Why do cones tend to grow near the tops of conifer trees?

As a rule-of-thumb, seed cones (female cones) grow more abundantly near the tops of trees, at least on conifers that are native to the Pacific Northwest. Why?

There are two main reasons:

First, on most Pacific NW conifer species, the seeds inside the cones have wings. Winged seeds are dispersed primarily by wind. If the cones grow high up in the tree, the seeds have a greater chance of spreading farther. Species whose seeds spread over a wider area have a greater chance of success.

(Note: The seeds of whitebark pine are not winged. The seeds are dispersed (i) primarily by birds, and (ii) secondarily by mammals. These cones do not tend to cluster near the tree tops.)

Second, if the seed cones (female cones) are mainly in the tree tops and the pollen cones (male cones) are not, it reduces the possibility of self-pollination or inbreeding. This promotes genetic diversity and reduces recessive gene expression that may have harmful results.

(Note: On most tree species that are native to the Pacific NW, male and female reproductive parts grow on the same tree. This is called "monoecious." Any tree that is monoecious will have many self-pollinated seeds. But that percentage tends to be surprisingly low.)


An exception to the rule-of-thumb?

Western hemlock seems to have a tendency to ignore the rule-of-thumb. This is based on my casual observations of western hemlocks loaded with cones near ground level. If you know of data supporting or refuting this, I would appreciate learning of it.

Occasionally, on a Douglas-fir or western redcedar, cones grow thickly near the ground. On those trees, it appears to me that cones are even more abundant higher up. Again, if you have data, please share it with me.

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