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Reproductive Strategy

An Overview

In poison-oak the sexes are separate. Heavy blossoming begins about April 1st, and peaks late that month; the odor of the pollen can be smelled then a distance of fifty feet. Poison-oak pollen is not toxic, perhaps because it uses insects as pollinators; plants in the same family that wind pollinate have poisonous pollens.

A huge amount of seed is set. Most of it is dropped as the soil dries out; only in the more favorable locations does the seed mature. This has the effect of seeding the best locations most heavily.

Poison-oak uses birds to distribute part of its seed; seasonally, birds get up to 25% of their food from poison-oak. The immature seeds are non-nutritious and cause stomach pain. However, the mature seed is sugar coated, and the poison has changed to a gentle laxative. Birds absorb the sugar, and also soften the seeds coat, which will help the seed germinate.

Having eaten, birds move to cover to digest their food, and poop in as little as 15 minutes (Morro Bay State Park Museum of Natural History, Bird Adaptations, pp. 25-26). At the time of year when the poison-oak seed is ripe, the deciduous trees like willow and poplar have lost their leaves; so the birds favor the coast live oak.

For germination and early growth, poison-oak prefers reduced light and constant moisture. Under the oaks it is always shady, and there is a six inch layer of leaf litter that holds the winter rains like a sponge.

It takes 3 to 5 years for the plant to reach sexual maturity. During those years it grows towards the strongest light. With a little luck it will penetrate a canopy, and be able to produce more seed.

 

All content copyright Dr. Curt Beebe. Please do not use without permission.