Botanical Barricades
I have a clonal colony of trees that are around 150 meters in height and live in a wetland habitat. These trees cover the majority of the wetland area, covering thousands of square miles.
What reasons would the trees have for growing a "wall" of aerial roots (like cypress knees) only at the edge of their range? This would effectively block the wetland area off from the rest of the area except for breaks in the barricade allowing fast moving water (large rivers) through or breaks caused by wildlife.
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1 answer
Your trees have been selected by evolution such that their aerial roots anchor themselves in the ground, but would rot and decay if the ground has a high content of water. Borrowing from L.Dutch's intuition about the wind, the actual problem is not bringing the nutrients, but rather avoiding excessive evaporation due to the continuous wind.
The process of root rotting is quite simple, and already present in our everyday plants. In fact, in many plants, "excess water makes it very difficult for the roots to get the air that they need, causing them to decay. To avoid root rot, it is best to only water plants when the soil becomes dry[..]" [1]
In this way, not only your trees get their shield at the edge of the wetland, where the soil becomes drier, but also continue to expand their dominion as the wetland increases in area. Trees whose trunk is not however deep in water will dry out, whither, and die, so that the wall will shrink if the wetland retreats.
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