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A Big Year for Doug Fir
| Looks like it’s a big cone year for Douglas fir! Cone production in Douglas fir, like most conifers, fluctuates greatly. They produce a heavy crop only once every several years. On the off years, the conifers produce a light number of cones, or sometimes no cones at all. The thought is that the trees are responding to climatic variation, and the process of reproduction may work better under certain weather conditions. Douglas fir seeds provide an important food resource for many woodland mammals, birds and insects. How do seed predators respond to this varying food supply? Having a diverse diet is one way to adapt. While trees of the same species in a forest tend to synchronize their seed production cycles, other conifer species may follow a different pattern, favoring different weather conditions for reproduction. Incorporating other tree cones in their diets allow seed-eaters greater flexibility when faced with a shortage of a particular species’ cone crop. Douglas squirrels, one of our region’s most abundant seedeaters, are especially fond of Douglas fir cones. They have evolved efficient and crafty techniques of harvesting, and storing seeds, some of which can last up to three years buried underground. During the years of limited cone production, around 99% of the seeds produced are harvested by seed eaters (a significant percentage of which the squirrels cache and forget about, still allowing seeds to germinate in new places.) After a few years of low cone production, squirrel numbers will drop. Inconsistent seed production, therefore, seems to be an effective ecological adaptation that helps to keep seed predator numbers in check. When the trees finally have a big cone year, they produce more seeds than the reduced squirrel population can eat, increasing the chance of germination for future generations of trees. Other animals exploit the varying seed production in different ways. Red crossbills are irruptive migrants, meaning they follow an irregular migration pattern that coincides with cone availability. They escape the problem of poor cone years by being nomadic, and ready to nest wherever they find a large crop. There is a common belief that the natural world finds itself in a constant state of balance and stability. A closer examination of this perceived stability reveals that both plant and animal communities are in fact part of a complex web of interactions that perpetually fluctuate. Balanced, but chaotic. Order, within disorder. (I am sure many of you have the adorable Douglas squirrels come visit your bird feeders. I wonder if fewer squirrels visit feeders during big cone years? Please report your observations this fall! 😊) Top Photo Credit: KA Wiersema (Douglas Squirrel Tamiasciurus douglasii) |
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| New Douglas Fir cones 6/1/2020 |