The Rocky Road…
The Rocky Road to Reproduction
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
Ah, spring! A time when plants at Tryon Creek State Natural Area are in bloom, with the promise of new generations of plants to come. Or not! While beautiful flowers are a vital step to a new generation of plants, it’s a rocky road to reproduction. If we follow through the process of plant reproduction, we see that the obstacles are numerous. Failure to reproduce is such a common result that every living plant at Tryon Creek is something of a miracle.
But let’s start at the beginning.
Each plant must first initiate a flower. For many species, for example, Douglas-fir (Pseudotsuga menziesii) and trillium (Trillium ovatum), this takes place the summer before the flowers appear. Each year a significant percentage of individual plants never form a flower. This is often the case if, for example, a plant is growing in a shady location, which just barely meets the needs of plant survival.
Perhaps the plant had an abundant crop of flowers the year before, and the plant’s reserves were drained in that effort.
Perhaps the weather conditions last year were not very good for initiating flowers.
Below is a picture showing a trillium that just did not produce a flower this year. Every year at Tryon Creek SNA, there are LOTS of trilliums that don’t produce a flower.
So they won’t be reproducing!
But let’s suppose a flower is initiated. That’s a nice start, but there’s still a long way to go. This spring I noticed several of Tryon Creek’s low Oregon grape (Mahonia nervosa) that had produced a flower stalk and flowers (an inflorescence), but it never actually opened up to show flowers. It dried up and died before it got to that point.
The picture below is of a low Oregon grape inflorescence that started to develop, and then for some reason, died.
But even if the plant has produced an inflorescence and it’s opened up to expose the flowers, many hazards still await. The weather can turn deadly. A late frost or an extra-dry spring can mean the end for flowers that have already emerged. And that’s not all, the picture below shows some bigleaf maple (Acer macrophyllum) flowers laying on the Old Main Trail that got blown out of a tree by a spring windstorm!
Well, they’re never going to produce seeds.
So suppose a flower has developed, opened and escaped the usual weather-related problems. That’s a good start, but that’s not the end of the story. In trilliums, like most other plants, seeds are produced only when pollen (produced by the male parts) lands on the stigma (the sticky female part of the flower) to fertilize the ova (egg). In trilliums, as in many plants, the male and female parts are found in the same flower.
Trilliums, like lots of other plants, can’t be fertilized by pollen from themselves, they need pollen from a different plant.
Here’s the bad news:
So much pollen is produced by each flower that scientists believe sometimes the flower’s own pollen completely covers the female stigma blocking pollen from other plants. Last year I did a survey of 88 trilliums at Tryon Creek State Natural Area along a portion of two trails. Of 88 trilliums that had produced flowers, only 33 produced any seeds! That’s just 37-1/2% of the flowers that produced seeds! Now before you get alarmed, this is about the same percentage of success that scientists have reported for trilliums in other areas. At this time of year, you can see the fat green seed pods on the successful plants (photo on the left), and the tiny brown dried up seed pods (photo on the right) of the flowers that failed.
Whew! What a struggle it’s been so far! But there’s still a couple more hurdles to go.
So suppose you’re a plant that’s managed to produce some seeds. Seeds are little packets stuffed full of high energy starches or fats that help young plants get a good start in life. Oh-oh! Turns out there are lots of critters at Tryon Creek that are interested in packets of high energy (the “seeds”!)
Can you guess who?
Douglas squirrels, spotted towhees, mice, and more! We can see the tragic (for the seeds!) end results in every squirrel midden where a squirrel has chewed apart a Douglas-fir cone and eaten all the seeds.
In the picture below, you can see the central axis (“stalk”) of the cone in the upper left part of the picture, surrounded by the pile of cone scales.
Oh no! They were so close to success.
Fortunately, there is a bright side.
Every year there actually are some seeds that survive the whole gauntlet. These seeds fall to the ground and germinate early in the spring, producing new plants.
Here is a close-up of one new maple germinant:
And some more hope for seeds
Here is a picture of a whole cluster of brand new bigleaf maple seedlings ready to grow up and become the queens of the forest.
There are more than 40 new trees started.
The photo below, taken just 4 weeks later, shows that all the new seedlings have been wiped out! Maybe the weather got too dry, maybe the soil was a little too hard for the roots to penetrate, or maybe a hungry mouse stopped by.
Whatever the reason, it’s the end of the road for those little maples!
It’s a rocky road to reproduction, but once in a great while a plant makes it all the way, like this majestic Douglas-fir near Old Main Trail in the photo below.
When you understand all the barriers to successful plant reproduction, it’s a lot easier to think of each and every plant as a miracle! The next time you’re at Tryon Creek, take a good look at all the plants around you! These are the survivors, the ones that were both lucky and tough!