|Pacific Silver Fir pollen cones|
|Douglas Fir pollen cones|
Most conifers are monoecious. That is, they produce both male and female cones on the same tree. This presents some problems, because it is usually not good to allow a tree to pollinate its own seed cones. Self-pollination seldom produces viable seeds, and when it does, the resulting trees are often inferior to those produced by cross-pollination from other trees. With this in mind, it is no surprise that conifers have developed various strategies to minimize self-pollination:
- Conifers often produce pollen cones lower in the tree than the seed cones. The wind is more likely to blow the pollen to another tree than up to the seed cones above on the same tree. This is particularly true of the firs, which produce seed cones near the treetop. Their pollen cones are typically lower in the tree.
- Some trees stagger the development of pollen cones and seed cones. The seed cones will be receptive to the pollen before or after the pollen cones release their pollen. Due to variability in the timing of the development of different trees, pollination will happen between trees. As you can see in the photo here, Western Hemlock (Tsuga heterophylla) produces both seed cones and pollen cones on the same branches. (The seed cone is older, but there is an old pollen cone near its top.) The timing of pollen release is different than the time that the seed cones are receptive to the pollen.
- Some conifers are dioecious. That is, they produce pollen cones and seed cones on separate trees. Self-pollination is impossible on these trees. The Pacific Yew (Taxus brevifolia) is the only dioecious native conifer in the Northwest. You can find these yews growing throughout the Northwest, usually a solitary tree growing in the shade of other conifers. In fact, they are so widely dispersed that they often live a solitary, celibate life and don't reproduce at all.
- Ponderosa Pine (Pinus ponderosa) has an interesting growth pattern that enhances cross-pollination. The young trees start producing pollen cones before they produce seed cones. These young trees can pollinate the cones on larger trees.
|Western Hemlock pollen cones|
|Ponderosa Pine pollen cones|
|Incense Cedar pollen cones|
Conifer Reproductive Biology by Claire G. Williams, pp. 126-128.
Lives of Conifers by Graham R. Powell, pp. 155-164.