As noted above, leaves need sunlight to produce chlorophyll and sugar - but too much sunlight may begin to destroy these chemicals.įinally, you can change the TEMPERATURE slider. The sun's strength (in terms of intensity of sunlight) is set with the SUN-INTENSITY slider. To make the wind blow, adjust the WIND-FACTOR slider. If the leaves appear to be losing chlorophyll due to a lack of water (which you can monitor in the "Leaf averages" plot), you can make it rain by adjusting the RAIN-INTENSITY slider. Now comes the interesting and/or tricky part, namely adjusting the sliders under the view so that the weather produces conditions you want to explore or study. This will create the tree trunk and branches, and will also create the leaves of the tree, which are the main agents in this model. So a chlorophyll-laden tree will have dark-green leaves, whereas one with only a little bit will have light-green leaves. Note that the intensity of the leaf colors varies with the level of chlorophyll, carotene, and/or anthocyanins. Below that, the leaf is given a yellow, red, or orange color, depending on if there is a majority of carotene, anthocyanins, or both, respectively. Whenever chlorophyll is above 50%, the leaf is green. (On a very windy day, leaves may blow off even if they're completely green.)īecause the NetLogo color space does not include all possible colors, this model uses a threshold algorithm to determine the color of the leaf, as an approximation of the real color. Attachedness rises with water, and declines in wind and rain. Leaves in the model have an "attachedness" attribute, which the model uses to indicate how strongly the leaf is clinging to the tree. Raindrops disappear when they have no more water left in them. Leaves collect water from nearby raindrops.
Similarly, all of the raindrops travel up the trunk of the tree, and then along the branches (which are not represented in the model), out to the leaves. In this model, the entire ground is assumed to contain tree roots, and thus all raindrops flow toward the trunk once they reach the ground. Water does not enter each leaf directly, but is absorbed by the tree's roots, from which it is pulled up the trunk and into the branches and leaves. (The higher the concentration of sugar, the more anthocyanins are produced.) Sugar concentration increases when cold weather causes the tree to shut down its water circulation to the rest of the tree whatever water and sugar are trapped in the leaf are then converted into anthocyanins.Įach tick of the clock in the model consists of two stages: (1) Weather (rain, wind, sun) affects the leaves, adding or removing sugar, water, or chlorophyll as appropriate, and (2) the leaf reacts to its environment, adding anthocyanins as appropriate, and changing color to reflect the modified environment. Anthocyanin molecules are created in the presence of high sugar concentrations and water concentrations in the leaf. Red comes from a substance called anthocyanins. As the chlorophyll dies, however, the presence of carotene becomes apparent, resulting in a yellow leaf. A leaf with lots more chlorophyll (typical in the summer) will be exclusively green, albeit with strong yellow tints masked behind the green. However, the yellow color is often masked by the chlorophyll's green color. The concentration of carotene remains constant throughout a leaf's life. Carotene molecules help give color to carrots and sweet potatoes. Yellow comes from a substance called carotene. Overall chlorophyll concentration rises again in the sunlight (as long as there is not too much!) and when there is water.
Thus, cold sunny fall days make the overall concentration of chlorophyll decrease. Chlorophyll molecules are destroyed and not replenished when they are exposed to excessive sunlight and when temperatures are low. Green comes from chlorophyll (or a set of related substances known as chlorophylls), which converts sunlight and water into sugar. Three substances contribute to a leaf's color: The colors that we see in each leaf stem from the presence of natural substances that are produced and stored in each leaf. (Leaves can be blown off by strong winds even if they have not yet changed color, so wind has a role too.) Why and how leaves change colors and fall is surprisingly complicated, and has to do with a combination of sunlight, heat, and rain. This model simulates the ways in which leaves change their colors and fall, making it possible to explore and understand this beautiful annual spectacle.
If you live in a climate that is warm during the summer and cold in the winter, then you are probably familiar with the beautiful autumn phenomenon in which leaves turn color before dying and falling off of the tree. You can also Try running it in NetLogo Web
#Netlogo pdf download
If you download the NetLogo application, this model is included. Beginners Interactive NetLogo Dictionary (BIND)
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