumberjacks who smells like pancakes)

A fore-warning: these rules are most probably not perfect. See them as a guideline, and if you need to tweak anything slightly that is fine (spawning rates have been pointed out as an issue, see kuroi neko's answer as an example of this.
Cycle of time:
The simulation will simulate by months. You will progessive forward in time with a "tick". Each "tick" represents a month. Every 12 "ticks" represents a year. Our forest will change and be in constant change. We will record the progress of our forest and analyze what happens to it.
Forest:
The forest will be a two dimensional forest. We will require an input of N to represent the size of the forest in a grid that is N x N in size. At each location you can hold Trees, Bears or Lumberjacks. They can occupy the same spot but often events occur when they occupy the same spot.
Our forest will be spawned randomly based on the size. For example if your value of N = 10. You will have a 10 by 10 forest and 100 spots.

10% of the Forest will hold a Lumberjack in 10 random spots. (using our 100 spot forest this should be 10 lumberjacks)
50% of the Forest will hold Trees (Trees can be one of 3 kinds and will start off as the middle one of "Tree") in random spots.
2% of the Forest will hold Bears.

How you receive the size of the forest is up to you (read from stdin, a file, or hardcode it in). I would recommend keeping N like 5 or higher. Small Forests are not much fun.
Events:
During the simulation there will be events. The events occur based on some logic which I will explain below. I will describe the events below in each description of the 3 elements of our forest.
The events follow the order of trees first, lumberjacks second and bears last.
Trees:

Every month a Tree has a 10% chance to spawn a new "Sapling". In a random open space adjacent to a Tree you have a 10% chance to create a "Sapling".
For example a Tree in the middle of the forest has 8 other spots around it. One of these (if they are empty) will become a "Sapling".
After 12 months of being in existence a "Sapling" will be upgrade to a "Tree". A "Sapling" cannot spawn other trees until it has matured into a "Tree".
Once a "Sapling" becomes a tree it can spawn other new "Saplings".
When a "Tree" has been around for 120 months (10 years) it will become an "Elder Tree".
Elder Trees have a 20% chance to spawn a new "Sapling" instead of 10%.
If there are no open adjacent spots to a Tree or Elder Tree it will not spawn any new Trees.

Lumberjacks:
Lumberjacks cut down trees, they skip and jump they like to press wild flowers.

Each month lumberjacks will wander. They will move up to 3 times to a randomly picked spot that is adjacent in any direction. So for example a Lumberjack in the middle of your grid has 8 spots to move to. He will wander to a random spot. Then again. And finally for a third time.  NB: This can be any spot (so they can walk into bears, resulting in a maul).
When the lumberjack moves, if he encounters a Tree (not a sapling), he will stop and his wandering for that month comes to an end. He will then harvest the Tree for lumber. Remove the tree. Gain 1 piece of lumber.
Lumberjacks will not harvest "Saplings".
Lumberacks also harvest Elder Trees. Elder Trees are worth 2 pieces of lumber.

Lumber Tracking:
Every 12 months the amount of lumber harvested is compared to the number of lumberjacks in the forest.

If the lumber collected equals or exceeds the amount of lumberjacks in the forest a number of new lumberjacks are hired and randomly spawned in the forest.
Work out the number of lumberjacks to hire with:
floor(lumber_collected / number_of_lumberjacks)
However if after a 12 month span the amount of lumber collected is below the number of lumberjacks then a lumberjack is let go to save money and 1 random lumberjack is removed from the forest. Note that you will never reduce your Lumberjack labor force below 0.

Bears:
Bears wander the forest much like a lumberjack. However instead of 3 spaces a Bear will roam up to 5 spaces.

If a bear comes across a Lumberjack he will stop his wandering for the month. (For example after 2 moves the bear lands on a space with a lumberjack he will not make any more moves for this month)
Lumberjacks smell like pancakes. Bears love pancakes. Therefore the Bear will unfortunately maul and hurt the lumberjack. The lumberjack will be removed from the forest (He will go home and shop on wednesdays and have buttered scones for tea).
We will track this as a "Maul" accident.
Note that the lumberjack population can never drop below 1 - so if the last lumberjack is mauled just spawn another one in.

Maul Tracking:

During the course of 12 months if there 0 "Maul" accidents then the Bear population will increase by 1. If however there are any "Maul" accidents the Lumberjacks will hire a Zoo to trap and take a Bear away. Remove 1 random Bear. Note that if your Bear population reaches 0 bears then there will be no "Maul" accidents in the next year and so you will spawn 1 new Bear next year.
If there is only 1 lumberjack in the forest and he gets Mauled, he will be sent home, but a new one will be hired immediately and respawned somewhere else in the forest. The lumberjack population can never drop below 1.

Time:
The simulation occurs for 4800 months (400 years), or until no Saplings, Trees or Elder Trees exist.
Output:
Every month you will print out a map of the forest - perhaps using an ASCII map, or using graphics and colours.
Optional Extras

You could output the populations of trees, lumberjacks and bears each tick.
You could output whenever an event occurs (e.g: "A bear mauled a lumberjack.")

Scoring
This is a popularity contest, so most upvotes wins!
EDIT - People have pointed out a number of flaws in my rules, and while you can feel free to ask me questions, it is also okay to tweak the rules a bit to suit your own program, or interpretation of the program.

About: Note that you will never reduce your Lumberjack labor force below 0 in lumberjack section list item 3. perhaps change this to 1 to be in line with what you mention in the bear section?

Good point, will edit that in now.

Will a lumberjack always grab a random cell to move to or will it check if a tree is nearby?

They should always go to a random cell

Yes, they can randomly move to a bear cell, and that would result in a maul. I'll clarify this in the question to avoid other people getting confused!

Can you discuss the timing of the movement? Is it "trees move/advance", then "lumberjacks move", then "bears move"? Also, can bears and trees occupy the same spaces?

How will lumberjacks and bears move when encountering an edge of the NxN grid?  Will it just stop, or perhaps wrap around to the opposite edge, or something else?

Do whatever works for you, but I would wrap around, just makes it easier to implement.

Can a bear walk into a spot occupied by a tree?

What happens if two bears both walk into the same spot?  And what about two lumberjacks?  Can they be in the same spot?

@Jerry - bears cannot walk into the same spot. Same with lumberjacks. If their random move ends up on a spot already occupied, just generate another random move.

Will a bear surrounded by bears (such that there is no legal move) result in an infinite loop or simply not moving?

Does each empty square adjacent to a given tree have a 10% chance of becoming a sapling? So potentially more than one could become a sapling on the same turn. Or can each tree only spawn a sapling in a single adjacent square per turn?

@githubphagocyte Probaly simply not moving - feel free to implement how you see fit though, these rules aren't perfect and if they need modifying, go ahead.

@githubphagocyte Each tree has a 10% chance of spawning a sapling, and if the 10% chance is met, one square will be picked.

@durron597 - I screwed up, they can occupy the same spots (it does say in the rules but it is a bit obscure, I will edit to make it more obvious)

What about the timing within the turn? Do the bears move in random order? Or sequential (the same bear moves first every turn?) Or simultaneous? What about, if there is no legal move (say the middle bear surrounded by 8 other bears), can a "move" randomly result in "stand still"?

It is identical to http://www.reddit.com/r/dailyprogrammer/comments/27h53e/662014_challenge_165_hard_simulated_ecology_the/ You ought to give it credit - at least such that people can go there for other interesting solutions.

@anon - I was debating whether to refer to it, for fear of ruining the challenge. Should I edit it into the question?

@JamesWilliams I think you should. And you can just add a warning that it contains "spoilers".

@Martin Okay, will do that now.

Javascript+HTML - try it
Updated as per popular request

General behaviour
The program is now somewhat interactive.
The source code is completely parametrized, so you can tweak a few more internal parameters with your favourite text editor.
You can change the forest size.
A minimum of 2 is required to have enough room to place a tree, a lumberjack and a bear on 3 different spots, and the max is arbitrarily fixed to 100 (which will make your average computer crawl).
You can also change the simulation speed.
Display is updated every 20 ms, so a greater time step will produce finer animations.
The buttons allow to stop/start the simulation, or run it for a month or a year.
Movement of the forest dwellers is now somewhat animated. Mauling and tree cutting events are also figured.
A log of some events is also displayed. Some more messages are available if you change the verbosity level, but that would flood you with "Bob cuts yet another tree" notifications.
I would rather not do it if I were you, but I ain't, so...
Beside the playground, a set of auto-scaled graphics are drawn:

bears and lumberjacks populations
total number of trees, divided in saplings, mature and elder trees

The legend also displays current quantities of each item.
System stability
The graphs show that the initial conditions do not scale that gracefully. If the forest is too big, too many bears decimate the lumberjack population until enough of the pancake lovers have been put behind bars. This causes an initial explosion of elder trees, that in turn helps the lumberjack population to recover.
It seems 15 is the minimal size for the forest to survive. A forest of size 10 will usually get razed after a few hundred years. Any size above 30 will produce a map nearly full of trees. Between 15 and 30, you can see the tree population oscillating significantly.
Some debatable rule points
In the comments of the original post, it seems various bipeds are not supposed to occupy the same spot. This contradicts somehow the rule about a redneck wandering into a pancake amateur.
At any rate, I did not follow that guideline. Any forest cell can hold any number of inhyabitants (and exactly zero or one tree). This might have some consequences on the lumberjack efficiency: I suspect it allows them to dig into a clump of elder trees more easily. As for bears, I don't expect this to make a lot of difference.
I also opted for having always at least one lumberjack in the forest, despite the point stating that the redneck population could reach zero (firing the last lumberjack on the map if the harvest was really poor, which will never happen anyway unless the forest has been chopped down to extinction).
Tweaking
In order to achieve stability, I added two tweaking parameters :
1) lumberjacks growth rate
a coefficient applied to the formula that gives the number of extra lumberjacks hired when there is enough timber. Set to 1 to get back to original definition, but I found a value of about .5 allowed the forest (esp. elder trees) to develop better.
2) bear removal criterion
a coefficient that defines the minimal percentage of mauled lumberjacks to send a bear to the zoo. Set to 0 to go back to original definition, but this drastic bear elimination will basically limit the population to a 0-1 oscillation cycle.
I set it to .15 (i.e. a bear is removed only if 15% or more of the lumberjacks have been mauled this year). This allows for a moderate bear population, sufficient to prevent the rednecks from wiping the area clean but still allowing a sizeable part of the forest to be chopped.
As a side note, the simulation never stops (even past the required 400 years). It could easily do so, but it doesn't.
The code
The code is entirely contained in a single HTML page.
It must be UTF-8 encoded to display the proper unicode symbols for bears and lumberjacks.
For the Unicode impaired systems (e.g. Ubuntu):
find the following lines:
    jack   :{ pic: '', color:'#bc0e11' },
    bear   :{ pic: '', color:'#422f1e' }},

and change the pictograms for characters easier to display (#, *, whatever)
<!doctype html>
<meta charset=utf-8>
<title>Of jacks and bears</title>

            <canvas id='forest'></canvas>

Forest size     <input type='text' size=10 onchange='create_forest(this.value);'>

Simulation tick <input type='text' size= 5 onchange='set_tick(this.value);'     > (ms)

                                <input type='button' value='◾'       onclick='stop();'>
                                <input type='button' value='▸'       onclick='start();'>
                                <input type='button' value='1 month' onclick='start(1);'>
                                <input type='button' value='1 year'  onclick='start(12);'>

                        <canvas id='graphs'></canvas>

                        evolution over 60 years

What next?
More remarks are still welcome.
N.B: I'm aware sapling/mature/elder trees count is still a bit messy, but to hell with it.
Also, I find document.getElementById more readable than $, so no need to complain about the lack of jQueryisms. It's jQuery free on purpose. To Each his own, right?

+1, This looks badass, I'd love to see the interactivity!

I can't see the bears and lumberjacks. What should I do to see them? Btw, only maximum of one bear should be removed per year, right?

@WilliamBarbosa If the vox populi screams loud enough, it might coax me into adding some :)

@justhalf see my edit about unicode characters. As for bears, if I understand the specs correctly, yes: only one bear picked at random sent to the zoo each year, if some mauling occured.

Great answer! I'd recommend adding a screenshot to the answer to show how the forest --and specially that sweet graph with population curves-- looks :)

@epidemian good advice. It's done.

The growing trees are marvelous. Good job!

Just to add - it's fine to tweak the rules if you see fit, they aren't perfect and your program works better as a result. Good job.

@JamesWilliams Thanks guv' :). I am thinking of a smoother way of adjusting the bear population, that would scale with the map. In its current state, the simulation has an initial bear overpopulation that can take quite a while to correct, since only one bear can be fired each year. Maybe having less initial bears or changing the population growth rules.

@kuroi neko Yeah that is something I have noticed happening! Give it a go and if you find a set of rules that work better I can always just edit them into the original question.

@kuroineko: I rolled back your change. Please keep the answer and do not make it a non-answer. Your answer is also good, is not the 10 upvotes encouraging? =)

Suggestions: allow the user to configure via the a GUI the debug level. Provide a legend with the plot. Have some sort of markers for years on the plot, maybe months too (I have no idea what the scale is). Show some sort of tally in the corner of # bears, # trees, # lumberjacks, and oldest tree.

@nhinkle see my edit. I removed the debug level completely, since messages were awfuly repetitive and not so informative after all :). Legend added, with some indication of time scale. Tally also added. Anything else, guv'?

AngularJS
Here is my version, which is still a Work In Progress: the code is a bit… well… ugly. And quite slow. I also plan to add more options to parametrize the evolution and to analyse the state of the forest. Comments and amelioration proposals are welcome!

Demonstration

    <form name="parametersForm" ng-hide="evolutionInProgress" autocomplete="off" novalidate>

            Size of the forest:
            <input type="number" ng-model="Parameters.forestSize" id="forestSize" min="5" ng-pattern="/^[0-9]+$/" required />

            Number of milliseconds between each tick
            <input type="number" ng-model="Parameters.simulationInterval" id="simulationInterval" min="10" ng-pattern="/^[0-9]+$/" required />

            Animations enabled?

(>= 300 ms between each tick is advisable)

            <input type="checkbox" ng-model="Parameters.animationsEnabled" id="animationsEnabled" />

            <button ng-disabled="parametersForm.$invalid || evolutionInProgress" ng-click="launchEvolution()">Launch the evolution!</button>

    </form>

Age of the forest:<samp>{{floor(Forest.age/12)}} year{{floor(Forest.age/12) > 1 ? 's' : ''}} and {{Forest.age%12}} month{{Forest.age%12 > 1 ? 's' : ''}}</samp>

Number of bears:<samp>{{Forest.bearsList.length}}</samp>

Number of lumberjacks:<samp>{{Forest.lumberjacksList.length}}</samp>

Number of lumbers collected:<samp>{{Forest.numberOfLumbers}}</samp>

Number of mauls:<samp>{{Forest.numberOfMauls}}</samp>

/** @link http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array */
function shuffle(array) {
    var currentIndex = array.length,
        temporaryValue, randomIndex;

    // While there remain elements to shuffle...
    while (0 !== currentIndex) {

        // Pick a remaining element...
        randomIndex = Math.floor(Math.random() * currentIndex);
        currentIndex -= 1;

        // And swap it with the current element.
        temporaryValue = array[currentIndex];
        array[currentIndex] = array[randomIndex];
        array[randomIndex] = temporaryValue;
    }

    return array;
}

var forestApp = angular.module('ForestApp', ['ngAnimate']);

forestApp.value('Parameters', {
    /** @var int[] Maximal number of moves by species */
    speed: {
        bear: 5,
        lumberjack: 3,
    },

    /** @var int[] Initial percentage of each species in the forest */
    initialPercentage: {
        bear: 2,
        lumberjack: 10,
        tree: 50,
    },

    /** @var int[] Spawing rate, in percentage, of new saplings around an existing tree */
    spawningPercentage: {
        0: 0,
        1: 10,
        2: 20,
    },

    /** @var int[] Age of growth for an existing tree */
    ageOfGrowth: {
        sapling: 12,
        tree: 120,
    },

    /** @var int[] Lumber collected on an existing tree */
    numberOfLumbers: {
        tree: 1,
        elderTree: 2,
    },

    /** @var int Size of each side of the forest */
    forestSize: 20,

    /** @var int Number of milliseconds between each tick (month in the forest) */
    simulationInterval: 50,
});

forestApp.constant('TREE_STAGE', {
    SAPLING: 0,
    TREE: 1,
    ELDER_TREE: 2,
});

forestApp.factory('Tree', ['Forest', 'Parameters', 'TREE_STAGE', function (Forest, Parameters, TREE_STAGE) {
    // Classes which represents a tree
    var Tree = function (stage, x, y) {
        /** @var TREE_STAGE Current stage of the tree */
        this.stage = stage;

        /** @var int Current age of the tree, in month */
        this.age = 0;

        /** @var int X coordinates of the tree */
        this.x = x;

        /** @var int Y coordinates of the tree */
        this.y = y;

        this.tick = function () {
            if (Math.random() < Parameters.spawningPercentage[this.stage] / 100) {
                var freePositionsList = shuffle(Forest.getFreePositionsAround(this.x, this.y));
                if (freePositionsList.length > 0) {
                    var saplingPosition = freePositionsList[0];

                    Tree.create(TREE_STAGE.SAPLING, saplingPosition[0], saplingPosition[1]);
                }
            }

            ++this.age;

            if (this.stage === TREE_STAGE.SAPLING && this.age == Parameters.ageOfGrowth.sapling) {
                this.stage = TREE_STAGE.TREE;
            } else if (this.stage === TREE_STAGE.TREE && this.age == Parameters.ageOfGrowth.tree) {
                this.stage = TREE_STAGE.ELDER_TREE;
            }
        };

        /**
         * Remove the entity
         */
        this.remove = function () {
            var index = Forest.treesList.indexOf(this);
            Forest.treesList.splice(index, 1);
        };
    };

    Tree.create = function (stage, x, y) {
        Forest.add.tree(new Tree(stage, x, y));
    };

    return Tree;
}]);

forestApp.factory('Lumberjack', ['Forest', 'Parameters', 'TREE_STAGE', function (Forest, Parameters, TREE_STAGE) {
    // Classes which represents a lumberjack
    var Lumberjack = function (x, y) {
        /** @var int X coordinates of the lumberjack */
        this.x = x;

        /** @var int Y coordinates of the lumberjack */
        this.y = y;

        this.tick = function () {
            for (movement = Parameters.speed.lumberjack; movement > 0; --movement) {
                var positionsList = shuffle(Forest.getPositionsAround(this.x, this.y));
                var newPosition = positionsList[0];
                this.x = newPosition[0];
                this.y = newPosition[1];

                var tree = Forest.getTreeAt(this.x, this.y);
                if (tree !== null) {
                    if (tree.stage === TREE_STAGE.SAPLING) {
                        return;
                    } else if (tree.stage === TREE_STAGE.TREE) {
                        Forest.numberOfLumbers += Parameters.numberOfLumbers.tree;
                    } else {
                        Forest.numberOfLumbers += Parameters.numberOfLumbers.elderTree;
                    }

                    tree.remove();
                    movement = 0;
                };
            }
        };

        /**
         * Remove the entity
         */
        this.remove = function () {
            if (Forest.lumberjacksList.length === 1) {
                this.x = Math.floor(Math.random() * Parameters.forestSize);
                this.y = Math.floor(Math.random() * Parameters.forestSize);
            } else {
                var index = Forest.lumberjacksList.indexOf(this);
                Forest.lumberjacksList.splice(index, 1);
            }
        };
    };

    Lumberjack.create = function (x, y) {
        Forest.add.lumberjack(new Lumberjack(x, y));
    };

    return Lumberjack;
}]);

forestApp.factory('Bear', ['Forest', 'Parameters', function (Forest, Parameters) {
    // Classes which represents a bear
    var Bear = function (x, y) {
        /** @var int X coordinates of the bear */
        this.x = x;

        /** @var int Y coordinates of the bear */
        this.y = y;

        this.tick = function () {
            for (movement = Parameters.speed.bear; movement > 0; --movement) {
                var positionsList = shuffle(Forest.getPositionsAround(this.x, this.y));
                var newPosition = positionsList[0];
                this.x = newPosition[0];
                this.y = newPosition[1];

                angular.forEach(Forest.getLumberjacksListAt(this.x, this.y), function (lumberjack) {
                    lumberjack.remove();
                    ++Forest.numberOfMauls;
                    movement = 0;
                });
            }
        };

        /**
         * Remove the entity
         */
        this.remove = function () {
            var index = Forest.bearsList.indexOf(this);
            Forest.bearsList.splice(index, 1);
        };
    };

    Bear.create = function (x, y) {
        Forest.add.bear(new Bear(x, y));
    };

    return Bear;
}]);

forestApp.service('Forest', ['Parameters', function (Parameters) {
    var forest = this;

    this.age = 0;
    this.numberOfLumbers = 0;
    this.numberOfMauls = 0;

    this.bearsList = [];
    this.lumberjacksList = [];
    this.treesList = [];

    this.getEntitiesList = function () {
        return forest.bearsList.concat(forest.lumberjacksList, forest.treesList);
    };

    /**
     * Age the forest by one month
     */
    this.tick = function () {
        angular.forEach(forest.getEntitiesList(), function (entity) {
            entity.tick();
        });

        ++forest.age;
    };

    this.add = {
        bear: function (bear) {
            forest.bearsList.push(bear);
        },
        lumberjack: function (lumberjack) {
            forest.lumberjacksList.push(lumberjack);
        },
        tree: function (tree) {
            forest.treesList.push(tree);
        },
    };

    /**
     * @return Tree|null Tree at this position, or NULL if there is no tree.
     */
    this.getTreeAt = function (x, y) {
        var numberOfTrees = forest.treesList.length;
        for (treeId = 0; treeId < numberOfTrees; ++treeId) {
            var tree = forest.treesList[treeId];
            if (tree.x === x && tree.y === y) {
                return tree;
            }
        }

        return null;
    };

    /**
     * @return Lumberjack[] List of the lumberjacks at this position
     */
    this.getLumberjacksListAt = function (x, y) {
        var lumberjacksList = [];
        angular.forEach(forest.lumberjacksList, function (lumberjack) {
            if (lumberjack.x === x && lumberjack.y === y) {
                lumberjacksList.push(lumberjack);
            }
        });

        return lumberjacksList;
    };

    /**
     * @return int[] Positions around this position
     */
    this.getPositionsAround = function (x, y) {
        var positionsList = [
            [x - 1, y - 1],
            [x, y - 1],
            [x + 1, y - 1],
            [x - 1, y],
            [x + 1, y],
            [x - 1, y + 1],
            [x, y + 1],
            [x + 1, y + 1]
        ];

        return positionsList.filter(function (position) {
            return (position[0] >= 0 && position[1] >= 0 && position[0] < Parameters.forestSize && position[1] < Parameters.forestSize);
        });
    };

    /**
     * @return int[] Positions without tree around this position
     */
    this.getFreePositionsAround = function (x, y) {
        var positionsList = forest.getPositionsAround(x, y);

        return positionsList.filter(function (position) {
            return forest.getTreeAt(position[0], position[1]) === null;
        });
    };
}]);

forestApp.controller('ForestController', ['$interval', '$scope', 'Bear', 'Forest', 'Lumberjack', 'Parameters', 'Tree', 'TREE_STAGE', function ($interval, $scope, Bear, Forest, Lumberjack, Parameters, Tree, TREE_STAGE) {
    $scope.Forest = Forest;
    $scope.Parameters = Parameters;
    $scope.evolutionInProgress = false;
    $scope.floor = Math.floor;

    var positionsList = [];

    /**
     * Start the evolution of the forest
     */
    $scope.launchEvolution = function () {
        $scope.evolutionInProgress = true;

        for (var x = 0; x < Parameters.forestSize; ++x) {
            for (var y = 0; y < Parameters.forestSize; ++y) {
                positionsList.push([x, y]);
            }
        }

        shuffle(positionsList);
        var numberOfBears = Parameters.initialPercentage.bear * Math.pow(Parameters.forestSize, 2) / 100;
        for (var bearId = 0; bearId < numberOfBears; ++bearId) {
            Bear.create(positionsList[bearId][0], positionsList[bearId][1]);
        }

        shuffle(positionsList);
        var numberOfLumberjacks = Parameters.initialPercentage.lumberjack * Math.pow(Parameters.forestSize, 2) / 100;
        for (var lumberjackId = 0; lumberjackId < numberOfLumberjacks; ++lumberjackId) {
            Lumberjack.create(positionsList[lumberjackId][0], positionsList[lumberjackId][1]);
        }

        shuffle(positionsList);
        var numberOfTrees = Parameters.initialPercentage.tree * Math.pow(Parameters.forestSize, 2) / 100;
        for (var treeId = 0; treeId < numberOfTrees; ++treeId) {
            Tree.create(TREE_STAGE.TREE, positionsList[treeId][0], positionsList[treeId][1]);
        }

        $interval(function () {
            Forest.tick();

            if (Forest.age % 12 === 0) {
                // Hire or fire lumberjacks
                if (Forest.numberOfLumbers >= Forest.lumberjacksList.length) {
                    shuffle(positionsList);
                    var numberOfLumberjacks = Math.floor(Forest.numberOfLumbers / Forest.lumberjacksList.length);
                    for (var lumberjackId = 0; lumberjackId < numberOfLumberjacks; ++lumberjackId) {
                        Lumberjack.create(positionsList[lumberjackId][0], positionsList[lumberjackId][1]);
                    }
                } else {
                    shuffle(Forest.lumberjacksList);
                    Forest.lumberjacksList[0].remove();
                }

                // Hire or fire bears
                if (Forest.numberOfMauls === 0) {
                    shuffle(positionsList);
                    Bear.create(positionsList[0][0], positionsList[0][1]);
                } else {
                    Forest.bearsList[0].remove();
                }

                Forest.numberOfLumbers = 0;
                Forest.numberOfMauls = 0;
            }

        }, Parameters.simulationInterval);
    };
}]);

also i like how we use the same code for randomize shuffle array

Interesting. The first time I ran your simulation, it ends with all bears and no lumberjacks, which led me to think that this simulation is imbalanced. But it never happens again afterwards, so I guess it was just "bad luck" that all the lumberjack got mauled by the bears (because if there are so many bears, lumberjacks will almost certainly die)

getEntitiesAt seems to be a CPU hog! running the system with a 50x50 grid takes more than one second per month on my PC. Also there is a case when all trees get chopped, then all lumberjacks are fired and the map slowly fills with bears :). Try a small size (10 or less) to see it happen.

@kuroineko: It's because there's a bug (or rather an unimplemented rule) where after a lumberjack gets mauled and if it respawned on a bear, it won't be there. So it gets to 0. Fix it with a check after Forest.tick(), if Forest.lumberjackList.length == 0, then Lumberjack.create(<number>, <number>).

@kuroineko and justhalf: Thanks for your comments! I've optimized my version (but I can't do better now, I think), and corrected the bug in order to forbidden the firing of the last lumberjack.

@Blackhole - awesome answer. Just letting you know, if you want to tweak the spawning rates go ahead - the rules I set out seem a little unbalanced.

I have tried tweaking your code to make bears prefer to stay in the forest (and also incorporate @kuroineko-like bear removal criteria, like add bears if there are less than 10% mauling, and remove bear if there are more than 15% mauling). It is interesting to see how the behaviour changes =)

Javascript
I think this mostly works. There's some wonky behavior where I spawn all the new bears/lumberjacks in sync and right next to each other because laziness in insertions.
This implementation does not allow lumberjacks to stand on saplings, cause you know, trampling saplings is bad. Fiddle art uses colored rectangles by default, change the second line to false to use letters to draw.
fiddle
HTML:
<canvas id="c" width="1" height="1"></canvas>

Js:
var n = 10; // Size of the grid
var drawUsingColor = true; // If true, draws colors for each entity instead :D
var intervalTime = 1000; // how often each tick happens, in milliseconds
var jackRatio = 0.1;
var treeRatio = 0.5;
var bearRatio = 0.02;
var size = 48; // Pixels allocated (in size x size) for each entity
var font = "30px Lucida Console"; // if drawUsingColor is false

var bearColor = '#8B4513'; // Saddlebrown
var elderColor = '#556B2F'; // DarkOliveGreen
var lumberjackColor = '#B22222'; // Firebrick
var treeColor = '#008000'; // Green
var saplingColor = '#ADFF2F'; // GreenYellow

// Game rules:
var spawnSaplingChance = 0.1;
var elderTreeAge = 120;
var elderSaplingChance = 0.2;
var treeAge = 12;
var lumberjackRange = 3;
var bearRange = 5;
var zooPeriod = 12; // If a maul happens within this period
var lumberPeriod = 12; // New lumberjacks hired in this period

var time = 1;

var world;
var n2 = n * n; //because one saved keystroke
var zooqueue = [];
var lumberqueue = [];
var canvas = document.getElementById('c'); // Needs more jquery
var context = canvas.getContext('2d');
context.font = font;

// various statistics
var treesAlive = 0;
var jacksAlive = 0;
var bearsAlive = 0;
var currentLumber = 0;
var lumberjacksMauled = 0;
var recentEvents = '';

// Entity is a bear, eldertree, lumberjack, tree, sapling, with age. aka belts.
function Entity(belts, birthday) {
    this.type = belts;
    this.age = 0;
    this.birthday = birthday;
}

function initWorld() {
    canvas.height = size * n;
    canvas.width = size * n;
    world = new Array(n2);

    // One pass spawning algorithm: numEntity = number of entity left to spawn
    // If rand() in range [0,numtrees), spawn tree
    // if rand() in range [numtrees, numtrees+numjacks), spawn lumberjack
    // if rand() in range [numtrees+numjacks, numtrees+numjacks+numbears), spawn bear

    var numTrees = treeRatio * n2;
    var numJacks = jackRatio * n2;
    var numBears = bearRatio * n2;

    var godseed = new Array(n2);
    for (var i = 0; i < n2; i++) {
        godseed[i] = i;
    }
    shuffle(godseed);

    for (var i = 0; i < n2; i++) {
        var god = godseed.pop();
        if (god < numTrees) {
            world[i] = new Entity('T', 0);
            treesAlive++;
        } else if (god < numTrees + numJacks) {
            world[i] = new Entity('L', 0);
            jacksAlive++;
        } else if (god < numTrees + numJacks + numBears) {
            world[i] = new Entity('B', 0);
            bearsAlive++;
        }
        // console.log(world, i);
    }

    // populate zoo array, lumber array
    for (var i = 0; i < zooPeriod; i++) {
        zooqueue.push(0);
    }

    for (var i = 0; i < lumberPeriod; i++) {
        lumberqueue.push(0);
    }
}

animateWorld = function () {
    recentEvents = '';
    computeWorld();
    drawWorld();
    time++;

    $('#p1').text(treesAlive + ' trees alive');
    $('#p2').text(bearsAlive + ' bears alive');
    $('#p3').text(jacksAlive + ' lumberjacks alive');
    $('#p4').text(recentEvents);
};

function computeWorld() {
    zooqueue.push(lumberjacksMauled);
    lumberqueue.push(currentLumber);

    // Calculate entity positions
    for (var i = 0; i < n2; i++) {
        if (world[i]) {
            switch (world[i].type) {
                case 'B':
                    bearStuff(i);
                    break;
                case 'E':
                    elderStuff(i);
                    break;
                case 'L':
                    lumberjackStuff(i);
                    break;
                case 'T':
                    treeStuff(i);
                    break;
                case 'S':
                    saplingStuff(i);
                    break;
            }
        }
    }

    // Pop the # mauls from zooPeriod's ago, if lumberjacksMauled > oldmauls, then someone was eaten.
    var oldmauls = zooqueue.shift();
    if (time % zooPeriod === 0) {
        if (lumberjacksMauled > oldmauls) {
            if (remove('B') == 1) {
                bearsAlive--;
                recentEvents += 'Bear sent to zoo! ';
            }
        } else {
            bearsAlive++;
            spawn('B');
            recentEvents += 'New bear appeared! ';
        }
    }

    var oldLumber = lumberqueue.shift();
    if (time % lumberPeriod === 0) {
        // # lumberjack to hire
        var hire = Math.floor((currentLumber - oldLumber) / jacksAlive);
        if (hire > 0) {
            recentEvents += 'Lumber jack hired! (' + hire + ') ';
            while (hire > 0) {
                jacksAlive++;
                spawn('L');
                hire--;
            }
        } else {
            if (remove('L') == 1) {
                recentEvents += 'Lumber jack fired!  ';
                jacksAlive--;
            }
            else {
            }
        }
    }

    // Ensure > 1 lumberjack
    if (jacksAlive === 0) {
        jacksAlive++;
        spawn('L');
        recentEvent += 'Lumberjack spontaneously appeared';
    }
}

// Not the job of spawn/remove to keep track of whatever was spawned/removed
function spawn(type) {
    var index = findEmpty(type);
    if (index != -1) {
        world[index] = new Entity(type, time);
    }
    // recentEvents += 'Spawned a ' + type + '\n';
}

function remove(type) {
    var index = findByType(type);
    if (index != -1) {
        world[index] = null;
        return 1;
    }
    return -1;
    // recentEvents += 'Removed a ' + type + '\n';
}

// Searches in world for an entity with type=type. Currently implemented as
// linear scan, which isn't very random
function findByType(type) {
    for (var i = 0; i < n2; i++) {
        if (world[i] && world[i].type == type) return i;
    }
    return -1;
}

// Also linear scan
function findEmpty(type) {
    for (var i = 0; i < n2; i++) {
        if (!world[i]) {
            return i;
        }
    }
    return -1;
}

function bearStuff(index) {
    if (world[index].birthday == time) {
        return;
    }

    // Wander around
    var tindex = index;
    for (var i = 0; i < lumberjackRange; i++) {
        var neighbors = get8Neighbor(tindex);

        var mov = neighbors[Math.floor(Math.random() * neighbors.length)];
        if (world[mov] && world[mov].type == 'L') {
            recentEvents += 'Bear (' + index % 10 + ',' + Math.floor(index / 10) + ') mauled a Lumberjack (' + mov % 10 + ',' + Math.floor(mov / 10) + ') !';
            lumberjacksMauled++;
            jacksAlive--;
            world[mov] = new Entity('B', time);
            world[mov].age = ++world[index].age;
            world[index] = null;
            return;
        }
        tindex = mov;
    }

    if (!world[tindex]) {
        world[tindex] = new Entity('B', time);
        world[tindex].age = ++world[index].age;
        world[index] = null;
    }
}

function elderStuff(index) {
    if (world[index].birthday == time) {
        return;
    }
    neighbors = get8Neighbor(index);

    // spawn saplings
    for (var i = 0; i < neighbors.length; i++) {
        if (!world[neighbors[i]]) {
            if (Math.random() < elderSaplingChance) {
                world[neighbors[i]] = new Entity('S', time);
                treesAlive++;
            }
        }
    }

    // become older
    world[index].age++;
}

function lumberjackStuff(index) {
    if (world[index].birthday == time) {
        return;
    }

    // Wander around
    var tindex = index;
    for (var i = 0; i < lumberjackRange; i++) {
        var neighbors = get8Neighbor(tindex);

        var mov = neighbors[Math.floor(Math.random() * neighbors.length)];
        if (world[mov] && (world[mov].type == 'T' || world[mov].type == 'E')) {
            world[mov].type == 'T' ? currentLumber++ : currentLumber += 2;
            treesAlive--;
            world[mov] = new Entity('L', time);
            world[mov].age = ++world[index].age;
            world[index] = null;
            return;
        }
        tindex = mov;
    }

    if (!world[tindex]) {
        world[tindex] = new Entity('L', time);
        world[tindex].age = ++world[index].age;
        world[index] = null;
    }
}

function treeStuff(index) {
    if (world[index].birthday == time) {
        return;
    }
    neighbors = get8Neighbor(index);

    // spawn saplings
    for (var i = 0; i < neighbors.length; i++) {
        if (!world[neighbors[i]]) {
            if (Math.random() < spawnSaplingChance) {
                world[neighbors[i]] = new Entity('S', time);
                treesAlive++;
            }
        }
    }

    // promote to elder tree?
    if (world[index].age >= elderTreeAge) {
        world[index] = new Entity('E', time);
        return;
    }

    // become older
    world[index].age++;
}

function saplingStuff(index) {
    if (world[index].birthday == time) {
        return;
    }

    // promote to tree?
    if (world[index].age > treeAge) {
        world[index] = new Entity('T', time);
        return;
    }
    world[index].age++;
}

// Returns array containing up to 8 valid neighbors.
// Prolly gonna break for n < 3 but oh well
function get8Neighbor(index) {
    neighbors = [];

    if (index % n != 0) {
        neighbors.push(index - n - 1);
        neighbors.push(index - 1);
        neighbors.push(index + n - 1);
    }
    if (index % n != n - 1) {
        neighbors.push(index - n + 1);
        neighbors.push(index + 1);
        neighbors.push(index + n + 1);
    }
    neighbors.push(index - n);
    neighbors.push(index + n);
    return neighbors.filter(function (val, ind, arr) {
        return (0 <= val && val < n2)
    });
}

// Each entity allocated 5x5px for their art
function drawWorld() {
    context.clearRect(0, 0, canvas.width, canvas.height);
    for (var i = 0; i < n2; i++) {
        if (world[i]) {
            var x = i % n;
            var y = Math.floor(i / n);
            switch (world[i].type) {
                case 'B':
                    drawBear(x, y);
                    break;
                case 'E':
                    drawElder(x, y);
                    break;
                case 'L':
                    drawJack(x, y);
                    break;
                case 'T':
                    drawTree(x, y);
                    break;
                case 'S':
                    drawSapling(x, y);
                    break;
            }
        }
    }
}

function drawBear(x, y) {
    if (drawUsingColor) {
        drawRect(x * size, y * size, size, size, bearColor);
    } else {
        drawLetter(x * size, y * size, 'B');
    }
}

function drawElder(x, y) {
    if (drawUsingColor) {
        drawRect(x * size, y * size, size, size, elderColor);
    } else {
        drawLetter(x * size, y * size, 'E');
    }
}

function drawJack(x, y) {
    if (drawUsingColor) {
        drawRect(x * size, y * size, size, size, lumberjackColor);
    } else {
        drawLetter(x * size, y * size, 'J');
    }
}

function drawTree(x, y) {
    if (drawUsingColor) {
        drawRect(x * size, y * size, size, size, treeColor);
    } else {
        drawLetter(x * size, y * size, 'T');
    }
}

function drawSapling(x, y) {
    if (drawUsingColor) {
        drawRect(x * size, y * size, size, size, saplingColor);
    } else {
        drawLetter(x * size, y * size, 'S');
    }
}

function drawLine(x1, y1, x2, y2, c) {
    context.beginPath();
    context.moveTo(x1, y1);
    context.lineTo(x2, y2);
    context.lineWidth = 3;
    context.strokeStyle = c;
    context.stroke();
}

function drawRect(x, y, w, h, c) {
    context.fillStyle = c;
    context.fillRect(x, y, w, h);
}

function drawLetter(x, y, l) {
    context.fillText(l, x, y);
}

$(document).ready(function () {
    initWorld();
    intervalID = window.setInterval(animateWorld, intervalTime);
    /*$('#s').click(function() {
        animateWorld();
    })*/
});

// http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array
function shuffle(array) {
    var currentIndex = array.length,
        temporaryValue, randomIndex;

    // While there remain elements to shuffle...
    while (0 !== currentIndex) {

        // Pick a remaining element...
        randomIndex = Math.floor(Math.random() * currentIndex);
        currentIndex -= 1;

        // And swap it with the current element.
        temporaryValue = array[currentIndex];
        array[currentIndex] = array[randomIndex];
        array[randomIndex] = temporaryValue;
    }
    return array;
}

There is something strange with high-size forest (try n = 50, for instance).

@Blackhole something strange = ____ ?

See by yourself ;).

I notice the bears getting stuck, and the forest taking over the lower part of the map since I spawn lumberjacks in the upper part of the map

There is something wrong with the way new bears and lumberjacks spawn. I think putting then all in the top left corner changes the global balance of the system quite a bit.

Python
Nothing fancy. I kept on adding stuff, so refactoring might be in order. (And I didn't do unitest so bugs might still be present).
I gave random names to lumberjacks and bears.
Trees are i, then I, then #,
Lumberjacks are x,
Bears are o
import os

from random import randint, choice, shuffle
from time import sleep

NGRID = 15
SLEEPTIME = 0.0125
DURATION = 4800
VERBOSE = True

###init
grid = [[[] for _ in range(NGRID)] for _ in range(NGRID)]
#Money earned this year
n_lumbers = 0
#Lumberjacks killed this year
n_maul = 0

tick = 0
events = []
#total number of
d_total = {'trees':0,
           'lumberjacks': 0,
           'bears': 0,
           'cut': 0,
           'maul': 0,
           'capture': 0,
           'lumbers': 0,
           'fired': 0}

d_oldest = {'tree': 0,
            'lumberjack': (0, ""),
            'bear': (0, "")}

d_most = {'n_maul': (0, ""),
          'n_lumber': (0, ""),
          'n_cut': (0, "")}

d_year = {'n_maul': 0,
          'n_lumber': 0}

###Classes
class Tree(object):
    """Represent a Sapling, Tree, or Elder Tree"""
    def __init__(self, coords, m=0, t='Sapling'):
        self.months = m
        self.typeof = t
        self.coords = coords
    def grow(self, m=1):
        """the tree grows 1 month and its type might change"""
        self.months = self.months + m
        if self.months == 12:
            self.typeof = 'Tree'
        elif self.months == 480:
            self.typeof = 'Elder Tree'
    def __str__(self):
        if self.typeof == 'Sapling':
            return 'i'
        elif self.typeof == 'Tree':
            return 'I'
        else:
            return '#'

class Animated(object):
    """Animated beings can move"""
    def __init__(self, coords):
        self.coords = coords
        self.old_coords = None
        self.months = 0
    def where(self):
        return c_neighbors(self.coords)
    def choose_new_coords(self):
        self.old_coords = self.coords
        possible = self.where()
        if possible:
            direction = choice(self.where())
            self.coords = [(self.coords[i]+direction[i]) % NGRID for i in range(2)]
#    def __del__(self):
#        print "died at "+ str(self.coords)

class Lumberjack(Animated):
    """Lumberjacks chop down trees"""
    def __init__(self, coords):
        super(Lumberjack, self).__init__(coords)
        self.nb_cut = 0
        self.nb_lumber = 0
        self.name = gen_name("l")
    def __str__(self):
        return "x"

class Bear(Animated):
    """Bears maul"""
    def __init__(self, coords):
        super(Bear, self).__init__(coords)
        self.nb_maul = 0
        self.name = gen_name("b")
    def where(self):
        return c_land_neighbors(self.coords)
    def __str__(self):
        return "o"

###list of coords
def c_neighbors(coords):
    """returns the list of coordinates of adjacent cells"""
    return [[(coords[0] + i) % NGRID, (coords[1] + j) % NGRID] \
            for i in [-1, 0, 1] \
            for j in [-1, 0, 1] \
            if (i,j) != (0, 0)]

def c_empty_neighbors(coords):
    """returns the list of coordinates of adjacent cells that are empty """
    return [[i, j] for [i,j] in c_neighbors(coords) if grid[i][j] == []]

def c_land_neighbors(coords):
    """returns the list of coordinates of adjacent cells that contain not Trees
    for bears"""
    return [[i, j] for [i,j] in c_neighbors(coords)\
            if (grid[i][j] == []) or (not isinstance(grid[i][j][0], Tree))]

def c_empty_cells():
    """returns list of coords of empty cells in the grid"""
    return [[i, j] for i in range(NGRID) for j in range(NGRID) if grid[i][j] == []]

def c_not_bear_cells():
    """returns list of coords of cells without bear"""
    return [[i, j] for i in range(NGRID) for j in range(NGRID) \
            if not isinstance(grid[i][j], Bear)]

###one less
def maul(lumberjack):
    """a lumberjack will die"""
    global n_maul
    n_maul = n_maul + 1
    d_total['maul'] = d_total['maul'] + 1
    remove_from_grid(lumberjack.coords, lumberjack)
    return lumberjack.name + " is sent to hospital" + check_lumberjacks()

def capture_bear():
    """too many mauls, a Zoo traps a bear"""
    d_total['capture'] = d_total['capture'] + 1
    bear = choice(get_bears())
    remove_from_grid(bear.coords, bear)
    return bear.name + " has been captured"

def fire_lumberjack():
    """the job is not done correctly, one lumberjack is let go"""
    d_total['fired'] = d_total['fired'] + 1
    lumberjack = choice(get_lumberjacks())
    remove_from_grid(lumberjack.coords, lumberjack)
    return lumberjack.name + " has been fired" + check_lumberjacks()

def remove_from_grid(coords, item):
    """remove item from the grid at the coords"""
    grid[coords[0]][coords[1]].remove(item)
    del item

###one more
def new_animate(class_):
    """a new lumberjack or bear joins the forest"""
    if class_==Bear:
        d_total['bears'] = d_total['bears'] + 1
        x, y = choice(c_empty_cells())
    else:
        d_total['lumberjacks'] = d_total['lumberjacks'] + 1
        x, y = choice(c_not_bear_cells())
    new_being = class_([x,y])
    grid[x][y].append(new_being)
    return "a new " + class_.__name__ + " enters the forest: " + new_being.name

def check_lumberjacks():
    """we will never reduce our Lumberjack labor force below 0"""
    if len(get_lumberjacks())==0:
        return " - no more lumberjack, " + new_animate(Lumberjack)
    return ""

###movements
def move_on_grid(being):
    [x, y] = being.old_coords
    grid[x][y].remove(being)
    [x, y] = being.coords
    grid[x][y].append(being)

def move_lumberjack(lumberjack):
    """Lumberjacks move 3 times if they don't encounter a (Elder) Tree or a Bear"""
    global n_lumbers
    for _ in range(3):
        lumberjack.choose_new_coords()
        move_on_grid(lumberjack)
        [x, y] = lumberjack.coords
        #is there something at the new coordinate?
        #move append so this lumberjack is at the end
        if grid[x][y][:-1] != []:
            if isinstance(grid[x][y][0], Tree):
                the_tree = grid[x][y][0]
                price = worth(the_tree)
                if price > 0:
                    lumberjack.nb_cut = lumberjack.nb_cut + 1
                    d_most['n_cut'] = max((lumberjack.nb_cut, lumberjack.name), \
                                           d_most['n_cut'])
                    d_total['cut'] = d_total['cut'] + 1
                    n_lumbers = n_lumbers + price
                    d_total['lumbers'] = d_total['lumbers'] + 1
                    lumberjack.nb_lumber = lumberjack.nb_lumber + price
                    d_most['n_lumber'] = max(d_most['n_lumber'], \
                                             (lumberjack.nb_lumber, lumberjack.name))
                    remove_from_grid([x, y], the_tree)
                    return lumberjack.name + " cuts 1 " + the_tree.typeof
            #if there is a bear, all lumberjacks have been sent to hospital
            if isinstance(grid[x][y][0], Bear):
                #the first bear is the killer
                b = grid[x][y][0]
                b.nb_maul = b.nb_maul + 1
                d_most['n_maul'] = max((b.nb_maul, b.name), d_most['n_maul'])
                return maul(lumberjack)
    return None

def move_bear(bear):
    """Bears move 5 times if they don't encounter a Lumberjack"""
    for _ in range(5):
        bear.choose_new_coords()
        move_on_grid(bear)
        [x, y] = bear.coords
        there_was_something = (grid[x][y][:-1] != [])
        if there_was_something:
            #bears wander where there is no tree
            #so it's either a lumberjack or another bear
            #can't be both.
            if isinstance(grid[x][y][0], Lumberjack):
                bear.nb_maul = bear.nb_maul + 1
                d_most['n_maul'] = max((bear.nb_maul, bear.name), \
                                       d_most['n_maul'])
                return maul(grid[x][y][0])
    return None

###get objects
def get_objects(class_):
    """get a list of instances in the grid"""
    l = []
    for i in range(NGRID):
        for j in range(NGRID):
          if grid[i][j]:
              for k in grid[i][j]:
                  if isinstance(k, class_):
                      l.append(k)
    return l

def get_trees():
    """list of trees"""
    return get_objects(Tree)

def get_bears():
    """list of bears"""
    return get_objects(Bear)

def get_lumberjacks():
    """list of lumberjacks"""
    return get_objects(Lumberjack)

###utils
def gen_name(which="l"):
    """generate random name"""
    name = ""
    for _ in range(randint(1,4)):
        name = name + choice("bcdfghjklmnprstvwxz") + choice("auiey")
    if which == "b":
        name = name[::-1]
    return name.capitalize()

def worth(tree):
    """pieces for a tree"""
    if tree.typeof == 'Elder Tree':
        return 2
    if tree.typeof == 'Tree':
        return 1
    return 0

def one_month():
    """a step of one month"""
    events = []
    global tick
    tick = tick + 1
    #each Tree can spawn a new sapling
    for t in get_trees():
        l_empty_spaces = c_empty_neighbors(t.coords)
        percent = 10 if t.typeof == 'Tree' else \
                  20 if t.typeof == 'Elder Tree' else 0
        if (randint(1,100) < percent):
            if l_empty_spaces:
                [x, y] = choice(l_empty_spaces)
                grid[x][y] = [Tree([x,y])]
                d_total['trees'] = d_total['trees'] + 1
        t.grow()
        d_oldest['tree'] = max(t.months, d_oldest['tree'])
    #each lumberjack/bear moves
    for l in get_lumberjacks():
        l.months = l.months + 1
        d_oldest['lumberjack'] = max((l.months, l.name), \
                                     d_oldest['lumberjack'])
        event = move_lumberjack(l)
        if event:
            events.append(event)
    for b in get_bears():
        b.months = b.months + 1
        d_oldest['bear'] = max((b.months, b.name), d_oldest['bear'])
        event = move_bear(b)
        if event:
            events.append(event)
    return events

def print_grid():
    """print the grid
    if more than 1 thing is at a place, print the last.
    At 1 place, there is
    - at most a tree and possibly several lumberjack
    - or 1 bear
    """
    print "-" * 2 * NGRID
    print '\n'.join([' '.join([str(i[-1]) if i != [] else ' ' \
                               for i in line]) \
                     for line in grid])
    print "-" * 2 * NGRID

def clean():
    """clear the console"""
    os.system('cls' if os.name == 'nt' else 'clear')

def print_grid_and_events():
    """print grid and list of events"""
    clean()
    print_grid()
    if VERBOSE:
        print '\n'.join(events)
        print "-" * 2 * NGRID

###populate the forest
l = c_empty_cells()
shuffle(l)
for x, y in l[:((NGRID*NGRID) / 2)]:
    grid[x][y] = [Tree([x, y], 12, 'Tree')]
    d_total['trees'] = d_total['trees'] + 1

l = c_empty_cells()
shuffle(l)
for x, y in l[:((NGRID*NGRID) / 10)]:
    grid[x][y] = [Lumberjack([x, y])]
    d_total['lumberjacks'] = d_total['lumberjacks'] + 1

l = c_empty_cells()
shuffle(l)
for x, y in l[:((NGRID*NGRID) / 10)]:
    grid[x][y] = [Bear([x, y])]
    d_total['bears'] = d_total['bears'] + 1

###time goes on
while (tick <= DURATION and len(get_trees())>0):
    events = one_month()
    #end of the year
    if (tick % 12)==0:
        events.append("End of the year")
        #lumber tracking
        nlumberjacks = len(get_lumberjacks())
        events.append(str(n_lumbers) + " lumbers VS " +\
                      str(nlumberjacks) + " Lumberjacks")
        if n_lumbers >= nlumberjacks:
            n_hire = n_lumbers/nlumberjacks
            events.append("we hire " + str(n_hire) +\
                          " new Lumberjack" + ("s" if (n_hire > 1) else ""))
            for _ in range(n_hire):
                events.append(new_animate(Lumberjack))
        else:
            events.append(fire_lumberjack())
        d_year['n_lumber'] = max(d_year['n_lumber'], n_lumbers)
        n_lumbers = 0
        #maul tracking
        events.append("maul this year: " + str(n_maul))
        if n_maul == 0:
            events.append(new_animate(Bear))
        else:
            events.append(capture_bear())
        d_year['n_maul'] = max(d_year['n_maul'], n_maul)
        n_maul = 0
    print_grid_and_events()
    sleep(SLEEPTIME)

print "-"*70
print "End of the game"
print "-"*70
print "month:" + str(tick - 1)
print "number of trees still alive: " + str(len(get_trees()))
print "number of lumberjacks still alive: " + str(len(get_lumberjacks()))
print "number of bears still alive: " + str(len(get_bears()))

print "-"*70
print "oldest Tree ever is/was: " + str(d_oldest['tree'])
print "oldest Lumberjack ever is/was: " + str(d_oldest['lumberjack'][0]) + \
    " yo " + d_oldest['lumberjack'][1]
print "oldest Bear ever is/was: " + str(d_oldest['bear'][0]) + \
    " yo " + d_oldest['bear'][1]
print "-"*70
print "max cut by a Lumberjack: " + str(d_most['n_cut'][0]) + \
    " by " + str(d_most['n_cut'][1])
print "max lumber by a Lumberjack: " + str(d_most['n_lumber'][0]) + \
    " by " + str(d_most['n_lumber'][1])
print "max maul by a Bear: " + str(d_most['n_maul'][0]) + \
    " by " + str(d_most['n_maul'][1])
print "-"*70
print "max lumber in a year: " + str(d_year['n_lumber'])
print "max maul in a year: " + str(d_year['n_maul'])
print "-"*70
print "Total of:"
for i, j in d_total.items():
    print i, str(j)

Some outputs:
------------------------------
          x

    I
    I
  x   i                     I

      i i i   i       I I x i
i   I   I i I I   i i     o
      i i I I I           i
    i I   x i
    I I   I I
      I     I i
            x
------------------------------
Dy is sent to hospital
Lehuniru cuts 1 Tree
------------------------------

End of the year
------------------------------
            x

    x

i I     I
    i     I               x
      I
                          i i
      x                   I I
  i I   i I     i       i
  I         i I
            i x i
    I         i I
          o
        x
------------------------------
Fuha cuts 1 Tree
Ka cuts 1 Tree
Ky is sent to hospital
End of the year
11 lumbers VS 4 Lumberjacks
we hire 2 new Lumberjacks
a new Lumberjack enters the forest: Di
a new Lumberjack enters the forest: Dy
maul this year: 6
Evykut has been captured
------------------------------

End of the game
------------------------------
          x
  i
        x     x

          x                 x
                  x i     x
    i               I
    I i x x   I i           x
                    x   i   i
      x i i i i I
      i i I   I i I   i
I       i     i i
        i   x   i
            I   i I
    I I   x i   I I         x
------------------------------
Vanabixy cuts 1 Tree
Fasiguvy cuts 1 Tree
------------------------------
----------------------------------------------------------------------
End of the game
----------------------------------------------------------------------
month:4800
number of trees still alive: 36
number of lumberjacks still alive: 15
number of bears still alive: 0
----------------------------------------------------------------------
oldest Tree ever is/was: 129
oldest Lumberjack ever is/was: 308 yo Cejuka
oldest Bear ever is/was: 288 yo Ekyx
----------------------------------------------------------------------
max cut by a Lumberjack: 44 by Cejuka
max lumber by a Lumberjack: 44 by Cejuka
max maul by a Bear: 52 by Ekyx
----------------------------------------------------------------------
max lumber in a year: 84
max maul in a year: 86
----------------------------------------------------------------------
Total of:
bears 211
cut 5054
fired 67
capture 211
lumberjacks 1177
lumbers 5054
maul 1095
trees 5090

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

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